Metabolic, cardiovascular, neuromuscular and perceptual responses to repeated military-specific load carriage treadmill simulations

Bouts of military load carriage are rarely completed in isolation; however, limited research has investigated the physiological responses to repeated load carriage tasks. Twelve civilian men (age, 28 ± 8 years; stature, 185.6 ± 5.8 cm; body mass 84.3 ± 11.1 kg and maximal oxygen uptake, 51.5 ± 6.4 mL·kg⁻¹ min⁻¹) attended the laboratory on two occasions to undertake a familiarisation and an experimental session. Following their familiarisation session, participants completed three bouts of a fast load carriage protocol (FLCP; ∼65 min), carrying 25 kg, interspersed with a 65-min recovery period. Physiological strain (oxygen uptake [V̇O₂] and heart rate [HR]) was assessed during the FLCP bouts, and physical performance assessments (weighted counter-movement jump [wCMJ], maximal isometric voluntary contraction of the quadriceps [MIVC] and seated medicine ball throw [SMBT]) was measured pre and post each FLCP bout. A main effect for bout and measurement time was evident for V̇O₂ and HR (both p < 0.001 and Ѡ² = 0.103–0.816). There was no likely change in SMBT distance (p = 0.201 and Ѡ² = 0.004), but MIVC peak force reduced by approximately 25% across measurement points (p < 0.001 and Ѡ² = 0.133). A mean percentage change of approximately −12% from initial values was also evident for peak wCMJ height (p = 0.001 and Ѡ² = 0.028). Collectively, these data demonstrate that repeated FLCP bouts result in an elevated physiological strain for each successive bout, along with a substantial reduction in lower body power (wCMJ and MIVC). Therefore, future research should investigate possible mitigation strategies to maintain role-related capability.