Noninvasive determination of exercise-induced vasodilation during bicycle exercise using near infrared spectroscopy.
BACKGROUND
The purpose of this study was to examine the changes in total hemoglobin (Delta[tHb]) response during bicycle exercise at various constant workloads using near infrared continuous wave spectroscopy (NIRcws) in humans. We hypothesized that the Delta[tHb] during exercise may progressively increase as a result of a dilation of the vascular bed and/or capillary recruitment at lower constant work rates.


METHODS
Seven healthy subjects performed bicycle exercise at 20, 40, 60, 80, and 100% of maximal work rates (Wmax) for 5 min. Muscle oxygenation change (Delta[Oxy]) and Delta[tHb] at the right vastus lateralis were monitored using a NIRcws device. Exercise-induced Delta[tHb] and Delta[Oxy] responses at each constant workload were evaluated as functional Delta[tHb] change (f-Delta[tHb]) and functional oxygenation change (f-Delta[Oxy]), respectively. Blood lactate concentration [La] was also evaluated after each exercise stage.


RESULTS
At work rates 60%Wmax and below, after an initial decrease at the start of exercise, both Delta[tHb] and Delta[Oxy] showed progressive increases until the end of exercise. A significant positive correlation was found between f-Delta[tHb] and f-Delta[Oxy] (p<0.01). In addition, there was a significant negative relationship of [La] to f-Delta[tHb] during exercise (p<0.05).


CONCLUSIONS
These results provide evidence that increased muscle oxygenation during bicycle exercise up to 60%Wmax may be caused by increased O2 supply due to exercise-induced blood volume expansion. Subsequently, the cessation of increase in f-Delta[tHb] at higher intensity exercise may lead to lower muscle tissue oxygenation and higher lactate accumulation.
Kime
Ryotaro
R
Department of Sports Medicine for Health Promotion, Tokyo Medical University, Tokyo, Japan. kime@tokyo-med.ac.jp
Im
Joohee
J
Moser
Daniel
D
Nioka
Shoko
S
Katsumura
Toshihito
T
Chance
Britton
B
D000328:Adult; D001810:Blood Volume; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D008297:Male; D010100:Oxygen / Q000378:metabolism; D015203:Reproducibility of Results; D019265:Spectroscopy, Near-Infrared / Q000379:methods*; D014664:Vasodilation / Q000502:physiology*
D006454:Hemoglobins; D019344:Lactic Acid; D010100:Oxygen