The effects of 12 weeks of static stretch training on the functional, mechanical, and architectural characteristics of the triceps surae muscle–tendon complex

• Published in: European journal of applied physiology Vol. 121; no. 6; pp. 1743 - 1758
• Main Authors: Longo, Stefano, Cè, Emiliano, Bisconti, Angela Valentina, Rampichini, Susanna, Doria, Christian, Borrelli, Marta, Limonta, Eloisa, Coratella, Giuseppe, Esposito, Fabio
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-06-2021; Springer Nature B.V
• Subjects: Ankle; Architecture; Biomedical and Life Sciences; Biomedicine; Contraction; Human Physiology; Mechanical properties; Muscle contraction; Occupational Medicine/Industrial Medicine; Original; Original Article; Sports Medicine; Triceps surae muscle; Electromechanical delay; Stiffness; Pennation angle; Muscle architecture; Flexibility; Stretching
• ISSN: 1439-6319; 1439-6327
• DOI: 10.1007/s00421-021-04654-z

Purpose
We investigated the effects of 12 weeks of passive static stretching training (PST) on force-generating capacity, passive stiffness, muscle architecture of plantarflexor muscles.
Methods
Thirty healthy adults participated in the study. Fifteen participants (STR, 6 women, 9 men) underwent 12-week plantarflexor muscles PST [(5 × 45 s-on/15 s-off) × 2exercises] × 5times/week (duration: 2250 s/week), while 15 participants (CTRL, 6 women, 9 men) served as control (no PST). Range of motion (ROM), maximum passive resistive torque (PRT
max
),
triceps surae
architecture [fascicle length, fascicle angle, and thickness], passive stiffness [muscle–tendon complex (MTC) and muscle stiffness], and plantarflexors maximun force-generating capacity variables (maximum voluntary contraction, maximum muscle activation, rate of torque development, electromechanical delay) were calculated Pre, at the 6th (Wk6), and the 12th week (Wk12) of the protocol in both groups.
Results
Compared to Pre, STR ROM increased (
P
 < 0.05) at Wk6 (8%) and Wk12 (23%). PRT
max
increased at Wk12 (30%,
P
 < 0.05), while MTC stiffness decreased (16%,
P
 < 0.05). Muscle stiffness decreased (
P
 < 0.05) at Wk6 (11%) and Wk12 (16%). No changes in
triceps surae
architecture and plantarflexors maximum force-generating capacity variables were found in STR (
P
 > 0.05). Percentage changes in ROM correlated with percentage changes in PRT
max
(
ρ
 = 0.62,
P
 = 0.01) and MTC stiffness (
ρ
 = − 0.78,
P
 = 0.001). In CTRL, no changes (
P
 > 0.05) occurred in any variables at any time point.
Conclusion
The expected long-term PST-induced changes in ROM were associated with modifications in the whole passive mechanical properties of the ankle joint, while maximum force-generating capacity characteristics were preserved. 12 weeks of PST do not seem a sufficient stimulus to induce
triceps surae
architectural changes.