BACKGROUND: Lean mass (LM) asymmetries may impact athlete availability and injury risk. Despite the known risks that asymmetries may present, clinically significant differences in LM have not been established and may not be detected by whole limb analysis. Segmental custom regions of interest (ROI) analysis may reveal LM differences that would otherwise go undetected. The purpose of this study was to assess LM at standard and custom ROIs to detect muscular imbalances and establish meaningful differences in Division I athletes. METHODS: Dual-energy x-ray absorptiometry testing was performed on 581 NCAA Division I athletes (mean±SD; Age=20.2±1.4 yrs, Height=176.4±12.6 cm, Weight=83.3±26.0 kg; 46% female) from August 2015 to July 2023. Full body scans were completed as part of normal testing for nine teams. Standard ROI analysis was used to determine total leg LM. Custom ROI analysis was completed for glute (G), quadriceps (Q), and calf (C) by using the polygon function on each leg. G ROI consisted of the tissue between the top of the pelvis and the bottom of the pubic symphysis. The Q ROI contained the tissue between the bottom of the pubic symphysis to the tibiofemoral joint. The C ROI consisted of the tissue between the tibiofemoral joint and the talocrural joint. Regional percent differences [(segment LM difference)/(total segment LM/2) *100] were calculated and meaningful differences were established from mean and standard deviations of each segment. RESULTS: Average segmental limb differences for male athletes were (mean ± SD): G=1.41±4.39%, Q=0.26±2.92%, C=0.64±4.65% and for female athletes: G=2.04±4.43%, Q=0.25±4.17%, C=0.79±4.61%. For males, values above G:5.8%, Q:3.2%, C:5.3% appeared to be clinically relevant. For females, differences above G:6.5%, Q:4.4%, C:5.4% resulted in meaningful cut-points. Segmental limb differences were prevalent amongst the whole sample, with clinically relevant imbalances occurring in 19% (G), 23% (Q), and 24% (C) of each respective region. CONCLUSION: Segmental LM analyses may provide a clinically relevant target to support injury prevention and rehabilitation, that often is not detected with whole limb analysis. Regional differences may provide insight into an acceptable target for LM asymmetry at each segment to better support injury prevention and return to play. Future research should evaluate the relationship between regional differences and injury.

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