FOSTER, C., J. J. DE KONING, F. HETTINGA, J. LAMPEN, K. L. LA CLAIR, C. DODGE, M. BOBBERT, and J. P. PORCARI. Pattern of Energy Expenditure during Simulated Competition. Med. Sci. Sports Exerc., Vol. 35, No. 5, pp. 826-831, 2003.
Purpose: To determine how athletes spontaneously use their energetic reserves when the only instruction was to finish in minimal time, and whether experience from repeated performance changes the strategy of recreational athletes.
Methods: Recreational road cyclists/speed skaters (N = 9) completed three laboratory time trials of 1500 m on a windload braked cycle. The pattern of energy use was calculated from total work and from the work attributable to aerobic metabolism, which allowed computation of anaerobic energy use. Regional level speed skaters (N = 8) also performed a single 1500-m time trial with the same protocol and measurements.
Results: The serial trials were completed in (mean ± SD) 133.8 ± 6.6, 133.9 ± 5.8, 133.8 ± 5.5 s (P > 0.05 among trials); and in 125.7 ± 10.9 s in the skaters (P < 0.05 vs cyclists). The V̇O2peak during the terminal 200 m was similar within trials (3.23 ± 0.44, 3.34 ± 0.44, 3.30 ± 0.51 (P > 0.05)) versus 3.91 ± 0.68 L·min-1 in the skaters (P < 0.05 vs cyclists). In all events, the initial power output and anaerobic energy use was high and decayed to a more or less constant value (∼25% of peak) over the remainder of the event. Contrary to predictions based on an assumed all out starting strategy, the subjects reserved some of their ability to perform anaerobic work for a terminal acceleration. The total work accomplished was not different between trials (43.53, 43.78, and 47.48 kJ in the recreational athletes, or between the cyclists and skaters (47.79 kJ). The work attributable to anaerobic sources was not different between the rides (20.67, 20.53, and 21.12 kJ in the recreational athletes). In the skaters, the work attributable to anaerobic sources was significantly larger versus the cyclists (24.67 kJ).
Conclusion: Energy expenditure during high-intensity cycling seems: 1) to be expended in a manner that allows the athlete to preserve an anaerobic energetic contribution throughout an event, 2) does not appear to have a large learning effect in already well trained cyclists, and 3) anaerobic energy expenditure may be the performance discriminating factor among groups of athletes.
To achieve optimal performance, it is essential for athletes to use their available energetic resources efficiently. To avoid wasting kinetic energy, all possible energy stores should have been used before finishing a race but not so far from the end of the race that a meaningful slowdown can occur. Despite the importance of how energetic resources are used (e.g., the pacing strategy), there are comparatively few data regarding the pattern of energy expenditure during competition. Recent studies have provided perspective regarding the pattern of energy system contribution during high-intensity exercise (2-5,7,8,11,14,25,26,30,31). However, studies that have attempted to document proportional energy contributions during high-intensity exercise have used either a fixed exercise intensity that the athlete is obligated to sustain for as long as possible (e.g., accumulated O2 deficit trials) or fixed duration trials with the pacing pattern dictated by the investigators (e.g., Wingate type tests). In competitions, athletes have a very different goal, finishing a certain distance in the shortest possible time. Studies in longer events have shown that the reliability of competitive simulations is much better than fixed duration trials (23,24). To our knowledge, there are only very limited data available regarding how athletes spontaneously expend their anaerobic resources in middle-distance (1-5 min) events (2,7,8,27).
Experimental studies of spontaneous patterns of energy expenditure are rare. In an experimental study of pacing patterns in a 2000-m time trial (∼2.5 min), we (7) observed that athletes recorded their best performances when the pacing pattern was relatively even, and fairly close to the spontaneously chosen pattern. Utilizing data on the pattern of energy expenditure derived from Wingate type tests, models have been constructed which appear to predict performances in both track cycling and speed skating with reasonable success (5,30,31). These models suggest that in events of less than ∼1.5-min duration, a relatively 'all out' pacing strategy might be optimal, with most of the energy attributable to anaerobic sources used during the first part of the event. As the duration of events increases beyond 1.5 min, a more constant pattern of energy expenditure appears to be optimal (5,31). However, these models still have significant limitations in that there are few data on how athletes spontaneously pace themselves, when the only goal is to finish in minimal time (32). Earlier experimental or observational studies (16,22) of pacing are limited by experimental design or have measured only velocity without direct measurement of aerobic and anaerobic power output (32). A better understanding of how athletes expend their energetic resources is critical to improving our fundamental understanding of how humans organize their available resources to optimize muscular performance. Accordingly, there were two overall purposes of this study. The first was to determine the pattern of expending energetic resources during spontaneously paced 1500-m time trials, particularly whether the anaerobic energy resources are fully expended before the end of the event. The second purpose was to determine how well-trained but nonelite athletes use their energetic resources in relation to the pattern adopted by more accomplished athletes, and whether the pattern evolves with repeated performance of a criterion time trial.