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Effects of prolonged walking on neural and mechanical components of stretch responses in the human soleus muscle
Author(s) -
Cronin Neil J.,
Ishikawa Masaki,
Af Klint Richard,
Komi Paavo V.,
Avela Janne,
Sinkjaer Thomas,
Voigt Michael
Publication year - 2009
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2009.174912
Subject(s) - fascicle , soleus muscle , stretch reflex , treadmill , anatomy , passive stretching , plantar flexion , reflex , tendon , medicine , muscle belly , physical medicine and rehabilitation , isometric exercise , tibialis anterior muscle , electromyography , ankle , anesthesia , skeletal muscle , physical therapy , range of motion
After repeated passive stretching, tendinous tissue compliance increases in the human soleus (SOL) muscle–tendon unit. During movement, such changes would have important consequences for neural and mechanical stretch responses. This study examined the existence of such effects in response to a 75 min walking intervention. Eleven healthy subjects walked on a treadmill at 4 km h −1 with a robotic stretch device attached to the left leg. Ultrasonography was used to measure SOL fascicle lengths, and surface EMG activity was recorded in the SOL and tibialis anterior (TA) muscles. Perturbations of 6 deg were imposed at three different measurement intervals: Pre (immediately before the walking intervention), Mid (after approximately 30 min of walking) and Post (immediately after the intervention). Between the Pre–Mid and Mid–Post intervals, subjects walked for 30 min at a gradient of 3%. After the intervention, the amplitude and velocity of fascicle stretch both decreased (by 46 and 59%, respectively; P < 0.001) in response to a constant external perturbation, as did short (33%; P < 0.01) and medium (25%; P < 0.01) latency stretch reflex amplitudes. A faster perturbation elicited at the end of the protocol resulted in a recovery of fascicle stretch velocities and short latency reflex amplitudes to the pre‐exercise values. These findings suggest that repeated stretching and shortening of a muscle–tendon unit can induce short‐term structural changes in the tendinous tissues during human walking. The data also highlight the effect of these changes on neural feedback from muscle sensory afferents.