Abstract
We investigated the effects of eccentric contraction velocity on oxygen uptake and oxygen dynamics in the rectus femoris. Knee extension exercise was performed in 15 healthy male subjects using an isokinetic dynamometer. The angular velocity was set at 60 and 180°/s with a near infrared spectroscope probe fixed on the rectus femoris in order to record muscle oxygenation (MO) levels during and after the exercises. Oxygen uptake was measured using the breath-by-breath method. MO levels at an angular velocity of 60°/s were significantly lower than at an angular velocity of 180°/s at 60 and 90 seconds after the onset of the exercises (p < 0.05). Oxygen uptake increased immediately after the onset of the exercises and reached the highest level at the end of the exercises at both angular velocities of 60 and 180°/s. When MO levels were the lowest (60 sec. after the onset of the exercise), oxygen uptake levels were significantly higher at an angular velocity of 60°/s versus 180°/s (p < 0.05). These results revealed that decreased MO levels at a lower muscle contraction velocity might be due to increased mechanical compression of the blood vessels resulting in impaired blood flow. In addition, low oxygen levels of active muscle may stimulate increases in oxygen uptake to avoid hypoxia. The hypoxic conditions in active muscle during the first half of the exercise was temporary, offset by the steady increase in alveolar oxygen uptake during exercise.