Do the recommended guidelines for physical activity impact percentage of body fat in normal-weight women?

Introduction: International exercise guidelines have been designed to prevent weight gain, and subsequently improve health, in adults. However, body mass is a proxy for assessing obesity, and fat distribution also plays an important role in metabolic and cardiovascular health. Given the importance of adiposity in obesity-related disease risk, it is imperative that prescribed exercise guidelines be relevant to preventing gains in both weight and fat mass. Therefore, this study investigated the impact of achieving recommended levels of physical activity (PA) on adiposity in normal-weight women with varying levels of percentage body fat (PBF). Methods: Anthropometric measures were performed in 107 women (age: 16-45 years; BMI: 18.5 – 24.9 kg/m2). Air-displacement plethysmography assessed PBF. Tri-axial accelerometers, worn over 7 days, assessed moderate and vigorous PA. Independent t-tests compared PBF levels between participants who achieved recommended levels of PA and those who did not. Results: Achieving current PA recommendations (≥150 min/week of moderate-to-vigorous PA) was associated with significantly lower PBF (27.4% ± 5.7 vs 30.3% ± 4.08; p=0.038). When PA was stratified, those achieving ≥300 min/week of moderate PA showed a trend towards lower PBF (p=0.076), while achieving ≥150 min/week of vigorous PA resulted in significantly lower PBF (24.5% ± 4.3 vs 28.3% ± 5.5; p=0.022). Discussion: Achieving current PA recommendations was associated with a moderate, but clinically relevant decrease in PBF. The findings suggest this association is strongest for vigorous activity. Conclusions: The findings suggest that while moderate-to-vigorous PA will help achieve lower levels of adiposity, an emphasis on vigorous PA may have the greatest impact on adiposity when prescribing exercise in normal-weight women