AbstractThe aim was to use a robust statistical approach to examine whether physical fitness at entry influences performance changes between men and women undertaking British Army basic training (BT). Performance of 2 km run, seated medicine ball throw (MBT) and isometric mid‐thigh pull (MTP) were assessed at entry and completion of Standard Entry (SE), Junior Entry‐Short (JE‐Short), and Junior Entry‐Long (JE‐Long) training for 2350 (272 women) recruits. Performance change was analyzed with entry performance as a covariate (ANCOVA), with an additional interaction term allowing different slopes for courses and genders (p < 0.05). Overall, BT courses saw average improvements in 2 km run performance (SE: −6.8% [−0.62 min], JE‐Short: −4.6% [−0.43 min], JE‐Long: −7.7% [−0.70 min]; all p < 0.001) and MBT (1.0–8.8% [0.04–0.34 m]; all p < 0.05) and MTP (4.5–26.9% [6.5–28.8 kg]; all p < 0.001). Regression models indicate an expected form of “regression to the mean” whereby test performance change was negatively associated with entry fitness in each course (those with low baseline fitness exhibit larger training improvements; all interaction effects: p < 0.001, > 0.006), particularly for women. However, when matched for entry fitness, men displayed considerable improvements in all tests, relative to women. Training courses were effective in developing recruit physical fitness, whereby the level of improvement is, in large part, dependent on entry fitness. Factors including age, physical maturity, course length, and physical training, could also contribute to the variability in training response between genders and should be considered when analyzing and/or developing physical fitness in these cohorts for future success of military job‐task performance.