Self-paced exercise is less physically challenging than enforced constant pace exercise of the same intensity: influence of complex central metabolic control.

OBJECTIVE To examine whether self-pacing reduces the physiological challenge of performing 5000 m rowing ergometry exercise in comparison with a matched-intensity exercise condition in which a constant effort pacing strategy is enforced. METHODS Nine healthy well-trained male participants volunteered to participate in three 5000 m rowing conditions (two submaximal and one maximal conditions) in an individualised order. In the submaximal conditions, participants were required to (1) perform 5000 m at a constant rating of perceived exertion (RPE 15-Hard) (SubRPE) or (2) perform 5000 m at an enforced constant pace equivalent to the mean power output (PO) of the SubRPE condition (SubEXT). A maximal condition (MaxTT) was included to disguise the purpose of the study and to facilitate an element of randomisation in the test sequence. Dynamic intratest responses were assessed every 30 s: PO, VO2, iEMG, core (Tc) and skin temperatures (Tsk). RESULTS There was no difference between performance times of the two submaximal trials. The mean PO represented 83.83 (SD 8.88)% (SubRPE) and 83.40 (8.84)% (SubEXT) of the mean MaxTT power output. Tc (SubRPE:38.46 (0.23) degrees C, SubEXT:38.72 (0.36) degrees C; p<0.01), post-test BLa (SubRPE:5.24 (2.18), SubEXT:6.19 (2.51) mmol/l; p<0.05) and iEMG (p<0.05) were significantly elevated in SubEXT compared with SubRPE. There were no differences in the dynamics of HR or VO2 between SubEXT and SubRPE. The intratest stroke-to-stroke variability of power output was significantly greater in the SubRPE condition compared with SubEXT (p<0.01). CONCLUSIONS Enforced constant paced exercise presents a significantly greater physiological challenge than self-paced exercise. The ability to dynamically self-pace effort via manipulations of power output during exercise is an important behavioural response to homeostatic challenges and thus forms an integral part of a complex central regulatory process.