Methods Trainee (n=774 men, 195 women) APFT performance data were obtained, and baseline anthropometrics were used to estimate %BF. APFT performance change (final−baseline) was analysed directly (t-tests) or by quartiles of baseline APFT performance or %BF (analysis of variance). Cochran-Armitage χ² for linear trend test and risk ratios allowed for comparison against the lowest initial performance referent quartile (Q1), providing the likelihood of fitness improvements. Significance was set at p≤0.05.

Results Performance improved (p<0.01) on all final APFT events for men and women, respectively (push-ups: +38.4% and +91.8% repetitions; sit-ups: +26.8% and +33.5% repetitions; 2-mile run: −9.6% and −10.4% time). Significant trends in both sexes indicated that moving from low-to-high initial APFT fitness quartiles, trainees were increasingly less likely to improve their fitness. Specifically, men and women in the highest initial fitness quartiles (Q4) were 22%–32% and 25%–34% less likely (p<0.01) to improve, respectively, versus the within-sex lowest initial fitness quartiles (Q1). Only the male trainee’s 2-mile run time change was related to the initial %BF.

Conclusions Although most trainees’ fitness improved by the end of IET, the likelihood and magnitude of improvement were clearly associated with initial fitness levels. Attention to individualised conditioning and training intensity in the physical readiness training programme of instruction may optimise training strategies across all trainee conditioning levels.