INTRODUCTION: Well-developed acceleration abilities are critical for performance in rugby sevens. In this pilot study, we investigated the effects of heavy-sled sprint training on acceleration in female rugby sevens athletes. METHODS: Eleven junior female rugby sevens athletes completed 3-weeks of resisted sprint training (5-30 m) with heavy sleds (30 to 85% of body mass). Acceleration performance and biomechanical outputs were computed pre- and post-intervention using the methods described by Samozino et al. (2016). Training-induced changes were calculated using effect size (ES) and magnitude-based inferences. Correlations (r) between changes in sprint performance and biomechanical outputs (pre-post changes, and at baseline) were calculated. RESULTS: Small improvements in 5 m and 10 m times, and changes in mechanical effectiveness of force application (RFmax), maximum power output (Pmax), and force-velocity slope (SFV) were observed (ES = 0.36-0.40). Very large to almost perfect correlations were found between changes in 5 m and 10 m times with changes in Pmax, theoretical maximal (horizontal) force (F0), RFmax, rate of decrease in mechanical effectiveness (DRF), and SFV (r = 0.85-0.96). Changes in 5 m and 10m times were also very largely to almost perfectly correlated with initial individual profiles (SFV, DRF, F0, and Pmax) (r = 0.73-0.91). DISCUSSION: Heavy-sled sprint training was likely to improve 5 m and 10 m times, maximum power, and sprint biomechanics. Changes in Pmax, F0, DRF, RFmax, and SFV explained over 72% of the variance associated with improvements in 5 m and 10 m times. Furthermore, retrospective analysis showed that the initial individual force-velocity profiles were associated with the magnitude of improvements in sprint characteristics. TAKE HOME MESSAGE: Heavy-sled sprint training is likely to increase acceleration capabilities over short distances in female rugby sevens athletes. Changes in defined biomechanical outputs, and individual force-velocity profiles appear to be associated with these improvements.