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Modulation of H-reflexes during hopping and jumping tasks
469
Abstracts ENERQY EFFICIENCY OF DIFFERENT OF WALKING AND JOGGING
FOOT
PROSTHBSES
Ulrich Glitach and Wolfgang Baurann, Institut Deutsche Sporthochechule KSln, W. GermanT.
DURING
STANCE
PHASE
fiir Biorechrnik,
In &signing foot prostheses the energy efficiency of the artificial feet seems to be of great significance. The intention is to compensate tbe absence of muscle function with elastic elements in the prosthesis. Especially during propulsion phase the energy return of the foot shall provide economical movement patterns. The energy efficiency of 5 different foot prostheses (SEATTLE, DYNAMIC, GREISSINGER, HULITFLEX-ANKLE and SACH foot) were determined by analyzing the 3-diaensional gait and and running pattern of a male below knee amputee. The energy balance calculations refered only to the work done by the ankle joint moment in the sagittal plane. Obviously, the other components don’t have this significance for the propulsion. The results showed that it is not sufficient to determine relative energy loss or energy return. The whole work done by the ankle joint moment depends on the prosthesis. We found a range from 8.4 J to 15.7 J for walking and 9.0 to 22.0 J for running (ca 3 m/s). The energy loss varied in a range from 27% to 56% for walking and from 36% to 69% for running. So the order for relative energy return is not the same as for absolute energy return. This indicates that the results from material tests can't be transfered directly into the human motion patterns.
MODULATION OF H-REFLEXES DURING HOPPING AND JUMPING TASKS. Paul Dyhre-Paulsen and Erik B. Simonsen Institute of Neurophysiology University of Copenhagen & National Institute of Occupational Health, Denmark We have investigated how the central nervous system controls the mechanical behavior of the muscles. Reflexes play an important role in controlling motor activity. Skeletal muscles have springlike pqerties and spinal tiexes can improve muscle stiffness and thereby the ability to absorb, store and release energy. In hopping tasks spring&e behavior is appropriate but when landing from a jump muscles should act as damping units. We measured the soleus H reflex and EMG in the soleus and the anterior tibial muscle during hopping and landing from a downward jump. In the downward jumps the EMG activity in the soleus and the anterior tibial musele produced B segmented pattern of alternating bursts, time locked to landing. At the time of an expected stretch reflex there was little or no EMG activity in the soleus muscle. The H-reflex decreased substantially to about 20% of resting value just after landing, then gradually returned towards normal. The segmented alternating EMG pattern is therefoR probably not produced by the afferent input from muscle spindles. During hopping the EMG showed little activity before landing, but increased to high lasting EMG activity during the stance phase and subsided just before lift-off. The H-reflex was inhibited to about 20% of resting value during flight, but returned towards normal before landing. It remained relatively high at landing and during the stance phase. The ankle stiffness, calculated from film and ground reaction forces was negative while landing from a downward jump but always positive while hopping. The segmented EMG pattern probably produced negative muscle stiffness and it is likely that reflex contribution to muscle EMG activity is inhibited when damping behavior is appropriate during landing but not inhibited when conservation of elastic energy is useful.
MODULATION OF H REFLEXES DURING WALKING AND RUNNING. Erik B. Simonsen and Poul Dyhre-Poulsen. National Institute of Occupational Health & Institute of Neurophysiology, University of Copenhagen, Denmark. The objective of the study was to examine the modulation of H (Hoffmann) reflexes during human locomotion and to discuss the functional implications of such a modulation. Three healthy male subjects were examined during level walking and running and during uphill and downhill walking. Overground level walking was also examined by high speed cinematography. The soleus H reflex was clearly modulated during the different kinds of locomotion. During the swing phase it was suppressed to only a few percentage of resting value. At heel strike a steep increase was seen while the EMG of the soleus muscle was still silent. During most of the stance phase the nflex was modulated by the EMG activity until it was suppressed at heel off. During downhill wallring and running the reflex showed a steep rise in excitability just before heel strike. The general level of H nflex excitability was lower during locomotion compared to resting conditions. This is believed to be due to pzqq~tic inhibition. The functional significance is suggested to be gain of control. If a stretch reflex would be elicited during the swing phase it could disturb the movement severely. During the fiit part of the stance phase in walking the soleus muscle showed negative stiffness during eccentric contraction. In the last part of the stance phase when the reflex excitability was still increasing the stiffness turned positive just prior to the concentric contraction at push off. We suggest that the reflex serves the purpose of regulating muscle stiffness in a way appropriateto the motor task. Negative stiffness probably implies that the muscle acted as a damping unir by absorbing strain energy and converting it to heat. The opposite happened during positive stiffness where the muscle probably stored energy to be released during the following concentric contraction.
Abstracts ENERQY EFFICIENCY OF DIFFERENT OF WALKING AND JOGGING
FOOT
PROSTHBSES
Ulrich Glitach and Wolfgang Baurann, Institut Deutsche Sporthochechule KSln, W. GermanT.
DURING
STANCE
PHASE
fiir Biorechrnik,
In &signing foot prostheses the energy efficiency of the artificial feet seems to be of great significance. The intention is to compensate tbe absence of muscle function with elastic elements in the prosthesis. Especially during propulsion phase the energy return of the foot shall provide economical movement patterns. The energy efficiency of 5 different foot prostheses (SEATTLE, DYNAMIC, GREISSINGER, HULITFLEX-ANKLE and SACH foot) were determined by analyzing the 3-diaensional gait and and running pattern of a male below knee amputee. The energy balance calculations refered only to the work done by the ankle joint moment in the sagittal plane. Obviously, the other components don’t have this significance for the propulsion. The results showed that it is not sufficient to determine relative energy loss or energy return. The whole work done by the ankle joint moment depends on the prosthesis. We found a range from 8.4 J to 15.7 J for walking and 9.0 to 22.0 J for running (ca 3 m/s). The energy loss varied in a range from 27% to 56% for walking and from 36% to 69% for running. So the order for relative energy return is not the same as for absolute energy return. This indicates that the results from material tests can't be transfered directly into the human motion patterns.
MODULATION OF H-REFLEXES DURING HOPPING AND JUMPING TASKS. Paul Dyhre-Paulsen and Erik B. Simonsen Institute of Neurophysiology University of Copenhagen & National Institute of Occupational Health, Denmark We have investigated how the central nervous system controls the mechanical behavior of the muscles. Reflexes play an important role in controlling motor activity. Skeletal muscles have springlike pqerties and spinal tiexes can improve muscle stiffness and thereby the ability to absorb, store and release energy. In hopping tasks spring&e behavior is appropriate but when landing from a jump muscles should act as damping units. We measured the soleus H reflex and EMG in the soleus and the anterior tibial muscle during hopping and landing from a downward jump. In the downward jumps the EMG activity in the soleus and the anterior tibial musele produced B segmented pattern of alternating bursts, time locked to landing. At the time of an expected stretch reflex there was little or no EMG activity in the soleus muscle. The H-reflex decreased substantially to about 20% of resting value just after landing, then gradually returned towards normal. The segmented alternating EMG pattern is therefoR probably not produced by the afferent input from muscle spindles. During hopping the EMG showed little activity before landing, but increased to high lasting EMG activity during the stance phase and subsided just before lift-off. The H-reflex was inhibited to about 20% of resting value during flight, but returned towards normal before landing. It remained relatively high at landing and during the stance phase. The ankle stiffness, calculated from film and ground reaction forces was negative while landing from a downward jump but always positive while hopping. The segmented EMG pattern probably produced negative muscle stiffness and it is likely that reflex contribution to muscle EMG activity is inhibited when damping behavior is appropriate during landing but not inhibited when conservation of elastic energy is useful.
MODULATION OF H REFLEXES DURING WALKING AND RUNNING. Erik B. Simonsen and Poul Dyhre-Poulsen. National Institute of Occupational Health & Institute of Neurophysiology, University of Copenhagen, Denmark. The objective of the study was to examine the modulation of H (Hoffmann) reflexes during human locomotion and to discuss the functional implications of such a modulation. Three healthy male subjects were examined during level walking and running and during uphill and downhill walking. Overground level walking was also examined by high speed cinematography. The soleus H reflex was clearly modulated during the different kinds of locomotion. During the swing phase it was suppressed to only a few percentage of resting value. At heel strike a steep increase was seen while the EMG of the soleus muscle was still silent. During most of the stance phase the nflex was modulated by the EMG activity until it was suppressed at heel off. During downhill wallring and running the reflex showed a steep rise in excitability just before heel strike. The general level of H nflex excitability was lower during locomotion compared to resting conditions. This is believed to be due to pzqq~tic inhibition. The functional significance is suggested to be gain of control. If a stretch reflex would be elicited during the swing phase it could disturb the movement severely. During the fiit part of the stance phase in walking the soleus muscle showed negative stiffness during eccentric contraction. In the last part of the stance phase when the reflex excitability was still increasing the stiffness turned positive just prior to the concentric contraction at push off. We suggest that the reflex serves the purpose of regulating muscle stiffness in a way appropriateto the motor task. Negative stiffness probably implies that the muscle acted as a damping unir by absorbing strain energy and converting it to heat. The opposite happened during positive stiffness where the muscle probably stored energy to be released during the following concentric contraction.