Age-related Differences In Impacts During Running And Loaded Walking In US Army Trainees

As many as 50% of Army trainees develop musculoskeletal injuries during Basic Combat Training (BCT), with a large proportion related to running and walking with load carriage (loaded walking). Older trainees are at an even greater risk for the overuse injuries associated with these activities. Overuse injuries in runners have shown associations with early stance, or impact, ground reaction forces (GRFs) and peak tibial accelerations (TAs). Therefore, age-related differences in these biomechanical variables might help to explain higher rates of injury in older trainees. PURPOSE: To investigate age-related differences in running and loaded walking impacts in US Army trainees METHODS: Data from 487 U.S. Army trainees (311 men, 176 women) were collected in the first week of BCT. Participants wore an inertial measurement unit on their distal antero-medial tibias. Participants ran (2.68-2.90 m/s) and walked with an 18.1 kg pack (1.21-1.34 m/s) on an instrumented treadmill. For each bout, 7 strides of data were collected after a 3-minute warm-up. Peak vertical and resultant TAs and vertical instantaneous GRF loading rates (VILR) were calculated and averaged across strides for the dominant leg. Participants were grouped by age as young (≤19 yrs), middle (20-24 yrs), or older (≥25 yrs). ANOVAs were used to compare variables across ages and by sex. RESULTS: There was no significant main effect of age (Table 1) or interaction of sex and age (p = 0.14 - 0.91). CONCLUSION: Our results show that impact related GRFs and TAs during running and loaded walking do not vary across age in Army trainees before BCT. Therefore, they may not explain higher injury rates reported in older trainees. Other factors, such as those relating to movement patterns, may play a more important role. Supported by US DoD award W81XWH-20-C-0123 P0001. The opinions/assertions in this manuscript are the private views of the authors and are not to be construed as official policy or reflecting the views of the US Army.