Effect of free versus constant pace on performance and oxygen kinetics in running VE ´ RONIQUE LOUISE BILLAT, JEAN SLAWINSKI, MATHIEU DANEL, and JEAN PIERRE KORALSZTEIN Faculty of Sport Science, University of Lille 2, Lille, FRANCE; and the Sport Medicine Center C.C.A.S., Paris, FRANCE ABSTRACT BILLAT, V. L., J. SLAWINSKI, M. DANEL, and J. P. KORALSZTEIN. Effect of free versus constant pace on performance and oxygen kinetics in running. Med. Sci. Sports Exerc., Vol. 33, No. 12, 2001, pp. 2082–2088. Purpose: This study tested the hypothesis that free versus constant pace enhanced the performance (i.e., distance run) in suprathreshold runs between 90 and 105% of the velocity associated with the maximal oxygen consumption determined in an incremental test (vV ˙ O 2max ). Moreover, we hypothesized that variable pace could decrease the slow phase of oxygen kinetics by small spontaneous recoveries during the same distance run at an average velocity. Method: Eleven long-distance runners performed nine track runs performed until exhaustion. Following an incremental test to determine vV ˙ O 2max , the runners performed, in a random order, four constant-velocity runs at 90, 95, 100, and 105% of vV ˙ O 2max to determine the time to exhaustion (tlim90, tlim95, tlim100, and tlim105) and the distance limit at 90, 95, 100 and 105% of vV ˙ O 2max (dlim90, dlim95, dlim100, and dlim105). Finally, they performed the distance limit determined in the constant velocity runs but at variable velocity according to their spontaneous choice. Results: The coefficient of variation of velocity (in percent of the average velocity) was small and not significantly different between the four free pace dlim (4.2  1.3%, 4.8  2.4%, 3.6  1.1%, and 4.6  1.9% for dlim90, dlim95, dlim100, and dlim105, respectively; P = 0.40). Performances were not improved by a variable pace excepted for the dlim at 105% vV ˙ O 2max (4.96  0.6 m·s -1 vs 4.86  0.5 m·s -1 , P = 0.04). Oxygen kinetics and the volume of oxygen consumed were not modified by this (low) variation in velocity. Conclusion: These results indicate that for long-distance runners, variable pace modifies neither performance nor the oxygen kinetics in all-out suprathreshold runs. Key Words: OXYGEN CONSUMPTION, EXHAUSTION, EXERCISE O n a track where the goal is to run a given distance as quickly as possible, athletes spontaneously choose to modulate their pace during the race to avoid becoming overfatigued before reaching the finishing line (1). Sports records are performed with free and not constant paces even during long-distance running, and an athlete in any event lasting more than 2 min has the oppor- tunity to use energy available from the cleavage of phosph- agen and from glycolysis in a flexible manner (15). If one considers the last three world records for middle- and long- distance running (1500 m, 3000 m, 5000 m, and 10,000 m), it can be observed that the range of the coefficient of variation of velocity is 1 to 5% (unpublished data computed from the International Amateur Athletic Federation books). However, in a review on pacing strategy and athletic per- formance, Foster et al. (14) recall that since the initial study of Robinson et al. (25) during a 1200-m run, there have been few systematic studies to determine how various pacing strategies might influence the outcome of competitive per- formance. The studies were true pacing studies (1,2,14,20) or controlled stochastic investigations (23,24). It has been demonstrated that under competitive condi- tions the physiological responses of athletes might be sig- nificantly greater than suggested by the conventional incre- mental test (9,12). Moreover, in a run at 90% of the velocity associated with V ˙ O 2max in an incremental test (vV ˙ O 2max ), oxygen consumption continues to increase with time by means of a V ˙ O 2 slow component (i.e., the second amplitude of the oxygen biexponential kinetics model) (6,16,26). Fos- ter et al. (14) suggested that athletes learn how to sense low values of muscle pH and adjust their pace accordingly so that they ideally reach critically low values of pH near the end of a race. During an all-out event of 3–15 min, the increase of type II fiber recruitment, which is correlated with the lactate accumulation, could increase V ˙ O 2 toward V ˙ O 2max . Therefore, a spontaneous decrease in the velocity around the third minute could prevent the development of the V ˙ O 2 slow component (26). Indeed, above the critical power, V ˙ O 2 rises inexorably until fatigue ensues, at V ˙ O 2max (5). Therefore, the purpose of this study was to examine whether a free versus a constant pace produces different performance results and, if so, whether this related to the slow V ˙ O 2 response. METHODS Subjects Eleven male long-distance runners (age, 41  10 yr; height, 175  5 cm; weight, 71  5 kg) participated in this study. They trained five times per week (70  20 km·wk -1 ). These subjects were long-distance runners training for the half-marathon. They were chosen to avoid a strategy (long- term planned) and to get a stochastic pace (i.e., a variation 0195-9131/01/3312-2082/$3.00/0 MEDICINE & SCIENCE IN SPORTS & EXERCISE ® Copyright © 2001 by the American College of Sports Medicine Submitted for publication August 2000. Accepted for publication February 2001. 2082