Associations Between Physical Activity And Drop-landing Tibial Accelerations In U.S. Army Trainees

Landing activities are associated with musculoskeletal injury during Basic Combat Training (BCT). This may be related to higher impacts, which have been shown to predict injury in runners. Physically active individuals, engaged in regular exercise, may be able to better attenuate landing impacts than less-active trainees. PURPOSE: To compare impacts during drop-landings in BCT trainees with varying levels of physical activity. METHODS: 216 Army trainees participated in the first week of BCT. Inertial measurement units were strapped around the distal antero-medial tibia bilaterally. After three practice trials, participants completed three trials of double- and single-leg drop-landings off 18” and 12” boxes, respectively. Peak vertical and resultant tibial accelerations (rTAs) in the dominant limbs were analyzed. Participants completed surveys on their exercise habits in the 2 months prior to BCT and were divided into 3 groups based on exercise frequency: low (0-2x/wk), medium (3-4x/wk) and high (>4x/wk). Participants who reported substantially changing their exercise habits prior to BCT were excluded (n = 116). ANOVAs were used to compare mean TAs between the three physical activity groups. RESULTS: Peak rTAs during double-leg landings differed by physical activity frequency. Pairwise comparisons revealed that trainees in the high frequency exercise group exhibited lower rTAs compared with those in the low frequency exercise group (p = 0.013). There were no differences in peak vertical TAs or rTAs during single-leg landings (p = 0.18-0.25). CONCLUSION: Army trainees who exercised more frequently before BCT had lower rTAs during double-leg drop-landings. Understanding whether this also relates to reduced injury risk requires further research. 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.