The delta concept does not effectively normalise exercise responses to exhaustive interval training

Bossi, Arthur Henrique; Timmerman, Wouter; Cole, Diana; Passfield, Louis; Hopker, James

Abstract

Objectives
This study was designed to quantify inter- and intra-individual variability in performance, physiological, and perceptual responses to high-intensity interval training (HIIT) prescribed using the percentage of delta (%Δ) method, in which the gas exchange threshold and maximal oxygen uptake (V̇O2max) are taken into account to normalise relative exercise intensity.

Design
Repeated-measures, within-subjects design with mixed-effects modelling.

Method
Eighteen male and four female cyclists (age: 36 ± 12 years, height: 178 ± 10 cm, body mass: 75.2 ± 13.7 kg, V̇O2max: 51.6 ± 5.3 ml·kg-1·min-1) undertook an incremental test to exhaustion to determine the gas exchange threshold and V̇O2max as prescription benchmarks. On separate occasions, participants then completed four HIIT sessions of identical intensity (70%Δ) and format (4-min on, 2- min off); all performed to exhaustion. Acute HIIT responses were modelled with participant as a random effect to provide estimates of inter- and intra-individual variability.

Results
Greater variability was generally observed at the between- compared with the within-individual level, ranging from 50% to 89% and from 11% to 50% of the total variability, respectively. For the group mean time to exhaustion of 20.3 min, inter- and intra-individual standard deviations reached 9.3 min (CV = 46%) and 4.5 min (CV = 22%), respectively.

Conclusions
Due to the high variability observed, the %Δ method does not effectively normalise the relative intensity of exhaustive HIIT across individuals. The generally larger inter- versus intraindividual variability suggests that day-to-day biological fluctuations and/or measurement errors cannot explain the identified shortcoming of the method.

Citation

Bossi, A. H., Timmerman, W., Cole, D., Passfield, L., & Hopker, J. (in press). The delta concept does not effectively normalise exercise responses to exhaustive interval training. Journal of Science and Medicine in Sport,

• Journal Article Type: Article
• Acceptance Date: Jul 29, 2024
• Deposit Date: Jul 30, 2024
• Print ISSN: 1440-2440
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Keywords: delta concept, intensity prescription, normalisation, adaptive variability, individual response, trainability