Modelling inter-individual variability in acute and adaptive responses to interval training: insights into exercise intensity normalisation

Abstract

Purpose To investigate the influence of exercise intensity normalisation on intra- and inter-individual acute and adaptive responses to an interval training programme. Methods Nineteen cyclists were split in two groups differing (only) in how exercise intensity was normalised: 80% of the maximal work rate achieved in an incremental test (%$$\dot{\text{W}}$$ W ˙ max) vs. maximal sustainable work rate in a self-paced interval training session (%$$\dot{\text{W}}$$ W ˙ max-SP). Testing duplicates were conducted before and after an initial control phase, during the training intervention, and at the end, enabling the estimation of inter-individual variability in adaptive responses devoid of intra-individual variability. Results Due to premature exhaustion, the median training completion rate was 88.8% for the %$$\dot{\text{W}}$$ W ˙ max group, but 100% for the %$$\dot{\text{W}}$$ W ˙ max-SP the group. Ratings of perceived exertion and heart rates were not sensitive to how intensity was normalised, manifesting similar inter-individual variability, although intra-individual variability was minimised for the %$$\dot{\text{W}}$$ W ˙ max-SP group. Amongst six adaptive response variables, there was evidence of individual response for only maximal oxygen uptake (standard deviation: 0.027 L·min−1·week−1) and self-paced interval training performance (standard deviation: 1.451 W·week−1). However, inter-individual variability magnitudes were similar between groups. Average adaptive responses were also similar between groups across all variables. Conclusions To normalise completion rates of interval training, %$$\dot{\text{W}}$$ W ˙ max-SP should be used to prescribe relative intensity. However, the variability in adaptive responses to training may not reflect how exercise intensity is normalised, underlining the complexity of the exercise dose–adaptation relationship. True inter-individual variability in adaptive responses cannot always be identified when intra-individual variability is accounted for.