MAXIMAL LACTATE STEADY STATE: INFLUENCE OF THE AGE-RELATED ADAPTATIONS OF SKELETAL MUSCLE
Increased participation of aged individuals in competitive athletics warrants basic research focused on delineating age-related changes in performance variables. PURPOSE: Based on potential age-related declines in aerobic enzyme activities and a shift in the expression of myosin heavy chain (MHC) isoforms, we hypothesized that maximal lactate steady state (MLSS) exercise intensity would be altered as a function of age. METHODS: Three age groups [(YA, n=10, 25.1±0.9 years, 8.3±1.0 % fat) (MA, n=10, 42.9±1.0 years, 13.6±1.9 % fat) (OA, n=10, 63.9±2.5 years, 16.4±1.4 % fat)] of male, competitive cyclists and triathletes matched for training intensity and duration were studied. Subjects performed a VO2max test followed by a series of 30 min exercise trials to determine MLSS. The intensity of the first trial was 60% of maximal power output measured during the VO2max test. Workload of each subsequent trial was increased by 5% until blood lactate increased by > 1 mMol/L in the last 20 min of the 30 min trial. A muscle biopsy of the vastus lateralis was procured on a separate visit. RESULTS: There were significant (p<0.05) differences in VO2max between all age groups (YA = 66.9±1.4 ml•kg-1•min-1, MA = 55.5±2.4 ml•kg-1•min-1, OA = 46.8±2.3 ml•kg-1•min-1). When expressed as a percentage of VO2max, there was also a significant (p<0.05) age-related decrease in the relative MLSS exercise intensity (YA = 82.2±1.7%, MA = 76.0±1.3%, OA = 70.1±1.4%). However, there were no significant age-related changes in citrate synthase (CS) activity or MHC isoform profile. CONCLUSION: The hypothesis is supported as there is an age-related decline in MLSS exercise intensity in athletes matched for training intensity and duration. Additionally, the rate of this decline is approximately 3.8% per decade. While CS activity is moderately related (r = 0.44, p = 0.008) to relative MLSS intensity, it does not explain the age-related decline in MLSS. The mechanism(s) responsible for the observed age-related decline in MLSS is unknown. Supported by The Gatorade Sports Science Institute.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:lactate aging metabolism
Date of Publication:01/01/2002