Paola Silvia Wood

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.

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.

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

Abstract 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−1). 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.

Mechanical properties of the triceps surae: Differences between football and non-football players

Abstract We investigated the mechanical properties of the triceps surae between professional, junior, and non-football players. Fifty-nine men participated in this study. The mechanical properties of the right legs’ triceps surae were measured in vivo using a free oscillation technique; no significant differences existed between the groups. The mean results for musculo-articular stiffness, damping coefficient, and damping ratio were as follows: professional football players (21523 N· m−1, 330.8 N · s · m−1, and 0.201); junior football players (21063 N · m−1, 274.4 N · s · m−1, and 0.173); and non-players (19457 N · m−1, 281.5 N · s · m−1, and 0.184). When analysed according to position, the results were as follows: defender (21447 N · m−1, 308.6 N · s · m−1, and 0.189); midfielder (20762 N · m−1, 250.7 N · s · m−1, and 0.157); winger (21322 N · m−1, 335.1 N · s · m−1, and 0.212); forward (22085 N · m−1, 416.2 N · s · m−1, and 0.254); and non-players (19457 N · m−1, 281.5 N · s · m−1, and 0.184). Thus, football training, football games, and the position played had no effect on triceps surae mechanical properties. These results may be attributed to opposing adaptations between different types of training that are usually implemented in football. Alternatively, the minimum strain amplitude and/or frequency threshold of the triceps surae required to trigger adaptations of mechanical properties might not be achieved by football players with football training and matches.

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.

Flexibility as risk factor for stress-fracture development in South African male soldiers

Background: Stress fractures are a common military training injury. Flexibility of muscles and joints may directly influence stress-fracture risk by way of altering the forces applied to bone. Hip external rotation and ankle plantar- and dorsiflexion have been inconsistently reported to pose a risk to stress fracture development in military soldiers. Thus this study aimed to present results that could help define the risk flexibility may pose in the development of stress fractures amongst military male soldiers. Methods: An experimental one-group pretest–posttest study design assessing the injury incidence, bilateral hip external rotation, ankle plantar- and dorsiflexion of South African male military soldiers (n = 100) undergoing 12 weeks of basic military training (BMT) was undertaken. The parametric t-test for dependent samples (α = 0.05) and effect size (ES) was used to analyse the data. Results: No stress fractures were diagnosed in the 100 operational military training injuries reported. BMT resulted in significant mean decreases of 10% (L) and 17% (R) in hip external rotation and 18% (L) and 14% (R) in ankle plantar flexion respectively, whilst a significant increase of 37% (L) and 39% (R) dorsiflexion was observed. Conclusions: Although normal ankle and limited hip external flexibility do not appear to predispose these male soldiers to stress fracture development these variables should not be excluded as possible intrinsic risk factors.

The correlation between the health-related fitness of healthy participants measured at home as opposed to fitness measured by sport scientists in a laboratory

Background: Fitness is defined in the health context as a state of good health or physical condition, primarily as a result of exercise and proper nutrition. Conventional methods of measuring fitness are expensive, time consuming and require specialised methods. There is a need for noninvasive, fast methods of assessing health-related fitness and activity in athlete and non-athlete populations. The aim of this study was to establish any correlation between participants’ self-assessed health-related fitness (HRF) index and the HRF index determined by sports scientists, as well as the laboratory-assessed HRF index and maximum oxygen uptake (VO2max) determined by sports scientists via direct methods in a laboratory, and finally, to determine any potential correlation between an activity-recall questionnaire (Kasari) and VO2max. Method: The participants consisted of 169 male and female volunteers between the ages of 18 and 55 years, taking neither supplements nor medication. The University of Pretoria’s HRF index protocol was first carried out by participants on their own at home, and then in the laboratory under the supervision of sport scientists. The complete datasets of 150 participants were statistically analysed to establish correlations. Results: The results indicated highly significant and substantial correlations (ρ = 0.696, p < 0.001) between the participants’ self-assessed HRF index and measurements by the sports scientists. There were moderate correlations between the laboratory-assessed HRF index and the direct VO2max (ρ = 0.512, p < 0.005), as well as the indirect VO2max (ρ = 0.588; p < 0.001). A significant correlation was found between the self-assessed HRF index and the indirect VO2max (ρ = 0.454; p < 0.001). The Kasari questionnaire correlated only weakly with the indirect VO2max (ρ = 0.278, p < 0.002) and not at all with the direct VO2max (ρ = 0.072, p < 0.731). Conclusion: Indications are that this test protocol may be conducted at home by individuals, without supervision, to determine exercise ability or fitness, or to monitor changes in physical fitness, thereby limiting expenses and costs.