Influence of muscular contraction on vascular conductance during exercise above versus below critical power

•Increases in limb vascular conductance were greater during immediate recovery from exercise above, compared to below, critical power.•The influence of muscular contraction on limb vascular conductance was intensity dependent above, but not below, critical power.•Our data suggest critical power represents a contraction intensity threshold above which a critical level of blood flow impedance is elicited.•These findings may help to explain the progressive metabolic and neuromuscular responses that occur during exercise above critical power. We tested the hypothesis that limb vascular conductance (LVC) would increase during the immediate recovery phase of dynamic exercise above, but not below, critical power (CP) indicating a threshold for muscular contraction-induced impedance of limb blood flow (LBF). CP (115 ± 26 W) was determined in 7 men and 7 women who subsequently performed ∼5 min of near-supine cycling exercise both below and above CP. LVC demonstrated a greater increase during immediate recovery and remained significantly higher following exercise above, compared to below, CP (all p < 0.001). Power output was associated with the immediate increases in LVC following exercise above, but not below, CP (p < 0.001; r = 0.85). Additionally, variance in percent LBF impedance was significantly lower above (CV: 10.7 %), compared to below (CV: 53.2 %), CP (p < 0.01). CP appears to represent a threshold above which the characteristics of LBF impedance by muscular contraction become intensity-dependent. These data suggest a critical level of LBF impedance relative to contraction intensity exists and, once attained, may promote the progressive metabolic and neuromuscular responses known to occur above CP.