Sarcopenia and Ageing.

Musculoskeletal ageing is a major health challenge as muscles and bones constitute around 55-60% of body weight. Ageing muscles will result in sarcopenia that is characterized by progressive and generalized loss of skeletal muscle mass and strength with a risk of adverse outcomes. In recent years, a few consensus panels provide new definitions for sarcopenia. It was officially recognized as a disease in 2016 with an ICD-10-CM disease code, M62.84, in the International Classification of Diseases (ICD). With the new definitions, there are many studies emerging to investigate the pathogenesis of sarcopenia, exploring new interventions to treat sarcopenia and evaluating the efficacy of combination treatments for sarcopenia. The scope of this chapter is to summarize and appraise the evidence in terms of (1) clinical signs, symptoms, screening, and diagnosis, (2) pathogenesis of sarcopenia with emphasis on mitochondrial dysfunction, intramuscular fat infiltration and neuromuscular junction deterioration, and (3) current treatments with regard to physical exercises and nutritional supplement.

The role of obesity in sarcopenia and the optimal body composition to prevent against sarcopenia and obesity.

Background: Elderly people with low lean and high fat mass, are diagnosed with sarcopenic obesity (SO), and often have poor clinical outcomes. This study aimed to explore the relationship between obesity and sarcopenia, and the optimal proportion of fat and muscle for old individuals. Methods: Participants aged 60 years or above were instructed to perform bioelectrical impedance analysis to obtain the muscle and fat indicators, and handgrip strength was also performed. Sarcopenia was diagnosed according to predicted appendicular skeletal muscle mass and function. Body mass index (BMI) and body fat percentage (BF%) were used to define obesity. The association of muscle and fat indicators were analyzed by Pearson's correlation coefficient. Pearson Chi-Square test was utilized to estimate odds ratios (OR) and 95% confidence intervals (CI) on the risk of sarcopenia according to obesity status. Results: 1637 old subjects (74.8 ± 7.8 years) participated in this study. Not only fat mass, but also muscle indicators were positively correlated to BMI and body weight (p < 0.05). Absolute muscle and fat mass in different positions had positive associations (p < 0.05). Muscle mass and strength were negatively related to appendicular fat mass percentage (p < 0.05). When defined by BMI (OR = 0.69, 95% CI [0.56, 0.86]; p = 0.001), obesity was a protective factor for sarcopenia, whilst it was a risk factor when using BF% (OR = 1.38, 95% CI [1.13, 1.69]; p = 0.002) as the definition. The risk of sarcopenia reduced with the increase of BMI in both genders. It was increased with raised BF% in males but displayed a U-shaped curve for females. BF% 26.0-34.6% in old females and lower than 23.9% in old males are recommended for sarcopenia and obesity prevention. Conclusion: Skeletal muscle mass had strong positive relationship with absolute fat mass but negative associations with the percentage of appendicular fat mass. Obesity was a risk factor of sarcopenia when defined by BF% instead of BMI. The management of BF% can accurately help elderly people prevent against both sarcopenia and obesity.

Diagnosis of sarcopenia by evaluating skeletal muscle mass by adjusted bioimpedance analysis validated with dual-energy X-ray absorptiometry.

BACKGROUND: This study aimed to adjust and cross-validate skeletal muscle mass measurements between bioimpedance analysis (BIA) and dual-energy X-ray absorptiometry (DXA) for the screening of sarcopenia in the community and to estimate the prevalence of sarcopenia in Hong Kong. METHODS: Screening of sarcopenia was provided to community-dwelling older adults. Appendicular skeletal muscle mass (ASM) was evaluated by BIA (InBody 120 or 720) and/or DXA. Handgrip strength and/or gait speed were assessed. Diagnosis of sarcopenia was based on the 2019 revised Asian Working Group for Sarcopenia cut-offs. Agreement analysis was performed to cross-validate ASM measurements by BIA and DXA. Multiple regression was used to explore contribution of measured parameters in predicting DXA ASM from BIA. RESULTS: A total of 1587 participants (age = 72 ± 12 years) were recruited; 1065 participants were screened by BIA (InBody 120) with 18 followed up by DXA, while the remaining 522 participants were assessed by the BIA (InBody 720) and DXA. The appendicular skeletal muscle mass index (ASMI) evaluated by BIA showed a mean difference of 2.89 ± 0.38 kg/m2 (InBody 120) and 2.97 ± 0.45 kg/m2 (InBody 720) against DXA gold standard. A significant overestimation of muscle mass was measured by BIA compared with DXA (P < 0.005). BIA data were adjusted using prediction equation and mean difference reduced to -0.02 ± 0.31 kg/m2 in cross-validation. Prevalence of sarcopenia in older adults ≥65 ranged from 39.4% (based on ASMI by DXA) to 40.8% (based on predicted DXA ASMI from BIA). Low ASMI by DXA was found in 68.5% of the older adults screened. The percentage of older adults exhibited low handgrip strength ranged from 31.3% to 56%, while 49% showed low gait speed. CONCLUSIONS: Bioimpedance analysis was found to overestimate skeletal muscle mass compared with DXA. With adjustment equations, BIA can be used as a quick and reliable tool for screening sarcopenia in community and clinical settings with limited access to better options.

Acute Inflammatory Response in Osteoporotic Fracture Healing Augmented with Mechanical Stimulation is Regulated In Vivo through the p38-MAPK Pathway.

Low-magnitude high-frequency vibration (LMHFV) has previously been reported to modulate the acute inflammatory response of ovariectomy-induced osteoporotic fracture healing. However, the underlying mechanisms are not clear. In the present study, we investigated the effect of LMHFV on the inflammatory response and the role of the p38 MAPK mechanical signaling pathway in macrophages during the healing process. A closed femoral fracture SD rat model was used. In vivo results showed that LMHFV enhanced activation of the p38 MAPK pathway at the fracture site. The acute inflammatory response, expression of inflammatory cytokines, and callus formation were suppressed in vivo by p38 MAPK inhibition. However, LMHFV did not show direct in vitro enhancement effects on the polarization of RAW264.7 macrophage from the M1 to M2 phenotype, but instead promoted macrophage enlargement and transformation to dendritic monocytes. The present study demonstrated that p38 MAPK modulated the enhancement effects of mechanical stimulation in vivo only. LMHFV may not have exerted its enhancement effects directly on macrophage, but the exact mechanism may have taken a different pathway that requires further investigation in the various subsets of immune cells.

Enhancement of osteoporotic fracture healing by vibration treatment: The role of osteocytes.

The prevalence of osteoporotic fracture is high due to global aging problem. Delayed and impaired healing in osteoporotic fractures increase the socioeconomic burden significantly. Through intensive animal and clinical research in recent years, the pathogenesis of osteoporotic fracture healing is unveiled, including decreased inflammatory response, reduced mesenchymal stem cells and deteriorated angiogenesis, etc. The enhancement of osteoporotic fracture healing is important in shortening hospitalization, thus reducing related complications. Mechanical stimulation is currently the most well-accepted approach for rehabilitation of osteoporotic fracture patients. Some new interventions providing mechanical signals were explored extensively in recent years, including vibration treatment, and osteoporotic fracture healing was found to respond very well to these signals. Vibration treatment could accelerate osteoporotic fracture healing with improved callus formation, mineralization and remodeling. However, the mechanism of how osteoporotic fracture bones sense mechanical signals and relay to bone formation remains unanswered. Osteocytes are the most abundant cells in bone tissues. Cumulative evidence confirm that osteocyte is a type of mechanosensory cell and shows altered morphology and reduced cell density during aging. Meanwhile, osteocytes serve as endocrine cells to regulate bone and mineral homeostasis. However, the contribution of osteocytes in osteoporotic fracture healing is largely unknown. A recent in vivo study was conducted to examine the morphological and functional changes of osteocytes after vibration treatment in an osteoporotic metaphyseal fracture rat model. The findings demonstrated that vibration treatment induced significant outgrowth of canaliculi and altered expression of various proteins (E11, DMP1, FGF23 and sclerostin), particularly osteocyte-specific dentin matrix protein 1 (DMP1) which was greatly increased. DMP1 may play a major role in relaying mechanical signals to bone formation, which may require further experiments to consolidate. Most importantly, vibration treatment significantly increased the mineralization and accelerated the osteoporotic fracture healing in metaphyseal fracture model. In summary, osteocyte is the major cell type to sense mechanical signals and facilitate downstream healing in osteoporotic fracture bone. Vibration treatment has good potential to be translated for clinical application to benefit osteoporotic fracture patients, while randomized controlled trials are required to validate its efficacy.

Elastic-band resistance exercise or vibration treatment in combination with hydroxymethylbutyrate (HMB) supplement for management of sarcopenia in older people: a study protocol for a single-blinded randomised controlled trial in Hong Kong.

INTRODUCTION: Sarcopenia is a geriatric syndrome characterised by progressive loss of skeletal muscle mass and function with risks of adverse outcomes and becomes more prevalent due to ageing population. Elastic-band exercise, vibration treatment and hydroxymethylbutyrate (HMB) supplementation were previously proven to have positive effects on the control of sarcopenia. The purpose of this study is to evaluate the effectiveness of elastic-band exercise or vibration treatment with HMB supplementation in managing sarcopenia. Our findings will provide a safe and efficient strategy to mitigate the progression of sarcopenia in older people and contribute to higher quality of life as well as improved long-term health outcomes of elderly people. METHODS AND ANALYSIS: In this single-blinded, randomised controlled trial (RCT), subjects will be screened for sarcopenia based on the Asian Working Group for Sarcopenia (AWGS) definition and 144 sarcopenic subjects aged 65 or above will be recruited. This RCT will have three groups evaluated at two time points to measure changes over 3 months-the control and the groups with combined HMB supplement and elastic-band resistance exercise or vibration treatment. Changes in muscle strength in lower extremity will be the primary outcome. Muscle strength in the upper extremity, gait speed, muscle mass (based on AWGS definition), functional performance in terms of balancing ability and time-up-and-go test and quality of life will be taken as secondary outcomes. In addition, each participant's daily activity will be monitored by a wrist-worn activity tracker. Repeated-measures analysis of variance will be performed to compare within-subject changes between control and treatment groups at two time points of pretreatments and post-treatments. ETHICS AND DISSEMINATION: The procedures have been approved by the Joint CUHK-NTEC Clinical Research Management Office (Ref. CREC 2018.602) and conformed to the Declaration of Helsinki. Results will be disseminated through peer-reviewed publications, conferences and workshops. TRIAL REGISTRATION NUMBER: NCT04028206.