The effect of citrate loading on exercise performance, acid-base balance and metabolism

Nine subjects (VO2max 65 +/- 2 ml.kg-1.min-1, mean +/- SEM) were studied on two occasions following ingestion of 500 ml solution containing either sodium citrate (C, 0.300 g.kg-1 body mass) or a sodium chloride placebo (P, 0.045 g.kg-1 body mass). Exercise began 60 min later and consisted of cycle ergometer exercise performed continuously for 20 min each at power outputs corresponding to 33% and 66% VO2max, followed by exercise to exhaustion at 95% VO2max. Pre-exercise arterialized-venous [H+] was lower in C (36.2 +/- 0.5 nmol.l-1; pH 7.44) than P (39.4 +/- 0.4 nmol.l-1; pH 7.40); the plasma [H+] remained lower and [HCO3-] remained higher in C than P throughout exercise and recovery. Exercise time to exhaustion at 95% VO2max was similar in C (310 +/- 69 s) and P (313 +/- 74 s). Cardiorespiratory variables (ventilation, VO2, VCO2, heart rate) measured during exercise were similar in the two conditions. The plasma [citrate] was higher in C at rest (C, 195 +/- 19 mumol.l-1; P, 81 +/- 7 mumol.l-1) and throughout exercise and recovery. The plasma [lactate] and [free fatty acid] were not affected by citrate loading but the plasma [glycerol] was lower during exercise in C than P. In conclusion, sodium citrate ingestion had an alkalinizing effect in the plasma but did not improve endurance time during exercise at 95% VO2max. Furthermore, citrate loading may have prevented the stimulation of lipolysis normally observed with exercise and prevented the stimulation of glycolysis in muscle normally observed in bicarbonate-induced alkalosis.     

Oxygen uptake during running as related to body mass in circumpubertal boys: a longitudinal study

To investigate the effect of endurance training on physiological characteristics during circumpubertal growth, eight young runners (mean starting age 12 years) were studied every 6 months for 8 years. Four other boys served as untrained controls. Oxygen uptake (VO2) and blood lactate concentrations were measured during submaximal and maximal treadmill running. The data were aligned with each individual's age of peak height velocity. The maximal oxygen uptake (VO2max; ml.kg-1.min-1) decreased with growth in the untrained group but remained almost constant in the training group. The oxygen cost of running at 15 km.h-1 (VO2 15, ml.kg-1.min-1) was persistently lower in the trained group but decreased similarly with age in both groups. The development of VO2max and VO2 15 (l.min-1) was related to each individual's increase in body mass so that power functions were obtained. The mean body mass scaling factor was 0.78 (SEM 0.07) and 1.01 (SEM 0.04) for VO2max and 0.75 (SEM 0.09) and 0.75 (SEM 0.02) for VO2 15 in the untrained and trained groups, respectively. Therefore, expressed as ml.kg-0.75.min-1, VO2 15 was unchanged in both groups and VO2max increased only in the trained group. The running velocity corresponding to 4 mmol.l-1 of blood lactate (nu la4) increased only in the trained group. Blood lactate concentration at exhaustion remained constant in both groups over the years studied. In conclusion, recent and the present findings would suggest that changes in the oxygen cost of running and VO2max (ml.kg-1.min-1) during growth may mainly be due to an overestimation of the body mass dependency of VO2 during running.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of prolonged exercise at a similar percentage of maximal oxygen consumption in trained and untrained subjects

Six trained male cyclists and six untrained but physically active men participated in this study to test the hypothesis that the use of percentage maximal oxygen consumption (%VO2max) as a normalising independent variable is valid despite significant differences in the absolute VO2max of trained and untrained subjects. The subjects underwent an exercise test to exhaustion on a cycle ergometer to determine VO2max and lactate threshold. The subjects were grouped as trained (T) if their VO2max exceeded 60 ml.kg-1.min-1, and untrained (UT) if their VO2max was less than 50 ml.kg-1.min-1. The subjects were required to exercise on the ergometer for up to 40 min at power outputs that corresponded to approximately 50% and 70% VO2max. The allocation of each exercise session (50% or 70% VO2max) was random and each session was separated by at least 5 days. During these tests venous blood was taken 10 min before exercise (- 10 min), just prior to the commencement of exercise (0 min), after 20 min of exercise (20 min), at the end of exercise and 10 min postexercise (+ 10 min) and analysed for concentrations of cortisol, [Na+], [K+], [Cl-], glucose, free fatty acid, lactate [la-], [NH3], haemoglobin [Hb] and for packed cell volume. The oxygen consumption (VO2) and related variables were measured at two time intervals (14-15 and 34-35 min) during the prolonged exercise tests. Rectal temperature was measured throughout both exercise sessions. There was a significant interaction effect between the level of training and exercise time at 50% VO2max for heart rate (fc) and venous [la-].(ABSTRACT TRUNCATED AT 250 WORDS)     

The response of runners to arduous triathlon competition

As very few of the competitors in a triathlon are truly specialist in more than one of the three disciplines, high levels of physical (and mental) stress may result during the course of the event. We investigated some of the physiological responses occurring in runners participating in an "Iron Man" triathlon consisting of canoeing (20 km), cycling (90 km) and running (42 km), in that sequence. Twenty-one male entrants volunteered as subjects for the study. Prior to the competition, maximal oxygen consumption (VO2max) was determined. Basal venous blood samples were collected on the day prior to the competition and post-exercise venous blood samples were collected within 5 minutes of completion of the race. Serum iron was significantly reduced from a mean basal value of 20.6 mumol X l-1 to a mean value of 8.4 mumol X l-1 after the race. Cortisol levels showed a 3 fold increase after the race. Gross VO2max (l X min-1) and mass standardised VO2max (ml X min-1 X kg-1) were both negatively correlated to cortisol levels after the race (p less than 0.05). Total performance time was not related to gross VO2max (l X min-1) but was well correlated to mass corrected VO2max (ml X min-1 X kg-1). The marked fall in serum iron may have been related to heavy sweating or prelatent iron deficiency. Chronic iron deficiency (without frank anaemia) can impair physical performance, although we were unable to show any significant correlation between serum iron level after the race and time taken to complete the event.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of endurance training on excessive CO2 expiration due to lactate production in exercise

We attempted to determine the change in total excess volume of CO2 output (CO2 excess) due to bicarbonate buffering of lactic acid produced in exercise due to endurance training for approximately 2 months and to assess the relationship between the changes of CO2 excess and distance-running performance. Six male endurance runners, aged 19-22 years, were subjects. Maximal oxygen uptake (VO2max), oxygen uptake (VO2) at anaerobic threshold (AT), CO2 excess and blood lactate concentration were measured during incremental exercise on a cycle ergometer and 12-min exhausting running performance (12-min ERP) was also measured on the track before and after endurance training. The absolute magnitudes in the improvement due to training for CO2 excess per unit of body mass per unit of blood lactate accumulation (delta la-) in exercise (CO2 excess.mass-1.delta la-), 12-min ERP, VO2 at AT (AT-VO2) and VO2max on average were 0.8 ml.kg-1.l-1.mmol-1, 97.8 m, 4.4 ml.kg-1. min-1 and 7.3 ml.kg-1.min-1, respectively. The percentage change in CO2 excess.mass-1.delta la- (15.7%) was almost same as those of VO2max (13.7%) and AT-VO2 (13.2%). It was found to be a high correlation between the absolute amount of change in CO2 excess.mass-1.delta la-, and the absolute amount of change in AT-VO2 (r = 0.94, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of incremental and steady state tests of endurance training

To compare the results obtained by incremental or constant work load exercises in the evaluation of endurance conditioning, a 20-week training programme was performed by 9 healthy human subjects on the bicycle ergometer for 1 h a day, 4 days a week, at 70-80% VO2max. Before and at the end of the training programme, (1) the blood lactate response to a progressive incremental exercise (18 W increments every 2nd min until exhaustion) was used to determine the aerobic and anaerobic thresholds (AeT and AnT respectively). On a different day, (2) blood lactate concentrations were measured during two sessions of constant work load exercises of 20 min duration corresponding to the relative intensities of AeT (1st session) and AnT (2nd session) levels obtained before training. A muscle biopsy was obtained from vastus lateralis at the end of these sessions to determine muscle lactate. AeT and AnT, when expressed as % VO2max, increased with training by 17% (p less than 0.01) and 9% (p less than 0.05) respectively. Constant workload exercise performed at AeT intensity was linked before training (60% VO2max) to a blood lactate steady state (4.8 +/- 1.4 mmol.l-1) whereas, after training, AeT intensity (73% VO2max) led to a blood lactate accumulation of up to 6.6 +/- 1.7 mmol.l-1 without significant modification of muscle lactate (7.6 +/- 3.1 and 8.2 +/- 2.8 mmol.kg-1 wet weight respectively). It is concluded that increase in AeT with training may reflect transient changes linked to lower early blood lactate accumulation during incremental exercise.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cardiorespiratory adaptation with short term training in older men

The purpose of this study was to assess the rate of training-induced cardiorespiratory adaptations in older men [mean (SD), 66.5 (1.2) years]. The eight subjects trained an average of 4.3 (0.3) times each week. The walk/jog training was in two phases with 4 weeks (phase 1) at a speed to elicit 70% of pre-training maximal oxygen consumption (VO2max), and 5 weeks (phase 2) at 80%. Maximal exercise treadmill tests and a standardized submaximal protocol were performed prior to training, at weekly intervals during the training programme, and after training. VO2max (ml.kg-1.min-1) increased significantly over both phases: 6.6% after the first 4 weeks, and an additional 5.2% after the final 5 weeks. The weekly changes in VO2max over phase 1 were well fitted by an exponential association curve (r = 0.75). The half-time for the rate of adaptation was 13.8 days, or 8.3 training sessions. Over phase 2, the change in VO2max did not plateau and a time course could not be determined. Submaximal exercise heart rate (fc) was reduced a significant 10 beats.min-1 after the first 4 weeks, and further 6 beats.min-1 over the final 5 weeks. The fc reductions showed half-times of 9.1 days (phase 1) and 9.8 days (phase 2) (or 5-6 training sessions). The anaerobic ventilation threshold was increased 13.9% over the 9 weeks of training and the respiratory exchange ratio during constant load heavy exercise was significantly reduced; however, these changes could not be described by an exponential time course. Thus, short-term exercise training of older men resulted in significant and rapid cardiorespiratory improvements.     

Plasma lactate and ventilation thresholds in trained and untrained cyclists

Six trained male cyclists and six untrained sedentary men were studied to determine whether the plasma lactate threshold (PLT) and ventilation threshold (VT) occur at the same work rate in both fit and unfit populations. The PLT was determined from a marked increase in plasma lactate concentration ([La]) and VT from a nonlinear increase in expired minute ventilation (VE) during incremental leg-cycling tests; work rate was increased 30 W every 2 min until volitional exhaustion. The trained subjects' mean VO2 max (63.8 ml O2 X kg-1 X min-1) and VT (65.8% VO2 max) were significantly higher (P less than 0.05) than the untrained subjects' mean VO2max (35.5 ml O2 X kg-1 X min-1) and VT (51.4% VO2 max). The trained subjects' mean PLT (68.8% VO2 max) and VT did not differ significantly, but the untrained subjects' mean PLT (61.6% VO2 max) was significantly higher than their VT. The trained subjects' mean peak [La] (10.5 mmol X l-1) did not differ significantly from the untrained subjects' mean peak [La] (11.5 mmol X l-1). However, the time of appearance of the peak [La] during passive recovery was inversely related to VO2 max. These results suggest that variance in lactate diffusion and/or removal processes between the trained and untrained subjects may account in part for the different relationships between the VT and PLT in each population.     

Sleep deprivation and cardiorespiratory function. Influence of intermittent submaximal exercise

The effects of 64 h of sleep deprivation upon cardiorespiratory function was studied in 11 young men (VO2max = 55.5 ml kg-1 min-1, STPD). Six subjects engaged in normal sedentary activities, while the others walked on a treadmill at 28% VO2max for one hour in every three; eight weeks later, sleep deprivation was repeated with a crossover of subjects. Immediate post-deprivation measurement of VO2max showed a small but statistically significant decrease (-3.8 ml min-1 kg-1, STPD), with no difference between exercise and control trials. The final decrement in aerobic power was not due to a loss of motivation, as 88% (21 of 24) of post-deprivation tests still showed a plateau of VO2max; in addition, terminal heart rates (198 vs 195 beats min-1), respiratory exchange ratios (1.14 vs 1.15) and blood lactate levels (12.1 vs 11.8 mmol l-1) were not significantly different after sleep deprivation. The decrease in VO2max was associated with a lower VEmax (127 vs 142 l min-1, BTPS) and a substantial haemodilution (13%). Physiological responses to sub-maximal exercise showed persistence of the normal diurnal rhythm in heart rate and oxygen consumption, with no added effects due to sleep deprivation. However, ratings of perceived exertion (Borg scale) increased significantly throughout sleep deprivation. The findings are consistent with a mild respiratory acidosis, secondary to reduced cortical arousal and/or a progressive depletion of tissue glycogen stores which are not altered appreciably by moderate physical activity.     

Effect of previous supramaximal work on lacticaemia during supra-anaerobic threshold exercise

Twelve male and female subjects (eight trained, four untrained) exercised for 30 min on a treadmill at an intensity of maximal O2 consumption (% VO2max) 90.0%, SD 4.7 greater than the anaerobic threshold of 4 mmol.l-1 (Than = 83.6% VO2max, SD 8.9). Time-dependent changes in blood lactate concentration [( lab]) during exercise occurred in two phases: the oxygen uptake (VO2) transient phase (from 0 to 4 min) and the VO2 steady-state phase (4-30 min). During the transient phase, [lab] increased markedly (1.30 mmol.l-1.min-1, SD (0.13). During the steady-state phase, [lab] increased slightly (0.02 mmol.l-1.min-1, SD 0.06) and when individual values were considered, it was seen that there were no time-dependent increases in [lab] in half of the subjects. Following hyperlacticaemia (8.8 mmol.l-1, SD 2.0) induced by a previous 2 min of supramaximal exercise (120% VO2max), [lab] decreased during the VO2 transient (-0.118 mmol.l-1.min-1, SD 0.209) and steady-state (-0.088 mmol.l-1.min-1, SD 0.103) phases of 30 min exercise (91.4% VO2max, SD 4.8). In conclusion, it was not possible from the Than to determine the maximal [lab] steady state for each subject. In addition, lactate accumulated during previous supramaximal exercise was eliminated during the VO2 transient phase of exercise performed at an intensity above the Than. This effect is probably largely explained by the reduction in oxygen deficit during the transient phase. Under these conditions, the time-course of changes in [lab] during the VO2 steady state was also affected.     

Effects of training on lactate production and removal during progressive exercise in humans.

To determine whether the reduced blood lactate concentrations [La] during submaximal exercise in humans after endurance training result from a decreased rate of lactate appearance (Ra) or an increased rate of lactate metabolic clearance (MCR), interrelationships among blood [La], lactate Ra, and lactate MCR were investigated in eight untrained men during progressive exercise before and after a 9-wk endurance training program. Radioisotope dilution measurements of L-[U-14C]lactate revealed that the slower rise in blood [La] with increasing O2 uptake (VO2) after training was due to a reduced lactate Ra at the lower work rates [VO2 less than 2.27 l/min, less than 60% maximum VO2 (VO2max); P less than 0.01]. At power outputs closer to maximum, peak lactate Ra values before (215 +/- 28 mumol.min-1.kg-1) and after training (244 +/- 12 mumol.min-1.kg-1) became similar. In contrast, submaximal (less than 75% VO2max) and peak lactate MCR values were higher after than before training (40 +/- 3 vs. 31 +/- 4 ml.min-1.kg-1, P less than 0.05). Thus the lower blood [La] values during exercise after training in this study were caused by a diminished lactate Ra at low absolute and relative work rates and an elevated MCR at higher absolute and all relative work rates during exercise.     

Effects of endurance training on hyperammonaemia during a 45-min constant exercise intensity

Eleven laboratory-pretrained subjects (initial VO2max = 54 ml.kg-1.min-1) took part in a study to evaluate the effect of a short endurance training programme [8-12 sessions, 1 h per session, with an intensity varying from 60% to 90% maximal oxygen consumption (VO2max)] on the responses of blood ammonia (b[NH+4]) and lactate (b[la]) concentrations during progressive and constant exercise intensities. After training, during which VO2max did not increase, significant decreases in b[NH+4], b[la] and muscle proton concentration were observed at the end of the 80% VO2max constant exercise intensity, although b[NH+4] and b[la] during progressive exercise were unchanged. On the other hand, no correlations were found between muscle fibre composition and b[NH+4] in any of the exercise procedures. This study demonstrated that a constant exercise intensity was necessary to reveal the effect of training on muscle metabolic changes inducing the decrease in b[NH+4] and b[la]. At a relative power of exercise of 80% VO2max, there was no effect of muscle fibre composition on b[NH+4] accumulation.     

Decline in VO2max with aging in master athletes and sedentary men

Fifteen well-trained master endurance athletes [62.0 +/- 2.3 (SE) yr] and 14 sedentary control subjects (61.4 +/- 1.4 yr) were reevaluated after an average follow-up period of approximately 8 yr to obtain information regarding the effects of physical activity on the age-related decline in maximal O2 uptake capacity (VO2max). The master athletes had been training for 10.2 +/- 2.9 yr before initial testing and continued to train during the follow-up period. The sedentary subjects' VO2max declined by an average of 3.3 ml.kg-1.min-1 (33.9 +/- 1.7 vs. 30.6 +/- 1.6, P less than 0.001) over the course of the study, a decline of 12% per decade. In these subjects maximal heart rate declined 8 beats/min (171 vs. 163) and maximal O2 pulse decreased from 0.20 to 0.18 ml.kg-1.beat (P less than 0.05). The master athletes' VO2 max decreased by an average of 2.2 ml.kg-1.min-1 (54.0 +/- 1.7 vs. 51.8 +/- 1.8, P less than 0.05), a 5.5% decline per decade. The master athletes' maximal heart rate was unchanged (171 +/- 3 beats/min) and their maximal O2 pulse decreased from 0.32 to 0.30 ml.kg-1.beat (P less than 0.05). These findings provide evidence that the age-related decrease in VO2max of master athletes who continue to engage in regular vigorous endurance exercise training is approximately one-half the rate of decline seen in age-matched sedentary subjects. Furthermore our results suggest that endurance exercise training may reduce the rate of decline in maximal heart rate that typically occurs as an individual ages.     

Effect of food intake on exercise fatigue in trained and untrained subjects

The effects of carbohydrate and fat intake on exercise-induced fatigue was investigated in 30 untrained--(VO2max of 40.6 +/- 2.7 ml X kg-1 X min-1) and 24 trained-subjects (VO2max of 52.3 +/- 2.7 ml X kg-1 X min-1) performing a 34 km march with a 25 kg backpack. Marching time was 8 1/2 h and 6 1/3 h in the untrained and trained-subjects respectively. The subjects were divided into 3 dietary groups. One group had free access to sugar cubes, the second group was offered almonds and the third one served as a control. Triglyceride levels decreased by 65 mg X dl-1 in untrained, and by 115 mg X dl-1 in trained subjects, while blood glucose remained at normal levels. In the untrained subjects, ingestion of almonds delayed the subjective sensation of exhaustion, while 50% of the controls and the sugar consuming subjects complained of exhaustion. The data suggest that ingestion of food containing fat delays exercise induced exhaustion or fatigue to a greater extent than does carbohydrate ingestion.     

Exercise intensity and glucose tolerance in trained and nontrained subjects

The improved glucose tolerance and increased insulin sensitivity associated with regular exercise appear to be the result, in large part, of the residual effects of the last bout of exercise. To determine the effects of exercise intensity on this response, glucose tolerance and the insulin response to a glucose load were determined in seven well-trained male subjects [maximal O2 uptake (VO2max) = 58 ml.kg-1.min-1] and in seven nontrained male subjects (VO2max = 49 ml.kg-1.min-1) in the morning after an overnight fast 1) 40 h after the last training session (control), 2) 14 h after 40 min of exercise on a cycle ergometer at 40% VO2max, and 3) 14 h after 40 min of exercise at 80% VO2max. Subjects replicated their diets for 3 days before each test and ate a standard meal the evening before the oral glucose tolerance test. No differences in the 3-h insulin or glucose response were observed between the control trial and before exercise at either 40 or 80% VO2max in the trained subjects. In the nontrained subjects the plasma insulin response was decreased by 40% after a single bout of exercise at either 40 or 80% VO2max (7.0 X 10(3) vs. 5.0 X 10(3), P less than 0.05; 3.8 X 10(3) microU.ml-1.180 min-1, P less than 0.01). The insulin response after a single bout of exercise in the nontrained subjects was comparable with the insulin responses found in the trained subjects for the control and exercise trials.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of pre-exercise carbohydrate feedings on muscle glycogen use during exercise in well-trained runners

The purpose of this study was to examine the effects of pre-exercise glucose and fructose feedings on muscle glycogen utilization during exercise in six well-trained runners (VO2max = 68.2 +/- 3.4 ml X kg-1 X min-1). On three separate occasions, the runners performed a 30 min treadmill run at 70% VO2max. Thirty minutes prior to exercise each runner ingested 75 g of glucose (trial G), 75 g of fructose (trial F) or 150 ml of a sweetened placebo (trial C). During exercise, no differences were observed between any of the trials for oxygen uptake, heart rate or perceived exertion. Serum glucose levels were elevated as a result of the glucose feeding (P less than 0.05) reaching peak levels at 30 min post-feeding (7.90 +/- 0.24 mmol X l-1). With the onset of exercise, glucose levels dropped to a low of 5.89 +/- 0.85 mmol X l-1 at 15 min of exercise in trial G. Serum glucose levels in trials F and C averaged 6.21 +/- 0.31 mmol X l-1 and 5.95 +/- 0.23 mmol X l-1 respectively, and were not significantly different (P less than 0.05). There were also no differences in serum glucose levels between any of the trials at 15 and 30 min of exercise.     

The effects of two levels of caffeine ingestion on excess postexercise oxygen consumption in untrained women

The effects of two levels of caffeine ingestion (5 mg.kg-1, CAF1, and 10 mg.kg-1, CAF2) on postexercise oxygen consumption was investigated in six untrained women aged 20.5 (SEM 0.5) years. After a test to determine maximal oxygen consumption (VO2max) each subject underwent three test sessions at 55% VO2max either in a control condition (CON) or with the CAF1 or CAF2 dose of caffeine. During exercise, oxygen consumption was found to be significantly higher in the CAF1 and CAF2 trials, compared to CON (P < 0.05). During the hour postexercise, oxygen consumption in CAF1 and CAF2 remained significantly higher than in CON (P < 0.05). At all times throughout the exercise, free fatty acid (FFA) concentrations were significantly higher in the caffeine trials than in CON. The FFA concentrations 1 h postexercise (+60 min) were further elevated above resting values for all three trials. Caffeine ingestion caused the greatest elevation above resting levels being 1.89 (SEM 0.19) mmol.l-1 and 1.96 (SEM 0.22) mmol.l-1 for the CAF1 and CAF2 trials, respectively. This was significantly higher (P < 0.0001) than the CON level which was 0.97 (SEM 0.19) mmol.l-1. Respiratory exchange ratio (R) values became significantly lower (P < 0.05) in CAF1 and CAF2 compared to CON at the onset of exercise and continued to decrease during the activity. Throughout the recovery period, R values were significantly lower for both caffeine trials compared to CON. The results of this study would suggest that caffeine is useful in significantly increasing metabolic rate above normal levels in untrained women during, as well as after, exercising at 55% VO2max.     

Effect of endurance exercise training on ventilatory function in older individuals

To evaluate the effect of endurance training on ventilatory function in older individuals, 1) 14 master athletes (MA) [age 63 +/- 2 yr (mean +/- SD); maximum O2 uptake (VO2max) 52.1 +/- 7.9 ml . kg-1 . min-1] were compared with 14 healthy male sedentary controls (CON) (age 63 +/- 3 yr; VO2max of 27.6 +/- 3.4 ml . kg-1 . min-1), and 2) 11 sedentary healthy men and women, age 63 +/- 2 yr, were reevaluated after 12 mo of endurance training that increased their VO2max 25%. MA had a significantly lower ventilatory response to submaximal exercise at the same O2 uptake (VE/VO2) and greater maximal voluntary ventilation (MVV), maximal exercise ventilation (VEmax), and ratio of VEmax to MVV than CON. Except for MVV, all of these parameters improved significantly in the previously sedentary subjects in response to training. Hypercapnic ventilatory response (HCVR) at rest and the ventilatory equivalent for CO2 (VE/VCO2) during submaximal exercise were similar for MA and CON and unaffected by training. We conclude that the increase in VE/VO2 during submaximal exercise observed with aging can be reversed by endurance training, and that after training, previously sedentary older individuals breathe at the same percentage of MVV during maximal exercise as highly trained athletes of similar age.     

Effects of incomplete pulmonary gas exchange on VO2 max

Recent evidence suggests that heavy exercise may lower the percentage of O2 bound to hemoglobin (%SaO2) by greater than or equal to 5% below resting values in some highly trained endurance athletes. We tested the hypothesis that pulmonary gas exchange limitations may restrict VO2max in highly trained athletes who exhibit exercise-induced hypoxemia. Twenty healthy male volunteers were divided into two groups according to their physical fitness status and the demonstration of exercise-induced reductions in %SaO2 less than or equal to 92%: 1) trained (T), mean VO2max = 56.5 ml.kg-1.min-1 (n = 13) and 2) highly trained (HT) with maximal exercise %SaO2 less than or equal to 92%, mean VO2max = 70.1 ml.kg-1.min-1 (n = 7). Subjects performed two incremental cycle ergometer exercise tests to determine VO2max at sea level under normoxic (21% O2) and mild hyperoxic conditions (26% O2). Mean %SaO2 during maximal exercise was significantly higher (P less than 0.05) during hyperoxia compared with normoxia in both the T group (94.1 vs. 96.1%) and the HT group (90.6 vs. 95.9%). Mean VO2max was significantly elevated (P less than 0.05) during hyperoxia compared with normoxia in the HT group (74.7 vs. 70.1 ml.kg-1.min-1). In contrast, in the T group, no mean difference (P less than 0.05) existed between treatments in VO2max (56.5 vs. 57.1 ml.kg-1.min-1). These data suggest that pulmonary gas exchange may contribute significantly to the limitation of VO2max in highly trained athletes who exhibit exercise-induced reductions in %SaO2 at sea level.(ABSTRACT TRUNCATED AT 250 WORDS)     

Training effects of cross-country skiing and running on maximal aerobic cycle performance and on blood lipids

Two experiments were carried out to compare the cardiorespiratory and metabolic effects of cross-country skiing and running training during two successive winters. Forty-year-old men were randomly assigned into skiing (n = 15 in study 1, n = 16 in study 2), running (n = 16 in study 1 and n = 16 in study 2) and control (n = 17 in study 1 and n = 16 in study 2) groups. Three subjects dropped out of the programme. The training lasted 9-10 weeks with 40-min exercise sessions three times each week. The training intensity was controlled at 75%-85% of the maximal oxygen consumption (VO2max) using portable heart rate metres and the mean heart rate was 156-157 beats.min-1 in the training groups. In the pooled data of the two studies the mean increase in the VO2max (in ml.min-1.kg-1) on a cycle ergometer was 17% for the skiing group, 13% for the running group and 2% for the control group. The increase in VO2max was highly significant in the combined exercise group compared to the control group but did not differ significantly between the skiing and running groups. The fasting serum concentrations of lipoproteins and insulin did not change significantly in any of the groups. These results suggested that training by cross-country skiing and running of the same duration and intensity at each session for 9-10 weeks improved equally the cardiorespiratory fitness of untrained middle-aged men.