TY - JOUR A1 - Zuur, Abraham T. A1 - Lundbye-Jensen, Jesper A1 - Leukel, Christan A1 - Taube, Wolfgang A1 - Grey, Michael J. A1 - Gollhofer, Albert A1 - Nielsen, Jens Bo A1 - Gruber, Markus T1 - Contribution of afferent feedback and descending drive to human hopping N2 - During hopping an early burst can be observed in the EMG from the soleus muscle starting about 45 ms after touch-down. It may be speculated that this early EMG burst is a stretch reflex response superimposed on activity from a supra-spinal origin. We hypothesised that if a stretch reflex indeed contributes to the early EMG burst, then advancing or delaying the touch-down without the subject's knowledge should similarly advance or delay the burst. This was indeed the case when touch-down was advanced or delayed by shifting the height of a programmable platform up or down between two hops and this resulted in a correspondent shift of the early EMG burst. Our second hypothesis was that the motor cortex contributes to the first EMG burst during hopping. If so, inhibition of the motor cortex would reduce the magnitude of the burst. By applying a low-intensity magnetic stimulus it was possible to inhibit the motor cortex and this resulted in a suppression of the early EMG burst. These results suggest that sensory feedback and descending drive from the motor cortex are integrated to drive the motor neuron pool during the early EMG burst in hopping. Thus, simple reflexes work in concert with higher order structures to produce this repetitive movement. Y1 - 2010 UR - http://jp.physoc.org/ U6 - https://doi.org/10.1113/jphysiol.2009.182709 SN - 0022-3751 ER - TY - JOUR A1 - Granacher, Urs A1 - Gruber, Markus A1 - Foerderer, Dominik A1 - Strass, Dieter A1 - Gollhofer, Albert T1 - Effects of ankle fatigue on functional reflex activity during gait perturbations in young and elderly men N2 - There is growing evidence that aging and muscle fatigue result in impaired postural reflexes in humans. Therefore, the objective of this study was to examine the effects of ankle fatigue on functional reflex activity (ERA) during gait perturbations in young and elderly men. Twenty-eight young (27.0 +/- 3.1 years, n = 14) and old (67.2 +/- 3.7 years, n = 14) healthy active men participated in this study. Fatigue of the plantarflexors and dorsiflexors was induced by isokinetic contractions. Pre and post-fatigue, subjects were tested for their ability to compensate for decelerating gait perturbations while walking on a treadmill. Latency, ERA of lower extremity muscles and angular velocity of the ankle joint complex were analysed by means of surface electromyography and goniometry. After the fatigue protocol, no significant main and interaction effects were detected for the parameter latency in m. tibialis anterior (TA). For both groups, a significant pre to post-test decrease in ERA in TA (P<.001) was observed coming along with increases in antagonist coactivity (P=.013) and maximal angular velocity of the ankle joint (p=.007). However, no significant group x test interactions were found for the three parameters. Ankle fatigue has an impact on the ability to compensate for gait perturbations in young and elderly adults. However, no significant differences in all analysed parameters were detected between young and elderly subjects. These results may imply that age-related deteriorations in the postural control system do not specifically affect the ability to compensate for gait perturbations under fatigued condition. Y1 - 2010 UR - http://www.sciencedirect.com/science/journal/09666362 U6 - https://doi.org/10.1016/j.gaitpost.2010.03.016 SN - 0966-6362 ER - TY - JOUR A1 - Fimland, Marius S. A1 - Helgerud, Jan A1 - Gruber, Markus A1 - Leivseth, Gunnar A1 - Hoff, Jan T1 - Enhanced neural drive after maximal strength training in multiple sclerosis patients N2 - Multiple sclerosis (MS) patients suffer from impaired muscle activation and lower limb strength. Strength training enhances muscle activation and muscle strength, but neural adaptations to strength training remain unexplored in MS patients. The hypothesis was that maximal strength training (MST) using high loads and few repetitions would improve central neural drive and thus strength capacity of MS patients. 14 MS patients staying at a national MS rehabilitation center were randomly assigned to a MST group or a control group (CG). Both groups received "today's treatment". In addition, the MST group trained 4 x 4 repetitions of unilateral dynamic leg press and plantar flexion 5 days a week for 3 weeks. Neural adaptations of the soleus muscle were assessed by surface electromyography (EMG) activity, and by superimposed H-reflexes and V-waves obtained during maximum voluntary isometric plantar flexor contractions (MVCs). H-reflexes and V-waves were normalized by the M-wave (H (SUP)/M (SUP), V/M (SUP), respectively). In the MST group, MVC increased by 20 +/- A 9% (P < 0.05). Soleus EMG activity and V/M (SUP) ratio increased by 40 and 55%, respectively, in the MST group compared to the CG (P a parts per thousand currency sign 0.05). The H (SUP)/M (SUP) ratio remained unchanged. No change was apparent in the CG. MST group subjects were able to complete all training sessions. No adverse effects were reported. This randomized study provides evidence that MST is effective of augmenting the magnitude of efferent motor output of spinal motor neurons in MS patients, alleviating some neuromuscular symptoms linked to the disease. Y1 - 2010 UR - http://www.springerlink.com/content/100513 U6 - https://doi.org/10.1007/s00421-010-1519-2 SN - 1439-6319 ER -