Assessing the Acute and Chronic Effects of Basic Training in New Zealand Army Recruits

Abstract

Initial military training (IMT), or "basic training" in New Zealand, is a mandatory transition from civilian to soldier. It builds essential soldiering skills by pushing mental and physical limits through high workloads, sleep and calorie restriction, and achieving strict fitness standards. This complicated mix of training is not always carefully managed, and accordingly, injury attrition is a large and costly issue for global militaries. Despite its importance, the physical and cognitive effects on recruits are poorly understood, likely due to heterogenous global practices. The overarching question of this thesis is: What are the effects of basic training on neuromuscular performance in army recruits? To address this question, this thesis included a narrative review, two experimental chapters and a practical commentary. The review synthesised global literature on acute and chronic physiological and neuromuscular effects of basic training, noting that high heterogeneity in duration, intensity and design, ultimately complicating synthesis of the effects identified in the literature. Findings suggest that while acute training bouts (e.g., load carriage, field exercises) temporarily decrease strength and power, cardiovascular strain and maximal oxygen consumption increase. Longitudinally, consistent improvements were identified in cardiorespiratory endurance, full body strength, upper body muscular endurance, and power. However, there was evidence gains often plateau or diminish in longer duration courses and seem to vary by sex and entry fitness levels. Subsequently, two experimental chapters were employed to better quantify the acute and chronic effects of basic training to determine how specific training modalities influence long-term health and readiness in the New Zealand Army. The first explored the effects of 14 weeks of basic training on countermovement jump height. A sample of convenience was recruited from two New Zealand Army recruit intakes (n = 388). Jump height did not clearly change over the duration of the course (e.g., p = .206, ω²p = 0.002). Descriptively, there was evidence of large baseline differences between intakes (p < .001, d = 0.71), complicating interpretation. The second explored the change in neuromuscular performance variables immediately after, 24 and 48 hours post-field exercise, adjusting for relative strength, and whether it varied between sexes. Estimates were variable, with few clear differences between sexes. Where jump height and power remained unchanged (p > .05), force production and movement strategy were altered (p < .05, ω²p = 0.01-0.07); specifically, concentric, eccentric and isometric peak force, flight time:contraction time and concentric duration, often persisting at 48-hours, particularly in males (Pre-48h: p < .05, d = -0.55 to 0.84). These learnings informed a commentary chapter providing practical guidance for neuromuscular profiling and monitoring during basic training. This thesis highlights significant heterogeneity in global recruit training practices and outcomes, a trend that may be present within New Zealand Army recruits. While sex-based differences exhibited high variability, the observation of shifts in force production and movement strategy in response to basic-training activities, but not more common assessments, suggests a more nuanced approach to assessing and managing recruit readiness may be warranted.