Muscle Power Research Papers - Academia.edu (original) (raw)

Paavolainen, Leena, Keijo Hä kkinen, Ismo Hämä lä inen, Ari Nummela, and Heikki Rusko. Explosivestrength training improves 5-km running time by improving running economy and muscle power. J. Appl. Physiol. 86(5): 1527-1533, 1999.-To investigate the effects of simultaneous explosive-strength and endurance training on physical performance characteristics, 10 experimental (E) and 8 control (C) endurance athletes trained for 9 wk. The total training volume was kept the same in both groups, but 32% of training in E and 3% in C was replaced by explosive-type strength training. A 5-km time trial (5K), running economy (RE), maximal 20-m speed (V 20 m ), and 5-jump (5J) tests were measured on a track. Maximal anaerobic (MART) and aerobic treadmill running tests were used to determine maximal velocity in the MART (V MART ) and maximal oxygen uptake (V O 2 max ). The 5K time, RE, and V MART improved (P Ͻ 0.05) in E, but no changes were observed in C. V 20 m and 5J increased in E (P Ͻ 0.01) and decreased in C (P Ͻ 0.05). V O 2 max increased in C (P Ͻ 0.05), but no changes were observed in E. In the pooled data, the changes in the 5K velocity during 9 wk of training correlated (P Ͻ 0.05) with the changes in RE [O 2 uptake (r ϭ Ϫ0.54)] and V MART (r ϭ 0.55). In conclusion, the present simultaneous explosive-strength and endurance training improved the 5K time in well-trained endurance athletes without changes in their V O 2 max . This improvement was due to improved neuromuscular characteristics that were transferred into improved V MART and running economy. distance running; neuromuscular characteristics; maximal oxygen uptake; maximal anaerobic treadmill running; endurance athletes ENDURANCE TRAINING ENHANCES the function of the cardiorespiratory system and the oxidative capacity and glycogen stores of the muscles (e.g., Refs. 1,. Heavyresistance strength training results in neural and muscle hypertrophic adaptations that are known to be primarily responsible for improved strength performance (e.g., Refs. 13,. A specific type of strength training, explosive-strength training, may lead to specific neural adaptations, such as the increased rate of activation of the motor units, whereas muscle hypertrophy remains much smaller than during typical heavyresistance strength training .

- by
- •
- Strength Training, Applied, Muscle Power, Running the economy

Physical therapy is often prescribed in Parkinson's disease. To facilitate the uniformity and efficacy of this intervention, we analyzed current evidence and developed practice recommendations. We carried out an evidence-based literature review. The results were supplemented with clinical expertise and patient values and translated into practice recommendations, developed according to international standards for guideline development. A systematic literature search yielded 6 systematic reviews and 23 randomized controlled trials of moderate methodological quality with sufficient data. Six specific core areas for physical therapy were identified: transfers, posture, reaching and grasping, balance, gait, and physical capacity. We extracted four specific treatment recommenda-tions that were based on evidence from more than two controlled trials: cueing strategies to improve gait; cognitive movement strategies to improve transfers; exercises to improve balance; and training of joint mobility and muscle power to improve physical capacity. These practice recommendations provide a basis for current physical therapy in Parkinson's disease in everyday clinical practice, as well as for future research in this field.

- by Erik Hendriks
- •
- Cognitive Science, Physical Therapy, Movement disorders, Literature Review

Background. Training cessation among older adults is associated with the loss of functional ability. However, exercise programs undertaken prior to activity cessation may offer functional protection. In the present study, the residual effects of muscle power or muscle strength training were investigated following extended detraining and subsequent retraining. Methods. Thirty-eight healthy independent older adults (65-84 years) entered a 24-week detraining

- by Tim Henwood
- •
- Skeletal muscle biology, Quality of life, Muscle strength, Walking
- by Hua-fang Liao
- •
- Mechanical Engineering, Skeletal muscle biology, Cerebral Palsy, Music Therapy

Objective: To examine the effect of functional strength training in subacute stroke. Design: A single-blinded randomized controlled trial. Setting: Two rehabilitation units. Subjects: Eighteen patients in the subacute phase post stroke, randomly allocated to a functional strength training (intervention) group (n ¼ 8) and a training-as-usual (comparison) group (n ¼ 10). Intervention: The functional strength training group participated in functional progressive strength training of the affected lower extremity. The training-as-usual group had traditional training, excessive muscle power being avoided to prevent associated reactions. All trained 50 minutes five days a week for four weeks. Main measures: Maximum weight-bearing in standing (primary outcome), isometric muscle strength, gait speed and items of Motor Assessment Scale. Results: Maximum weight-bearing on the affected leg improved more in the functional strength training group (mean 17.4% of body weight) than in the training-as-usual group (mean 5.6% of body weight), but taking test data at inclusion into consideration, the difference in change was not statistically significant (P ¼ 0.056). More patients in the functional strength training group (57%) could weight-bear on the affected leg while stepping forward, than in the training-as-usual group (17%). Improvement was clinically significant in 7 of 9 outcome measures in the functional strength training group (effect size 0.80, large), but in only 3 of 9 in the training-as-usual group. All patients in the functional strength training group and 70% of the patients in the training-as-usual group rated their overall status as 'much' or 'very much' improved. Conclusions: This pilot study indicates that functional strength training of lower extremities improves physical performance more than traditional training.

- by Liv Strand
- •
- Nonparametric Statistics, Treatment Outcome, Muscle strength, Gait

This study was carried out to investigate the importance of maximal oxygen uptake (VO 2max ) and so-called muscle power factors relating to neuromuscular and anaerobic characteristics as determinants of peak horizontal and uphill treadmill running velocity (V max ). Muscle power factors were measured as peak velocity (V MART ) and blood lactate concentration (Bla MART ) in a maximal anaerobic running test and as maximal 30-m run velocity (V 30m ). Seven middle-distance runners, eight triathletes and eight cross-country skiers performed an incremental VO 2maxtest at horizontal (subscript max0) and 7ae uphill (subscript max7) and the MART at 3ae uphill on a treadmill and V 30m -test on a track. The MART consisted of n ¡ 20-s runs with a 100-s recovery between the runs and the velocity was increased by 0.41 m ¡ s ª1 for each consecutive run until exhaustion. At 0ae V max was significantly higher but VO 2max , ventilation and Bla were significantly lower than

- by Heikki Rusko
- •
- Scandinavian, Muscle Power

Background. Muscle power (force 3 velocity) recedes at a faster rate than strength with age and may also be a stronger predictor of fall risk and functional decline. The optimal training paradigm for improving muscle power in older adults... more

- by Nathan de Vos
- •
- Skeletal muscle biology, Risk assessment, Linear models, Probability

The purposes of this study were firstly to determine the relationship between the peak power output (W peak) and maximal oxygen uptake (VO2max) attained during a laboratory cycling test to exhaustion, and secondly to assess the relationship betweenW peak and times in a 20-km cycling trial. One hundred trained cyclists (54 men, 46 women) participated in the first part of this investigation. Each cyclist performed a minimum of one maximal test during whichW max andVO2max were determined. For the second part of the study 19 cyclists completed a maximal test for the determination ofW peak, and also a 20-km cycling time trial. Highly significant relationships were obtained betweenW peak andVO2max (r=0.97,P<0.0001) and betweenW peak and 20-km cycle time (r= −0.91,P<0.001). Thus,W peak explained 94% of the variance in measuredVO2max and 82% of the variability in cycle time over 20 km. We concluded that for trained cyclists, theVO2max can be accurately predicted fromW peak, and thatW peak is a valid predictor of 20-km cycle time.

- by Timothy Noakes
- •
- Fatigue, Bicycling, Cycle Time, Muscle Power

This study compares dominant and non-dominant hand strength in both right-and left-handed participants. Maximum voluntary contraction (MVC) of the first dorsal interosseous (FDI) muscle, power grip strength and pulp-to-pulp pinch strength were assessed under carefully controlled conditions. No significant differences were observed between dominant and non-dominant hands in left-handed participants for all tests. Small but significant differences (0.1-3%) were observed between dominant and non-dominant hands in right-handed participants for all three tests. These differences were much smaller than those reported in other studies. Furthermore, considerable variability was observed in the relative strengths of the two hands for each participant. We conclude that clinicians must be cautious when using the '10% rule' to make comparisons between injured and uninjured hands.

- by Michele R Colonna
- •
- Comparative Study, Exploration, Clinical Sciences, Aged

Izquierdo, M., J. Ibañ ez, J.pering effects on hormonal responses and strength performance. J. Strength. Cond. Res. 21(3): 768-775. 2007.-This study examined the impact of 4 weeks of either complete cessation of training (DTR) or a tapering period (TAP; short-term reduction of the strength training volume, while the intensity is kept high), subsequent to 16 weeks of periodized heavy resistance training (PRT) on strength/power gains and the underlying physiologic changes in basal circulating anabolic/catabolic hormones in strength-trained athletes. Forty-six physically active men were matched and randomly assigned to a TAP (n ϭ 11), DTR (n ϭ 14), or control group (C; n ϭ 21), subsequent to a 16-week PRT program. Muscular and power testing and blood draws to determine basal hormonal concentrations were conducted before the initiation of training (T0), after 16 weeks of training (T1), and after 4 weeks of either DTR or TAP (T2). Short-term DTR (4 weeks) results in significant decreases in maximal strength (Ϫ6 to Ϫ9%) and muscle power output (Ϫ17 and Ϫ14%) of the arm and leg extensor muscles. However, DTR had a significant (p Ͻ 0.01) larger effect on muscle power output more than on strength measurements of both upper and lower extremity muscles. Short-term (4 weeks) TAP reached further increases for leg (2%) and arm (2%) maximal strength, whereas no further changes were observed in both upper and lower muscle power output. Short-term DTR resulted in a tendency for elevation resting serum insulin-like growth factor (IGF)-1 concentrations, whereas the corresponding TAP experienced elevation in resting serum insulin-like binding protein-3 (IGFBP-3). These data indicated that DTR may induce larger declines in muscle power output than in maximal strength, whereas TAP may result in further strength enhancement (but not muscle power), mediated, in part, by training-related differences in IGF-1 and IGFBP-3 concentrations.

- by Juan Badillo
- •
- Strength & Conditioning, Skeletal muscle biology, Physical Activity, Spain

- by Bastiaan Bloem
- •
- Cognitive Science, Physical Therapy, Movement disorders, Literature Review

Muscle strength and, to a greater extent, power inexorably decline with ageing. Quantitative loss of muscle mass, referred to as ''sarcopenia'', is the most important factor underlying this phenomenon. However, qualitative changes of muscle fibres and tendons, such as selective atrophy of fast-twitch fibres and reduced tendon stiffness, and neural changes, such as lower activation of the agonist muscles and higher coactivation of the antagonist muscles, also account for the age-related decline in muscle function. The selective atrophy of fast-twitch fibres has been ascribed to the progressive loss of motoneurons in the spinal cord with initial denervation of fast-twitch fibres, which is often accompanied by reinnervation of these fibres by axonal sprouting from adjacent slow-twitch motor units (MUs). In addition, single fibres of older muscles containing myosin heavy chains of both type I and II show lower tension and shortening velocity with respect to the fibres of young muscles. Changes in central activation capacity are still controversial. At the peripheral level, the rate of decline in parameters of the surface-electromyogram power spectrum and in the action-potential conduction velocity has been shown to be lower in older muscle. Therefore, the older muscle seems to be more resistant to isometric fatigue (fatigueparadox), which can be ascribed to the selective atrophy of fast-twitch fibres, slowing in the contractile properties and lower MU firing rates. Finally, specific training programmes can dramatically improve the muscle strength, power and functional abilities of older individuals, which will be examined in the second part of this review.

- by Giuseppe De Vito
- •
- Skeletal muscle biology, Aging, Muscle strength, Older people

Maximal concentric one repetition maximum half-squat (1RM HS ), bench-press (1RM BP ), power-load curves during concentric actions with loads ranging from 30% to 100% of 1RM HS and 1RM BP were examined in 70 male subjects divided into five groups: weightlifters (WL, n=11), handball players (HP, n=19), amateur road cyclists (RC, n=18), middle-distance runners (MDR, n=10) and age-matched control subjects (C, n=12). The 1RM HS values in WL, HP and RC were 50%, 29% and 28% greater, respectively, (P< 0.001-0.01) than those recorded for MDR and C. The half-squat average power outputs at all loads examined (from 30% to 100%) in WL and HP (P<0.001 at 45% and 60% with HP) were higher (P<0.05-0.001) than those in MDR, RC and C. Average power output at the load of 30% of 1RM HS in RC was higher (P<0.05) than that recorded in MDR and C. Maximal power output was produced at the load of 60% for HP, MDR and C, and at the load of 45% for WL and RC. The 1RM BP in WL was larger (P<0.05) than those recorded in HP, RC, MDR and C. In the bench press, average muscle power outputs in WL and HP were higher (P<0.05-0.001) than those in MDR, RC and C, and were maximized at a load of 30% of 1RM for WL and HP, and at 45% for RC, MDR and C. In addition, the velocities that elicited the maximal power in the lower extremities were lower (0.75 mAEs -1 ) than those occurring in the upper extremities (1 mAEs -1 ). The data suggest that the magnitude of the sport-related differences in strength and/or muscle power output may be explained in part by differences in muscle cross-sectional area, fibre type distribution and in the muscle mechanics of the upper and lower limbs as well as by training background.

- by Juan Badillo
- •
- Skeletal muscle biology, Muscle strength, Sports, Exercise

The purpose of this study was to identify the profile of the Olympic champions and the other competitors who were involved in the Games. The information on each of the athletes was obtained from the "Official Site of the Sydney 2000 Olympic Games, www.olympics.com/eng/sports/TK "and included weight category, weight, height, age, points obtained, warnings, deduction point, defensive/offensive kicks and punches. One hundred and two athletes competed (54 males and 48 females) in the Games. The mean average age and BMI (Body Mass Index) of 16 male winners was 24.4 ± 3.3 years and 21.9 ± 2.4 respectively compared to 25.2 ± 4.3 years and 22.8 ± 3.3 for the 38 male non-winners. The mean average age and BMI of the 16 female winners was 23.1 ± 3.9 years and 20.8 ± 2.3 respectively compared to 24.9 ± 4.7 years and 21.3 ± 2.7 for the 32 female non-winners. For all four types of athletes, offensive kicks accounted for at least 52% of the techniques to score a point. Ninety-eight perce...

- by Mohsen Kazemi
- •
- Mechanical Engineering, Reaction Time, Statistical Significance, Body Mass Index
- by Armando Malanda
- •
- Mechanical Engineering, Demography, Sports Medicine, Skeletal muscle biology

Summary This study aims to evaluate the effect of 18-week progressive muscular strength and proprioception training program on the muscle strength of the quadriceps, in prevention of falls in postmenopausal women with osteoporosis. The incidence of falls in the intervention group was significantly lower than in the control group (incidence rate ratio (IRR) = 0.263, 95% CI 0.10–0.68). Introduction This study aims to evaluate the effect of a progressive muscular strength and proprioception training program on the muscle strength of the quadriceps, balance, quality of life, and reduction in the risk of falls in postmenopausal women with osteoporosis. Methods One hundred sedentary postmenopausal women with osteoporosis, ages ranging from 55 to 75, were selected and randomized into two groups: the intervention group comprised of 50 patients who underwent a 18-week of progressive load training for the quadriceps muscle (50% up to 80% of 1-RM—one maximum repetition) and proprioception training associated to a drug treatment of osteoporosis and the control group that included 50 patients who only underwent a drug treatment of osteoporosis. The muscular strength, balance, functional mobility, and quality of life were evaluated in the beginning and end of the research. The number of falls was evaluated 24 weeks post-treatment. Results Eighty-five patients concluded the research. The program promoted a significant difference among the groups for SF-36 in the eight sub-scales (p ≤ 0.0018), Timed Up & Go Test (p < 0.0001), 1-RM test (p < 0.0001), Berg Balance Scale (p < 0.0001) and also a decrease in the number of falls in the intervention group compared to control (IRR = 0.263, 95% CI 0.10–0.68, p = 0.0064). Conclusion The association of progressive strength training for the quadriceps and the proprioceptive training is effective for the prevention of falls, increasing the muscle power, the static and dynamic balance and increasing the speed of the motor responses, therefore improving the performance of daily activities.

- by Kelson Silva
- •
- Quality of life, Muscle strength, Proprioception, Postmenopausal Women

We tested the hypothesis that the performance of rapid movements represents body size-independent indices of muscle power. Physical education students (n ¼ 159) were tested on various vertical jump (jump height and average power calculated from the ground reaction force) and muscle strength tests. When non-normalized data were used, a principal components analysis revealed a complex and inconsistent structure where jump height and muscle power loaded different components, while muscle strength and power partially overlapped. When the indices of muscle strength and power were properly normalized for body size, a simple and consistent structure of principal components supported the hypothesis. Specifically, the recorded height and muscle power calculated from the same jumps loaded the same components, separately for the jumps predominantly based on concentric actions and jumps based on a rapid stretch -shortening cycle of the leg extensors. The finding that the performance of rapid movements assesses the same physical ability as properly normalized tests of muscle power could be important for designing and interpreting the results of batteries of physical performance tests, as well as for understanding some basic principles of human movement performance.

- by Slobodan Jaric
- •
- Anthropometry, Principal Component Analysis, Physics Education, Adolescent

This study compared anthropometric (body height, body mass, percent body fat, fat-free body mass) and physical fitness characteristics (vertical jump height, power-load curve of the leg, 5 and 15 m sprint running time and blood lactate concentrations ([La]b) at submaximal running velocities) among 15 elite male indoor soccer (IS) and 25 elite male outdoor soccer (OS) players. IS players had similar values in body height, body mass, fat-free body mass and endurance running than OS players. However, the IS group showed higher (P P b at submaximal running velocities. Percent body fat correlated positively with maximal sprint time and [La]b, but correlated negatively with vertical jump height. The present results show that compared to elite OS players, elite IS players present clearly lower physical fitness (lower maximal leg extension power production) characteristics associated with higher values of percent body fat. This should give IS players a disadvantage during soccer game actions.

- by ion navarro
- •
- Anthropometry, Soccer, Running, Muscle strength

Certain typical gait characteristics such as foot-drop and foot supination are well described in Charcot-Marie-Tooth disease. These are directly related to the primary disease and due to the weakness of ankle dorsiflexors and everters characteristic of this hereditary neuropathy. We analysed 16 subjects aged 8-52 years old (11 with type I, 5 with type II Charcot-Marie-Tooth disease) using three-dimensional gait analysis and identified kinematic features previously unreported. These patients showed a combination of tight tendo achillei, foot-drop, failure of plantar flexion and increased foot supination, but also presented with excessive internal rotation of the knee and/or tibia, knee hyperextension in stance, excessive external rotation at the hips and decreased hip adduction in stance (typical of a broad based gait). These proximal features could have been an adaptation to or consequence of the disrupted ankle and foot biomechanics, however a direct relation to the neuropathy is also possible since sub-normal muscle power was observed at the proximal levels in most subjects on both manual testing and kinetic analysis. Gait analysis is a useful tool in defining the characteristic gait of patients with Charcot-Marie-Tooth disease. #

- by Bryan Lynch
- •
- Mechanical Engineering, Adolescent, Gait, Child

The purpose of this study was to examine the efficacy of 11 weeks of resistance training to failure vs. non-failure, followed by an identical 5-week peaking period of maximal strength and power training for both groups as well as to examine the underlying physiological changes in basal circulating anabolic/catabolic hormones. Forty-two physically-active men were matched and then randomly assigned to either a training to failure (RF; n=14), non-failure (NRF; n=15) or control groups (C;n=13). Muscular and power testing and blood draws to determine basal hormonal concentrations were conducted before the initiation of training (T0), after 6 wk of training (T1), after 11 wk of training (T2), and after 16 wk of training (T3). Both RF and NRF resulted in similar gains in 1RM bench press (23% and 23%) and parallel squat (22% and 23%), muscle power output of the arm (27% and 28%) and leg extensor muscles (26% and 29%) and maximal number of repetitions performed during parallel squat (66% and 69%). RF group experienced larger gains in the maximal number of repetitions performed during the bench press The peaking phase (T2 to T3) followed after NRF resulted in larger gains in muscle power output of the lower extremities, whereas after RF resulted in larger gains in the maximal number of repetitions performed during the bench press. Strength training leading to RF resulted in reductions in resting concentrations of IGF-1 and elevations in IGFBP-3, whereas NRF resulted in reduced resting cortisol concentrations and an elevation in resting serum total testosterone concentration. This investigation demonstrated a potential beneficial stimulus of NRF for improving strength and power, especially during the subsequent peaking training period, whereas performing sets to failure resulted in greater gains in local muscular endurance.

- by Juan Badillo
- •
- Skeletal muscle biology, Biological Sciences, Power, Testosterone

Fish skulls are complex kinetic systems with movable components that are powered by muscles. Cranial muscles for jaw closing pull the mandible around a point of rotation at the jaw joint using a third-order lever mechanism. The present study develops a lever model for the jaw of fishes that uses muscle design and the Hill equation for nonlinear length-tension properties of muscle to calculate dynamic power output. The model uses morphometric data on skeletal dimensions and muscle proportions in order to predict behavior and force transmission mediated by lever action. The computer model calculates a range of dynamic parameters of jaw function including muscle force, torque, effective mechanical advantage, jaw velocity, bite duration, bite force, work and power. A complete list of required morphometrics is presented and a software program (MandibLever 2.0) is available for implementing lever analysis. Results show that simulations yield kinematics and timing profiles similar to actual fish feeding events. Simulation of muscle properties shows that mandibles reach their peak velocity near the start of jaw closing, peak force at the end of jaw closing, and peak power output at about 25% of the closing cycle time. Adductor jaw muscles with different mechanical designs must have different contractile properties and/or different muscle activity patterns to coordinate jaw closing. The effective mechanical advantage calculated by the model is considerably lower than the mechanical advantage estimated from morphological lever ratios, suggesting that previous studies of morphological lever ratios have overestimated force and underestimated velocity transmission to the mandible. A biomechanical model of jaw closing can be used to interpret the mechanics of a wide range of jaw mechanisms and will enable studies of the functional results of developmental and evolutionary changes in skull morphology and physiology. r

- by Mark Westneat
- •
- Biomechanics, Functional Morphology, Kinetics, Mechanism Design

- by Jackie Oldham
- •
- Comparative Study, Exploration, Clinical Sciences, Aged

The goal of our study was to explore the mechanical power requirements associated with jumping in yellowfooted rock wallabies and to determine how these requirements are achieved relative to steady-speed hopping mechanics. Whole body power output and limb mechanics were measured in yellow-footed rock wallabies during steady-speed hopping and moving jumps up to a landing ledge 1.0·m high (~3 times the animals' hip height). High-speed video recordings and ground reaction force measurements from a runway-mounted force platform were used to calculate whole body power output and to construct a limb stiffness model to determine whole limb mechanics. The combined mass of the hind limb extensor muscles was used to estimate muscle massspecific power output. Previous work suggested that a musculoskeletal design that favors elastic energy recovery, like that found in tammar wallabies and kangaroos, may impose constraints on mechanical power generation. Yet rock wallabies regularly make large jumps while maneuvering through their environment. As jumping often requires high power, we hypothesized that yellowfooted rock wallabies would be able to generate substantial amounts of mechanical power. This was confirmed, as we found net extensor muscle power outputs averaged 155·W·kg -1 during steady hopping and 495·W·kg -1 during jumping. The highest net power measured reached nearly 640·W·kg -1 . As these values exceed the maximum power-producing capability of vertebrate skeletal muscle, we suggest that back, trunk and tail musculature likely play a substantial role in contributing power during jumping. Inclusion of this musculature yields a maximum power output estimate of 452·W·kg -1 muscle.

- by Craig McGowan
- •
- Skeletal muscle biology, Locomotion, Biological Sciences, Macropodidae

The purpose of this study was (1) to determine the relationship between each individual's anaerobic power reserve (APR) [i.e., the difference between the maximum anaerobic (P ana ) and aerobic power (P aer )] and fatigability during repeated-sprint exercise and (2) to examine the acute effects of repeated sprints on neuromuscular activity, as evidenced by changes in the surface electromyogram (EMG) signals. Eight healthy males carried out tests to determine P ana (defined as the highest power output attained during a 6-s cycling sprint), P aer (defined as the highest power output achieved during a progressive, discontinuous cycling test to failure) and a repeated cycling sprint test (10 9 6-s max sprints with 30 s rest). Peak power output (PPO) and mean power output (MPO) were calculated for each maximal 6-s cycling bout. Root mean square (RMS) was utilized to quantify EMG activity from the vastus lateralis (VL) muscle of the right leg. Over the ten sprints, PPO and MPO decreased by 24.6 and 28.3% from the maximal value (i.e., sprint 1), respectively.

- by Peter Hamer
- •
- Exercise, Electromyography, Root-Mean Square Error, Muscle Power

The user has requested enhancement of the downloaded file.

- by Mark Haub
- •
- Strength & Conditioning, Strength, Volume, Muscle Power

The purpose of this study was to determine if three minutes of petrissage and tapotement forms of massage would influence plantar flexors' flexibility, and muscle power. Nineteen participants were randomly subjected to three conditions (control and two massages) before performing two power tests. Prior to the intervention, subjects completed ankle joint flexibility assessments. The conditions were; (1) control, where subjects lay prone and had a therapist's hands resting, (2) vigorous petrissage, and (3) tapotement applied at a rate of 4Hz; all on the triceps surae. Following completion of the intervention, subjects immediately completed a post- ankle joint flexibility test, followed by a drop-jump and concentric calf raise. The power measures were; concentric peak force, rate of force development, and drop-jump height / contact time. The data showed a significant increase (p < 0.05) in ankle joint angle on the right leg and a corresponding tendency on the left. No signif...

- by David G Behm
- •
- Mechanical Engineering, Bioinformatics, Life Sciences, Massage

In exercise physiology, it has been traditionally assumed that high-intensity aerobic exercise stops at the point commonly called exhaustion because fatigued subjects are no longer able to generate the power output required by the task despite their maximal voluntary eVort. We tested the validity of this assumption by measuring maximal voluntary cycling power before (mean § SD, 1,075 § 214 W) and immediately after (731 § 206 W) (P < 0.001) exhaustive cycling exercise at 242 § 24 W (80% of peak aerobic power measured during a preliminary incremental exercise test) in ten Wt male human subjects. Perceived exertion during exhaustive cycling exercise was strongly correlated (r = ¡0.82, P = 0.003) with time to exhaustion (10.5 § 2.1 min). These results challenge the long-standing assumption that muscle fatigue causes exhaustion during high-intensity aerobic exercise, and suggest that exercise tolerance in highly motivated subjects is ultimately limited by perception of eVort.

- by Samuele Marcora
- •
- Perception, Performance, Muscle strength, Motivation

ACE (I/D), ACTN3 (R/X), PPARGC1A (Gly482Ser) and PPARA (G/C) polymorphisms have been linked to the success in power-oriented sports through the intermediate phenotypes. The study involved 193 Lithuanian elite athletes and 250 controls. The measured phenotypic variables included short-term explosive muscle power (STEMP) and anaerobic alactic maximum power (AAMP). ACE DD genotype was more common among endurance athletes compared to the power athletes. The ACTN3 genotype frequencies of the elite athletes differed from those of non-elite athletes; however, there were no differences among the athletes and the control group across the PPARGC1A Gly482Ser genotypes. The frequency of PPARA CC genotype increased with the growing skill level of athletes (non-elite 2%, sub-elite 7.7%, elite 11.6%). The STEMP and AAMP were higher in the males than females and they were also higher in the power-oriented group compared to the endurance sports group. Success in power sports can be attributed to the ACE II, PPARGC1A SerSer, PPARA CC genotype in association with phenotypic characteristics such as AAMP and STEMP. ACTN3 XX genotype may not be critical but rather additive to endurance performance. The results show that high muscle power depends on both environmental and genetic factors.

- by Valentina Ginevičienė
- •
- Polymorphism, Muscle Power, Control Group

Introduction: Radial nerve compression by a ganglion in the radial tunnel is not common. Compressive neuropathies of the radial nerve in the radial tunnel can occur anywhere along the course of the nerve and may lead to various clinical manifestations, depending on which branch is involved. We present two unusual cases of ganglions located in the radial tunnel and requiring surgical excision. Case presentation: A 31-year-old woman complained of difficulty in fully extending her fingers at the metacarpophalangeal joint for 2 weeks. Before her first visit, she had noticed a swelling and pain in her right elbow over the anterolateral forearm. The extension muscle power of the metacarpophalangeal joints at the fingers and the interphalangeal joint at the thumb had decreased. Sonography and magnetic resonance imaging of the elbow revealed a cystic lesion located at the area of the arcade of Frohse. A thin-walled ovoid cyst was found against the posterior interosseous nerve during surgical excision. Pathological examination was compatible with a ganglion cyst. The second case involved a 36-year-old woman complaining of numbness over the radial aspect of her hand and wrist, but without swelling or tumor in this area. The patient had slightly decreased sensitivity in the distribution of the sensory branch of the radial nerve. There was no muscle weakness on extension of the fingers and wrist. Surgical exposure defined a ganglion cyst in the shoulder of the division of the radial nerve into its superficial sensory and posterior interosseous components. There has been no disease recurrence after following both patients for 2 years. Conclusion: Compression of nerves by extraneural soft tissue tumors of the extremities should be considered when a patient presents with progressive weakness or sensory changes in an extremity. Surgical excision should be promptly performed to ensure optimal recovery from the nerve palsy.

- by Wei-ren Su
- •
- Case Report, Muscle Power, Soft Tissue Tumor, Medical Case Reports

Size and proportions of the postcranial skeleton differ markedly between Australopithecus afarensis and Homo ergaster, and between the latter and modern Homo sapiens. This study uses computer simulations of gait in models derived from the best-known skeletons of these species (AL 288-1, Australopithecus afarensis, 3.18 million year ago) and KNM-WT 15000 (Homo ergaster, 1.5-1.8 million year ago) compared to models of adult human males and females, to estimate the required muscle power during bipedal walking, and to compare this with those in modern humans. Skeletal measurements were carried out on a cast of KNM-WT 15000, but for AL 288-1 were taken from the literature. Muscle attachments were applied to the models based on their position relative to the bone in modern humans. Joint motions and moments from experiments on human walking were input into the models to calculate muscle stress and power. The models were tested in erect walking and ‘bent-hip bent-knee’ gait. Calculated muscle forces were verified against EMG activity phases from experimental data, with reference to reasonable activation/force delays. Calculated muscle powers are reasonably comparable to experimentally derived metabolic values from the literature, given likely values for muscle efficiency. The results show that: 1) if evaluated by the power expenditure per unit of mass (W/kg) in walking, AL 288-1 and KNM-WT 15000 would need similar power to modern humans; however, 2) with distance-specific parameters as the criteria, AL 288-1 would require to expend relatively more muscle power (W/kg.m−1) in comparison to modern humans. The results imply that in the evolution of bipedalism, body proportions, for example those of KNM-WT 15000, may have evolved to obtain an effective application of muscle power to bipedal walking over a long distance, or at high speed.

- by Tanya Carey
- •
- Evolutionary Biology, Archaeology, Anthropology, Human Evolution
- by Imed Latiri
- •
- Mechanical Engineering, Sports Medicine, Skeletal muscle biology, Anthropometry

The local intramuscular application of botulinum toxin into the triceps, temporarily blocks activity and thus reduces the resistance to the weak but contracting biceps. Six children (2-4 years of age) presenting with severe biceps/triceps co-contractions after nerve regeneration (spontaneous regeneration in three cases, early microsurgical reconstruction in three cases) of an obstetrical brachial plexus lesion, were treated with local injections

- by Robert Hierner
- •
- Nerve Regeneration, Muscle Power, Brachial Plexus, Botulinum Toxin

Size and proportions of the postcranial skeleton differ markedly between Australopithecus afarensis and Homo ergaster, and between the latter and modern Homo sapiens. This study uses computer simulations of gait in models derived from the best-known skeletons of these species (AL 288-1, Australopithecus afarensis, 3.18 million year ago) and KNM-WT 15000 (Homo ergaster, 1.5-1.8 million year ago) compared to models of adult human males and females, to estimate the required muscle power during bipedal walking, and to compare this with those in modern humans. Skeletal measurements were carried out on a cast of KNM-WT 15000, but for AL 288-1 were taken from the literature. Muscle attachments were applied to the models based on their position relative to the bone in modern humans. Joint motions and moments from experiments on human walking were input into the models to calculate muscle stress and power. The models were tested in erect walking and 'bent-hip bent-knee' gait. Calculated muscle forces were verified against EMG activity phases from experimental data, with reference to reasonable activation/force delays. Calculated muscle Journal of Human Evolution 47 powers are reasonably comparable to experimentally derived metabolic values from the literature, given likely values for muscle efficiency. The results show that: 1) if evaluated by the power expenditure per unit of mass (W/kg) in walking, AL 288-1 and KNM-WT 15000 would need similar power to modern humans; however, 2) with distancespecific parameters as the criteria, AL 288-1 would require to expend relatively more muscle power (W/kg.m ÿ1 ) in comparison to modern humans. The results imply that in the evolution of bipedalism, body proportions, for example those of KNM-WT 15000, may have evolved to obtain an effective application of muscle power to bipedal walking over a long distance, or at high speed.

- by Tanya Carey and +1
- •
- Evolutionary Biology, Archaeology, Anthropology, Human Evolution

The purpose of this study was to examine acute exercise-induced changes on muscle power output and surface electromyography (sEMG) parameters (amplitude and spectral indices of muscle fatigue) during a dynamic fatiguing protocol. Fifteen trained subjects performed five sets consisting of 10 leg presses (10RM), with 2 min rest between sets. Surface electromyography was recorded from vastus medialis (VM) and lateralis (VL) and biceps femoris (BF) muscles. A number of EMG-based parameters were compared for estimation accuracy and sensitivity to detect peripheral muscle fatigue. These were: Mean Average Voltage, median spectral frequency, Dimitrov spectral index of muscle fatigue (FI nsm5 ), as well as other parameters obtained from a time-frequency analysis (Choi-Williams distributions) such as mean and variance of the instantaneous frequency and frequency variance. The log FI nsm5 as a single parameter predictor accounted for 37% of the performance variance of changes in muscle power and the log FI nsm5 and MFM as a two factor combination predictor accounted for 44%. Peripheral impairments assessed by sEMG spectral index FI nsm5 may be a relevant factor involved in the loss of power output after dynamic high-loading fatiguing task.

- by Fermin Mallor
- •
- Algorithms, Skeletal muscle biology, Electromyography, Time Frequency Analysis

A 31-year-old Nepali man was admitted to the intensive care unit with a 3-day history of fever associated with four-limb weakness, followed by difficulty in swallowing. The patient came from Nepal 20 days before admission. On examination the patient was conscious and appeared ill, with a temperature of 38.0 • C. His four limbs were weak (grades 2-3) and he was areflexic with mild facial weakness and absent gag reflex. Brain CT and MRI were normal. Cerebrospinal fluid analysis showed high protein. A neurophysiologic study showed data consistent with motor axonal polyradiculopathy. The patient was diagnosed with Guillain-Barré syndrome (GBS), and intravenous immunoglobulin (0.4 g/kg day for 5 days) was administered. On the third hospitalization day, the patient developed respiratory failure for which he was intubated and mechanically ventilated. On the same day, blood samples grew Salmonella paratyphi A (S. paratyphi A), which was sensitive to ceftriaxone. The patient was then diagnosed with GBS associated with S. paratyphi A, and treated with ceftriaxon (2 g administered intravenously, daily for 10 days). On the eleventh hospitalization day the patient was weaned from ventilator and extubated successfully. Subsequently, the patient improved, his fever subsided, and he regained muscle power satisfactorily.

- by Fy-za Khan
- •
- Surgery, Cerebrospinal Fluid, Blood sampling, Respiratory Failure

We investigated reliability, construct validity, and feasibility of two sprint tests for children with cerebral palsy (CP). Methods: Twenty-six children with CP participated (7-18 years of age; Gross Motor Function Classification System [GMFCS] level I or II). On different occasions, the 10 ϫ 5-Meter Sprint Test and the Muscle Power Sprint Test were scored by different assessors. Results: Excellent interobserver reliability (intraclass correlation [ICC] ϭ 1.0 and ICC Ն 0.97) and testϪretest reliability (ICC ϭ 0.97 and ICC Ն 0.97) were obtained. Scores differed significantly on both sprint tests for children classified at GMFCS level I and level II. Mean scores for feasibility ranged from 8.8 to 9.2 on a 10-cm visual analog scale (10 ϭ the best). Conclusions: Both exercise tests are reliable and have good feasibility for children and adolescents with CP (GMFCS level I or II). Construct validity is supported for both sprint tests in children classified at GMFCS level I and level II. (Pediatr Phys Ther 2007;19:108 -115)

- by Marjolijn Ketelaar
- •
- Skeletal muscle biology, Cerebral Palsy, Running, Adolescent

The aim of the present study was to examine muscle mechanical characteristics before and after a marathon race. Eight elite runners underwent a pre-test 1 week before the marathon and post-tests 30 min, two and fiveday-post-marathon. Actual marathon race performance was 2:34:40 ± 0:04:13. Energy expenditure at marathon pace (EE Mpace ) was elevated 4% post-marathon (pre: 4,465 ± 91 vs. post 4,638 ± 91 J kg bodyweight -1 km -1 , P < 0.05), but was lowered by 6 and 9.5% two-and five-day-postmarathon compared to EE Mpace pre-marathon. Countermovement jump (CMJ) power decreased 13% post-marathon (pre: 21.5 ± 0.9 vs. post: 18.9 ± 1.2 W kg -1 ; P < 0.05) and remained depressed two-(18%) and five-day (12%) post-marathon. CMJ force was unaltered across all four tests occasions. Knee extensor and plantar flexor maximal voluntary contraction (MVC) decreased from 176.6 ± 9.5 to 136.7 ± 16.8 Nm and 144.9 ± 8.7 to 119.2 ± 15.1 Nm post-marathon corresponding to 22 and 17%, respectively (P < 0.05). No significant changes were detected in evoked contractile parameters, except a 25% increase in force at 5 Hz, and low frequency fatigue was not observed. In conclusion, leg muscle power decreased acutely post-marathon race and recovered very slowly. The post-marathon increase in EE Mpace might be attributed to a reduction in stretch shortening cycle efficiency. Finally, since MVC was reduced after the marathon race without any marked changes in evoked muscle contractile properties, the strength fatigue experienced by the subjects in this study seems to be related to central rather than peripheral mechanisms.

- by Klavs Madsen
- •
- Skeletal muscle biology, Running, Low Frequency, Muscle strength

systems with techniques linking genes and pathways to physiology, from prokaryotes to eukaryotes. It is published publishes results of a wide variety of studies from human and from informative model Physiological Genomics by guest on June 11, 2013 http://physiolgenomics.physiology.org/ Downloaded from CrM supplementation on targeted mRNA expression and pro-Article published online before print. See web site for date of publication (http://physiolgenomics.physiology.org).

- by Simon Melov
- •
- Creatine, Cell Signaling, Gene expression, real time PCR

Weakness of the sound side in hemiparetic cerebral palsy is one of the serious complications which affect these children. Many children with hemiparetic cerebral palsy have diminished muscle power in the neglected sound side, and the application of strengthening exercises aim to improve the muscle strength and function activities and so may be helpful in the management of such cases. In this study, endurance exercises and treadmill training was conducted to investigate its effect on increasing the strength of the quadriceps femoris and hamstring muscles of the sound side in spastic diaplegic cerebral palsy in comparison to the effect of an endurance exercise program. Thirty spastic hemiparetic children were the sample of this work. There were divided randomly into two equal groups. The ratio of peak torque of quadriceps femoris muscle and the hamstring muscle and balance were measured before and after six months of the application of the treatment program. Group A received the physiotherapy program and treadmill training, while group B received endurance exercise in the form of DeLorme resistance exercise in addition to the same physiotherapy program given to group A. Significant improvement were observed in all measuring variables when comparing the post-treatment results in both groups.

- by Khaled A. Olama
- •
- Cerebral Palsy, Muscle strength, Balance, Muscle Power

- by Liv Strand
- •
- Nonparametric Statistics, Treatment Outcome, Muscle strength, Gait

The relationships between absolute peak muscle power (Wp~ak), muscle cross sectional area (CSAtot, i.e. the sum of both thigh and calf CSA) and muscle high energy phosphate concentration (adenosine 5'-triphosphate [ATP] and phosphocreatine concentrations [PC]) were studied in 47 subjects classified into five groups: A, 10 sedentary (S) subjects aged 20-35 years; B, 9 S aged 35-50 years; C, 9 S aged more than 50 years; D, 13 children aged 8-13 years; and E, 6 athletes (top level volleyball players) aged 24 (SD 3) years. The Wpeak was measured during a maximal vertical high jump off both feet on a force platform. The CSAtot was measured anthropometrically. The [ATP] and [PC] were determined by 31Phosphorus nuclear magnetic resonance spectroscopy. The Wpeak decreased with age, was 65% lower in D than in A, and 43% higher in E than in A. The CSAtot did not vary with age, was 45% smaller in D than in A, and 15% greater in E than in A. The [ATP] and [PC] were essentially the same in all groups. The changes observed in Wpeak were only partially accounted for by changes in CSAtot. Therefore, in addition to the variables investigated, other factors appear to have been involved in the determination of Wpeak with increasing age and training.

- by Tiziano Binzoni
- •
- Aging, Adolescent, Sports, Child

Purpose: Fifteen elite male handball players were studied to examine the effects of an entire season of play on physical fitness and throwing velocity. Methods: One repetition maximal bench press (1RM BP), jumping explosive strength, power-load relationship of the leg and arm extensor muscles, 5-and 15-m sprint running time, endurance running, and handball throwing velocity (standing and three-step running throw) were assessed on four times (T1, T2, T3, and T4), during a 45-wk season. Individual volumes and intensities of training and competition were quantified for 11 activities. Results: From T1 to T3, significant increases occurred in free fatty mass (1.4%), 1RM BP (1.9%), standing throwing velocity (6.5%), and three-step throwing velocity (6.2%). No significant changes were observed throughout the season in endurance running and explosive strength-related variables. Significant correlations (P G 0.05-0.01) were observed between strength training time and changes in standing throwing velocity as well as between high-intensity endurance training time and changes in endurance running. In addition, linear inverse relationships were observed between low-intensity endurance training time and changes in muscle power output of the lower extremities. Conclusion: The handball season resulted in significant increases in maximal and specific strength of the upper-extremity but not in the lower-extremity actions. The correlations observed suggest that training time at low intensity should be given less attention, whereas the training stimuli for high-intensity endurance running and leg strength training should be given more careful attention in the full training season program.

- by Javier Ibañez
- •
- Skeletal muscle biology, Anthropometry, Muscle strength, Sports

The objective of this research was to compare the effect of Post-Activation Performance Enhancement (PAPE) exerted on the back squat (BS) versus the barbell hip thrust (HT) on the sprint performance (5- and 10-m). 17 male amateur rugby players participated in the study (age 22.14 ± 2.52 years; body mass 81.06 ± 9.6 kg; height 1.78 ± 0.05 m). All participants performed a dynamic maximum strength test (3RM) in BS and HT at maximum speed. Two randomized sessions were performed inducing PAPE using BS or HT trough three series with three repetitions at 85% 1RM eight minutes before the sprint tests. An ANOVA of repeated measurement, found no differences in the time for 5-m (F = 0.398, P = 0.537, η2p = 0.024) or 10-m (F = 2.589, P = 0.127, η2p = 0.139). There were no significant differences in the Protocol effect between HT and BS in 5-m or 10-m (F = 2.963, P = 0.104, η2p = 0.156 and F = 1.472, P = 0.243 η2p = 0.084, respectively). There were also no differences in the Time x Protocol interaction at 5-m (F = 0.001, P = 0.976, η2p < 0.001) or 10-m (F = 4.174, P = 0.058, η2p = 0.207). The effect size obtained in the results of the sprint tests was small in both exercises (ES < 0.2). None of the BS or HT exercises performed with heavy load induced a significant PAPE phenomenon on the ability to sprint in rugby players.

In spite of the ecological relevance of terrestrial locomotion for many bird species, this function remains poorly studied to date. Gait preferences and transitions seem present, but it is not known which factors might determine the running style. Morphological and morphometric data needed for further biomechanical modelling are presented for the black-billed magpie (Pica pica), a species which walks, runs and hops. Detailed descriptions of the muscle-tendon systems and the attachment sites on the hindlimb skeleton are given. Pinnation angles, fibre lengths and muscle masses are determined. From the latter two, physiological cross-sections of the muscle bundles are calculated. Tendon ossifications are qualitatively scored. Further, information on the mechanical variables of the body segments are collected (i.e. mass, length, position of the centre of gravity and moment of inertia of digits, tarsometatarsus, lower leg, upper leg, body, and head/neck).

- by Frits De Vree
- •
- Zoology, Functional Morphology, Cross Section, Muscle Power

Muscular power, an integral component in most sport, is the product of force and velocity. Power is often viewed as synonymous, yet incorrectly, with strength. Where power has an inherent speed component, strength is independent of movement velocity, and is a measure of a muscle’s ability to produce a maximal force. In a majority of athletic events power is requisite to success, and is often more decisive in performance outcomes than strength alone. Currently, results from existing research examining the effectiveness of differing velocities of contraction in improving maximal power are mixed. Common methodologies used in research settings to study muscular power changes are isotonic training, isokinetic training, isometric training, and plyometric training. However, little research has been done examining the potential efficacy of training using inertial loading. This report examines existing research on movement velocities and loads, compares the effects of training velocities for increasing maximal power, identifies shortfalls and information gaps, and recommends future research in training for muscular power adaptations and improved athletic performance. This report also provides a detailed description of inertial load training and establishes a theoretical study design, hypothesis, and reasoning outlining why and how inertial load training may elicit muscular power increases and improved athletic performance.

- by Mike Brenneman
- •
- Muscle strength, Muscle Power, Muscle Contractions, muscular contraction

Aquaculture of sea bass is widely spread in the Mediterranean and employs a variety of husbandry protocols that need to be evaluated in terms of fish well-being. Behavioural tests can be used as operational indicators of short-term stress, because changes in swimming performance and/or muscle activity (e.g. electromyograms) can be interpreted as response associated with a wide variety of stressors. Diagnostic procedures, based on physiological telemetry, will thus enable appropriate mitigative strategies to be implemented to ensure the well-being of cultured fish. The objective of this study was to examine the contribution of two muscle types to the swimming activity of sea bass (Dicentrarchus labrax, L. 1758). Hard-wire technology was used to 'fine-tune' measures obtained using a physiological transmitter. Fine-tuning showed that the Guest editors: be utilised to monitor the proportion of the scope of activity utilised in response to external stressors. This proportion and the level of compensatory ability remaining could represent a measure of well-being in cultured fish.

- by M. Scolamacchia and +2
- •
- Earth Sciences, Biological Sciences, Environmental Sciences, Swimming speed

Current antispastic medications are unsatisfactory for spasticity treatment, but botulinum toxin type A (BTX-A) shows promise as a new therapeutic option. This open-label, prospective study aimed to assess the effectiveness of BTX-A in improving functional mobility in the early post-stroke population using an individualised, flexible range of doses and targeted muscle groups. Twenty-one stroke patients (13 male, 8 female) were enrolled and injected with BTX-A (Botox, Allergan, mean dose: 255 U; range: 185-300) according to individual spasticity patterns. Assessments were made at baseline and weeks 2, 4,

- by jarosław sławek
- •
- Skeletal muscle biology, Treatment Outcome, Stroke, Prospective studies

Previous work had identi"ed six biomechanical functions that need to be executed by each limb in order to produce a variety of pedaling tasks. The functions can be organized into three antagonistic pairs: an Ext/Flex pair that accelerates the foot into extension or #exion with respect to the pelvis, an Ant/Post pair that accelerates the foot anteriorly or posteriorly with respect to the pelvis, and a Plant/Dorsi pair that accelerates the foot into plantar#exion or dorsi#exion. Previous analyses of experimental data have inferred that muscles perform the same function during di!erent pedaling tasks (e.g. forward versus backward pedaling) because the EMG timing was similar, but they did not present rigorous biomechanical analyses to assess whether a muscle performed the same biomechanical function, and if so, to what degree. Therefore, the objective of this study was to determine how individual muscles contribute to these biomechanical functions during two di!erent motor tasks, forward and backward pedaling, through a theoretical analysis of experimental data. To achieve this objective, forward and backward pedaling simulations were generated and a mechanical energy analysis was used to examine how muscles generate, absorb or transfer energy to perform the pedaling tasks. The results showed that the muscles contributed to the same primary biomechanical functions in both pedaling directions and that synergistic performance of certain functions e!ectively accelerated the crank. The gluteus maximus worked synergistically with the soleus, the hip #exors worked synergistically with the tibialis anterior, and the vasti and hamstrings functioned independently to accelerate the crank. The rectus femoris used complex biomechanical mechanisms including negative muscle work to accelerate the crank. The negative muscle work was used to transfer energy generated elsewhere (primarily from other muscles) to the pedal reaction force in order to accelerate the crank. Consistent with experimental data, a phase shift was required from those muscles contributing to the Ant/Post functions as a result of the di!erent limb kinematics between forward and backward pedaling, although they performed the same biomechanical function. The pedaling simulations proved necessary to interpret the experimental data and identify motor control mechanisms used to accomplish speci"c motor tasks, as the mechanisms were often complex and not always intuitively obvious.