INTRODUCTION Work to rest ratio in interval training (IT) has been a focus of scientific research in order to understand how different interval training patterns effect energy metabolism and therefore the possible training stimulus2. For example the time spent at >90% of VO2max has shown correlate with improvements of VO2max (X). To our knowledge, little to no information exists how the physiological make up of an athlete effects energetic contribution and possible training stimulus during IT. METHODS Two metabolic profiles were compared, both with different VO2max, glycolytic power (VLamax) and Energy demand for 200m freestyle at a speed of 1.82 m/s: Athlete 1 (A1): 85 ml/min/kg, 0.8 mmol/l/s, 4.7 kcal/kg/km; Athlete 2 (A2): 80 ml/min/kg, 0.4 mmol/l/s, 4.3 kcal/kg/km. We compared the kinetics of the muscular energy metabolism for both athletes completing an interval set of: 10x 100m @57s with 13s passive rest, using a computer model (INSCYD.com, Switzerland). The computed possible best time for 200 freestyle for both athletes would be 108s (1.85 m/s). RESULTS Both athletes showed similar ratios of aerobic vs. glycolytic energy contribution at the end of the first interval: A1 = 77% vs. 21%, A2 = 76% vs. 22%, but different results for the last interval: A1= 81% vs. 17%; A2=78% vs 14%. Utilization of VO2max increased for both athletes from 1st to 10th interval: A1= 90% to 96%; A2 = 93% to 100%. Utilization of glycolytic power differed significantly between 1st and 10th interval as well as in between athletes: A1= 26% vs. 21%; A2 = 61% vs. 40%. DISCUSSION Our analysis show that the percentual energy contribution was similar beside different metabolic profiles of the athletes. However the utilization of the individual maximum aerobic and glycolytic capacity of each athlete changes during the training set and was significant different between both athletes. In between intervals the continuous decrease in muscular pH inhibited the glycolytic pathway, hence shifting energy contribution to aerobic energy supply and increased breakdown of PCr. More important is the more than twofold different in glycolytic stimulus in A1 vs A2. Following the widel appreciated logic that training stimulus can partly be quantified as fractional use of the maximum capacity, the anticipated adaptation of the glycolytic energy system would be significant different between A1 and A2.
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