Responses to static stretching are dependent on stretch intensity and duration

Critical evaluation and recalculation of current systematic reviews with meta-analysis on the effects of acute and chronic stretching on passive properties and passive peak torque

PURPOSE

Muscle, tendon, and muscle-tendon unit (MTU) stiffness as well as passive peak torque (PPT) or delayed stretching pain sensation are typical explanatory approaches for stretching adaptations. However, in literature, differences in the study inclusion, as well as applying meta-analytical models without accounting for intrastudy dependency of multiple and heteroscedasticity of data bias the current evidence. Furthermore, most of the recent analyses neglected to investigate PPT adaptations and further moderators.

METHODS

The presented review used the recommended meta-analytical calculation method to investigate the effects of stretching on stiffness as well as on passive torque parameters using subgroup analyses for stretching types, stretching duration, and supervision.

RESULTS

Chronic stretching reduced muscle stiffness ( -  0.38, p = 0.01) overall, and also for the supervised ( -  0.49, p = 0.004) and long static stretching interventions ( -  0.61, p < 0.001), while the unsupervised and short duration subgroups did not reach the level of significance (p = 0.21, 0.29). No effects were observed for tendon stiffness or for subgroups (e.g., long-stretching durations). Chronic PPT (0.55, p = 0.005) in end ROM increased. Only long-stretching durations sufficiently decreased muscle stiffness acutely. No effects could be observed for acute PPT.

CONCLUSION

While partially in accordance with previous literature, the results underline the relevance of long-stretching durations when inducing changes in passive properties. Only four acute PPT in end ROM studies were eligible, while a large number were excluded as they provided mathematical models and/or lacked control conditions, calling for further randomized controlled trials on acute PPT effects.

Does elastic taping on soles improve flexibility? A randomized controlled trial with equivalence test design

BACKGROUND

Elastic taping that applies shear force affects joint movement. However, it remains uncertain whether elastic taping or stretching is more effective in improving flexibility.

OBJECTIVE

We investigated whether elastic taping for flexibility improvement is comparable to traditional stretching.

METHODS

In this randomized controlled trial, 64 university students were randomly allocated to two groups: elastic taping on the sole or 30 s of static stretching. The primary outcome measures were the straight leg raising angle, tested with an equivalence margin (± 9.61∘ on changes), and the fingertip-to-floor distance. Secondary outcomes were the hip flexor and knee extensor strength, two-step distance, adverse events, and pain intensity during the intervention, which were compared using conventional statistical methods.

RESULTS

The mean differences in straight leg raising between the two groups after the interventions were not greater than the equivalence margin (mean [95% CI]: 1.4 [-6.9, 9.5]; equivalence margin, -9.61∘ to 9.61∘). There were no consistent differences between groups in terms of secondary outcomes except for pain intensity during the intervention (p> 0.05). Elastic taping did not induce pain.

CONCLUSION

Elastic taping augments the flexibility-improving effect comparable to static stretching, based on an equivalence margin. Elastic taping of the sole appears to be an alternative method of improving flexibility.

The Effects of Static Stretching Intensity on Range of Motion and Strength: A Systematic Review

The aim of this study was to systematically review the evidence on the outcomes of using different intensities of static stretching on range of motion (ROM) and strength. PubMed, Web of Science and Cochrane controlled trials databases were searched between October 2021 and February 2022 for studies that examined the effects of different static stretching intensities on range of motion and strength. Out of 6285 identified records, 18 studies were included in the review. Sixteen studies examined outcomes on ROM and four on strength (two studies included outcomes on both ROM and strength). All studies demonstrated that static stretching increased ROM; however, eight studies demonstrated that higher static stretching intensities led to larger increases in ROM. Two of the four studies demonstrated that strength decreased more following higher intensity stretching versus lower intensity stretching. It appears that higher intensity static stretching above the point of discomfort and pain may lead to greater increases in ROM, but further research is needed to confirm this. It is unclear if high-intensity static stretching leads to a larger acute decrease in strength than lower intensity static stretching.

Acute passive stretching has no effect on gastrocnemius medialis stiffness in children with unilateral cerebral palsy

PURPOSE

The aim of this study was to investigate the effects of an acute high-intensity, long-duration passive stretching session of the plantar flexor muscles, on maximal dorsiflexion (DF) angle and passive stiffness at both ankle joint and gastrocnemius medialis (GM) muscle levels in children with unilateral cerebral palsy (CP).

METHODS

13 children [mean age: 10 years 6 months, gross motor function classification system (GMFCS): I] with unilateral CP underwent a 5 min passive stretching session at 80% of maximal DF angle. Changes in maximal DF angle, slack angle, passive ankle joint and GM muscle stiffness from PRE- to POST-intervention were determined during passive ankle mobilization performed on a dynamometer coupled with shear wave elastography measurements (i.e., ultrasound) of the GM muscle.

RESULTS

Maximal DF angle and maximal passive torque were increased by 6.3° (P < 0.001; + 50.4%; 95% CI 59.9, 49.9) and 4.2 Nm (P < 0.01; + 38.9%; 95% CI 47.7, 30.1), respectively. Passive ankle joint stiffness remained unchanged (P = 0.9; 0%; 95% CI 10.6, - 10.6). GM muscle shear modulus was unchanged at maximal DF angle (P = 0.1; + 34.5%; 95% CI 44.7, 24.7) and at maximal common torque (P = 0.5; - 4%; 95% CI - 3.7, - 4.3), while it was decreased at maximal common angle (P = 0.021; - 35%; 95% CI - 11.4, - 58.5). GM slack angle was shifted in a more dorsiflexed position (P = 0.02; + 20.3%; 95% CI 22.6, 18).

CONCLUSION

Increased maximal DF angle can be obtained in the paretic leg in children with unilateral CP after an acute bout of stretching using controlled parameters without changes in passive stiffness at joint and GM muscle levels.

CLINICAL TRIAL NUMBER

NCT03714269.

Sex differences in stretch-induced hypertrophy, maximal strength and flexibility gains

Introduction: If the aim is to increase maximal strength (MSt) and muscle mass, resistance training (RT) is primarily used to achieve these outcomes. However, research indicates that long-duration stretching sessions of up to 2 h per day can also provide sufficient stimuli to induce muscle growth. In RT literature, sex-related differences in adaptations are widely discussed, however, there is a lack of evidence addressing the sex-related effects on MSt and muscle thickness (MTh) of longer duration stretch training. Therefore, this study aimed to investigate the effects of 6 weeks of daily (1 h) unilateral static stretch training of the plantar flexors using a calf-muscle stretching device. Methods: Fifty-five healthy (m = 28, f = 27), active participants joined the study. MSt and range of motion (ROM) were measured with extended and flexed knee joint, and MTh was investigated in the medial and lateral heads of the gastrocnemius. Results: Statistically significant increases in MSt of 6%-15% (p < .001-.049, d = 0.45-1.09), ROM of 6%-21% (p < .001-.037, d = 0.47-1.38) and MTh of 4%-14% (p < .001-.005, d = 0.46-0.72) from pre-to post-test were observed, considering both sexes and both legs. Furthermore, there was a significant higher increase in MSt, MTh and ROM in male participants. In both groups, participants showed more pronounced adaptations in MSt and ROM with an extended knee joint as well as MTh in the medial head of the gastrocnemius (p < .001-.047). Results for relative MSt increases showed a similar result (p < .001-.036, d = 0.48-1.03). Discussion: Results are in accordance with previous studies pointing out significant increases of MSt, MTh and ROM due to long duration static stretch training. Both sexes showed significant increases in listed parameters however, male participants showed superior increases.

Ankle rehabilitation robot training for stroke patients with foot drop: Optimizing intensity and frequency

BACKGROUND

Robotic solutions for ankle joint physical therapy have extensively been researched. The optimal frequency and intensity of training for patients when using the ankle robot is not known which can affect rehabilitation outcome.

OBJECTIVE

To explore the optimal ankle robot training protocol on foot drop in stroke subjects.

METHODS

Subjects were randomly divided into four groups, with 9 in each group. The subjects received different intensities (low or high intensity) with frequencies (1 session/day or 2 sessions/day) of robot combination training. Each session lasted 20 minutes and all subjects were trained 5 days a week for 3 weeks.

RESULTS

After 3 weeks of treatment, all groups showed an improvement in passive and active ankle dorsiflexion range of motion (PROM and AROM) and Fugl-Meyer Assessment for lower extremity (FMA-LE) compared to pre-treatment. When training at the same level of intensity, patients who received 2 sessions/day of training had better improvement in ankle dorsiflexion PROM than those who received 1 session/day. In terms of the improvement in dorsiflexion AROM and FMA-LE, patients who received 2 sessions/day with high intensity training improved better than other protocols.

CONCLUSION

High frequency and high intensity robot training can be more effective in improving ankle dysfunction.

Acute Effects of Different Intensity and Duration of Static Stretching on the Muscle-Tendon Unit Stiffness of the Hamstrings

The effects of static stretching are influenced by prescribed and applied loads of stretching. The prescribed load is calculated from the stretching duration and intensity, whereas the applied load is assessed from the force of static stretching exerted on the targeted muscle. No previous study has investigated the prescribed and applied loads of static stretching on the muscle-tendon unit stiffness simultaneously. Therefore, the purpose of the present study was to examine the acute effects of the prescribed and applied load of static stretching on the change in the muscle-tendon unit stiffness of the hamstrings by using different intensities and durations of static stretching. Twenty-three participants underwent static stretching at the intensity of high (50 seconds, 3 sets), moderate (60 seconds, 3 sets), and low (75 seconds, 3 sets), in random order. The parameters were the range of motion, passive torque, and muscle-tendon unit stiffness. These parameters were measured before stretching, between sets, and immediately after stretching by using a dynamometer machine. The static stretching load was calculated from the passive torque during static stretching. The muscle-tendon unit stiffness decreased in high- and moderate-intensity after 50 (p < 0.01, d = -0.73) and 180 seconds (p < 0.01, d = -1.10) of stretching respectively, but there was no change in low-intensity stretching for 225 seconds (p = 0.48, d = -0.18). There were significant correlations between the static stretching load and relative change in the muscle-tendon unit stiffness in moderate- (r = -0.64, p < 0.01) and low-intensity (r = -0.54, p < 0.01), but not in high-intensity (r = -0.16, p = 0.18). High-intensity static stretching was effective for a decrease in the muscle-tendon unit stiffness even when the prescribed load of static stretching was unified. The applied load of static stretching was an important factor in decreasing the muscle-tendon unit stiffness in low- and moderate-intensity static stretching, but not in high-intensity stretching.

Differential effects of dynamic and ballistic stretching on contralateral lower limb flexibility

BACKGROUND: Dynamic stretching (DS) and ballistic stretching (BS) are similar stretching methods, but the differences between them are unclear. OBJECTIVE: To examine the immediate effects of unilateral hamstring DS and BS on straight leg raise (SLR), knee flexion range of motion (KF-ROM), and KF and knee extension maximal isokinetic peak torque (KF-MIPT and KE-MIPT) of the bilateral limbs. METHODS: Twelve healthy adult men performed four sets of 2 min each of non-stretching, DS, or BS of the right lower extremity. Bilateral SLR, KF-ROM, KF-MIPT, and KE-MIPT were measured pre- and post-intervention; a three-way (intervention × limb × time) repeated-measures analysis of variance (ANOVA) was used. RESULTS: The SLR of the stretched limb (p< 0.01) was higher with DS than that pre-intervention. SLR (p< 0.01) and KF-ROM (p< 0.05) of the stretched limb and SLR (p< 0.05) and KF-ROM (p< 0.05) of the contralateral limb were higher with BS than those pre-intervention. There was no significant main effect or interaction between KF-MIPT and KE-MIPT. CONCLUSION: DS and BS had slightly different effects on ROM, and neither affected muscle strength; thus, combining the techniques during warm-up might be helpful.

Is There a "Window of Opportunity" for Flexibility Development in Youth? A Systematic Review with Meta-analysis

BACKGROUND

Flexibility is an important component of physical fitness for competitive and recreational athletes. It is generally suggested that flexibility training should start from childhood (6-11 years of age) to optimize joint range of motion (ROM) increases; however, evidence is limited and inconsistent.

OBJECTIVE

To examine whether there is a difference in the effect of stretching training on flexibility during childhood (6-11 years of age) and adolescence (12-18 years of age).

DESIGN

Systematic review and meta-analysis.

METHODS

We searched PubMed Central, Web of Science, Scopus, Embase, and SPORTDiscus, to conduct this systematic review. Randomized controlled trials and non-randomized controlled trials were eligible. No language and date of publication restrictions were applied. Risk of bias was assessed using Cochrane RoB2 and ROBINS-I tools. Meta-analyses were conducted via an inverse variance random-effects model. GRADE analysis was used to assess the methodological quality of the studies.

RESULTS

From the 2713 records retrieved 28 studies were included in the meta-analysis (n = 1936 participants). Risk of bias was low in 56.9% of all criteria. Confidence in cumulative evidence was moderate. We found that stretching was effective in increasing ROM in both children (SMD = 1.09; 95% CI = 0.77-1.41; Z = 6.65; p < 0.001; I² = 79%) and adolescents (SMD = 0.90; 95% CI = 0.70-1.10; Z = 8.88; p < 0.001; I² = 81%), with no differences between children and adolescents in ROM improvements (p = 0.32; I² = 0%). However, when stretching volume load was considered, children exhibited greater increases in ROM with higher than lower stretching volumes (SMD = 1.21; 95% CI = 0.82-1.60; Z = 6.09; p < 0.001; I² = 82% and SMD = 0.62; 95% CI = 0.29-0.95; Z = 3.65; p < 0.001; I² = 0%, respectively; subgroup difference: p = 0.02; I² = 80.5%), while adolescents responded equally to higher and lower stretching volume loads (SMD = 0.90; 95% CI = 0.47-1.33; Z = 4.08; p < 0.001; I² = 83%, and SMD = 0.90; 95% CI = 0.69-1.12; Z = 8.18; p < 0.001; I² = 79%, respectively; subgroup difference: p = 0.98; I² = 0%).

CONCLUSIONS

Systematic stretching training increases ROM during both childhood and adolescence. However, larger ROM gains may be induced in childhood than in adolescence when higher stretching volume loads are applied, while adolescents respond equally to high and low stretching volume loads.

REGISTRATION

INPLASY, registration number: INPLASY202190032; https://inplasy.com/inplasy-2021-9-0032/.

The effects of eccentric exercise on passive hamstring muscle stiffness: Comparison of shear-wave elastography and passive knee torque outcomes

The aim of our study was to assess eccentric-exercise-induced changes in passive knee joint torque, passive knee joint stiffness and shear modulus at of the hamstring muscles. We hypothesized that eccentric exercise would elicit an increase in all outcomes. Fourteen healthy volunteers (age = 25.5±4.7 years) performed eccentric exercise protocol. Before and after 0h, 1h, 24h and 48h, we measured the shear modulus of hamstring muscles using shear-wave elastography and passive knee joint stiffness on isokinetic dynamometer. After eccentric exercise, the shear modulus of biceps femoris increased after 0h (22.4 ± 34.1 %; p = 0.021) and for semitendinosus after 0h (14.5 ± 4.9 %), 1h (16.2 ± 6.5 %) and 24h (16.6 ± 8.3 %) (p = 0.005-0.015). There were no changes for semimembranosus and no changes in passive knee joint moment measures. There were also no correlations between the two methods. Eccentric exercise increased shear modulus of hamstring muscles, while passive joint torque was not affected. This suggests that shear-wave elastography could be more sensitive than torque measures to intra-muscular changes induced by eccentric exercise.

Comparison Between High- and Low-Intensity Static Stretching Training Program on Active and Passive Properties of Plantar Flexors

The purpose of this study was to compare two static stretching (SS) training programs at high-intensity (HI-SS) and low-intensity (LI-SS) on passive and active properties of the plantar flexor muscles. Forty healthy young men were randomly allocated into three groups: HI-SS intervention group (n = 14), LI-SS intervention group (n = 13), and non-intervention control group (n = 13). An 11-point numerical scale (0–10; none to very painful stretching) was used to determine SS intensity. HI-SS and LI-SS stretched at 6–7 and 0–1 intensities, respectively, both in 3 sets of 60 s, 3×/week, for 4 weeks. Dorsiflexion range of motion (ROM), gastrocnemius muscle stiffness, muscle strength, drop jump height, and muscle architecture were assessed before and after SS training program. The HI-SS group improved more than LI-SS in ROM (40 vs. 15%) and decreased muscle stiffness (−57 vs. −24%), while no significant change was observed for muscle strength, drop jump height, and muscle architecture in both groups. The control group presented no significant change in any variable. Performing HI-SS is more effective than LI-SS for increasing ROM and decreasing muscle stiffness of plantar flexor muscles following a 4-week training period in young men. However, SS may not increase muscle strength or hypertrophy, regardless of the stretching discomfort intensity.

Sex differences in stretch-induced hypertrophy, maximal strength and flexibility gains

Introduction: If the aim is to increase maximal strength (MSt) and muscle mass, resistance training (RT) is primarily used to achieve these outcomes. However, research indicates that long-duration stretching sessions of up to 2 h per day can also provide sufficient stimuli to induce muscle growth. In RT literature, sex-related differences in adaptations are widely discussed, however, there is a lack of evidence addressing the sex-related effects on MSt and muscle thickness (MTh) of longer duration stretch training. Therefore, this study aimed to investigate the effects of 6 weeks of daily (1 h) unilateral static stretch training of the plantar flexors using a calf-muscle stretching device. Methods: Fifty-five healthy (m = 28, f = 27), active participants joined the study. MSt and range of motion (ROM) were measured with extended and flexed knee joint, and MTh was investigated in the medial and lateral heads of the gastrocnemius. Results: Statistically significant increases in MSt of 6%-15% (p < .001-.049, d = 0.45-1.09), ROM of 6%-21% (p < .001-.037, d = 0.47-1.38) and MTh of 4%-14% (p < .001-.005, d = 0.46-0.72) from pre-to post-test were observed, considering both sexes and both legs. Furthermore, there was a significant higher increase in MSt, MTh and ROM in male participants. In both groups, participants showed more pronounced adaptations in MSt and ROM with an extended knee joint as well as MTh in the medial head of the gastrocnemius (p < .001-.047). Results for relative MSt increases showed a similar result (p < .001-.036, d = 0.48-1.03). Discussion: Results are in accordance with previous studies pointing out significant increases of MSt, MTh and ROM due to long duration static stretch training. Both sexes showed significant increases in listed parameters however, male participants showed superior increases.

Effects of Robot-Aided Rehabilitation on the Ankle Joint Properties and Balance Function in Stroke Survivors: A Randomized Controlled Trial

Background: Stroke survivors with impaired control of the ankle due to stiff plantarflexors often experience abnormal posture control, which affects balance and locomotion. Forceful stretching may decrease ankle stiffness and improve balance. Recently, a robot-aided stretching device was developed to decrease ankle stiffness of patient post-stroke, however, their benefits compared to manual stretching exercises have not been done in a randomized controlled trial, and the correlations between the ankle joint biomechanical properties and balance are unclear.

Objective: To compare the effects of robot-aided to manual ankle stretching training in stroke survivors with the spastic ankle on the ankle joint properties and balance function post-stroke, and further explore the correlations between the ankle stiffness and balance.

Methods: Twenty inpatients post-stroke with ankle spasticity received 20 minutes of stretching training daily over two weeks. The experimental group used a robot-aided stretching device, and the control group received manual stretching. Outcome measures were evaluated before and after training. The primary outcome measure was ankle stiffness. The secondary outcome measures were passive dorsiflexion ranges of motion, dorsiflexor muscle strength, Modified Ashworth Scale (MAS), Fugl-Meyer Motor Assessment of Lower Extremity (FMA-LE), Berg Balance Scale (BBS), Modified Barthel Index (MBI), and the Pro-Kin balance test.

Results: After training, two groups showed significantly within-group improvements in dorsiflexor muscle strength, FMA-LE, BBS, MBI (P < 0.05). The between-group comparison showed no significant differences in all outcome measures (P > 0.0025). The experimental group significantly improved in the stiffness and passive range of motion of dorsiflexion, MAS. In the Pro-Kin test, the experimental group improved significantly with eyes closed and open (P < 0.05), but significant improvements were found in the control group only with eyes open (P < 0.05). Dorsiflexion stiffness was positively correlated with the Pro-Kin test results with eyes open and the MAS (P < 0.05).

Conclusions: The robot-aided and manual ankle stretching training provided similar significant improvements in the ankle properties and balance post-stroke. However, only the robot-aided stretching training improved spasticity and stiffness of dorsiflexion significantly. Ankle dorsiflexion stiffness was correlated with balance function.

Clinical Trial Registration:www.chictr.org.cn ChiCTR2000030108.

Static Stretching Intensity Does Not Influence Acute Range of Motion, Passive Torque, and Muscle Architecture

CONTEXT

Although stretching exercises are commonly used in clinical and athletic practice, there is a lack of evidence regarding the methodological variables that guide the prescription of stretching programs, such as intensity.

OBJECTIVE

To investigate the acute effects of different stretching intensities on the range of motion (ROM), passive torque, and muscle architecture.

DESIGN

Two-group pretest-posttest design.

SETTING

Laboratory.

PARTICIPANTS

Twenty untrained men were allocated into the low- or high-intensity group.

MAIN OUTCOME MEASURES

Subjects were evaluated for initial (ROMinitial) and maximum (ROMmax) discomfort angle, stiffness, viscoelastic stress relaxation, muscle fascicle length, and pennation angle.

RESULTS

The ROM assessments showed significant changes, in both groups, in the preintervention and postintervention measures both for the ROMinitial (P < .01) and ROMmax angle (P = .02). There were no significant differences for stiffness and viscoelastic stress relaxation variables. The pennation angle and muscle fascicle length were different between the groups, but there was no significant interaction.

CONCLUSION

Performing stretching exercises at high or low intensity acutely promotes similar gains in flexibility, that is, there are short-term/immediate gains in ROM but does not modify passive torque and muscle architecture.

Effects of Static Stretching With High-Intensity and Short-Duration or Low-Intensity and Long-Duration on Range of Motion and Muscle Stiffness

This study investigated the effects of static stretching (SS) delivered with the same load but using two protocols – high-intensity and short-duration and low-intensity and long-duration – on range of motion (ROM) and muscle stiffness. A total of 18 healthy students participated in the study. They randomly performed high-intensity and short-duration (120% and 100 s) or low-intensity and long-duration (50% and 240 s) SS. Outcomes were assessed on ROM, passive torque at dorsiflexion ROM, and shear elastic modulus of the medial gastrocnemius before and after static stretching. The results showed that ROM increased significantly at post-stretching compared to that at pre-stretching in both high-intensity and short-duration [+6.1° ± 4.6° (Δ25.7 ± 19.9%)] and low-intensity and long-duration [+3.6° ± 2.3° (Δ16.0 ± 11.8%)]. Also, the ROM was significantly higher at post-stretching in high-intensity and short-duration conditions than that in low-intensity and long-duration. The passive torque at dorsiflexion ROM was significantly increased in both high-intensity and short-duration [+5.8 ± 12.8 Nm (Δ22.9 ± 40.5%)] and low-intensity and long-duration [+2.1 ± 3.4 Nm (Δ6.9 ± 10.8%)] conditions, but no significant differences were observed between both conditions. The shear elastic modulus was significantly decreased in both high-intensity and short-duration [−8.8 ± 6.1 kPa (Δ − 38.8 ± 14.5%)] and low-intensity and long-duration [−8.0 ± 12.8 kPa (Δ − 22.2 ± 33.8%)] conditions. Moreover, the relative change in shear elastic modulus in the high-intensity and short-duration SS was significantly greater than that in low-intensity and long-duration SS. Our results suggest that a higher intensity of the static stretching should be conducted to increase ROM and decrease muscle stiffness, even for a short time.

The Relationship between Stretching Intensity and Changes in Passive Properties of Gastrocnemius Muscle-Tendon Unit after Static Stretching

This study aimed to investigate the relationship between relative or absolute intensity and changes in range of motion and passive stiffness after static stretching. A total of 65 healthy young adults voluntarily participated in this study and performed static stretching of the plantar flexor-muscle for 120 s. Dorsiflexion range of motion and passive torque during passive dorsiflexion before and after stretching were assessed. We measured the passive torque at a given angle when the minimum angle was recorded before and after stretching. The angle during stretching was defined as the absolute intensity. Dorsiflexion range of motion before stretching was defined as 100%, and the ratio (%) of the angle during stretching was defined as the relative intensity. A significant correlation was found between absolute intensity and change in passive torque at a given angle (r = -0.342), but relative intensity and range of motion (r = 0.444) and passive torque at dorsiflexion range of motion (r = 0.259). A higher absolute intensity of stretching might be effective in changing the passive properties of the muscle-tendon unit. In contrast, a higher relative intensity might be effective in changing the range of motion, which could be contributed by stretch tolerance.

Immediate effects of neurodynamic nerve gliding versus static stretching on hamstring neuromechanical properties

PURPOSE

We investigated the immediate effects of neurodynamic nerve gliding (ND) on hamstring flexibility, viscoelasticity, and mechanosensitivity, compared with traditional static stretching (ST).

METHODS

Twenty-two physically active men aged 21.9 ± 1.9 years were divided randomly into two equal intervention groups using ST or ND. An isokinetic dynamometer was used to measure the active knee joint position sense, perform passive knee extension, record the passive extension range of motion (ROM) and the passive-resistive torque of hamstrings. Stiffness was determined from the slope of the passive torque-angle relationship. A stress relaxation test (SRT) was performed to analyze the viscoelastic behavior of the hamstrings. The passive straight leg raise (SLR) test was used to evaluate hamstring flexibility.

RESULTS

A significant interaction was observed for ROM and passive ultimate stiffness, reflected by an increase in these indicators after ND but not after SD. SLR increased significantly in both groups. After ST, a significantly faster initial stress relaxation was observed over the first 4 s. than after ND. There was no significant change in the active knee joint position sense.

CONCLUSIONS

ND provided a slightly greater increase in hamstring extensibility and passive stiffness, possibly by decreasing nerve tension and increasing strain in connective tissues than ST. The ST mostly affected the viscoelastic behavior of the hamstrings, but neither intervention had a significant impact on proprioception.

The Effect of Static Stretching Duration on Muscle Blood Volume and Oxygenation

Matsuo, H, Kubota, M, Shimada, S, Kitade, I, Matsumura, M, Nonoyama, T, Koie, Y, Naruse, H, Takahashi, A, Oki, H, Kokubo, Y, and Matsumine, A. The effect of static stretching duration on muscle blood volume and oxygenation. J Strength Cond Res XX(X): 000-000, 2020-Muscle blood volume increases due to stretching; however, the minimum duration of stretching to sustainably increase the muscle blood volume after stretching has not yet been elucidated. This study examined whether the duration of static stretching influenced the muscle blood volume and oxygenation. Ten healthy male subjects participated in this controlled laboratory study. Static stretching of the gastrocnemius muscle was performed for 5 durations (20 seconds, and 1, 2, 5, and 10 minutes). Changes in both the total-Hb (ΔtHb), as an index of blood volume, and tissue oxygenation index (ΔTOI) from baseline were determined using near-infrared spectroscopy. Both the ΔtHb and ΔTOI decreased during stretching and increased after stretching. The minimum value of ΔtHb during stretching did not differ in each of the 5 durations, but minimum ΔTOI progressively decreased with longer durations of stretching. The peak value of ΔtHb after stretching increased with longer durations of stretching. The value of ΔtHb at 5 minutes after the end of stretching increased with more than 2 minutes of stretching compared with 20 seconds of stretching, although the value of ΔtHb did not significantly differ between the 2, 5, and 10 minutes' durations. These findings suggest that a longer duration of stretching elicits a decrease in muscle oxygenation during stretching, and an increase in both the muscle blood volume and oxygenation after stretching. The results indicated that the minimum duration of stretching to sustain an increase in the muscle blood volume after stretching is 2 minutes.

Effects of a 12-Week Chronic Stretch Training Program at Different Intensities on Joint and Muscle Mechanical Responses: A Randomized Clinical Trial

CONTEXT

Stretching intensity is an important variable that can be manipulated with flexibility training. However, there is a lack of evidence regarding this variable and its prescription in stretching programs.

OBJECTIVE

To investigate the effects of 12 weeks of knee flexor static stretching at different intensities on joint and muscle mechanical properties.

DESIGN

A randomized clinical trial.

SETTING

Laboratory.

PARTICIPANTS

A total of 14 untrained men were allocated into the low- or high-intensity group.

MAIN OUTCOME MEASURES

Assessments were performed before, at 6 week, and after intervention (12 wk) for biceps femoris long head architecture (resting fascicle length and angle), knee maximal range of motion (ROM) at the beginning and maximal discomfort angle, knee maximal tolerated passive torque, joint passive stiffness, viscoelastic stress relaxation, knee passive torque at a given angle, and affective responses to training.

RESULTS

No significant differences were observed between groups for any variable. ROM at the beginning and maximal discomfort angle increased at 6 and 12 weeks, respectively. ROM significantly increased with the initial angle of discomfort (P < .001, effect size = 1.38) over the pretest measures by 13.4% and 14.6% at the 6- and 12-week assessments, respectively, and significantly improved with the maximal discomfort angle (P < .001, effect size = 1.25) by 15.6% and 18.8% from the pretest to the 6- and 12-week assessments, respectively. No significant effects were seen for muscle architecture and affective responses. Initial viscoelastic relaxation for the low-intensity group was lower than ending viscoelastic relaxation.

CONCLUSION

These results suggest that stretching with either low or high discomfort intensities are effective in increasing joint maximal ROM, and that does not impact on ROM, stiffness, fascicle angle and length, or affective response differences.

Effects of ankle position during static stretching for the hamstrings on the decrease in passive stiffness

Static stretching is frequently performed to improve flexibility of the hamstrings, although the ankle position during hamstring stretching has not been fully investigated. We investigated the effects of ankle position during hamstring stretching on the decrease in passive stiffness. Fourteen healthy men performed static stretching for the hamstrings with the ankle dorsiflexed and plantar-flexed in a randomized order on different days. The hip was passively flexed to the maximum angle which could be tolerated without stretch pain with the knee fully extended; this was maintained for 5 min, with 1-min stretching performed in 5 sessions. Final angles and passive stiffness were measured before and after stretching. The final angle was defined as that formed by the tibia and horizontal plane when the knee was passively extended from hip and knee angles at 90° flexion to the maximum extension angle which could be tolerated without stretch pain. Passive stiffness was determined by the slope of torque-angle curve during the measurement of the final angle. The final angle significantly increased after stretching with the ankle dorsiflexed and plantar-flexed, whereas passive stiffness significantly decreased only after stretching with the ankle planter-flexed. The results suggest that passive stiffness decreases after stretching with the ankle planter-flexed but not after stretching with the ankle dorsiflexed, although the range of joint motion increases regardless of the ankle position during 5-min stretching for the hamstrings. These results indicate that static stretching should be performed with the ankle plantar-flexed when aiming to decrease passive stiffness of the hamstrings.

Different volumes and intensities of static stretching affect the range of motion and muscle force output in well-trained subjects

The manipulation of the volume and intensity of static stretching (SS) can affect the range of motion (ROM) and muscle force output. The purpose of this study was to investigate the effect of two different SS protocols with different intensities (50% and 85% POD) and volumes (120-s and 240-s) on ROM, peak force, and muscle activity during maximal isometric leg curl exercise in well-trained participants. Fifteen young males (age:27.5 ± 6.1years, height:175.6 ± 4.7cm, and body mass:81.5 ± 10.4kg, 6 ± 2 years of resistance training experience) performed passive hip flexion with two different SS protocols: six stretches of 40-s, with 15-sec rest between each stretch at 50% of the point of discomfort (POD) and three stretches of 40-s, with 15-sec rest between each stretch at 85%POD. The passive hip flexion ROM, biceps femoris muscle activation (integrated electromyography: IEMG), and knee flexors force were monitored during a 3-s maximal voluntary isometric leg curl exercise. ROM increased between pre- and post-intervention for both SS protocols (50%POD: p = 0.016, Δ% = 4.6% and 85%POD: p < 0.001, Δ% = 11.42%). Peak force decreased between pre- and post-intervention only for 85%POD (p = 0.004, Δ% = 23.6%). There were no significant IEMG differences. In conclusion, both SS protocols increased ROM, however, the high-intensity and short-duration SS protocol decreased peak force.

The effects of 6 weeks of constant-angle muscle stretching training on flexibility and muscle function in men with limited hamstrings' flexibility

PURPOSE

The aim of the present study was to evaluate the effects of 6 weeks of a constant-angle hamstring muscle flexibility training on muscle-tendon stiffness and the range of motion (ROM) in young men with limited hamstring ROM.

METHODS

13 participants performed unilateral stretching training (EL), while the contralateral limb acted as control (CL). ROM, relative and peak passive torque, passive stiffness, dynamic knee flexion strength, and active optimum joint angle were assessed before and after the last training session. In addition, participants were tested during the first and last training sessions for first stretch sensation during the stretching procedure only in the EL.

RESULTS

Straight-leg raise and isokinetic knee ROM tests (both p < 0.0001; from 59.4 ± 8.1 to 70.3 ± 9.8, from 28.3 ± 7.6 to 18.5 ± 5.2, respectively) and peak passive torque (p = 0.001; from 53.1 ± 11.7 to 64.9 ± 12.3) increased only in EL and no changes in relative passive torque, passive stiffness, dynamic knee flexion strength, and active optimum joint angle (p > 0.05) were observed. At the point of first stretch sensation, significant increases in passive torque (p = 0.004) and angle (p < 0.001) were found from pre- to post-training.

CONCLUSION

The flexibility training induced significant increases in ROM alongside increases in peak passive torque (stretch tolerance) and the ROM at which stretch was first perceived. However, this occurred without changes in muscle-tendon mechanical properties or transfer to the untrained limb (CL). These results suggest that limb-specific ROM increases were underpinned by neural adaptations.

A novel approach to improve hamstring flexibility: A single-blinded randomised clinical trial

Background

The hamstrings play a major role in body posture. Shortening or tightness of the hamstrings affects postural alignment and results in possible musculoskeletal pain.

Objectives

The aim of this study was to develop a novel approach to improve hamstring flexibility in young adults.

Method

A single-blinded randomised clinical trial included 60 participants aged 18-24 with shortened hamstrings recruited from the Hashemite University, Zarqa, Jordan. The range of motion of knee extension was measured with the hip at 90° flexion using a simple goniometer to detect the level of hamstring flexibility. Participants received either a passive hamstring stretch (PS), followed by two sets of 10 tibial nerve neurodynamic technique (ND), or PS followed by three sets of 10 repetitions of active knee extension-quadriceps activation (QA), or PS only.

Results

There was a significant improvement of hamstring flexibility in the QA group compared to the PS group (13.4 ± 12.1° vs. 6.2 ± 6.4°, p = 0.05). There was a significant improvement in hamstring flexibility post-intervention compared to pre-intervention in the PS group by 6.2 ± 6.4 (30.5 ± 10.8° vs. 36.6 ± 9.5°, p = 0.001), ND group by 9.3 ± 6.2 (26.7 ± 10.9° vs. 36.0 ± 9.5°, p = 0.001) and QA group by 13.4 ± 12.1 (20.3 ± 9.0° vs. 33.4 ± 8.9°, p = 0.001).

Conclusion

Quadriceps muscle activation following passive stretching of the hamstrings appears to be superior to the PS and ND techniques in improving hamstring muscle flexibility.

Clinical implications

Quadriceps activation following passive hamstring stretching can be used in physiotherapy settings to improve hamstring muscle flexibility.

Easy method for measuring stretching intensities in real clinical settings and effects of different stretching intensities on flexibility

BACKGROUND

Flexibility changes according to stretching intensity have been rarely investigated. I aimed to assess the effect of different stretching intensities on hamstring flexibility by measuring them in a setting similar to real clinical settings.

METHODS

Stretching intensities were quantified using an easy method, and participants were grouped according to intensity: 100% (P100), 70% (P70), 40% (P40), and 10% (P10) of maximum voluntary isometric contraction. Proprioceptive neuromuscular facilitation stretching intensities were measured using a sling system and tension dynamometer. Hamstring flexibility was measured (before; immediately after; and 3, 6, 9, 12, and 15 min after stretching) using the active knee extension test. Flexibility was compared between subgroups, and longitudinal changes in flexibility were additionally observed in each group.

RESULTS

At identical time points, no significant difference in hamstring flexibility was found between the high-intensity (P100) and moderate-intensity (P70, P40) groups. A significant difference was found between P100 and P10 immediately after and 12 and 15 min after stretching. Increased flexibility was maintained until the end in P100 and P70 but not P40 and P10.

CONCLUSIONS

High-intensity and moderate-intensity stretching increases flexibility compared with low-intensity stretching. Furthermore, high-intensity stretching was superior to moderate-intensity stretching in terms of maintaining flexibility over time.

Baseline muscle tendon unit stiffness does not affect static stretching of the ankle plantar flexor muscles

[Purpose] The aim of this study was to investigate the influence of baseline muscle tendon unit stiffness on static stretching. [Participants and Methods] Eighteen healthy males were divided into two groups according to their muscle tendon unit stiffness as follows: High (n=9) and Low (n=9). Flexibility assessment was performed before and after 10 minutes of static stretching. Alterations in range of motion, passive torque at the terminal range of motion, muscle tendon unit stiffness, muscle tendon junction displacement, and tendon length were examined. [Results] No significant interactions were found in all the measurements. After static stretching, the range of motion, passive torque, muscle tendon junction displacement, and tendon length increased, while muscle tendon unit stiffness decreased. There were significant differences in range of motion, muscle tendon unit stiffness, and muscle tendon junction displacement between the groups. [Conclusion] Ten minutes of static stretching increased the range of motion through a decrease in muscle tendon unit stiffness and an increase in tolerance in both groups. Differences in muscle tendon unit stiffness and muscle tendon junction displacement caused the differences in range of motion. Baseline muscle tendon unit stiffness had no effects on static stretching.

Instrument-assisted soft tissue mobilization and proprioceptive neuromuscular facilitation techniques improve hamstring flexibility better than static stretching alone: a randomized clinical trial

Objectives: Tight hamstrings contribute to inefficiency of movement and increased risk for injury. Static stretching is the most common intervention for this problem, but the use of alternatives like instrument-assisted soft tissue mobilization (IASTM) and proprioceptive neuromuscular facilitation (PNF) is increasing among clinicians. This study examined two prospective studies with the common aim of demonstrating the effectiveness of IASTM or PNF over static stretching for improving hamstring tightness. Methods: Nondisabled adults were recruited on a university campus. IASTM study: N = 17 (11 males and 6 females). PNF study: N = 23 (7 males and 16 females). Hip flexion range of motion was measured with a passive straight leg raise (for IASTM) or active straight leg raise (for PNF) before and after stretching. Participants performed a self-static stretch on one leg and received the alternative intervention on the contralateral leg. The two studies were analyzed separately for reliability indices and significant differences between interventions. Results: Hip flexion measures showed good reliability in both studies (intraclass correlation coefficient = 0.97) with a minimal detectable change of <4.26. Both studies showed significant interactions between time and intervention (p < 0.05). Follow-up analyses revealed PNF and IASTM interventions resulted in greater increases in hip flexion range than static stretching. Discussion: These findings demonstrate the effectiveness of PNF and IASTM techniques over static stretching for hamstring flexibility. These interventions provide more efficient alternatives for improving flexibility in the clinic, allowing greater progress in a shorter period of time than an equivalent static stretching program. Level of Evidence: 1b.

Influence of chronic stretching on muscle performance: Systematic review

The aim of the current study was to investigate the influence of chronic stretching on muscle performance (MP) by a systematic review. The search strategy included MEDLINE, PEDro, Cochrane CENTRAL, LILACS, and manual search from inception to June 2016. Randomized and controlled clinical trials, non-randomized, and single group studies that have analyzed the influence of flexibility training (FT) (using any stretching technique) on MP were included. Differently, studies with special populations (children, elderly, and people with any dysfunction/disease), and articles that have used FT protocols shorter than three weeks or 12 sessions were excluded. The MP assessment could have been performed by functional tests (e.g. jump, sprint, stretch-shortening cycle tasks), isometric contractions, and/or isotonic contractions. Twenty-eight studies were included out of 513. Seven studies evaluated MP by stretch-shortening cycle tasks, Ten studies evaluated MP by isometric contractions, and 13 studies assessed MP by isotonic contractions. We were unable to perform a meta-analysis due to the high heterogeneity among the included studies. In an individual study level analysis, we identified that 14 studies found positive effects of chronic stretching on MP. The improvements were observed only in functional tests and isotonic contractions, isometric contractions were not affected by FT. Therefore, FT might have an influence on dynamic MP. However, more studies are necessary to confirm whether FT can positively affect MP.

The acute benefits and risks of passive stretching to the point of pain

PURPOSE

This study evaluated the acute effects of two different stretch intensities on muscle damage and extensibility.

METHODS

Twenty-two physically active women (age 20 ± 1.0 years) were divided into two matched groups and undertook eight sets of 30-s passive hamstring stretching. One group stretched to the point of discomfort (POD) and the other to the point of pain (POP). Hamstring passive torque, sit and reach (S&R), straight leg raise (SLR), and markers of muscle damage were measured before, immediately after stretching and 24 h later.

RESULTS

S&R acutely increased and was still increased at 24 h with median (interquartile range) of 2.0 cm (0.5-3.75 cm) and 2.0 cm (0.25-3.0 cm) for POP and POD (p < 0.05), respectively, with no difference between groups; similar changes were seen with SLR. Passive stiffness fully recovered by 24 h and there was no torque deficit. A small, but significant increase in muscle tenderness occurred at 24 h in both groups and there was a very small increase in thigh circumference in both groups which persisted at 24 h in POP. Plasma CK activity was not raised at 24 h.

CONCLUSION

Stretching to the point of pain had no acute advantages over stretching to the discomfort point. Both forms of stretching resulted in very mild muscle tenderness but with no evidence of muscle damage. The increased ROM was not associated with changes in passive stiffness of the muscle but most likely resulted from increased tolerance of the discomfort.

Acute muscle and joint mechanical responses following a high-intensity stretching protocol

PURPOSE

A previous study observed a joint passive torque increase above baseline ~30 min after a high-intensity stretching. This study examined the effect of a high-intensity stretching on ankle dorsiflexion passive torque, medial gastrocnemius (MG) shear modulus, and plantar flexors maximal voluntary isometric force (MVIC).

METHOD

Participants (n = 11, age 27.2 ± 6.5 years, height 172.0 ± 10.0 cm, weight 69.5 ± 10.4 kg) underwent two stretching sessions with plantar flexors isometric contractions performed: (1) 5 min before, 1 min after, and every 10 min after stretching (MVC session); (2) 5 min before, and 60 min after the stretching (no-MVC session).

RESULTS

In both sessions, no changes were observed for MG shear modulus (p > 0.109). In the no-MVC session, passive torque decreased 1 min after stretching (-7.5 ± 8.4 %, p = 0.015), but increased above baseline 30 min after stretching (+6.3 ± 9.3 %, p = 0.049). In the MVC session, passive torque decreased at 1 min (-10.1 ± 6.3 %, p < 0.001), 10 min (-6.3 ± 8.2 %, p = 0.03), 20 min (-8.0 ± 9.2 %, p = 0.017), and 60 min (-9.2 ± 12.4 %, p = 0.034) after the stretching, whereas the MVIC decreased at 1 min (-5.0 ± 9.3 %, p = 0.04) and 10 min (-6.7 ± 8.7 %, p = 0.02) after stretching.

CONCLUSION

The ankle passive torque increase 30 min following the stretch was not due to the MG shear modulus response; consequently, response may be due to changes in surrounding connective tissue mechanical properties.

Home-Based Versus Laboratory-Based Robotic Ankle Training for Children With Cerebral Palsy: A Pilot Randomized Comparative Trial

OBJECTIVE

To examine the outcomes of home-based robot-guided therapy and compare it to laboratory-based robot-guided therapy for the treatment of impaired ankles in children with cerebral palsy.

DESIGN

A randomized comparative trial design comparing a home-based training group and a laboratory-based training group.

SETTING

Home versus laboratory within a research hospital.

PARTICIPANTS

Children (N=41) with cerebral palsy who were at Gross Motor Function Classification System level I, II, or III were randomly assigned to 2 groups. Children in home-based and laboratory-based groups were 8.7±2.8 (n=23) and 10.7±6.0 (n=18) years old, respectively.

INTERVENTIONS

Six-week combined passive stretching and active movement intervention of impaired ankle in a laboratory or home environment using a portable rehabilitation robot.

MAIN OUTCOME MEASURES

Active dorsiflexion range of motion (as the primary outcome), mobility (6-minute walk test and timed Up and Go test), balance (Pediatric Balance Scale), Selective Motor Control Assessment of the Lower Extremity, Modified Ashworth Scale (MAS) for spasticity, passive range of motion (PROM), strength, and joint stiffness.

RESULTS

Significant improvements were found for the home-based group in all biomechanical outcome measures except for PROM and all clinical outcome measures except the MAS. The laboratory-based group also showed significant improvements in all the biomechanical outcome measures and all clinical outcome measures except the MAS. There were no significant differences in the outcome measures between the 2 groups.

CONCLUSIONS

These findings suggest that the translation of repetitive, goal-directed, biofeedback training through motivating games from the laboratory to the home environment is feasible. The benefits of home-based robot-guided therapy were similar to those of laboratory-based robot-guided therapy.

Muscle and joint responses during and after static stretching performed at different intensities

PURPOSE

We investigated the effects of plantarflexor static stretching of different intensities on the medial gastrocnemius (GAS) shear elastic modulus, GAS fascicle length and ankle passive torque-angle responses during and after stretching.

METHODS

Participants performed three stretching sessions of different intensities: 40 % (R40) of maximal dorsiflexion range of motion (ROM), 60 % (R60) of ROM, and 80 % (R80) of ROM. Each stretching lasted 10 min. The GAS architecture, GAS shear elastic modulus, ankle passive torque-angle, and muscle activity were assessed before, during, and after the stretching.

RESULTS

The absolute and relative (i.e., normalized to the static stretching start value) GAS shear elastic modulus relaxation varied across stretching intensities. The absolute passive torque relaxation varied across intensities (p < 0.05) but not when normalized to the stretching start value. No significant changes were observed in GAS fascicle length during the stretching (p = 0.93). After stretching, passive torque at a given angle was significantly decreased for R60 [-0.99 ± 0.59 Nm (-6.5 ± 3.8 %), p < 0.001] and R80 [-1.05 ± 1.12 Nm (-6.8 ± 6.3 %), p = 0.004], and GAS shear elastic modulus decreased only for the R80 [-9.3 ± 7.2 kPa (-14.1 %), p = 0.003]. No significant correlations were found between the magnitude of relaxation during stretching and post-stretching effect in the GAS shear elastic modulus or ankle passive torque variables. No significant relation was found between the shear elastic modulus and the ankle passive torque responses during and after stretching.

CONCLUSION

The effects of stretching on joint passive torque do not reflect changes in the medial gastrocnemius shear elastic modulus, and these responses to stretching depend on its intensity.