This study investigated the effects of prolonged constant load cycling exercise on cycling efficiency and local muscle oxygen uptake responses. Fourteen well trained cyclists each completed a 2h steady state cycling bout at 60% of their maximal minute power output to assess changes in gross cycling efficiency (GE) and muscle oxygen

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Purpose: Rating of perceived exertion (RPE) as a training-intensity prescription has been extensively used by athletes and coaches. However, individual variability in the physiological response to exercise prescribed using RPE has not been investigated. Methods: Twenty well-trained competitive cyclists (male = 18, female = 2, maximum oxygen consumption =55.07 [11.06] mL·kg−1·min−1) completed 3 exercise trials each consisting of 9 randomized self-paced exercise bouts of either 1, 4, or 8 minutes at RPEs of 9, 13, and 17. Within-athlete variability (WAV) and between-athletes variability (BAV) in power and physiological responses were calculated using the coefficient of variation. Total variability was calculated as the ratio of WAV to BAV. Results: Increased RPEs were associated with higher power, heart rate, work, volume of expired oxygen (VO2), volume of expired carbon dioxide (VCO2), minute ventilation (VE), deoxyhemoglobin (ΔHHb) (P < .001), and lower tissue saturation index (ΔTSI%) and ΔO2Hb (oxyhaemoglobin; P < .001). At an RPE of 9, shorter durations resulted in lower VO2 (P < .05) and decreased ΔTSI%, and the ΔHHb increased as the duration increased (P < .05). At an RPE of 13, shorter durations resulted in lower VO2, VE, and percentage of maximum oxygen consumption (P < .001), as well as higher power, heart rate, ΔHHb (P < .001), and ΔTSI% (P < .05). At an RPE of 17, power (P < .001) and ΔTSI% (P < .05) increased as duration decreased. As intensity and duration increased, WAV and BAV in power, work, heart rate, VO2, VCO2, and VE decreased, and WAV and BAV in near-infrared spectroscopy increased. Conclusions: Self-paced intensity prescriptions of high effort and long duration result in the greatest consistency on both a within- and between-athletes basis.

To investigate the physiological and metabolic effects of different torso angles (TA; while systematically controlling the aerodynamic time-trial position; AP), during submaximal exercise and self-paced time-trial efforts. Twelve participants completed four visits to the laboratory: Visit 1 being an incremental exercise test to identify power at maximal pulmonary oxygen uptake (PV?O2max) and Visits 2 to 4 being 20-minute time-trials with pre and post gross efficiency (GE) tests, performed at three different TAs (0o, 12o, 24o). GE was significantly reduced at the 0o TA, when compared to the 24o TA (P = 0.039). GE was significantly lower after the time-trials when compared to Pre GE (P < 0.001). There was no significant difference in the magnitude of decline in GE between TA. Combined data from all TA revealed a significant positive correlation between GE and mean time-trial power output (PO; R = 0.337; R2 = 0.114; P = 0.044). Mean time-trial PO was significantly higher at the 24o TA, when compared to the 12o TA (P = 0.012) and 0o TA (P = 0.007). There was a significant positive correlation between relative TA and mean time-trial PO (R = 0.374; R2 = 0.140; P = 0.025). GE declines during time-trial exercise, while lower TAs do not further exacerbate the magnitude of decline in GE. Lowering TA results in a reduction in physiological and metabolic performance at submaximal and time-trial intensity. There remains a trade-off between physiological functioning and aerodynamic drag.