An increased fluid intake leads to feet swelling in 100-km ultra-marathoners - an observational field study

Background: an association between fluid intake and changes in volumes of the upper and lower limb has been described in 100-km ultra-marathoners. the purpose of the present study was (i) to investigate the association between fluid intake and a potential development of peripheral oedemas leading to an increase of the feet volume in 100-km ultra-marathoners and (ii) to evaluate a possible association between the changes in plasma sodium concentration ([na+]) and changes in feet volume.methods: in seventy-six 100-km ultra-marathoners,body mass,plasma [na+],haematocrit and urine specific gravity were determined pre- and post-race. fluid intake and the changes of volume of the feet were measured where the changes of volume of the feet were estimated using plethysmography.results: body mass decreased by 1.8 kg (2.4%) (p < 0.0001); plasma [na+] increased by 1.2% (p < 0.0001). haematocrit decreased (p = 0.0005). the volume of the feet remained unchanged (p > 0.05). plasma volume and urine specific gravity increased (p < 0.0001). fluid intake was positively related to the change in the volume of the feet (r = 0.54,p < 0.0001) and negatively to post-race plasma [na+] (r = -0.28,p = 0.0142). running speed was negatively related to both fluid intake (r = -0.33,p = 0.0036) and the change in feet volume (r = -0.23,p = 0.0236). the change in the volume of the feet was negatively related to the change in plasma [na+] (r = -0.26,p = 0.0227). the change in body mass was negatively related to both post-race plasma [na+] (r = -0.28,p = 0.0129) and running speed (r = -0.34,p = 0.0028).conclusions: an increase in feet volume after a 100-km ultra-marathon was due to an increased fluid intake. © 2012 cejka et al; licensee biomed central ltd.