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

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 (%(W)over dot(max)) vs. maximal sustainable work rate in a self-paced interval training session (%(W)over dot(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 %(W)over dot(max) group, but 100% for the %(W)over dot(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 %(W)over dot(max-SP) group. Amongst six adaptive response variables, there was evidence of individual response for only maximal oxygen uptake (standard deviation: 0.027 L center dot min(-1)center dot week(-1)) and self-paced interval training performance (standard deviation: 1.451 W center dot 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, %(W)over dot(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.