Dorgo, S, Perales, JJ, Boyle, JB, Hausselle, J, and Montalvo, S. Sprint training on a treadmill vs. overground results in modality-specific impact on sprint performance but similar positive improvement in body composition in young adults. J Strength Cond Res 34(2): 463–472, 2020—The effects of different sprint training modalities on body composition are not yet known, and the effectiveness of using motorized treadmills for sprint training is yet to be assessed accurately. The following study investigated the effects of motorized treadmill and overground training on sprint performance and body composition. Sixty-four young adults (33 men and 31 women) completed 12 sprint training sessions over a 6-week period either on a treadmill (TM) or overground (TR), or followed their normal exercise routine (CONTROL). Fifty-yard sprint time, 20-yard maximal sprint speed split time, and maximal treadmill speed were used as sprint performance indicators. Body composition and sprint performance assessments were completed before and after the 6-week intervention. On completion of the 6-week training program, maximal treadmill speed significantly increased for all 3 groups, while split sprint time significantly decreased for the TR group. The CONTROL group's 50-yd sprint time and split sprint time significantly worsened after 6 weeks. Improvements in sprint time and speed were significantly greater for the TR and TM groups compared with the CONTROL group for 50-yd sprint time, 20-yard maximal sprint speed split time, and maximal treadmill sprint speed. The change in maximal treadmill sprint speed for the TM group was significantly greater than that of the TR group. TR and TM subjects also showed significant decrease in total body fat and increase in leg lean muscle mass. These findings indicate that although overground sprint training resulted in the greatest performance improvements within overground sprint tests, sprint training on a motorized treadmill may be a beneficial alternative modality to overground sprint training and may also positively impact subjects' body composition.