Influence of Smoking Status on Physical Performance Adaptation and Endocrine and Inflammatory Markers during Initial Military Training

Habitual smoking has been associated with reduced physical performance adaptation, increased risk of injury and failure to complete military training, but the underlying mechanisms remain unclear. We examined physical performance and resting endocrine (cortisol, testosterone, insulin-like growth factor-1) and inflammatory (C-reactive protein (CRP), interleukin-6) markers in British infantry trainees during 14 weeks of military training. A validated lifestyle questionnaire was administered to 46 male trainees (age 21 ± 4 yr; mass 76.3 ± 8.3 kg; height 1.78 ± 0.07 m) for determination of smoking status. Waking fasted blood samples and physical performance measures (chest press, seated row, leg press, static lift and jump exercises) were obtained at weeks 1, 5 and 10 of training. Performance in military physical fitness tests (press ups and sit ups in two minutes, 2.4-km run) at weeks 1 and 14 were also recorded. At weeks 1 and 10, lower-leg muscle and adipose cross-sectional area (CSA) and density were measured by peripheral Quantitative Computed Tomography (pQCT, XCT2000L, Stratec Pforzheim, Germany). Two-way repeated measures ANOVA was used to identify differences over time between non-smokers (NS, n=22) and habitual smokers (S, n=24). There were no significant differences in endocrine and inflammatory markers, or in physical performance measures (main group effect; P>0.05). Higher CRP concentrations in S approached significance (mean (SD); NS, 1.80(2.06); S, 2.83(3.29) mg·L-1; P=0.059). Military training, irrespective of smoking status, significantly improved physical performance in all parameters (main time effect; P<0.05) except vertical jump height. An interaction effect existed whereby improvement in bench press performance was significantly greater in S than NS (P=0.031). Performance in 2.4-km run improved more in S than NS, but this was not significant (P=0.069). There were significant changes from weeks 1 to 10 in muscle CSA (8232(831) and 8604(901) mm2; P<0.001), total density of muscle and fat (66(4) and 67(4) mg·cm-3; P<0.001) and fat/muscle CSA ratio (22(8) and 20(7)%; P=0.012) as a result of training. No effect of smoking was evident on muscle and adipose characteristics of the lower leg (P>0.05). Physical performance improved with 10 weeks of military training irrespective of smoking status, with the exception of greater improvement in bench press performance in smokers. Therefore, it appears that smoking, while chronically elevating resting CRP, does not have a marked effect on physical performance improvement in the early stages of military training.