Search

Background: 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., Objective: 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., Methods: 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., Results: 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., Conclusions: 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., Competing Interests: Declarations. Registration and Protocol: Not applicable. Support: No sources of funding were used to assist in the preparation of this article. Competing Interests: M.R., J.W., J.A., G.T., Ø.S., S.S., J.E.-L., L.F., L.F., I.M., S.G., D.J.R.-C., P.S., S.S.-P., T.S., R.T., and C.Z. declare that they have no conflicts of interest relevant to the content of this review. Availability of Data, Code and Other Material: All aggregate data generated or analyzed during this study are included in this published article (and its Supplementary Information files). The IPD for the studies included in the review may be available upon request to the corresponding authors of the respective articles. Authors’ Contributions: Michael Rosenblat was the project lead, conceived and designed the study, conducted article screening, data extraction, risk of bias analysis, statistical analysis, drafted the manuscript, and incorporated revisions. Jennifer Watt participated in the statistical analysis and reviewed the study methodology critically for important intellectual content. Jem Arnold participated in data extraction, risk of bias analysis, drafted the manuscript, and made substantial contributions before and during the review process of the manuscript. Gunnar Treff participated in article screening, drafted the manuscript, and made substantial contributions before and during the review process of the manuscript. Øyvind Sandbakk drafted the manuscript and incorporated revisions. Stephen Seiler participated in study design and drafted the manuscript. Jonathan Esteve-Lanao, Luca Festa, Luca Filipas, Iker Muñoz, Stuart Galloway, Domingo J. Ramos-Campo, Patrick Schneeweiss, Sergio Sellés-Pérez, Thomas Stöggl, Rune Talsnes, and Christoph Zinner all participated in data extraction, data collection and the aggregation of individual participant intervention data of the respective studies, and reviewed the manuscript critically for important intellectual content. All authors read and approved the final version of the manuscript., (© 2025. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)