Determination of "Fatmax"with 1 h cycling protocols of constant load.

Several earlier studies were aimed at determining an exercise intensity that elicits maximal fat oxidation (Fatmax). However, these studies employed few different intensities or used exercise periods of too short a duration. All investigators described intensity with reference to maximal ergometric values, which might lead to metabolically inhomogeneous workloads between individuals. The aim of this study was to determine Fatmax by overcoming these methodological shortcomings of earlier investigations. Ten healthy recreational athletes (29 +/- 5 y; 75 +/- 6 kg; 1.81 +/- 0.04 m) conducted an initial incremental cycling test to determine VO2 peak (59.2 +/- 6.1 mL.min-1.kg-1) and individual anaerobic threshold (IAT; 221 +/- 476 W). Within 4 weeks, 5 constant-load tests of 1 h duration were carried out at 55%, 65%, 75%, 85%, and 95% IAT. During all tests indirect calorimetry (MetaMax I, Cortex, Leipzig, Germany) served to quantify fat oxidation. Capillary blood sampling for lactate measurements was conducted every 15 min. All subjects remained in a lactate steady state during the constant load tests, which minimized influences from excess CO2. There was no difference between the 5 intensities for the percentage of energy from fat metabolism (p = 0.12). Additionally, the intensities led to similar absolute amounts of oxidized fat (p = 0.34). However, there was a significant increase in fat metabolism with increasing exercise duration (p = 0.04). It is impossible to define one theoretical optimal intensity for fat oxidation that is true in all individuals. It is thus mandatory to perform an individual assessment with indirect calorimetry. Intra-individual day-to-day variation might render the use of several tests of long duration less applicable than incremental testing with stages of sufficient duration.