Affiliations: [a] Faculty of Social Welfare, Kinki Welfare University,
1966-5, Takaoka, Fukusaki, Kanzaki, Hyogo, 679-2217, Japan. Tel.: +81 790 22
2620; Fax: +81 790 23 0662; E-mail: tokamoto@kinwu.ac.jp | [b] Department of Exercise Physiology and Biochemistry,
Osaka University of Health and Sport Sciences, Osaka, Japan | [c] School of Health and Sport Sciences, Osaka University,
Osaka, Japan
Note: [] Corresponding author
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.
