Fifty-five male runners aged between 30 to 80 years were examined to determine the relative roles of various cardiovascular parameters which may account for the decrease in maximal oxygen uptake (VO2max) with aging. All subjects had similar body fat composition and trained for a similar mileage each week. The parameters tested were VO2max, maximal heart rate (HRmax), cardiac output (Q), and arteriovenous difference in oxygen concentration (Ca-Cv)O2 during graded, maximal treadmill running. Average body fat and training mileage were roughly 12% and 50 km.week-1, respectively. The average 10-km run-time slowed significantly by 6.0%.decade-1 [( 10-km run-time (min) = 0.323 x age (years) + 24.4] (n = 49, r = 0.692, p less than 0.001]. A strong correlation was found between age and VO2max [( VO2max (ml.kg-1.min-1) = -0.439 x age + 76.5] (n = 55, r = -0.768, p less than 0.001]. Thus, VO2max decreased by 6.9%.decade-1 along with reductions of HRmax (3.2%.decade-1, p less than 0.001) and Q (5.8%.decade-1, p less than 0.001), while no significant change with age was observed in estimated (Ca-Cv)O2. It was concluded that the decline of VO2max with aging in runners was mainly explained by the central factors (represented by the decline of HR and Q in this study), rather than by the peripheral factor (represented by (Ca-Cv)O2).

The purpose of this study was to investigate the physical activity levels in eleven 9-10 year old boys with reference to aerobic power or lactate threshold (LT). Daily physical activity levels were evaluated from a HR monitoring system for 12 h on three different days. VO2max, VO2-HR relationship and LT were determined by the progressive treadmill test. LT was 36.7 +/- 3.1 ml X kg-1 X min-1 and 71.0 +/- 6.6% VO2max. Mean total time of activities with HR above the level corresponding to 60% VO2max (T-60%) and that above LT (T-LT) were 34 +/- 7 and 18 +/- 7 min, respectively. VO2max (ml X kg-1 X min-1) correlated significantly with T-60% (p less than 0.01), while no significant relationship was found with LT in ml X kg-1 X min-1. In conclusion, longer daily physical activities at moderate to higher intensity for preadolescent children seem to increase VO2max rather than LT.

Six males performed cycle ergometer exercise on two occasions in random order. Each exercise was preceded by a 2-h period in which matched capsules were administered orally, containing either starch (C) or NaHC03 (E) in a dose of a 0.2 g • kg-1 body wt; pre-exercise blood pH and [HC03 -] were 7.34±0.01 and 23.7±0.5 mM (mean + S.E.) for the C study, and 7.41±0.01 and 28.6 + 1.3 mM for the E study (p < 0.001 and p < 0.01, respectively). Exercise was continuous and maintained for 10 min at 40 of maximal oxygen uptake (40°c Vo z max)' followed by 15 min at 12W above the respiratory compensation threshold ([+ RCT]) which was determined by the increase of the ventilatory equivalent for carbon dioxide (VE V~oz 1), and for as long as possible at 95 % Voz max. Endurance time at 95 % Voz max was significantly longer in E than in C (2.98±0.64 min vs. 2.00 ± 0.44 min, p <0.05). The rate of increase in arterialized venous lactate (LA) was higher in E than in C from rest to exercise at [+ RCT], while there was no significant difference in the hydrogen ions ([H+]). Consequently, [H +] • LA 1 (nM . mM -1) was significantly lower in E than in C. The change of VE V~oz-' was shifted downward in E compared to C during exercise with the lowest value being observed at the same exercise stage. These results suggest that the respiratory responses to exercise are not affected by the higher level of [HC03 -] induced by NaHC03 ingestion, and appear to reflect the net change of plasma During intense exercise, lactic acid is formed and accumulates in the muscle. The decrease of muscle pH is one of the major factors limiting exercise performance (HERMANSEN and OsNES, 1972) by impairing enzyme activities (TRIVEDI and

To examine the possible gender differences in lactate threshold (LT) and respiratory compensation threshold (RCT) and their relations to running performance, ten male and eight female college distance runners performed an incremental running test on the level treadmill. Both groups of runners were matched as closely as possible on the basis of maximal aerobic power relative to lean body mass (VO2.max.LBM-1). LT, determined from an inflection point in blood lactate, was significantly higher in males than in females (49.2 vs 45.5 ml.kg-1 LBM.min-1 P less than 0.05), while RCT, determined from a marked increase in ventilatory equivalent for CO2 (VE.VCO2(-1], was not significantly different between the two groups (51.5 vs 52.3 ml.kg-1 LBM.min-1). No significant difference was observed either in LT or in RCT expressed as %VO2max. RCT and running velocity at RCT were strongly related to the run times of 800 and 1500 m in females and 5000 and 10000 min males (r = -0.76 approximately 0.95; P less than 0.05 approximately 0.001), while it was not the case with VO2max and LT. These results suggest that there are no remarkable gender differences in LT and RCT when compared in relative terms and that RCT is a sensitive parameter for evaluating an endurance performance despite its controversial status.

To delineate the possible age-related differences in blood lactate response during exercise and its relations to endurance performance, 34 male runners (aged 21 to 69 years) performed an incremental treadmill running test. There were no significant differences in training distance and relative body fat among younger runners (YR), middle-aged runners (MR), and older runners (OR). The 5-km run time slowed with age, but was ranked at relatively the same level in each age group. OR had a 23% (P less than 0.001) and 12% (P less than 0.01) lower maximal oxygen uptake (VO2max) and a 22% (P less than 0.001) and 11% (P less than 0.001) slower 5-km run time than YR and MR, respectively. However, mean VO2 corresponding to 4 mM of blood lactate (OBLA VO2) was the same among the groups when expressed as %VO2max (YR; 84.3%, MR; 85.9%, OR; 85.9%). Significant correlations were found between OBLA VO2 (ml.kg-1.min-1) and 5-km run time in each group (YR; r = -0.648, P less than 0.05; MR; r = -0.658, P less than 0.01; OR; r = -0.680, P less than 0.05). These results suggest that OR attain a given blood lactate level at almost similar %VO2max to YR and MR and that OBLA VO2 in OR is useful for evaluating an endurance performance as well as in YR and in MR.