1-s-duration maximum isometric ankle dorsiflexion contractions resulted in peak postcontractile muscle BOLD signal intensity changes that significantly correlated with peak blood flow (r=0.61).
Observational (n=11)
How do brief, single contractions affect blood flow, magnetic resonance image signal intensity, and oxygenation in human skeletal muscle?
Muscle postcontractile BOLD signal intensity changes depend critically on the balance between oxygen delivery and consumption, which are influenced by chronic physical activity.
Effect estimate: r = 0.61
Previous studies show that transient increases in both blood flow and magnetic resonance image signal intensity (SI) occur in human muscle after brief, single contractions, and that the SI increases are threefold larger in physically active compared with sedentary subjects. This study examined the relationship between these transient changes by measuring anterior tibial artery flow (Doppler ultrasound), anterior muscle SI (3T, one-shot echo-planar images, TR/TE = 1,000/35), and muscle blood volume and hemoglobin saturation near-infrared spectroscopy (NIRS) in the same subjects after 1-s-duration maximum isometric ankle dorsiflexion contractions. Arterial flow increased to a peak 5.9 ± 0.7-fold above rest (SE, n = 11, range 2.6-10.2) within 7 s and muscle SI increased to a peak 2.7 ± 0.6% (range 0.0-6.0%) above rest within 12 s after the contractions. The peak postcontractile SI change was significantly correlated with both peak postcontractile flow (r = 0.61, n = 11) and with subject activity level (r = 0.63, n = 10) estimated from 7-day accelerometer recordings. In a subset of 7 subjects in which NIRS data acquisition was successful, the peak magnitude of the postcontractile SI change agreed well with SI calculated from the NIRS blood volume and saturation changes (r = 0.80, slope = 1.02, intercept = 0.16), confirming the blood-oxygenation-level-dependent (BOLD) mechanism underlying the SI change. The magnitudes of postcontractile changes in blood saturation and SI were reproduced by a simple one-compartment muscle vascular model that incorporated the observed pattern of postcontractile flow, and which assumed muscle O(2) consumption peaks within 2 s after a brief contraction. The results show that muscle postcontractile BOLD SI changes depend critically on the balance between O(2) delivery and O(2) consumption, both of which can be altered by chronic physical activity.
Towse et al. (2011) reported an observational. 1-s-duration maximum isometric ankle dorsiflexion contractions vs. Rest was evaluated on Correlation between peak postcontractile signal intensity (SI) change and peak postcontractile flow (r = 0.61). 1-s-duration maximum isometric ankle dorsiflexion contractions resulted in peak postcontractile muscle BOLD signal intensity changes that significantly correlated with peak blood flow (r=0.61).