A common method of assessing lower-body asymmetry is to record left and right side ground reaction force during vertical jumping. The dominant side is identified as the one that produces the largest force. Differences between dominant (D) and non-dominant (ND) side are calculated so that relative risk can be assessed. However, asymmetry has been calculated from peak (PF) and mean force (MF), and consistency between the PF and MF methods has not been established. PURPOSE: The aim of this study was to establish consistency between PF and MF methods of assessing asymmetry. METHODS: Thirty-one men (mean ± SD: age 22 ± 1 years, mass 88.1 ± 12.2 kg, vertical jump height 31.8 ± 5.7 cm) provided informed consent to perform three maximal effort countermovement vertical jumps. Left and right side ground reaction force was recorded independently from two force plates at 1000 Hz, and the highest jumps were analysed. The propulsion phase was identified as the phase between the lowest post countermovement displacement of the center of mass and take off (<10 N). Propulsion phase PF and MF side dominance was established, and D and ND differences assessed using 1-way ANOVA. A chi-square goodness of fit test was performed to determine whether the left and right side were preferred equally across the PF and MF methods. RESULTS: Differences between D and ND force were larger when the PF method was used (6±5% vs. 5±3%; PF = 1007±162 N vs. 942±149 N, MF = 802±129 N vs. 762±117 N, p=0.01). Results of the chi-square test suggested that the left and right side were favoured equally when the PF and MF methods were used to assess asymmetry (Figure 1). However, while 21 subjects consistently favoured the same (left) side across the PF and MF methods, 10 subjects did not. CONCLUSIONS: Differences between the D and ND side are larger when PF is used to assess lower-body asymmetry. Furthermore, the D side may change depending on whether PF or MF is used to assess lower-body asymmetry. This may have implications for strength and conditioning professionals interested in monitoring lower-body asymmetry. PRACTICAL APPLICATIONS: Vertical jumping force is often used to assess lower-body asymmetry. The results of this study highlight the importance of carefully selecting whether PF or MF is used to assess lower-body asymmetry. They also highlight the need for greater consistency in strength and conditioning research and practical application because the side that is favoured may change during different parts of the propulsion phase of vertical jumping. Therefore, it is recommended that propulsion phase MF is used to assess lower-body asymmetry because it provides an indication of the distribution of average mechanical output.