CHANGES IN MUSCLE OXYGENATION AND BLOOD LACTATE DURING EXERCISE IN HUMANS 1521

Abstract

The purpose of this study was to compare the changes in oxygenation of skeletal muscle and lactate threshold (LT) during cycle ergometry exercise. Muscle oxygenation in vastus lateralis was evaluated using near infrared spectroscopy (NIRS), while pulmonary oxygen uptake was measured by an expiratory gas analysis. Blood sample were obtained from the brachial vein for measurements of blood lactate concentration. Muscle oxygenation (%) was calculated from 100% at rest and 0% at the lowest levels during femoral arterial occlusion. Twelve male subjects performed a ramp loaded cycling at a work rate of 20 watts/minute until exhaustion. Maximal oxygen uptake was 50.2±7.9 (mean±SD) ml/kg/min. Initially in the exercise, oxygenation levels increased rapidly relative to resting levels, but then immediately began to decrease in a linear fashion. Six out of 12 subjects reached the deoxygenation break point - the point in exercise at which the rate of deoxygenation increases noticeably. Although the work load at deoxygenation break point tended to larger than that at LT, these results were not statistically significant (165.0±55.3 vs. 125.0±43.1 watts, P=0.06). Minimal muscle oxygenation level during exercise was 67.6±15.4%. In conclusion, only 50% of the test subjects achieved the deoxygenation break point during exercise. Therefore, unlike LT, deoxygenation break point is less likely to be able to be used in the prescription of exercise intensity.