Abstract
<title>Abstract</title> <p>Unilateral transtibial amputation results in structural and microvascular changes that may influence muscle oxygenation during functional and weight-bearing activities. Understanding these alterations is essential for optimizing rehabilitation and assistive device use. This study examined limb-specific differences in muscle oxygenation under varying postural and isometric conditions using near-infrared spectroscopy (NIRS). Forty-one individuals with unilateral transtibial amputation were assessed during four standardized conditions: sitting rest, sitting isometric contraction, standing rest, and standing isometric contraction. Muscle oxygen saturation (SmO₂), oxygenated hemoglobin (O₂Hb), deoxygenated hemoglobin (HHb), total hemoglobin (tHb), and hemoglobin difference (HbDiff) were analysed using a two-way repeated measures ANOVA (limb × condition) with post-hoc comparisons. Significant main effects of limb and condition were observed across all parameters (p < 0.05), with the sound limb consistently demonstrating higher oxygenation and perfusion values. Standing and isometric conditions elicited greater physiological responses compared with sitting, reflecting increased metabolic demand. Significant limb × condition interactions for SmO₂, tHb, O₂Hb, and HHb indicated distinct microvascular responses to mechanical loading. The largest interlimb differences were observed during standing conditions, suggesting increased physiological demand on the amputated limb during weight-bearing tasks. These findings highlight an imbalance between oxygen delivery and utilization in the residual limb and emphasize the importance of posture in modulating muscle oxygenation. Integrating NIRS-based monitoring into assistive technology and rehabilitation strategies may support individualized load management, improve prosthetic use, and enhance functional outcomes in individuals with lower-limb amputation.</p>