The O2 pulse (mL·beat−1) was calculated as the ratio between O2 consumption and HR and was used as an indicator of stroke volume during submaximal and maximal exercise (40).
NIRS measurements.
Subjects were equipped with an NIRS probe to monitor the absorption of light across muscle tissues throughout the exercise test (Oxymon Mk III; Artinis Medical Systems, Zetten, The Netherlands). The emitter-and-detector pair was placed on the belly of the right vastus lateralis muscle, midway between the lateral epicondyle and greater trochanter of the femur. The vastus lateralis muscle is highly active during cycling (23), making it suitable for examining exercise-induced changes in active muscle oxygenation. Adipose tissue thickness has been reported to have substantial confounding influence on in vivo NIRS measurements (18). Therefore, we ensured that the vastus lateralis skinfold was