Creatine enhance oxygen uptake and performance during alternating intensity exercise

Purpose: The main purpose of the present study was to measure the total oxy gen consumed, accumulation of blood metabolites. and performance during alt ernating intensity exercise before and after a period of creatine (Cr) load ing in well-trained humans. Methods: Fourteen males were randomly assigned to two groups of seven males and were tested before and after 5 d of placeb o (PL) or Cr monohydrate (CR) loading (20 g.d(-1)). Oxygen uptake was measu red using a breath-by-breath system during bicycle exercise alternating eve ry 3 min between bouts at 30% (-30%) and 90% (-90%) of the maximal power ou tput to exhaustion. Blood samples were also obtained at rest, before the en d of each cycling load, at exhaustion, and 5-min postexercise. Results: The oxygen consumed during 1-90% (5.08 +/- 0.39 L) and 2-90% (5.32 +/- 0.30 L) was larger after CR (5.67 +/- 0.34 and 5.78 +/- 0.35 L, P < 0.01 and P < 0 .05, respectively). Blood ammonia accumulation at the end of 1-90% (23.1 +/ - 6.5 mu mol.L-1) and 3-30% (64.7 +/- 15.2 mu mol.L-1) was lower after CR ( P < 0.05), whereas plasma uric acid accumulation was lower at exhaustion (P < 0.05) and 5-min postexercise (P < 0.01). Time to exhaustion increased (P < 0.05) from 29.9 +/- 3.8 to 36.5 +/- 5.7 min after CR, whereas it remaine d the same after PL. Conclusions: The results indicate that Cr feeding incr eases the capacity of human muscle to perform work during alternating inten sity contraction, possibly as a-consequence of increased aerobic phosphoryl ation and flu through the creatine kinase system.