Fig. 4

Magnitude of beat-to-beat LBF (a) and the efficiency of IMC mechanical compression (b). a Mean LBF (dotted line) during IMC showed no change among target contraction workloads, although the magnitude of beat-to-beat LBF represented a slight exponential increase from onset to the end of IMC at all target workloads. There is a close positive linear relationship between mean LBF and %MVC during muscle relaxation (solid line, r ² = 0.984, P < 0.01 for L1 without 90 % MVC and dashed line, r ² = 0.990, P < 0.001 for L2 with 90 % MVC), although the magnitude in beat-to-beat LBF represented a linear decline from onset to the end of muscle relaxation at all target workloads represented in Fig. 3. b The effect of IMC mechanical compression on LBF restriction in muscle relaxation is indicated. In the duty cycle of exercise, increasing mean LBF during muscle relaxation showed an exponential decay-like reduction during IMC with increasing in target workload (a solid line), resulting in a difference (inflection point) in mechanical restriction of LBF by IMC between 30 and 50 % MVC. The regression lines (dotted lines) were indicated as the formula y = −2.11x + 95.8 (r = −0.985) for “Pre-ex.–30 % MVC” and y = −0.27x + 35.39 (r = −0.998) for “50– 90 % MVC.” The slope for the efficiency of muscle mechanical compression was relatively higher under 30 % MVC than over 50 % MVC. There was a significant difference (P < 0.01) compared to Pre-ex. (a), 10 % MVC (b), and 30 % MVC (c). LBF leg blood flow, Pre-ex. pre-exercise, NS not significant, %MVC percentage of maximum voluntary contraction. The values are expressed as means ± standard error