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) μM 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) μM; time delay (TD), 0.2 (0.2) s, and time constant (τ), 5.9 (0.6) s. Fifteen subjects had a secondary decay phase characterized by A, 1.9 (0.7) μM; TD, 59.2 (6.4) s; and τ, 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 τ, 4.2 (0.3) s. Then, %HbO2 grew exponentially, being characterized by A, 7.9 (0.9) %; TD, 10.1 (1.0) s; and τ, 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 τ, 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.
1Institute of Imaging Science and Departments of 2Biomedical Engineering, 3Radiology and Radiological Sciences, and 4Molecular Physiology and Biophysics, Vanderbilt University, Nashville TN
Address for correspondence: Bruce M. Damon, Ph.D., Vanderbilt University Institute of Imaging Science, AA3105 Medical Center North, 1161 21st Avenue South, Nashville, TN 37232-0675; E-mail: email@example.com.
Submitted for publication April 2006.
Accepted for publication September 2006.