Energy balance
Higher habitual physical activity (measured as Physical Activity Level, PAL) is associated with significantly higher fat-free mass (FFM) during growth (under 18 years) and in early adulthood, but this positive association diminishes and is counteracted by aging in older adults.
Stay physically active throughout your life to maximize your muscle mass. The biggest benefits for building fat-free mass occur during growth and early adulthood (up to age 30). In older age, exercise won't fully stop muscle loss, but active individuals still retain significantly more muscle than sedentary peers, which helps maintain independence and functional capacity.
PAL was a main determinant of body composition at all ages... In participants < 18 y old, mean FM-adjusted FFM was 1.7 kg... and 3.4 kg... higher in a very active participant with PAL = 2.0 than in a sedentary participant with PAL = 1.5... At age 18 y... higher... and at age 80 y 0.7 kg... and 1.0 kg... higher... If these associations are causal, they suggest physical activity is a major determinant of body composition as reflected in peak FFM, and that a physically active lifestyle can only partly protect against loss of FFM in aging adults.
Why this rating
Large sample size (n=2000), gold-standard measurement methods (Doubly Labeled Water and Isotope Dilution), but the cross-sectional design limits causal inference.
Source
Physical activity and fat-free mass during growth and in later life
Klaas R. Westerterp et al. · American Journal of Clinical Nutrition · 2021
DOI 10.1093/ajcn/nqab260
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