The effect of the aerodynamic time-trial position on gross efficiency and self-paced time-trial performance

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 \u003c 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.