Despite an improved aerobic endurance, still high attrition rates in initially low-fit recruits—results of a randomised controlled trial

Background: Low baseline fitness of recruits entering basic military training (BMT) is associated with an increased risk of musculoskeletal injuries (MSIs) and attrition from training. Objective: To determine the effects of a pre-training conditioning program (PCP) on aerobic endurance, incidence of musculoskeletal injuries (MSIs), and attrition rates in BMT of a special infantry unit of the Netherlands Armed Forces. Participants: Recruits were considered eligible for this study when they were ‘low-fit’ at the start of BMT (time to complete a 2.7-km run ≥ 12′23″). Interventions: ‘Low-fit’ recruits were deferred to a seven to twelve week—depending on the time between two consecutive training platoons—PCP consisting of functional training to improve several fitness domains. The control (CON) group started regular BMT without delay. Results: Forty-nine recruits were included in this study; 26 in the PCP-group and 23 in the CON-group. Recruits who followed the PCP started BMT with better aerobic endurance than the CON-group who started BMT immediately (2.7 km run timings: PCP 11′32″, CON 13′16″). The risk of dropout was lower in the PCP-group (incidence density ratio (IDR) 0.63, 95%CI 0.32; 1.26), but dropout due to training-related MSIs was more frequent (IDR 1.23, 95%CI 0.32; 4.76 (per-protocol 0.94, 95%CI 0.24; 3.63), without statistically significant differences between the groups. Conclusion: Although a PCP was effective to improve aerobic endurance in low-fit recruits to return to meet pre-enlistment fitness criteria, we could not demonstrate an effect on dropout from military training. Trial registration: Dutch trial register Trial NL6791 (NTR6977) https://www.trialregister.nl/trial/6791