Maximal voluntary force and rate of force development in humans--importance of instruction (original) (raw)
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Relationship between maximal rate of force development and maximal voluntary contraction
The aim of this research was to examine relationships between the maximal rate of force development (MRFD) expressed in absolute and relative values and the maximal voluntary contraction (MVC) in the knee and elbow flexors and extensors. The sample consisted of thirty male PE students. Eight measuring sessions were performed using the BIODYNA dynamometer. During maximal isometric contraction of the knee and elbow flexors and extensors MVC and MRFD were recorded. The results showed that the relationship between MVC and MRFD is dependent on the expression of the MRFD. Regardless of the studied muscle group, there were significant correlations between MVC and MRFD [Nm/s]. When MRFD was expressed in relative values [%MVC/s] the relationships between its parameters were not significant. Due to the significant influence of the MVC level on MRFD expressed in absolute values, it may be more appropriate to use MRFD expressed in relative values for the assessment of muscle contractile propert...
The research has been carried out in order to measure the variability of the development of muscle force control achieved by the arms extensor muscle within the task requirements. The experiment involved testing the arm extensor muscle by using the isometric Flat Bench Press Test. The sample consisted of 28 subjects who were students of the College of Internal Affairs in Zemun-Belgrade. The subjects had underwent five individual test trials, within which the first trial measured the maximum isometric muscle force (F max izo) and in the other four cases depended on the acquired percentage of F max izo at the levels of 30%, 50%, 70% and 90%. The testing was developed by using a hardware-software system applied in the Special Physical Education Laboratory at the College of Internal Affairs. The variability differences among the observed variables were measured by implementing the ANOVA variance analysis, Kandall′s and Wilcoxon′s Test. In order to establish the differences among individual variables, the Student′s t-test of equal samples was used. The ANOVA results showed a statistically significant difference between the mean values and variability among all of the observed variables at the F = 6.065, p = 0.001 level, in relation to the absolute values and F = 9.956, p = 0.000 and in relation to relative force values. The results of the Student′s t-test showed a statistically significant difference among the mean value of errors in the developed force between the level of 30 percent (as the smallest force of the level tested) and all the other levels of 50%, 70% and 90% (as the middle, large and submaximum level of force). Kandall′s test showed that the error distribution, that is, the level of force deviation from the force level required by the task, differs from the aspect of absolute and the aspect of relative values (values in percents) at the p = 0.000 level. According to the results, it can be concluded that in regards to the control of muscle force distribution as part of the task, a healthy and untrained male population mostly makes errors in the sense of a low level of force (at
Clinical Physiology and Functional Imaging, 2017
Rate of force development (RFD) refers to the ability of the neuromuscular system to increase contractile force from a low or resting level when muscle activation is performed as quickly as possible, and it is considered an important muscle strength parameter, especially for athletes in sports requiring high-speed actions. The assessment of RFD has been used for strength diagnosis, to monitor the effects of training interventions in both healthy populations and patients, discriminate high-level athletes from those of lower levels, evaluate the impairment in mechanical muscle function after acute bouts of eccentric muscle actions and estimate the degree of fatigue and recovery after acute exhausting exercise. Notably, the evaluation of RFD in human skeletal muscle is a complex task as influenced by numerous distinct methodological factors including mode of contraction, type of instruction, method used to quantify RFD, devices used for force/torque recording and ambient temperature. Another important aspect is our limited understanding of the mechanisms underpinning rapid muscle force production. Therefore, this review is primarily focused on (i) describing the main mechanical characteristics of RFD; (ii) analysing various physiological factors that influence RFD; and (iii) presenting and discussing central biomechanical and methodological factors affecting the measurement of RFD. The intention of this review is to provide more methodological and analytical coherency on the RFD concept, which may aid to clarify the thinking of coaches and sports scientists in this area.
Evaluation of the Isometric and Dynamic Rates of Force Development in Multi-Joint Muscle Actions
Journal of Human Kinetics, 2022
The rate of force development (RFD) in the isometric leg press (ILP), the countermovement jump (CMJ) and the squat jump (SJ) were examined in twenty-three (9 females) team sport athletes aged 21-24 years. Peak force (Fpeak), peak rate of force development (RFDpeak) and RFD at different time epochs (0-50, 50-100, 100-150, 150-200) were calculated from the force-time curve, as well as CMJ and SJ height and the center of mass displacement. RFDpeak, RFD at 0-50, 50-100 and 100-150 ms and Fpeak were similar between the CMJ and the SJ (p = 0.26 to 0.99). Furthermore, RFD0-50 ms was similar between the ILP, the CMJ, and the SJ (p = 0.99 to 0.57). Higher values were observed in the ILP compared with the CMJ and the SJ in RFD50-100 ms and RFD100-150 ms (p < 0.001) and these differences were maintained even when RFD was scaled to body mass. The higher RFD normalized to Fpeak was attained at the 50-100 ms time interval with no differences between the ILP, CMJ and SJ and between males and fe...
This study examined the effect of fast-velocity concentric isokinetic resistance training (FV) on the rate of force development (RFD) at early (<100 ms) and late phases (>100 ms) of rising muscle force. Nine men participated in a 6-week resistance training intervention for the lower body, and nine matched subjects participated as controls (CON). During concentric isokinetic (180°s À1 ) knee extension training, subjects were instructed to do each contraction 'as fast and forcefully as possible'. Maximal muscle strength (MVC) and RFD (0-10, 0-20, …, 0-250 ms from the onset of contraction) were measured during maximal voluntary isometric contraction of the knee extensors (KE). There were no significant changes in MVC of KE in both groups after intervention (FV = 314Á2 AE 101Á1 versus 338Á7 AE 88Á0 N•m, P>0Á05; CON = 293Á3 AE 94Á8 versus 280Á0 AE 72Á2 N•m, P>0Á05). The RFD increased 39-71% at time intervals up to 90 ms from the onset of the contraction (P<0Á05), whereas no change occurred at later time intervals. Similarly, relative RFD (i.e.%MVC•s À1 ) (RFDr) increased 33-56% at time intervals up to 70 ms from the onset of the contraction (P<0Á05). It can be concluded that a short period of resistance training performed with concentric fast-velocity isokinetic muscle contractions is able to enhance RFD and RFDr obtained at the early phase of rising muscle force.
European Journal of Applied Physiology, 2002
The present study was aimed at investigating differences of maximal strength (F max) of the elbow flexors and characteristics of the surface electromyogram (EMG) between six gymnasts (G) and six untrained (UT) 10-year-old boys during brief and maintained maximal voluntary isometric contraction (MVC). The F max was estimated during 5 s MVC (maximal test, MT) and normalized to the cross sectional area (CSA) of the arm. The EMG signal of the biceps brachii was recorded during MT and during a 25 s maintained MVC (fatigue test). Values were calculated for root-mean-square (rmsMT) and mean power frequency (MPFMT) of the EMG signal for the duration of the MT. For the fatigue test, MPF were normalized to the initial value (MPFn) and kinetics were expressed by the slope coefficient of linear regression. Although F max and F max/CSA tended to be higher for G than UT, the differences did not reach significance. The MPFMT was significantly higher for G [mean (SD)][136 (8) Hz] than for UT [125 (9) Hz]. The MPFn slope coefficients were significantly greater for G than for UT [–1.0 (0.2) and –0.5 (0.3), respectively]. When all the children were considered, F max was significantly correlated to MPFMT (r=0.61). These results showed that gymnasts tend to have higher F max and F max/CSA accompanied by a significantly higher MPFMT and a steeper MPF downshift. Moreover, children with greater strength tended to have higher MPFMT. It is suggested that spatial and/or temporal recruitment of more fatigable fast motor units could have been enhanced in G and more generally, that it could be a mechanism that would explains, in part, the level of force production in children.
Rapid Force Production in Children and Adults
Medicine & Science in Sports & Exercise, 2013
Purpose: Children demonstrate lower force production capacities compared with adults, which has often been attributed to ''neuromuscular immaturity.'' However, tendon stiffness, which influences both the electromechanical delay (EMD) and rate of force development (RFD) in adults, is lower in children and may influence rapid force production. The aims of this study were 1) to document EMD and RFD variation as a function of age, 2) to determine the relationships between tendon stiffness and parameters relating to rapid force production in children and adults, and 3) to estimate the relative neural and mechanical contributions to age-related changes in force production by examining the effects of tendon stiffness and muscle activation rate (rate of EMG increase [REI]) on RFD. Methods: Achilles tendon stiffness, EMD, RFD, and REI were measured during plantarflexion contractions in 47 prepubertal children (5-12 yr) and 19 adults. Relationships were determined between 1) stiffness and EMD, 2) stiffness and RFD, and 3) REI and RFD. The relative contributions of age, stiffness, and REI on RFD were determined using a multiple regression analysis. Age-related differences in tendon stiffness, EMD, RFD, and REI were also examined according to chronological age (5-6, 7-8, and 9-10 yr) and compared with adults. Results: Increases in tendon stiffness with age were correlated with decreases in EMD (r G j0.83). Stiffness and REI could account for up to 35% and 30% of RFD variability in children, respectively, which increased to 58% when these variables were combined. Conclusions: Both neural and mechanical factors influence rapid force production in prepubertal children. Children's longer EMD and slower RFD indicate a less effective development and transfer of muscular forces, which may have implications for complex movement performance.
Reactive strength index-modified (RSImod) may be an important variable to measure in the performance testing and monitoring of athletes, and very little work has examined this particular variable. One hundred six Division-I collegiate athletes performed countermovement jumps and the isometric mid-thigh pull. The relationship between the RSImod and variables from the isometric mid-thigh pull representative of explosive performance were evaluated with Pearson's r. Relationships between RSImod and variables related to explosiveness ranged from moderate to large. Maximum and relative maximum strength had the strongest correlations to RSImod. RSImod appears to be a measure of explosiveness. Furthermore, an athlete's isometric strength may be an indicator of their reactive strength.
Muscle strength testing: evaluation of tests of explosive force production
European Journal of Applied Physiology, 2004
The purpose of the study was to evaluate four tests of explosive force production (EFP). Specifically, the main aims of the study were to assess the reliability of different EFP tests, to examine their relationship with maximum muscle strength, and to explore the relationship between EFP tests and functional movement performance. After an extensive preliminary familiarization with the tasks, subjects (n=26) were tested on maximum explosive strength of the elbow extensor and flexor muscle, as well as on rapid elbow extension and flexion movements performed in both an oscillatory and a discrete fashion. In addition to maximum force (F max ), four different EFP tests were assessed from the recorded force-time curves: the time interval elapsed between achieving 30% and 70% of F max (F 30-70% ), the maximum rate of force development (RFD), the same value normalized with respect to F max (RFD/F max ), and the force exerted 100 ms after the contraction initiation (F 100 ms ). Excluding F 30-70% , all remaining EFP tests revealed either good or fair reliability (intraclass correlation coefficients being within 0.8-1 and 0.6-0.8 intervals, respectively) which was also comparable with the reliability of F max . RFD and F 100 ms demonstrated a positive relationship with F max , but not T 30-70% and RFD/F max . Stronger elbow flexor muscles also demonstrated higher values of RFD and F 100 ms than weaker elbow extensor muscles, while no difference was observed between either T 30-70% or RFD/F max recorded from two muscles. Despite the simplicity of the tested movement tasks, the relationship observed between the EFP tests and the peak movement velocity remained moderate and partly insignificant. It was concluded that most of the EFP tests could be reliable for assessing neuromuscular function in their muscle-force-(or, indirectly, muscle size) dependent (such as RFD and F 100 ms ), or muscle-force-independent (T 30-70% and RFD/ F max ) forms. However, their ''external validity'' when applied to assess the ability to perform rapid movements could be questioned.
Variability of Multiangle Isometric Force-Time Characteristics in Trained Men
Journal of Strength and Conditioning Research, 2019
Measurements of isometric force, rate of force development (RFD) and impulse are widely reported. However, little is known about the variability and reliability of these measurements at multiple angles, over repeated testing occasions in a homogenous, resistance-trained population. Thus, understanding the intersession variability of multi-angle isometric force-time characteristics provides the purpose of this paper. Three sessions of isometric knee extensions at 40º, 70º and 100º of flexion were performed by 26 subjects across 51 limbs. All assessments were repeated on three occasions separated by 5-8 days. Variability was qualified by doubling the typical error of measurement (TEM), with thresholds of 0.2-0.6 (small), 0.6-1.2 (moderate), 1.2-2.0 (large), 2.0-4.0 (very large) and >4.0 (extremely large). Additionally, variability was deemed large when the intraclass correlation coefficient (ICC) was <0.67 and coefficient of variation (CV)>10%; moderate when ICC>0.67 or CV<10% (but not both); and small when both ICC>0.67 and CV<10%. Small to moderate between-session variability (ICC=0.68-0.95, CV=5.2-18.7%, TEM=0.24-0.49) was associated with isometric peak force, regardless of angle. Moderate to large variability was seen in early-stage (0-50 ms) RFD and impulse (ICC=0.60-0.80, CV=22.4-63.1%, TEM=0.62-0.74). Impulse and RFD at 0-100 ms, 0-200 ms and 100-200 ms were moderately variable (ICC=0.71-0.89, CV=11.8-42.1%, TEM=0.38-0.60) at all joint angles. Isometric peak force and late-stage isometric RFD and impulse measurements were found to have low intersession variability regardless of joint angle. However, practitioners need to exercise caution when making inferences about early-stage RFD and impulse measures due to moderate-large variability.