Inter‐individual differences in coupling oxygen delivery to demand during a progressive exercise test

Oxygen delivery (O 2 del) to exercising muscle is thought to be tightly coupled to metabolic demand, as evidenced by proportional increases in O 2 del with increasing exercise intensity. Little consideration has been given to investigation of inter‐individual differences in this coupling. PURPOSE To characterize inter‐individual differences in O 2 del:metabolism coupling during progressive increases in exercise intensity. METHODS 8 healthy males (24.4 ±6.4 yrs) performed rhythmic isometric handgrip contractions (1 s:2 s contraction:relaxation duty cycle, contraction force increased by 2.5 kg every 3 min. until failure). Forearm O 2 del was calculated as arterial oxygen content (O 2 saturation via pulse oximeter; [hemoglobin] via venous blood sample) x brachial artery blood flow (BABF; Doppler and Echo ultrasound). RESULTS Data are mean ±SD. From rest to end of the 17.5 kg stage the 1) total blood delivered to the forearm was 3565.282 ±1013.584 mL, coefficient of variation (CV) 28%, range 2321.132 to 5384.500 mL and 2) total O 2 delivered to the forearm was 533.306 ±153.192 mL, CV 29%, range 312.520 to 786.140 mL. Mean blood flow at 17.5 kg was 345.510 ±89.782 mL. CONCLUSIONS Inter‐individual differences in blood flow and O 2 del:metabolism coupling during small muscle mass ramp exercise protocol can be substantial. Implications for understanding O 2 del:metabolism coupling need to be considered.