Effects Of Leg Extension Range Of Motion On Proximal Vs Distal Vastus Lateralis Microvascular Response

Near-infrared spectroscopy (NIRS) can measure a muscle’s microvascular response to exercise. This response varies along the muscle proximo-distally and is predictive of regional hypertrophy. While range of motion (ROM) is an essential factor of any exercise, its effects on regional microvascular response are unknown. PURPOSE: To compare the effects of ROM on regional microvascular response. METHODS: Twenty-one healthy, active participants performed both isokinetic (IK) and isometric (IM) leg extensions utilizing contralateral limbs. A set of 10 repetitions was performed for IM and IK at both short and long muscle lengths, resulting in 4 exercise conditions. Each set was separated by 15 min. IK was performed at 30°/s between 30-75° (short muscle length) and 75-120° (long muscle length) knee flexion. IM was performed with 70% of previously assessed maximal isometric strength at 55° (short length) and 95° (long length). Vastus lateralis microvascular response was measured at 33% (proximal) and 67% (distal) thigh length using NIRS with changes in oxygen saturation (StO2), oxygenated hemoglobin (O2), and deoxygenated hemoglobin (CO2) reported in one-minute averages for 5 minutes post-exercise. These results were then compared using separate 2x2x5 (muscle length x muscle region x time) repeated measures MANOVAs with Bonferroni post-hoc tests for IM and IK. RESULTS: The overall microvascular response did not significantly differ between proximal and distal positions when leg extensions were completed in either exercise condition (IK: p = 0.251-0.266, IM: p = 0.075-0.086). However, post-hoc analysis revealed a greater physiological response distally when the exercise was performed at long muscle length than short muscle lengths as evident by a greater hyperoxic response 1-3 min post-exercise in IK and 2-3 min post-exercise in IM (p < 0.05). CONCLUSION: Performing leg extensions with greater knee flexion (long-muscle length) resulted in a greater distal microvascular response. These results suggest that ROM inhomogenously stresses the muscle in a manner which may affect patterns of hypertrophy. This study was supported by departmental funds, no external funding was received.