Contraction induced muscle injury: towards personalized training and recovery programs

VISUAL SENSOR-BASED OBSERVATION AND IMAGE ANALYSIS OF MUSCLE INJURIES IN ATHLETES

ABSTRACT Introduction: Athletes and fitness enthusiasts often suffer muscle injuries during their training. These injuries can worsen when not treated properly, generating an accumulation of severe tissue damage, preventing optimal physical performance, and impacting low immunity. Despite a large number of researches on muscle injuries, its vast majority is limited to the pathological perspective, and there are few studies related to the specific impact of the body sport muscle injury index. Objective: Analyze the body-specific indicators of sports injury to prevent further damage to its practitioners. Methods: Laser scanning confocal electron microscopy is the main observation tool in studying muscle injury in athletes. In further research, an experimental animal model was established. The test samples were 40 male rats over 12 weeks old, randomly divided into four groups, treadmill exercise, swimming at 8% of the weight, and other sports training items. Results: Through the comparative experiment of three indicators, it is found that muscle damage has a widespread impact on the whole body, particularly on blood serum indicators. The period of one hour after injury is considered to have the most impact. However, the symptoms subside after 24 hours. Conclusion: As the main observation tool in this experiment, the microscope showed its good prospect of application in the field of biomedicine. Level of evidence II; Therapeutic studies - investigation of treatment outcomes.

Preliminary Investigations Into the Effect of Exercise-Induced Muscle Damage on Systemic Extracellular Vesicle Release in Trained Younger and Older Men

Background: Exercise-induced muscle damage (EIMD) results in transient muscle inflammation, strength loss, and muscle soreness and may cause subsequent exercise avoidance. Research has recently proven that skeletal muscle can also release extracellular vesicles (EVs) into the circulation following a bout of exercise. However, EV’s potential role, including as a biomarker, in the response to eccentric resistance exercise stimulus remains unclear.

Methods: Twelve (younger, n=7, 27.0±1.5years and older, n=5, 63.0±1.0years) healthy, physically active males, undertaking moderate, regular physical activity (3–5 times per week) performed a unilateral high intensity eccentric exercise protocol. Venous plasma was collected for assessment of EVs and creatine kinase (CK) prior to EIMD, immediately after EIMD, and 1–72h post-EIMD, and maximal voluntary isometric contraction (MVIC) and delayed onset muscle soreness (DOMS) were assessed at all time points, except 1 and 2h post-EIMD.

Results: A significant effect of both time (p=0.005) and group (p<0.001) was noted for MVIC, with younger participants’ MVIC being higher throughout. Whilst a significant increase was observed in DOMS in the younger group (p=0.014) and in the older group (p=0.034) following EIMD, no significant differences were observed between groups. CK was not different between age groups but was altered following the EIMD (main effect of time p=0.026), with increased CK seen immediately post-, at 1 and 2h post-EIMD. EV count tended to be lower in older participants at rest, relative to younger participants (p=0.056), whilst EV modal size did not differ between younger and older participants pre-EIMD. EIMD did not substantially alter EV modal size or EV count in younger or older participants; however, the alteration in EV concentration (ΔCount) and EV modal size (ΔMode) between post-EIMD and pre-EIMD negatively associated with CK activity. No significant associations were noted between MVIC or DOMS and either ΔCount or ΔMode of EVs at any time point.

Conclusion: These findings suggest that profile of EV release, immediately following exercise, may predict later CK release and play a role in the EIMD response. Exercise-induced EV release profiles may therefore serve as an indicator for subsequent muscle damage.

Perception of musculoskeletal pain in the state of confinement: associated factors

OBJECTIVE

to describe the perception of musculoskeletal pain in the population and how the state of confinement (adopted as a measure to control contagion by COVID-19) has interfered with it, as well as identifying the sociodemographic, occupational, physical, and psychosocial factors involved.

METHOD

an observational, cross-sectional and analytical study, with simple random probabilistic sampling, aimed at residents in Spain over 18 years old during the confinement period. An ad hoc survey was conducted, consisting in 59 items.

RESULTS

a total of 3,247 surveys were answered. Persistent musculoskeletal pain or significant episodes thereof increased 22.2% during confinement. The main location was the spine (49.5%). The related factors were decreased physical activity, increased seated position, and use of electronic devices. The psychological impact of confinement was also related to the perception of musculoskeletal pain.

CONCLUSION

the state of confinement causes an increase in the perception of musculoskeletal pain. The identification of a particularly sensitive population profile, as well as that of the related factors, allows establishing multidisciplinary approaches in health promotion.

Theoretical elastic tensile behavior of muscle fiber bundles in traumatic loading events

BACKGROUND

The mechanical characterization of skeletal muscle under high-rate loading regimes is important for predicting traumatic injuries due to traffic accidents and contact sports. However, it is difficult to perform dynamic mechanical tests at rates relevant to such rapid loading events.

METHODS

In the present study, a series of stress relaxation tests were conducted on rabbit hind-limb muscle fiber bundles using a custom tensile tester. Using relatively moderate loading conditions compared to those typically associated with traumatic injuries, the passive stress-decaying mechanical properties of muscle fiber bundles were characterized. In addition, stress relaxation responses to various ramp-hold stretches were theoretically predicted by a custom-built code.

FINDINGS

The results showed that the muscle fiber bundles exhibit greater stress relaxation at higher loading rates and greater stretch magnitudes. Based on these results, the data points representing the "elastic" stress-strain tensile behavior typical of traumatic injury were extrapolated using curve fitting. The theoretical model revealed rate-dependent characteristics of the muscle fiber bundles under traumatic loading conditions, which would result in tensile strengths of 300-500 kPa at the maximum engineering strain of 54%. This strength is on the order of magnitude as the maximum isometric stress of an active muscle contraction.

INTERPRETATION

The proposed numerical model is expected to serve as a powerful research tool to investigate injury mechanisms of the skeletal muscle. Moreover, the elastic response that was theoretically predicted here will be useful in the development of effective countermeasures to prevent traumatic injuries due to rapid loading events.

Insights into the molecular etiology of exercise-induced inflammation: opportunities for optimizing performance

The study of exercise-induced muscle damage (EIMD) is of paramount importance not only because it affects athletic performance but also because it is an excellent model to study the mechanisms governing muscle cachexia under various clinical conditions. Although, a large number of studies have investigated EIMD and its associated inflammatory response, several aspects of skeletal muscles responses remain unclear. In the first section of this article, the mechanisms of EIMD are reviewed in an attempt to follow the events that result in functional and structural alterations of skeletal muscle. In the second section, the inflammatory response associated with EIMD is presented with emphasis in leukocyte accumulation through mechanisms that are largely coordinated by pro- and anti-inflammatory cytokines released either by injured muscle itself or other cells. The practical applications of EIMD and the subsequent inflammatory response are discussed with respect to athletic performance. Specifically, the mechanisms leading to performance deterioration and development of muscle soreness are discussed. Emphasis is given to the factors affecting individual responses to EIMD and the resulting interindividual variability to this phenomenon.