Acute effects of resistance training at different range of motions on plantar flexion mechanical properties and force.

The effects obtained from resistance training depend on the exercise range of motion (ROM) performed. We aimed to examine the acute effects of different exercise ROM resistance training on the plantar flexor muscles. Eighteen healthy untrained male adults participated in three conditions: calf raises in 1) partial condition [final (short muscle length) partial ROM], 2) full condition (full ROM), and 3) control condition. The ankle dorsiflexion (DF) ROM, passive torque at DF ROM, passive stiffness of muscle-tendon unit, and maximal voluntary isometric contraction (MVC-ISO) torque were measured before and immediately after the interventions. There were significant increases in DF ROM, passive torque at DF ROM, and a decrease in MVC-ISO, but no significant interaction in passive stiffness. Post hoc test, DF ROM demonstrated moderate magnitude increases in the full condition compared to the partial (p = 0.023, d = 0.74) and control (p = 0.003, d = 0.71) conditions. Passive torque at DF ROM also showed moderate magnitude increases in the full condition compared to the control condition (p = 0.016, d = 0.69). MVC-ISO had a moderate magnitude decrease in the full condition compared to the control condition (p = 0.018, d=-0.53). Resistance training in the full ROM acutely increases joint ROM to a greater extent than final partial ROM, most likely due to stretch tolerance.

The Acute Effect of Percussive Massage Intervention with and without Heat Application on Plantar Flexor Muscles' Passive and Active Properties.

Recently, percussive massage (PM) intervention using a handheld percussive massage device, namely a massage gun, has been used as an easy way to perform vibration functions. Additionally, a product has been developed that allows PM intervention and heat application to be performed simultaneously. Thus, this study aimed to compare the acute effects of PM intervention with and without heat application on dorsiflexion (DF) range of motion (ROM), passive stiffness, and muscle strength in the gastrocnemius muscle. Fifteen healthy young men (20.9 ± 0.2 years) participated in this study. We measured the DF ROM, passive torque at DF ROM (an indicator of stretch tolerance), passive stiffness, and maximum voluntary isometric contraction (MVIC) torque of the plantar flexor muscles before and immediately after 120 seconds PM intervention with and without heat application. The results showed that PM intervention with and without heat application significantly increased DF ROM and passive torque at DF ROM and decreased passive stiffness, not MVIC torque. These results suggest that PM intervention increased ROM and decreased passive stiffness regardless of the presence or absence of the heat application.

Stretch tolerance and elastic passive reaction of the quadriceps femoris seem to depend more on the fascia profundis taut surfaces than on the underlying stretched muscle.

The rectus femoris and its covering, the fascia lata (i.e., fascia profundis), are two anatomical structures involved in anterior thigh stretching. This study aimed to identify the role of strain changes in the fascia lata in limiting stretch tolerance. The reaction force intensity of 11 men and 5 women was assessed during passive stretching of the anterior thigh at 130, 110, 90, and 70° of knee flexion. Recent data suggest that the fascia lata strain field is modified with knee flexion. Therefore, the relationship between knee flexion angle and stretch tolerance was assessed. We found that the reaction force of the anterior thigh increased almost linearly with the degree of knee extension between 130° and 70°. The fascia lata stretched surface proprioceptive information seems responsible for stretch tolerance. Fascia profundis strain field must be considered during stretching experiments.

Sex Differences in the Mechanical and Neurophysiological Response to Roller Massage of the Plantar Flexors.

Self-massage using foam rollers, sticks, or balls has become a popular technique to enhance joint range of motion (ROM). Although increases are reported to be larger in females than males, the mechanisms of this observation are unclear. The present study aimed to investigate the effect of roller massage (RM) on ROM, passive tissue stiffness, and neurophysiological markers as a function of sex. Males (n = 15, 22.8 ± 2.9 yrs.) and females (n = 14, 21.1 ± 0.7 yrs.) performed three 60-second bouts of calf RM. Outcomes assessed pre-, and post-intervention included passive dorsiflexion (DF) ROM, passive tissue stiffness, passive torque, DF angle at the first stretch sensation, shear elastic modulus, and spinal excitability. DF ROM (+35.9 %), passive torque at DF ROM (+46.4 %), DF angle at first stretch sensation (+32.9 %), and pain pressure threshold (+25.2 %) increased in both groups (p<.05) with no differences between males and females (p > 0.05). No changes were observed for passive stiffness, shear elastic modulus, and spinal excitability (p > 0.05). Roller massage may increase ROM independently of sex, which, in the present study, could not be ascribed to alterations in passive stiffness or neurophysiological markers. Future studies may further elucidate the role of sensory alterations as possible factors driving RM-induced changes in flexibility.

Immediate Effects of Dry Needling as a Novel Strategy for Hamstring Flexibility: A Single-Blinded Clinical Pilot Study.

CONTEXT: There are numerous studies on the benefits of dry needling (DN) for pain relief. No studies exist examining the effects of DN on hamstring flexibility. OBJECTIVE: To determine the immediate effects of DN on hamstring flexibility in healthy subjects with shortened hamstrings. DESIGN: A single-blinded, pretest-posttest clinical pilot study. SETTING: A university physiotherapy clinic. SUBJECTS: A total of 15 healthy subjects (female = 11; age = 23.26 [4.3] y) with shortened hamstrings participated in this study. INTERVENTION: Subjects received a single session of DN. Three locations on the hamstring muscle group were needled, each for 1 minute. MAIN OUTCOME MEASURES: The active knee extension test, muscle compliance, passive peak torque, and stretch tolerance were measured at baseline, immediately, and 15 minutes after DN. RESULTS: There were statistically significant improvements in all outcome measures immediately after DN and at the 15-minute follow-up. The effect sizes for all outcome measures were large (Cohen's d ≥ 0.8). No serious adverse events were observed with DN. CONCLUSIONS: This is the first study that demonstrates the beneficial effects of DN on hamstring flexibility, muscle compliance, and stretch tolerance without added stretching. The beneficial effects of DN should encourage clinicians to use DN as a novel strategy for increasing muscle flexibility.

Dry Needling for Hamstring Flexibility: A Single-Blind Randomized Controlled Trial.

CONTEXT: Hamstring muscle tightness is one of the most common problems in athletic and healthy people. Dry needling (DN) was found to be an effective approach for improving muscle flexibility, but there is no study to compare this approach with static stretching (SS) as a common technique for the increase of muscle length. OBJECTIVE: To compare the immediate effects of DN and SS on hamstring flexibility in healthy subjects with hamstring tightness. STUDY DESIGN: A single-blind randomized controlled trial. SETTING: A musculoskeletal physiotherapy clinic at Tehran University of Medical Sciences. SUBJECTS: Forty healthy subjects (female: 32, age range: 18-40 y) with hamstring tightness were randomly assigned into 2 groups of DN and SS. INTERVENTION: The DN group received a single session of DN on 3 points of the hamstring muscles, each for 1 minute. The SS group received a single session of SS of the hamstrings, consisting of 3 sets of 30-second SS with a 10-second rest between sets in the active knee extension test (AKET) position. MAIN OUTCOME MEASURES: The AKET, muscle compliance, passive peak torque, and stretch tolerance were measured at the baseline, immediately, and 15 minutes after the interventions. RESULTS: Improvements in all outcomes was better for the DN group than for the SS group. DN increased muscle compliance significantly 15 minutes after the intervention, but it did not improve in the SS group. CONCLUSION: DN is effective in improving hamstring flexibility compared with SS. One session of DN can be an effective treatment for hamstring tightness and increase hamstring flexibility. The improvements suggest that DN is a novel treatment for hamstring flexibility.

Dynamic Stretching Has Sustained Effects on Range of Motion and Passive Stiffness of the Hamstring Muscles.

Dynamic stretching (DS) is often performed during warm-up to help avoid hamstring muscle injuries, increase joint flexibility, and optimize performance. We examined the effects of DS of the hamstring muscles on passive knee extension range of motion (ROM), passive torque (PT) at the onset of pain (as a measure of stretch tolerance), and passive stiffness of the muscle-tendon unit over an extended period after stretching. Twenty-four healthy subjects participated, with 12 each in the experimental and control groups. Stretching was performed, and measurements were recorded using an isokinetic dynamometer pre-intervention, and at 0, 15, 30, 45, 60, 75, and 90 min post-intervention. DS consisted of ten 30-s sets of 15 repetitions of extension and relaxation of the hamstrings. ROM increased significantly (range, 7%-10%) immediately after DS, and the increase was sustained over 90 min. PT at the onset of pain also increased immediately by 10% but returned to baseline by 30 min. Passive stiffness decreased significantly (range, 7.9%-16.7%) immediately after DS, and the decrease was sustained over 90 min. Post-DS values were normalized to pre-DS values for the respective outcomes in both groups. ROM was significantly higher (range, 7.4%-10%) and passive stiffness was significantly lower (range, 5.4%-14.9%) in the experimental group relative to the control group at all time points. Normalized PT values at the onset of pain were significantly higher in the experimental group at 0-15 min than in the controls, but the differences were smaller at 30-45 min and not significant thereafter. We conclude that DS increases ROM and decreases passive stiffness in a sustained manner, and increases PT at the onset of pain for a shorter period. Overall, our results indicate that when performed prior to exercise, DS is beneficial for the hamstring muscles in terms of increasing flexibility and reducing stiffness.

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.

Changes in Passive Properties of the Gastrocnemius Muscle-Tendon Unit During a 4-Week Routine Static-Stretching Program.

CONTEXT: Static stretching (SS) is commonly performed in a warm-up routine to increase joint range of motion (ROM) and to decrease muscle stiffness. However, the time course of changes in ankle-dorsiflexion (DF) ROM and muscle stiffness during a routine SS program is unclear. OBJECTIVE: To investigate changes in ankle-DF ROM, passive torque at DF ROM, and muscle stiffness during a routine SS program performed 3 times weekly for 4 wk. DESIGN: A quasi-randomized controlled-trial design. PARTICIPANTS: The subjects comprised 24 male volunteers (age 23.8 ± 2.3 y, height 172.0 ± 4.3 cm, body mass 63.1 ± 4.5 kg) randomly assigned to either a group performing a 4-wk stretching program (SS group) or a control group. MAIN OUTCOME MEASURES: DF ROM, passive torque, and muscle stiffness were measured during passive ankle dorsiflexion in both groups using a dynamometer and ultrasonography once weekly during the 4-wk intervention period. RESULTS: In the SS group, DF ROM and passive torque at DF ROM significantly increased after 2, 3, and 4 wk compared with the initial measurements. Muscle stiffness also decreased significantly after 3 and 4 wk in the SS group. However, there were no significant changes in the control group. CONCLUSIONS: Based on these results, the SS program effectively increased DF ROM and decreased muscle stiffness. Furthermore, an SS program of more than 2 wk duration effectively increased DF ROM and changed the stretch tolerance, and an SS program more than 3 wk in duration effectively decreased muscle stiffness.

Effect of 6-Week Instrument-Assisted Soft Tissue Mobilization on Joint Flexibility and Musculotendinous Properties.

Instrument-assisted soft tissue mobilization (IASTM) stimulates soft subcutaneous tissues by applying pressure to the skin with a specialized bar or spurtle-like instrument. No studies have verified whether several weeks of continuous IASTM alone can alter joint flexibility and musculotendinous properties in healthy participants. We examined the effect of a 6-week IASTM program on joint flexibility and the musculotendinous properties of the lower limbs. Fourteen healthy men (aged 19-35 years) who participated in a 6-week IASTM program (3 days weekly) for the soft tissue of the posterior aspect of one lower leg were included. The other leg served as the control. Before and after the intervention, we measured the maximal ankle joint dorsiflexion angle (dorsiflexion range of motion: DFROM) and maximal passive torque (MPT), a measure of stretch tolerance. We measured muscle and tendon stiffness using shear wave elastography on the gastrocnemius and Achilles tendon. IASTM significantly increased the DFROM and MPT (p < 0.05 for both). However, no significant changes were observed in muscle and tendon stiffness. None of the parameters changed significantly in the control group. The 6-week IASTM program increased stretch tolerance and joint flexibility but did not change muscle and tendon stiffness.

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.

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.

The Effects of Foam Rolling Training on Performance Parameters: A Systematic Review and Meta-Analysis including Controlled and Randomized Controlled Trials.

Foam rolling (FR) is a new and popular technique for increasing range of motion. While there are a few studies that demonstrate increased performance measures after an acute bout of FR, the overall evidence indicates trivial performance benefits. As there have been no meta-analyses on the effects of chronic FR on performance, the objective of this systematic meta-analytical review was to quantify the effects of FR training on performance. We searched PubMed, Scopus, the Cochrane library, and Web of Science for FR training studies with a duration greater than two weeks, and found eight relevant studies. We used a random effect meta-analysis that employed a mixed-effect model to identify subgroup analyses. GRADE analysis was used to gauge the quality of the evidence obtained from this meta-analysis. Egger's regression intercept test (intercept 1.79; p = 0.62) and an average PEDro score of 6.25 (±0.89) indicated no or low risk of reporting bias, respectively. GRADE analysis indicated that we can be moderately confident in the effect estimates. The meta-analysis found no significant difference between FR and control conditions (ES = -0.294; p = 0.281; I2 = 73.68). Analyses of the moderating variables showed no significant differences between randomized control vs. controlled trials (Q = 0.183; p = 0.67) and no relationship between ages (R2 = 0.10; p = 0.37), weeks of intervention (R2 = 0.17; p = 0.35), and total load of FR (R2 = 0.24; p = 0.11). In conclusion, there were no significant performance changes with FR training and no specific circumstances leading to performance changes following FR training exceeding two weeks.

Effects of stretching intensity on range of motion and muscle stiffness: A narrative review.

BACKGROUND: No review has yet investigated acute and chronic effects of different stretching intensities, including constant-angle (CA) and constant-torque (CT) stretching. OBJECTIVE: This review aimed to investigate the acute and chronic effects of different stretching intensities on the range of motion (ROM) and passive properties. METHODS: PubMed, Scopus, and Google Scholar were used for literature search. Advanced search functions were used to identify original studies using the terms stretching intensity, constant-torque stretching, constant-angle stretching, ROM, passive stiffness, shear elastic modulus in the title or abstract. The keywords were combined using the Boolean operators "AND" and "OR". The search for articles published from inception until 2021 was done in electronic databases. RESULTS AND CONCLUSION: Five studies compared CA and CT stretching. Three studies reported a greater decrease in passive stiffness, and two studies reported a greater ROM increase after CT than CA stretching. Twelve studies investigated the acute effects of different stretching intensities, and six reported a greater ROM increase at higher stretching intensities. Five studies reported a greater decrease in passive stiffness at higher stretching intensities, but three reported no significant differences in passive stiffness among stretching intensities. Five studies investigated the chronic effect, and four reported no significant difference in ROM change among different intensities. Three studies reported no significant changes in passive stiffness after the stretching program. We suggest that the acute effect of higher stretching intensity, including CT stretching, was more effective for changes in ROM and passive stiffness, but the chronic effect was weak.

Training and Detraining Effects Following a Static Stretching Program on Medial Gastrocnemius Passive Properties.

A stretching intervention program is performed to maintain and improve range of motion (ROM) in sports and rehabilitation settings. However, there is no consensus on the effects of stretching programs on muscle stiffness, likely due to short stretching durations used in each session. Therefore, a longer stretching exercise session may be required to decrease muscle stiffness in the long-term. Moreover, until now, the retention effect (detraining) of such an intervention program is not clear yet. The purpose of this study was to investigate the training (5-week) and detraining effects (5-week) of a high-volume stretching intervention on ankle dorsiflexion ROM (DF ROM) and medial gastrocnemius muscle stiffness. Fifteen males participated in this study and the plantarflexors of the dominant limb were evaluated. Static stretching intervention was performed using a stretching board for 1,800 s at 2 days per week for 5 weeks. DF ROM was assessed, and muscle stiffness was calculated from passive torque and muscle elongation during passive dorsiflexion test. The results showed significant changes in DF ROM and muscle stiffness after the stretching intervention program, but the values returned to baseline after the detraining period. Our results indicate that high-volume stretching intervention (3,600 s per week) may be beneficial for DF ROM and muscle stiffness, but the training effects are dismissed after a detraining period with the same duration of the intervention.

Comparison Between Contract-Relax Stretching and Antagonist Contract-Relax Stretching on Gastrocnemius Medialis Passive Properties.

Antagonist contract-relax stretching and contract-relax stretching is commonly used in sports practice and rehabilitation settings. To date, no study has compared these modalities regarding muscle stiffness and stretch tolerance. This study aimed to investigate the effects of contract-relax and antagonist contract-relax stretching on dorsiflexion range of motion (ROM), stretch tolerance, and shear elastic modulus. Forty healthy participants (24 men and 16 women) took part in the study. Participants were randomly assigned to perform either contract-relax stretching or antagonist contract-relax stretching for 2 min. Outcomes were assessed on ROM, stretch tolerance, and shear elastic modulus before and after stretching. The ROM and stretch tolerance significantly increased after both contract-relax stretching (+ 5.4 ± 5.8°, p < 0.05; + 3.5 ± 8.0 Nm, p < 0.05) and antagonist contract-relax stretching (+ 6.1 ± 4.9°, p < 0.05; + 4.2 ± 6.4 Nm, p < 0.05); however, no significant difference was found between the two groups. Alternatively, the shear elastic modulus significantly decreased after both contract-relax (-31.1 ± 22.6 kPa, p < 0.05) and antagonist contract-relax stretching (-11.1 ± 22.3 kPa, p < 0.05); however, contract-relax stretching (-41.9 ± 19.6%) was more effective than antagonist contract-relax stretching (-12.5 ± 61.6%). The results of this study suggest that contract-relax stretching instead of antagonist contract-relax stretching should be conducted to decrease muscle stiffness. However, either contract-relax or antagonist contract-relax stretching can increase ROM.

The tolerance to stretch is linked with endogenous modulation of pain.

OBJECTIVES: The effect of stretching on joint range of motion is well documented, and although sensory perception has significance for changes in the tolerance to stretch following stretching the underlining mechanisms responsible for these changes is insufficiently understood. The aim of this study was to examine the influence of endogenous pain inhibitory mechanisms on stretch tolerance and to investigate the relationship between range of motion and changes in pain sensitivity. METHODS: Nineteen healthy males participated in this randomized, repeated-measures crossover study, conducted on 2 separate days. Knee extension range of motion, passive resistive torque, and pressure pain thresholds were recorded before, after, and 10 min after each of four experimental conditions; (i) Exercise-induced hypoalgesia, (ii) two bouts of static stretching, (iii) resting, and (iv) a remote, painful stimulus induced by the cold pressor test. RESULTS: Exercise-induced hypoalgesia and cold pressor test caused an increase in range of motion (p<0.034) and pressure pain thresholds (p<0.027). Moderate correlations in pressure pain thresholds were found between exercise-induced hypoalgesia and static stretch (Rho>0.507, p=0.01) and exercise-induced hypoalgesia and the cold pressor test (Rho=0.562, p=0.01). A weak correlation in pressure pain thresholds and changes in range of motion were found following the cold pressor test (Rho=0.460, p=0.047). However, a potential carryover hypoalgesic effect may have affected the results of the static stretch. CONCLUSIONS: These results suggest that stretch tolerance may be linked with endogenous modulation of pain. Present results suggest, that stretch tolerance may merely be a marker for pain sensitivity which may have clinical significance given that stretching is often prescribed in the rehabilitation of different musculoskeletal pain conditions where reduced endogenous pain inhibition is frequently seen.

High-Intensity Static Stretching in Quadriceps Is Affected More by Its Intensity Than Its Duration.

A previous study reported that 3-min of high-intensity static stretching at an intensity of 120% of range of motion (ROM) did not change the muscle stiffness of the rectus femoris, because of the overly high stress of the stretching. The purpose of this study was to examine the effects of high-intensity static stretching of a shorter duration or lower intensity on the flexibility of the rectus femoris than that of the previous study. Two experiments were conducted (Experiment 1 and 2). In Experiment 1, eleven healthy men underwent static stretching at the intensity of 120% of ROM for two different durations (1 and 3 min). In Experiment 2, fifteen healthy men underwent 3-min of static stretching at the intensity of 110% of ROM. The shear elastic modulus of the quadriceps were measured. In Experiment 1, ROM increased in both interventions (p < 0.01), but the shear elastic modulus of the rectus femoris was not changed. In Experiment 2, ROM significantly increased (p < 0.01), and the shear elastic modulus of the rectus femoris significantly decreased (p < 0.05). It was suggested that the stretching intensity (110%) is more important than stretching duration to decrease the muscle stiffness of the rectus femoris.

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 Comparison of Different Stretching Intensities on the Range of Motion and Muscle Stiffness of the Quadriceps Muscles.

Muscle strain is one of the most frequent sports injuries, having the rectus femoris (RF) muscle as the reported preferred site of quadriceps muscle strain. The decrease muscle stiffness could be an effective RF muscle strain prevention. In recent studies, a high-intensity static stretching intervention decreased passive stiffness, though no study has investigated on the effect of the different static stretching intervention intensities on quadriceps muscle stiffness. The purpose of this study was to investigate the three different quadriceps muscle stiffness intensities (120 vs. 100 vs. 80%). Eighteen healthy, sedentary male volunteers participated in the study and randomly performed three intensities. The static stretching intervention was performed in knee flexion with 30° hip extension. Three 60-second stretching intervention with a 30-second interval were performed at each stretching intensity. We measured knee flexion range of motion and shear elastic modulus of the RF muscle used by ultrasonic shear-wave elastography before and after the static stretching intervention. Our results showed that the knee flexion range of motion was increased after 100% (p < 0.01) and 120% intensities (p < 0.01) static stretching intervention, not in 80% intensity (p = 0.853). In addition, our results showed that the shear elastic modulus of the RF muscle was decreased only after 100% intensity static stretching intervention (p < 0.01), not after 80% (p = 0.365), and 120% intensities (p = 0.743). To prevent the quadriceps muscle strain, especially the RF muscle, 100%, not 120% (high) and 80% (low), intensity stretching could be beneficial in sports setting application.