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

Revisiting the stretch-induced force deficit: A systematic review with multilevel meta-analysis of acute effects

BACKGROUND

When recommending avoidance of static stretching prior to athletic performance, authors and practitioners commonly refer to available systematic reviews. However, effect sizes (ES) in previous reviews were extracted in major part from studies lacking control conditions and/or pre-post testing designs. Also, currently available reviews conducted calculations without accounting for multiple study outcomes, with ES: -0.03 to 0.10, which would commonly be classified as trivial.

METHODS

Since new meta-analytical software and controlled research articles have appeared since 2013, we revisited the available literatures and performed a multilevel meta-analysis using robust variance estimation of controlled pre-post trials to provide updated evidence. Furthermore, previous research described reduced electromyography activity-also attributable to fatiguing training routines-as being responsible for decreased subsequent performance. The second part of this study opposed stretching and alternative interventions sufficient to induce general fatigue to examine whether static stretching induces higher performance losses compared to other exercise routines.

RESULTS

Including 83 studies with more than 400 ES from 2012 participants, our results indicate a significant, small ES for a static stretch-induced maximal strength loss (ES = -0.21, p = 0.003), with high magnitude ES (ES = -0.84, p = 0.004) for stretching durations ≥60 s per bout when compared to passive controls. When opposed to active controls, the maximal strength loss ranges between ES: -0.17 to -0.28, p < 0.001 and 0.040 with mostly no to small heterogeneity. However, stretching did not negatively influence athletic performance in general (when compared to both passive and active controls); in fact, a positive effect on subsequent jumping performance (ES = 0.15, p = 0.006) was found in adults.

CONCLUSION

Regarding strength testing of isolated muscles (e.g., leg extensions or calf raises), our results confirm previous findings. Nevertheless, since no (or even positive) effects could be found for athletic performance, our results do not support previous recommendations to exclude static stretching from warm-up routines prior to, for example, jumping or sprinting.

Acute effects of static and dynamic stretching for ankle plantar flexors on postural control during the single-leg standing task

Static stretching (SS) and dynamic stretching (DS) are widely used as warm-ups before sports. However, whether stretching affects postural control remains unclear. We compared the effects of SS and DS on the plantar flexors and postural control during single-leg standing. Fifteen healthy young participants performed SS, DS, or no stretching (control). The stretch condition consisted of four sets lasting 30 s each. The control condition was a rest with standing for 210 s. Center of pressure (COP) displacement was measured using a force plate before and after each intervention to assess postural control during the single-leg standing task. The COP area, COP velocity, and anteroposterior (COPAP) and mediolateral (COPML) range were calculated. DS significantly decreased in the COPML range (21.5 ± 4.1 to 19.0 ± 2.5 mm; P = 0.02), COP velocity (33.8 ± 7.6 to 29.8 ± 6.5 mm/s; P < 0.01), and COP area (498.6 ± 148.3 to 393.3 ± 101.1 mm2; P < 0.01), whereas SS did not change in the COP parameters (COP area 457.2 ± 108.3 to 477.8 ± 106.1 mm2, P = .49; COP velocity 31.2 ± 4.2 to 30.7 ± 5.8 mm/s, P = 0.60; COPAP 25.4 ± 3.1 to 25.3 ± 3.2 mm, P = 0.02; COPML 20.7 ± 3.3 to 21.1 ± 2.5 mm, P = 0.94). Therefore, DS of the plantar flexors enhances postural control during single-leg standing and may be effective for both injury prevention and performance enhancement.

Acute and Long-Term Effects of Static Stretching on Muscle-Tendon Unit Stiffness: A Systematic Review and Meta-Analysis

Static stretching can increase the range of motion of a joint. Muscle-tendon unit stiffness (MTS) is potentially one of the main factors that influences the change in the range of motion after static stretching. However, to date, the effects of acute and long-term static stretching on MTS are not well understood. The purpose of this meta-analysis was to investigate the effects of acute and long-term static stretching training on MTS, in young healthy participants. PubMed, Web of Science, and EBSCO published before January 6, 2023, were searched and finally, 17 papers were included in the meta-analysis. Main meta-analysis was performed with a random-effect model and subgroup analyses, which included comparisons of sex (male vs. mixed sex and female) and muscle (hamstrings vs. plantar flexors) were also performed. Furthermore, a meta-regression was conducted to examine the effect of total stretching duration on MTS. For acute static stretching, the result of the meta-analysis showed a moderate decrease in MTS (effect size = -0.772, Z = -2.374, 95% confidence interval = -1.409 - -0.325, p = 0.018, I2 = 79.098). For long-term static stretching, there is no significant change in MTS (effect size = -0.608, Z = -1.761, 95% CI = -1.284 - 0.069, p = 0.078, I2 = 83.061). Subgroup analyses revealed no significant differences between sex (long-term, p = 0.209) or muscle (acute, p =0.295; long-term, p = 0.427). Moreover, there was a significant relationship between total stretching duration and MTS in acute static stretching (p = 0.011, R2 = 0.28), but not in long-term stretching (p = 0.085, R2 < 0.01). Whilst MTS decreased after acute static stretching, only a tendency of a decrease was seen after long-term stretching.

Short-Term Effects of Three Types of Hamstring Stretching on Length, Neurodynamic Response, and Perceived Sense of Effort-A Randomised Cross-Over Trial

Background: Stretching techniques for hamstring muscles have been described both to increase muscle length and to evaluate nerve mechanosensitivity. Aim: We sought to evaluate the short-term effects of three types of hamstring stretching on hamstring length and report the type of response (neural or muscular) produced by ankle dorsiflexion and perceived sense of effort in asymptomatic subjects. Methods: A randomised cross-over clinical trial was conducted. A total of 35 subjects were recruited (15 women, 20 men; mean age 24.60 ± 6.49 years). Straight leg raises (SLR), passive knee extensions (PKE), and maximal hip flexion (MHF) were performed on dominant and non-dominant limbs. In addition, the intensity of the applied force, the type and location of the response to structural differentiation, and the perceived sensation of effort were assessed. Results: All stretching techniques increased hamstring length with no differences between limbs in the time*stretch interaction (p < 0.05). The perceived sensation of effort was similar between all types of stretching except MHF between limbs (p = 0.047). The type of response was mostly musculoskeletal for MHF and the area of more neural response was the posterior knee with SLR stretch. Conclusions: All stretching techniques increased hamstring length. The highest percentage of neural responses was observed in the SLR stretching, which produced a greater increase in overall flexibility.

Usefulness of Surface Electromyography Complexity Analyses to Assess the Effects of Warm-Up and Stretching during Maximal and Sub-Maximal Hamstring Contractions: A Cross-Over, Randomized, Single-Blind Trial

This study aimed to apply different complexity-based methods to surface electromyography (EMG) in order to detect neuromuscular changes after realistic warm-up procedures that included stretching exercises. Sixteen volunteers conducted two experimental sessions. They were tested before, after a standardized warm-up, and after a stretching exercise (static or neuromuscular nerve gliding technique). Tests included measurements of the knee flexion torque and EMG of biceps femoris (BF) and semitendinosus (ST) muscles. EMG was analyzed using the root mean square (RMS), sample entropy (SampEn), percentage of recurrence and determinism following a recurrence quantification analysis (%Rec and %Det) and a scaling parameter from a detrended fluctuation analysis. Torque was significantly greater after warm-up as compared to baseline and after stretching. RMS was not affected by the experimental procedure. In contrast, SampEn was significantly greater after warm-up and stretching as compared to baseline values. %Rec was not modified but %Det for BF muscle was significantly greater after stretching as compared to baseline. The a scaling parameter was significantly lower after warm-up as compared to baseline for ST muscle. From the present results, complexity-based methods applied to the EMG give additional information than linear-based methods. They appeared sensitive to detect EMG complexity increases following warm-up.

Comparison of A Single Vibration Foam Rolling and Static Stretching Exercise on the Muscle Function and Mechanical Properties of the Hamstring Muscles

Knee extension and hip flexion range of motion (ROM) and functional performance of the hamstrings are of great importance in many sports. The aim of this study was to investigate if static stretching (SS) or vibration foam rolling (VFR) induce greater changes in ROM, functional performance, and stiffness of the hamstring muscles. Twenty-five male volunteers were tested on two appointments and were randomly assigned either to a 2 min bout of SS or VFR. ROM, counter movement jump (CMJ) height, maximum voluntary isometric contraction (MVIC) peak torque, passive resistive torque (PRT), and shear modulus of semitendinosus (ST), semimembranosus (SM), and biceps femoris (BFlh), were assessed before and after the intervention. In both groups ROM increased (SS = 7.7%, P < 0.01; VFR = 8.8%, P < 0.01). The MVIC values decreased after SS (-5.1%, P < 0.01) only. Shear modulus of the ST changed for -6.7% in both groups (VFR: P < 0.01; SS: P < 0.01). Shear modulus decreased in SM after VFR (-6.5%; P = 0.03) and no changes were observed in the BFlh in any group (VFR = -1%; SS = -2.9%). PRT and CMJ values did not change following any interventions. Our findings suggest that VFR might be a favorable warm-up routine if the goal is to acutely increase ROM without compromising functional performance.

The effect of static stretching on key hits and subjective fatigue in eSports

[Purpose] To explore the effects of static stretching for 20 s on key hits and subjective fatigue in an eSports-like setting. [Participants and Methods] The participants comprised of 15 healthy males who were instructed to hit a particular key on a computer keyboard using the left ring finger to achieve the maximum number of hits possible over a period of 30 s. Subjective fatigue of the forearm was assessed using a visual analog scale (VAS) before the experiment and after each trial. Trials 1, 2, and 3 were conducted in succession, with an inter-trial interval of 60 s to ensure a loaded state. Static stretching for 20 s preceded Trial 4. [Results] Over the first three trials, the number of key hits in the first 10 s gradually decreased, while the feeling of subjective fatigue gradually increased. After stretching, the number of key hits in the first 10 s of Trial 4 was similar to that observed in Trial 1, and there was no increase in subjective fatigue. [Conclusion] Static stretching for 20 s restored the number of key hits for 10 s after stretching to that before the load application and suppressed the increase in subjective fatigue.

Changes in neural drive to calf muscles during steady submaximal contractions after repeated static stretches

KEY POINTS

Repeated static-stretching interventions consistently increase the range of motion about a joint and decrease total joint stiffness, but findings on the changes in muscle and connective-tissue properties are mixed. The influence of these stretch-induced changes on muscle function at submaximal forces is unknown. To address this gap in knowledge, the changes in neural drive to the plantar flexor muscles after a static-stretch intervention were estimated. Neural drive to the plantar flexor muscles during a low-force contraction increased after repeated static stretches. These findings suggest that adjustments in motor unit activity are necessary at low forces to accommodate reductions in the force-generating and transmission capabilities of the muscle-tendon unit after repeated static stretches of the calf muscles.

ABSTRACT

Static stretching decreases stiffness about a joint, but its influence on muscle-tendon unit function and muscle activation is unclear. We investigated the influence of three static stretches on changes in neural drive to the plantar flexor muscles, both after a stretch intervention and after a set of maximal voluntary contractions (MVCs). Estimates of neural drive were obtained during submaximal isometric contractions by decomposing high-density electromyographic signals into the activity of individual motor units from medial gastrocnemius, lateral gastrocnemius and soleus. Motor units were matched across contractions and an estimate of neural drive to the plantar flexors was calculated by normalizing the cumulative spike train to the number of active motor units (normalized neural drive). Mean discharge rate increased after the stretch intervention during the 10% MVC task for all recorded motor units and those matched across conditions (all, P = 0.0046; matched only, P = 0.002), recruitment threshold decreased for motor units matched across contractions (P = 0.022), and discharge rate at recruitment was elevated (P = 0.004). Similarly, the estimate of normalized neural drive was significantly greater after the stretch intervention at 10% MVC torque (P = 0.029), but not at 35% MVC torque. The adjustments in motor unit activity required to complete the 10% MVC task after stretch may have been partially attenuated by a set of plantar flexor MVCs. The increase in neural drive required to produce low plantar-flexion torques after repeated static stretches of the calf muscles suggests stretch-induced changes in muscle and connective tissue properties.

Mechanisms underlying performance impairments following prolonged static stretching without a comprehensive warm-up

Whereas a variety of pre-exercise activities have been incorporated as part of a "warm-up" prior to work, combat, and athletic activities for millennia, the inclusion of static stretching (SS) within a warm-up has lost favor in the last 25 years. Research emphasized the possibility of SS-induced impairments in subsequent performance following prolonged stretching without proper dynamic warm-up activities. Proposed mechanisms underlying stretch-induced deficits include both neural (i.e., decreased voluntary activation, persistent inward current effects on motoneuron excitability) and morphological (i.e., changes in the force-length relationship, decreased Ca²⁺ sensitivity, alterations in parallel elastic component) factors. Psychological influences such as a mental energy deficit and nocebo effects could also adversely affect performance. However, significant practical limitations exist within published studies, e.g., long-stretching durations, stretching exercises with little task specificity, lack of warm-up before/after stretching, testing performed immediately after stretch completion, and risk of investigator and participant bias. Recent research indicates that appropriate durations of static stretching performed within a full warm-up (i.e., aerobic activities before and task-specific dynamic stretching and intense physical activities after SS) have trivial effects on subsequent performance with some evidence of improved force output at longer muscle lengths. For conditions in which muscular force production is compromised by stretching, knowledge of the underlying mechanisms would aid development of mitigation strategies. However, these mechanisms are yet to be perfectly defined. More information is needed to better understand both the warm-up components and mechanisms that contribute to performance enhancements or impairments when SS is incorporated within a pre-activity warm-up.

Acute Effects of Static Stretching on Muscle Strength and Power: An Attempt to Clarify Previous Caveats

The effects of static stretching (StS) on subsequent strength and power activities has been one of the most debated topics in sport science literature over the past decades. The aim of this review is (1) to summarize previous and current findings on the acute effects of StS on muscle strength and power performances; (2) to update readers’ knowledge related to previous caveats; and (3) to discuss the underlying physiological mechanisms of short-duration StS when performed as single-mode treatment or when integrated into a full warm-up routine. Over the last two decades, StS has been considered harmful to subsequent strength and power performances. Accordingly, it has been recommended not to apply StS before strength- and power-related activities. More recent evidence suggests that when performed as a single-mode treatment or when integrated within a full warm-up routine including aerobic activity, dynamic-stretching, and sport-specific activities, short-duration StS (≤60 s per muscle group) trivially impairs subsequent strength and power activities (∆1–2%). Yet, longer StS durations (>60 s per muscle group) appear to induce substantial and practically relevant declines in strength and power performances (∆4.0–7.5%). Moreover, recent evidence suggests that when included in a full warm-up routine, short-duration StS may even contribute to lower the risk of sustaining musculotendinous injuries especially with high-intensity activities (e.g., sprint running and change of direction speed). It seems that during short-duration StS, neuromuscular activation and musculotendinous stiffness appear not to be affected compared with long-duration StS. Among other factors, this could be due to an elevated muscle temperature induced by a dynamic warm-up program. More specifically, elevated muscle temperature leads to increased muscle fiber conduction-velocity and improved binding of contractile proteins (actin, myosin). Therefore, our previous understanding of harmful StS effects on subsequent strength and power activities has to be updated. In fact, short-duration StS should be included as an important warm-up component before the uptake of recreational sports activities due to its potential positive effect on flexibility and musculotendinous injury prevention. However, in high-performance athletes, short-duration StS has to be applied with caution due to its negligible but still prevalent negative effects on subsequent strength and power performances, which could have an impact on performance during competition.