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

Abstract

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.

Keywords: combatant; military personnel; occupational physiology; physical functional performance; physiological stress.

FIGURE 1

The relative V̇O₂ and heart rate during the three Fast Load Carriage Protocol bouts. Data are presented as mean ± SD. The light grey, white and dark grey areas denote the 5.1 km·h⁻¹, 6.5 km·h⁻¹ and simulated fire and manoeuver portions of the protocol, respectively. Circle, square and triangle symbols denote data for bout 1, 2 and 3, respectively.

FIGURE 2

The relative Ratings of Perceived Exertion, Comfort Affective Labeled magnitude and thermal comfort scales during the three Fast Load Carriage Protocol bouts. Data are presented as mean ± SD, where light grey, white and dark grey areas denote the 5.1 km·h⁻¹, 6.5 km·h⁻¹ and simulated fire and manoeuver portions of the protocol, respectively. Circle, square and triangle symbols denote data for bout 1, 2 and 3, respectively.

FIGURE 3

The percentage change in medicine ball throw distance, peak maximal isometric force of the quadriceps and weighted countermovement jump height across the three Fast Load Carriage Protocol bouts. Where black circles (o) denote individual data points with dotted lines connecting these across assessment points; thick black line (−) denotes the group mean average across assessment points and greyed areas denote each of the three fast load carriage protocols completed.