Enhanced protein breakdown after eccentric exercise in young and older men.
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.
Fielding
R A
RA
Human Physiology Laboratory, US Department of Agriculture Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts 02111.
Meredith
C N
CN
O'Reilly
K P
KP
Frontera
W R
WR
Cannon
J G
JG
Evans
W J
WJ
D000328:Adult; D000375:Aging / Q000378:metabolism*; D002151:Calorimetry; D002245:Carbon Dioxide / Q000378:metabolism; D003402:Creatine Kinase / Q000378:metabolism; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D008297:Male; D008762:Methylhistidines / Q000652:urine; D008875:Middle Aged; D009584:Nitrogen / Q000652:urine; D010101:Oxygen Consumption / Q000502:physiology; D011506:Proteins / Q000378:metabolism*
D008762:Methylhistidines; D011506:Proteins; D002245:Carbon Dioxide; D003402:Creatine Kinase; D007930:Leucine; C028118:3-methylhistidine; D009584:Nitrogen