Switching to minimalist shoes went with more injuries in runners new to them: a meta-analysis of 7 trials and prospective cohorts (313 healthy runners, transitions of at least 4 weeks) reports a pooled effect of 3.529 (95% CI 2.41-4.646, low heterogeneity) that the authors call a moderate increase in injury risk, without naming the effect measure; the most reported problems were bone marrow oedema in the metatarsals, Achilles tendinopathy and calf pain, which the authors tie to adopting a forefoot strike

Río and colleagues asked how often runners get injured when they move to minimalist footwear, and which biomechanical and musculoskeletal changes go with that risk. They searched international databases covering the previous 15 years for randomised trials and prospective cohorts in healthy runners with no minimalist experience who transitioned for at least four weeks.

Twelve studies entered the qualitative synthesis and seven, with 313 participants, the fixed-effect meta-analysis. The transition was associated with what the authors call a moderate increase in injury risk (overall effect 3.529, 95% CI 2.41-4.646) with low heterogeneity.

The injuries reported most often were bone marrow oedema in the metatarsals, Achilles tendinopathy and calf pain, which the authors relate to a change to a forefoot strike.

They conclude that the transition raises injury risk and the prevalence of musculoskeletal injury through changed foot strike and overload of the forefoot and Achilles tendon, and that supervised retraining of at least 12 weeks may support adaptation and reduce risk.

Our reading: the direction is clear, but the size cannot be read, because the abstract does not say whether 3.529 is a risk ratio, an odds ratio or another measure, and its interval is symmetric on the linear scale, which is unusual for a ratio (our arithmetic: 3.529 − 2.41 = 1.119; 4.646 − 3.529 = 1.117).