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Authors G Neumayr, R Pfister, H Hoertnagl, G Mitterbauer, W Prokop, M Joannidis
Title   Renal function and plasma volume following ultramarathon cycling
Full source     International Journal of Sports Medicine, 2005, Vol 26, Iss 1, 
pp 2-8

In recreational cyclists marathon cycling influences renal function only on a 
minimal scale. Respective information on extreme ultramarathon cycling in 
better trained athletes is not available. The objective was to evaluate the 
renal and haematological effects of ultraendurance cycling in the world's best 
ultramarathon cyclists. Creatinine (CR), urea, haemoglobin (Hb), haematocrit 
(Hct) and plasma volume (PV) were investigated in 16 male ultramarathon 
cyclists during the 1st Race Across the Alps in 2001 (distance: 525 km; 
cumulative altitude difference: 12600 in). All renal functional parameters were 
normal pre-exercise. During the race serum CR, urea and uric acid rose 
significantly by 33, 97% and 18% (p < 0.001 respectively) and nearly normalised 
again on the following day. The decline in calculated CR clearance was 25%. 
There was a negative correlation (r = -0.575, p = 0.02) between the rise in 
serum CR and the athlete's training kilometers. The serum urea/CR ratio rose 
above 40 in 12 athletes (75%). Mean fractional sodium excretion and fractional 
uric acid excretion fell below 0.5% (p < 0.001) and 7%, indicating reduced 
renal perfusion. The deflection of the renal functional parameters was 
temporary and nearly gone after 24 hours of recovery. Hct declined during the 
race from 0.44 to 0.42, and continued falling on the next day (0.42 --> 0.40; p 
< 0.001). The corresponding rises in calculated PV were +8% and +22%. The study 
affirms that in world class cyclists the enormous strains of ultramarathon 
cycling influence renal function only on a minimal scale. The impact on the PV, 
however, is pronounced leading to marked haemodilution post-exercise. This very 
temporary ''impairment of renal function'' seems to be the physiological 
response to ultramarathon cycling and may be attenuated to some extent by 
preceding high-volume training.


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