Additive effects of training and high-fat diet on energy metabolism during exercise

This study was conducted to obtain additional information about the adaptations after 12 wk of high-fat diet (HFD) per se or HFD combined with endurance training in the rat using a two [diet: carbohydrate (CHO) or HFD] by two (training: sedentary or trained) by two (condition at death: rested or exercised) factorial design. Adaptation to prolonged HFD increases maximal O2 uptake (VO2max; 13%, P less than 0.05) and submaximal running endurance (+64%, P less than 0.05). This enhancement in exercise capacity could be attributed to 1) an increase in skeletal muscle aerobic enzyme activities (3-hydroxyacyl-CoA dehydrogenase and citrate synthase in soleus and red quadriceps) or 2) a decrease in liver glycogen breakdown in response to 1 h exercise at 80% VO2max. When training is superimposed to HFD, the most prominent finding provided by this study is that the diet-induced effects are cumulative with the well-known training effect on VO2max, exercise endurance, oxidative capacity of red muscle, and metabolic responses to exercise, with a further reduction in liver glycogen breakdown.     

Effect of an iron supplement on body iron status and aerobic capacity of young training women

Serum iron deficiency has a high incidence in female athletes. We investigated the effects of a daily oral iron supplement, (160 mg) administered during an intensive 7-week physical training programme, on body iron status, and the maximal aerobic capacity (VO2max) of 13 women (group A) compared to 15 who took a placebo (group B). The subjects were 19 years old. Blood samples were obtained before training began and on days 1, 7, 21 and 42 of training. They were analysed for packed cell volume (PVC) and for haemoglobin (Hb), 2,3-diphosphoglycerate (2,3-DPG), haptoglobin, iron and ferritin concentrations. The VO2max was measured on days 0, 21 and 42 of training. Following 21 days of training Hb, PCV and ferritin were significantly higher (P less than or equal to 0.01) in group A compared to group B. Over the training period Hb rose by 9.3% and 2.4% in groups A and B, respectively. At the end of training 66% of group B exhibited ferritin concentrations below 10 ng.ml-1, while none of group A had such low values. Mean VO2max of group A had increased by 7.5% following 21 days of training (P less than or equal to 0.01) and by 15.3% after 42 days. No appreciable increase in VO2max had occurred in group B by day 21 (significantly lower than VO2max of group A; P less than or equal to 0.05), however by day 42 it had increased by 14.3% (P less than or equal to 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Exercise training and "ventilation threshold" in elderly

Dynamic exercise training of the elderly increases maximal O2 uptake (VO2max); however, the effects of training on the ventilation threshold (VET) have not been studied. VET was identified as the final point before the ventilatory equivalent for O2 (VE/VO2) increased, without an increase in the ventilatory equivalent for CO2 (VE/VCO2). Inactive elderly males (mean age, 62 yr) were randomly assigned to a control (C, n = 44) or activity (A, n = 45) group. VO2max and VET were determined from an incremental treadmill test. Initial VO2max was not different between the C (2.34 +/- 0.42 l X min-1) and A (2.28 +/- 0.44 l X min-1) groups, nor was there a significant difference in the VO2 at the VET (C = 1.39 +/- 0.26 l X min-1; A = 1.31 +/- 0.23 l X min-1). The activity group trained for 30 min/day, 3 days/wk at an intensity of approximately 65-80% of VO2max. After 1 yr of training the activity group exhibited an 18% increase in VO2max (A = 2.70 +/- 0.54 l X min-1), but the change in VET was not significant (A = 1.39 +/- 0.28 l X min-1). There was no significant change in VO2max (C = 2.45 +/- 0.68 l X min-1) or VET (C = 1.38 +/- 0.31 l X min-1) in the control group. VET/VO2max declined significantly in the activity group (from 58 to 52% of VO2max). Change in VET/VO2max with training was not correlated with the initial VO2max value. We conclude that increases in aerobic capacity are more readily effected than alterations of the VET in elderly subjects.     

Metabolic adaptations to training precede changes in muscle mitochondrial capacity.

To determine whether increases in muscle mitochondrial capacity are necessary for the characteristic lower exercise glycogen loss and lactate concentration observed during exercise in the trained state, we have employed a short-term training model involving 2 h of cycling per day at 67% maximal O2 uptake (VO2max) for 5-7 consecutive days. Before and after training, biopsies were extracted from the vastus lateralis of nine male subjects during a continuous exercise challenge consisting of 30 min of work at 67% VO2max followed by 30 min at 76% VO2max. Analysis of samples at 0, 15, 20, and 60 min indicated a pronounced reduction (P less than 0.05) in glycogen utilization after training. Reductions in glycogen utilization were accompanied by reductions (P less than 0.05) in muscle lactate concentration (mmol/kg dry wt) at 15 min [37.4 +/- 9.3 (SE) vs. 20.2 +/- 5.3], 30 min (30.5 +/- 6.9 vs. 17.6 +/- 3.8), and 60 min (26.5 +/- 5.8 vs. 17.8 +/- 3.5) of exercise. Maximal aerobic power, VO2max (l/min) was unaffected by the training (3.99 +/- 0.21 vs. 4.05 +/- 0.26). Measurements of maximal activities of enzymes representative of the citric acid cycle (succinic dehydrogenase and citrate synthase) were similar before and after the training. It is concluded that, in the voluntary exercising human, altered metabolic events are an early adaptive response to training and need not be accompanied by changes in muscle mitochondrial capacity.     

Effects of training at and above the lactate threshold on the lactate threshold and maximal oxygen uptake

Thirty-three college women (mean age = 21.8 years) participated in a 5 d X wk-1, 12 week training program. Subjects were randomly assigned to 3 groups, above lactate threshold (greater than LT) (N = 11; trained at 69 watts above the workload associated with LT), = LT (N = 12; trained at the work load associated with LT) and control (C) (N = 10). Subjects were assessed for VO2max, VO2LT, VO2LT/VO2max, before and after training, using a discontinuous 3 min incremental (starting at 0 watts increasing 34 watts each work load) protocol on a cycle ergometer (Monark). Respiratory gas exchange measures were determined using standard open circuit spirometry while LT was determined from blood samples taken immediately following each work load from an indwelling venous catheter located in the back of a heated hand. Body composition parameters were determined before and after training via hydrostatic weighing. Training work loads were equated so that each subject expended approximately 1465 kJ per training session (Monark cycle ergometer) regardless of training intensity. Pretraining, no significant differences existed between groups for any variable. Post training the greater than LT group had significantly higher VO2max (13%), VO2LT (47%) and VO2LT/VO2max (33%) values as compared to C (p less than .05). Within group comparisons revealed that none of the groups significantly changed VO2max as a result of training, only the greater than LT group showed a significant increase in VO2LT (48%) (p less than .05), while both the = LT and greater than LT group showed significant increases in VO2LT/VO2max (= LT 16%, greater than LT 42% (p less than .05)).(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of heat stress and acclimation on maximal aerobic power

Thirteen male volunteers performed cycle ergometer maximal oxygen uptake (VO2max tests) in moderate (21 degrees C, 30% rh) and hot (49 degrees C, 20% rh) environments, before and after a 9-day heat acclimation program. This program resulted in significantly decreased (P less than 0.01) final heart rate (24 bt X min-1) and rectal temperature (0.4 degrees C) from the first to last day of acclimation. The VO2max was lower (P less than 0.01) in the hot environment relative to the moderate environment both before (8%) and after (7%) acclimation with no significant difference (P greater than 0.05) shown for maximal power output (PO max, watts) between environments either before or after acclimation. The VO2max was higher (P less than 0.01) by 4% after acclimation in both environments. Also, PO max was higher (P less than 0.05) after acclimation in both the moderate (4%) and hot (2%) environments. The reduction in VO2max in the hot compared to moderate environment was not related to the difference in core temperature at VO2max between moderate and hot trials, nor was it strongly related with aerobic fitness level. These findings indicate that heat stress, per se, reduced the VO2max. Further, the reduction in VO2max due to heat was not affect be state of heat acclimation, the degree of elevation in core temperature, or level of aerobic fitness.     

Exercise training prevents decline in stroke volume during exercise in young healthy subjects.

Stroke volume (SV) increases above the resting level during exercise and then declines at higher intensities of exercise in sedentary subjects. The purpose of this study was to determine whether an attenuation of the decline in SV at higher exercise intensities contributes to the increase in maximal cardiac output (Qmax) that occurs in response to endurance training. We studied six men and six women, 25 +/- 1 (SE) yr old, before and after 12 wk of endurance training (3 days/wk running for 40 min, 3 days/wk interval training). Cardiac output was measured at rest and during exercise at 50 and 100% of maximal O2 uptake (Vo2max) by the C2H2-rebreathing method. VO2max was increased by 19% (from 2.7 +/- 0.2 to 3.2 +/- 0.3 l/min, P less than 0.001) in response to the training program. Qmax was increased by 12% (from 18.1 +/- 1 to 20.2 +/- 1 l/min, P less than 0.01), SV at maximal exercise was increased by 16% (from 97 +/- 6 to 113 +/- 8 ml/beat, P less than 0.001) and maximal heart rate was decreased by 3% (from 185 +/- 2 to 180 +/- 2 beats/min, P less than 0.01) after training. The calculated arteriovenous O2 content difference at maximal exercise was increased by 7% (14.4 +/- 0.4 to 15.4 +/- 0.4 ml O2/100 ml blood) after training. Before training, SV at VO2max was 9% lower than during exercise at 50% VO2max (P less than 0.05). In contrast, after training, the decline in SV between 50 and 100% VO2max was only 2% (P = NS). Furthermore, SV was significantly higher (P less than 0.01) at 50% VO2max after training than it was before. Left ventricular hypertrophy was evident, as determined by two-dimensional echocardiography at the completion of training. The results indicate that in young healthy subjects the training-induced increase in Qmax is due in part to attenuation of the decrease in SV as exercise intensity is increased.     

Step ergometry: is it task-specific training?

Maximal exercise responses were measured before and after 10 weeks of training in two groups of men, one trained on a treadmill (n = 12) and the other on a step ergometer (n = 9); the groups were pre- and post-tested on both machines to examine the specificity of the training modes. Training for both groups consisted of 3 days week-1, 30 min day-1, progressing to 50 min day-1, at an intensity of 75%-80% heart rate maximum reserve. Pre-training maximal oxygen uptake (VO2max) was significantly higher on the treadmill for both groups (X = 8.5%). VO2max increased 6.9% on the treadmill (P less than 0.05) and 6.9% (P greater than 0.05) on the step ergometer after treadmill training. The small increases may be attributed to the specificity of the testing protocols used to elicit VO2max. Significant (P less than 0.01) increases in VO2max were found for both modalities after step-ergometry training (treadmill = 11.8%; step ergometer = 23.2%). These increases resulted in equal post-test VO2max values (4.05 l min-1; 51 ml kg-1 min-1) on the step ergometer and treadmill. The significant increases in VO2max found for both modalities after step-ergometry training shows that (1) step ergometry is an effective training modality, and (2) its effects can be measured on the treadmill and therefore it is not task-specific training.     

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.     

Dissociation of changes in VO2 max, muscle QO2, and performance with training in rats

Before the start and after 4, 8, and 12 wk of a treadmill training program male rats were randomly selected and tested for running performance, maximum O2 consumption (VO2 max), running economy (VO2 submax), and skeletal muscle oxidative capacity (QO2). Data were compared with values from untrained weight-matched control rats. Maximum running time to exhaustion increased significantly (P less than 0.01) by 4 wk and again at 12 wk (P less than 0.01). Submaximal running endurance increased by 120 (4 wk), 320 (8 wk), and 372% (12 wk) (P less than 0.01). VO2 max was increased only at 12 wk (86.0 +/- 2.7 vs. 75.5 +/- 1.9 ml O2.kg-1.min-1); VO2 submax was decreased at 4 and 8 wk but not at 12 wk. Soleus QO2 was unchanged after 4 wk of training and increased by 50% at 8 wk and by 77% at 12 wk. This study is the first to show a dissociation in both the time course and the magnitude of longitudinal changes in VO2 max, VO2 submax, QO2, and maximal and submaximal running performance. We conclude that factors other than those measured explain the improvement in running performance that resulted from endurance training in these rats.     

Limb skeletal muscle adaptation in athletes after training at altitude

Morphological and biochemical characteristics of biopsies obtained from gastrocnemius (GAS) and triceps brachii muscle (TRI), as well as maximal O2 uptake (VO2 max) and O2 deficit, were determined in 10 well-trained cross-country skiers before and after a 2-wk stay (2,100 m above sea level) and training (2,700 m above sea level) at altitude. On return to sea level, VO2 max was the same as the prealtitude value, whereas an increase in O2 deficit (29%) and in short-term running performance (17%) was observed (P less than 0.05). GAS showed maintained capillary supply but a 10% decrease in mitochondrial enzyme activities (P less than 0.05), whereas an increase in capillary supply (P less than 0.05) but unchanged mitochondrial enzyme activities were observed in TRI. Buffer capacity was increased by 6% in both GAS and TRI (P less than 0.05). A positive correlation was found between the relative increase in buffer capacity of GAS and short-term running time (P less than 0.05). Thus the present study indicates no effect of 2 wk of altitude training on VO2 max but provides evidence to suggest an improvement in short-term exercise performance, which may be the result of an increase in muscle buffer capacity.     

Physiological and performance changes from the addition of a sprint interval program to wrestling training

Increasing the level of physical fitness for competition is the primary goal of any conditioning program for wrestlers. Wrestlers often need to peak for competitions several times over an annual training cycle. Additionally, the scheduling of these competitions does not always match an ideal periodization plan and may require a modified training program to achieve a high level of competitive fitness in a short-time frame. The purpose of this study was to examine the effects of 4 weeks of sprint-interval training (SIT) program, on selected aerobic and anaerobic performance indices, and hormonal and hematological adaptations, when added to the traditional Iranian training of wrestlers in their preseason phase. Fifteen trained wrestlers were assigned to either an experimental (EXP) or a control (CON) group. Both groups followed a traditional preparation phase consisting of learning and drilling technique, live wrestling and weight training for 4 weeks. In addition, the EXP group performed a running-based SIT protocol. The SIT consisted of 6 35-m sprints at maximum effort with a 10-second recovery between each sprint. The SIT protocol was performed in 2 sessions per week, for the 4 weeks of the study. Before and after the 4-week training program, pre and posttesting was performed on each subject on the following: a graded exercise test (GXT) to determine VO(2)max, the velocity associated with V(2)max (νVO(2)max), maximal ventilation, and peak oxygen pulse; a time to exhaustion test (T(max)) at their νVO(2)max; and 4 successive Wingate tests with a 4-minute recovery between each trial for the determination of peak and mean power output (PPO, MPO). Resting blood samples were also collected at the beginning of each pre and posttesting period, before and after the 4-week training program. The EXP group showed significant improvements in VO(2)max (+5.4%), peak oxygen pulse (+7.7%) and T(max) (+32.2%) compared with pretesting. The EXP group produced significant increases in PPO and MPO during the Wingate testing compared with pretesting (p < 0.05). After the 4-week training program, total testosterone and the total testosterone/cortisol ratio increased significantly in the EXP group, whereas cortisol tended to decrease (p = 0.06). The current findings indicate that the addition of an SIT program with short recovery can improve both aerobic and anaerobic performances in trained wrestlers during the preseason phase. The hormonal changes seen suggest training-induced anabolic adaptations.     

The effect of one-legged sprint training on intramuscular pH and nonbicarbonate buffering capacity

To determine the effect of one-legged sprint training on muscle pH and nonbicarbonate buffering capacity (BC), 9 subjects completed 15 to 20 intervals at 90 RPM, 4 days a week for 7 weeks on a bicycle ergometer adapted for one-legged pedaling. Needle biopsies from the vastus lateralis and blood samples from an antecubital vein were taken at rest and twice during recovery (1 and 4 minutes) from a 60 s one-legged maximal power test on a cycle ergometer. pH one minute after exercise in both the trained and untrained legs following the training period was not different but both were higher than before training. BC increased from 49.9 to 57.8 mumol HCl x g-1 x pH-1 after training (p less than 0.05). Blood lactate levels after exercise were significantly higher for the trained leg when compared to the untrained leg after spring training. Peak and average power output on the 60 s power test increased significantly after training. One-legged aerobic power (VO2max) was significantly increased in the untrained and trained legs. Two-legged VO2max also improved significantly after training. These data suggest that nonbicarbonate buffering capacity and power output can be enhanced with one-legged sprint training. Also, small but significant improvements in VO2max were also observed.     

Endurance training in older men and women II. Blood lactate response to submaximal exercise

Seven men and four women (age 63 +/- 2 yr, mean +/- SD, range 61-67 yr) participated in a 12-mo endurance training program to determine the effects of low-intensity (LI) and high-intensity (HI) training on the blood lactate response to submaximal exercise in older individuals. Maximal oxygen uptake (VO2max), blood lactate, O2 uptake (VO2), heart rate (HR), ventilation (VE), and respiratory exchange ratio (R) during three submaximal exercise bouts (65-90% VO2max) were determined before training, after 6 mo of LI training, and after an additional 6 mo of HI training. VO2max (ml X kg-1 X min-1) was increased 12% after LI training (P less than 0.05), while HI training induced a further increase of 18% (P less than 0.01). Lactate, HR, VE, and R were significantly lower (P less than 0.05) at the same absolute work rates after LI training, while HI training induced further but smaller reductions in these parameters (P greater than 0.05). In general, at the same relative work rates (ie., % of VO2max) after training, lactate was lower or unchanged, HR and R were unchanged, and VO2 and VE were higher. These findings indicate that LI training in older individuals results in adaptations in the response to submaximal exercise that are similar to those observed in younger populations and that additional higher intensity training results in further but less-marked changes.     

Metabolic and cardiovascular adjustment to arm training

Maximal and submaximal metabolic and cardiovascular measures and work capacity were studied in control (n = 7) and experimental (n = 9) subjects (S's) during arm work prior to and following 10 wk of interval arm training. These measures were oxygen uptake (VO2), minute ventilation (VE), heart rate (HR), respiratory exchange ratio (R), cardiac output (Q), stroke volume (SV), and arteriovenous oxygen difference ((a--v)O2 diff). In addition, maximal oxygen uptake (VO2max) was measured in both groups during treadmill running. Experimental S's showed significant increases (P less than 0.01) in peak VO2 (438 ml.min-1), max VE (17.7 l.min-1), max (a--v)O2 diff (20.8 ml.l-1), and work time (9.2 min) during arm ergometry, while maximum values of Q, SV, HR, and R remained unchanged. In addition, submaximal heart rates were significantly lower during arm ergometry after training. VO2max during treadmill running remained essentially unchanged. No changes in metabolic and physiological measures were noted for the controls after the 10-wk training period. The results support the concept of training specificity for VO2max, and indicate that the improvement in peak VO2 in arm ergometry reflects enhanced oxygen utilization due to an expanded (a--v)O2 diff.     

Do hockey players need aerobic fitness? Relation between VO2max and fatigue during high-intensity intermittent ice skating

The primary objective of this study was to assess the relationship between aerobic capacity, as measured by the VO(2)max test, and recovery from high-intensity intermittent exercise. Eleven female collegiate hockey players agreed to participate. Subjects skated 5 1-lap intervals around the hockey rink at maximal intensity with a 30-second recovery period between skates. The VO(2)max test was performed on a motor-driven treadmill after a modified Bruce protocol. A fatigue index was calculated by measuring the total increase in skate time from trial 1 to trial 5. This fatigue index was then correlated to VO(2)max. This correlation coefficient (-0.422) was not significant (p > 0.05) and indicated that only 17.8% of the variance in VO(2)max could be explained by the fatigue index. It was concluded that ability to recover from high-intensity intermittent exercise is not related to aerobic capacity. Coaches and trainers probably do not need to include aerobic training in their practices, because the high-intensity interval training commonly seen in hockey training also improves aerobic capacity, as reflected in the high VO(2)max values of these subjects.     

Endurance training in humans: aerobic capacity and structure of skeletal muscle

The adaptation of muscle structure, power output, and mass-specific rate of maximal O2 consumption (VO2max/Mb) with endurance training on bicycle ergometers was studied for five male and five female subjects. Biopsies of vastus lateralis muscle and VO2max determinations were made at the start and end of 6 wk of training. The power output maintained on the ergometer daily for 30 min was adjusted to achieve a heart rate exceeding 85% of the maximum for two-thirds of the training session. It is proposed that the observed preferential proliferation of subsarcolemmal vs. interfibrillar mitochondria and the increase in intracellular lipid deposits are two possible mechanisms by which muscle cells adapt to an increased use of fat as a fuel. The relative increase of VO2max/Mb (14%) with training was found to be smaller by more than twofold than the relative increase in maximal maintained power (33%) and the relative change in the volume density of total mitochondria (+40%). However, the calculated VO2 required at an efficiency of 0.25 to produce the observed mass-specific increase in maximal maintained power matched the actual increase in VO2max/Mb (8.0 and 6.5 ml O2 X min-1 X kg-1, respectively). These results indicate that despite disparate relative changes the absolute change in aerobic capacity at the local level (maintained power) can account for the increase in aerobic capacity observed at the general level (VO2max).     

Uniqueness of interval and continuous training at the same maintained exercise intensity.

The present study sought to evaluate the inconsistencies previously observed regarding the predominance of continuous or interval training for improving fitness. The experimental design initially equated and subsequently maintained the same relative exercise intensity by both groups throughout the program. Twelve subjects were equally divided into continuous (CT, exercise at 50% maximal work) or interval (IT, 30 s work, 30 s rest at 100% maximal work) training groups that cycled 30 min day-1, 3 days.week-1, for 8 weeks. Following training, aerobic power (VO2max), exercising work rates, and peak power output were all higher (9-16%) after IT than after CT (5-7%). Vastus lateralis muscle citrate synthase activity increased 25% after CT but not after IT. A consistent increase in adenylate kinase activity (25%) was observed only after IT. During continuous cycling testing the CT group had reduced blood lactate (lab) levels and respiratory quotient at both the same absolute and relative (70% VO2max) work rates after training, while the IT group displayed similar changes only at the same absolute work rates. By contrast, both groups responded similarly during intermittent cycling testing with lower lab concentrations seen only at absolute work rates. These results show that, of the two types of training programs currently employed, IT produces higher increases in VO2max and in maximal exercise capacity. Nevertheless, CT is more effective at increasing muscle oxidative capacity and delaying the accumulation of lab during continuous exercise.     

Early adaptations in gas exchange, cardiac function and haematology to prolonged exercise training in man

In order to determine the effect of short-term training on central adaptations, gas exchange and cardiac function were measured during a prolonged submaximal exercise challenge prior to and following 10-12 consecutive days of exercise. In addition, vascular volumes and selected haematological properties were also examined. The subjects, healthy males between the ages of 19 and 30 years of age, cycled for 2 h per day at approximately 59% of pre-training peak oxygen consumption (VO2) i.e., maximal oxygen consumption (VO2max). Following the training, VO2max (l.min-1) increased (P less than 0.05) by 4.3% (3.94, 0.11 vs 4.11, 0.11; mean, SE) whereas maximal exercise ventilation (VE,max) and maximal heart rate (fc,max) were unchanged. During submaximal exercise, VO2 was unaltered by the training whereas carbon dioxide production (VE) and respiratory exchange ratio were all reduced (P less than 0.05). The altered activity pattern failed to elicit adaptations in either submaximal exercise cardiac output or arteriovenous O2 difference. fc was reduced (P less than 0.05). Plasma volume (PV) as measured by 125I human serum albumin increased by 365 ml or 11.8%, while red cell volume (RCV) as measured by 51chromium-labelled red blood cells (RBC) was unaltered. The increase in PV was accompanied by reductions (P less than 0.05) in haematocrit, haemoglobin concentration (g.100 ml-1), and RBCs (10(6) mm-3). Collectively these changes suggest only minimal adaptations in maximal oxygen transport during the early period of prolonged exercise training. However, as evidenced by the changes during submaximal exercise, both the ventilatory and the cardiodynamic response were altered.(ABSTRACT TRUNCATED AT 250 WORDS)     

Increased epinephrine response and inaccurate glucoregulation in exercising athletes

Epinephrine responses to insulin-induced hypoglycemia have indicated that athletes have a higher adrenal medullary secretory capacity than untrained subjects. This view was tested by an exercise protocol aiming at identical stimulation of the adrenal medulla in the two groups. Eight athletes (T) and eight controls (C) ran 7 min at 60% maximal O2 consumption (VO2max), 3 min at 100% VO2max, and 2 min at 110% VO2max. Plasma epinephrine both at rest and at identical relative work loads [110% VO2max: 8.73 +/- 1.51 (T) vs. 3.60 +/- 1.09 mmol X l-1 (C)] was higher [P less than 0.05) in T than in C. Norepinephrine, as well as heart rate, increased identically in the two groups, indicating identical sympathetic nervous activity. Lactate and glycerol were higher in T than in C after running. Glucose production peaked immediately after exercise and was higher in T than in C. Glucose disappearance increased less than glucose production and was identical in T and C. Accordingly plasma glucose increased, more in T than in C (P less than 0.01). In T glucose levels approached the renal threshold greater than 20 min postexercise. Glucose clearance increased less in T than in C during exercise and decreased postexercise to or below (T, P less than 0.05) basal levels, despite increased insulin levels. Long-term endurance training increases responsiveness of the adrenal medulla to exercise, indicating increased secretory capacity. During maximal exercise this may contribute to higher glucose production, lower clearance, more inaccurate glucoregulation, and higher lypolysis in T compared with C.