Blazevich, Anthony John4; Cannavan, Dale5; Waugh, Charlie M6; Miller, Stuart C7; Thorlund, Jonas Bloch9; Aagaard, Per9; Kay, Anthony David8
1 Department of Sports Science and Clinical Biomechanics, Det Sundhedsvidenskabelige Fakultet, SDU2 Musculoskeletal Function and Physiotherapy, Department of Sports Science and Clinical Biomechanics, Det Sundhedsvidenskabelige Fakultet, SDU3 Muscle Physiology and Biomechanics, Department of Sports Science and Clinical Biomechanics, Det Sundhedsvidenskabelige Fakultet, SDU4 Edith Cowan University5 Seattle Pacific University.6 Brunel University7 Middlesex University8 University of Northampton9 Department of Sports Science and Clinical Biomechanics, Det Sundhedsvidenskabelige Fakultet, SDU
The neuromuscular adaptations in response to muscle stretch training have not been clearly described. In the present study, changes in muscle (at fascicular and whole muscle levels) and tendon mechanics, muscle activity and spinal motoneuron excitability were examined during standardized plantar flexor stretches after 3 wk of twice-daily stretch training (4×30-s). No changes were observed in a non-exercising control group (N=9), however stretch training elicited a 19.9% increase in dorsiflexion range of motion (ROM) and 28% increase in passive joint moment at end ROM (N=12). Only a trend toward a decrease in passive plantar flexor moment during stretch (-9.9%, p=0.15) was observed and no changes in EMG amplitudes during or at end ROM were detected. Decreases in Hmax:Mmax (tibial nerve stimulation) were observed at plantar flexed (gastrocnemius medialis and soleus) and neutral (soleus only) joint angles, but not with the ankle dorsiflexed. Muscle and fascicle strain increased (12 vs. 23%) along with a decrease in muscle stiffness (-18%) during stretch to a constant target joint angle. Muscle length at end ROM increased (13%) without a change in fascicle length, fascicle rotation, tendon elongation or tendon stiffness following training. A lack of change in MVC moment and RFD at any joint angle was taken to indicate a lack of change in series compliance of the muscle-tendon unit. Thus, increases in end ROM were underpinned by increases in maximum tolerable passive joint moment ('stretch tolerance') and both muscle and fascicle elongation rather than changes in volitional muscle activation or motoneuron pool excitability.
Journal of Applied Physiology, 2014, Vol 117, Issue 5, p. 452-462