Toward a sex-specific relationship between muscle strength and appendicular lean body mass index?

BACKGROUND: In spite of some dissociation between muscle mass and strength, muscle strength is often used as a proxy to identify individuals with low muscle mass (sarcopenia). Thus, the aim of the present study was to investigate the relationship between muscle strength and the appendicular lean body mass index (app LBMI). METHODS: One hundred and five individuals were recruited. Knee extension and handgrip strength were measured. Body composition was assessed by DXA. App LBMI was calculated as appendicular lean body mass divided by height squared. RESULTS: At le level of the entire cohort, both handgrip (r = 0.73; p < 0.001) and knee extension strength (r = 0.57; p < 0.001) were associated with app LBMI. However, in women, knee extension strength (r = 0.32; p < 0.05) but not handgrip strength (r = 0.14; p = 0.35) was associated with app LBMI; while in men, handgrip strength (r = 0.43; p < 0.01) but not knee extension strength (r = 0.27; p = 0.09) was associated with app LBMI. CONCLUSIONS: Muscle strength appears to be associated with lean body mass; however, handgrip strength may be preferentially used in men and knee extension strength in women to detect sarcopenic individuals. Future larger studies are now needed to confirm our findings and their clinical relevance.

Muscle quality as a potential explanation of the metabolically healthy but obese and sarcopenic obese paradoxes.

BACKGROUND: Obesity has been associated with metabolic complications. However, two subgroups of obese individuals (namely "sarcopenic obese" and "metabolically healthy but obese" individuals) with low muscle mass appear to have a better metabolic profile. Despite having a lower muscle mass, these individuals appear to have higher muscle strength, suggesting higher muscle quality. Studies have reported insulin sensitivity to be related to muscle quality. Therefore, the aim of the present study was to test the hypothesis that low muscle mass was associated with better muscle quality in obese individuals. METHODS: A total of 112 postmenopausal women aged between 50 and 77 years (means, 61±6 years) were recruited. Body composition (bioelectrical impedancemetry), muscle strength (hand dynamometer), and functional capacity (chair stand test, alternate step test and balance test) were measured. RESULTS: Skeletal muscle mass (SM; kg) was significantly positively correlated with muscle strength (kg) in normal weight (r=0.43; P=0.003) and overweight (r=0.42; P=0.020) women, but not in obese (r=0.28; P=0.13) women. Muscle mass (kg) was significantly negatively correlated with muscle quality (kg/SMkg) in normal weight (r=-0.41, P=0.005), overweight (r=-0.59; P<0.001) and obese (r=-0.59; P<0.001) individuals. Skeletal muscle mass index (kg/m(2)) was significantly negatively correlated with muscle quality in normal weight (r=-0.33, P=0.025), overweight (r=-0.47, P=0.008), and obese (r=-0.43, P=0.015) women. Finally, type II sarcopenic individuals had higher muscle quality than type I sarcopenic (P=0.002) and nonsarcopenic (P=0.001) individuals. CONCLUSIONS: Our results support our hypothesis and showed that muscle quality increased as muscle mass and muscle mass index decreased. Thus, muscle quality may potentially explain the favorable metabolic profile observed in metabolically healthy but obese and sarcopenic obese postmenopausal women. Further studies including metabolic data are needed to confirm our results.

Is functional capacity related to the daily amount of steps in postmenopausal women?

OBJECTIVE: The aim of this study was to investigate the relationship between functional capacity, muscle function, and daily step count in postmenopausal women. METHODS: Fifty-seven postmenopausal women aged 50 to 70 years were recruited. Body composition (body weight, body mass index, fat mass, and skeletal muscle mass), energetic metabolism (maximal oxygen consumption, total energy expenditure, daily step count), and functional capacity (muscle strength, muscle quality, chair stand, balance and alternate step tests) were measured. Women were divided into three groups (sedentary [n = 19], <7,500 steps; moderately active [n = 20], 7,500-10,000 steps; active [n = 18], >10,000 steps). RESULTS: A higher number of steps per day was associated with higher maximal oxygen consumption (mL/min per kg; P = 0.001) and total energy expenditure (P = 0.004) as well as lower body weight (P = 0.035) and fat mass (P = 0.048). Surprisingly, no differences for skeletal muscle mass, muscle strength, muscle quality, and functional capacity were observed between the groups, although this could have been because of the small sample size. CONCLUSIONS: A daily amount of 10,000 steps seems to be associated with better body composition and higher cardiovascular functions. However, neither functional capacity nor muscle functions seem to be related to the daily amount of steps in postmenopausal women. Further prospective studies are needed to confirm our preliminary results because cross-sectional study designs do not permit the understanding of temporal relations.