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2 Aim: To investigate the effect of task familiarisation on the spontaneous pattern of energy expenditure during a series of 2000 m cycling time trials (TTs). Method: Nine trained males completed three 2000 m TTs on a Velotron cycling ergometer. To examine pacing strategy the data were assigned to 250 m ‘bins’, with the pattern of aerobic and anaerobic energy expenditure calculated from total work accomplished and gas exchange data. Results: There were no significant differences between trials in performance times (191.4 ± 4.3, 189.4 ± 4.6, 190.1 ± 5.6 s), total aerobic (58.3 ± 2.7, 58.4 ± 3.1, 58.0 ± 3.4 KJ) and total anaerobic energy expenditure (16.4 ± 3.3, 17.3 ± 2.8, 16.5 ± 3.1 KJ). Pacing strategy in the second and third TT differed from the first TT in that a lower power output was adopted during the first 500 m, enabling a higher power output during the final 750 m of the TT. This adjustment in the pattern of energy expenditure was mediated by an alteration in the pattern of anaerobic energy expenditure, which paralleled changes in total energy expenditure