Combined Effects Of Load, Posture, And Tactical Sprints On Gait Mechanics During A Marksmanship Task

Soldiers perform many tasks under load, including marksmanship in different postures. It is well documented that load significantly impacts gait mechanics during aerobic bouts of walking and running. Yet, little is known about the impacts of load on anaerobic tasks like short quick movements between firing positions. Additionally, marksmanship posture while engaging threats may impact how Soldiers approach and transition out of firing positions. The combined effects of load and posture may also be exacerbated as repeated anaerobic sprints are performed during a marksmanship task. PURPOSE: Examine the impact of load, posture, and sprint bout on gait mechanics and sprint duration. METHODS:16 active-duty male Soldiers (age: 22.8 ± 4.9 yrs) completed 4 trials of a tactical stress marksmanship assessment (TSMA) course over 2 days. The course included 6x35m sprints separated by 10s rest, where volunteers engaged targets from a prescribed posture. On separate days, volunteers performed the course under unloaded (0 kg) and loaded (~30 kg) conditions. Volunteers completed 2 trials each day, once engaging targets while kneeling (KN) and once while standing (ST). Means of gait mechanics (stride length and duration, using foot-mounted inertial measurement units) and time between firing positions were measured for each sprint. RESULTS:A generalized linear model with generalized estimating equations showed significant interactions of posture and bout on gait mechanics (stride length and duration; p ≤ 0.011) and sprint time (p = 0.001). As bout number increased, stride length decreased (ST slope = 2.8 vs KN slope: 5.1 cm/bout), while stride duration (ST slope = 15 vs KN slope: 19 ms/bout) and sprint time increased (ST slope = 0.33 vs KN slope: 0.44 s/bout) more quickly while kneeling as compared to standing when engaging targets. Significant main effects of load were also observed for stride length and sprint time (p ≤ 0.01). CONCLUSIONS: When using a KN firing posture during TSMA, volunteers’ gait mechanics and sprint time was more impacted than when using a ST posture. This may indicate that transitioning into and out of a KN firing posture may become more fatiguing overtime and may have an added impact than load alone on gait mechanics. Further analysis is needed to describe changes within each bout of the course. Supported by US Army MASTR-E Program