Muscle Damage and Its Relationship with Muscle Fatigue During a Half-Iron Triathlon

Background: To investigate the cause/s of muscle fatigue experienced during a half-iron distance triathlon. Methodology/Principal Findings: We recruited 25 trained triathletes (3667 yr; 75.169.8 kg) for the study. Before and just after the race, jump height and leg muscle power output were measured during a countermovement jump on a force platform to determine leg muscle fatigue. Body weight, handgrip maximal force and blood and urine samples were also obtained before and after the race. Blood myoglobin and creatine kinase concentrations were determined as markers of muscle damage. Results: Jump height (from 30.365.0 to 23.466.4 cm; P,0.05) and leg power output (from 25.662.9 to 20.764.6 W? kg21; P,0.05) were significantly reduced after the race. However, handgrip maximal force was unaffected by the race (430659 to 430662 N). Mean dehydration after the race was 2.361.2 % with high inter-individual variability in the responses. Blood myoglobin and creatine kinase concentration increased to 5166248 mg? L21 and 4426204 U? L21, respectively (P,0.05) after the race. Pre- to post-race jump change did not correlate with dehydration (r = 0.16; P.0.05) but significantly correlated with myoglobin concentration (r = 0.65; P,0.001) and creatine kinase concentration (r = 0.54; P,0.001). Conclusions/significance: During a half-iron distance triathlon, the capacity of leg muscles to produce force was notably diminished while arm muscle force output remained unaffected. Leg muscle fatigue was correlated with blood markers o