Step-specific distribution of whole-body angular momentum in unilateral transfemoral sprinters at maximal speed

Unilateral transfemoral (TF) sprinters run with pronounced mechanical asymmetries between the prosthetic and intact limbs. Whole-body angular momentum (WBAM) provides a mechanical descriptor of whole-body rotation, yet how WBAM differs between prosthetic and intact steps across planes at maximal sprinting speed remains unclear. We investigated three-dimensional WBAM in nine unilateral TF sprinters running at maximal speed with a running-specific prosthesis. For each step, we quantified peak-to-peak WBAM-range, net integrated WBAM (iWBAM), and positive and negative angular-momentum contributions from five segment groups: head-trunk-pelvis, stance-leg-side arm, swing-leg-side arm, stance leg and swing leg. In the sagittal plane, WBAM-range was 45% larger during the intact step than during the prosthetic step, and net iWBAM was 126% more negative, indicating a greater forward-rotation bias. Segment analyses showed that this intact-step bias was mainly associated with the larger forward-rotation contribution of the intact stance leg. In contrast, the head-trunk-pelvis contributed in the opposite direction, partially offsetting the leg-driven forward-rotation bias. In the frontal plane, iWBAM was 34% more negative during the intact step, indicating a greater bias from the swing-leg side toward the stance-leg side, despite no significant difference in WBAM-range. In the transverse plane, WBAM-range was 40% larger during the intact step, whereas iWBAM did not differ significantly. Neither plane showed significant between-step differences in segment contributions. These findings indicate plane-specific rotational asymmetries not fully captured by WBAM-range alone. Sagittal-plane trunk motion should be evaluated in relation to its potential compensatory role before attempting to minimize trunk excursion or enforce between-step symmetry.