Lower leg EMG and H-reflex activity during double-leg hopping and landing

This study aimed to examine generation and modulation of the triceps surae electromyographic (EMG) and H-reflex activity during submaximal- and maximal-height double-leg hopping and during landing. During hopping, flight time that reflects hop height was positively correlated with triceps surae EMG amplitudes during ground contact. The H-reflexes elicited near the moment of ground contact (touchdown) were larger during maximal- than submaximal-height hopping. During maximal-height hopping, the soleus H-reflex was phase-dependently modulated within each individual, with no consistent patterns across individuals, whereas the medial gastrocnemius H-reflex was larger just before touchdown and during ground contact than during midflight, consistently across individuals. During landing, the triceps surae EMG and H-reflexes were strongly suppressed after touchdown. The present results support the link between higher hops and larger triceps surae activity during ground contact, to which the spinal reflexes may contribute. A clear interindividual variability in the soleus H-reflex modulation and a consistent pattern in the medial gastrocnemius H-reflex modulation across hopping cycle may suggest use-dependent shaping of reflex phase-dependent modulation in hopping. H-reflex suppression after touchdown during landing supports the presence of robust task-dependent reflex modulation at the key moments of hopping and landing.NEW & NOTEWORTHY This study investigated triceps surae H-reflexes during double-leg hopping and landing. For hopping, higher hops were associated with more robust triceps surae activity and larger H-reflexes around ground contact. During maximal-height hopping, the H-reflexes were phase-dependently modulated within individuals but not in consistent patterns across individuals. During landing, the H-reflexes were strongly suppressed. Our results support the presence of neural mechanisms to regulate triceps reflex activity at the key moments/phases of hopping and landing.