PURPOSES - To characterize the total hemoglobin concentration ([THb]) and oxyhemoglobin saturation (%HbO2) time courses after brief dorsiflexion maximal voluntary contractions (MVC) and to determine whether these responses varied by gender.
METHODS - Eighteen healthy, moderately physically active subjects (nine male) lay supine and performed two or more 3-s dorsiflexion MVC. [THb] and %HbO2 were measured continuously in the tibialis anterior muscle using near-infrared spectroscopy (NIRS). The data from 0 to 150 s postcontraction were analyzed using single- and multicomponent exponential models.
RESULTS - The mean (standard error) precontraction [THb] and %HbO2 values were 78.5 (7.3) microM and 65.0 (0.8) %, respectively, and decreased during the contraction. After the contraction, [THb] grew exponentially, characterized by amplitude (A), 8.7 (1.3) microM; time delay (TD), 0.2 (0.2) s, and time constant (tau), 5.9 (0.6) s. Fifteen subjects had a secondary decay phase characterized by A, 1.9 (0.7) microM; TD, 59.2 (6.4) s; and tau, 12.4 (2.3) s. Eight subjects experienced an initial decay in %HbO2, characterized by A, 1.8 (0.8) %; TD, 0.0 (0) s; and tau, 4.2 (0.3) s. Then, %HbO2 grew exponentially, being characterized by A, 7.9 (0.9) %; TD, 10.1 (1.0) s; and tau, 9.7 (2.0) s. Finally, in 16 subjects, there was a secondary decay phase, characterized by A, 2.6 (0.4) %; TD, 54.4 (7.5) s; and tau, 18.9 (2.6) s. There were no gender differences in any kinetic parameter.
CONCLUSIONS - There are three phases to the post-MVC oxygen supply-demand coupling: 1) rising oxygen demand relative to supply; 2) rising oxygen supply relative to demand; and 3) restoration of precontraction oxygen supply-demand matching. These processes are unaffected by gender.