European Journal of Clinical Investigation (2005) 35, 491–498 © 2005 Blackwell Publishing Ltd Blackwell Publishing, Ltd. Is the intensity of the highest fat oxidation at the lactate concentration of 2 mmol L -1 ? A comparison of two different exercise protocols S. Bircher *‡ , B. Knechtle *§ and H. Knecht †¶ * Institute of Sports Medicine, Swiss Paraplegic Centre, Nottwil, Switzerland, † Institute for Clinical Research, Swiss Paraplegic Centre, Nottwil, Switzerland, ‡ Division of Health Sciences, University of South Australia, Australia, § Gesundheitszentrum, St. Gallen, Switzerland and ¶ Division d’Hématologie, Département de Médecine, Université de Sherbrooke, Québec, Canada Abstract Background The exercise intensity eliciting highest fat oxidation is important for a variety of populations and its precise determination requires an adequate exercise protocol. The aim of this study was to compare fat oxidation, concentration of lactate and lactate threshold during an established exercise protocol using fixed workloads with a protocol based upon the subject’s individual heart rate response to exercise. Materials and methods Highest fat oxidation, concentration of lactate and lactate threshold were compared between two different exercise protocols in moderately trained men (n = 48) and women (n = 30). In randomized order subjects completed a standardized (STAND) and an individual (IND) submaximal exercise test. The increments during IND were adapted by the subjects’ individual heart rate response to exercise compared to STAND with defined steps. Results In men, fat oxidation was significantly higher at the intensity eliciting highest fat oxidation in STAND than in IND (P = 0·019), but not in women. In both genders lactate concentration (P < 0·001) and heart rate (HR) (P < 0·001) were significantly higher in IND compared to STAND at this intensity. A significant correlation between ◊O 2 at lactate threshold and the intensity eliciting the highest fat oxidation was found in both genders in IND (women r = 0·73; men r = 0·43) and in STAND (women r = 0·57; men r = 0·56). Conclusion Different exercise increments and stage durations have an influence on lactate concentration and HR at the intensity eliciting the highest fat oxidation. The shorter test duration of STAND favours this protocol to determine maximal fat oxidation. For the untrained, start of exercise should be at very low intensity. Keywords Exercise intensity, exercise testing, lactate threshold, substrate oxidation. Eur J Clin Invest 2005; 35 (8): 491–498 Introduction The exercise intensity eliciting maximal fat oxidation is of great interest for both athletes and overweight or obese people. Endurance athletes should know the intensity necessary for an effective training to increase fat oxidation, as a high correlation between the capacity to oxidize fatty acids and exercise performance is known [1,2]. During exercise, endurance-trained athletes rely more on their intramuscular triglycerides [3] and can save their intramuscular glycogen stores [4] in order to enhance performance. For obese sub- jects, exercise at this intensity might be beneficial in order to reduce body fat [5]. Institute of Sports Medicine, Swiss Paraplegic Centre, Nottwil, Switzerland (S. Bircher, B. Knechtle); Institute for Clinical Research, Swiss Paraplegic Centre, Nottwil, Switzerland (H. Knecht); Division of Health Sciences, University of South Australia, Australia (S. Bircher); Gesundheitszentrum, St. Gallen, Switzerland (B. Knechtle); Division d’Hématologie, Département de Médecine, Université de Sherbrooke, Québec, Canada (H. Knecht). Correspondence to: Dr. Beat Knechtle, Facharzt FMH für Allgemeinmedizin, Gesundheitszentrum St. Gallen, Vadianstr. 26, CH-St. Gallen, Switzerland. Tel.: +41 (0) 71 226 82 82; fax: +41 (0) 71 226 82 72; e-mail: beat.knechtle@ecr.ch Received 11 October 2004; accepted 16 June 2005