Enhanced protein breakdown after eccentric exercise in young and older men

Abstract

The effects of eccentric exercise on whole body protein metabolism were compared in five young untrained [age 24 +/- 1 yr, maximal O2 uptake (VO2max) = 49 +/- 6 ml.kg-1.min-1] and five older untrained men (age 61 +/- 1 yr, VO2max = 34 +/- 2 ml.kg-1.min-1). They performed 45 min of eccentric exercise on a cycle ergometer at a power output equivalent to 80% VO2max (182 +/- 18 W). Beginning 5 days before exercise and continuing for at least 10 days after exercise, they consumed a eucaloric diet providing 1.5 g.kg-1.day-1 of protein. Leucine metabolism in the fed state was measured before, immediately after, and 10 days after exercise, with intravenous L-[1-13C]leucine as a tracer (0.115 mumol.kg-1.min-1). Leucine flux increased 9% immediately after exercise (P less than 0.011) and remained elevated 10 days later, with no effect of age. Leucine oxidation increased 19% immediately after exercise and remained 15% above baseline 10 days after exercise (P less than 0.0001), with no effect of age. In the young men, urinary excretion of 3-methylhistidine per gram of creatinine did not increase until 10 days postexercise (P less than 0.05), but in the older men, it increased 5 days after exercise and remained high through 10 days postexercise (P less than 0.05), averaging 37% higher than in the young men. These data suggest that eccentric exercise produces a similar increase in whole body protein breakdown in older and young men, but myofibrillar proteolysis may contribute more to whole body protein breakdown in the older group.

Indirect measures of substrate utilisation following exercise‐induced muscle damage

“…Recently it has been hypothesised that EIMD causes alterations in homeostasis through the requirement of energy to repair muscle tissue (Dolezal, Potteiger, Jacobsen, & Benedict, 2000). This has been confirmed in number of studies (Chesley, MacDougall, Tarnopolsky, Atkinson, & Smith, 1992;Fielding et al, 1991) where maximum rates of muscle protein turnover lasted for 2 days in response to an acute bout of heavy eccentric resistance exercise. Although the present study did not measure protein turnover, it could be speculated that the stepping protocol influenced myofibrillar protein metabolism for a period of time post exercise.…”

Elevated Serum Cardiac Markers in Asymptomatic Marathon Runners after Competition: Is the Myocardium Stunned?

“…Biome chanical trauma from the eccentric physical stress of downhill running as on the Boston Marathon course com pounds the biochemical insult [12]. Repetitive exerciseinduced injury elevates the CK-MB activity in skeletal muscle due to its enhancement in regenerating fibers anal ogous to chronic myopathic conditions [13].…”

Comparison between old and young men for responses to fast velocity maximal lengthening contractions of the elbow flexors

“…Thus, it appears that exercise consisting of fast velocity lengthening contractions is of greater beneWt to older adults in preventing type II Wbre atrophy with ageing. However, it is important to note that exercise consisting of lengthening contractions (eccentric exercise) induces muscle damage (Clarkson and Dedrick 1988;Fielding et al 1991).…”