The rate of force development obtained at early contraction phase is not influenced by active static stretching

The Time-Course Changes in Knee Flexion Range of Motion, Muscle Strength, and Rate of Force Development After Static Stretching

Previous studies have shown that longer-duration static stretching (SS) interventions can cause a decrease in muscle strength, especially explosive muscle strength. Furthermore, force steadiness is an important aspect of muscle force control, which should also be considered. However, the time course of the changes in these variables after an SS intervention remains unclear. Nevertheless, this information is essential for athletes and coaches to establish optimal warm-up routines. The aim of this study was to investigate the time course of changes in knee flexion range of motion (ROM), maximal voluntary isometric contraction (MVIC), rate of force development (RFD), and force steadiness (at 5 and 20% of MVIC) after three 60-s SS interventions. Study participants were sedentary healthy adult volunteers (n = 20) who performed three 60-s SS interventions of the knee extensors, where these variables were measured before and after SS intervention at three different periods, i.e., immediately after, 10 min, and 20 min the SS intervention (crossover design). The results showed an increase in ROM at all time points (d = 0.86-1.01). MVIC was decreased immediately after the SS intervention (d = -0.30), but MVIC showed a recovery trend for both 10 min (d = -0.17) and 20 min (d = -0.20) after the SS intervention. However, there were significant impairments in RFD at 100 m (p = 0.014, F = 6.37, η_p ² = 0.101) and 200 m (p < 0.01, F = 28.0, η_p ² = 0.33) up to 20 min after the SS intervention. Similarly, there were significant impairments in force steadiness of 5% (p < 0.01, F = 16.2, η_p ² = 0.221) and 20% MVIC (p < 0.01, F = 16.0, η_p ² = 0.219) at 20 min after the SS intervention. Therefore, it is concluded that three 60-s SS interventions could increase knee flexion ROM but impair explosive muscle strength and muscle control function until 20 min after the SS intervention.

Duration-Dependent Effects of Passive Static Stretching on Musculotendinous Stiffness and Maximal and Rapid Torque and Surface Electromyography Characteristics of the Hamstrings

Palmer, TB, Pineda, JG, Cruz, MR, and Agu-Udemba, CC. Duration-dependent effects of passive static stretching on musculotendinous stiffness and maximal and rapid torque and surface electromyography characteristics of the hamstrings. J Strength Cond Res 33(3): 717-726, 2019-This study aimed to examine the effects of stretching duration on passive musculotendinous stiffness and maximal and rapid torque and surface electromyography (EMG) characteristics of the hamstrings. Thirteen young females (age = 21 ± 2 years) underwent 2 passive straight-leg raise (SLR) assessments and 2 isometric maximal voluntary contractions (MVCs) of the hamstrings before and after 4 randomized conditions that included a control treatment and 3 experimental treatments of passive static stretching for 30-, 60-, and 120-second durations. Passive stiffness was calculated during each SLR as the slope of the final 10% of the angle-torque curve. Isometric peak torque (PT), rate of torque development (RTD), peak EMG amplitude (PEMG), and rate of EMG rise (RER) were extracted from each MVC. Results indicated that PT and PEMG were not affected (p = 0.993 and 0.422, respectively) by any of the experimental treatments. Rate of torque development and RER decreased from pre- to post-treatment for 120 seconds (p = 0.001 and 0.001) but not for the control (p = 0.616 and 0.466), 30- (p = 0.628 and 0.612), and 60-second (p = 0.396 and 0.815) interventions. The slope coefficient decreased from pre- to post-treatment for the 30- (p = 0.001), 60- (p = 0.002), and 120-second (p = 0.001) stretching interventions but not for the control (p = 0.649). Given the significant stiffness reductions and lack of changes in PT and RTD for the 30- and 60-second interventions, it may be advantageous for practitioners who are using hamstring passive stretching as part of a warm-up routine, to perform such stretching on their clients for short (30-60 seconds) rather than moderate (120-second) stretching durations.

The relevance of stretch intensity and position-a systematic review

Stretching exercises to increase the range of motion (ROM) of joints have been used by sports coaches and medical professionals for improving performance and rehabilitation. The ability of connective and muscular tissues to change their architecture in response to stretching is important for their proper function, repair, and performance. Given the dearth of relevant data in the literature, this review examined two key elements of stretching: stretch intensity and stretch position; and their significance to ROM, delayed onset muscle soreness (DOMS), and inflammation in different populations. A search of three databases, Pub-Med, Google Scholar, and Cochrane Reviews, identified 152 articles, which were subsequently categorized into four groups: athletes (24), clinical (29), elderly (12), and general population (87). The use of different populations facilitated a wider examination of the stretching components and their effects. All 152 articles incorporated information regarding duration, frequency and stretch position, whereas only 79 referred to the intensity of stretching and 22 of these 79 studies were deemed high quality. It appears that the intensity of stretching is relatively under-researched, and the importance of body position and its influence on stretch intensity, is largely unknown. In conclusion, this review has highlighted areas for future research, including stretch intensity and position and their effect on musculo-tendinous tissue, in relation to the sensation of pain, delayed onset muscle soreness, inflammation, as well as muscle health and performance.

Changes in force and stiffness after static stretching of eccentrically-damaged hamstrings

PURPOSE

This study compared responses to static stretching between eccentrically damaged and non-damaged muscles.

METHODS

Twelve young men performed 60 maximum knee flexor eccentric contractions of one leg, and received a 300-s continuous passive static stretching at tolerable intensity without pain to both knee flexors at 2 and 4 days after the eccentric exercise. Range of motion (ROM) and passive stiffness during knee extension, passive torque at onset of pain (PT), maximum voluntary isometric (MVC-ISO) and isokinetic concentric contraction torque (MVC-CON), and visual analogue scale (VAS) for muscle soreness were measured before, immediately after, 60 min, 2 and 4 days after exercise as well as before, immediately after, 20 and 60 min after the stretching. Changes in these variables after eccentric exercise and stretching were compared between limbs.

RESULTS

The eccentric exercise decreased MVC-ISO, MVC-CON, ROM and PT, and increased passive stiffness and VAS (p < 0.05), suggesting that muscle damage was induced to the knee flexors. ROM and PT increased after stretching for both limbs; however, the magnitude of the increase was greater (p < 0.05) for the damaged than non-damaged limb. Passive stiffness decreased for both limbs similarly (4-7 %) at immediately after stretching (p < 0.05). Significant decreases in MVC-ISO torque (7-11 %) after stretching were observed only for the non-damaged limb (p < 0.05), but MVC-CON torque did not change after stretching for both limbs. VAS decreased for the exercised limb after stretching (p < 0.05).

CONCLUSIONS

These results suggest that the static stretching at tolerable intensity without pain produced greater positive effects on damaged than non-damaged muscles.

Effects of stretching on performances involving stretch-shortening cycles

BACKGROUND

Alongside its role in athletic conditioning, stretching has commonly been integrated in warm-up routines prior to athletic performance. Numerous studies have reported detrimental acute effects on strength following stretching. Consequently, athletes have been recommended to discontinue stretching as part of warm-ups. In contrast, studies indicate that chronic stretching performed as a separate bout from training or competition may enhance performance. However, the influence of stretching on complex performances has received relatively little attention.

OBJECTIVE

The purpose of this study was to review both the acute and chronic effects of stretching on performances involving the stretch-shortening cycle (SSC).

METHODS

A systematic search for literature was undertaken (January 2006-December 2012) in which only randomized controlled trials (RCTs) or studies with repeated measures designs were included. The Physiotherapy Evidence Database (PEDro) rating scale was used for quality assessment of the evidence.

RESULTS

The review included 43 studies, from which conflicting evidence emerged. Approximately half of the studies assessing the acute effect of static stretching reported a detrimental effect on performance, while the remainder found no effect. In contrast, dynamic stretching showed no negative effects and improved performance in half of the trials. The effect size associated with static and dynamic stretching interventions was commonly low to moderate, indicating that the effect on performance might be limited in practice. Factors were identified that might have contributed to the conflicting results reported across studies, such as type of SSC performance and carrying out dynamic activity between the stretching bout and performance. Few studies since 2006 have addressed the chronic effect of stretching on functional and sports performance. Although negative effects were not reported, robust evidence of the overall beneficial effects within current bibliographic databases remains elusive. Plausible mechanisms for the observed effects from stretching are discussed, as well as possible factors that may have contributed to contradictory findings between studies.

LIMITATIONS

Considerable heterogeneity in study design and methods makes comparison between studies challenging. No regression analysis of the contribution of different predictors to variation between trials had previously been performed. Hence, predictors had to be selected on the basis of a qualitative analysis of the predictors that seemed most influential, as well as being identified in previous narrative reviews.

CONCLUSION

Different types of stretching have differential acute effects on SSC performances. The recommended volume of static stretching required to increase flexibility might induce a negative acute effect on performances involving rapid SSCs, but the effect sizes of these decrements are commonly low, indicating that the acute effect on performance might be limited in practice. No negative acute effects of dynamic stretching were reported. For athletes that require great range of motion (ROM) and speed in their sport, long-term stretching successfully enhances flexibility without negatively affecting performance. Acute dynamic stretching may also be effective in inducing smaller gains in ROM prior to performance without any negative effects being observed.