No Effect Of Cigarette Smoking On Calf Muscle Size And Density Changes Following Military Training

Abstract

Training results in adaptations including reductions in body fatness, increases in muscle cross-sectional area and a reduction in ectopic fat in skeletal muscle (increased muscle density). Cigarette smoking has been reported to inhibit performance adaptations in response to military training, but little is known about the effect of smoking on training-induced changes in muscle size and composition. PURPOSE: The aim of this study was to: (1) characterise the effect of 10 weeks of military training on muscle and fat cross-sectional areas and muscle density, and (2) evaluate the effect of cigarette smoking on these changes. METHODS: Seventy-eight male military trainees (age, 20.3 (3.3) years; height, 178.1 (7.0) cm; mass 74.5 (8.4) kg) consented to take part and completed a validated lifestyle questionnaire before undertaking 10 weeks of infantry training. At weeks 0 and 10, body mass was measured and a lower-leg peripheral QCT (pQCT) scan (Stratec/ Norland XCT 2000LTM) was performed to evaluate muscle and subcutaneous adipose cross-sectional areas of the calf and average calf muscle density. RESULTS: Smokers (n = 49) and non-smokers (n= 29) were not different at baseline for muscle area (smokers vs. non-smokers; 8283 (836) vs. 8058 (828) mm2, P=0.25), subcutaneous adipose area (1735 (5022) vs. 1650 (595) mm2, P=0.52), muscle density (75.8 (1.1) vs. 75.8 (2.0) mg/cm3, P=0.98) or body mass (74.9 (8.7) vs. 73.9 (8.1) kg, P=0. 62). Ten weeks of military training increased muscle area (week 0 vs. week 10; time effect, P<0.01; 8199(835) vs. 8532 (925) mm2), muscle density (time effect, P=0.02; 75.8 (1.5) vs. 76.2 (1.3) mg/cm3) and body mass (time effect, P=0.05; 74.5 (8.4) vs. 75.3 (7.2) kg) in smokers and non-smokers, but there was no interaction effect. Subcutaneous adipose cross-sectional area did not change significantly over the period of training (time effect, P=0.22; 1703 (536) vs. 1662 (493) mm2). CONCLUSIONS: Ten weeks of military training resulted in significant increases in calf muscle cross-sectional area and muscle density, but did not influence subcutaneous adipose cross-sectional area. Smoking status did not influence the magnitude of any changes.