Greater Absolute Deoxygenation In Deep Versus Superficial Quadriceps Muscles At Vo2max During Cycle Ergometry

Abstract

Skeletal muscle deoxygenation ([HHb]) during exercise is dependent on the ratio of oxygen utilization (Vo2) to oxygen delivery (Qo2). Assessment of regional muscle deoxygenation by near infrared spectroscopy (NIRS) has previously been limited technically to superficial muscles. PURPOSE: To use a new high-power Time Resolved (TR) NIRS to investigate deep and superficial muscle deoxygenation during exercise. Because deep muscle has a greater oxidative fiber expression and Qo2/Vo2, we hypothesized that deep quadriceps muscle would deoxygenate less during exercise than superficial muscle. METHODS: Deep and superficial [HHb] was measured by TR NIRS in eight men during incremental cycle ergometry in: superficial vastus lateralis (VL), superficial vastus medialis (VM), and superficial (RF-s) and deep rectus femoris (RF-d). Pulmonary Vo2 was measured breath-by-breath. RESULTS: Vo2max was 2.6±0.4 L/min. On average, for all muscle regions, [HHb] increased from 55±7 μM at baseline to 80±20 μM at peak exercise. [HHb] was less (P<0.05) in RF-d than superficial VL at 70% and 80% peak power, but greater (88±33 μM; P<0.05) than superficial VM (75±20 μM) and VL (77±18 μM) at peak power (Fig.). CONCLUSION: Compared with the superficial muscles, [HHb] was significantly less in deep muscles at submaximal high-intensity work rates: Likely reflecting better maintenance of Qo2/Vo2 in oxidative deep muscle fibers. At peak exercise however, greater [HHb] in deep muscle reveals a greater absolute capacity for O2 extraction compared to more glycolytic superficial muscles. High power NIRS has substantial potential to address important questions regarding vascular and muscle function during exercise. Supported by BBSRC UK, BB/I024798/1, JSPS-24247046