From cycling races to football matches: sparing carbohydrates and utilising fat as a fuel is of pinnacle importance in many sports competitions. Especially in competitions with non steady load patterns (cycling, basketball, soccer, olympic triathlon, XC skiing) the race decisive moments depend highly on anaerobic energy supply and therefore on the availability of glucose as a fuel. In contrast the assessment of substrate utilisation using coventional testing methods such as a metabolic cart is limited to quasi steady state and submaximum load patterns. Hence the typical laboratory assessment of fat and carbohydrate utilisation cannot be applied to analyse substrate utilisation in may sporting events.

Experiments

Fifteen healthy trained males were recruited for this project. Each of them underwent a series of load tests on a cycling ergometer (Cyclus 2, RBM Electronic, Leizpzig Germany): 1) A series of three sub-maximum efforts including pre and post efforts lactate measurements. 2) An all out test with an intensity set to results in fatigue after 3 – 5min; including pre and post efforts lactate measurements as well as measuring of gas exchange using the mixing chamber technology (Cosmed K5, Rome Italy). During each test power, heart rate and cadence is recorded with 1Hz.

This data is used to create a metabolic profile in INSCYD (VLamax, VO2max, MLSS, MMSS, lactate production and combustion kinetics, etc.)

Afterwards each subject undergoes two different training sessions, on three different days in randomized order:

1. an interval training: The test consists of a 10-min warm up (1,5 W/kg) followed by a high intensity interval workout, as follows:

   1. 10min @ 85% power at maximal lactate steady state (MLSS)

   2. 10min@105 % MLSS

   3. 10min@ 65% MLSS

   4. 6x (4min@VO_2max-power followed by 6min@FatMax recovery)

   5. 10min@75% MLSS

2. a 100min endurance training: The test consists of a 10-min warm up (1,5 W/kg) followed by an 80-min workout which incorporates stochastic load changes, as described below:

   4 intervals of 20 min duration, each interval is composed of:

   a. 15min work-interval composed of 6 workbouts of 1-5 min duration and 70-110% VO_2max power intensity. The duration and the intensity of these efforts are randomly assigned by the computer (Microsoft Excel Rand-function), with following restrictions: (1) workbouts of 100-110% VO_2max are limited to 1 min duration (2) a maximum of 2 workbouts of 100-110% VO_2max can be programmed one after the other.

   b. 5 min recovery-interval at fatmax-power