title: Range of motion, neuromechanical, and architectural adaptations to plantar flexor stretch training in humans.
abstract: 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 nonexercising control group (n = 9), however stretch training elicited a 19.9% increase in dorsiflexion range of motion (ROM) and a 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 electromyographic amplitudes during ROM or at end ROM were detected. Decreases in H(max):M(max) (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 maximum voluntary contraction moment and rate of force development 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.
authors.affiliation: Centre for Exercise and Sports Science Research, School of Exercise and Health Sciences, Edith Cowan University, Joondalup, Australia; Centre for Sports Medicine and Human Performance, Brunel University, Uxbridge, Middlesex, United Kingdom; a.blazevich@ecu.edu.au.
authors.forename: A J
authors.initials: AJ
authors.lastname: Blazevich
authors.affiliation: Department of Health and Human Performance, Seattle Pacific University, Seattle, WA;
authors.forename: D
authors.initials: D
authors.lastname: Cannavan
authors.affiliation: Centre for Sports Medicine and Human Performance, Brunel University, Uxbridge, Middlesex, United Kingdom;
authors.forename: C M
authors.initials: CM
authors.lastname: Waugh
authors.affiliation: Centre for Sports Medicine and Human Performance, Brunel University, Uxbridge, Middlesex, United Kingdom; London Sport Institute, Middlesex University, London, United Kingdom;
authors.forename: S C
authors.initials: SC
authors.lastname: Miller
authors.affiliation: Department of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark; and.
authors.forename: J B
authors.initials: JB
authors.lastname: Thorlund
authors.affiliation: Department of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark; and.
authors.forename: P
authors.initials: P
authors.lastname: Aagaard
authors.affiliation: Sport, Exercise and Life Sciences, The University of Northampton, Northampton, United Kingdom.
authors.forename: A D
authors.initials: AD
authors.lastname: Kay
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000293:Adolescent; D000843:Ankle Joint / Q000000981:diagnostic imaging / Q000502:physiology; D001696:Biomechanical Phenomena; D004576:Electromyography; D006181:H-Reflex / Q000502:physiology; D006801:Humans; D008297:Male; D052580:Muscle Stretching Exercises / Q000379:methods*; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology*; D013710:Tendons / Q000000981:diagnostic imaging / Q000502:physiology; D014463:Ultrasonography; D055815:Young Adult
keywords: elasticity; flexibility; muscle stiffness; stretch tolerance; tendon stiffness