Modulation of the biceps femoris tendon jerk reflex during human locomotion

During gait it is generally accepted that there is a reduction in amplitude of H-reflexes as compared to standing. For short-latency stretch reflexes, however, it is less clear whether a similar reduction in reflex gain is pr esent during locomotion. Stretches of constant amplitude are hard to produc e under these circumstances and for this reason some previous studies on th e biceps femoris (BF) have used "reduced gait" in which the stimulated leg is stepping on the spot while the contralateral leg is walking on a treadmi ll. With this method it was possible to show that BF tendon jerk reflexes a re larger at end swing and therefore are likely to contribute to the EMG bu rst normally occurring in that part of the step cycle when the BF is rapidl y stretched. In the present study two questions were addressed: first, whet her the reflex is different in size during gait compared to standing and, s econd, whether it is modulated in size during the gait cycle not only durin g reduced but also during normal gait. It was found that during both types of gait there was a general reflex depression with regard to the respective control values obtained during standing at similar EMG activity levels. In previous studies on soleus and quadriceps, discrepancies between EMG activ ity and reflex amplitude have been ascribed to changes in presynaptic inhib ition of Ia terminals mediating the afferent volley of the reflex, Based on the data presented, this may also be true for the BE In both normal and re duced gait the reflex was similarly modulated in size, showing a maximum at the end of swing. This similarity implies that reduced gait may be useful as an acceptable alternative for normal gait in studies on phase-dependent reflex modulation during locomotion.