The Difference Between Exercise-Induced Autonomic and Fitness Changes Measured After 12 and 20 Weeks of Medium-to-High Intensity Military Training.

Grant, CC, Mongwe, L, Janse van Rensburg, DC, Fletcher, L, Wood, PS, Terblanche, E, and du Toit, PJ. The difference between exercise-induced autonomic and fitness changes measured after 12 and 20 weeks of medium-to-high intensity military training. J Strength Cond Res 30(9): 2453-2459, 2016-The aim of this study was to compare the physical fitness, based on VO2max and exercise-induced cardiac autonomic changes, measured by heart rate variability (HRV) of 12 weeks with 20 weeks of training in the South African National Defence Force. Recruits (n = 154) participated in a medium-to-high intensity exercise intervention (daily energy expenditure: 8,485 kJ·d). The significant effect on VO2max between weeks 1 and 12 (48.57, SD = 9.25 vs. 53.36, SD = 7.21] did not continue during weeks 12-20 (53.36, SD = 7.21 vs. 53.87, SD = 7.87). No changes in the supine low frequency (LF)/high frequency (HF) (0.48, SD = 0.51 vs. 0.41, SD = 0.64) or the standing LF/HF (4.02, SD = 5.14 vs. 3.91, SD = 5.28), an indicator of autonomic balance and a possible indicator of overtraining syndrome, suggests that overtraining did not take place during weeks 12-20. This was confirmed with further decreases in supine and standing heart rate. However, the power of the vagal-induced variability continued to increase after 12 weeks. Increased vagal influence without concurrent change in autonomic balance may be interpreted as decreased sympathetic cardiac control. It is important to note that although no fitness changes were detected, positive cardiac autonomic conditioning did continue between weeks 12 and 20, as measured by increased vagal-induced HRV and decreased sympathetic influence on cardiac control. Results may be extrapolated to training in the normal population/athletes after a medium-to-high intensity exercise program, as this intervention was a closely monitored and standardized exercise program.

Heart rate variability assessment of the effect of physical training on autonomic cardiac control.

BACKGROUND: The effect of exercise interventions on autonomic nervous system (ANS) control of the heart by heart rate variability (HRV) is often investigated in just one position. It was hypothesized that results of exercise-induced changes on ANS are dependent on body position and that it is possible to distinguish between exercise induced changes in vagal and sympathetic influence by taking measurements in different body positions. METHODS: One hundred eighty-three (male = 100, female = 83) healthy volunteers, between 18 and 22 years, participated in a prospective twelve week medium to high intensity exercise intervention study with a self-control design. The influence of the exercise intervention was investigated on supine, rising, and standing as well as on the orthostatic response. Time domain, frequency domain and nonlinear (Poincaré) HRV analysis were performed. RESULTS: The exercise intervention lead to a significant increase (P < 0.05) in vagal influence during supine, rising, and standing. Sympathetic control in the supine position was decreased and increased during rising and standing. In the initial orthostatic response to rising from the supine position, the exercise intervention lead to increased (P < 0.05) vagal withdrawal as well as increased sympathetic control. The orthostatic response measured as the difference between standing and supine indicated only an exercise induced increase in sympathetic control. CONCLUSIONS: Exercise-induced changes in sympathetic and parasympathetic ANS control differ, depending on posture and period of measurement. Exercise induced changes in parasympathetic and sympathetic outflow, respectively, can be extracted from measurements from supine, through the orthostatic response, to standing, thereby detecting changes in ANS that are otherwise obscured.

DEXA-assessed regional body composition changes in young female military soldiers following 12-weeks of periodised training.

Dual-energy X-ray absorptiometry (DEXA) was used to assess whole body and regional soft tissue mass, fat mass and lean body mass compositional changes in 68 female recruits (age 20.8 +/- 1.14 years; body mass 59.5 +/- 8.79 kg; stature 159.57 +/- 5.53 cm) pre- and post 12-weeks of military basic training. A decrease in total body fat tissue mass (10.2%) and regional percent fat (10.9%) was measured with an increase in total lean body mass (8.7%). Of interest were the differences in the responses in the tissue composition of the arms (16.2% loss in fat mass with an 11.6% gain in lean mass), trunk (17.0% decrease in fat mass with a 10.4% increase in lean mass) and the legs (10.5% increase in lean mass but no change in fat mass). These findings show the importance of considering regional rather than whole body composition changes when assessing the effects of a training programme. STATEMENT OF RELEVANCE: Female soldiers experienced a change in total body fat tissue (-10.2%) and lean body mass (+8.7%) after basic training; however, no significant fat mass decrease was evident in the leg region. Regional rather than whole body composition changes need to be considered when assessing the effects of a training programme.

Effect of Mixed Basic Military Training on the Physical Fitness of Male and Female Soldiers.

INTRODUCTION: Mixed gender basic military training (BMT) is adopted to integrate the female South African soldier into the military. This study aimed to assess gender differences before, during (12 weeks), and after a 20-week mixed BMT course and determine if BMT significantly reduced these differences. METHODS: A total of 186 soldiers (114 male: mean age = 21.0 ± 1.1 year; 72 female: mean age = 20.5 ± 1.2 year) completed the BMT course and all anthropometric, physical fitness, explosive power, and hand grip strength measurements. Repeated-measures analysis of variance was used to model BMT data with main effects for gender comparison between males and females, and time main effect for evaluation of differences between weeks 1, 12, and 20 of BMT, as well as an interaction effect for differences in changes over time for males and females. Alpha was set at α ≤0.05. RESULTS: Male soldiers were significantly taller (p < 0.001) and scored better in all measurements at the start of BMT, differences ranged from 1.6% to 50% between genders. Differences narrowed by up to 18.5% in aerobic, push-up, abdominal measurements, and to 4.6% in the South African National Defense Force fitness test. Differences in power output and hand grip strength remained unchanged. CONCLUSION: Large initial anthropometrical and physical fitness differences decreased but were still obvious at the end of BMT. BMT should bridge the physical gap between male and female soldiers to ensure they can all perform the same duties. The enforcing of equal minimum physical fitness requirements for acceptance into BMT; conditional acceptance into the military subject to the successful completion of a bridging course aimed at improving physical fitness in individuals who do not meet the minimum physical fitness requirements for acceptance; and developing a cyclic physical training program with different entry points, dependent on initial physical performance at the start of BMT, ensuring adequate progression and overload for all soldiers are possible avenues to explore to achieve this goal.