A systematic review of hormone levels, biomarkers of cellular injury and oxidative stress in multi-stressor military field training exercises

Abstract

The fundamental objective of military field training exercises (FTX) is to prepare military personnel for real-life operations through simulated scenarios. These training sessions often require extreme physical efforts with prolonged, high-intensity exercises that can be combined with food restrictions and partial, or total, sleep deprivation. Such conditions can compromise an individual's physical performance and cause tissue damage, thus affecting their health. This study aimed to perform a systematic review of the literature to identify studies that measured the changes in hormone levels and biomarkers of cellular injury and oxidative stress resulting from FTX with high levels of energy expenditure combined with food and sleep restrictions. PubMed and the Scopus database were searched for articles that combined physical effort/food restriction/sleep deprivation with military training. The initial database search identified 158 articles that were reduced to 18 after confirmation. Significant reductions were reported in thyroid hormones, T3, T4, and anabolic hormones such as testosterone, insulin and androstenedione. An exception for GH was found, which increased throughout FTX. Less distinct responses to FTX were observed with cortisol, TSH and LH. The presence of biomarkers for cellular damage (myoglobin, TNF, and CRP) and increased immune response activities were also described. The scarcity of information on oxidative stress, analyses of cellular injury and biomarkers of inflammatory responses warrants the future study of these topics, which could be helpful in facilitating the safe and effective physical preparations of the members of the armed forces.

Sleep and Performance in Professional Athletes

“…In contrast, Serpell and colleagues (2019) did not find any significant correlations between assessed sleep parameters and general daily muscle soreness-a measure of physical strain and potential proxy into developing injury-across 6 weeks of training in professional rugby athletes [24]. However, this study did demonstrate adverse effects of poor sleep health characteristics on hormones that play central roles in musculoskeletal growth and repair, including testosterone and cortisol [23,29]. This finding aligns with the work of Swinbourne and colleagues (2018) that evidenced a decrease in mean cortisol levels following a sleep extension intervention in professional rugby players [28•].…”

Biochemical and Hormone Markers in Firefighters: Effects of “Search, Rescue, and Survival Training” and Its Recovery

“…Military training is well known to induce high levels of physical and mental stress in response to great physical exertion, sleep deprivation, and food restriction (26). This type of training could negatively affect hormonal modulation, muscle damage, oxidative stress markers (7,20), and, consequently, physical and cognitive performance (26,43). Therefore, subject evaluation to determine the ideal recovery period is essential to understand the magnitude of the impact of training, improve performance, and preserve the health of military personnel (4,33,35).…”

“…Previous studies from our group showed acute reductions in certain body composition variables and a slow return to baseline values in response to search, rescue, and survival training (SRST) (4), and there is a gap in the literature regarding studies evaluating biochemical and hormonal markers in response to military physical training involving sleep and food restriction (7). Considering that there are inconsistencies in the modulation of some hormones (13,16), as well as conflicting results for the alterations in oxidative stress markers and antioxidant capacity (20,41), more studies are needed to understand these changes in this population.…”