Muscle blood flow is influenced by the metabolic demands placed upon the exercising musculature. Since the metabolic cost of eccentric exercise is lower than that of concentric exercise (Woledge et al. 1985), at an equivalent degree of force/power production, it has been suggested that the blood flow would be concomitantly lower (Nadel et al. 1972). Whether this difference in blood flow exists has not to our knowledge been tested. The aim of the present investigation was to measure blood flow during 6 min of single leg knee-extensor exercise when the mode of contraction was concentric on one occasion and eccentric on another.
With ethics committee approval seven healthy subjects (6 males and 1 female) volunteered for the present study. Their physical characteristics were (mean ± S.D.) age 26 ± 4 years, mass 80.1 ± 7.9 kg and height 1.78 ± 0.05 m. Subjects completed two exercise trials on an isokinetic dynamometer (Lido, Loredan Biomedical Inc., Davis, CA, USA) where the mode of contraction was either concentric (CON) or eccentric (ECC) in nature. Total exercise duration was 6 min, consisting of four 90 s bouts interspersed with 15 s of rest. Exercise mode was completed in randomised order and the trials were separated by 70 min of passive rest. Femoral artery diameter and blood velocity was measured by ultrasound Doppler (Esaote Biomedica AU4 Idea) at an imaging frequency of 10 MHz. Blood velocity was measured at rest and immediately after each exercise bout. Pulmonary oxygen uptake was measured continuously through exercise using an Oxycon Alpha (Erich Jaeger B.V., The Netherlands). Data were analysed using two-way ANOVA with repeated measures and post-hoc Tukey test, and where appropriate Student’s paired t test.
The total work done on the muscle was greater (P < 0.01) during the eccentric mode of exercise compared with total work done by the muscle during the concentric mode (30.70 ± 8.37 vs. 20.04 ± 4.24 kJ). However, the metabolic cost of exercise, as estimated from net oxygen consumption, was higher (P < 0.05) during CON compared with ECC (52.6 ± 23.4 vs. 41.7 ± 23.4 l). Blood flow at rest was similar between conditions (CON, 1.00 ± 0.28 l min-1; ECC 1.05 ± 0.18 l min-1). Throughout each exercise trial blood flow was higher (P < 0.01) during CON than ECC, so that the average blood flow was 2.96 ± 0.95 l min-1 during CON and 1.92 ± 1.02 l min-1 during ECC.
The results of the present study confirm the suggestion that blood flow during eccentric mode contractions is lower than concentric contractions. The fact that during eccentric exercise work is done on the muscle rather than work by the muscle is reflected by the lower oxygen cost of eccentric exercise that would result in a reduced metabolic drive to increase blood flow.
All procedures accord with the Declaration of Helsinki.