Abstract
The aim of this study was to replicate the study titled “Effect of different loading conditions on running mechanics at different velocities” by Carretero-Navarro et al., (2019) as part of a large replication project. The selected variable of interest was leg stiffness. Twenty-six recreationally active and healthy males (age: 23 ± 2 years, body mass: 80.20 ± 11.54kg, height: 177.96 ± 6.29cm) participated in two testing sessions, one week apart. Subjects completed an incremental maximal running test on a treadmill to determine their maximal aerobic speed (MAS). During the second session, participants completed nine, one-minute runs under different loading (+0%, +10%, and +20% of body mass using a weighted vest) and speed (60%, 80%, and 100% of their MAS) conditions. A two-way repeated measures ANOVA showed a significant main effect for speed on leg stiffness (F1.7, 38.6 = 5.94, p = 0.008, ηp2 = 0.205), similar to the original study (F2, 24 = 52.577, p < 0.001). However, the replication effect size estimate for speed on leg stiffness (ηp2 = 0.205) was significantly smaller than the original (ηp2 = 0.814) (z = 4.56, p < 0.001). The original effect size estimate for the main effect of speed was deemed incompatible with the replication estimate, therefore, the original study was not replicated fully. As there are growing demands for enhancing the quality of sports science research, one should focus on the accumulation of evidence for the effect of speed on leg stiffness to maximize athletic performance.