Physiological and Subjective Responses to a Novel Military Specific Load Carriage Treadmill Protocol

Purpose: Treadmill-based load carriage protocols typically use a single fixed speed; however, these are not representative of occupational load carriage tasks. This study aimed to quantify the metabolic, cardiovascular, thermal, neuromuscular, and perceptual responses to a treadmill-based, military-specific, fast load carriage protocol (FLCP). This protocol comprised of carrying 25 kg, for 20 minutes at 5.1 km·h-1; 40 minutes, at 6.5 km·h-1; and 8 x 9 s shuttles, at 11 km·h-1 with 11 s recovery. Methods: Twelve men (age, 27 ± 6 y; stature, 1.83 ± 0.05 m; body mass, 80.6 ± 8.0 kg; maximal oxygen uptake, 52.7 ± 5.5 mL·kg-1·min-1), completed a FLCP during which oxygen consumption (VO2), heart rate, core body temperature, and perceptual ratings were recorded. Performance assessments (weighted counter-movement jump [wCMJ], maximal isometric voluntary contraction [MIVC] of the quadriceps, seated medicine ball throw [SMBT]) were completed pre-FLCP, immediately-post and, 30, 60, 120 minutes’ post. Results: V̇O2 was similar for 5.1 km·h-1, but increased by 7.4% during the 40 minutes at 6.5 km·h-1 (p = 0.013). Core temperature increased by 0.92 ± 0.22 ºC in response to the FLCP. Post-FLCP, SMBT was not dissimilar across measurement points, (p = 0.315), however, MIVC peak force reduced by 12.6 ± 10.9% 60 minutes post-FLCP (p = 0.031), and wCMJ height decreased by 8.7 ± 5.9% 120 minutes post-FLCP (p = 0.011). Conclusion: The completion of the FLCP does not affect upper body power (SMBT), but appears to modestly decrease lower body explosiveness (wCMJ and MIVC) up to two hours post. Future investigations can use the FLCP protocol to investigate occupationally relevant scenarios, such as the interaction between physical and cognitive performance during load carriage, or the implications of multiple repeated load carriage bouts.