Effects of foam rolling on hamstrings stiffness in damaged and non-damaged muscle states.

Introduction: The aim of this study was to examine the effects of foam rolling (FR) on hamstring muscles stiffness in both non-damaged and exercise-induced muscle damage (EIMD) states, using shear wave ultrasound elastography to measure changes in shear modulus. Methods: Fourteen healthy adults (25.5 ± 4.7 years) participated in a within-participant repeated measures design, with a 2-minute FR intervention applied on one leg and contralateral leg serving as a control. The damaging protocol encompassed maximal eccentric knee extensions performed on an isokinetic dynamometer and the Nordic hamstring exercise, consisting of 3 sets of 10 and 6 repetitions, respectively. Measurement were taken at baseline and then 1 h, 24 h and 48 h after the damaging protocol. Results: The results indicated no significant time × leg interaction for shear modulus in biceps femoris, semimembranosus, and semitendinosus muscles in both non-damaged and damaged states. Notably, there was a significant increase in biceps femoris (p = 0.001; η2 = 0.36) and semitendinosus (p < 0.001; η2 = 0.44) shear modulus after EIMD, but no significant differences were found between the FR and control leg, which was also the case for muscle soreness, range of motion, and passive resistive torque (p = 0.239-0.999 for interactions). Discussion: The absence of significant changes post-FR intervention suggests a limited role of short-duration FR in altering muscle stiffness during recovery from EIMD. These findings contribute to the understanding of FR's role in muscle recovery. Although this was not directly investigated, our results suggest a predominance of central mechanisms rather than direct mechanical modifications in muscle properties. This research highlights the necessity for additional investigations to explore how FR interventions influence muscles in different states and to elucidate the mechanisms underlying these influences.

Changes of trunk muscle stiffness in individuals with low back pain: a systematic review with meta-analysis.

BACKGROUND: Low back pain (LBP) is one of the most common musculoskeletal conditions. People with LBP often display changes of neuromuscular control and trunk mechanical properties, including trunk stiffness. Although a few individual studies have examined back muscle stiffness in individuals with LBP, a synthesis of the evidence appears to be lacking. Therefore, the aim of this systematic review with meta-analysis was to synthesize and evaluate the available literature investigating back muscle stiffness in association with LBP. METHODS: We conducted a systematic review of the literature according to the PRISMA guidelines. We searched Pubmed, Scopus, Web of Science and ScienceDirect for studies, that compared back muscle stiffness, measured either by ultrasound-based elastography or myotonometry, between individuals with and without LBP. Pooled data of the included studies were presented descriptively. Additionally, we performed two meta-analyses to calculate the standardized mean difference between the two groups for resting stiffness of the multifidus and erector spinae muscle. For both meta-analyses, the random effect model was used and the weight of individual studies was calculated using the inverse-variance method. The quality of the included studies was assessed using the Joanna Briggs Institute Critical Appraisal Checklist for Analytical Cross-Sectional studies. Furthermore, the certainty of evidence was evaluated using the GRADE approach. RESULTS: Nine studies were included in our systematic review. Our results suggest that individuals with LBP have higher stiffness of the multifidus (SMD = 0.48, 95% CI: 0.15 - 0.81, p < 0.01; I2 = 48 %, p = 0.11) and erector spinae at rest (SMD = 0.37, 95% CI: 0.11 - 0.62, p < 0.01; I2 = 39 %, p = 0.14) compared to asymptomatic controls. On the other hand, the evidence regarding muscle stiffness during submaximal contractions is somewhat contradictory. CONCLUSIONS: Based on the findings of this systematic review we conclude that people with LBP may have higher back muscle stiffness compared to asymptomatic controls. Addressing muscle stiffness might represent an important goal of LBP treatment. Nevertheless, our findings should be interpreted with extreme caution due to a limited quality of evidence, small number of included studies and differences in measurement methodology.

The Effects of Isometric Fatigue on Trunk Muscle Stiffness: Implications for Shear-Wave Elastography Measurements.

Muscle stiffness has been implicated as a possible factor in low back pain risk. There are few studies on the effects of isometric fatigue on the shear modulus of trunk muscles. This study aimed to investigate the effects of trunk isometric fatigue on the passive and active (during low and high-level contractions) shear moduli of the erector spinae (ES) and superficial and deep multifidus (MF) muscles. We assessed passive and active shear modulus using shear-wave elastography in healthy young participants (n = 22; 11 males, 11 females), before and after an isometric trunk extension fatigue protocol. Maximal voluntary force decreased from 771.2 ± 249.8 N before fatigue to 707.3 ± 204.1 N after fatigue (-8.64%; p = 0.003). Passive shear modulus was significantly decreased after fatigue in the MF muscle (p = 0.006-0.022; Cohen's d = 0.40-46), but not the ES muscle (p = 0.867). Active shear modulus during low-level contraction was not affected by fatigue (p = 0.697-0.701), while it was decreased during high-level contraction for both muscles (p = 0.011; d = 0.29-0.34). Sex-specific analysis indicated the decrease in ES shear modulus was significant in males (p = 0.015; d = 0.31), but not in females (p = 0.140). Conversely, the shear modulus in superficial MF had a statistically significant decrease in females (p = 0.002; d = 0.74) but not in males (p = 0.368). These results have important implications for further investigations of the mechanistic interaction between physical workloads, sex, muscle stiffness (and other variables affecting trunk stability and neuromuscular control), and the development/persistence of low back pain.

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

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

Effects of Nordic hamstring exercise combined with glider exercise on hip flexion flexibility and hamstring passive stiffness.

Eccentric training proved to be effective in hamstring injury prevention; however, little is known about effects of eccentric hamstring training at long muscle length on hamstring flexibility. Hence, the aim was to evaluate the effect of eccentric training at long muscle lengths on flexibility and passive properties of the hamstring muscles. 34 physically active young adults were randomized to either the control or intervention group (6 weeks of eccentric hamstring training at long muscle length; control group resumed with their usual activities). Maximal passive hip flexion range of motion (ROM), passive hamstring stiffness, shear modulus and tendon length of the biceps femoris long head (BFlh) were measured pre- and post-intervention. A significant time × group effect was observed for maximal passive hip ROM. Post-hoc testing revealed a significant increase in the intervention group (+11.2%; p < 0.001; d = 1.55). Additionally, a significant time effect was shown for shear modulus in a relaxed position (p < 0.001). No significant interaction was shown for other parameters. Results indicate that eccentric hamstring training at long muscle length elicits large gains in hamstring flexibility, which are most likely not related to changes in passive hamstring stiffness or BFlh distal tendon length.

Effects of eccentric training at long-muscle length on architectural and functional characteristics of the hamstrings.

Hamstring strain injuries during sprinting or stretching frequently occur at long-muscle length. Yet, previous research has mainly focused on studying the effectiveness of eccentric hamstring strengthening at shorter muscle length on hamstring performance, morphology, and hamstring strain injury risk factors. Here, we evaluated the effects of 6-week eccentric hamstring training at long-muscle length on functional and architectural characteristics of the hamstrings. Healthy and injury-free participants (n = 40; age 23.7 ± 2.5 years) were randomly assigned to control or intervention group. Training intervention consisted of 12 sessions with two eccentric hamstring exercises in a lengthened position. Outcome measures included isokinetic and isometric knee flexion peak torque, Nordic hamstring exercise peak torque, voluntary activation level, and countermovement jump performance. Ultrasonography was used to determine muscle thickness, pennation angle, and fascicle length of biceps femoris long head (BFlh). A significant time × group interaction effect was observed for all measured parameters except countermovement jump performance and muscle thickness. The training intervention resulted in increased concentric and eccentric knee flexion peak torque at 60°/s (d = 0.55-0.62, P = .02 and .03) and concentric peak torque at 180°/s (d = 0.99, P = .001), increased isometric knee flexion peak torque (d = 0.73, P = .008) and Nordic hamstring exercise peak torque (d = 1.19, P < .001), increased voluntary activation level (d = 1.29, P < .001), decreased pennation angle (d = 1.31, P < .001), and increased fascicle length (d = 1.12, P < .001) of BFlh. These results provide evidence that short-term eccentric hamstring strengthening at long-muscle length can have significant favorable effects on various architectural and functional characteristics of the hamstrings.

Exercise interventions to prevent hamstring injuries in athletes: A systematic review and meta-analysis.

The aim of this meta-analysis was to assess the effectiveness of exercise-based interventions for prevention of hamstring injuries in sport. PubMed, Cochrane Central Register of Controlled Trials, Web of Science, ResearchGate, CINAHL, PEDro, ScienceDirect and Google Scholar databases were searched for randomized controlled trials and prospective cohort studies exploring the effects of exercise interventions on hamstring injury incidence. Subgroup analyses were performed to determine effects of several independent variables related to the interventions. Altogether, 17 studies were included. Exercise interventions decreased hamstring injury risk (RR = 0.49; 95%CI = 0.40-0.59; p < 0.001). There were similar effects found for interventions performed ≤2 times per week (RR = 0.35; 95%CI = 0.15-0.82) and the interventions performed >2 times per week (RR = 0.44; 95%CI = 0.31-0.61). Similarly, there were similar effects found for the interventions with progressive increase in load (RR = 0.53; 95%CI = 0.37-0.74) and the interventions with constant loads (RR = 0.46; 95%CI = 0.36-0.58). Other subgroup analyses (intervention supervision, sport type, inclusion of Nordic hamstring exercise and type of the trial) also showed no indications on specific characteristics of the interventions, that increase the preventive effects. Our findings showed that hamstring injury incidence can be decreased with exercise-based interventions, and that weekly frequency and load progression are not among the most important variables to consider in prevention programmes design.