Malisoux et al. 2015, Parallel use of different running shoes and injury risk

Prospective cohort of 264 recreational runners over five months (Scandinavian Journal of Medicine & Science in Sports 25(1):110–115). Runners who rotated between several pairs of shoes had about 39% lower running-related injury risk than predominantly single-shoe users (hazard ratio 0.61), plausibly because alternating shoes varies the load applied to the tissues; taking part in other sports was protective too. Observational. Moderate.