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  -