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muscle breakdown is one of the most relevant sources of muscle fatigue during a triathlon.

From: owen r.
Sent on: Sunday, August 26, 2012 11:09 PM
PLoS One. 2012;7(8):e43280. Epub 2012 Aug 10.

Muscle damage and its relationship with muscle fatigue during a half-iron triathlon.


Exercise Physiology Laboratory, Camilo José Cela University, Madrid, Spain.



To investigate the cause/s of muscle fatigue experienced during a half-iron distance triathlon.


We recruited 25 trained triathletes (36±7 yr; 75.1±9.8 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.


Jump height (from 30.3±5.0 to 23.4±6.4 cm; P<0.05) and leg power output (from 25.6±2.9 to 20.7±4.6 W · kg(-1); P<0.05) were significantly reduced after the race. However, handgrip maximal force was unaffected by the race (430±59 to 430±62 N). Mean dehydration after the race was 2.3±1.2% with high inter-individual variability in the responses. Blood myoglobin and creatine kinase concentration increased to 516±248 µg · L(-1) and 442±204 U · L(-1), 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).


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 of muscle damage suggesting that muscle breakdown is one of the most relevant sources of muscle fatigue during a triathlon.

Ken’s Takeaway: Elevated acidosis (from lactate) promotes myoglobin (muscle protein) breakdown when the liver cannot access alanine to combine with lactate for synthesis of new glucose. The takeaway is that insufficient amino acid uptake in the liver is likely the be a major contributor to the muscle breakdown. It may be suggested that the mix of carbohydrate and protein nutrition before and during events requires re-examination.

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