Determinants of musculoskeletal flexibility: viscoelastic properties, cross-sectional area, EMG and stretch tolerance

Cross-Education Effects of Isokinetic Eccentric Plantarflexor Training on Flexibility, Strength, and Muscle-Tendon Mechanics

INTRODUCTION

Large increases in joint range of motion (ROM) have been reported after eccentric resistance training; however, limited data exist describing the associated mechanisms or potential cross-education effects in the contralateral limb. Therefore, the effects of a 6-wk isokinetic eccentric plantarflexor training program were examined in 26 participants.

METHODS

Before and after the training program, dorsiflexion ROM, plantarflexor strength, and muscle-tendon unit (MTU) morphology and mechanics were measured in control ( n = 13) and experimental ( n = 13) young adult groups. Training consisted of 5 sets of 12 maximal isokinetic eccentric plantarflexor contractions twice weekly on the right limb.

RESULTS

Significant ( P < 0.05) increases in dorsiflexion ROM (4.0-9.5°), stretch tolerance (40.3-95.9%), passive elastic energy storage (47.5-161.3%), and isometric (38.1-40.6%) and eccentric (46.7-67.0%) peak plantarflexor torques were detected in both trained and contralateral limbs in the experimental group. Significant increases in gastrocnemius medialis and soleus thickness (5.4-6.1%), gastrocnemius medialis fascicle length (7.6 ± 8.5%), passive plantarflexor MTU stiffness (30.1 ± 35.5%), and Achilles tendon stiffness (5.3 ± 4.9%) were observed in the trained limb only. Significant correlations were detected between the changes in trained and contralateral limbs for dorsiflexion ROM ( r = 0.59) and both isometric ( r = 0.79) and eccentric ( r = 0.73) peak torques. No significant changes in any metric were detected in the control group.

CONCLUSIONS

Large ROM increases in the trained limb were associated with neurological, mechanical, and structural adaptations, with evidence of a cross-education effect in the contralateral limb being primarily driven by neurological adaptation (stretch tolerance). The large improvements in ROM, muscle size, and strength confirm that isokinetic eccentric training is a highly effective training tool, with potential for use in athletic and clinical populations where MTU function is impaired and current therapies are ineffective.

Biceps femoris long head stiffens after 2 weeks of training cessation in highly trained sprinters

PURPOSE

Most athletes experience short-term training cessation because of illness, injury, post-season vacation, or other reasons. Passive muscle stiffness is a potential risk factor for a sprint-type hamstring strain injury, but limited information is available about the effect of short-term training cessation on passive muscle stiffness. The present study aimed to identify whether and how passive muscle stiffness of the biceps femoris long head (BFlh) would vary due to 2 weeks of training cessation in sprinters.

METHODS

Passive BFlh shear-wave speed (a proxy for stiffness) was measured using ultrasound shear-wave elastography in 28 male sprinters, before and after 2 weeks of intervention. During the 2 weeks, the participants in the training-cessation group (n = 14) were allowed to maintain their normal daily activities but not to perform any physical training, including stretching and resistance exercises. The participants in the training continuation group (n = 14) performed the training (including maximum speed sprint, plyometric, and weight training) prescribed by their coaches 5 days per week.

RESULTS

In the training-cessation group, passive BFlh shear-wave speed increased after the 2 weeks of training cessation (4.75 ± 0.77 to 5.00 ± 0.88 m/s, P < 0.001). In contrast, there was no significant difference before and after the 2 weeks of training continuation (4.90 ± 0.85 to 4.93 ± 0.85 m/s, P = 0.521).

CONCLUSIONS

The present findings indicate that muscles stiffen by training cessation in sprinting athletes.

Acute and Long-Term Effects of Stretching with Whole-Body Vibration on Young's Modulus of the Soleus Muscle Measured Using Shear Wave Elastography

The effect of whole-body vibration (WBV) stretching on soleus (SOL) muscle stiffness remains unclear. Therefore, we aimed to investigate the acute and long-term effects of stretching with WBV on SOL muscle stiffness. This study employed a repeated-measures experimental design evaluating 20 healthy young males. SOL muscle stretching with WBV was performed for 5 min per day (1 min per set, five sets) over 4 weeks, for 4 days a week. Participants stretched the SOL muscle with ankle dorsiflexion in a loaded flexed knee position on a WBV device. Data were obtained to examine acute effects before stretching, immediately after stretching, and at 5, 10, 15, and 20 min. Moreover, data were obtained to examine the long-term effects before stretching, immediately after the completion of the 4-week stretching program, and at 2 and 4 weeks later. SOL muscle stiffness was measured using Young's modulus with shear wave elastography. The acute effect of SOL muscle stretching with WBV persisted for up to 20 min. Additionally, the long-term effect of stretching was better maintained than the acute effect, which was effective for up to 4 weeks (p < 0.001). Clinically, continuous stretching with WBV may be used to improve SOL muscle stiffness in rehabilitation programs.

Relationship between pectoralis major stiffness and shoulder extension range of motion

This study aimed to investigate the correlation between the passive muscle stiffness of the pectoralis major muscle pars clavicularis (PMc) and shoulder extension range of motion (ROM) in both male and female participants. Thirty-nine (23 male/16 female) physically active and healthy participants volunteered in this study. After a standardized warm-up, the PMc stiffness was tested via shear wave elastography at a slightly stretched position (long muscle length) and in a non-stretched position (short muscle length). Additionally, a custom-made device and 3D motion capture assessed the active shoulder extension ROM. We found a significant moderate and negative relationship between shoulder extension ROM and PMc stiffness at long muscle length (rs = -0.33; p = 0.04) but not at short muscle length (r = -0.23; p = 0.17). Additionally, there was no significant difference between male and female participants in the correlation analyses at both elbow angles. The moderate correlation between PMc stiffness at a slightly stretched position and shoulder extension ROM suggests that additionally, other structures such as nerves/fascia stiffness or even stretch tolerance might be factors that can be related to shoulder extension ROM.

Acute effects of static and proprioceptive neuromuscular facilitation stretching on hamstrings muscle stiffness and range of motion: a randomized cross-over study

This study aimed to compare the acute effects of static stretching (SS) and proprioceptive neuromuscular facilitation (PNF) stretching on hamstrings flexibility and shear modulus. Sixteen recreationally active young volunteers participated in a randomized cross-over study. Participants underwent an aerobic warm-up (WU), followed by either SS or PNF stretching. Range of motion (RoM) during passive straight leg raise and active knee extension, as well as shear modulus of the biceps femoris (BF) and semitendinosus (ST) muscles, were measured at baseline, post-WU, and post-stretching. Both stretching techniques significantly increased RoM, with no differences observed between SS and PNF (p < 0.001; η2 = 0.59-0.68). However, only PNF stretching resulted in a significant decrease in BF shear modulus (time×stretching type interaction: p = 0.045; η2 = 0.19), indicating reduced muscle stiffness. No changes in ST shear modulus were observed after either stretching technique. There was no significant correlation between changes in RoM and shear modulus, suggesting that the increase in RoM was predominantly due to changes in stretch tolerance rather than mechanical properties of the muscles. These findings suggest that both SS and PNF stretching can effectively improve hamstring flexibility, but PNF stretching may additionally reduce BF muscle stiffness. The study highlights the importance of considering individual muscle-specific responses to stretching techniques and provides insights into the mechanisms underpinning acute increases in RoM.

Corticospinal excitability and reflex modulation in a contralateral non-stretched muscle following unilateral stretching

PURPOSE

Muscle stretching effect on the range of motion (ROM) and force deficit in non-stretched muscle, and the underlying mechanisms, is an ongoing issue. This study aimed to investigate crossover stretching effects and mechanisms on the plantar flexor muscles.

METHODS

Fourteen recreationally active females (n = 5) and males (n = 9) performed six sets of 45-s static stretching (SS) (15-s recovery) to the point of discomfort of the dominant leg (DL) plantar flexors or control (345-s rest). Participants were tested for a single 5-s pre- and post-test maximal voluntary isometric contraction (MVIC) with each plantar flexor muscle and were tested for DL and non-DL ROM. They were tested pre- and post-test (immediate, 10-s, 30-s) for the Hoffman (H)-reflex and motor-evoked potentials (MEP) from transcranial magnetic stimulation in the contralateral, non-stretched muscle.

RESULTS

Both the DL and non-DL-MVIC force had large magnitude, significant (↓10.87%, p = 0.027, pƞ2 = 0.4) and non-significant (↓9.53%, p = 0.15, pƞ2 = 0.19) decreases respectively with SS. The SS also significantly improved the DL (6.5%, p < 0.001) and non-DL (5.35%, p = 0.002) ROM. The non-DL MEP/MMax and HMax/MMax ratio did not change significantly.

CONCLUSION

Prolonged static stretching improved the stretched muscle's ROM. However, the stretched limb's force was negatively affected following the stretching protocol. The ROM improvement and large magnitude force impairment (statistically non-significant) were transferred to the contralateral muscles. The lack of significant changes in spinal and corticospinal excitability confirms that the afferent excitability of the spinal motoneurons and corticospinal excitability may not play a substantial role in non-local muscle's ROM or force output responses.

Potential Effects of Dynamic Stretching on Injury Incidence of Athletes: A Narrative Review of Risk Factors

The use of dynamic stretching as a replacement for static stretching in the warm-up is widespread based on the reports of static stretching-induced performance impairments. While acute and chronic static stretching has been reported to reduce musculotendinous injuries, especially with explosive and change of direction actions, the influence of dynamic stretching on injury incidence lacks a similar volume of literature for acute and chronic responses. It was the objective of this narrative review to examine the acute and training effects of dynamic stretching on injury incidence and possible moderating variables such as dynamic stretching effects on range of motion, strength, balance, proprioception, muscle morphology, and psycho-physiological responses. One study demonstrated no significant difference regarding injury incidence when comparing a dynamic stretching-only group versus a combined dynamic stretching plus static stretching group. The only other study examined functional dynamic stretching training with injured dancers and reported improved ankle joint stability. However, several studies have shown that dynamic activity with some dynamic stretching exercises within a warm-up consistently demonstrates positive effects on injury incidence. Regarding moderating variables, while there is evidence that an acute bout of dynamic stretching can enhance range of motion, the acute and training effects of dynamic stretching on strength, balance, proprioception, and musculotendinous stiffness/compliance are less clear. The acute effects of dynamic stretching on thixotropic effects and psycho-physiological responses could be beneficial for injury reduction. However, the overall conflicting studies and a lack of substantial literature compared with SS effects points to a need for more extensive studies in this area.

Hamstrings fascicle length and physical performance changes after a single bout of dynamic stretching or neurodynamic gliding in healthy young and older adults

INTRODUCTION

The physiological and structural alterations have been less reported in response to dynamic stretching (DS) or neurodynamic nerve gliding (NG). Accordingly, this study investigated the changes in fascicle lengths (FL), popliteal artery velocity, and physical fitness in response to a single bout of DS or NG.

METHODS

The study included 15 healthy young adults (20.9 ± 0.7 yrs) and 15 older adults (66.6 ± 4.2 yrs) who randomly performed three different interventions (DS, NG, and rest control) for 10 min and 3 days apart. The biceps femoris and semitendinosus FL, popliteal artery velocity, sit and reach (S&R), straight leg raise (SLR), and fast walking speed were measured before and immediately after the intervention.

RESULTS

After NG intervention, S&R was largely greater by 2 cm (1.2, 2.8 cm) and 3.4 cm (2.1, 4.7 cm) with largely increased SLR angles of 4.9° (3.7°, 6.1°) and 4.6° (3.0°, 6.2°) with all p < 0.001 for the older adults and young groups, respectively. A similar magnitude improvement in the S&R and SLR testing was also seen for both groups after DS (p < 0.05). Moreover, no changes were seen in FL, popliteal artery velocity, fast gait speed, and age effect following all three intervention occasions.

CONCLUSION

Stretching with DS or NG immediately increased flexibility, which appeared to be largely due to changes in stretch tolerance rather than an increase in fascicle length. Furthermore, age dependency in response to stretching exercise was not seen in the present study.

Muscle Architecture Adaptations to Static Stretching Training: A Systematic Review with Meta-Analysis

BACKGROUND

Long-term stretching of human skeletal muscles increases joint range of motion through altered stretch perception and decreased resistance to stretch. There is also some evidence that stretching induces changes in muscle morphology. However, research is limited and inconclusive.

OBJECTIVE

To examine the effect of static stretching training on muscle architecture (i.e., fascicle length and fascicle angle, muscle thickness and cross-sectional area) in healthy participants.

DESIGN

Systematic review and meta-analysis.

METHODS

PubMed Central, Web of Science, Scopus, and SPORTDiscus were searched. Randomized controlled trials and controlled trials without randomization were included. No restrictions on language or date of publication were applied. Risk of bias was assessed using Cochrane RoB2 and ROBINS-I tools. Subgroup analyses and random-effects meta-regressions were also performed using total stretching volume and intensity as covariates. Quality of evidence was determined by GRADE analysis.

RESULTS

From the 2946 records retrieved, 19 studies were included in the systematic review and meta-analysis (n = 467 participants). Risk of bias was low in 83.9% of all criteria. Confidence in cumulative evidence was high. Stretching training induces trivial increases in fascicle length at rest (SMD = 0.17; 95% CI 0.01-0.33; p = 0.042) and small increases in fascicle length during stretching (SMD = 0.39; 95% CI 0.05 to 0.74; p = 0.026). No increases were observed in fascicle angle or muscle thickness (p = 0.30 and p = 0.18, respectively). Subgroup analyses showed that fascicle length increased when high stretching volumes were used (p < 0.004), while no changes were found for low stretching volumes (p = 0.60; subgroup difference: p = 0.025). High stretching intensities induced fascicle length increases (p < 0.006), while low stretching intensities did not have an effect (p = 0.72; subgroup difference: p = 0.042). Also, high intensity stretching resulted in increased muscle thickness (p = 0.021). Meta-regression analyses showed that longitudinal fascicle growth was positively associated with stretching volume (p < 0.02) and intensity (p < 0.04).

CONCLUSIONS

Static stretching training increases fascicle length at rest and during stretching in healthy participants. High, but not low, stretching volumes and intensities induce longitudinal fascicle growth, while high stretching intensities result in increased muscle thickness.

REGISTRATION

PROSPERO, registration number: CRD42021289884.

National Strength and Conditioning Association Position Statement on Weightlifting for Sports Performance

ABSTRACT

Comfort, P, Haff, GG, Suchomel, TJ, Soriano, MA, Pierce, KC, Hornsby, WG, Haff, EE, Sommerfield, LM, Chavda, S, Morris, SJ, Fry, AC, and Stone, MH. National Strength and Conditioning Association position statement on weightlifting for sports performance. J Strength Cond Res XX(X): 000-000, 2022-The origins of weightlifting and feats of strength span back to ancient Egypt, China, and Greece, with the introduction of weightlifting into the Olympic Games in 1896. However, it was not until the 1950s that training based on weightlifting was adopted by strength coaches working with team sports and athletics, with weightlifting research in peer-reviewed journals becoming prominent since the 1970s. Over the past few decades, researchers have focused on the use of weightlifting-based training to enhance performance in nonweightlifters because of the biomechanical similarities (e.g., rapid forceful extension of the hips, knees, and ankles) associated with the second pull phase of the clean and snatch, the drive/thrust phase of the jerk and athletic tasks such as jumping and sprinting. The highest force, rate of force development, and power outputs have been reported during such movements, highlighting the potential for such tasks to enhance these key physical qualities in athletes. In addition, the ability to manipulate barbell load across the extensive range of weightlifting exercises and their derivatives permits the strength and conditioning coach the opportunity to emphasize the development of strength-speed and speed-strength, as required for the individual athlete. As such, the results of numerous longitudinal studies and subsequent meta-analyses demonstrate the inclusion of weightlifting exercises into strength and conditioning programs results in greater improvements in force-production characteristics and performance in athletic tasks than general resistance training or plyometric training alone. However, it is essential that such exercises are appropriately programmed adopting a sequential approach across training blocks (including exercise variation, loads, and volumes) to ensure the desired adaptations, whereas strength and conditioning coaches emphasize appropriate technique and skill development of athletes performing such exercises.

Acute changes in passive stiffness of the individual hamstring muscles induced by resistance exercise: effects of muscle length and exercise duration

PURPOSE

A previous study revealed that resistance exercise with eccentric contraction and a wide range of motion (ROM) can acutely decrease muscle stiffness of a specific muscle. To explore further approaches to decrease the stiffness, we examined the acute changes in passive stiffness of the individual hamstring muscles after eccentric-only resistance exercise with different combinations of muscle lengths and exercise durations.

METHODS

Thirteen healthy young male participants performed three sessions of eccentric-only exercises that comprised stiff-leg deadlift with different muscle lengths and exercise durations (duration per repetition × the total number of repetitions) on separate days as follows: (1) short muscle lengths with a short duration (SS); (2) long muscle lengths with a short duration (LS); and (3) long muscle lengths with a long duration (LL). Maximal joint ROM, passive torque, shear modulus of each hamstring muscle, and maximal isometric torque of knee flexion were measured before, and at 3, 30, and 60 min after each session.

RESULTS

The shear modulus of the semimembranosus was significantly lower at 3 min post-exercise (129.8 ± 22.7 kPa) than at pre-exercise (140.5 ± 19.1 kPa, p < 0.01) in LL, but not in SS or LS. No significant differences were observed in the shear moduli of the biceps femoris long head or semitendinosus between pre-exercise and 3 min post-exercise in any session.

CONCLUSION

The combination of long muscle lengths and a long duration during eccentric-only resistance exercise is important to immediately decrease the stiffness (shear modulus) of a specific muscle.

The Relationship Between Lower Limb Passive Muscle and Tendon Compression Stiffness and Oxygen Cost During Running

Studies have reported that a stiff triceps surae muscle and tendon-aponeurosis and also a more compliant quadriceps muscle and tendon-aponeurosis, are related to lower oxygen cost during running. However, to date, no study has investigated in a single experiment how oxygen cost during running is related to the stiffness of the free tendons (Achilles tendon, patellar tendon) and all the superficial muscles of two major muscle groups for running (i.e., quadriceps, triceps surae). Thus, 17 male trained runners/triathletes participated in this study and visited the laboratory on three occasions. On the first day, the participants were familiarized with the tests. On the second day, the passive compression stiffness of the triceps surae muscle (i.e., gastrocnemii), Achilles tendon, quadriceps muscle (i.e., vastii, rectus femoris), and patellar tendon was non-invasively measured using a digital palpation device (MyotonPRO). In addition, an incremental test was applied to test the VO2max of the participants. Thereafter, in the third visit, after at least 48-h of rest, participants performed a 15-min run on the treadmill with a speed reflecting a velocity of 70% VO2max, to assess oxygen costs during running. The Spearman correlation showed a significant negative correlation between passive Achilles tendon compression stiffness and running oxygen consumption, with a large effect size (rρ = -0.52; CI (95%) -0.81 to -0.33; P = 0.03). Moreover, no further significant relationship between oxygen cost during running and the passive compression stiffness of the quadriceps muscle and patellar tendon, as well as the triceps surae muscle, was detected. The significant correlation indicates that a stiffer passive Achilles tendon can lead to a lower oxygen cost during running. Future studies will have to test the causality of this relationship with training methods such as strength training that are able to increase the Achilles tendon stiffness.

Effects of Speed and Amplitude of Dynamic Stretching on the Flexibility and Strength of the Hamstrings

Dynamic stretching for more than 90 seconds is useful for improving muscle strength, although dynamic stretching for 30 seconds or less is commonly used in sports settings. The effects of dynamic stretching are influenced by the speed and amplitude of stretching, but no study examined these factors for 30 seconds of dynamic stretching. Therefore, the purpose of the present study was to examine the effects of speed (fast- or slow-speed) and amplitude (normal- or wide amplitude) of dynamic stretching for 30 seconds on the strength (peak torque during maximum isokinetic concentric contraction) and flexibility (range of motion, passive torque at maximum knee extension angle, and muscle-tendon unit stiffness) of the hamstrings. The passive torque and muscle-tendon unit stiffness reflect stretching tolerance and viscoelastic properties of the hamstrings, respectively. Fifteen healthy participants performed 4 types of 30 seconds of dynamic stretching. The muscle strength and flexibility were measured before and immediately after the dynamic stretching. The range of motion did not change after dynamic stretching at low speed and normal amplitude (p = 0.12, d = 0.59, 103.3%), but it was increased by other interventions (p < 0.01, d = 0.90-1.25, 104.5-110.1%). In all interventions, the passive torque increased (main effect for time, p < 0.01, d = 0.51 - 0.74, 111.0 - 126.9%), and muscle-tendon unit stiffness did not change. The muscle strength increased only after dynamic stretching at fast speed with normal amplitude (p < 0.01, d = 0.79, 107.1%). The results of the present study indicated that 30 seconds of dynamic stretching at fast speed and with normal amplitude can be beneficial for the measured parameters.

Acute changes in passive stiffness of the individual hamstring muscles induced by resistance exercise: effects of contraction mode and range of motion

PURPOSE

Recent studies raise an interesting possibility that resistance exercise also decreases passive muscle stiffness, as does stretching exercise. However, little is known about how program variables of resistance exercise acutely influence muscle stiffness. We aimed to examine the acute changes in passive stiffness of the individual hamstring muscles after resistance exercises using different combinations of contraction modes and ranges of motion (ROMs).

METHODS

Thirteen healthy young male participants performed three sessions of resistance exercises that comprised stiff-leg deadlift with different contraction modes and exercise ROMs on separate days as follows: (1) eccentric contractions with a wide exercise ROM (EW); (2) eccentric contractions with a narrow exercise ROM (EN); and (3) concentric contractions with a wide exercise ROM (CW). Maximal joint ROM, passive torque, shear modulus of the individual hamstring muscles, and maximal isometric torque of knee flexion were measured before and 3 min, 30 min, and 60 min after completing each session.

RESULTS

The shear modulus of the semimembranosus was significantly lower at 3 min post-exercise (121.8 ± 16.0 kPa) than at pre-exercise (129.0 ± 18.9 kPa, p = 0.021, r = 0.45) in EW, but not in EN or CW. There were no significant changes in the shear moduli of the biceps femoris long head or the semitendinosus at any timepoint in any exercise protocols.

CONCLUSIONS

The present results suggest that the combination of eccentric contraction and wide ROM during resistance exercise has the potential to acutely decrease passive stiffness (shear modulus) of a specific muscle.

Relationship between Eccentric-Exercise-Induced Loss in Muscle Function to Muscle Soreness and Tissue Hardness

It is well-known that unusual exercise, especially eccentric contraction (ECC), could cause delayed-onset muscle soreness. However, the factors related to the loss of muscle strength and range of motion (ROM) caused by eccentrically damaged muscle, such as increases in muscle soreness, tissue hardness, and pain threshold, have not been investigated in detail. Thus, this study was conducted to investigate the factors related to the loss of muscle strength and ROM caused by eccentrically damaged muscle in a large sample. Fifty-six sedentary healthy young male volunteers were instructed to perform 60 repetitions of ECC exercise. The outcome variables were measured before and 48 h after the ECC exercise. The results showed that a decrease in ROM was correlated to an increase in tissue hardness, whereas a decrease in muscle strength was correlated to an increase in muscle soreness. Our results suggested that tissue hardness must be controlled for ROM loss, and muscle soreness must be controlled for muscle-strength loss.

The effect of Liquid ice after high-intensity exercise on muscle function compared to Block ice

Cryotherapy is used to recover muscle damage after exercise and to treat acute sports injuries. Liquid ice (LI) can keep cold for a long time, and is assumed more effective than block ice (BI). From this, the aim of this study was to investigate the effects of LI on the change of passive stiffness (PS) as muscle function and to validate the effectiveness of LI compared to BI. We performed the experiment as part of a case series of verification of the effects of cryotherapy. 22 healthy men (target area: right leg) were randomized to two groups: LI group and BI group. PS was measured three times during experiment protocol, pre: before exercise; post; after treating each cryotherapy after exercise; 48h: 48 hours after pre. Statistical analysis compared the PS, the amount of change in PS, and the rate of change in PS between the two groups. The rate of change between pre and 48h in LI was significantly lower compared to that in BI (p = 0.03). There was no significant difference regarding other results between groups. It revealed that the difference of effect between LI and BI for PS of muscles after high-intensity exercises. These results could be helpful for the choice of intervention for reducing muscle stiffness after exercise and at sports field.

Age-Related Differences in Hamstring Flexibility in Prepubertal Soccer Players: An Exploratory Cross-Sectional Study

This study aimed to investigate the hamstring flexibility rate among prepubertal soccer players from U8 to U12 and the role of age and soccer years of practice on the course of hamstring flexibility. Six hundred eleven young Italian soccer players from a local soccer school in Turin were recruited for this research and assigned to each group according to their chronological age (U8 = 124 players; U9 = 130 players; U10 = 151 players; U11 = 89 players; and U12 = 120 players). Hamstring flexibility was measured using the Sit and Reach Test (SAR), while data analysis was run using a one-way analysis of variance (one-way ANOVA). Furthermore, Tuckey’s post hoc was used to determine differences among the classes of age. Finally, a bivariate ordinal regression analysis was used to evaluate a potential association between age categories and hamstrings flexibility. In addition, multivariable ordinal regression was used to analyze this relationship adjusted for the Body Mass Index (BMI). The one-way ANOVA showed significant differences in flexibility among groups (F = 32.76, P < 0.0001). Tuckey’s post hoc identified significant differences between U8 and U10 (p < 0.01; −2,39 cm of hamstring stretching), U8 and U11 (p < 0.05; −2.19 cm), U8 and U12 (p < 0.0001; −5.90), U9 and U12 (p < 0.0001; −4.98 cm), U10 and U12 (p < 0.0001; −3.5 cm), U11 and U12 (p < 0,001; −3.70 cm). In the bivariate ordinal regression analysis, there was a negative association between the age categories and hamstrings flexibility (R² = 0.137; p < 0.0001). The association persisted in multivariable ordinal regression analysis adjusted for BMI (R² = 0.138; p < 0.0001). This study underlines changes in hamstring flexibility across different age groups of prepubertal soccer players. The older and more experienced in soccer are less flexible than the younger, considering the hamstring muscles. Thus, appropriate stretching protocols should be included in prepubertal soccer training to avoid the risk of lead players to excess hamstring tightness.

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.

Effects of Self-Myofascial Release Using a Foam Roller on the Stiffness of the Gastrocnemius-Achilles Tendon Complex and Ankle Dorsiflexion Range of Motion

Increased muscle stiffness can contribute to reduced range of motion (ROM) and impaired function. Reduced ankle dorsiflexion ROM has been associated with increased injury risk in the ankle. Self-myofascial release (SMR) has been widely used in clinical and sports settings, but the effects of SMR on gastrocnemius and Achilles tendon (AT) stiffness are unclear. Therefore, we investigated the effects of self-myofascial release using a foam roller (FR) on the stiffness of the gastrocnemius–AT complex and ankle dorsiflexion ROM. Fifty healthy, untrained, and non-sedentary participants (age=22.5±2.6years) were randomly divided into an intervention group (FR group) and a control group. The subjects in the intervention group received a single foam roller intervention (three sets of 1min), while the subjects in the control group performed a 5-min sedentary rest. Stiffness of the gastrocnemius–AT complex was evaluated using MyotonPRO and the ankle dorsiflexion ROM was assessed using the weight-bearing lunge test. For the foam roller and control groups, the between-group analysis revealed a statistically significant difference in gastrocnemius stiffness and ankle dorsiflexion ROM after intervention (p<0.05). Within-group analysis revealed a significant increase in ROM and a significant decrease in medial and lateral gastrocnemius (LG) stiffness for the foam roller group after the intervention (p<0.05). In addition, further analysis of the preintervention data revealed a significant negative correlation between ankle dorsiflexion ROM and AT stiffness (r=−0.378 and p=0.007). These results suggest that self-myofascial release using a foam roller on the calf is an effective method for decreasing the stiffness of the gastrocnemius and increasing ankle dorsiflexion ROM.

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.

Bankart Repair With Subscapularis Augmentation in Athletes With Shoulder Hyperlaxity

PURPOSE

The purpose of this study was to demonstrate that arthroscopic Bankart repair with associated arthroscopic subscapularis augmentation (ASA) could be a valid surgical option in the treatment of anterior shoulder instability, in collision and contact sports athletes, affected by shoulder hyperlaxity.

METHODS

In total, 591 arthroscopic Bankart repairs plus ASA were performed in 6 shoulder centers from 2009 to 2017. Inclusion criteria were the following: collision and contact sports activities, recurrent anterior instability associated with hyperlaxity and glenoid bone loss (GBL) < 15%. Exclusion criteria were GBL > 15%, voluntary instability, multidirectional instability, pre-existing osteoarthritis and throwing athletes. The minimum follow-up was 24 months. Hyperlaxity was clinically evaluated according to Neer and Coudane-Walch tests. Before surgery, all patients underwent magnetic resonance imaging and computed tomography scanning. Pico area method was used to assess the percentage of GBL. Patients were operated on by 6 surgeons, and their functional outcomes were evaluated by 2 independent observers. The Western Ontario Shoulder Instability Index (WOSI), Rowe, American Shoulder and Elbow Surgeons (ASES) scores were used to assess results.

RESULTS

Overall, 397 patients with evidence of shoulder hyperlaxity (positive sulcus sign in ER1 position and Coudane-Walch test > 85°) met all inclusion criteria. The mean WOSI score was 321; the mean Rowe score rose from 68.5 to 92.5 (P = .037), and the ASES score rose from 71.5 to 97.4 (P = .041). Seven patients (1.6%) had atraumatic redislocation, and 9 patients (2.2%) had post-traumatic redislocation. At final follow-up the mean functional deficit of external rotation was 15° with the arm in adduction (ER1 position) and 10° in abduction (ER2 position).

CONCLUSIONS

The Bankart repair plus ASA has been demonstrated to be safe and effective for restoring joint stability in patients practicing collision and contact sports or affected by chronic anterior shoulder instability associated with GBL (<15%) and hyperlaxity, without compromising external rotation.

LEVEL OF EVIDENCE

Level IV, case series.

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.

Trunk muscle endurance, strength and flexibility in rural subsistence farmers and urban industrialized adults in western Kenya

OBJECTIVES

High trunk muscle endurance, strength, and moderate flexibility reportedly help maintain musculoskeletal health, but there is evidence for tradeoffs among these variables as well as sex differences in trunk muscle endurance and strength. To test if these observations extend similarly to both men and women in nonindustrial and industrial environments, we investigated intra-individual associations and group and sex differences in trunk muscle endurance, strength, and flexibility among 74 (35 F, 39 M; age range: 18-61 years) adults from the same Kalenjin-speaking population in western Kenya. We specifically compared men and women from an urban community with professions that do not involve manual labor with rural subsistence farmers, including women who frequently carry heavy loads.

METHODS

Trunk muscle endurance, strength, and flexibility were measured with exercise tests and electromyography (EMG).

RESULTS

We found a positive correlation between trunk extensor strength and endurance (R = .271, p ≤ .05) and no associations between strength or endurance and flexibility. Rural women had higher trunk extensor and flexor endurance, EMG-determined longissimus lumborum endurance, and trunk extensor strength than urban women (all p ≤ .05). Rural women had higher trunk extensor and flexor endurance than rural men (both p ≤ .05). Urban women had lower trunk flexor and extensor endurance than urban men (both p ≤ .01).

CONCLUSIONS

High levels of physical activity among nonindustrial subsistence farmers, particularly head carrying among women, appear to be associated with high trunk muscle endurance and strength, which may have important benefits for helping maintain musculoskeletal health.

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.

Non-local acute stretching effects on strength performance in healthy young adults

BACKGROUND

Static stretching (SS) can impair performance and increase range of motion of a non-exercised or non-stretched muscle, respectively. An underdeveloped research area is the effect of unilateral stretching on non-local force output.

OBJECTIVE

The objective of this review was to describe the effects of unilateral SS on contralateral, non-stretched, muscle force and identify gaps in the literature.

METHODS

A systematic literature search following preferred reporting items for systematic review and meta-analyses Protocols guidelines was performed according to prescribed inclusion and exclusion criteria. Weighted means and ranges highlighted the non-local force output response to unilateral stretching. The physiotherapy evidence database scale was used to assess study risk of bias and methodological quality.

RESULTS

Unilateral stretching protocols from six studies involved 6.3 ± 2 repetitions of 36.3 ± 7.4 s with 19.3 ± 5.7 s recovery between stretches. The mean stretch-induced force deficits exhibited small magnitude effect sizes for both the stretched (-6.7 ± 7.1%, d = -0.35: 0.01 to -1.8) and contralateral, non-stretched, muscles (-4.0 ± 4.9%, d = , 0.22: 0.08 to 1.1). Control measures exhibited trivial deficits.

CONCLUSION

The limited literature examining non-local effects of prolonged SS revealed that both the stretched and contralateral, non-stretched, limbs of young adults demonstrate small magnitude force deficits. However, the frequency of studies with these effects were similar with three measures demonstrating deficits, and four measures showing trivial changes. These results highlight the possible global (non-local) effects of prolonged SS. Further research should investigate effects of lower intensity stretching, upper versus lower body stretching, different age groups, incorporate full warm-ups, and identify predominant mechanisms among others.

Association between the Range of Motion and Passive Property of the Gastrocnemius Muscle-Tendon Unit in Older Population

Range of motion has been widely known to decrease with age; however, factors associated with its decrease in the elderly population and especially its gender difference have been unclear. Therefore, this study aimed to investigate the factors associated with ankle dorsiflexion range of motion in the older population. Both male (n = 17, mean ± SD; 70.5 ± 4.2 years; 165.4 ± 5.3 cm; 63.8 ± 7.7 kg) and female (n = 25, 74.0 ± 4.0 years; 151.2 ± 4.9 cm; 50.1 ± 5.6 kg) community-dwelling older adults participated in this study. The ankle dorsiflexion and passive torque of both legs were measured using a dynamometer, and shear elastic modulus of the medial gastrocnemius muscle at 0° ankle angle was measured using ultrasonic shear wave elastography. In this study, we defined the passive torque at dorsiflexion range of motion (DF ROM) as the index of stretch tolerance, and shear elastic modulus as the index of passive muscle stiffness. The partial correlation coefficient adjusted by age, height, weight, and side (dominant or nondominant side) was used to analyze the relationship between DF ROM and passive torque at DF ROM or shear elastic modulus of MG in each male and female participant, respectively. Our results revealed that dorsiflexion range of motion was significantly associated with passive torque at dorsiflexion range of motion in both male (r = 0.455, p = 0.012) and female (r = 0.486, p < 0.01), but not with shear elastic modulus in both male (r = -0.123, p = 0.519) and female (r = 0.019, p = 0.898). Our results suggested that the ankle dorsiflexion range of motion could be related to the stretch tolerance, but not to passive muscle stiffness in community-dwelling elderly population regardless of gender.

Association between medial gastrocnemius muscle-tendon unit architecture and ankle dorsiflexion range of motion with and without consideration of slack angle

Joint flexibility is theoretically considered to associate with muscle-tendon unit (MTU) architecture. However, this potential association has not been experimentally demonstrated in humans in vivo. We aimed to identify whether and how MTU architectural parameters are associated with joint range of motion (RoM), with a special emphasis on slack angle. The fascicle length, pennation angle, tendinous tissue length, MTU length, and shear modulus of the medial gastrocnemius (MG) were assessed during passive ankle dorsiflexion using ultrasound shear wave elastography in 17 healthy males. During passive dorsiflexion task, the ankle joint was rotated from 40° plantar flexion to the maximal dorsiflexion joint angle at which each subject started experiencing pain. From the ankle joint angle-shear modulus relationship, the angle at which shear modulus began to rise (slack angle) was calculated. Two dorsiflexion RoMs were determined as follows; 1) range from the anatomical position to maximal angle (RoM_anat-max) and 2) range from the MG slack angle to maximal angle (RoM_slack-max). The MTU architectural parameters were analyzed at the anatomical position and MG slack angle. The resolved fascicle length (fascicle length × cosine of pennation angle) and ratios of resolved fascicle or tendinous tissue length to MTU length measured at the MG slack angle significantly correlated with the RoM_slack-max (r = 0.491, 0.506, and -0.506, respectively). Any MTU architectural parameters assessed at the anatomical position did not correlate with RoM_anat-max or RoM_slack-max. These results indicate that MTUs with long fascicle and short tendinous tissue are advantageous for joint flexibility. However, this association cannot be found unless MTU architecture and joint RoM are assessed with consideration of muscle slack.

The Acute and Prolonged Effects of Different Durations of Foam Rolling on Range of Motion, Muscle Stiffness, and Muscle Strength

"Foam Rolling" has been used in sports settings to increase range of motion and decrease muscle stiffness without decreasing muscle strength and athletic performance. However, there has been no study investigating the acute and prolonged effect of different durations of foam rolling intervention on muscle stiffness, and the minimum foam rolling intervention duration required to decrease muscle stiffness is unclear. Therefore, the purpose of this study was to investigate the acute and prolonged effect of different durations of foam rolling intervention on ROM, muscle stiffness, and muscle strength. The 45 participants were randomly allocated to 1 of 3 groups (30 s × 1 times group vs 30 s × 3 times group vs 30 s× 10 times group). The outcome measures were dorsiflexion range of motion, shear elastic modulus of medial gastrocnemius, and muscle strength before, 2 min and 30 min after foam rolling intervention. There were no significant differences before and 2 min after foam rolling intervention in 30 s×1 time group, whereas dorsiflexion range of motion was increased in both 30 s×3 times group (p = 0.042, d = 0.26) and 30 s× 10 times group (p < 0.01, d = 0.33). However, the increase in dorsiflexion range of motion was returned to baseline value after 30 minutes in both 30 s × 3 times group and 30 s × 10 times group. In addition, there were no significant changes in shear elastic modulus and muscle strength in all groups. This study suggested that foam rolling for more than 90 s or more of foam rolling was effective in order to increase the range of motion immediately without changing muscle stiffness and muscle strength.

Decreased passive muscle stiffness of vastus medialis is associated with poorer quadriceps strength and knee function after anterior cruciate ligament reconstruction

BACKGROUND

Muscle deficits of the quadriceps and hamstrings are common after anterior cruciate ligament reconstruction, and increase the risk of knee reinjury. Muscle stiffness is an important factor for dynamic joint stability. However, the changes in quadriceps and hamstring muscle stiffness and its influence after anterior cruciate ligament reconstruction remain unclear.

METHOD

Twenty-five male subjects with anterior cruciate ligament reconstruction and twenty-one matched healthy subjects participated in this study. The passive muscle stiffness of the quadriceps and hamstrings was assessed by shear modulus using ultrasound shear wave elastography. The isokinetic muscle strengths of the quadriceps and hamstrings were tested. Knee function was evaluated by the International Knee Documentation Committee and Lysholm score. Muscle stiffness was compared between limbs via non-parametric tests. Correlation analysis was used to detect the relationship between muscle stiffness, isokinetic muscle strength and knee functional scores.

FINDINGS

The involved limb exhibited significantly decreased shear modulus in the vastus medialis compared to the dominant limbs(z = -3.585;P = 0.001;ES = 1.13) and non-dominant limbs(z = -3.551;P = 0.002;ES = 1.24) of healthy controls. The shear modulus of ST was also significantly lower in the involved limb when compared with the contralateral limbs(z = -3.996;P < 0.001;ES = 1.33), dominant limbs(z = -4.477;P < 0.001;ES = 1.65) and non-dominant limbs(z = -4.234;P = 0.001;ES = 1.43) of healthy controls. The shear modulus of the vastus medialis was associated with quadriceps peak torque at 60°/s(r = 0.470; p < 0.001) and knee functional score(r = 0.459; p = 0.021).

INTERPRETATION

The passive muscle stiffness of the vastus medialis decreased after anterior cruciate ligament reconstruction, which is associated with poorer quadriceps strength and knee function. The effect of modulation of muscle stiffness on improving knee function warrants future investigation.

Passive stiffness of fibrotic skeletal muscle in mdx mice relates to collagen architecture

KEY POINTS

The amount of fibrotic material in dystrophic mouse muscles relates to contractile function, but not passive function. Collagen fibres in skeletal muscle are associated with increased passive muscle stiffness in fibrotic muscles. The alignment of collagen is independently associated with passive stiffness in dystrophic skeletal muscles. These outcomes demonstrate that collagen architecture rather than collagen content should be a target of anti-fibrotic therapies to treat muscle stiffness.

ABSTRACT

Fibrosis is prominent in many skeletal muscle pathologies including dystrophies, neurological disorders, cachexia, chronic kidney disease, sarcopenia and metabolic disorders. Fibrosis in muscle is associated with decreased contractile forces and increased passive stiffness that limits joint mobility leading to contractures. However, the assumption that more fibrotic material is directly related to decreased function has not held true. Here we utilize novel measurement of extracellular matrix (ECM) and collagen architecture to relate ECM form to muscle function. We used mdx mice, a model for Duchenne muscular dystrophy that becomes fibrotic, and wildtype mice. In this model, extensor digitorum longus (EDL) muscle was significantly stiffer, but with similar total collagen, while the soleus muscle did not change stiffness, but increased collagen. The stiffness of the EDL was associated with increased collagen crosslinking as determined by collagen solubility. Measurement of ECM alignment using polarized light microscopy showed a robust relationship between stiffness and alignment for wildtype muscle that broke down in mdx muscles. Direct visualization of large collagen fibres with second harmonic generation imaging revealed their relative abundance in stiff muscles. Collagen fibre alignment was linked to stiffness across all muscles investigated and the most significant factor in a multiple linear regression-based model of muscle stiffness from ECM parameters. This work establishes novel characteristics of skeletal muscle ECM architecture and provides evidence for a mechanical function of collagen fibres in muscle. This finding suggests that anti-fibrotic strategies to enhance muscle function and excessive stiffness should target large collagen fibres and their alignment rather than total collagen.

Association between plantar flexor muscle volume and dorsiflexion flexibility in healthy young males: ultrasonography and magnetic resonance imaging studies

Background

Although joint flexibility is important for human locomotion, the determinants of joint flexibility are not fully understood. In this study, we examined the relationship between dorsiflexion flexibility and plantar flexor muscle size in healthy young males.

Methods and results

The dorsiflexion flexibility was assessed using range of motion (ROM) and stiffness during active and passive dorsiflexion. Active ROM was defined as the maximal angle during voluntary dorsiflexion. Passive ROM was defined as the angle at the onset of pain during passive dorsiflexion. Passive stiffness was calculated as the slope of the linear portion of the torque-angle curve between 10º and 20º dorsiflexion of the ankle during passive dorsiflexion. In the first study, the plantar flexor muscle volume (MV) in 92 subjects was estimated on the basis of the lower leg length and plantar flexor muscle thickness, as measured using ultrasonography. The estimated plantar flexor MV correlated significantly with active ROM (r = -0.433), passive ROM (r = -0.299), and passive stiffness (r = 0.541) during dorsiflexion (P = 0.01 for all). In the second study, the plantar flexor MV in 38 subjects was measured using magnetic resonance imaging. The plantar flexor MV correlated significantly with plantar flexor active ROM (r = -0.484), passive ROM (r = -0.383), and passive stiffness (r = 0.592) during dorsiflexion (P = 0.05 for all).

Conclusions

These findings suggest that a larger plantar flexor MV is related to less dorsiflexion flexibility in healthy young males.

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.

Non-local Acute Passive Stretching Effects on Range of Motion in Healthy Adults: A Systematic Review with Meta-analysis

BACKGROUND

Stretching a muscle not only increases the extensibility or range of motion (ROM) of the stretched muscle or joint but there is growing evidence of increased ROM of contralateral and other non-local muscles and joints.

OBJECTIVE

The objective of this meta-analysis was to quantify crossover or non-local changes in passive ROM following an acute bout of unilateral stretching and to examine potential dose-response relations.

METHODS

Eleven studies involving 14 independent measures met the inclusion criteria. The meta-analysis included moderating variables such as sex, trained state, stretching intensity and duration.

RESULTS

The analysis revealed that unilateral passive static stretching induced moderate magnitude (standard mean difference within studies: SMD: 0.86) increases in passive ROM with non-local, non-stretched joints. Moderating variables such as sex, trained state, stretching intensity, and duration did not moderate the results. Although stretching duration did not present statistically significant differences, greater than 240-s of stretching (SMD: 1.24) exhibited large magnitude increases in non-local ROM compared to moderate magnitude improvements with shorter (< 120-s: SMD: 0.72) durations of stretching.

CONCLUSION

Passive static stretching of one muscle group can induce moderate magnitude, global increases in ROM. Stretching durations greater than 240 s may have larger effects compared with shorter stretching durations.

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.

Effects of Active and Passive Warm-ups on Range of Motion, Strength, and Muscle Passive Properties in Ankle Plantarflexor Muscles

ABSTRACT

Takeuchi, K, Takemura, M, Nakamura, M, Tsukuda, F, and Miyakawa, S. Effects of active and passive warm-ups on range of motion, strength, and muscle passive properties in ankle plantarflexor muscles. J Strength Cond Res 35(1): 141-146, 2021-The purpose of this study was to examine the effects of active and passive warm-ups on flexibility and strength of calf muscles. Fourteen healthy males (age: 23.1 ± 2.6 years, height: 172.7 ± 5.6 cm, and body mass: 64.5 ± 7.0 kg) performed 3 types of warm-ups respectively for 10 minutes in a random order: an active warm-up by pedaling a cycling ergometer, an active warm-up doing repeated isometric contractions, and a passive warm-up in a hot water bath. To assess flexibility, range of motion (ROM) of ankle dorsiflexion, passive torque of ankle plantarflexion, and muscle tendon junction (MTJ) displacement were measured and then muscle tendon unit (MTU) stiffness was calculated. After the flexibility assessment, peak torque during maximum voluntary isometric contraction was measured to assess the isometric strength. These data were compared before and after each warm-up. As a result, all 3 types of warm-ups increased ROM (p < 0.05) and passive torque at terminal ROM (p < 0.01), but there were no significant changes in MTU stiffness or MTJ displacement. The active warm-up by pedaling a cycling ergometer increased peak torque during isometric contraction (p < 0.05), whereas the other warm-ups did not show significant alterations. In conclusion, the active warm-up with aerobic exercise increased flexibility and strength of the calf muscles.

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.

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

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

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.

The effects of stretching with cryotherapy, stretching with heat and stretching alone on hamstring flexibility in physically active females

Background/Aims

A pre- and post-intervention study was conducted to examine the effects of acute cryotherapy with stretching, heat with stretching, and stretching alone on hamstring flexibility.

Methods

Thirty female participants were randomly allocated into three groups: stretching with cryotherapy, stretching with heat, or stretching without an intervention. A sit and reach test and the 90/90 active knee extension test were conducted before and after a 20-minute stretching routine to measure hamstring flexibility.

Results

Differences were observed pre- and post-test in the sit and reach test and knee 90/90 extension tasks (P<0.05) within all three groups. However, there were no significant differences (P>0.05) between the three intervention groups.

Conclusions

Combining stretching with cryotherapy or heat application potentially provides no additional benefit to stretching alone in short-term enhancements to hamstring muscle flexibility in physically active females.

Genetics of Muscle Stiffness, Muscle Elasticity and Explosive Strength

Muscle stiffness, muscle elasticity and explosive strength are the main components of athletes' performance and they show a sex-based as well as ethnicity variation. Muscle stiffness is thought to be one of the risk factors associated with sports injuries and is less common in females than in males. These observations may be explained by circulating levels of sex hormones and their specific receptors. It has been shown that higher levels of estrogen are associated with lower muscle stiffness responsible for suppression of collagen synthesis. It is thought that these properties, at least in part, depend on genetic factors. Particularly, the gene encoding estrogen receptor 1 (ESR1) is one of the candidates that may be associated with muscle stiffness. Muscle elasticity increases with aging and there is evidence suggesting that titin (encoded by the TTN gene), a protein that is expressed in cardiac and skeletal muscles, is one of the factors responsible for elastic properties of the muscles. Mutations in the TTN gene result in some types of muscular dystrophy or cardiomyopathy. In this context, TTN may be regarded as a promising candidate for studying the elastic properties of muscles in athletes. The physiological background of explosive strength depends not only on the muscle architecture and muscle fiber composition, but also on the central nervous system and functionality of neuromuscular units. These properties are, at least partly, genetically determined. In this context, the ACTN3 gene code for α-actinin 3 has been widely researched.

Muscle stretching - the potential role of endogenous pain inhibitory modulation on stretch tolerance

Background and aims The effect of stretching on joint range of motion is well documented and is primarily related to changes in the tolerance to stretch, but the mechanisms underlying this change are still largely unknown. The aim of this study was to investigate the influence of a remote, painful stimulus on stretch tolerance. Methods Thirty-four healthy male subjects were recruited and randomly assigned to an experimental pain group (n=17) or a control group (n=17). Passive knee extension range of motion, the activity of hamstring muscles and passive resistive torque were measured with subjects in a seated position. Three consecutive measures were performed with a 5-min interval between. A static stretch protocol was utilized in both groups to examine the effect of stretching and differences in stretch tolerance between groups. Following this, the pain-group performed a cold pressor test which is known to engage the endogenous pain inhibitory system after which measurements were repeated. Results A significant increase in knee extension range of motion was found in the pain group compared with controls (ANCOVA: p<0.05). No difference was found in muscle activity or passive resistive torque between groups (ANCOVA p>0.091). Conclusions Passive knee extension range of motion following stretching increased when following a distant, painful stimulus, potentially engaging the endogenous pain inhibitory systems. Current findings indicate a link between increased tolerance to stretch and endogenous pain inhibition. Implications The current findings may have implications for clinical practice as they indicate that a distant painful stimulus can influence range of motion in healthy individuals. This implies that the modulation of pain has significance for the efficacy of stretching which is important knowledge when prescribing stretching as part of rehabilitation.

Exercise interventions to improve postural malalignments in head, neck, and trunk among adolescents, adults, and older people: systematic review of randomized controlled trials

Despite the widespread use of postural correction in exercise interventions, limited experimental evidence exists for its effectiveness. The present study aimed to systematically review the literature on the efficacy of exercise interventions in improving postural malalignment in head, neck, and trunk. A systematic review was performed by screening four scientific databases (MEDLINE, Web of Science, EBSCO, and Cochrane database) for published randomized controlled trials (RCTs) in English from 1996–2019. The review followed the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement guidelines. Two researchers independently performed study screening, extracting data and assessing the risk of bias for each included study using the Cochrane Collaboration tool for evaluating the risk of bias. A total of 22 RCTs comprising 1,209 participants were identified for inclusion in the review. There was a high risk of bias across most of the included studies (12 studies). Only two studies were classified as low risk of bias, and eight studies were classified as moderate risk of bias. The intervention duration ranged from 2 to 13 weeks, frequency from 2 to 4 days per week, and duration of each session between 15 to 60 min. The insufficiency and quality of included studies did not allow an integrated assessment of the efficacy of exercise interventions on postural malalignments; however, the positive effects noticed in most of the studies indicate some advantages but underscores the necessity of adequately designed RCTs in this field.

Effect of Static Stretching, Dynamic Stretching, and Myofascial Foam Rolling on Range of Motion During Hip Flexion: A Randomized Crossover Trial

Siebert, T, Donath, L, Borsdorf, M, and Stutzig, N. Effect of static stretching, dynamic stretching, and myofascial foam rolling on range of motion during hip flexion: A randomized crossover trial. J Strength Cond Res XX(X): 000-000, 2020-Static and dynamic stretching (DS) are commonly used in sports and physical therapy to increase the range of motion (ROM). However, prolonged static stretching (SS) can deteriorate athletic performance. Alternative methods to increase ROM are thus needed. Foam rolling (FR) may initiate muscle relaxation, improve muscular function, physical performance, and ROM. Previous studies that examined effects of FR on ROM did not control for increased tissue compliance or shifted pain threshold. In this study, the isolated influence of altered tissue compliance on ROM after FR, SS, and DS was investigated using a randomized crossover design. Hip flexion ROM at given joint torques before and after SS, DS, and FR was randomly assessed in 14 young male adults (age: 23.7 +/- 1.3 years; height: 182 +/- 8 cm; body mass: 79.4 +/- 6.9 kg). Hip flexion ROM was measured in the sagittal plane with the subjects lying in a lateral position (no gravitational effects on ROM measurements). Surface electromyographic (EMG) analysis of 2 representative hip extensors (M. biceps femoris and M. semitendinosus) was applied to control for active muscle contribution during ROM measurements. Significant increases in ROM for SS (3.8 +/- 1.1[degrees]; p < 0.001) and DS (3.7 +/- 1.8[degrees]; p < 0.001) were observed, but not for FR (0.8 +/- 3.1[degrees]; p = 0.954). Because stretch forces on tendon and muscle tissue during SS and DS predominately act in longitudinal direction, FR induces mainly transversal forces in the muscle tissue. Thus, increased ROM after FR reported in the literature is more likely due to a shift in the pain threshold. These results provide a better understanding of differential loading conditions during SS, DS, and FR for coaches and practitioners.

COL5A1 rs12722 polymorphism is not associated with passive muscle stiffness and sports-related muscle injury in Japanese athletes

BACKGROUND

Poor joint flexibility has been repeatedly proposed as a risk factor for muscle injury. The C-to-T polymorphism (rs12722) in the 3'-untranslated region of the collagen type V α1 chain gene (COL5A1) is reportedly associated with joint flexibility. Flexibility of a normal joint is largely determined by passive muscle stiffness, which is influenced by intramuscular collagenous connective tissues including type V collagen. The present study aimed to test the hypothesis that the COL5A1 rs12722 polymorphism influences joint flexibility via passive muscle stiffness, and is accordingly associated with the incidence of muscle injury.

METHODS

In Study 1, we examined whether the rs12722 polymorphism is associated with joint flexibility and passive muscle stiffness in 363 healthy young adults. Joint flexibility was evaluated by passive straight-leg-raise and sit-and-reach tests, and passive muscle stiffness was measured using ultrasound shear wave elastography. In Study 2, the association of the rs12722 polymorphism with sports-related muscle injury was assessed in 1559 Japanese athletes. Muscle injury history and severity were assessed by a questionnaire. In both Study 1 and Study 2, the rs12722 C-to-T polymorphism in the COL5A1 was determined using the TaqMan SNP Genotyping Assay.

RESULTS

Study 1 revealed that the rs12722 polymorphism had no significant effect on range of motion in passive straight-leg-raise and sit-and-reach tests. Furthermore, there was no significant difference in passive muscle stiffness of the hamstring among the rs12722 genotypes. In Study 2, rs12722 genotype frequencies did not differ between the muscle injury and no muscle injury groups. Moreover, no association was observed between rs12722 polymorphism and severity of muscle injury.

CONCLUSIONS

The present study does not support the view that COL5A1 rs12722 polymorphism has a role as a risk factor for sports-related muscle injury, or that it is a determinant for passive muscle stiffness in a Japanese population.

Transcutaneous electrical nerve stimulation improves fatigue performance of the treated and contralateral knee extensors

PURPOSE

Transcutaneous electrical nerve stimulation (TENS) can reduce acute and chronic pain. Unilateral fatigue can produce discomfort in the affected limb and force and activation deficits in contralateral non-exercised muscles. TENS-induced local pain analgesia effects on non-local fatigue performance are unknown. Hence, the aim of the study was to determine if TENS-induced pain suppression would augment force output during a fatiguing protocol in the treated and contralateral muscles.

METHODS

Three experiments were integrated for this article. Following pre-tests, each experiment involved 20 min of TENS, sham, or a control condition on the dominant quadriceps. Then either the TENS-treated quadriceps (TENS_Treated) or the contralateral quadriceps (TENS_Contra) was tested. In a third experiment, the TENS and sham conditions involved two\; 100-s isometric maximal voluntary contractions (MVC) (30-s recovery) followed by testing of the contralateral quadriceps (TENS_Contra-Fatigue). Testing involved single knee extensors (KE) MVCs (pre- and post-test) and a post-test 30% MVC to task failure.

RESULTS

The TENS-treated study induced greater (p = 0.03; 11.0%) time to KE (treated leg) failure versus control. The TENS_Contra-Fatigue induced significant (p = 0.04; 11.7%) and near-significant (p = 0.1; 7.1%) greater time to contralateral KE failure versus sham and control, respectively. There was a 14.5% (p = 0.02) higher fatigue index with the TENS (36.2 ± 10.1%) versus sham (31.6 ± 10.6%) conditions in the second fatigue intervention set (treated leg). There was no significant post-fatigue KE fatigue interaction with the TENS_Contra.

CONCLUSIONS

Unilateral TENS application to the dominant KE prolonged time to failure in the treated and contralateral KE suggesting a global pain modulatory response.

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.

ESR1 rs2234693 Polymorphism Is Associated with Muscle Injury and Muscle Stiffness

Supplemental digital content is available in the text.

Purpose

Muscle injury is the most common sports injury. Muscle stiffness, a risk factor for muscle injury, is lower in females than in males, implying that sex-related genetic polymorphisms influence muscle injury associated with muscle stiffness. The present study aimed to clarify the associations between two genetic polymorphisms (rs2234693 and rs9340799) in the estrogen receptor 1 gene (ESR1) and muscle injury or muscle stiffness.

Methods

In study 1, a questionnaire was used to assess the muscle injury history of 1311 Japanese top-level athletes. In study 2, stiffness of the hamstring muscles was assessed using ultrasound shear wave elastography in 261 physically active young adults. In both studies, rs2234693 C/T and rs9340799 G/A polymorphisms in the ESR1 were analyzed using the TaqMan SNP Genotyping Assay.

Results

In study 1, genotype frequencies for ESR1 rs2234693 C/T were significantly different between the injured and noninjured groups in a C-allele dominant (CC + CT vs TT: odds ratio, 0.62; 95% confidence interval, 0.43–0.91) and additive (CC vs CT vs TT: odds ratio, 0.70; 95% confidence interval, 0.53–0.91) model in all athletes. In study 2, hamstring muscle stiffness was lower in subjects with the CC + CT genotype than in those with the TT genotype; a significant linear trend (CC < CT < TT) was found (r = 0.135, P = 0.029). In contrast, no associations were observed between ESR1 rs9340799 G/A and muscle injury or stiffness.

Conclusions

Our results suggest that the ESR1 rs2234693 C allele, in contrast to the T allele, provides protection against muscle injury by lowering muscle stiffness.

Stress Relaxation and Targeted Nutrition to Treat Patellar Tendinopathy

Patellar tendinopathy is one of the most common afflictions in jumping sports. This case study outlines the rehabilitation of a professional basketball player diagnosed by magnetic resonance imaging (MRI) with a central core patellar tendinopathy within the proximal enthesis. The player undertook a nutrition and strength-based rehabilitation program combining gelatin ingestion and heavy isometric loading of the patellar tendon designed to produce significant stress relaxation as part of their competition schedule and a whole-body training plan. On follow-up one and a half years into the program an independent orthopedic surgeon declared the tendon normal on MRI. Importantly, the improved MRI results were associated with a decrease in pain and improved performance. This case study provides evidence that a nutritional intervention combined with a rehabilitation program that uses stress relaxation can improve clinical outcomes in elite athletes.

Involuntary hamstring muscle activity reduces passive hip range of motion during the straight leg raise test: a stimulation study in healthy people

Background

Involuntary hamstring muscle activity is present in some people during the straight leg raise test, but it is not known to what extent involuntary muscle activity limits passive joint range of motion. This study aimed to determine whether small amounts of involuntary hamstring activity limit passive hip range of motion during the straight leg raise test in healthy people.

Methods

Thirty healthy subjects were recruited from The University of Sydney. As the hamstring muscles were continuously stimulated to generate 0, 2.5, 5, 7.5 and 10% of knee flexion maximal voluntary contraction force, an investigator blinded to the amount of stimulation performed a straight leg raise test by passively raising the tested leg while keeping the knee extended. The test was stopped when the knee started to flex, at which point hip range of motion was recorded.

Results

On average, passive hip range of motion decreased by 0.6° for every 1% increase in knee flexion force caused by muscle activation (95% CI 0.3 to 0.9°, p = 0.0012). Subjects were instructed to fully relax when the straight leg raise test was performed, but a small amount of involuntary muscle activity (median 2.4% of maximal activation) was present during the trial without stimulation.

Conclusions

Small amounts of involuntary hamstring muscles activity reduce passive hip range of motion during the straight leg raise test in healthy people.

Trial registration

The protocol for this study was registered with the Open Science Framework, reference: https://osf.io/fejpf/. Registered 9 March 2017.

Effects of whole body vibration on spinal proprioception in healthy individuals

BACKGROUND

Low back pain (LBP) is a common health problem with high reoccurrence rate. As patients with LBP are often found to be proprioception impaired, new proprioception exercises should be explored. Whole body vibration (WBV) has been proven to improve muscle function and proprioception.

OBJECTIVE

The aim of this study was to determine the effects of WBV on spinal proprioception when WBV was administered in standing and seated postures.

METHODS

Twenty healthy male individuals (mean age: 23.2±1.2 years) were recruited and randomly assigned to two WBV groups: WBV in standing or WBV in seated posture. Their body posture, lumbar repositioning ability, maximum reaching distance and lumbopelvic coordination during dynamic motion in flexion and extension were assessed before, immediately after, 30 minutes after and 1 hour after 5 minutes of WBV (18 Hz, 6 mm amplitude) exposure. A Mixed ANOVA was used to analyze the effects of group and time factors on these four outcome measures.

RESULTS

There were no significant interaction (group and time) and group effects on all outcome measures. Participants were found to have significant different time effect on body posture, lumbar repositioning ability, maximum reaching distance and lumbopelvic coordination.

CONCLUSIONS

WBV could significantly improve spinal proprioception including body posture, lumbar repositioning ability, maximum reaching distance and lumbopelvic coordination in healthy individuals. WBV protocol is recommended to confirm its clinical application for improving spinal proprioception and its effects on patients with LBP is warranted.