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Abstract Background Long-term stretching of human skeletal muscles increases joint range of motion through altered stretch perception and decreased resistance to stretch. There is also some evidence that stretching induces changes in muscle morphology. However, research is limited and inconclusive. Objective To examine the effect of static stretching training on muscle architecture (i.e., fascicle length and fascicle angle, muscle thickness and cross-sectional area) in healthy participants. Design Systematic review and meta-analysis. Methods PubMed Central, Web of Science, Scopus, and SPORTDiscus were searched. Randomized controlled trials and controlled trials without randomization were included. No restrictions on language or date of publication were applied. Risk of bias was assessed using Cochrane RoB2 and ROBINS-I tools. Subgroup analyses and random-effects meta-regressions were also performed using total stretching volume and intensity as covariates. Quality of evidence was determined by GRADE analysis. Results From the 2946 records retrieved, 19 studies were included in the systematic review and meta-analysis (n = 467 participants). Risk of bias was low in 83.9% of all criteria. Confidence in cumulative evidence was high. Stretching training induces trivial increases in fascicle length at rest (SMD = 0.17; 95% CI 0.01–0.33; p = 0.042) and small increases in fascicle length during stretching (SMD = 0.39; 95% CI 0.05 to 0.74; p = 0.026). No increases were observed in fascicle angle or muscle thickness (p = 0.30 and p = 0.18, respectively). Subgroup analyses showed that fascicle length increased when high stretching volumes were used (p

The association between force–time characteristics of isometric leg press (ILP) and countermovement jump (CMJ) with vastus lateralis (VL) muscle architecture, was examined in 19 female athletes (aged 23.2 ± 5.4 years). Peak force (PF), average rate of force development (ARFD) and rate of force development (RFD) at different time epochs were calculated from the force–time curve, as well as CMJ jump height and power. Significant correlations were found between ILP-PF and CMJ power (r = 0.658, p < 0.01), while both variables were correlated with VL thickness and fascicle length (r = 0.471 to 0.648, p < 0.05). Significant correlations were also observed between ILP-RFD epochs and VL fascicle length (r = 0.565 to 0.646, p < 0.05) and between CMJ height with VL thickness (r = 0.523, p < 0.05). Furthermore, positive correlations were found between ILP and CMJ in ARFD (r = 0.625, p < 0.01) and RFD epochs (r = 0.464 to 0.566, p < 0.05). ILP-PF and muscle thickness accounted for 52.8% (p = 0.002) of the variance in CMJ power. These results suggest that isometric force time characteristics are associated with power generation during dynamic muscle actions. Furthermore, VL muscle thickness and fascicle length are associated with rapid force production in female athletes, irrespective of the type of muscle action.

Gastrocnemius medialis (GM) architecture and ankle angle were compared between flexibility trained (n = 10) and not trained (n = 6) female athletes, aged 8−10 years. Ankle angle, fascicle length, pennation angle and muscle thickness were measured at the mid-belly and the distal part of GM, at rest and at the end of one min of static stretching. Flexibility trained (FT) and not trained athletes (FNT) had similar fascicle length at the medial (4.19 ± 0.37 vs. 4.24 ± 0.54 cm, respectively, p = 0.841) and the distal part of GM (4.25 ± 0.35 vs. 4.18 ± 0.65 cm, respectively, p = 0.780), similar pennation angles, and muscle thickness (p > 0.216), and larger ankle angle at rest (120.9 ± 4.2 vs. 110.9 ± 5.8°, respectively, p = 0.001). During stretching, FT displayed greater fascicle elongation compared to FNT at the medial (+1.67 ± 0.37 vs. +1.28 ± 0.22 cm, respectively, p = 0.048) and the distal part (+1.84 ± 0.67 vs. +0.97 ± 0.97 cm, respectively, p = 0.013), larger change in joint angle and muscle tendon junction displacement (MTJ) (p < 0.001). Muscle thickness was similar in both groups (p > 0.053). Ankle dorsiflexion angle significantly correlated with fascicle elongation at the distal part of GM (r = −0.638, p < 0.01) and MTJ displacement (r = −0.610, p < 0.05). Collectively, FT had greater fascicle elongation at the medial and distal part of GM and greater MTJ displacement during stretching than FNT of similar age.

AIM: Rate of force development (RFD) of the leg extensor muscles is important for jumping performance. Static stretching has been shown to reduce explosive force generation, but little is known regarding changes in muscle architectural characteristics due to stretching and jumping performance alterations. Τhe aim of this study was to determine the effects of two different static stretching protocols (20 or 60 s) on gastrocnemius medialis (GM) muscle architectural characteristics and RFD during jumping in a population with long-term flexibility training background. MATERIAL & METHOD: Twelve female professional ballet dancers (age, 25.3 ± 2.2 years) performed 5 days of testing using a single leg stretching and jumping design. RFD during one-leg countermovement jump and jump height were measured on the first visit. On the other four visits, dancers stretched their hamstrings, quadriceps and plantar flexors for 20 or 60 s per muscle group, in a counterbalanced order. Immediately after stretching, RFD and jump height were measured. Fascicle length (FL), pennation angle (PA), and muscle thickness (MT) at the medial and the distal part of GM were assessed at rest and during static stretching for each protocol, using ultrasonography. RESULTS: There was a main effect of time for FL, PA, and MT (p < 0.01) with no difference between stretching protocols, at the medial and distal parts of GM, in FL (p = 0.373 and p = 0.651, respectively), PA (p = 0.724 and p = 0.477, respectively) and MT (p = 0.314 and p = 0.444, respectively). Greater FL elongation was observed at the medial compared to the distal part of GM (p = 0.013) during the long stretching protocol. RFD significantly decreased after the long stretching protocol (p = 0.019), while it remained unchanged in the short stretching protocol (p = 0.061). Significant correlations were found between resting FL at the medial part of GM and RFD (r = −0.645, p = 0.05) and between fascicle elongation at the medial part of GM and CMJ height (r = 0.717, p = 0.01). CONCLUSIONS: The long static stretching protocol induced non-uniform adaptations along GM length and decreased RFD, suggesting that prolonged stretching durations should be avoided immediately before activities requiring rapid force production.

AIM: Τhe mechanisms underpinning long-term changes in muscle architectural characteristics and joint range of motion (ROM) following static stretching in humans remain under question, and data are sparse for growing athletes. It is possible that the characteristics of the stretching protocols used in previous training studies were not adequate to induce significant changes. An alternative approach would be to compare populations with different chronic flexibility training backgrounds. Thus, the purpose of this study was to examine differences in gastrocnemius medialis (GM) architectural characteristics at rest and during 1 min of static stretching between child athletes with different flexibility training backgrounds. MATERIAL & METHOD: Ten female rhythmic gymnasts (RG; age. 9.0 ± 0.7 years) were compared to six volleyball athletes (VA; age, 9.0 ± 0.6 years). Fascicle length, pennation angle and muscle thickness at the medial and distal part of GM, and ankle ROM were measured at rest and during 1 min of static stretching using ultrasonography. Data were analysed using two-way ANOVA for repeated measures on two factors (time x sport). RESULTS: At rest, RG displayed similar fascicle length compared to VA at the medial (4.19 ± 0.37 vs. 4.24 ± 0.54 cm, respectively, p = 0.841) and the distal part of GM (4.25 ± 0.35 vs. 4.18 ± 0.65 cm, respectively, p = 0.780). Pennation angle and muscle thickness were also similar in the two groups at the medial (p = 0.519 and p = 0.216, respectively) and the distal part of the gastrocnemius (p = 0.998 and p = 0.433, respectively). Ankle angle before stretching was greater in RG compared with VA (120.9 ± 4.2 vs. 110.9 ± 5.8°, respectively, p = 0.001). During the 1 min of static stretching, RG displayed greater fascicle elongation compared to the VA at the medial (5.86 ± 0.29 vs 5.52 ± 0.53 cm, p = 0.048) and the distal part (6.09 ± 0.49 vs 5.15 ± 0.65 cm, p = 0.013), as well as greater maximal ankle dorsiflexion (p < 0.001) and muscle tendon junction displacement (p < 0.001). No differences were found between groups in pennation angle (p > 0.458) and muscle thickness (p ˃ 0.237). CONCLUSIONS: Muscle architectural properties are similar at rest in child athletes with different flexibility backgrounds. However, muscle fascicle elongation is greater in rhythmic gymnasts compared to volleyball athletes and this may contribute to the greater ankle ROM observed in rhythmic gymnasts.

Background: This study examined gastrocnemius medialis (GM) architectural properties and ankle joint range of motion (ROM) between female athletes with different flexibility training background. Methods: Elite rhythmic gymnasts (n = 10) were compared to national level volleyball athletes (n = 10). Fascicle length, pennation angle and muscle thickness at the medial and the distal part of GM, and ankle ROM were measured at rest and during 1 min of static stretching. Results: At rest, rhythmic gymnasts displayed longer fascicles compared to volleyball athletes, at the medial (5.93 ± 0.27 vs. 4.74 ± 0.33 mm, respectively, p = 0.001) and the distal part of GM (5.63 ± 0.52 vs. 4.57 ± 0.51 mm, respectively, p = 0.001), smaller pennation angle at the medial part (22.4 ± 2.5 vs. 25.8 ± 2.4°; respectively, p = 0.001) and greater ankle angle (121.7 ± 4.1 vs. 113.2 ± 3.7°, respectively, p = 0.001). During the 1 min of static stretching, gymnasts displayed greater fascicle elongation at the distal part (p = 0.026), greater maximal ankle dorsiflexion (p < 0.001) and muscle tendon junction displacement (p < 0.001) with no difference between groups in pennation angles (p > 0.145), muscle thickness (p > 0.105), and fascicle elongation at mid-belly (p = 0.063). Conclusions: Longer muscle fascicles at rest and greater fascicle elongation at the distal part of GM may contribute to the greater ankle ROM observed in rhythmic gymnasts.