REF-1032 · Cejka et al., 2012 · Journal of the International Society of Sports Nutrition, · Paper · PubMed
Over a 100-km ultramarathon mean foot volume did not change
It fell in half the runners — and an increase went with higher fluid intake and slower running
Key Findings
Foot volume was unchanged on average after 100 km: it increased in 20 runners, did not change in 18 and decreased in 38 (76 male ultramarathoners, water-displacement measurement).
Fluid intake was positively related to the change in foot volume (r = 0.54, p < 0.0001).
Running speed was negatively related to fluid intake (r = −0.33) and to the change in foot volume (r = −0.23).
Body mass fell by 1.8 kg (2.4%).
Practical Application
"Feet always swell in an ultra" is not what was measured: in most runners they did not. Where they did, it went with drinking more and running slower.
So for a runner whose feet do swell, the first question is fluid intake against thirst, before a bigger shoe: swelling of feet, hands or lower legs with weight gain during a race is a reason to drink less, not more.
Sizing shoes up remains practice — sensible when the runner's own long runs show it, unproven as a rule.
Limitations
Correlation only; the paper's title ("leads to feet swelling") overstates its own data. Men only, measured after the race, with a crude method that produced some implausible individual values.
A companion study found fluid intake related to arm and lower-leg volume changes in 50 male 100-km runners (Bracher 2012, DOI 10.1007/s00421-011-2056-3).
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