Assessing VO₂max Trainability: The Role of Standard Deviation in Individual Response to Aerobic Exercise

Background: Despite extensive research on the effects of exercise training on VO2max, current literature still lacks to be more conclusive regarding the optimal protocols for maximizing these effects. Variability in study designs, participant populations, and measurement techniques has contributed to inconsistencies in findings, leaving important questions unanswered regarding the most effective exercise strategies. This systematic review aimed to assess whether significant inter-individual differences exist in VO₂max trainability across different aerobic training protocols, using non-exercising comparator groups. Methods: A comprehensive literature search was conducted using Covidence, a web-based platform for systematic reviews to screen studies from three databases: EMBASE, PubMed, and SCOPUS. The search focused on two key concepts VO₂max and aerobic exercise training. Studies were included if they met the following criteria: involved human participants, implemented supervised and standardized training protocols, measured absolute or relative VO₂max, included a non-exercising control group, reported VO₂max change scores for both groups, and provided standard deviation (SD) of change. The standard deviation of individual response (SDIR) was calculated to evaluate variability in trainability across studies. Results: Out of 32,968 screened studies, 24 met the inclusion criteria and were analyzed. The findings indicated that: (1) most observed variation in VO₂max change scores can be attributed to measurement error, (2) estimating SDIR from a single study lacks precision due to typically small sample sizes, and (3) meta-analysis of SDIR across studies does not provide compelling evidence for meaningful inter-individual differences in VO₂max response. Discussion: While past research has debated whether some people respond better to aerobic training than others, our findings indicate that much of the variation in VO₂max improvements is due to measurement error rather than true biological differences. One major challenge in studying VO₂max trainability is the small sample sizes in most studies. When only a few participants are included in a study, it becomes difficult to tell whether differences in VO₂max improvements are real or just due to random variation. Even when data is combined across multiple studies in a meta-analysis, there is still no strong evidence that meaningful individual differences in VO₂max response exist. Another factor that complicates this research is the inconsistency in training programs, participant characteristics, and VO₂max measurement methods. Differences in exercise intensity, duration, and frequency, as well as variations in how VO₂max is tested, make it harder to compare results across studies. If future research aims to better understand VO₂max trainability, it will need more standardized training protocols and measurement techniques. These findings also challenge the idea that some people are naturally “high responders” or “low responders” to aerobic exercise. Instead of focusing on predicting individual responses, training programs should prioritize general strategies that help most people improve their VO₂max. If true individual differences in trainability exist, they are difficult to detect with the methods currently used. Conclusion: The meta-analysis does not support the existence of strong inter-individual variability in VO₂max trainability within single interventions. Consequently, the likelihood of identifying clinically significant predictors of VO₂max response appears to be low.