Creatine enhances oxygen uptake and performance during alternating intensity exercise

Purpose: The main purpose of the present study was to measure the total oxygen consumed, accumulation of blood metabolites, and performance during alternating intensity exercise before and after a period of creatine (Cr) loading 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 placebo (PL) or Cr monohydrate (CR) loading (20 g·d-1). Oxygen uptake was measured using a breath-by-breath system during bicycle exercise alternating every 3 min between bouts at 30%(-30%) and 90% (-90%) of the maximal power output to exhaustion. Blood samples were also obtained at rest, before the end 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 μmol·L-1) and 3-30% (64.7 ± 15.2 μmol·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 remained the same after PL. Conclusions: The results indicate that Cr feeding increases the capacity of human muscle to perform work during alternating intensity contraction, possibly as a consequence of increased aerobic phosphorylation and flux through the creatine kinase system.