The role of passive muscle stiffness in symptoms of exercise-induced muscle damage

Evaluating the Reliability of MyotonPro in Assessing Muscle Properties: A Systematic Review of Diagnostic Test Accuracy

Background and Objectives: Muscle properties are critical for performance and injury risk, with changes occurring due to physical exertion, aging, and neurological conditions. The MyotonPro device offers a non-invasive method to comprehensively assess muscle biomechanical properties. This systematic review evaluates the reliability of MyotonPro across various muscles for diagnostic purposes. Materials and Methods: Following PRISMA guidelines, a comprehensive literature search was conducted in Medline (PubMed), Ovid (Med), Epistemonikos, Embase, Cochrane Library, Clinical trials.gov, and the WHO International Clinical Trials platform. Studies assessing the reliability of MyotonPro across different muscles were included. A methodological quality assessment was performed using established tools, and reviewers independently conducted data extraction. Statistical analysis involved summarizing intra-rater and inter-rater reliability measures across muscles. Results: A total of 48 studies assessing 31 muscles were included in the systematic review. The intra-rater and inter-rater reliability were consistently high for parameters such as frequency and stiffness in muscles of the lower and upper extremities, as well as other muscle groups. Despite methodological heterogeneity and limited data on specific parameters, MyotonPro demonstrated promising reliability for diagnostic purposes across diverse patient populations. Conclusions: The findings suggest the potential of MyotonPro in clinical assessments for accurate diagnosis, treatment planning, and monitoring of muscle properties. Further research is needed to address limitations and enhance the applicability of MyotonPro in clinical practice. Reliable muscle assessments are crucial for optimizing treatment outcomes and improving patient care in various healthcare settings.

Comparison of ultrasonography-based masticatory muscle thickness between temporomandibular disorders bruxers and temporomandibular disorders non-bruxers

To compare masticatory muscle thickness in patients with temporomandibular disorders (TMDs) during rest and clenching, and by body position, using ultrasonography. This prospective study included 96 patients with TMD (67 females, 29 males; mean age: 40.41 ± 17.88 years): group 1, comprising 66 patients with TMD without bruxism (TMD_nonbruxer), and group 2, comprising 30 patients with concurrent TMD and bruxism (TMD_bruxer). In patients with TMD, bruxism was correlated with the presence of tinnitus, muscle stiffness, sleep problems, psychological stress, and restricted mouth opening. The masseter muscle significantly thickened during clenching (11.16 ± 3.03 mm vs 14.04 ± 3.47 mm, p < 0.001), whereas the temporalis muscle showed no significant increase in thickness from resting to clenching in an upright position (7.91 ± 1.98 vs 8.39 ± 2.08, p = 0.103). Similarly, during clenching in the supine position, the masseter muscle was significantly thicker compared with rest (11.24 ± 2.42 vs 13.49 ± 3.09, p < 0.001), but no significant difference was observed in temporal muscle thickness (8.21 ± 2.16 vs 8.43 ± 1.94, p = 0.464). In comparison between two groups, the average thickness of the masseter muscle was greater among TMD_bruxers than among TMD_nonbruxers in both the upright and supine positions (all p < 0.05). In the generalized lineal model, female sex (B = - 1.018, 95% confidence interval [CI] - 1.855 to - 0.181, p = 0.017) and bruxism (B = 0.868, 95% CI 0.567 to 1.169, p = 0.048) significantly predicted changes in masseter muscle thickness. Female sex (B = - 0.201, 95% CI - 0.299 to - 0.103, p = 0.011), increased age (B = - 0.003, 95% CI - 0.005 to 0.000, p = 0.038), and muscle stiffness (B = - 1.373, 95% CI - 2.369 to - 0.376, p = 0.007) were linked to decreased temporal muscle thickness. Comparing TMD nonbruxer and bruxer muscle thicknesses in upright and supine positions revealed significant increased thickness in the masseter muscle during clenching but not in the temporalis muscle. Masseter muscle thickness varied significantly by sex, body position, and resting/clenching, notably influenced by bruxism. These findings emphasize the relevance of these factors in clinical examinations of patients with TMD.

Scapular muscle dynamic stiffness of asymptomatic subjects and subjects with chronic shoulder pain, at rest and isometric contraction conditions

Muscle stiffness had a crucial role in joint stability, particularly, at the shoulder complex. Although changes in upper trapezius muscle stiffness have been described for shoulder pain, contradictory findings have been obtained. Also, existing data regarding scapular muscles are, majorly, about trapezius. Myotonometry is a method used to assess stiffness; however, the reliability values of scapular muscle stiffness through this method have not been assessed in shoulder pain conditions. The present study aims to compare scapular muscles' stiffness (trapezius, serratus anterior, and levator scapulae) between subjects with and without chronic shoulder pain and to evaluate the related test-retest reliability. Twenty-two symptomatic and twenty-two asymptomatic subjects participated in a cross-sectional study. The dynamic muscular stiffness of scapular muscles, at rest and during an isometric contraction, was measured bilaterally with myotonometry, in two moments. The differences in bilateral averaged values between symptomatic and asymptomatic subjects and the effect of the group (group presenting pain in the dominant or non-dominant side, and asymptomatic group) and of the limb (unilateral painful or asymptomatic limb, and bilateral asymptomatic limbs) were investigated. Test-retest intra-rater reliability was determined. An effect of the group was observed at rest, for middle trapezius stiffness, and during contraction, for middle and lower trapezius stiffness. For middle trapezius, increased values were observed in the group presenting pain in non-dominant side comparing to both groups or to group presenting pain in dominant side. The intraclass correlation coefficient, majorly, ranged between 0.775 and 0.989. Participants with pain in the non-dominant side presented an increased middle trapezius' stiffness. Globally, high reliability was observed for scapular muscles dynamic stiffness.

Effects of Unilateral Eccentric versus Concentric Training of Nonimmobilized Arm during Immobilization

INTRODUCTION

The present study tested the hypothesis that eccentric training (ET) of nonimmobilized arm would attenuate negative effects of immobilization and provide greater protective effects against muscle damage induced by eccentric exercise after immobilization, when compared with concentric training (CT).

METHODS

Sedentary young men were placed to ET, CT, or control group ( n = 12 per group), and their nondominant arms were immobilized for 3 wk. During the immobilization period, the ET and CT groups performed five sets of six dumbbell curl eccentric-only and concentric-only contractions, respectively, at 20%-80% of maximal voluntary isometric contraction (MVCiso) strength over six sessions. MVCiso torque, root-mean square (RMS) of electromyographic activity during MVCiso, and bicep brachii muscle cross-sectional area (CSA) were measured before and after immobilization for both arms. All participants performed 30 eccentric contractions of the elbow flexors (30EC) by the immobilized arm after the cast was removed. Several indirect muscle damage markers were measured before, immediately after, and for 5 d after 30EC.

RESULTS

ET increased MVCiso (17% ± 7%), RMS (24% ± 8%), and CSA (9% ± 2%) greater ( P < 0.05) than CT (6% ± 4%, 9% ± 4%, 3% ± 2%) for the trained arm. The control group showed decreases in MVCiso (-17% ± 2%), RMS (-26% ± 6%), and CSA (-12% ± 3%) for the immobilized arm, but these changes were attenuated greater ( P < 0.05) by ET (3% ± 3%, -0.1% ± 2%, 0.1% ± 0.3%) than CT (-4% ± 2%, -4% ± 2%, -1.3% ± 0.4%). Changes in all muscle damage markers after 30EC were smaller ( P < 0.05) for the ET and CT than the control group, and ET than the CT group (e.g., peak plasma creatine kinase activity: ET, 860 ± 688 IU·L -1 ; CT, 2390 ± 1104 IU·L -1 ; control, 7819 ± 4011 IU·L -1 ).

CONCLUSIONS

These results showed that ET of the nonimmobilized arm was effective for eliminating the negative effects of immobilization and attenuating eccentric exercise-induced muscle damage after immobilization.

Muscle damage induced by maximal eccentric exercise of the elbow flexors after 3-week immobilization

The present study investigated the effects of a 3-week immobilization (IM) on muscle damage induced by maximal eccentric exercise (MaxEC) to test the hypothesis that the IM would make muscles prone to muscle damage. Young healthy sedentary men were pseudo-randomly assigned to IM or control group (n = 12/group). Non-dominant arms of the IM group participants were immobilized at 90° elbow flexion by a cast for 21 days. All participants performed MaxEC consisting of five sets of six elbow flexor contractions by lowering a dumbbell set at 100% of pre-exercise maximal voluntary isometric contraction (MVC) strength of the non-dominant arm. This was performed at 2 days after the cast removal for the IM group. MVC torque, range of motion (ROM), muscle thickness (MT), muscle hardness, position sense (PS), and joint reaction angle (JRA) of the elbow flexors were measured at baseline, post-immobilization, and before, immediately after, and one to 5 days after MaxEC. The IM decreased MVC torque (-17 ± 2%), ROM (-2 ± 1%), MT (-7 ± 3%), and JRA (-12 ± 6%), and increased in muscle hardness (20 ± 6%) and PS (11 ± 2%) (p < 0.05). Changes in MVC (e.g., 2 days: -40 ± 5 vs. -30 ± 9%), ROM (2 days: -11 ± 2 vs. -9 ± 3%), muscle soreness (peak: 63 ± 22 vs. 48 ± 14 mm), plasma CK activity (peak: 7820 ± 4011 vs. 4980 ± 1363 IU/L), PS (maximal change: -23 ± 2 vs. -18 ± 3%), and JRA (maximal change: -37 ± 4 vs. -26 ± 3%) after MaxEC were greater (p < 0.05) for the IM than control group. These results supported the hypothesis and showed that the IM made the muscles more vulnerable to muscle damage induced by eccentric exercise.

CARACTERÍSTICAS DEL TENDÓN ROTULIANO Y DE AQUILES EN JUGADORES SENIOR DE BÁDMINTON

Los objetivos del estudio fueron describir las propiedades estructurales y mecánicas de los tendones rotuliano y de Aquiles en jugadores senior (>35 años) de bádminton y detectar posibles asimetrías entre el lado dominante y no dominante. La muestra estuvo compuesta por 206 jugadores senior de bádminton (Edad: 52.2±9.6 años) que participaron en el campeonato de Europa Senior en 2018. Se evaluaron las propiedades estructurales (grosor, anchura y área de sección transversal) por medio de un ecógrafo Logiq® S8 y las propiedades mecánicas (elasticidad, tono, rigidez e índice de elastografía) con miotonometría y sonoelastografía de los tendones rotuliano y de Aquiles. Los resultados mostraron que fueron mayores el grosor (5.34±19.90%, p = 0.027) y la anchura (1.57±8.52%, p=0.036) en el tendón de Aquiles no dominante mientras que el tendón rotuliano dominante mostró unos valores mayores para el tono (2.09±12.96%, p=0.002) y para la rigidez (4.41±21.11%, p=0.002) respecto al no dominante.

Reliability of a New Indentometer Device for Measuring Myofascial Tissue Stiffness

Changes in tissue stiffness are associated with pathological conditions such as myofascial pain and increased risk of muscle injury. Furthermore, they have been shown to modify performance indicators such as running economy or jump height. Indentometry is an affordable way to assess tissue stiffness. However, to date, there is a paucity of studies examining the measurement properties of available devices. With this trial, we aimed to evaluate the reliability of the “IndentoPro”. Two investigators repeatedly measured the stiffness of the lateral head of the gastrocnemius muscle in healthy participants (N = 35), using 5 and 10 mm indentation depths. Intraclass Correlation Coefficients (ICC) revealed moderate inter-rater reliability (5 mm: ICC3,1 0.74, 95%CI = 0.54 to 0.86, p < 0.001; 10 mm: ICC3,1 0.59, 95%CI = 0.27 to 0.78, p < 0.001) and good intra-rater reliability (5 mm: ICC3,1 0.84, 95%CI = 0.71 to 0.92, p < 0.001; 10 mm: ICC3,1 0.83, 95%CI = 0.69 to 0.91, p < 0.001). No correlations between age, height, weight, BMI, skinfold thickness and myofascial tissue stiffness were observed (p > 0.5). In conclusion, the IndentoPro is reliable in assessing calf tissue stiffness, but the predictors of stiffness remain unclear.

The Biomechanics Effect of Hamstring Flexibility on the Risk of Osgood-Schlatter Disease

Background

The relationship between hamstring flexibility and the risk of OSD continues to be a debate, and whether hamstring stretching exercises should be considered as one of the conservative treatments of OSD is still unclear.

Objectives

To investigate the relationship between hamstring flexibility and the risk of OSD by assessing the changes of loading on the tibial tuberosity caused by the changes of hamstring optimal lengths.

Methods

Experimental data of a young adult running at 4 m/s were used, which were collected by an eight-camera motion capture system together with an instrumented treadmill. Muscle forces were estimated in OpenSim when hamstring optimal lengths changed in the range of 70–130% of the control case in 5% increments. The force and accumulated force of quadriceps muscle were calculated to evaluate the impact of hamstring optimal lengths on the loading on tibial tuberosity. The changes in muscle forces throughout the gait cycle were compared by using statistical parametric mapping (SPM). The average peak force and accumulated force of five gait cycles were compared.

Results

Although the maximum force of the quadriceps muscle was slightly affected by changes in hamstring optimal lengths, the accumulated force of quadriceps muscle increased by 21.97% with hamstring optimal lengths decreased by 30% of the control case. The increase of the muscle force mainly occurred in the early stance phase and terminal swing phase (P < 0.05). However, when hamstring optimal lengths were longer than the control, it had a little effect on accumulated force of quadriceps muscle.

Conclusions

The results of this study indicate that a shorter hamstring optimal length, which means lack of flexibility, can cause a high accumulated force on tibial tuberosity, thus increasing the risk of OSD. Hamstring stretching exercise is only effective for people with lack of hamstring flexibility.

Evaluation of Muscle Mass and Stiffness with Limb Ultrasound in COVID-19 Survivors

BACKGROUND

acute illnesses, like COVID-19, can act as a catabolic stimulus on muscles. So far, no study has evaluated muscle mass and quality through limb ultrasound in post-COVID-19 patients.

METHODS

cross sectional observational study, including patients seen one month after hospital discharge for SARS-CoV-2 pneumonia. The patients underwent a multidimensional evaluation. Moreover, we performed dominant medial gastrocnemius ultrasound (US) to characterize their muscle mass and quality.

RESULTS

two hundred fifty-nine individuals (median age 67, 59.8% males) were included in the study. COVID-19 survivors with reduced muscle strength had a lower muscle US thickness (1.6 versus 1.73 cm, p =0.02) and a higher muscle stiffness (87 versus 76.3, p = 0.004) compared to patients with normal muscle strength. Also, patients with reduced Short Physical Performance Battery (SPPB) scores had a lower muscle US thickness (1.3 versus 1.71 cm, p = 0.01) and a higher muscle stiffness (104.9 versus 81.07, p = 0.04) compared to individuals with normal SPPB scores. The finding of increased muscle stiffness was also confirmed in patients with a pathological value (≥ 4) at the sarcopenia screening tool SARC-F (103.0 versus 79.55, p < 0.001). Muscle stiffness emerged as a significant predictor of probable sarcopenia (adjusted OR 1.02, 95% C.I. 1.002 - 1.04, p = 0.03). The optimal ultrasound cut-offs for probable sarcopenia were 1.51 cm for muscle thickness (p= 0.017) and 73.95 for muscle stiffness (p = 0.004).

DISCUSSION

we described muscle ultrasound characteristics in post COVID-19 patients. Muscle ultrasound could be an innovative tool to assess muscle mass and quality in this population. Our preliminary findings need to be confirmed by future studies comparing muscle ultrasound with already validated techniques for measuring muscle mass and quality.

Impact of varying doses of omega-3 supplementation on muscle damage and recovery after eccentric resistance exercise

BACKGROUND

Exercise-induced muscle damage (EIMD) commonly occurs following intense resistance exercise and is associated with decrements in exercise performance and delayed muscle recovery. Thus, practical methods to attenuate EIMD would prove useful to both training and athletic populations. Omega-3 (n-3) supplementation has been shown to mitigate EIMD with evidence of increasing efficacy at higher doses (up to 6 g/day). However, data of its efficacy in trained individuals is limited. Therefore, this study investigated the effects of 6 and 8 g of n-3 supplementation on markers of muscle damage and muscle recovery after eccentric resistance exercise in resistance-trained males.

METHODS

Using a double-blind, randomized, placebo-controlled design, 26 resistance trained males (23 ± 4 years; 173.6 ± 20.5 cm; 81.9 ± 9.7 kg; 14.2 ± 3.7% body fat) supplemented with 6 (n=10) or 8 g (n=7) of n-3 polyunsaturated fatty acids, or placebo (n=9) for 33 days. On day 30, participants performed a lower body muscle-damaging eccentric resistance exercise bout. Measures of muscle performance, soreness, and damage were taken pre-exercise on day 30 as well as on days 31-33, including vertical jump height (VJH), perceived muscle soreness (PMS), hip and knee range of motion (ROM), repetitions to fatigue (RTF) at 70% 1-RM, and serum creatine kinase (CK) while participants continued to supplement until day 33.

RESULTS

There were significant differences in VJH, PMS, and serum CK following the muscle-damaging exercise bout compared to pre-exercise (p<0.05). However, there were no significant (p>0.05) differences between supplementation groups (6 g, 8 g, and placebo) at any time point post-exercise (day 31-33). There were no changes in hip and knee ROM or RTF at any time point or between groups. Vertical jump height and PMS returned to pre-exercise levels despite CK remaining elevated post-exercise.

CONCLUSIONS

Thirty-three days of 6 and 8 g of n-3 supplementation did not attenuate EIMD or enhance muscle recovery following muscle-damaging eccentric resistance exercise in resistance-trained males. Further research using various n-3 supplementation durations, doses, and eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) concentrations may be needed to establish its efficacy in attenuating EIMD, which may vary between trained and untrained individuals. Furthermore, while circulating CK is commonly used to assess muscle damage, elevated CK levels may not reflect muscle recovery status following muscle-damaging exercise.

Prediction and injury risk based on movement patterns and flexibility in a 6-month prospective study among physically active adults

Background

Physical activity has many health benefits but also carries a risk of injury. Some universal factors are connected with an increased risk regardless of the type of sport. Identifying these factors may help predict injuries and aid in their prevention.

Aim

The aim of this study is to determine the level of injury risk and the accuracy of injury prediction during a prospective 6-month period based on the quality of movement patterns and level of flexibility among average physically active young adults.

Material and Methods

A group of 123 young, physically active adults were recruited for this study. The International Physical Activity Questionnaire (IPAQ) was used to determine their level of physical activity. The author’s own Injury History Questionnaire (IHQ) was used to retrospectively collect injury data from the 12 months before the study and prospectively collect data during the six month observation period. The Functional Movement Screen (FMS) test was conducted to assess the movement patterns quality and a sit-and-reach test was conducted to measure lower back and hamstrings flexibility.

Results

Low-quaility movement patterns (14≥ FMS) increased the injury risk level sevenfold. A level of flexibility reduced by one cm increased the risk of injury by 6%. Previous injuries also increased the risk of injury reccurence 6.4 times. Predicting injury occurrence based on the quality of movement patterns allows for an accuracy of 73%, whereas flexibility allows for a 41% accuracy. The simultaneous use of these two factors did not improve injury prediction accuracy.

Conclusion

The risk of an injury increases with low-quality movement patterns, a low level of flexibility, and previous injuries. Preventative strategies should include shaping high-quality movement patterns, the right level of flexibility, and the full healing of injuries before resuming activities. The quality of movement patterns is an accurate predictor of injury risk, but lower back and hamstrings flexibility is not a reliable predictor of injury.

Effects of Eccentric Single-Leg Decline Squat Exercise on the Morphological and Structural Properties of the Vastus Lateralis and Patellar Tendon

The purpose was to examine the effect of 6-week eccentric single-leg decline squat (SLDSe) training with two technical execution times (3 s or 6 s) on changes related to the structural properties of the vastus lateralis (VL) and patellar tendon (PT). Thirty-six physical active volunteers were randomly divided into three groups: control group (CG, n = 13, age = 20.8 ± 1.9 years, no intervention program), experimental group 1 (EG1, n = 11, age = 21.6 ± 2.5 years, execution time = 6 s) and experimental group 2 (EG2, n = 12, 21.1 ± 1.2 years, execution time = 3 s). Participants completed a 6-week SLDSe training program (80% of 1-RM) three days a week. The structural characteristics of the VL and the PT were measured with ultrasonography before and after 6-week SLDSe training and after 6 weeks of de-training. Our results indicate that EG1 increased ≈21.8% the thickness of the PT and EG2 increased ≈15.7% the thickness of the VL after the 6-week intervention program. EG1 and EG2 showed greater values (p < 0.05) of lean mass and lower values (p < 0.05) of fat percentage on the thigh after the intervention program. In conclusion, the SLDSe training carried out with the execution time of 6 s had greater effects on the structural and elastic properties of the PT, and the exercise with the execution time of 3 s caused greater structural adaptations in the VL musculature.

Usability and Pitfalls of Shear-Wave Elastography for Evaluation of Muscle Quality and Its Potential in Assessing Sarcopenia: A Review

Sarcopenia is age-related progressive and generalized loss of skeletal muscle mass and strength. Its prevalence is rising, which poses a burden for society because it increases disability and dependency and therefore raises health care costs. Muscle mass quality, however-an essential part of sarcopenia-is not easily diagnosable yet. Recent interest has risen for ultrasonographic evaluation of muscle. This review introduces muscle elastography as a possible, easy and cheap tool to evaluate qualitative muscle parameters. Basic principles of muscle elastography are described, as well as different elastography techniques and some technical considerations. Furthermore, a proposal for practical guidelines is offered and factors influencing muscle stiffness are highlighted.

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Acute effects of training load on contractile properties during a competitive microcycle in elite soccer players

The aim of this study was to examine changes in muscle contractile properties across a microcycle of training in professional soccer players during the in-season period. Nineteen professional soccer players were assessed with tensiomyography (TMG) on the biceps femoris and rectus femoris before and after 5 training sessions of an in-season microcycle. Training load was quantified during each training session. Significant differences were observed in training load variables across different training sessions, with the last training session prior to match day showing the lowest values for all training load variables. Significant pre- to post-session increases were observed in muscle stiffness of the rectus femoris and biceps femoris during the first four training sessions (effect size range, 0.5 to 0.9). However, no significant differences were observed in muscle contraction time and contraction velocity from pre- to post-session. In addition, repeated measures correlation analysis revealed significant relationships between absolute change in muscle stiffness of the rectus femoris and training duration, high-speed distance covered during training, and training average distance. The current study shows that players are physically taxed on their muscular stiffness by the training load. Post-session muscular stiffness assessment should be recommended to determine neuromuscular status and readiness in professional soccer players during the competitive season.

Beneficial effects of a negative ion patch on eccentric exercise-induced muscle damage, inflammation, and exercise performance in badminton athletes

Complementary and alternative medicines (CAMs) are widely applied and accepted for therapeutic purposes because of their numerous benefits. Negative ion treatment belongs to one of the critical categories defined by the National Center for CAM, with such treatment capable of air purification and ameliorating emotional disorders (e.g., depression and seasonal affective disorder). Negative ions can be produced naturally and also by a material with activated energy. Exercise-induced muscle damage (EIMD) often occurs due to inadequate warm up, high-intensity exercise, overload, and inappropriate posture, especially for high-intensive competition. Few studies have investigated the effects of negative ion treatment on muscular injury in the sports science field. In the current study, we enrolled badminton athletes and induced muscle damage in them through eccentric exercise in the form of a high-intensity squat program. We evaluated the effects of negative ion patches of different intensities at three points (preexercise, postexercise, and recovery) by analyzing physiological indexes (tumor necrosis factor [TNF]-α, interleukin [IL]-6, IL-10, creatine kinase [CK], and lactate dehydrogenase [LDH] levels) and performing a functional assessment (a countermovement jump [CMJ] test). We found that a high-intensity negative ion patch could significantly reduce the levels of TNF-α, an injury-associated inflammatory cytokine, and related markers (CK and LDH). In addition, muscular overload-caused fatigue could be also ameliorated, as indicated by the functional CMJ test result, and related muscular characteristics (tone and stiffness) could be effectively improved. Thus, the negative ion treatment could effectively improve physiological adaption and muscular fatigue recovery after EIMD in the current study. The negative ion patch treatment can be further integrated into a taping system to synergistically fulfill exercise-induced damage protection and functional elevation. However, the effects of this treatment require further experimental validation.

Acute Effects of Constant-Angle and Constant-Torque Static Stretching on Passive Stiffness of the Posterior Hip and Thigh Muscles in Healthy, Young and Old Men

Palmer, TB. Acute effects of constant-angle and constant-torque static stretching on passive stiffness of the posterior hip and thigh muscles in healthy, young and old men. J Strength Cond Res 33(11): 2991-2999, 2019-The purpose of this study was to examine the acute effects of constant-angle (CA) and constant-torque (CT) static stretching on passive stiffness of the posterior hip and thigh muscles in healthy, young and old men. Fifteen young (25 ± 3 years) and 15 old (71 ± 4 years) men underwent 2 passive straight-leg raise (SLR) assessments before and after 8 minutes of CA and CT stretching using an isokinetic dynamometer. Passive stiffness was calculated during each SLR as the slope of the final 10% of the angle-torque curve. The results indicated that passive stiffness decreased from pre- to post-stretching for both treatments (p ≤ 0.001-0.002) and age groups (p ≤ 0.001-0.046); however, greater decreases were observed for the CT than the CA stretching (p = 0.045) and for the old than the young men (p < 0.001). In addition, baseline stiffness was greater for the old than the younger men (p = 0.010) and was also negatively related (r = -0.721; p < 0.001) to the changes in stiffness from pre- to post-stretching. These findings suggest that holding stretches at a constant tension may be a more effective strategy for altering passive stiffness of the posterior hip and thigh muscles. The greater stretch-induced stiffness decreases observed for the older men provide support that acute static stretching may be particularly effective for reducing stiffness in the elderly. As a result, it may be advantageous to prescribe static stretching before exercise for older adults, as this may be used to elicit substantial declines in passive stiffness, which could help reduce the risk of subsequent injury events in this population.

Feasibility of Ultrasound-Guided Trigger Point Injection in Patients with Myofascial Pain Syndrome

We compared the feasibility of ultrasound (US)-guided myofascial trigger point (MTrP) injection with that of a blind injection technique following the use of shear wave elastography (SWE) for the measurement of stiffness at the MTrPs in patients with trapezius myofascial pain syndrome (MPS). A total of 41 patients (n = 41) were randomized to either the trial group (n = 21, SWE combined with US-guided injection) or the control group (n = 20, SWE combined with blind injection). At baseline and four weeks, they were evaluated for the manual muscle test (MMT), the range of motion (ROM), pain visual analogue scale (VAS) scores, Shoulder Pain and Disability Index (SPADI) scores and Neck Disability Index (NDI) scores during the abduction, adduction, flexion, extension, external rotation and internal rotation of the shoulder joint. Differences in changes in pain VAS scores, NDI scores and SPADI scores at four weeks from baseline between the two groups reached statistical significance (p = 0.003, 0.012, and 0.018, respectively). US-guided MTrP injection is a more useful modality as compared with a blind injection in patients with MPS.

Passive Stiffness and Maximal and Explosive Strength Responses After an Acute Bout of Constant-Tension Stretching

CONTEXT

Constant-tension (CT) stretching has been used to reduce hamstrings passive stiffness; however, the time course of hamstrings stiffness responses during a short bout of this type of stretching and the effects on maximal and explosive strength remain unclear.

OBJECTIVE

To examine the time course of hamstrings passive-stiffness responses during a short, practical bout of manual straight-legged-raise (SLR) CT passive stretches and their effects on maximal and explosive strength in healthy young women.

DESIGN

Descriptive laboratory study.

SETTING

Research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Eleven healthy women (age = 24 ± 4 years, height = 167 ± 4 cm, mass = 65 ± 8 kg) participated.

INTERVENTION(S)

Participants underwent four 15-second SLR CT passive stretches of the hamstrings.

MAIN OUTCOME MEASUREMENT(S)

Hamstrings passive stiffness was calculated from the slopes of the initial (phase 1) and final (phase 2) portions of the angle-torque curves generated before and after the stretching intervention and at the beginning of each 15-second stretch. Hamstrings peak torque and rate of torque development were derived from maximal voluntary isometric contractions performed before and after the stretching intervention.

RESULTS

The slope coefficients (collapsed across phase) for the third and fourth stretches and the poststretching assessment were lower than the prestretching assessment (P range = .004-.04), but they were not different from each other (P > .99). In addition, no differences in peak torque (t₁₀ = -0.375, P = .72) or rate of torque development (t₁₀ = -0.423, P = .68) were observed between prestretching and poststretching.

CONCLUSIONS

A short bout of SLR CT passive stretching may effectively reduce hamstrings stiffness without negatively influencing maximal and explosive strength.

Eccentric Muscle Contractions: Risks and Benefits

Eccentric contractions, characterized by the lengthening of the muscle-tendon complex, present several unique features compared with other types of contractions, which may lead to unique adaptations. Due to its specific physiological and mechanical properties, there is an increasing interest in employing eccentric muscle work for rehabilitation and clinical purposes. However, unaccustomed eccentric exercise is known to cause muscle damage and delayed pain, commonly defined as “Delayed-Onset Muscular Soreness” (DOMS). To date, the most useful preventive strategy to avoid these adverse effects consists of repeating sessions involving submaximal eccentric contractions whose intensity is progressively increased over the training. Despite an increased number of investigations focusing on the eccentric contraction, a significant gap still remains in our understanding of the cellular and molecular mechanisms underlying the initial damage response and subsequent adaptations to eccentric exercise. Yet, unraveling the molecular basis of exercise-related muscle damage and soreness might help uncover the mechanistic basis of pathological conditions as myalgia or neuromuscular diseases. In addition, a better insight into the mechanisms governing eccentric training adaptations should provide invaluable information for designing therapeutic interventions and identifying potential therapeutic targets.

Reliability and validity of a semi-electronic tissue compliance meter to assess muscle stiffness

BACKGROUND

Most methods assessing soft tissue stiffness are associated with high costs and considerable technical effort. A previous study demonstrated that the tissue compliance meter represents an affordable alternative with straightforward handling. However, little data exists describing its measurement properties.

OBJECTIVE

The study aimed to elucidate the reliability and validity of a semi-electronic tissue compliance meter (STCM).

METHODS

Tissue stiffness at the lateral calf was examined in 34 healthy participants (24 ± 5 yrs, 21 men). Measurements on two consecutive days were used to estimate test-retest reliability, day-to-day reliability and inter-rater reliability. Validity was examined twofold. Firstly, STCM data were correlated with those of another method, the myotonometry. Secondly, STCM measurements at different levels of isometric contraction (M.gastrocnemius) were examined for systematic differences.

RESULTS

Intraclass correlations (ICC) revealed high test-retest reliability (ICC 0.84, 95% CI: 0.70 to 0.92; p< 0.05) and day-to-day reliability (0.84, 0.71 to 0.92; p< 0.05). Inter-rater reliability was sufficient to good (0.75, 0.56 to 0.87; p< 0.05). Cross-validation with myotonometry revealed a strong correlation of both methods (r= 0.86; p< 0.05). Stiffness assessments during isometric contraction demonstrated that the STCM can discriminate different force levels (χ2= 57.1, p< 0.05).

CONCLUSIONS

The STCM provides valid and reliable measurements of tissue stiffness. Further study is needed to provide norm values for different body regions and to reveal alterations in patients with musculoskeletal disorders.

Biomechanical response of skeletal muscle to eccentric contractions

The forced lengthening of an activated skeletal muscle has been termed an eccentric contraction (EC). This review highlights the mechanically unique nature of the EC and focuses on the specific disruption of proteins within the cell known as cytoskeletal proteins. The major intermediate filament cytoskeletal protein, desmin, has been the focus of work in this area because changes to desmin occur within minutes of ECs and because desmin has been shown to play both a mechanical and biologic role in a muscle's response to EC. It is hoped that these types of studies will assist in decreasing the incidence of muscle injury in athletes and facilitating the development of new therapies to treat muscle injuries.

Minimizing Injury and Maximizing Return to Play: Lessons from Engineered Ligaments

Musculoskeletal injuries account for more than 70% of time away from sports. One of the reasons for the high number of injuries and long return to play is that we have only a very basic understanding of how our training alters tendon and ligament (sinew) structure and function. Sinews are highly dense tissues that are difficult to characterize both in vivo and in vitro. Recently, engineered ligaments have been developed in vitro using cells from human anterior cruciate ligaments or hamstring tendons. These three-dimensional tissues can be grown in a laboratory, treated with agents thought to affect sinew physiology, and then mechanically tested to determine their function. Using these tissues, we have learned that sinews, like bone, quickly become refractory to an exercise stimulus, suggesting that short (<10 min) periods of activity with relatively long (6 h) periods of rest are best to train these tissues. The engineered sinews have also shown how estrogen decreases sinew function and that a factor released following intense exercise increases sinew collagen synthesis and function. Last, engineered sinews are being used to screen possible nutritional interventions that may benefit tendon or ligament function. Using the data derived from these tissue-engineered sinews, new nutritional and training regimes are being designed and tested with the goal of minimizing injury and accelerating return to play.

Effects of an acute bout of dynamic stretching on biomechanical properties of the gastrocnemius muscle determined by shear wave elastography

AIMS

The aim of this study was to examine the acute effects of dynamic stretching (DS) exercise on passive ankle range of motion (RoM), resting localized muscle stiffness, as measured by shear wave speed (SWS) of medial gastrocnemius muscle, fascicle strain, and thickness.

METHODS/RESULTS

Twenty-three participants performed a DS protocol. Before and after stretching, SWS was measured in the belly of the resting medial gastrocnemius muscle (MGM) using shear wave elastography. DS produced small improvements in maximum dorsiflexion (+1.5° ±1.5; mean difference ±90% confidence limits) and maximum plantarflexion (+2.3° ±1.8), a small decrease in fascicle strain (-2.6% ±4.4) and a small increase in SWS at neutral resting angle (+11.4% ±1.5). There was also a small increase in muscle thickness (+4.1mm ±2.0).

CONCLUSIONS

Through the use of elastography, this is the first study to suggest that DS increases muscle stiffness, decreases fascicle strain and increases muscle thickness as a result of improved RoM. These results can be beneficial to coaches, exercise and clinical scientists when choosing DS as a muscle conditioning or rehabilitation intervention.

The effects of flexibility training on exercise-induced muscle damage in young men with limited hamstrings flexibility

Adaptations to 6 weeks of supervised hamstring stretching training and its potential impact on symptoms of eccentric exercise-induced muscle damage (EIMD) were studied in 10 young, untrained men with limited hamstrings flexibility. Participants performed unilateral flexibility training (experimental leg; EL) on an isokinetic dynamometer, while the contralateral limb acted as control (CL). Hip range of motion (ROM), passive, isometric, and concentric torques, active optimum angle, and biceps femoris and semitendinosus muscle thickness and ultrasound echo intensity were assessed both before and after the training. Additionally, muscle soreness was assessed before and after an acute eccentric exercise bout in both legs (EL and CL) at post-training only. Hip ROM increased (P < .001) only in EL after the training (EL = 10.6° vs CL = 1.6°), but no changes (P > .05) in other criterion measurements were observed. After a bout of eccentric exercise at the end of the program, isometric and dynamic peak torques and muscle soreness ratings were significantly altered at all time points equally in EL and CL. Also, active optimum angle was reduced immediately, 48 and 72 hours post-exercise, and hip ROM was reduced at 48 and 72 hours equally in EL and CL. Finally, biceps femoris muscle thickness was significantly increased at all time points, and semitendinosus thickness and echo intensity significantly increased at 72 hours, with no significant differences between legs. The stretching training protocol significantly increased hip ROM; however, it did not induce a protective effect on EIMD in men with tight hamstrings.

Influence of Maturation Status on Eccentric Exercise-Induced Muscle Damage and the Repeated Bout Effect in Females

This study compared changes in indirect muscle damage markers, proprioception and arterial stiffness after elbow flexor eccentric exercise between pre-pubescent (9-10 y), pubescent (14-15 y), and post-pubescent (20-24 y) healthy, untrained females (n = 13/group). The maturation of the participants was confirmed by the hand bone age. All participants performed two bouts of 30 sub-maximal eccentric contractions (EC1, EC2) using a dumbbell set at 60% of pre-exercise maximal voluntary isometric elbow flexion strength at 90°. Changes in maximal voluntary concentric contraction (MVC) torque, muscle soreness (SOR), plasma creatine kinase activity, proprioception (position sense, joint reaction angle) and arterial stiffness (carotid-femoral pulse-wave velocity: cfPWV) before to 5 days after EC1 and EC2 were compared among groups by a mixed-design two-way ANOVA. Pre-exercise MVC torque and cfPWV were smaller (P < 0.05) for the pre-pubescent (MVC: 10.0 ± 0.9 Nm, cfPWV: 903 ± 60 cm/s) and the pubescent (14.3 ± 1.1 Nm, 967 ± 61 cm/s) than the post-pubescent (19.1 ± 1.4 Nm, 1,103 ± 73 cm/s). Changes in all variables after EC1 were smaller (P < 0.05) for the pre-pubescent (e.g., MVC at 1 d post-exercise: -10 ± 6%, peak SOR: 5 ± 2 mm) than the pubescent (-15 ± 9%, 12 ± 6 mm) and the post-pubescent (-25 ± 7%, 19 ± 13 mm). After EC2, changes in all variables were smaller (P < 0.05) than those after EC1 for all groups (e.g., MVC at 1 d post-exercise, pre-pubescent: -4 ± 6%, pubescent: -9 ± 4%, post-pubescent: -14 ± 5%; peak SOR: 3 ± 2, 7 ± 3, 11 ± 6 mm), but the magnitude of the repeated bout effect was not different (P > 0.05) among the groups. These results show that the extents of muscle damage, and proprioception and arterial stiffness changes after eccentric exercise are greater at later stages of maturation, but the repeated bout effect is not affected by maturation.

The effect of topical thiocolchicoside in preventing and reducing the increase of muscle tone, stiffness, and soreness: A real-life study on top-level road cyclists during stage competition

In professional road cyclists, the majority of overuse injuries affect the lower limbs and are mostly represented by contractures or muscle shortening, characterized by an increase of tone and stiffness and a variation of elasticity. Treatment and prevention of these specific conditions may include physical, supplementary, and pharmacologic support. The aim of this real-life study was to determine: first, the alterations of tone, stiffness, elasticity, and soreness of rectus femoris (RF) and biceps femoris (BF) in top class cyclists engaged in 3 multistage races, and second, whether any variable in the management of the athletes may affect the prevention and/or reduction of such alterations.Twenty-three professional cyclists competing in 3 international, cycling stage races were assessed. Athletes could receive, upon the approval of the medical staff, physical, dietary, and/or pharmacological management which could include treatments with topical over-the-counter myorelaxants to prevent and/or reduce muscle contractures. MyotonPro was used to daily measure tone, stiffness, and elasticity in RF and BF in relaxed and contracted state after every stage. In parallel, BF and RF soreness was also assessed with a Likert scale.All athletes received the same general massage management; none of them received dietary supplements; some of the athletes were treated with a topical myorelaxant thiocolchicoside (TCC 0.25%) foam 3 times daily. TCC was identified as the only variable able to affect these muscle parameters in the cyclists. Tone, stiffness (regardless of the state), and soreness significantly increased over time either in BF or RF in all athletes. In the group of athletes that used TCC (n = 11; TCC+) the increase in tone, stiffness, and soreness was significantly lower than in the group not receiving TCC (n = 12; No-TCC). Elasticity varied coherently with tone and stiffness.A very intense and protracted sport activity increases muscular tone, stiffness, and soreness over time. Topical TCC foam significantly attenuates these alterations and might represent an efficient strategy both to prevent and manage contractures and their consequences in professional cyclists as well in athletes from other disciplines involving similar workloads.

Flexibility training and the repeated-bout effect: priming interventions prior to eccentric training of the knee flexors

Both the repeated-bout effect and increased flexibility have been linked to reduced muscle damage, fatigue, and strength loss after intense eccentric exercise. Our purpose was to compare the eccentric-training (ECC) response after first priming the muscles with either static flexibility training or a single intense bout of eccentric exercise. Twenty-five participants were randomly assigned to flexibility training (n = 8; 3×/week; 30 min/day), a single bout of intense eccentric exercise (n = 9), or no intervention (control; n = 8) during a 4-week priming phase, prior to completing a subsequent 4-week period of eccentric training of the knee flexors. Testing was completed prior to the priming phase, before ECC, during acute ECC (0 h, 24 h, and 48 h after bouts 1 and 4), and after ECC. Measures included muscle thickness (MT; via ultrasound); isometric, concentric, and eccentric strength; muscle power (dynamometer); electromyography; range of motion; optimal angle of peak torque; and soreness (visual analog scale). Flexibility training and single-bout groups had 47% less soreness at 48 h after the first bout of ECC compared with control (p < 0.05). The flexibility training group had 10% less soreness at 48 h after the fourth ECC bout compared with both the single-bout and control groups (p < 0.05). Isometric strength loss was attenuated for the flexibility training group (-9%) after the fourth ECC bout compared with control (-19%; p < 0.05). All groups had similar increases in strength, MT, and power after ECC (p < 0.05). Prior flexibility training may be more effective than a single session of eccentric exercise in reducing adverse symptoms during the acute stages of eccentric training; however, these benefits did not translate into greater performance after training.

Effect of Extracorporeal Shock Wave Therapy on Hamstring Tightness in Healthy Subjects: A Pilot Study

PURPOSE

To assess the effect of extracorporeal shock wave therapy (ESWT) for healthy participants with hamstring tightness.

MATERIALS AND METHODS

This study was performed at a university rehabilitation hospital. Twenty nine healthy adults with hamstring tightness were enrolled and randomly allocated into four groups (ESWT, stretching exercise, ESWT with stretching exercise, and control). The effects of individual treatments were compared by the finger-to-floor test and popliteal angle.

RESULTS

The ESWT group, stretching exercise group and ESWT with stretching exercise group had decreased finger-to-floor distances and right popliteal angles immediately after intervention, compared with the control group (p<0.05). At 4 weeks after completion of the interventions, finger-to-floor distances and the right popliteal angle in only the ESWT with stretching exercise group showed a significant improvement, compared with the control group (p=0.008 and 0.023).

CONCLUSION

While ESWT and stretching both reduced hamstring tightness immediately after interventions, only ESWT with stretching exercise maintained the significantly improved relief of hamstring tightness significantly after 4 weeks.

Effects of a systemic enzyme therapy in healthy active adults after exhaustive eccentric exercise: a randomised, two-stage, double-blinded, placebo-controlled trial

Background

Systemic enzyme therapy may improve symptoms of exhaustive eccentric exercise due to anti-inflammatory properties.

Methods

In a randomised, placebo-controlled, two-stage clinical trial, systemic enzyme therapy (Wobenzym) was administered for 72 hours before and 72 hours following a day on which subjects performed an exhaustive eccentric exercise (isokinetic loading of the quadriceps). Efficacy criteria (maximal strength and pain) and time points were selected to account for the multidimensional nature of exercise-induced muscle damage symptoms. Subjects were randomised in a crossover (stage I, n=28) and parallel group design (stage II, n=44).

Results

Analysis of stage I data demonstrated a significant superiority (Mann-Whitney=0.6153; p=0.0332; one sided) for systemic enzyme therapy compared with placebo. Stage II was designed as a randomised controlled parallel group comparison. Heterogeneity (I²>0.5) between stages led to separate analyses of stage I (endurance-trained subjects) and stage II (strength-trained subjects). Combined analysis resulted in no evidence for corresponding treatment effects. Analysis of pooled biomarker data, however, demonstrated significant favourable effects for systemic enzyme therapy in both stages.

Conclusion

Systemic enzyme therapy before and after exhaustive eccentric exercise resulted in higher maximal concentric strength in the less strength-trained subjects (stage I) and in significant favourable effects on biomarkers (inflammatory, metabolic and immune) in all subjects. The application of these findings needs further evaluation.

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

PURPOSE

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

METHOD

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

RESULTS

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

CONCLUSION

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

Muscle Damage following Maximal Eccentric Knee Extensions in Males and Females

Aim

To investigate whether there is a sex difference in exercise induced muscle damage.

Materials and Method

Vastus Lateralis and patella tendon properties were measured in males and females using ultrasonography. During maximal voluntary eccentric knee extensions (12 reps x 6 sets), Vastus Lateralis fascicle lengthening and maximal voluntary eccentric knee extensions torque were recorded every 10° of knee joint angle (20–90°). Isometric torque, Creatine Kinase and muscle soreness were measured pre, post, 48, 96 and 168 hours post damage as markers of exercise induced muscle damage.

Results

Patella tendon stiffness and Vastus Lateralis fascicle lengthening were significantly higher in males compared to females (p<0.05). There was no sex difference in isometric torque loss and muscle soreness post exercise induced muscle damage (p>0.05). Creatine Kinase levels post exercise induced muscle damage were higher in males compared to females (p<0.05), and remained higher when maximal voluntary eccentric knee extension torque, relative to estimated quadriceps anatomical cross sectional area, was taken as a covariate (p<0.05).

Conclusion

Based on isometric torque loss, there is no sex difference in exercise induced muscle damage. The higher Creatine Kinase in males could not be explained by differences in maximal voluntary eccentric knee extension torque, Vastus Lateralis fascicle lengthening and patella tendon stiffness. Further research is required to understand the significant sex differences in Creatine Kinase levels following exercise induced muscle damage.

Effects of long-term self-massage at the musculotendinous junction on hamstring extensibility, stiffness, stretch tolerance, and structural indices: A randomized controlled trial

OBJECTIVES

The purpose of this study was to examine the effect of long-term self-massage at the musculotendinous junction on hamstring extensibility, stiffness, stretch tolerance, and structural indices.

DESIGN

Single-blind, randomized, controlled trial.

SETTING

Laboratory.

PARTICIPANTS

Thirty-seven healthy men.

INTERVENTION

The right or left leg of each participant was randomly assigned to the massage group, and the other leg was assigned to the control group. The participants conducted self-massage at the musculotendinous junction for 3 min daily, five times per week, for 12 weeks.

MAIN OUTCOME MEASURES

Hamstring extensibility, stiffness, stretch tolerance, and structural indices were measured by a blinded examiner prior to the massage intervention and after 6 and 12 weeks of intervention.

RESULTS

The maximum hip flexion angle (HFA) and the maximum passive pressure after 6 and 12 weeks of intervention in the massage group were significantly higher than prior to intervention. The visual analog scale (for pain perception) at maximum HFA, the stiffness of the hamstring, and the structural indices did not differ in either group over the 12 week period.

CONCLUSIONS

Our results suggest that long-term self-massage at the musculotendinous junction increases hamstring extensibility by improving stretch tolerance. However, this intervention does not change hamstring stiffness.

CLINICAL TRIAL REGISTRATION NUMBER

University Hospital Medical Information Network registration number UMIN000011233.

Chronic refractory myofascial pain and denervation supersensitivity as global public health disease

Chronic pain with a 30.3% global prevalence significantly impacts universal health. Low back pain has a 9.4% prevalence worldwide causing the most widespread disability. Neck pain ranks 4th highest regarding years lived with disability with a 4.9% prevalence worldwide. The principal cause of pain in 85% of patients visiting a tertiary pain clinic has a myofascial origin. The root cause is multifocal neuromuscular ischaemia at myofascial trigger points from muscle tightening and shortening following spondylotic radiculopathy induced partial denervation. Chronic refractory myofascial pain (CRMP) is a neuromusculoskeletal disease needing management innovations. Using electrical twitch-obtaining intramuscular stimulation (eToims), we provide objective evidence of denervation supersensitivity in multiple myotomes as cause, aggravation and maintenance of CRMP. This study underscores our previous findings that eToims is safe and efficacious for long-term use in CRMP. eToims aids potential prevention (pre-rehabilitation), simultaneous diagnosis, treatment (rehabilitation) and prognosis in real time for acute and CRMP management.

Attenuation of eccentric exercise-induced muscle damage conferred by maximal isometric contractions: a mini review

Although, beneficial in determined contexts, eccentric exercise-induced muscle damage (EIMD) might be unwanted during training regimens, competitions and daily activities. There are a vast number of studies investigating strategies to attenuate EIMD response after damaging exercise bouts. Many of them consist of performing exercises that induce EIMD, consuming supplements or using equipment that are not accessible for most people. It appears that performing maximal isometric contractions (ISOs) 2–4 days prior to damaging bouts promotes significant attenuation of EIMD symptoms that are not related to muscle function. It has been shown that the volume of ISOs, muscle length in which they are performed, and interval between them and the damaging bout influence the magnitude of this protection. In addition, it appears that this protection is not long-lived, lasting no longer than 4 days. Although no particular mechanisms for these adaptations were identified, professionals should consider applying this non-damaging stimulus before submitting their patients to unaccustomed exercised. However, it seems not to be the best option for athletes or relatively trained individuals. Future, studies should focus on establishing if ISOs protect other populations (i.e., trained individuals) or muscle groups (i.e., knee extensors) against EIMD, as well as investigate different mechanisms for ISO-induced protection.

Elastography Study of Hamstring Behaviors during Passive Stretching

INTRODUCTION

The mechanical properties of hamstring muscles are usually inferred from global passive torque/angle relationships, in combination with adjoining tissues crossing the joint investigated. Shear modulus measurement provides an estimate of changes in muscle-tendon stiffness and passive tension. This study aimed to assess the passive individual behavior of each hamstring muscle in different stretching positions using shear wave elastography.

METHODS/RESULTS

The muscle shear modulus of each hamstring muscle was measured during a standardized slow passive knee extension (PKE, 80% of maximal range of motion) on eighteen healthy male volunteers. Firstly, we assessed the reliability of the measurements. Results were good for semitendinosus (ST, CV: 8.9%-13.4%), semimembranosus (SM, CV: 10.3%-11.2%) and biceps femoris long-head (BF-lh, CV: 8.6%-13.3%), but not for biceps femoris short-head (BF-sh, CV: 20.3%-44.9%). Secondly, we investigated each reliable muscle in three stretch positions: 70°, 90° and 110° of hip flexion. The results showed different values of shear modulus for the same amount of perceived stretch, with the highest measurements in the high-flexed hip situation. Moreover, individual muscles displayed different values, with values increasing or BF-lh, SM and ST, respectively. The inter-subject variability was 35.3% for ST, 27.4% for SM and 30.2% for BF-lh.

CONCLUSION

This study showed that the hip needs to be high-flexed to efficiently tension the hamstrings, and reports a higher muscle-tendon stress tolerance at 110° of hip angle. In addition muscles have different passive behaviors, and future works will clarify if it can be linked with rate of injury.

Comparing passive angle-torque curves recorded simultaneously with a load cell versus an isokinetic dynamometer during dorsiflexion stretch tolerance assessments

The purpose of the present study was to compare the passive angle-torque curves and the passive stiffness (PS, N m °(-)(1)) values recorded simultaneously from a load cell versus an isokinetic dynamometer during dorsiflexion stretch tolerance assessments in vivo. Nine healthy men (mean ± SD age = 21.4 ± 1.6 years) completed stretch tolerance assessments on a custom-built apparatus where passive torque was measured simultaneously from an isokinetic dynamometer and a load cell. Passive torque values that corresponded with the last 10° of dorsiflexion, verified by surface electromyographic amplitude, were analyzed for each device (θ1, θ2, θ3, …, θ10). Passive torque values measured with the load cell were greater (p ≤ 0.05) than the dynamometer torque values for θ4 through θ10. There were more statistical differentiations among joint angles for passive torque measured by the load cell, and the load cell measured a greater (p ≤ 0.01) increase in passive torque and PS than the isokinetic dynamometer. These findings suggested that when examining the angle-torque curves from passive dorsiflexion stretch tolerance tests, a load cell placed under the distal end of the foot may be more sensitive than the torque recorded from an isokinetic dynamometer.

Effects of repetitive shoulder activity on the subacromial space in manual wheelchair users

This study investigated (1) the effect of repetitive weight-relief raises (WR) and shoulder external rotation (ER) on the acromiohumeral distance (AHD) among manual wheelchair users (MWUs) and (2) the relationship between shoulder pain, subject characteristics, and AHD changes. Twenty-three MWUs underwent ultrasound imaging of the nondominant shoulder in an unloaded baseline position and while holding a WR position before and after the WR/ER tasks. Paired t-tests and Spearman correlational analysis were used to assess differences in the AHD before and after each task and the relationships between pain, subject characteristics, and the AHD measures. A significant reduction in the subacromial space (P<0.01) occurred when subjects performed a WR position compared to baseline. Individuals with increased years of disability had greater AHD percentage narrowing after WR (P=0.008). Increased shoulder pain was associated with AHD percentage narrowing after ER (P≤0.007). The results support clinical practice guidelines that recommend MWUs limit WR to preserve shoulder function. The isolated repetitive shoulder activity did not contribute to the changes of subacromial space in MWUs. The ultrasonographic measurement of the AHD may be a target for identifying future interventions that prevent pain.

Lower hamstring extensibility in men compared to women is explained by differences in stretch tolerance

BACKGROUND

This study examined whether passive hamstring tissue stiffness and/or stretch tolerance explain the relationship between sex and hamstring extensibility.

METHODS

Ninety healthy participants, 45 men and 45 women (mean ± SD; age 24.6 ± 5.9 years, height 1.72 ± 0.09 m, weight 74.6 ± 14.1 kg) volunteered for this study. The instrumented straight leg raise was used to determine hamstring extensibility and allow measurement of stiffness and stretch tolerance (visual analog pain score, VAS).

RESULTS

Hamstring extensibility was 9.9° greater in women compared to men (p = 0.003). VAS scores were 16 mm lower in women (p = 0.001). Maximal stiffness (maximal applied torque) was not different between men and women (p = 0.42). Passive stiffness (slope from 20-50° hip flexion) was 0.09 Nm.°(-1) lower in women (p = 0.025). For women, linear and stepwise regression showed that no predictor variables were associated with hamstring extensibility (adjusted r(2) = -0.03, p = 0.61). For men, 44% of the variance in hamstring extensibility was explained by VAS and maximal applied torque (adjusted r(2) = 0.44, p < 0.001), with 41% of the model accounted for by the relationship between higher VAS scores and lower extensibility (standardized β coefficient = -0.64, p < 0.001).

CONCLUSIONS

The results of this study suggest that stretch tolerance and not passive stiffness explains hamstring extensibility, but this relationship is only manifest in men.

Relationship Between Head Position and the Muscle Hardness of the Masseter and Trapezius Muscles: A Pilot Study

The purpose of this study was to examine the hardness of the masseter and trapezius muscles at various head positions and to explore the relationship of these two muscles to each other in terms of their respective levels of muscle hardness at different head positions. Twenty-two asymptomatic male subjects participated in this study. Using a hand-held hardness meter, muscle hardness was first measured in a relaxed position as a baseline. The subjects were then asked to assume five deviated head positions, and the muscle hardness was measured again. The data obtained at each deviated head position were compared to those at baseline. In addition, the subjects were asked to maintain a five minute sustained anterior flexion of the head, and muscle hardness was also measured and compared to the baseline. As a result, there was a significant increase in muscle hardness at the point of the whole trapezius with 30-degree anterior flexion, while there was a significant decrease at the point of the right masseter. A significant increase in hardness was seen in the upper trapezius muscle in conjunction with right side bending and in the right upper trapezius muscle on left side bending. Also, a significant decrease in hardness was observed in the right masseter with right side bending. With reference to the axial rotation, there was a significant increase in hardness in the upper right trapezius muscle upon right axial rotation. Moreover, there was a significant increase in the muscle hardness in the whole trapezius after the five minute anteriorly sustained head task. This study provides evidence that deviated head positions lead to an increase in hardness of the trapezius muscle. The data also revealed the simultaneous occurrence of the elevation of muscle hardness in the upper trapezius muscle and the decrease in muscle hardness in the masseter muscle associated with right side bending and anterior flexion.