Which Training Intensity Distribution Intervention will Produce the Greatest Improvements in Maximal Oxygen Uptake and Time-Trial Performance in Endurance Athletes? A Systematic Review and Network Meta-analysis of Individual Participant Data.

Abstract

Endurance athletes tend to accumulate large training volumes, the majority of which are performed at a low intensity and a smaller portion at moderate and high intensity. However, different training intensity distributions (TID) are employed to maximize physiological and performance adaptations. The objective of this study was to conduct a systematic review and network meta-analysis of individual participant data to compare the effect of different TID models on maximal oxygen uptake (VO_2max) and time-trial (TT) performance in endurance-trained athletes. Studies were included if: (1) they were published in peer reviewed academic journals, (2) they were in English, (3) they were experimental or quasi-experimental studies, (4) they included trained endurance athletes, (5) they compared a polarized (POL) TID intervention to a comparator group that utilized a different TID model, (6) the duration in each intensity domain could be quantified, and (7) they reported VO_2max or TT performance. Medline and SPORTDiscus were searched from inception until 11 February 2024. We included 13 studies with 348 (n = 296 male, n = 52 female) recreational (n = 150) and competitive (n = 198) endurance athletes. Mean age ranged from 17.6 to 41.5 years and VO_2max ranged from 46.6 to 68.3 mL·kg^-1·min^-1, across studies respectively. Based on the time in heart rate zone approach, there was no difference in VO_2max (SMD = - 0.06, p = 0.68) or TT performance (SMD = - 0.05, p = 0.34) between POL and pyramidal (PYR) interventions. There were no statistically significant differences between POL and any of the other TID interventions. Subgroup analysis showed a statistically significant difference in the response of VO_2max between recreational and competitive athletes for POL and PYR (SMD = - 0.63, p < 0.05). Competitive athletes may have greater improvements to VO_2max with POL, while recreational athletes may improve more with a PYR TID. Our results indicate that the adaptations to VO_2max following different TID interventions are dependent on performance level. Athletes at a more competitive level may benefit from a POL TID intervention and recreational athletes from a PYR TID intervention.