Abstract
PurposeWe investigated the effects of 12 weeks of passive static stretching training (PST) on force-generating capacity, passive stiffness, muscle architecture of plantarflexor muscles.MethodsThirty 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 (PRTmax), 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.ResultsCompared to Pre, STR ROM increased (P < 0.05) at Wk6 (8%) and Wk12 (23%). PRTmax 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 PRTmax (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.ConclusionThe 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.
Highlights
Passive stretching is widely performed in sport and rehabilitation mainly to improve joint range of motion (ROM) and muscle performance
Other works reported no effects of passive stretching training (PST) on maximum muscle strength (Akagi and Takahashi 2014; Konrad and Tilp 2014; Blazevich et al 2014; Sato et al 2020), amplitude of surface electromyographic (sEMG) detected during maximum voluntary force production (Blazevich et al 2014) and whole-joint (Konrad and Tilp 2014; Blazevich et al 2014) and muscle stiffness (Konrad and Tilp 2014)
Since previous studies showed that the different triceps surae muscles can undergo different strain during stretch exercise (Hirata et al 2016) and within the same muscle different portions can be unequally affected by the stretch manoeuvre (Andrade et al 2020), we examined the possible PST-induced architectural adaptations in all triceps surae heads at different regions
Summary
Passive stretching is widely performed in sport and rehabilitation mainly to improve joint range of motion (ROM) and muscle performance. Evidence exists that passive stretching, when performed acutely, may induce negative changes in muscle function, such as a reduced force-generating capacity (Power et al 2004; Kay and Blazevich 2012; Longo et al 2014; Behm et al 2016; Trajano et al 2017; Cè et al 2020) and a depressed rate of torque development (RTD) (Simic et al 2013; Trajano et al 2019) These alterations are often accompanied by a reduction in the amplitude of the surface electromyographic (sEMG) signal from the contracting muscle after stretching (Behm et al 2001, 2016; Cramer et al 2005). This apparent discrepancy could be justified by differences in methodological approach, PST duration, number and duration of weekly stretching sessions, and stretch intensity (Freitas et al 2018)
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