Systematic review and meta-analysis of cross-training effects on VO2max and running performance in active individuals

Cross-training between running and cycling is widely used in endurance sports to maintain aerobic capacity while modulating sport-specific mechanical load. However, the extent to which physiological and performance adaptations transfer bidirectionally between these modalities remains unclear. This systematic review and meta-analysis compared the effects of running-only (run-only) and cycling-only (cyc-only) training interventions to evaluate cross-training transfer to sport-specific VO2max and running performance. Randomized controlled trials with intervention durations of at least four weeks were included. Studies comparing run-only training with cyc-only or combined running–cycling interventions in trained or recreationally active individuals were eligible (n = 7). Outcomes included VO2max assessed on the treadmill and cycle ergometer, as well as running performance in time trial (TT) (1 mile, 3,000 m, 5,000 m). Random-effects meta-analyses were performed to estimate pooled effects. Standardized mean differences (Hedges' g) were calculated based on change scores (post–pre), and between-study heterogeneity was assessed using Cochran's Q and the I2 statistic. Sensitivity analyses were conducted to evaluate the robustness of the results. No statistically significant differences between run-only and cyc-only interventions were observed for any outcome. For treadmill-assessed VO2max, cyc-only interventions showed a small, non-significant trend favoring run-only training [Hedges' g = −0.32, 95% CI (−0.76, 0.13), p = 0.16]. For cycle ergometer–assessed VO2max, run-only training resulted in comparable adaptations to cyc-only training, with a small, non-significant trend favoring cycling [Hedges' g = −0.34, 95% CI (−0.79, 0.11), p = 0.14]. Running performance outcomes demonstrated no meaningful differences between interventions [Hedges' g = 0.02, 95% CI (−0.62, 0.66), p = 0.88]. Effect estimates varied across studies and outcomes, and all confidence intervals included the null effect, indicating substantial uncertainty regarding the direction of potential effects. The small magnitude of these effects suggests that they are unlikely to translate into meaningful practical differences between training modalities. Variability across studies may be related to differences in participant training status and training dose rather than exercise modality. Current evidence does not indicate clear improvements or decrements in sport-specific VO2max or running performance following cross-training between running and cycling over short to moderate intervention periods. However, these findings should be interpreted with caution due to the limited number of studies, methodological heterogeneity, the use of relatively old training protocols, and the presence of studies with some concerns or high risk of bias, as well as wide confidence intervals crossing zero. Accordingly, the available evidence does not support conclusions regarding the interchangeability of training modalities or the effectiveness of cross-training in maintaining sport-specific performance, but rather indicates that no clear between-group differences were detected.