Infantry training outcomes: are they improved with an initial reduction in load carriage mass and additional sprint intensity exercise?

Introduction: Infantry is a physically demanding trade that is associated with elevated rates of musculoskeletal injury. A 17-week longitudinal intervention assessed the effect of a progressive increase in load carriage mass and sprint-intensity intervals on physical performance, physical complaints, medical encounters, physical activity and sleep in infantry trainees.

Methods: 91 infantry trainees from 2 separate platoons, randomly assigned as control (CON) or experimental (EXP), provided written voluntary consent. Both completed a 17-week training syllabus that included physical training and military education lessons. Compared with CON, EXP completed a modified regimen that included; a 25%-30% reduction in load carriage mass (weeks 1-4), sprint (weeks 1-7) and 3 min running intervals. Endurance, strength, power and functional performance were assessed (weeks 1, 6-8), physical activity and sleep were recorded using actigraphy (each day of training, weeks 1-17), with daily physical complaints tabulated (weeks 1-7) and frequency of medical encounters retrospectively extracted from defence health records (weeks 1-17).

Results: On-time completion of training was attained in 93% and 79% of CON and EXP, respectively. Total load carriage mass (weeks 1-4) was 27% lower in EXP (10.1 kg/hour) than CON (13.9 kg/hour). Push-up repetitions in CON (5 reps) improved compared with EXP, with functional performance improving markedly in both groups (71 m, 23%). All other fitness assessments were similar between groups. No difference in sleep quality and quantity was observed between groups, with 77% and 16% of trainees sleeping <7 hours (suboptimal) and <6 hours (sleep restricted) per night, respectively. Physical complaints in CON were higher (62), despite no difference observed in medical encounters.

Conclusions: The reduction in load carriage mass and inclusion of sprint interval training did not modify the adaptative or maladaptive responses to infantry training. Most trainees experienced chronic suboptimal sleep quantity and quality with over 15% classified as sleep restricted.