Background:Pacing strategy is closely linked with energy expenditure that can lead to different competition performance in time trial events. However, there is a lack of research into
how pacing strategy impacts the runner’s performance and energy expenditure，and whether the pacing strategy the medalists adopt in competitions is the best. This study compared the effects of
self-selected pace (SP) and race-model pace (RP) on the performance and energy expenditure in 1500m running.
Methods:21 well-trained male middle-distance runners (Chinese National Standard) performed an incremental load test, eight bouts constant load tests and two 1500m running tests with
SP and RP in synthetic track with Cosmed K4b2 measuring equipment. Maximal oxygen uptake and anaerobic threshold were measured in incremental load test. The relative intensities of constant load
tests run ranged between 75% and 115% AT, then the velocity-oxygen uptake (VO2) equation was established to calculate accumulated oxygen deficit (AOD). Four men’s 1500m running competitions were
selected from recent eight international competitions (2 Olympic Games and 6 World Athletic Championships) due to the similarity of the pace adopted by medalists. And RP was designed according to this
pace. There were four sectors in RP model, fast start sector (0-100m), plateau sector (100-800m), acceleration sector (800-1300m) and final spurt sector (1300-1500m). Respectively, the normalized
velocities of four sectors were 105.98%, 93.44%, 106.33% and 107.55% of the mean velocity. In SP trial, the subjects were instructed to finish in the shortest time possible with self-selected pace. In
RP trial, the subjects were asked to finish the 100-1300m with the model pace, but finish the 0-100m and 1300-1500m with the self-selected pace. The aerobic and anaerobic energy expenditure were
calculated by measured VO2 and AOD respectively, and the aerobic power, anaerobic power and total power were aerobic, anaerobic and total energy expenditure divided by time.
Results:Compared with the parameters in SP trial, the performance, total power and the aerobic power decreased significantly (P<0.01) in RP trial, but there were no differences in
anaerobic power and post test peak blood lactate (P>0.05) between them. Subjects retained 7.84% more anaerobic reserve during plateau sector in RP trial than in SP trial (50.22%±3.96% VS
42.38%±4.45%，P<0.01), but used 11.03% more anaerobic reserve during acceleration sector (27.60%±2.97% VS 16.57%±7.33%, P<0.01). The time to reach peak VO2 plateau was longer (P<0.05), and the peak VO2
plateau span was shorter (p<0.01) in RP trial than in SP trial. There was no statistical difference in peak VO2 (P>0.05) between two 1500m running tests, but the average VO2 in RP trial was lower than
in SP trial (52.15±4.05ml/kg/min VS 53.47±4.69ml/kg/min，P<0.01).
Conclusions:The Race-Model pace that athletes adopted for the better race ranking could impair the performance by inhibiting the aerobic energy metabolism rather than the anaerobic