Muscle contraction-induced limb blood flow variability during dynamic knee extensor.

PURPOSE

To evaluate whether muscle contraction-induced variability of limb femoral arterial blood flow (FABF) can be reduced with longer sampling durations. This was assessed in relation to muscle contraction-relaxation cycles (CRcycles) during steady-state, one-legged, dynamic knee-extensor exercise (KEE) at varying "exercise intensities" and "contraction frequencies."

METHODS

Eleven male subjects performed steady-state KEE at 10-40 W at 30 and 60 contractions per minute (cpm). FABF (Doppler ultrasound) and contraction-relaxation-induced variability in FABF was determined for 1-, 2-, 5-, 10-, 15-, 20-, and 30-CRcycles during approximately 4-min steady-state KEE. Variability was determined as coefficients of variation (CV).

RESULTS

During KEE at 30 and 60 cpm CVFABF was significantly higher for 1-CRcycles (12.3% and 15.5%) and 2-CRcycles (9.6% and 11.8%) than for 30-CRcycles (4.0% and 5.2%), but similar for 10-CRcycles to 30-CRcycles at all work rates and contraction frequencies. The CVFABF between work rates at 30 and 60 cpm did not statistically differ (P = NS) for any of the CRcycle measurements. However, the single CRcycles-induced CVFABF at 60 cpm was significantly higher (P < 0.05) than that at 30 cpm at the lower exercise intensities of 10 and 20 W, but with no significant difference at 30 and 40W.

CONCLUSION

Limb blood flow variability was markedly reduced with a longer sampling measurement of at least 10-CRcycles, which had a CVFABF of approximately 5%. Furthermore, the 1-CRcycle-induced FABF variability was similar at each exercise intensity, but significant variations were seen between contraction frequencies at lower exercise intensities. It is speculated the difference between the contraction frequencies at lower exercise intensities may be due to the muscle contraction-relaxation-induced variations in muscle force (intramuscular pressure), along with the superimposed blood pressure waves.