Biomechanics of Load Carriage

The effect of weapon handling during load carriage across a range of military-relevant walking speeds

This study investigated the effects of weapon handling on the physiological responses and walking-gait kinematics during load carriage. Seventeen soldiers completed four twelve-minute bouts of treadmill walking at incremental speeds (3.5, 5.5, 6.5 km.h-1 and self-selected) carrying 23.2-kg of additional load, while either handling a weapon or not handling a weapon. Physiological, perceptual and biomechanical outcomes were measured throughout each trial. A weapon-by-speed interaction (p < .05) was observed for hip flexion-extension during loading response and mid-swing. Weapon handling elevated (p < .05) cardiorespiratory responses at 6.5 km.h-1. Main effects (p < .05) of weapon handling were observed for ventilation, oxygen pulse, effort perception, stride length and knee flexion-extension during toe-off. No main effects of weapon handling were observed for any other biomechanical measures. These findings demonstrate that physiological and biomechanical responses to weapon handling are likely walking-speed dependent.Practitioner summary: Weapon handling is an important part of many load-carriage tasks but is rarely investigated. Physiological and biomechanical responses were assessed at incremental speeds during load carriage. Despite similar biomechanics, there was greater physiological demands at faster walking speeds, suggesting an increased contribution from isometric muscle contractions for weapon stabilisation.

ADAPTations to low load blood flow restriction exercise versus conventional heavier load resistance exercise in UK military personnel with persistent knee pain: protocol for the ADAPT study, a multi-centre randomized controlled trial

BACKGROUND

Muscle atrophy, muscle weakness and localised pain are commonly reported following musculoskeletal injury (MSKI). To mitigate this risk and prepare individuals to return to sport or physically demanding occupations, resistance training (RT) is considered a vital component of rehabilitation. However, to elicit adaptations in muscle strength, exercise guidelines recommend lifting loads ≥ 70% of an individual's one repetition maximum (1-RM). Unfortunately, individuals with persistent knee pain are often unable to tolerate such high loads and this may negatively impact the duration and extent of their recovery. Low load blood flow restriction (LL-BFR) is an alternative RT technique that has demonstrated improvements in muscle strength, hypertrophy, and pain in the absence of high mechanical loading. However, the effectiveness of high-frequency LL-BFR in a residential rehabilitation environment remains unclear. This study will compare the efficacy of high frequency LL-BFR to 'conventional' heavier load resistance training (HL-RT) on measures of physical function and pain in adults with persistent knee pain.

METHODS

This is a multicentre randomised controlled trial (RCT) of 150 UK service personnel (aged 18-55) admitted for a 3-week residential rehabilitation course with persistent knee pain. Participants will be randomised to receive: a) LL-BFR delivered twice daily at 20% 1-RM or b) HL-RT three-times per week at 70% 1-RM. Outcomes will be recorded at baseline (T1), course discharge (T2) and at three-months following course (T3). The primary outcome will be the lower extremity functional scale (LEFS) at T2. Secondary outcomes will include patient reported perceptions of pain, physical and occupational function and objective measures of muscle strength and neuromuscular performance. Additional biomechanical and physiological mechanisms underpinning both RT interventions will also be investigated as part of a nested mechanistic study.

DISCUSSION

LL-BFR is a rehabilitation modality that has the potential to induce positive clinical adaptations in the absence of high mechanical loads and therefore could be considered a treatment option for patients suffering significant functional deficits who are unable to tolerate heavy load RT. Consequently, results from this study will have a direct clinical application to healthcare service providers and patients involved in the rehabilitation of physically active adults suffering MSKI.

TRIAL REGISTRATION

ClinicalTrials.org reference number, NCT05719922.

Mechanical Differences between Men and Women during Overground Load Carriage at Self-Selected Walking Speeds

Few studies have directly compared physical responses to relative loading strategies between men and women during overground walking. This study aimed to compare gait mechanics of men and women during overground load carriage. A total of 30 participants (15 male, 15 female) completed three 10-min walking trials while carrying external loads of 0%, 20% and 40% of body mass at a self-selected walking speed. Lower-body motion and ground reaction forces were collected using a three-dimensional motion capture system and force plates, respectively. Female participants walked with a higher cadence (p = 0.002) and spent less absolute time in stance (p = 0.010) but had similar self-selected walking speed (p = 0.750), which was likely due to the female participants being shorter than the male participants. Except for ankle plantarflexion moments, there were no sex differences in spatiotemporal, kinematic, or kinetic variables (p > 0.05). Increasing loads resulted in significantly lower self-selected walking speed, greater stance time, and changes in all joint kinematics and kinetics across the gait cycle (p < 0.05). In conclusion, there were few differences between sexes in walking mechanics during overground load carriage. The changes identified in this study may inform training programs to increase load carriage performance.

Treadmill load carriage overestimates energy expenditure of overground load carriage

This study compared physiological and biomechanical responses between treadmill and overground load carriage. Thirty adults completed six 10-minute walking trials across three loads (0, 20, and 40% body mass) and two surfaces (treadmill and overground). Relative oxygen consumption was significantly greater on the treadmill for 20% (1.54 ± 0.20 mL⋅kg^-1⋅min^-1) and 40% loads (1.08 ± 0.20 mL⋅kg^-1⋅min^-1). All other physiological and perceptual responses were significantly higher in the treadmill condition and with increases in load. Stance time was longer (0%: 0.05 s; 20%: 0.02 s, 40%: 0.05 s, p < 0.001) and cadence was lower (0%: 1 step·min^-1; 20%: 2 steps·min^-1; 40%: 3 steps·min^-1, p < 0.05) on the treadmill. Peak lower limb joint angles were similar between surfaces except for ankle plantar flexion, which was 8˚ greater on the treadmill. The physiological responses to treadmill-based load carriage are generally not transferable to overground load carriage and caution must be taken when conducting treadmill-based load carriage research to inform operational-based scenarios. Practitioner Summary: Literature is limited when comparing the physiological and biomechanical responses to treadmill and overground load carriage. Using a repeated measures design, it was shown that although walking kinematics are generally similar between surfaces, there was a greater physiological demand while carrying a load on a treadmill when compared with overground. Abbreviations: BM: body mass; e.g: for example; HR: heart rate; HR_max: heart rate maximum; Hz: hertz; kg: kilograms; km·h^-1: kilometres per hour; L⋅min^-1: litres per minute; m: metres; MD: mean difference; mL·kg^-1·min^-1: millilitres per kilogram per minute; mL⋅min^-1: millilitres per minute; η²p: partial-eta squared; OG: overground; RPE: rating of perceived exertion; s: seconds; SD: standard deviation; SE: standard error; steps·min^-1: steps per minute; TM: treadmill; V̇CO₂: volume of carbon dioxide; V̇E: ventilation; V̇O₂: volume of oxygen; V̇O_2max: maximum volume of oxygen; y: years.