Purpose <p>Sprint interval training (SIT) is a time-efficient strategy for improving cardiorespiratory fitness (CRF). However, existing systematic reviews show conflicting results and variable quality. This umbrella review synthesizes this evidence to appraise the certainty of SIT’s effects on CRF.</p> Methods <p>A systematic search was conducted in six databases for systematic reviews with meta-analyses comparing SIT with non-exercise control conditions and other comparator training modalities such as moderate-intensity continuous training (MICT), or high-intensity interval training (HIIT). The methodological quality of included systematic reviews was assessed using AMSTAR-2.</p> Results <p>Sixteen systematic reviews were included, with a majority (9/16) rated as ‘Low’ or ‘Critically Low’ methodological quality. The 16 included reviews synthesized data from 393 unique primary studies and more than 8642 participants, encompassing populations from healthy sedentary adults and athletes to individuals with cardiovascular risk factors. Pooled data showed SIT elicited a significant improvement in CRF versus control (Standardized Mean Difference [SMD] = 0.59; 95% CI 0.43–0.74). In contrast, no significant difference was found between SIT and MICT (SMD = 0.07; 95% CI  – 0.03 to 0.16). Evidence comparing SIT to HIIT was inconclusive.</p> Conclusion <p>SIT is an effective intervention for improving CRF compared to no exercise. However, current evidence, especially from higher-quality systematic reviews, does not support SIT’s superiority over MICT. Confidence in these findings is limited by prevalent methodological flaws, underscoring the need for more rigorous primary and secondary research.</p> Trial registration <p>PROSPERO ID CRD420251074348.</p>