The dataset includes the individual participant source data for the following publication: Howe, C.C.F., Swann, N., Spendiff, O. et al. Performance determinants, running energetics and spatiotemporal gait parameters during a treadmill ultramarathon. Eur J Appl Physiol (2021). https://doi.org/10.1007/s00421-021-04643-2