Maria Ekblom - Profile on Academia.edu (original) (raw)

Papers by Maria Ekblom

Endpoint control in a bimanual striking task : application to the golfswing

Passive muscle length changes affects twitch potentiation in power athletes

Effects of training with concurrent EMG feedback on Quadriceps stength and activation

Balance mechanisms in children with and without motor coordination difficulties

Trunk muscle activation at the initiation and breaking of bilateral arm flexion movements of different amplitudes

Acute effects of concurrent EMG feedback on knee extensor strength and activation

Effects of arm movement amplitude on the initial trunk muscle activation pattern during raptid bilateral shoulder flexions during standing

Resistance training improves aerobic capacity and glucose tolerance in elderly

The primary aim of this study was to examine central fatigue of the plantar flexor muscle group a... more The primary aim of this study was to examine central fatigue of the plantar flexor muscle group after prolonged running using the twitch interpolation technique. Eight healthy, habitually active male subjects ran on a motorized treadmill for 2 h at a speed corresponding to 75% of peak oxygen uptake (VO 2peak ). Maximal voluntary isometric contraction (MVC) strength as well as the electrically induced twitch produced during MVC [interpolated twitch (IT)] and at rest [resting twitch (RT)] were measured before and after running. The level of activation (LOA) during each MVC was calculated as LOA (%) 5 100(1 À IT/RT). Both MVC and LOA decreased (17 AE 16% and 19 AE 15%, respectively, Po0.05) after running, whereas RT did not change. The decrease in MVC was correlated with the decrease in LOA (r 5 0.87, Po0.05). The results demonstrate that after 2 h of treadmill running at an intensity of 75% of VO 2peak , there was a reduction in maximal voluntary plantar flexor muscle strength that was mainly related to central fatigue.

Motor control of the trunk during a modified clean and jerk lift

The purpose of the present study was to investigate the pattern of trunk muscle activation and in... more The purpose of the present study was to investigate the pattern of trunk muscle activation and intra-abdominal pressure (IAP) in a somewhat modified version of the clean and jerk lift. Nine healthy physically active male amateurs performed the exercise with a 30-kg barbell. Muscle activity was registered with electromyography from transversus abdominis (TrA) and obliquus internus (OI) using intramuscular electrodes and from rectus abdominis (RA) and erector spinae (ES) with surface electrodes. IAP was recorded with a nasogastric catheter. Measurements were made in various static positions throughout the lift and in the transitional phases separating them, both during lifting and lowering. The results demonstrated that the innermost abdominal muscle, TrA, showed increased activation levels in the two highest positions, whereas ES was most active, together with the highest IAP, in the lowest position. OI and RA showed generally little activation and no obvious trend throughout the lift. The results strengthen the view of a contributing role of TrA to the upright control of the trunk and indicate that the clean and jerk lift might constitute a whole-body exercise, still targeting the TrA muscle, in late-stage rehabilitation, especially for athletes during return to sports.

Post activation potentiation can be induced without impairing tendon stiffness

This study aimed to investigate conditioning effects from a single 6-s plantar flexion maximal vo... more This study aimed to investigate conditioning effects from a single 6-s plantar flexion maximal voluntary isometric contraction (MVIC) on Achilles tendon stiffness (ATS) and twitch properties of the triceps surae in athletes. Peak twitch (PT), rate of torque development (RTD), rising time (RT₁₀₋₉₀%) and half relaxation time (HRT) were measured from supramaximal twitches evoked in the plantar flexors of 10 highly trained athletes. Twitches were evoked before and at seven occasions during 10 min of recovery after a 6-s MVIC. In a second session, but at identical post-conditioning time points, ATS was measured at 30 and 50% of MVIC (ATS₃₀% and ATS₅₀%) using an ultrasonography-based method. The magnitude and duration of the conditioning MVIC on muscle contractile properties were in accordance with previous literature on post activation potentiation (PAP), i.e., high potentiation immediately after MVIC, with significant PAP for up to 3 min after the MVIC. While PT and RTD were significantly enhanced (by 60.6 ± 19.3 and 90.1 ± 22.5%, respectively) and RT₁₀₋₉₀% and HRT were reduced (by 10.1 ± 7.7 and 18.7 ± 5.6%, respectively) after conditioning, ATS remained unaffected. Previous studies have suggested that changes in stiffness after conditioning may interfere with the enhancements in twitch contractile properties. The present study, however, provided some evidence that twitch enhancements after a standard PAP can be induced without changes in ATS. This result may suggest that athletes can use this protocol to enhance muscle contractile properties without performance deficits due to changes in ATS.

The Journal of Physiology, 2001

Scandinavian Journal of Medicine and Science in Sports, 2006

Whole-body vibration (WBV) has been suggested to have a beneficial effect on muscle strength. Man... more Whole-body vibration (WBV) has been suggested to have a beneficial effect on muscle strength. Manufacturers of vibration platforms promote WBV as an effective alternative or complement to resistance training. This study aimed to review systematically the current (August 2005) scientific support for effects of WBV on muscle strength and jump performance. MEDLINE and SPORT DISCUS were searched for the word vibration in combination with strength or training. Twelve articles were included in the final analysis. In four of the five studies that used an adequate design with a control group performing the same exercises as the WBV group, no difference in performance improvement was found between groups, suggesting no or only minor additional effects of WBV as such. Proposed neural mechanisms are discussed.

Neuroscience Letters, 2004

Despite higher neural activation during active as compared to passive muscle shortening, Hoffman ... more Despite higher neural activation during active as compared to passive muscle shortening, Hoffman reflexes (H-reflexes) are similar. This may be explained by homosynaptic post-activation depression (HPAD) of Ia-afferents being present during active shortening. Accordingly, it was investigated whether conditioning electrical stimulation of the tibial nerve reduced the H-reflex less during active than passive shortening. The effects of two conditioning modes (0.2 and 1 Hz) were compared to a control mode without conditioning. H-reflexes and M-waves were elicited as the ankle passed 90 • with the soleus muscle undergoing passive or active (20% MVC) lengthening or shortening. Conditioning had no effect during active shortening. In contrast, during passive shortening, the H:M of the 1 Hz mode was significantly less than that of the 0.2 Hz and control modes. In lengthening, H:M was unaffected by conditioning. These findings support that HPAD reduces the synaptic efficacy of Ia-afferents during active shortening, active and passive lengthening, but not passive shortening.

Passive Muscle Length Changes Affect Twitch Potentiation in Power Athletes

Medicine & Science in Sports & Exercise, 2014

A conditioning maximal voluntary muscle action (MVC) has been shown to induce postactivation pote... more A conditioning maximal voluntary muscle action (MVC) has been shown to induce postactivation potentiation, that is, improved contractile muscle properties, when muscles are contracted isometrically. It is still uncertain how the contractile properties are affected during ongoing muscle length changes. The purpose of this study was to investigate the effects of a 6-s conditioning MVC on twitch properties of the plantarflexors during ongoing muscle length changes. Peak twitch, rate of torque development, and rate of torque relaxation, rising time, and half relaxation time were measured from supramaximal twitches evoked in the plantarflexors of 11 highly trained athletes. Twitches were evoked before a 6-s MVC and subsequently on eight different occasions during a 10-min recovery for five different modes: fast lengthening, slow lengthening, isometric, fast shortening, and slow shortening of the plantarflexors. The magnitude and the duration of effects from the conditioning MVC were significantly different between modes. Peak twitch, rate of torque development, and rate of torque relaxation significantly increased for all modes but more so for twitches evoked during fast and slow shortening as compared with lengthening. Rising time was reduced in the lengthening modes but slightly prolonged in the shortening modes. Half relaxation time was significantly reduced for all modes, except fast lengthening. The findings show that the effects of a conditioning MVC on twitch contractile properties are dependent on direction and velocity of ongoing muscle length changes. This may imply that functional enhancements from a conditioning MVC might be expected to be greatest for concentric muscle actions but are still present in isometric and eccentric parts of a movement.

Effects of Prolonged Vibration on H-Reflexes, Muscle Activation, and Dynamic Strength

Medicine & Science in Sports & Exercise, 2011

Neural activation is generally lower during maximal voluntary lengthening compared with shortenin... more Neural activation is generally lower during maximal voluntary lengthening compared with shortening and isometric muscle actions, but the mechanisms underlying these differences are unclear. In maximal voluntary isometric actions, reduced Ia-afferent input induced by prolonged tendon vibration has been shown to impair neural activation and strength. This study aimed to investigate whether reducing Ia-afferent input influences neural activation in maximal voluntary dynamic muscle actions and, if so, whether it affects shortening and lengthening muscle actions differently. Eight women participated in three familiarization sessions and two randomly ordered experiments. In one experiment, 30-min vibration at 100 Hz was applied to the Achilles tendon to decrease Ia-afferent input as measured by the H-reflex. In the control experiment, rest substituted the vibration. Root mean square EMG from plantar and dorsiflexor muscles and plantar flexor strength were measured during maximal voluntary plantar flexor shortening and lengthening actions (20°·s(-1)) before and after vibration and rest, respectively. Soleus H-reflexes and M-waves were elicited before each set of strength tests. The vibration caused a decrease in H-reflex amplitude by, on the average, 33%, but root mean square EMG and plantar flexor strength remained largely unaffected in both action types. The findings suggest that Ia-afferent input may not substantially contribute to maximal voluntary dynamic muscle strength of the plantar flexor muscles, as tested here, and thus, the results do not support the notion that Ia-afferent excitation would contribute differently to neural activation in maximal voluntary lengthening and shortening muscle actions.

Manual Therapy, 2010

The deepest muscle of the human ventro-lateral abdominal wall, the Transversus Abdominis (TrA), h... more The deepest muscle of the human ventro-lateral abdominal wall, the Transversus Abdominis (TrA), has been ascribed a specific role in spine stabilization, which has motivated special core stability exercises and hollowing instruction to specifically involve this muscle. The purpose here was to evaluate the levels of activation of the TrA and the superficial Rectus Abdominis (RA) muscles during five common stabilization exercises performed in supine, bridging and four-point kneeling positions, with and without instruction to hollow, i.e. to continuously pull the lower part of the abdomen towards the spine. Nine habitually active women participated and muscle activity was recorded bilaterally from TrA and RA with intramuscular fine-wire electrodes introduced under the guidance of ultrasound. Results showed that subjects were able to selectively increase the activation of the TrA, isolated from the RA, with the specific instruction to hollow and that side differences in the amplitude of TrA activity, related to the asymmetry of the exercises, remained even after the instruction to hollow. The exercises investigated caused levels of TrA activation from 4 to 43% of that during maximal effort and can thus be used clinically to grade the load on the TrA when designing programs aiming at training that muscle.

Central and peripheral contributions to fatigue in relation to level of activation during repeated maximal voluntary isometric plantar flexions

Journal of Applied Physiology, 2003

This study aimed to investigate central and peripheral contributions to fatigue during repeated m... more This study aimed to investigate central and peripheral contributions to fatigue during repeated maximal voluntary isometric plantar flexions (MVCs). Changes in joint torque, level of activation (LOA), resting twitch amplitude (RT), electromyographic signals (EMG), and presynaptic inhibition of Ia afferents were investigated during 9 bouts of 10 MVCs. MVCs lasted for 2 s and were separated by 1 s. The interval between bouts was 10 s. Electrical stimulation was applied to the tibial nerve; at rest to evoke RTs, M waves, and two (1.5-s interval) H reflexes; with the soleus EMG at 30% of that during MVC to evoke M waves and two H reflexes; and during MVCs to measure LOA. Over the nine bouts, LOA decreased by 12.6% and RT by 16.2%. EMG root mean square during MVCs remained unchanged for the soleus and tibialis anterior muscles, but it decreased for medial gastrocnemius. Peripheral fatigue (decrease in RT) was positively correlated to LOA, whereas central fatigue (decrease in LOA) was not. Depression of both H reflexes suggests that presynaptic inhibition after the first bout was partly induced by homosynaptic postactivation depression of the Ia terminal. The H-reflex-to-M-wave ratio increased with fatigue in both passive and active states, with no change in the ratio of the second H reflex to the first, thereby indicating a decrease of presynaptic inhibition during fatigue. The results indicate that both central and peripheral mechanisms contributed to the fatigue observed during repeated MVCs and that the development of peripheral fatigue was influenced by the level of voluntary activation and initial plantar flexor torque.

Gait & Posture, 2011

M.E. Crommert), maria.ekblom@gih.se (M.M. Ekblom), alf.thorstensson@gih.se (A. Thorstensson).

European Journal of Applied Physiology, 2012

The purpose of this study was to investigate the acute effects of electromyographic (EMG) feedbac... more The purpose of this study was to investigate the acute effects of electromyographic (EMG) feedback on muscle activation and strength during maximal voluntary concentric and eccentric muscle actions. 15 females performed two sets of three lengthening and three shortening maximal voluntary isokinetic knee extensions at 20°s -1 over 60°range of motion. After the first set, subjects were randomized to either a control group (n = 8) or a feedback group (n = 7). In the second set, the control group performed tasks identical to those in the first set, whereas the feedback group additionally received concurrent visual feedback of the EMGrms from Vastus Medialis (VM). Knee extensor strength and EMG activation of VM, Vastus lateralis (VL) and hamstrings (HAM) were measured during the MVCs. Analyses were performed separately in a 1 s preactivation phase, a 1 s initial movement phase and a 1 s late movement phase. EMG feedback was associated with significantly higher knee extensor strength in all phases (20.5% p \ 0.05, 18.2% p \ 0.001 and 19% p \ 0.001, respectively) for the eccentric MVCs and in the preactivation phase (16.3%, p \ 0.001) and initial movement phases (7.2%, p \ 0.05) for concentric MVCs. EMG feedback from VM further improved activation in VM and HAM but not VL. These findings suggested that concurrent visual EMG feedback from VM could acutely enhance muscle strength and activation. Before recommending implementation of EMG feedback in resistance training paradigms, the feedback parameters needs to be optimized and its long-term effects needs to be scrutinized.