Skeletal Muscle Damage Produced by Electrically Evoked Muscle Contractions

The effect of neuromuscular electrical stimulation applied at different muscle lengths on muscle architecture and sarcomere morphology in rats

Neuromuscular electrical stimulation (NMES) is often used to increase muscle strength and functionality. Muscle architecture is important for the skeletal muscle functionality. The aim of this study was to investigate the effects of NMES applied at different muscle lengths on skeletal muscle architecture. Twenty-four rats were randomly assigned to four groups (two NMES groups and two control groups). NMES was applied on the extensor digitorum longus muscle at long muscle length, which is the longest and stretched position of the muscle at 170° plantar flexion, and at medium muscle length, which is the length of the muscle at 90° plantar flexion. A control group was created for each NMES group. NMES was applied for 8 weeks, 10 min/day, 3 days/week. After 8 weeks, muscle samples were removed at the NMES intervention lengths and examined macroscopically, and microscopically using a transmission electron microscope and streo-microscope. Muscle damage, and architectural properties of the muscle including pennation angle, fibre length, muscle length, muscle mass, physiological cross-sectional area, fibre length/muscle length, sarcomere length, sarcomere number were then evaluated. There was an increase in fibre length and sarcomere number, and a decrease in pennation angle at both lengths. In the long muscle length group, muscle length was increased, but widespread muscle damage was observed. These results suggest that the intervention of NMES at long muscle length can increase the muscle length but also causes muscle damage. In addition, the greater longitudinal increase in muscle length may be a result of the continuous degeneration-regeneration cycle.

Effectiveness of neuromuscular electrical stimulation training combined with exercise on patient-reported outcomes measures in people with knee osteoarthritis: A systematic review and meta-analysis

OBJECTIVE

This study examined the effectiveness of neuromuscular electrical stimulation (NMES) added to the exercise or superimposed on voluntary contractions on patient-reported outcomes measures (PROMs) in people with knee osteoarthritis (OA).

METHODS

This systematic review was described according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Randomized controlled trials (RCTs) were obtained from a systematic literature search in five electronic databases (PubMed, PEDro, LILACS, EMBASE, and SPORTDiscus) in April 2022. We described the effects of intervention according to each PROMs (scores for Pain; Self-reported functional ability; Symptoms (hear clicking, swelling, catching, restricted range of motion, and stiffness); Daily living function; Sports function; and Quality of life) and used a random-effect model to examine the impact of NMES plus exercise on pain compared with exercise in people with knee OA.

RESULTS

Six RCTs (n = 367) were included. In the qualitative synthesis, the systematic literature analysis showed improvement in pain after NMES plus exercise compared with exercise alone in three studies. The other three studies revealed no difference between groups in pain, although similar improvement after treatments. In the meta-analysis, NMES at a specific joint angle combined with exercise was not superior to exercise alone in pain management (standardized mean difference = -0.33, 95% CI = -1.05 to 0.39, p = 0.37). There was no additional effect of NMES on exercise on self-reported functional ability, stiffness, and physical function compared with exercise alone. In only one study, symptoms, activities of daily living, sports function, and quality of life improved after whole-body electrostimulation combined with exercise.

CONCLUSION

This review found insufficient evidence for the effectiveness of NMES combined with exercise in treating knee OA considering PROMs. While pain relief was observed in some studies, more high-quality clinical trials are needed to support the use of NMES added to the exercise in clinical practice. Electrical stimulation in a whole-body configuration combined with exercise shows promise as an alternative treatment option.

Influence of sexual dimorphism on satellite cell regulation and inflammatory response during skeletal muscle regeneration

After injury, skeletal muscle regenerates thanks to the key role of satellite cells (SC). The regeneration process is supported and coordinated by other cell types among which immune cells. Among the mechanisms involved in skeletal muscle regeneration, a sexual dimorphism, involving sex hormones and more particularly estrogens, has been suggested. However, the role of sexual dimorphism on skeletal muscle regeneration is not fully understood, likely to the use of various experimental settings in both animals and human. This review aims at addressing how sex and estrogens regulate both the SC and the inflammatory response during skeletal muscle regeneration by considering the different experimental designs used in both animal models (i.e., ovarian hormone deficiency, estrogen replacement or supplementation, treatments with estrogen receptors agonists/antagonists and models knockout for estrogen receptors) and human (hormone therapy replacement, pre vs. postmenopausal, menstrual cycle variation…).

Exercise builds the scaffold of life: muscle extracellular matrix biomarker responses to physical activity, inactivity, and aging

Skeletal muscle extracellular matrix (ECM) is critical for muscle force production and the regulation of important physiological processes during growth, regeneration, and remodelling. ECM remodelling is a tightly orchestrated process, sensitive to multi-directional tensile and compressive stresses and damaging stimuli, and its assessment can convey important information on rehabilitation effectiveness, injury, and disease. Despite its profound importance, ECM biomarkers are underused in studies examining the effects of exercise, disuse, or aging on muscle function, growth, and structure. This review examines patterns of short- and long-term changes in the synthesis and concentrations of ECM markers in biofluids and tissues, which may be useful for describing the time course of ECM remodelling following physical activity and disuse. Forces imposed on the ECM during physical activity critically affect cell signalling while disuse causes non-optimal adaptations, including connective tissue proliferation. The goal of this review is to inform researchers, and rehabilitation, medical, and exercise practitioners better about the role of ECM biomarkers in research and clinical environments to accelerate the development of targeted physical activity treatments, improve ECM status assessment, and enhance function in aging, injury, and disease.

Does increasing the number of channels during neuromuscular electrical stimulation reduce fatigability and produce larger contractions with less discomfort?

PURPOSE

Neuromuscular electrical stimulation (NMES) is often delivered at frequencies that recruit motor units (MUs) at unphysiologically high rates, leading to contraction fatigability. Rotating NMES pulses between multiple electrodes recruits subpopulations of MUs from each site, reducing MU firing rates and fatigability. This study was designed to determine whether rotating pulses between an increasing number of stimulation channels (cathodes) reduces contraction fatigability and increases the ability to generate torque during NMES. A secondary outcome was perceived discomfort.

METHODS

Fifteen neurologically intact volunteers completed four sessions. NMES was delivered over the quadriceps through 1 (NMES₁), 2 (NMES₂), 4 (NMES₄) or 8 (NMES₈) channels. Fatigability was assessed over 100 contractions (1-s on/1-s off) at an initial contraction amplitude that was 20% of a maximal voluntary contraction. Torque-frequency relationships were characterized over six frequencies from 20 to 120 Hz.

RESULTS

NMES₄ and NMES₈ resulted in less decline in peak torque (42 and 41%) over the 100 contractions than NMES₁ and NMES₂ (53 and 50% decline). Increasing frequency from 20 to 120 Hz increased torque by 7, 13, 21 and 24% MVC, for NMES₁, NMES₂, NMES₄ and NMES₈, respectively. Perceived discomfort was highest during NMES₈.

CONCLUSION

NMES₄ and NMES₈ reduced contraction fatigability and generated larger contractions across a range of frequencies than NMES₁ and NMES₂. NMES₈ produced the most discomfort, likely due to small electrodes and high current density. During NMES, more is not better and rotating pulses between four channels may be optimal to reduce contraction fatigability and produce larger contractions with minimal discomfort compared to conventional NMES configurations.