Changes in muscle strength after diet-induced weight reduction in adult men with obesity: a prospective study

BACKGROUND AND OBJECTIVE: The benefits of weight reduction for musculoskeletal disorders are well understood. Steep declines in muscle mass following considerable weight reduction can decrease muscle strength and, consequently, physical performance. However, only a limited number of studies have examined the changes in muscle mass and strength in the context of interventional weight reduction programs. Thus, we investigated the influence of muscle mass decrease caused by diet-induced weight reduction on muscle strength in obese men. METHODS: A total of 24 men with obesity (body mass index [BMI]: 29.2 ± 2.6 kg/m(2); age: 52.4 ± 10.0 years) attended a 12-week weight reduction program that implemented dietary restrictions. Each participant underwent assessments of body weight (by a digital scale), body composition (by whole-body dual-energy X-ray absorptiometry [DEXA]), and upper and lower extremity muscle strength (by a hand-held dynamometer and a Biodex System 3 dynamometer, respectively) before and after the program. RESULTS: The program led to significant reductions of 10.5% of weight and 6.1% of lower extremity muscle mass. Similarly, lower extremity muscle strength (measured using a Biodex System 3 dynamometer) was significantly decreased (isometric 60° peak torque decreased by 10% and isokinetic 60°/s peak torque decreased by 9.4%); however, the level of body weight-normalized lower extremity muscle strength did not significantly change (increased by +1.2% and +1.4%). The decrease in muscle strength was related to but did not entirely depend on decrease in muscle mass. Although handgrip strength did not significantly differ (−2.2%), the weight-normalized level of this parameter significantly improved (+9.1%). In addition, decrease in the percentage of whole-body fat mass and increase in the percentage of muscle mass index were observed. CONCLUSION: We recommend performing exercise after diet-induced weight reduction to regain muscle mass and strength and improve body weight-normalized lower extremity muscle strength.