Air Displacement Plethysmography Weakly Predicts Changes in Percent Body Fat in Comparison to Dual X‐ray Absorptiometry After Aerobic Exercise Training in Women

Abstract

We determined whether changes in body fat after aerobic exercise training in women could be tracked equally well by air displacement plethysmography (ADP) in comparison to Dual X‐ray Absorptiometry (DXA). Seventy‐three healthy non‐vigorously active females (age: 30.5 ± 7.9 yrs; ht: 164.7 ± 7.5 cm; wt: 67.2 ± 14.4 kg; %fat: 37.5 ± 8.7%) had body fat assessed by ADP and DXA before and after a 12‐wk exercise program of treadmill walking 3 days/wk for 30 min at 70% of VO2max. Overall, ADP underestimated %fat compared to DXA (31.9 ± 8.5% vs. 37.3 ± 8.6%; P < 0.001). Bland‐Altman analysis revealed a considerably wide limit of agreement in %fat at baseline (Mean difference = 6.5 %fat; 95% CI: −15.2 to +2.2) and at 12 weeks (Mean difference = 5.2 %fat; 95% CI: −11.8 to +1.4). There was a reduction in %fat DXA after 12 weeks of training (− 0.5 ± 1.9 %; Range: −8.8% to +2.4%; P = 0.019) but not in %fat ADP (−0.9 ± 4.3%; Range: − 18.7% to +11.3%; P = 0.09). DXA and ADP were strongly correlated at baseline (r = 0.873; P < 0.001) and after 12 weeks of training (r = 0.923; P < 0.001). However, Δ %fat values (12 weeks – baseline) for ADP and DXA were only weakly correlated (r = .321; P = 0.006). Although ADP may be suitable for assessing %fat at discrete time points, ADP may not be reliable for tracking changes in percent body fat in females after aerobic exercise training that produces negligible mean fat loss despite considerable between‐subject variation in %fat changes.