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

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

doi:10.1016/j.jsams.2024.07.019

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

J Sci Med Sport. 2024 Jul 31:S1440-2440(24)00260-3. doi: 10.1016/j.jsams.2024.07.019. Online ahead of print.

Authors

Arthur Henrique Bossi¹, Wouter Timmerman², Diana Cole³, Louis Passfield⁴, James Hopker⁵

Affiliations

¹ School of Sport and Exercise Sciences, University of Kent, United Kingdom; School of Applied Sciences, Edinburgh Napier University, United Kingdom; The Mountain Bike Centre of Scotland, Edinburgh Napier University, United Kingdom. Electronic address: a.bossi@napier.ac.uk.
² School of Sport and Exercise Sciences, University of Kent, United Kingdom; School of Medical and Health Sciences, Edith Cowan University, Australia.
³ School of Mathematics, Statistics and Actuarial Science, University of Kent, United Kingdom.
⁴ Faculty of Kinesiology, University of Calgary, Canada.
⁵ School of Sport and Exercise Sciences, University of Kent, United Kingdom.

PMID: 39138044
DOI: 10.1016/j.jsams.2024.07.019

Abstract

Objectives: This study was designed to quantify inter- and intra-individual variability in performance, physiological, and perceptual responses to high-intensity interval training prescribed using the percentage of delta (%Δ) method, in which the gas exchange threshold and maximal oxygen uptake (V̇O_2max) are taken into account to normalise relative exercise intensity.

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

Methods: Eighteen male and four female cyclists (age: 36 ± 12 years, height: 178 ± 10 cm, body mass: 75.2 ± 13.7 kg, V̇O_2max: 51.6 ± 5.3 ml·kg^-1·min^-1) undertook an incremental test to exhaustion to determine the gas exchange threshold and V̇O_2max as prescription benchmarks. On separate occasions, participants then completed four high-intensity interval training sessions of identical intensity (70 %Δ) and format (4-min on, 2-min off); all performed to exhaustion. Acute high-intensity interval training 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 (coefficient of variation = 46 %) and 4.5 min (coefficient of variation = 22 %), respectively.

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

Keywords: Adaptive variability; Delta concept; Individual response; Intensity prescription; Normalisation; Trainability.