Paquette, MR, Peel, SA, Smith, RE, Temme, M, and Dwyer, JN. The impact of different cross-training modalities on performance and injury-related variables in high school cross country runners. J Strength Cond Res 32(6): 1745–1753, 2018—There are many different types of aerobic cross-training modalities currently available. It is important to consider the effects that these different modalities have on running performance and injury risks. The purpose of this study was to compare movement quality, running economy (RE) and performance, injury-related biomechanical variables, and hip muscle strength before and after training with different cross-training modalities in high school runners. Thirty-one high school male runners trained for 4 weeks in 1 of 3 cross-training modalities, in addition to a running-only (n = 9) group, for which training sessions replaced 2 easy runs per week: cycling (CYCLE; n = 6), indoor elliptical (n = 7), and outdoor elliptical bike (EBIKE; n = 9). Functional movement screen (FMS), RE, 3,000-m performance, hip kinematics, and hip muscle strength were assessed. Paired t-tests and Cohen's d effect sizes were used to assess mean differences for each variable before and after training within each group. Elliptical bike training was the only modality that improved FMS scores (d = 1.36) and RE before and after training (d = 0.48). All groups showed improvements in 3,000-m performance, but large effects were found only for the CYCLE (d = 1.50) and EBIKE (d = 1.41) groups. Running-only (d = 1.25), CYCLE (d = 1.17), and EBIKE (d = 0.82) groups showed improvements in maximal hip extensor strength. Outdoor cycling and EBIKE cross-training may be the most effective cross-training modalities to incorporate in early season training to improve running performance in high school runners.