Mechanic stress generated by a time-varying electromagnetic field on bone surface

Effects of physical exercise on bone mineral density in older postmenopausal women: a systematic review and meta-analysis of randomized controlled trials

Osteoporosis or decreased bone mineral density (BMD) is the most important risk factor for fractures, especially in older postmenopausal women (PMW). However, the interactions between exercise training and bone mineral density are not completely understood. We evaluated the effects of physical exercise on BMD in women aged ≥ 60 years postmenopausal.

PURPOSE

This systematic review and meta-analysis sets out to determine the effects of physical exercise on BMD in older postmenopausal women.

METHODS

A systematic search was conducted in Medline, Science Direct, Cochrane, PubMed, CINAHL, Google Scholar, Scopus, and ProQuest up to December 25, 2021. Fifty-three studies, which assessed a total of 2896 participants (mean age: between 60 and 82 years), were included and analyzed using a random-effects model to estimate weighted mean differences (WMD) with 95% confidence intervals (CI).

RESULTS

The meta-analysis found that exercise training significantly (p < 0.05) increased femoral neck (WMD: 0.01 g/cm²; 95% CI, 0.00 to 0.01], p = 0.0005; I² = 57%; p < 0.0001), lumbar spine (WMD: 0.01 g/cm², 95% CI, 0.01 to 0.02], I² = 81%; p = 0.0001), and trochanter (WMD: 0.01 g/cm², 95% CI 0.00, 0.02]; p = 0.009; I² = 17%; p = 0.23). There were no significant differences between the intervention and control groups for total body and total hip BMD.

CONCLUSION

Our findings suggest that exercise training may improve bone mineral density in older PMW. This improvement is mediated by increases in the femoral neck, lumbar spine, and trochanter BMD. Further long-term studies are required to confirm these findings.

EFFECT OF LOW-FREQUENCY ELECTROMAGNETICS (LFE) ON MUSCLE SATELLITE CELLS DIFFERENTIATION AND IMMUNE SYSTEM IN RAT

Spinal cord injury (SCI) is a severe neurological disease. Although surgery within 8[Formula: see text]h after SCI can substantially reduce paraplegia, most patients still suffer from hypomusculariasis after neuron recovery, which results in insufficient lower limb muscles to support bodyweight. Currently, there is no effective method to prevent muscle atrophy. Previous studies have shown that low-frequency electromagnetics (LFE) can stimulate the differentiation, proliferation and fusion of muscle satellite cells, however, the optimal electromagnetic strength and effects on the immune system have not been established. Here, we investigated the influence of LFE at different electromagnetic strengths on muscle cell recovery and assessed the impact of chronic LFE on the immune system of SCI rats. The rat immune system was rapidly activated after SCI. High-energy LFE provoked intensive immune responses, while low-energy LFE did not affect immune responses. Simultaneously, LFE effectively prevented myotube reduction and atrophy in SCI rats. The mRNA and protein levels of Pax7 and MyoD were increased after LFE at both high and low electromagnetic strengths, with the latter leading to more robust increases. Indeed, LFE remarkably induced muscle cell fusion. Together, our results demonstrated that LFE activates muscle satellite cells via stimulating myogenic factors. Chronic low-energy LFE is a safe therapy with no adverse impact on the immune system of SCI rats. LFE with 1.5 mT energy should be considered as an optimal therapeutic strategy.

Role of Physical Activity in Bone-Muscle Crosstalk: Biological Aspects and Clinical Implications

Bone and muscle tissues influence each other through the integration of mechanical and biochemical signals, giving rise to bone-muscle crosstalk. They are also known to secrete osteokines, myokines, and cytokines into the circulation, influencing the biological and pathological activities in local and distant organs and cells. In this regard, even osteoporosis and sarcopenia, which were initially thought to be two independent diseases, have recently been defined under the term "osteosarcopenia", to indicate a synergistic condition of low bone mass with muscle atrophy and hypofunction. Undoubtedly, osteosarcopenia is a major public health concern, being associated with high rates of morbidity and mortality. The best current defence against osteosarcopenia is prevention based on a healthy lifestyle and regular exercise. The most appropriate type, intensity, duration, and frequency of exercise to positively influence osteosarcopenia are not yet known. However, combined programmes of progressive resistance exercises, weight-bearing impact exercises, and challenging balance/mobility activities currently appear to be the most effective in optimising musculoskeletal health and function. Based on this evidence, the aim of our review was to summarize the current knowledge about the role of exercise in bone-muscle crosstalk, highlighting how it may represent an effective alternative strategy to prevent and/or counteract the onset of osteosarcopenia.