REF-715 · Ridge, Johnson, Mitchell, Hunter, Robinson, Rich & Brown, 2013 · Medicine & Science in Sports & Exercise, 2013 Jul;45 · Paper · PubMed
Ten weeks of gradual transition to Vibram FiveFingers put bone marrow edema into the feet of half the group
The specific shoe, the specific timeline, and a measured cost
Protocol
n=36 experienced recreational runners, MRI of the foot before and after a 10-week period. 17 controls continued in their traditional shoes; 19 transitioned gradually to Vibram FiveFingers. Bone marrow edema was graded 0-4 per bone (0 = none; 4 = edema in more than 50% of the bone's length, which the authors define as a stress fracture).
Key Findings
Pre-training MRI scores did not differ between groups.
10 of 19 in the Vibram group showed an increase in bone marrow edema in at least one bone after 10 weeks, versus the control group (p = 0.009).
Authors' conclusion, verbatim in substance: runners moving to minimalist shoes such as Vibram FiveFingers should transition very slowly and gradually to avoid potential stress injury in the foot.
Practical Application
In 36 experienced recreational runners, 10 of the 19 who transitioned gradually to Vibram FiveFingers over 10 weeks showed increased bone marrow edema in at least one foot bone on MRI, more than the 17 controls who stayed in their usual shoes (p=0.009). A published "gradual" 10-week transition was not gradual enough for about half the group; the authors advise transitioning very slowly.
Inference, not tested: edema can precede symptoms, so an athlete feeling fine partway through a minimalist transition is not evidence that the transition is going well. The study measured MRI edema, not pain.
Inference, not tested: if minimalist footwear is used as a foot-strengthening stimulus rather than as running shoes (REF-717), the running volume in it stays small and the bone-loading exposure studied here is much smaller.
Limitations
n=36 (19 transitioning), 10 weeks, recreational runners. Small and short. The abstract does not say whether allocation was randomised.
The abstract does not report how many participants reached a score of 4 (the stress-fracture grade). The outcome established here is increased edema, not a counted number of fractures; any claim that participants progressed to stress fracture needs the full text.
Bone marrow edema on MRI is a sensitive but non-specific finding; it also occurs in asymptomatic runners, so it indexes bone stress rather than diagnosing injury.
The transition protocol was prescribed by the study, not self-selected — a runner switching on their own may go faster or slower.
No performance or economy outcome, and no long-term follow-up: whether the edema resolved and whether the group adapted after 10 weeks is not addressed.
How this entry was checked and changed
Content correction 2026-09-27
Lead rewritten as the study's finding with its numbers (10 of 19 vs 17 controls, p=0.009).
Removed the unsourced "week 6" example; the pre-symptomatic-edema point and the foot-strengthening point are labelled as inference; screening advice labelled as the base's own practice.
Removed the statement that REF-621 claims participants progressed to stress fracture (that entry no longer says so).