Compositional Analysis of Time- and Work-Based Intensity Distributions in Elite Cyclists During Training and Stage Racing

Cycling coaches frequently use training zones and zone distributions based around time in zone (TIZ) to analyse training data and to understand race demands. This study compared the intensity distribution of highly trained cyclists during training and racing using a novel work-in-zone (WIZ) method alongside the traditional TIZ approach. Twelve cyclists recorded their power output during 25 weeks of training and a 7-day stage race. Intensity zones were defined using a three-zone peak-power model, and intensity distribution (TIZ or WIZ) was analysed with compositional data analysis. There were significant main effects for context (training vs. racing) and zone type (TIZ vs. WIZ) on the ILR coordinates. ILR-1, which reflects the balance between Z1 and higher-intensity zones, was higher in training than racing and in TIZ compared with WIZ (p < 0.0001), indicating a relatively greater proportion of Z1 in these conditions. ILR-2, representing the balance within the higher-intensity zones, was significantly lower during racing and higher in TIZ compared with WIZ (p < 0.0001). These findings indicate the cyclists’ training distribution differed substantially from the demands of racing, and that TIZ and WIZ can provide meaningfully different interpretations of intensity distribution. Where TIZ reflects only the time distribution spent within each zone, WIZ incorporates the weighting of intensity. This leads to particularly different results in racing, where intensity is more stochastic and characterised by greater extremes. Combining both methods may enhance understanding of training intensity distribution, race demands, and the difference between these contexts in endurance cyclists. Consequently, WIZ should be used in a complementary manner rather than as a replacement for TIZ.