Challenging O2 delivery: metabolism coupling in small muscle mass exercise

PURPOSE To understand how O 2 del: metabolism matching is defended in the face of increased duration of contraction‐induced mechanical impedance to exercising muscle blood flow. METHODS 7 healthy young males, (21.8 ±1.8 yrs) performed a handgrip ramp exercise protocol (increase contraction force 2.5 kg every 3 min) under Control (CON; 2 s isometric contraction + forearm compression cuff inflation: 4 s relaxation duty cycle) and Impedance (IMP; 2 s contraction + forearm compression + extra 2 s of forearm compression: 2 s relaxation duty cycle). Forearm blood flow ((FBF (ml/min); brachial artery Doppler and Echo ultrasound), mean arterial blood pressure (MAP (mmHg); finger photoplethysmography) were measured. Forearm vascular conductance during relaxation (FVCrelax ml/min/100 mmHg)) was calculated (FBFrelax/MAP x 100). RESULTS Data are mean ± SD. Up to 7.5 kg workload, FBF (therefore O 2 del) was not different between conditions due to compensatory vasodilation in IMP (eg. 7.5 kg FVCrelax IMP 596 ±140 vs. CON 396 ±60, P<0.05). Above 7.5 kg workload a small pressor response in IMP was added (MAP IMP 103.5 ±7.8 vs. CON 98.8 ±8.6, P<0.05), but O 2 del: metabolism matching was not achieved. CONCLUSIONS Compensatory vasodilation successfully maintains O 2 del: metabolism matching at lower workloads. When it fails, a pressor response is evoked, but cannot maintain O 2 del: metabolism matching at higher workloads. NSERC.