Energy cost and knee extensor strength changes following multiple day military load carriage

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.

Not according to plan: Cognitive failures in marksmanship due to effects of expertise, unknown environments, and the likelihood of shooting unintended targets

Shooting errors have multi-faceted causes with contributing factors that include sensorimotor activity and cognitive failures. Empirical investigations often assess mental errors through threat identification, yet other cognitive failures could contribute to poor outcomes. The current study explored several possible sources of cognitive failures unrelated to threat identification with live fire exercises. Experiment 1 examined a national shooting competition to compare marksmanship accuracy, expertise, and planning in the likelihood of hitting no-shoot or unintended targets. Experts demonstrated an inverse speed/accuracy trade-off and fired upon fewer no-shoot targets than lesser skilled shooters, yet overall, greater opportunity to plan produced more no-shoot errors, thereby demonstrating an increase in cognitive errors. Experiment 2 replicated and extended this finding under conditions accounting for target type, location, and number. These findings further dissociate the roles of marksmanship and cognition in shooting errors while suggesting that marksmanship evaluations should be re-designed to better incorporate cognitive variables.

Task demand and load carriage experience affect gait variability among military cadets

Load carriage is an inevitable daily task for soldiers. The purposes of this study were to explore the extent to which gait variability (GV) is affected by load carriage and experience among military cadets, and whether experience-related differences in GV are dependent on task demand. Two groups of cadets (30 experienced, 30 less experienced) completed a load carriage task in each of three load conditions (no load, 16 kg, 32 kg). Three categories of GV measures were obtained: spatiotemporal variability, joint kinematic variability, and Lyapunov exponents. Compared to traditional mean gait measures, GV measures were more discriminative of experience: although both groups showed similar mean gait measures, the experienced participants had reduced variability in spatiotemporal measures (p ≤ 0.008) and joint kinematics (p ≤ 0.004), as well as lower levels of long-term local dynamic stability at the ankle (p = 0.040). In both groups, heavier loads were also caused increased GV (p ≤ 0.018) and enhanced short-term local dynamic stability at the knee (p = 0.014). These results emphasize the importance of GV measures, which may provide a more complete description of adaptability, stability, and control; highlight alternate movement strategies during more difficult load carriage; and capture experience-related differences in load carriage strategies.

Multiday load carriage decreases ability to mitigate ground reaction force through reduction of ankle torque production

The aim of this study was to examine the impact of backpack load carriage on lower limb strength and loading rate change in a cohort that match military recruit profiles. Twenty-six participants walked on a treadmill either carrying a military load carriage system (32 kg) or unloaded for 2 h on two consecutive days. Participants ground reaction forces and strength measures were assessed using a force platform and dynamometry, respectively. Testing included assessments before and after treadmill walking on days one and two, and 24 h following day 2. When assessed by mixed methods ANOVA (alpha: 0.05) statistically significant interaction effects were observed for loading peak (p = 0.031), loading rate (p = 0.035) and plantarflexor torque dynamometry variables at 60°s^-1 (p = 0.011) and 120°s^-1 (p = 0.024). Repeated measures correlation highlighted associations between plantarflexor torque at 60°s^-1 and loading rate (r = -0.901, p < 0.001). Load carriage reduced lower limb torque which did not recover between days. Plantarflexor torque reductions were associated with increases in loading rate. Practitioners should consider that load bearers are more likely to experience lower limb injury during multi-day load carriage. Future work should develop protocols to reduce plantarflexor torque loss in order to reduce ground reaction force change.