Resistance exercise is an effective method to improve muscle function, muscle mass, and quality of life in older adults. However, little attention has been given to this topic in frail older adults.PURPOSE: To evaluate the effects of bodyweight squat exercise on muscle mass, muscle strength, and function in frail older adults.METHODS: Fifteen older adults (mean age=78.7 yr) who needed assistance performing ADL according to long term care insurance regulations in the Japan participated in the study. Participants performed squat exercise using bodyweight as resistance for one set consisting of 48 reps twice weekly for 12 weeks. Body mass, thigh girth, thigh muscle thickness assessed by B-mode ultrasound, knee extension strength (KES), static and dynamic balance (static (SB): sway velocity (SV) standing on firm or foam surfaces with eyes open or closed; dynamic (DB): limits of stability) were measured before and after the intervention.RESULTS: Following the intervention, participants decreased (p<0.05) body mass by 1.6% (7.4±11.4 to 56.5±11.1 kg (mean±SD)), and increased KES by 10.0% (66.9±22.2 to 73.6±24 Nm/kg) and KES relative to body mass by 16.7% (1.2±0.4 to 1.3±0.4 Nm/kg). Although thigh girth did not change, thigh muscle thickness did increase by 2.7% (29.2±5.8 cm to 31.0±5.4 cm). There were no changes in DB nor in SB, except SV standing on a firm surface with the eyes open improved by 26.2 (0.42±0.25 to 0.31±0.13 mm/sec).CONCLUSIONS: Bodyweight squat exercise improves muscle mass and strength but have little effect on balance parameters in frail older adults. Further research is needed to determine the effects of additional exercises on balance in this population.