Acute Fatigue Responses to Occupational Training in Military Personnel: A Systematic Review and Meta-Analysis

This article was published in Military Medicine in 2023 (DOI: 10.1093/milmed/usac144).

Note: This article was not submitted to ExultX Spotlight by the authors. However, due to its relevance, we have decided to share it with our community. This text is a commentary on the original article, attempting to highlight the key points. For a more thorough and complete understanding of the content, we strongly recommend everyone to read the original article.

All rights to the findings belong to the authors of the article. Responsibility for the commentary lies with ExultX.

The study of acute fatigue responses to occupational training is crucial in a tactical context, as it directly impacts the physical and cognitive performance of military personnel, both of which are critical for mission success and operational safety. Acute fatigue, resulting from intense operational activities, can impair physical readiness, compromising an operator’s ability to manoeuvre, carry heavy loads, or effectively engage in combat tasks. Furthermore, fatigue-induced physiological stress, such as hormonal imbalances and increased muscle damage, may elevate the risk of injury, hinder recovery, and reduce overall combat readiness. By understanding and monitoring acute fatigue responses, military organisations can optimise recovery protocols, tailor training regimens, and ensure personnel maintain operational readiness while minimising the risk of injury or suboptimal decision-making in high-pressure scenarios.

The article investigates the physiological impacts of military-specific training activities, focusing on muscle damage, inflammation, and hormonal changes in personnel. This study synthesised findings from 14 studies involving 431 participants, primarily male, to evaluate acute fatigue responses caused by training modalities such as physical training (PT), military skills training (MST), and field training exercises (FTX). The meta-analysis revealed significant muscle damage and reduced strength and power performance lasting up to 96 hours post-activity, with minimal inflammatory changes and varied hormonal responses. The authors emphasised the importance of monitoring biomarkers such as testosterone, muscle damage indicators, and performance metrics to optimise recovery and training adaptations. By examining these responses, the study offers valuable insights into the physiological challenges faced by military personnel during and after rigorous occupational training.

1. Description of the Methodology

The article redaction followed PRISMA guidelines, involving a systematic search across databases including PubMed, Scopus, and Web of Science, which initially yielded 7,220 records. After screening, 14 studies were selected based on specific PICO criteria: the population consisted of military personnel without injuries, the intervention involved examining the physiological effects of training activities, the comparison assessed outcomes before and after activity, and the outcomes measured biomarkers and physical performance between 12 and 96 hours post-training.

Studies without relevant biomarker data, physical performance metrics, or those in languages other than English were excluded. Biomarkers such as creatine kinase (CK), cortisol, testosterone, and inflammation markers were examined alongside physical performance metrics. Statistical analyses utilised forest plots and random-effects models to address study heterogeneity, as indicated by I2 scores.

2. Key Takeaways

The key findings demonstrated that military training caused significant muscle damage, evidenced by elevated CK levels, and reduced strength and power, which persisted for up to 96 hours post-activity.

Inflammatory markers did not show consistent increases, possibly due to methodological limitations in the studies reviewed.

Testosterone levels significantly decreased following training, while cortisol and IGF-1 levels remained inconsistent.

Physiological responses varied depending on the training modality, sampling methods, and participant demographics.

These findings highlight the value of routine monitoring of strength, power, and anabolic hormones such as testosterone to optimise recovery and minimise the risk of injury in military personnel.

3. Day-to-Day Applications

In practical terms, the study’s findings suggest several day-to-day applications.

Monitoring Fatigue: Fatigue can be monitored using simple, low-cost strength tests, such as countermovement jumps (CMJs) or repetition maximums, to assess readiness for further training.

Biomarker Tracking: Regular testing of biomarkers such as testosterone, cortisol, or CK, via salivary or blood samples, can help identify levels of fatigue and recovery needs.

Customized Recovery Plans: Training schedules can be adapted based on individual recovery profiles to prevent overtraining and promote better adaptations.

Enhanced Readiness:  Incorporating these insights into training protocols can reduce the risk of injury and maintain operational effectiveness.

Learn more about the article here.