Decrements in stiffness are restored within 10 min

Acute and Prolonged Effects of 300 sec of Static, Dynamic, and Combined Stretching on Flexibility and Muscle Force

Static stretching (SS), dynamic stretching (DS), and combined stretching (CS; i.e., DS+SS) are commonly performed as warm-up exercises. However, the stretching method with the greatest effect on flexibility and performance remains unclear. This randomized crossover trial examined acute and prolonged effects of SS, DS, and CS on range of motion (ROM), peak passive torque (PPT), passive stiffness, and isometric and concentric muscle forces. Twenty healthy young men performed 300 sec of active SS, DS, or CS (150-sec SS followed by 150-sec DS and 150-sec DS followed by 150-sec SS) of the right knee flexors on four separate days, in random order. Subsequently, we measured ROM, PPT, and passive stiffness during passive knee extension. We also measured maximum voluntary isometric and concentric knee flexion forces and surface electromyographic activities during force measurements immediately before, immediately after, and 20 and 60 min after stretching. All stretching methods significantly increased ROM and PPT, while significantly decreasing isometric knee flexion force (all p < 0.05). These changes lasted 60 min after all stretching methods; the increases in ROM and PPT and the decreases in isometric muscle force were similar. All stretching methods also significantly decreased passive stiffness immediately after stretching (all p < 0.05). Decreases in passive stiffness tended to be longer after CS than after SS or DS. Concentric muscle force was decreased after SS and CS (all p < 0.05). On the other hand, concentric muscle force was unchanged after DS, while the decreases in surface electromyographic activities during concentric force measurements after all stretching methods were similar. Our results suggest that 300 sec of SS, DS, and CS have different acute and prolonged effects on flexibility and muscle force.

Effects of patterned electrical sensory nerve stimulation and static stretching on joint range of motion and passive torque

Static stretching and proprioceptive neuromuscular facilitation stretching techniques can modulate specific neural mechanisms to improve the range of motion. However, the effects of modulation of these neural pathways on changes in the range of motion with static stretching remain unclear. Patterned electrical stimulation of the sensory nerve induces plastic changes in reciprocal Ia inhibition. The present study examined the effects of patterned electrical stimulation and static stretching on a range of motion and passive torque in plantarflexion muscles. The subjects were 14 young men (age 20.8 ± 1.3 years). The effects of patterned electrical stimulation (10 pulses at 100 Hz every 1.5 s) or uniform electrical stimulation (one pulse every 150 ms) to the common peroneal nerve for 20 min on reciprocal Ia inhibition of the Hoffman reflex (H-reflex) were examined. Reciprocal Ia inhibition was evaluated as short-latency suppression of the soleus H-reflex by conditioning stimulation of the common peroneal nerve. Then, the effects of transcutaneous electrical nerve stimulation (patterned electrical stimulation or uniform electrical stimulation) or prolonged resting (without electrical stimulation) and static 3-min stretching on the maximal dorsiflexion angle and passive torque were investigated. The passive ankle dorsiflexion test was performed on an isokinetic dynamometer. Stretch tolerance and stiffness of the muscle-tendon unit were evaluated by the peak and slope of passive torques, respectively. Patterned electrical stimulation significantly increased reciprocal Ia inhibition of soleus H-reflex amplitude (9.7 ± 6.1%), but uniform electrical stimulation decreased it significantly (19.5 ± 8.8%). The maximal dorsiflexion angle was significantly changed by patterned electrical stimulation (4.0 ± 1.4°), uniform electrical stimulation (3.8 ± 2.3°), and stretching without electrical stimulation (2.1 ± 3.3°). The increase in stretch tolerance was significantly greater after patterned electrical stimulation and uniform electrical stimulation than after stretching without electrical stimulation. Stiffness of the muscle-tendon unit was significantly decreased by patterned electrical stimulation, uniform electrical stimulation, and stretching without electrical stimulation. Transcutaneous electrical nerve stimulation and static stretching improve stretch tolerance regardless of the degree of reciprocal Ia inhibition.

Systematic review: exercise training for equinus deformity in children with cerebral palsy

Background

Children with spastic cerebral palsy have motor deficits that can lead to joint contractures. Ankle equinus deformity is the most common foot deformity among children with CP. It is caused by spasticity and muscular imbalance in the gastrocnemius-soleus complex. Exercise enhances ankle function, improves gait in children with CP, and prevents permanent impairment. Therefore, there is a need to investigate the effectiveness of different types of exercise used in equine management. The aim of this review is to assess the evidence of the effectiveness of exercise training on equinus deformity in children with cerebral palsy.

Methodology

The American Academy for Cerebral Palsy and Developmental Medicine and Preferred Reporting Items for Systematic Reviews and Meta-Analyses methodology were used to conduct this systematic review. Four databases (PubMed, Cochrane Library, Physiotherapy Evidence Database (PEDro), and Google Scholar) were searched till January 2022 using predefined terms by two independent reviewers. Randomized controlled trials published in English were included. This review included seven studies with 203 participants ranging in age from 5 to 18 years. Methodological quality was assessed using AACPDM, PEDro scale; also, levels of evidence adopted from modified Sacket’s scale were used for each study. Primary outcomes were dorsiflexion angle, plantar flexion angle, and plantar flexors strength.

Results

The quality of studies ranged from good (six studies) to fair (one study). The level of evidence was level 1 (six studies) and level 2 (one study) on modified Sacket’s scale. There is a low risk of bias in the included studies. Meta-analysis revealed a non-significant difference in plantar flexor strength, plantar flexion angle, and dorsiflexion angle between the study and control group.

Conclusions

There is a need for high-quality studies to draw a clear conclusion as the current level of evidence supporting the effectiveness of various types of exercises on equinus deformity in children with cerebral palsy is still weak.

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.

Effects of High-Intensity Stretch with Moderate Pain and Maximal Intensity Stretch without Pain on Flexibility

In this study, we aimed to identify the time course effects of different intensities of static stretch (SST) (maximal intensity without pain vs. high-intensity with moderate pain) on flexibility. This study included 16 healthy students (8 men and 8 women) who performed 1) 5-minute SST at 100%, 2) 110%, and 3) 120% intensity, as well as 4) no stretching (control) in a random sequence on four separate days. Static passive torque (SPT), hamstring electromyography (EMG), and pain intensity were continuously recorded during SST. We assessed markers of stiffness, range of motion (ROM), and maximal dynamic passive torque (DPTmax) before SST and 0, 15, 30, 45, 60, 75, and 90 minutes after SST. Stiffness decreased and ROM and DPTmax increased significantly immediately after SST at the three different intensity levels (p < 0.05). The effects of SST at 120% intensity were stronger and lasted longer than the effects of SST at 110% and 100% intensity (stiffness: -17%, -9%, and -7%, respectively; ROM: 14%, 10%, and 6%, respectively; DPTmax: 15%, 15%, and 9%, respectively). SPT decreased after SST at all intensities (p < 0.05). SST at 120% intensity caused a significantly greater reduction in SPT than SST at 100% intensity (p < 0.05). Pain intensity and EMG activity increased immediately after the onset of SST at 120% intensity (p < 0.05), although these responses were attenuated over time. Stretching intensity significantly correlated with the degree of change in ROM and stiffness (p < 0.05). These results support our hypothesis that stretch-induced flexibility is amplified and prolonged with an increase in stretch intensity beyond the pain threshold. Additional studies with more participants and different demographics are necessary to examine the generalizability of these findings.

Association between static stretching load and changes in the flexibility of the hamstrings

The purpose of the present study was to examine the association between static stretching load and changes in the flexibility of the hamstrings. Twelve healthy men received static stretching for 60 s at two different intensities based on the point of discomfort (100%POD and 120%POD intensity), in random order. To assess the flexibility of the hamstrings, the knee extension range of motion (ROM). Passive torque at end ROM, and muscle–tendon unit stiffness were measured before and after stretching. The static stretching load was calculated from the passive torque throughout static stretching. The knee extension ROM and passive torque at end ROM increased in both intensities (p < 0.01). The muscle–tendon unit stiffness decreased only in the 120%POD (p < 0.01). There were significant correlations between the static stretching load and the relative changes in the knee extension ROM (r = 0.56, p < 0.01) and muscle–tendon unit stiffness (r = − 0.76, p < 0.01). The results suggested that the static stretching load had significant effects on changes in the knee extension ROM and muscle–tendon unit stiffness of the hamstrings, and high-intensity static stretching was useful for improving the flexibility of the hamstrings because of its high static stretching load.

Time course of changes in the range of motion and muscle-tendon unit stiffness of the hamstrings after two different intensities of static stretching

Objectives

The purpose of this study was to examine the time course of changes in the range of motion and muscle-tendon unit stiffness of the hamstrings after two different intensities of static stretching.

Methods

Fourteen healthy men (20.9 ± 0.7 years, 169.1 ± 7.5cm, 61.6 ± 6.5kg) received static stretching for 60 seconds at two different intensities based on the point of discomfort (100%POD and 120%POD) of each participant, in random order. To evaluate the time course of changes in the flexibility of the hamstrings, the knee extension range of motion (ROM), passive torque at end ROM, and muscle-tendon unit stiffness were measured pre-stretching, post-stretching, and at both 10 and 20 minutes after static stretching.

Results

For both intensities, ROM and passive torque at pre-stretching were significantly smaller than those at post-stretching (p < 0.01 in both intensities), 10 minutes (p < 0.01 in both intensities), and 20 minutes (p < 0.01 in both intensities). The muscle-tendon unit stiffness at pre-stretching was significantly higher than that at post-stretching (p < 0.01), 10 minutes (p < 0.01), and 20 minutes (p < 0.01) only in the 120%POD, but it showed no change in the 100%POD.

Conclusion

The results showed that ROM and passive torque increased in both intensities, and the effects continued for at least 20 minutes after stretching regardless of stretching intensity. However, the muscle-tendon unit stiffness of the hamstrings decreased only after static stretching at the intensity of 120%POD, and the effects continued for at least 20 minutes after stretching.

The acute effects of high-intensity jack-knife stretching on the flexibility of the hamstrings

The purpose of the present study was to examine the acute effects of high-intensity jack-knife stretching for 60 s on flexibility of the hamstrings. Twelve healthy participants underwent jack-knife stretching for 60 s (3 repetitions of 20 s stretching with 30 s intervals) at two different intensities based on the point of discomfort (POD and PODmax). To examine any change in flexibility, knee extension range of motion (ROM), passive torque at end ROM, and muscle-tendon unit stiffness were measured before and after stretching. To evaluate hamstrings pain, a numerical rating scale (NRS) was described. The knee extension ROM (p < 0.01) and passive torque at end ROM (p < 0.05) were significantly increased at both intensities. The muscle-tendon unit stiffness was significantly decreased in PODmax intensity (p < 0.01), but there was no change in POD intensity (p = 0.18). The median values of NRS during the stretching were 0 and 6-7 in POD and PODmax intensity, respectively, although it was 0 immediately after the stretching protocol in both intensities. These data suggested that high-intensity jack-knife stretching is an effective and safe method to decrease muscle-tendon unit stiffness of the hamstrings.

The effects of using a combination of static stretching and aerobic exercise on muscle tendon unit stiffness and strength in ankle plantar-flexor muscles

The purpose of the present study was to investigate the effects of using a combination of static stretching and aerobic exercise on muscle tendon unit stiffness and muscle strength in the ankle plantar-flexor muscles. Fifteen healthy males (23.3 ± 2.7 years, 170.3 ± 6.5 cm, 64.9 ± 8.7 kg) received three different interventions, in random order. Intervention 1 received 10 min of aerobic exercise after five cycles of one minute of static stretching. Intervention 2 received 10 min of aerobic exercise before the static stretching. Intervention 3 received 5 min of aerobic exercise both before and after the static stretching. The range of motion of ankle dorsiflexion, stretch tolerance, muscle tendon unit stiffness, peak torque of ankle plantarflexion, and the amplitude of electromyography were measured. In all interventions, the range of motion and stretch tolerance significantly increased (p < 0.05), but muscle tendon unit stiffness decreased significantly for all interventions (p < 0.05). Peak torque of ankle plantar flexion and amplitude of electromyography significantly increased for Interventions 1 and 3 (p < 0.05), while these significantly decreased for Intervention 2 (p < 0.05). These data indicated that range of motion and stretch tolerance were increased, but muscle tendon unit stiffness was decreased regardless of the order of static stretching and aerobic exercise. Aerobic exercise after static stretching increased the peak torque and amplitude of electromyography.

Influence of Aerobic Exercise After Static Stretching on Flexibility and Strength in Plantar Flexor Muscles

Aerobic exercise could improve stretch-induced strength deficits. However, mechanisms of the improvement were unclear. The purpose of the study was to examine the effects of aerobic exercise after static stretching (SS) on flexibility and isometric strength in ankle plantar-flexor muscles. Fifteen healthy males received two interventions after SS of their ankle plantar-flexor muscles for 5 min. One was aerobic exercise for 10-min on a cycling ergometer, and the other was a 10-min rest as a control. Range of motion (ROM) of ankle dorsiflexion, passive torque at terminal ROM, muscle-tendon unit (MTU) stiffness, muscle tendon junction displacement, peak torque of ankle plantarflexion, and the amplitude of electromyography (EMG) were measured. Immediately after the SS, in both interventions, ROM, passive torque, and muscle tendon junction displacement increased significantly (p < 0.05), while MTU stiffness, peak torque, and the amplitude of EMG were significantly decreased (p < 0.05). After 10-min on a cycling ergometer, the decreased peak torque and amplitude of EMG indicated higher values than those before SS (p < 0.05), while MTU stiffness was no change. In conclusion, SS increased ROM because of the decreased MTU stiffness as well as increased tolerance for stretching. Aerobic exercise could increase the muscle strength and amplitude of EMG which decreased after static stretching.

Acute and chronic effects of static stretching at 100% versus 120% intensity on flexibility

PURPOSE

The acute effects of static stretching have been frequently studied, but the chronic effects have not been studied concurrently. Thus, this study aimed to investigate both the acute and chronic effects of static stretching at different intensities on flexibility.

METHODS

Twenty-three healthy men were randomly assigned to perform 1 min of static stretching 3 days/week for 4 weeks at 100% intensity (n = 12) or 120% intensity (n = 11). The acute effects of stretching were assessed by measuring the range of motion (ROM), peak passive torque, and passive stiffness before and after every stretching session; the chronic effects of stretching were assessed by measuring these outcomes at baseline and after 2 and 4 weeks of stretching.

RESULTS

Compared with the 100% intensity group, the 120% intensity group had significantly greater acute increases in ROM after all 12 sessions, a significantly greater decrease in passive stiffness after 11 of 12 sessions, and a significantly greater increase in peak passive torque after six of 12 sessions. Regarding the chronic effects, ROM was significantly increased in both groups after 2 and 4 weeks of stretching. Peak passive torque significantly increased in the 100% intensity group after 2 and 4 weeks of stretching, and after 4 weeks in the 120% intensity group.

CONCLUSION

Stretching at 120% intensity resulted in significantly greater acute improvements in ROM, peak passive torque, and stiffness than stretching at 100% intensity. Four weeks of stretching increased ROM and peak passive torque but did not decrease passive stiffness, regardless of the stretching intensity.

The optimal duration of high-intensity static stretching in hamstrings

Objectives

The purpose of this study was to compare the duration of high-intensity static stretching on flexibility and strength in the hamstrings.

Methods

Fourteen healthy males (20.8 ± 0.6 years, 170.7 ± 6.5 cm, 66.4 ± 9.9 kg) underwent high-intensity static stretching for three different durations (10, 15, and 20 seconds). The intensity of static stretching was set at the maximum point of discomfort. To examine the change in flexibility and strength, range of motion, peak passive torque, relative passive torque, muscle-tendon unit stiffness, peak torque of isokinetic knee flexion, and knee angle at peak torque of isokinetic knee flexion were measured. To evaluate a time course of pain, a numerical rating scale was described.

Results

Range of motion (P < 0.01), peak passive torque (P < 0.01), and knee angle at peak torque were increased at all interventions. Relative passive torque (P < 0.01) and muscle-tendon unit stiffness (P < 0.01) were decreased at all interventions. Peak torque decreased after 10 seconds of stretching (P < 0.05). Numerical rating scale during stretching was 8–9 levels in all interventions, the pain disappeared immediately after the post-measurements (median = 0).

Conclusion

The results suggested that muscle-tendon unit stiffness decreased regardless of duration of high-intensity static stretching. However, peak torque of isokinetic knee flexion decreased after 10 seconds of high-intensity static stretching, though it was no change after for more than 15 seconds of stretching.

Acute Static Stretching Results in Muscle-Specific Alterations amongst the Hamstring Muscles

This study aimed to explore the acute effects of static stretching on the musculotendinous properties of two hamstring muscles. Twelve male volunteers underwent two testing sessions. One session was dedicated to the evaluation of the semitendinosus muscle before (PRE) and after (POST) static stretching (five sets of 30-s stretching), and the other session similarly explored the long head of biceps femoris muscle. In addition to the displacement of the myotendinous junction (MTJ), passive torque and maximal voluntary isometric torque (MVIT) were evaluated. MVIT (-8.3 ± 10.2%, p = 0.0036, d = 0.497) and passive torque (-28.4 ± 16.9%, p = 0.0003, d = 1.017) were significantly decreased POST stretching. PRE stretching, MTJ displacement was significantly greater for semitendinosus muscle than biceps femoris muscle (27.0 ± 5.2 vs. 18.6 ± 3.6, p = 0.0011, d = 1.975). After the stretching procedure, greater MTJ displacement relative changes were observed for biceps femoris muscle as compared to semitendinosus muscle (22.4 ± 31.6 vs. -8.4 ± 17.9, p = 0.0167, d = 1.252). Because of the smaller MTJ displacement PRE stretching and greater alteration POST stretching in biceps femoris muscles, the present study demonstrated muscle-specific acute responses of hamstring muscles during stretching. Although stretching acutely impairs torque production, the passive torque reduction and alteration of MTJ displacement might impact hamstring injury prevention.

High-impact Routines to Ameliorate Trunk and Lower Limbs Flexibility in Women

Several types of routines and methods have been experimented to gain neuro/muscular advantages, in terms of overall range of motion, in athletes and fitness enthusiasts. The aim of the present study was to evaluate the impact of different routines on trunk- and lower limbs flexibility in a sample of young women. In a randomized-crossover fashion, eleven subjects underwent to: hamstrings stretching [S]; hamstrings stretching plus whole-body vibration [S+WBV]; partial-body cryotherapy [Cryo]; rest [Control]. Standing hamstrings stretch performance and sit-and-reach amplitude resulted to be improved with [S+WBV] compared to all other protocols (p<0.05). [Cryo] ameliorated the active knee extension performance with respect to all other interventions (p<0.05). These flexibility improvements were obtained without a loss in the trunk position sense proprioception. These results represent the first evidence that a single session of either vibration or cryotherapy can ameliorate flexibility without losing the trunk position sense proprioception in young women.

The time course of passive stiffness responses following an acute bout of static stretching in healthy, elderly men

BACKGROUND

The time course of passive stiffness responses following an acute bout of static stretching has received little research attention, particularly in older adults.

OBJECTIVE

To determine the time course of the acute effects of static stretching on passive stiffness of the hamstrings in healthy, elderly men.

METHODS

Fifteen elderly men (age = 70 ± 7 years) underwent two randomized conditions that included a control treatment and an experimental treatment of four, 15-s straight-leg raise static stretches. Passive stiffness was calculated as the slopes of the initial and final phases of the angle-torque curve at pre-treatment (Pre) and post-treatment time points of zero (Post0), five (Post5), and ten (Post10) minutes.

RESULTS

Passive stiffness collapsed across phase was lower at Post0 (P= .029, d= 0.64) and Post5 (P= .042, d= 0.54) but not Post10 (P> .999, d= 0.15) compared to Pre for the stretching treatment. There were no significant differences in passive stiffness (collapsed across phase) between any of the time points (P> .999, d≤ 0.14) for the control.

CONCLUSIONS

An acute bout of static stretching produced significant decreases in the passive stiffness characteristics of elderly men; however, these decreases returned to baseline values within 5 to 10 minutes.

Effect of deep transverse friction massage vs stretching on football players’ performance

BACKGROUND

Flexibility, agility and muscle strength are key factors to either win or lose a game. Recently the effect of a new technique, deep transverse friction massage (DTFM) on muscle extensibility as compared to traditional stretching techniques has been examined.

AIM

To compare the effect of DTFM vs static and dynamic stretching techniques on the hamstring’s extensibility, agility, and strength amongst Lebanese and Syrian football players. Recording the incidence of non-contact hamstring muscle injury was a secondary objective.

METHODS

This study is a single-blinded prospective longitudinal randomized controlled trial. The experiment took place over a period of four weeks. Football players were randomized into three intervention groups (static stretching; dynamic stretching; DTFM). Participants of each group were followed-up carefully by assessors during their intervention sessions three times per week, for a total of 12 sessions and during the data collection. Extensibility, agility, and strength were compared between intervention groups at (baseline; acute; and chronic) phases. Straight leg raise and 1 repetition maximum tests were used to measure the dominant leg hamstring muscle extensibility and maximal strength respectively. T-drill test was used to assess the lower extremities agility.

RESULTS

Of 103 Lebanese and Syrian male football players aged between 18 and 35 were sampled from Damascus-Syria and South of Lebanon to participate in this study. Between-groups measures of acute strength (P = 0.011) and chronic extensibility (P = 0.000) solely showed a significant difference, and the static group showed to be superior as compared to the other groups. No loss to follow-up or protocol violation was recorded.

CONCLUSION

Static stretching is showing to be superior to the other techniques used, regarding gaining long-term extensibility and short-term maximal muscle strength. In addition, DTFM showed improvements but did not outweigh the effects on footballers’ performance when comparing it to static and dynamic techniques. Finally, no difference between the interventions is recorded regarding the rate of muscle injuries incidence.

The time course of muscle-tendon properties and function responses of a five-minute static stretching exercise

The purpose of this study was to investigate the time course of the changes of muscle-tendon mechanical properties and the function responses of the plantar flexor muscles following 5 × 60 s of static stretching.

Fourteen healthy volunteers were tested on four separate days in a random order with three different rest times (0, 5, 10 min) after 5 × 60 s of stretching or following a control period without stretching. During each test, the dorsiflexion range of motion (RoM), passive resistive torque (PRT), and maximum voluntary contraction (MVC) were measured with a dynamometer. Ultrasonography of the gastrocnemius medialis (GM) muscle-tendon junction displacement and motion capture allowed us to determine the length changes in the tendon and muscle, respectively, and hence to calculate their stiffness.

We observed an increase in RoM and decrease in MVC at 0, 5, and 10 min post-stretching. This could be attributed to an increase in muscle elongation which lasted at least 10 min. A decrease in muscle-tendon stiffness was observed immediately, but not 5 or 10 min after the stretching. A decrease in PRT and muscle stiffness was observed up to 5 min after the stretching. No changes were detected in tendon stiffness or in any variable in the control group.

The effects of a 5 × 60 s static stretching exercise changes the muscle-tendon functions (RoM, MVC), which are related to mechanical changes of the muscle but not the tendon structure, respectively. Although the functional changes last for at least 10 min, changes in muscle stiffness were only observed up to 5 min after the stretching exercise.

Dynamic stretching alone can impair slower velocity isokinetic performance of young male handball players for at least 24 hours

There are many adult studies reporting static stretch (SS)-induced deficits and dynamic stretch (DS) performance improvements shortly after the intervention. However, there is only a single study examining stretch-induced performance changes with youth at 24 hours' post-stretch. The objective of this study was to examine physiological responses of young trained athletes at 24-hours after experiencing SS or DS protocols. Eight young male, elite handball players (age: 16.1±5.1 years) were tested prior to-, 3-minutes and 24-hours following the three conditions (DS, SS, Control) in a randomized and counterbalanced order. Similar volumes of SS (2 repetitions of 75s for each leg) and DS (5 repetitions of 30s for each leg) involved one stretch each for the quadriceps and hamstrings. Tests included (i) two 4s maximal voluntary isometric contractions (MVC) at 60° of knee flexion with 2-min rest, (ii) two maximal isokinetic contractions each at 60°/sec and 300°/sec with 1-min rest, and (iii) two drop jumps with 30-sec rest. To simulate a full warm-up, dynamic activity including 5 minutes of aerobic cycling (70 rpm; 1 kilopond), 4 submaximal isometric contractions and 4 drop jumps were instituted before the pre-tests and following the interventions. Two-way repeated measures ANOVAs revealed that 1) both the SS and control conditions exhibited knee extensor 60°.s-1 (SS:-10.3%; p = 0.04, Control: -8.7%; p = 0.07) and 300°.s-1 (SS: -12.9%; p = 0.005, Control: -16.3%; p = 0.02) isokinetic deficits at post-test, 2) DS impaired knee flexor 60°.s-1 isokinetic work and power-related measures at post-test (Work: -10.1%; p = 0.0006; Power: -19.1%; p = 0.08) and at 24-hours' post-test (Work: 9.9%; p = 0.023; Power: -9.6%; p = 0.01), 3) DS (12.07% and 10.47%) and SS (13.7% and 14.6%) enhanced knee flexor 300°.s-1 isokinetic force and power-related measures compared to control. In conclusion, testing-induced knee extensor isokinetic impairments were counterbalanced by DS, however the hip flexion DS could have produced minor muscle damage for at least 24-hours decreasing knee flexor forces and power at 60°.s-1.

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.

Acute effects of static stretching on muscle-tendon mechanics of quadriceps and plantar flexor muscles

PURPOSE

This study aimed to determine the acute effects of static stretching on stiffness indexes of two muscle groups with a contrasting difference in muscle-tendon proportion.

METHODS

Eleven active males were tested on an isokinetic dynamometer during four sessions randomly presented. Two sessions were dedicated to quadriceps and the two others to triceps surae muscles. Before and immediately after the stretching procedure (5 × 30 s), gastrocnemius medialis and rectus femoris fascicle length and myotendinous junction elongation were determined using ultrasonography. Passive and maximal voluntary torques were measured. Fascicle and myotendinous junction stiffness indexes were calculated.

RESULTS

After stretching, maximal voluntary torque similarly decreased for both muscle groups. Passive torque significantly decreased on triceps surae and remained unchanged on quadriceps muscles. Fascicle length increased similarly for both muscles. However, myotendinous junction elongation remained unchanged for gastrocnemius medialis and increased significantly for rectus femoris muscle. Fascicle stiffness index significantly decreased on medial gastrocnemius and remained unchanged on rectus femoris muscle. In contrast, myotendinous junction stiffness index similarly decreased on both muscles.

CONCLUSION

Depending on the muscle considered, the present results revealed different acute stretching effects. This muscle dependency appeared to affect primarily fascicle stiffness index rather than the myotendinous junction.

Changes in joint range of motion and muscle-tendon unit stiffness after varying amounts of dynamic stretching

The purpose of this study was to examine the effects of varying amounts of dynamic stretching (DS) on joint range of motion (ROM) and stiffness of the muscle-tendon unit (MTU). Fifteen healthy participants participated in four randomly ordered experimental trials, which involved one (DS1), four (DS4) and seven (DS7) sets of DS, or control conditions/seated at rest (CON). Each DS set consisted of 15 repetitions of an ankle dorsiflexion-plantarflexion movement. The displacement of the muscle-tendon junction (MTJ) was measured using ultrasonography while the ankle was passively dorsiflexed at 0.0174 rad · s^‒1 to its maximal dorsiflexion angle. Passive torque was also measured using an isokinetic dynamometer. Ankle ROM was significantly increased after DS4 and DS7 compared with the pre-intervention values (P < 0.05), but there were no significant differences in ankle ROM between DS4 and DS7. No differences were observed in ankle ROM after DS1 and CON. In addition, the stiffness of the MTU, passive torque and displacement of the MTJ at submaximal dorsiflexion angles did not change in any of the experimental conditions. These results indicate that DS4 increased ankle ROM without changing the mechanical properties of the MTU, and that this increase in ankle ROM plateaued after DS4.

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.

Shear elastic modulus is a reproducible index reflecting the passive mechanical properties of medial gastrocnemius muscle belly

Background

Passive mechanical properties are important in muscle function because they are related to the muscle extensibility. Recently, the assessment of muscle shear elastic modulus using shear-wave elastographic (SWE) imaging was developed. However, reliability and validity of shear elastic modulus measurements during passive stretching remain undefined.

Purpose

To investigate the reproducibility and validity of the shear elastic modulus measured by SWE imaging during passive stretching.

Material and Methods

Ten healthy men volunteered for this study. The shear elastic modulus of medial gastrocnemius (MG) muscle belly was measured using ultrasonic SWE imaging during passive dorsiflexion. To assess the intra-session and inter-day reliabilities, the protocol was performed twice by the same investigator with a 5-min rest period between measurement sessions and twice on two different days by the same investigator with a 1–2-week interval between the two sessions. To assess the inter-investigator reliability, the protocol was performed on the same day by two investigators with a 5-min rest between measurement sessions. In addition, B-mode ultrasonography was used to determine the displacement of myotendinous junction (MTJ) of MG during passive ankle dorsiflexion.

Results

The intra-session, inter-day, and inter-investigator reliabilities of the method was confirmed on the basis of acceptably low coefficient of variations and substantially high intraclass correlation coefficients. In addition, a significant correlation was found between MTJ displacement and shear elastic modulus.

Conclusion

These results suggested that shear elastic modulus measured using SWE imaging is a reproducible index reflecting the passive mechanical properties.

Acute and Time-Course Effects of Traditional and Dynamic Warm-Up Routines in Young Elite Junior Tennis Players

Despite the large number of studies that have examined the acute effects of different warm up modalities (WU) on physical performance, none of them have documented the time course of potential performance recovery in tennis players. The aim of this study was twofold: (a) to analyze and compare the acute effects of two different WU modalities (traditional WU [TWU] and dynamic WU [DWU]) on physical performance (i.e., CMJ, sprint, serve speed and accuracy) in elite junior players, as well as (b) to monitor the time course of any WU-induced changes after 30 and 60 min of simulated match-play. Twelve junior elite players completed both WUs modalities (TWU and DWU) in a counterbalanced order on separate days. In each experimental session, counter movement jump (CMJ), 20-m sprint, tennis serve speed and accuracy tests were performed before (immediately after TWU or DWU) during (30 min) and after 60 min of a simulated match play. Measures were compared via four factorial (WU intervention and time) repeated measures ANOVAs. There were main effects of WU (TWU and DWU) throughout the time for all the variables analysed. The results indicate that DWU routine led to significantly faster 20 m sprint times and higher CMJs as well as faster and more accurate tennis serves at both post warm-up and 30 min match-play testing moments in comparison with the scores reported by the TWU routine (p < 0.05; positive effects with a probability of >75-99%). No significant intergroup differences were found at 60-min match-play testing moment in any variable (except for the 20 m sprint). Therefore, the findings of this study recommend for optimal performance in these elite tennis players, DWU routines should be performed prior to formal training and competition rather than TWU routines.

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.

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.

Effects of short duration static stretching on jump performance, maximum voluntary contraction, and various mechanical and morphological parameters of the muscle-tendon unit of the lower extremities

Purpose

Static stretching is used in sport practice but it has been associated with decrements in force and performance. Therefore, we examined the effect of short duration static stretch on the mechano-morphological properties of the m. vastus lateralis (VL) muscle tendon unit (MTU) and on the jumping performance.

Methods

Eight males and three females (mean ± SD, 25.5 ± 3.1 years) stretched their lower legs for a 15 or 60 s duration or acted as their own control without stretching in a randomized order. In a pre-post design, a passive movement (5°/s) and a maximum voluntary knee extension contraction (MVC) were performed on dynamometer while the VL tendon and aponeurosis was observed via ultrasound. Furthermore, the participants performed countermovement (CMJ) and squat jumps (SJ).

Results

Repeated measures ANOVA did not show significant differences in MVC, active and passive strain, stiffness, elongation, knee joint angle range, and jump performance between and within groups.

Conclusions

The applied stretch stimuli (15 or 60 s) were not sufficient to trigger adaptations in the mechano-morphological properties of the lower extremities MTU which therefore did neither affect jump performance nor MVC. As a possible mechanism, we hypothesized that the dose-time dependency effect of static stretch might have important implications when measuring functional parameters of the MTU and performance. Further examination is necessary to elucidate its impact in the examination of the MTU mechano-morphological properties.

Static stretching alters neuromuscular function and pacing strategy, but not performance during a 3-km running time-trial

PURPOSE

Previous studies report that static stretching (SS) impairs running economy. Assuming that pacing strategy relies on rate of energy use, this study aimed to determine whether SS would modify pacing strategy and performance in a 3-km running time-trial.

METHODS

Eleven recreational distance runners performed a) a constant-speed running test without previous SS and a maximal incremental treadmill test; b) an anthropometric assessment and a constant-speed running test with previous SS; c) a 3-km time-trial familiarization on an outdoor 400-m track; d and e) two 3-km time-trials, one with SS (experimental situation) and another without (control situation) previous static stretching. The order of the sessions d and e were randomized in a counterbalanced fashion. Sit-and-reach and drop jump tests were performed before the 3-km running time-trial in the control situation and before and after stretching exercises in the SS. Running economy, stride parameters, and electromyographic activity (EMG) of vastus medialis (VM), biceps femoris (BF) and gastrocnemius medialis (GA) were measured during the constant-speed tests.

RESULTS

The overall running time did not change with condition (SS 11:35±00:31 s; control 11:28±00:41 s, p = 0.304), but the first 100 m was completed at a significantly lower velocity after SS. Surprisingly, SS did not modify the running economy, but the iEMG for the BF (+22.6%, p = 0.031), stride duration (+2.1%, p = 0.053) and range of motion (+11.1%, p = 0.0001) were significantly modified. Drop jump height decreased following SS (-9.2%, p = 0.001).

CONCLUSION

Static stretch impaired neuromuscular function, resulting in a slow start during a 3-km running time-trial, thus demonstrating the fundamental role of the neuromuscular system in the self-selected speed during the initial phase of the race.