european college of sport science

Thursday, June 25th, 2009
Eight healthy young male subjects participated in the experiment. They performed ten drop jumps on a sledge ergometer with free preactivity
(FREE) and ten with pre-activity corresponding to 60% of isometric maximal voluntary contraction (60%MVC). For this purpose a
special ankle support was designed and used, where subjects could induce different levels of isometric contractions during the landing.
Dropping height corresponded to 200% of the maximal squat jumping height. Transcranial magnetic stimulation (TMS) over the motor
cortex and peripheral nerve stimulation over the tibialis nerve were induced during the early post-impact phase (on average 17ms after
the impact). Motor evoked (MEP) and H-reflex responses were recorded from the soleus muscle. Stability of the TMS coil was verified with
three dimensional motion analyses.
Interestingly, our data suggest that the increased pre-contact activity of the plantar flexor muscles prior to ground contact does not modify
the neural strategy during the early post-impact phase. There were no differences in MEP and H-reflex peak-to-peak amplitudes or in
their ratios between the FREE (approx. 20%MVC) and 60%MVC conditions. It would be logical to suggest that the increased voluntary
activity was not able to counteract the inhibitory effects probably originating from Golgi tendon organs. However, high and unaffected SLR
reflex amplitudes invalidate this suggestion. Since there were similarities in the EMG patterns towards the impact, it could be suggested
that increased voluntary effort was not able to bypass the effect of the pre-programmed landing strategy.
Melvill Jones G, Watt DGD. (1971) J Physiol 219:729-737.
Santello M. (2005) Gait and Posture 21: 85-94.
Santello M, McDonagh MJN. (1998) Exp Physiol 83: 857-874.
PROLONGED WALKING INCREASES COMPLIANCE IN THE HUMAN SOLEUS MUSCLE-TENDON UNIT: IMPLICATIONS
FOR THE SHORT LATENCY STRETCH REFLEX
CRONIN, N.J., ISHIKAWA, M., AF KLINT, R., KOMI, P.V., AVELA, J., SINKJAER, T., VOIGT, M.
AALBORG UNIVERSITY, DENMARK; UNIVERSITY OF JYVÄSKYLÄ, FINLAND
After repeated passive stretching, tendinous tissue compliance increases in the human soleus muscle-tendon unit (1,2). If present in
dynamic conditions, this would influence force transfer between muscle fibres, tendons and bones, and could decrease the stretch
stimulus to the spindles, thus influencing stretch reflex responses. The existence of such changes in locomotion is yet to be investigated.
Eleven healthy subjects walked on a treadmill at a gradient of 3% for approximately 60 minutes with the left leg attached to a robotic
actuator capable of rapidly dorsiflexing the ankle joint (3). Ultrasound was used to measure soleus fascicle lengths and surface EMG
activity was recorded. Stretch reflexes were elicited by applying 6° (250°/s) stretches at three time intervals; Pre (immediately before the
walking intervention), Mid (after approximately 30 minutes of walking) and Post (immediately after the intervention). If the intervention did
cause an increase in tendinous tissue compliance, it was anticipated that stretch reflex amplitudes would be lower at the end of the
protocol. As muscle spindle Ia afferents are velocity sensitive, an additional series of faster stretches (approximately 270°/s) were performed
at the Post interval.
Between the Pre and Post intervals, the amplitude and velocity of fascicle stretch decreased (by 46% and 59%, respectively) in response to
a constant external stretch, as did stretch reflex amplitudes (33%). A faster stretch elicited at the end of the protocol resulted in a recovery
of fascicle stretch velocities and reflex amplitudes to approximately the pre-exercise values. These findings, in addition to a lack of
change in electrically evoked muscle twitch properties, support the theory that repeated stretching and shortening of a muscle-tendon
unit can induce structural changes in the tendinous tissues (1), and provide evidence for the existence of this phenomenon during low
intensity human locomotion. As muscle spindles are mostly velocity- and length-sensitive receptors, any reduction in fascicle stretch
velocity and amplitude due to changes in tendinous tissue compliance could reduce muscle spindle afferent feedback, and thus decrease
the amplitude of the resulting stretch reflex response. The increase in tendinous tissue compliance may also compromise the
efficacy of storage and reutilization of elastic energy in the tendinous tissues.
1 Avela, J., Finni, T., Liikavainio, T., Niemela, E. & Komi, PV. (2004). Neural and mechanical
responses of the triceps surae muscle group after 1h of repeated fast passive stretches. J Appl Physiol. 96; 6; 2325-2332.
2 Avela, J., Kyrolainen, H. & Komi, PV. (1999). Altered reflex sensitivity after repeated and
prolonged passive muscle stretching. J Apply Physiol. 86; 4; 1283-1291.
3 Andersen, JB. & Sinkjaer, T. (2003). Mobile ankle and knee perturbator. IEEE Trans Biomed Eng.
50; 10; 1208-1211.
SHORT-TERM PRESSURE INDUCED SUPPRESSION OF THE SHORT LATENCY RESPONSE – A NEW METHODOLOGY FOR
INVESTIGATING FUNCTIONAL STRETCH REFLEXES
LEUKEL, C., TAUBE, W., LUNDBYE-JENSEN, J., GOLLHOFER, A.
UNIVERSITY OF FREIBURG; UNIVERSITY HOSPITAL BALGRIST, ZÜRICH; UNIVERSITY OF COPENHAGEN
Peripheral afferent feedback during movement is used not only for controlling the actual performance but also to drive the αmotoneurons
and thereby enhance the motor output. Especially stretch-shortening cycle contractions provide an experimental model in
which afferent feedback is used as the latter: the short-latency response (SLR) of the spinal stretch reflex has been argued to enhance
tendomuscular stiffness and thereby enable elastic energy to be stored during the eccentric phase of the contraction (Komi & Gollhofer,
1997). To investigate functional stretch reflexes, many studies applied an ischemic nerve block to annihilate the SLR (e.g. Grey et al., 2001).
However, ischemia is accompanied with several methodological drawbacks, including the associated pain and therefore the restricted
movement behaviour as well as the short time window allowed for investigation, which limit its application in highly functional tasks.
Here, we present a new methodology to investigate functional stretch reflexes possessing none of the abovementioned limitations.
10 healthy subjects (age 27±2 years) participated in this study. A conventional blood pressure cuff was used to apply short-term pressure
to the right calf muscles by inflating the cuff to 220 – 240 mmHg immediately (10 seconds) before the measurement started. EMG recordings
were obtained from m. soleus of the right leg. Subjects were asked to perform hopping movements at a submaximal intensity.
40 hops were averaged with the cuff deflated and inflated in a randomized order.
Inflation of the pneumatic cuff decreased the size of the SLR in m. soleus during hopping in 7 out of 10 subjects (cuff deflated: 0.67±0.32
mV versus cuff inflated: 0.55±0.32 mV). The three remaining subjects showed no difference in the size of the SLR between deflated and
inflated cuff.
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