MAXIMAL LACTATE STEADY-STATE DURING THE 2ND DECADE OF AGE

Maximal lactate steady state (MLSS) presumably corresponds to the high est constant workload that can be performed by oxidative metabolism. T he anaerobic and, to a minor extent, the oxidative metabolism have bee n reported to be affected by age. The second decade of life is the key period in the change in energy metabolism between children and adults . The aim of this study was to evaluate the effects of age on MLSS in 34 male subjects (age: 15.4 +/- 2.8 yr, range: 11-20 yr; height: 171.8 +/- 14.9 cm, range: 134-191 cm; body mass: 59.6 +/- 15.5 kg, range: 2 7-90 kg) performing an incremental load test to determine maximal work load and several constant load tests for MLSS measurement on a cycle e rgometer. MLSS (4.2 +/- 0.7 mmol . l(-1), range: 2.8 to 5.5 mmol . l(- 1)) and MLSS intensity related to maximal workload (66.5 +/- 7.7%, ran ge: 50-84%) were independent of age. MLSS heart rate (180.1 +/- 10.1 m in(-1), range: 156-208 min(-1)) decreased (P < 0.01) with increasing a ge, whereas absolute (157.2 +/- 54.8 W, range: 65-240 W) and relative MLSS workload (2.6 +/- 0.5 W . kg(-1), range: 1.5 to 4.1 W . kg(-1)) a nd absolute (236.9 +/- 79.0 W, range: 100-350 W) and relative maximal workload (3.9 +/- 0.6 W . kg(-1), range: 2.7 to 5.5 W . kg(-1)) increa sed (P < 0.001) with age. The age independence of MLSS supports the th eory that neuromuscular factors may contribute to the frequently obser ved changes in response to given exercises with physical maturity more than changes in oxidative metabolism and/or glycolysis.