Foot-strike Hemolysis: A Scoping Review of Long-Distance Runners.
Level 3 - non-randomized controlled study
Scoping review of non-randomized pre-post observational studies
PubMed 39758544 · doi:10.17161/kjm.vol17.22146
What was done
This scoping review searched PubMed, Embase, Cochrane, and grey literature for human studies evaluating runners completing sanctioned races of marathon distance or greater with pre- and post-race hematological testing. Three reviewers extracted demographic, performance, complete blood count, reticulocyte, and iron data, assessing study quality using MINORS criteria.
What was found
From 334 identified studies, 9 met inclusion criteria, representing 267 runners (88% male, weighted mean age 37 years). Pre- to post-race measurements showed a 16% increase in reticulocyte count (remaining within normal limits) and a 21% decrease in haptoglobin levels. Hemoglobin, hematocrit, and red blood cell counts showed no notable changes and remained within accepted normal limits.
Why it matters
The findings suggest long-distance running causes transient, subclinical intravascular hemolysis that is compensated for by increased reticulocytes rather than causing overt acute anemia.
Limits
The pooled sample size is small (267 runners across 9 studies) and heavily male-skewed (88%). The included studies had heterogeneous race conditions, course terrains, and runner experience levels, and potential hemolysis at distances under 42.2 km was not evaluated.
Cited by
- supports Running and physical impact in combat sports physically break red blood cells in the feet and body through footstrike hemolysis, releasing iron and contributing to iron loss in athletes.