The effects of dietary manipulation on blood acid-base status and the performance of high intensity exercise

The effect of a pattern of exercise and dietary modification, which is normally used to alter muscle glycogen content, upon the acid-base status of the blood and the ability to perform high intensity exercise was studied. Eleven healthy male subjects cycled to exhaustion on an electrically braked cycle ergometer at a workload equivalent to 100% of their maximal oxygen uptake (VO2max) on three separate occasions. The first exercise test took place after a normal diet (46.2 +/- 6.7% carbohydrate (CHO)), and was followed by prolonged exercise to exhaustion to deplete muscle glycogen stores. The second test was performed after three days of a low carbohydrate diet (10.1 +/- 6.8% CHO) and subsequently after three days of a high CHO diet (65.5 +/- 9.8% CHO) the final test took place. Acid-base status and selected metabolites were measured on arterialised venous blood at rest prior to exercise and during the post-exercise period. Exercise time to exhaustion was longer after the normal (p less than 0.05) and high (p less than 0.05). CHO dietary phases compared with the low CHO phase. Resting pre-exercise pH was higher after the high CHO diet (p less than 0.05) compared with the low CHO diet. Pre-exercise bicarbonate, PCO2 and base excess measurements were higher after the high CHO treatment compared with both the normal (p less than 0.01, p less than 0.05, p less than 0.01 respectively) and low CHO phases (p less than 0.001, p less than 0.01, p less than 0.001 respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of high intensity training upon respiratory gas exchanges during fixed term maximal incremental exercise in man

The response of respiratory gas exchanges to a 6 week high intensity training program was examined in 5 healthy males during fixed term maximal incremental treadmill exercise. Training was performed 3 d.wk-1 and consisted of a progressive series of repeated 15 sec and 30 sec maximal runs, and weight training exercises for the leg extensor muscles. Respiratory gases during the tests were continuously monitored using an on-line system. Muscle biopsy samples were obtained from the m. vastus lateralis before and after training for histochemical determination of fibre distribution based on myosin ATP-ase activity, and fibre cross-sectional area based on NADH-Tetrazolium Reductase activity. Training significantly increased the proportion of type IIa fibres (+5.9 +/- 2.0%, p less than 0.001) and decreased type I fibres (-6.3 +/- 2.0%, p less than 0.001), the distribution of type IIb fibres remained unchanged (+0.4 +/- 0.9%). Muscle cross-sectional area also showed a significant increase after training in type I (+318 +/- 215 microns 2, p less than 0.05), IIa (+652 +/- 207 microns 2, p less than 0.001) and IIb (+773 +/- 196 microns 2, p less than 0.001) fibres. During fixed term maximal incremental exercise the mean carbon dioxide output (VCO2) and mean respiratory exchange ratio (R = VCO2/VO2) were significantly increased (p less than 0.01) after training. The R-time relationship was at all times shifted to the left after training, being significantly (p less than 0.01) so over the final five min of exercise. No changes in mean exercise oxygen uptake (VO2), maximum oxygen uptake (VO2max) and maximum heart rate (FHRmax) were observed between tests.(ABSTRACT TRUNCATED AT 250 WORDS)     

Diet-induced metabolic acidosis and the performance of high intensity exercise in man

The influence of four isolated periods of dietary manipulation upon high intensity exercise capacity was investigated in six healthy male subjects. Subjects consumed their 'normal' (N) diet (45 +/- 2% carbohydrate (CHO), 41 +/- 3% fat, 14 +/- 3% protein) for four days after which they exercised to voluntary exhaustion at a workload equivalent to 100% VO2max. Three further four-day periods of dietary manipulation took place; these were assigned in a randomised manner and each was followed by a high intensity exercise test. The dietary treatments were: a low CHO (3 +/- 1%), high fat (71 +/- 5%), high protein (26 +/- 3%) diet (HFHP); a high CHO (73 +/- 2%), low fat (12 +/- 2%), normal protein (15 +/- 1%) diet (HCLF); and a normal CHO (47 +/- 3%), low fat (27 +/- 2%), high protein (26 +/- 2%) diet (LFHP). Acid-base status and blood lactate concentration were measured on arterialised-venous blood at rest prior to dietary manipulation on each day of the different diets, immediately prior to exercise and at 2, 4, 6, 10 and 15 min post-exercise. Other metabolite concentrations were measured in the blood samples obtained prior to dietary manipulation and immediately prior to exercise. Exercise time to exhaustion after the HFHP diet (179 +/- 63 s) was shorter when compared with the N (210 +/- 65 s; p less than 0.01) and HCLF (219 +/- 69 s; p less than 0.05) diets.(ABSTRACT TRUNCATED AT 250 WORDS)     

The influence of dietary manipulation on plasma ammonia accumulation during incremental exercise in man

The influence of a pattern of exercise and dietary manipulation, intended to alter carbohydrate (CHO) availability, on pre-exercise acid-base status and plasma ammonia and blood lactate accumulation during incremental exercise was investigated. On three separate occasions, five healthy male subjects underwent a pre-determined incremental exercise test (IET) on an electrically braked cycle ergometer. Each IET involved subjects exercising for 5 min at 30%, 50%, 70% and 95% of their maximal oxygen uptake (VO2max) and workloads were separated by 5 min rest. The first IET took place after 3 days of normal dietary CHO intake. The second and third tests followed 3 days of low or high CHO intake, which was preceded by prolonged exercise to exhaustion in an attempt to deplete muscle and liver glycogen stores. Acid-base status and plasma ammonia and blood lactate levels were measured on arterialised venous blood samples immediately prior to and during the final 15 s of exercise at each workload and for 40 min following the completion of each IET. Three days of low CHO intake resulted in the development of a mild metabolic acidosis in all subjects. Plasma ammonia (NH3) accumulation on the low-CHO diet tended to be greater than normal at each exercise workload. Values returned towards resting levels during each recovery period. After the normal and high-CHO diets plasma NH3 levels did not markedly increase above resting values until after exercise at 95% VO2max. Plasma NH3 levels after the high-CHO diet were similar to those after the normal CHO diet.(ABSTRACT TRUNCATED AT 250 WORDS)     

Kinetics of CO uptake and diffusing capacity in transition from rest to steady-state exercise.

In the transition from rest to steady-state exercise, O2 uptake from the lungs (VO2) depends on the product of pulmonary blood flow and pulmonary arteriovenous O2 content difference. The kinetics of pulmonary blood flow are believed to be somewhat faster than changes in pulmonary arteriovenous O2 content difference. We hypothesized that during CO breathing, the kinetics of CO uptake (VCO) and diffusing capacity for CO (DLCO) should be faster than VO2 because changes in pulmonary arteriovenous CO content difference should be relatively small. Six subjects went abruptly from rest to constant exercise (inspired CO fraction = 0.0005) at 40, 60, and 80% of their peak VO2, measured with an incremental test (VO2peak). At all exercise levels, DLCO and VCO rose faster than VO2 (P less than 0.001), and DLCO rose faster than VCO (P less than 0.001). For example, at 40% VO2peak, the time constant (tau) for DLCO in phase 2 was 19 +/- 5 (SD), 24 +/- 5 s for VCO, and 33 +/- 5 s for VO2. Both VCO and DLCO increased with exercise intensity but to a lesser degree than VO2 at all exercise intensities (P less than 0.001). In addition, no significant rise in DLCO was observed between 60 and 80% VO2peak. We conclude that the kinetics of VCO and DLCO are faster than VO2, suggesting that VCO and DLCO kinetics reflect, to a greater extent, changes in pulmonary blood flow and thus recruitment of alveolar-capillary surface area. However, other factors, such as the time course of ventilation, may also be involved.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of alterations in dietary carbohydrate intake on the performance of high-intensity exercise in trained individuals

This study was designed to examine the effects of alterations in dietary carbohydrate (CHO) intake on the performance of high-intensity exercise lasting approximately 10 min (EXP 1) and 30 min (EXP 2). Trained subjects exercised to exhaustion on four occasions on a cycle ergometer at 90% of maximal oxygen consumption (VO2max; EXP 1, n = 5) and 80% of VO2max (EXP 2, n = 7). The first two tests were familiarisation trials and were carried out following the subjects' normal diet. Normal training was continued but standardised during the periods of dietary control. The subsequent two tests were performed 2 weeks apart after 7 days of dietary manipulation. The two diets were a 70% and a 40% CHO diet, isoenergetic with each subject's normal diet and administered in a randomised order. At both exercise intensities, time to exhaustion following the high CHO and low CHO diets was not different [mean (SD) EXP 1: 11.56 (3.78) min and 8.95 (2.35) min, P = 0.22; EXP 2: 26.9 (7.4) min and 26.5 (6.5) min, P = 0.90]. No differences in resting blood metabolite concentrations were found apart from a lower beta-hydroxybutyrate (beta-HB) level following the high CHO diet in EXP 2. Blood lactate was higher after exercise at 90% of VO2max following the high CHO diet. Blood lactate was higher, and beta-HB lower during exercise at 80% of VO2max following the high CHO diet. No differences were found in the other blood metabolites tested. The respiratory exchange ratio after 15 min of exercise at 80% of VO2max was higher on the high CHO diet. No differences in oxygen uptake, heart rate (EXP 2) or ratings of perceived exertion (both experiments) were found between conditions. These results indicate that moderate changes in diet composition during training do not affect the performance of high-intensity exercise in trained individuals when the total energy intake is moderately high.     

The effect of dietary carbohydrate intake on the metabolic response to prolonged walking on consecutive days

Six healthy subjects walked 37 km per day for four consecutive days on two occasions one month apart; on one walk, subjects consumed a high carbohydrate (CHO) diet (85 +/- 1% CHO, Mean +/- SE) and on the other walk an isocaloric low CHO diet (2 +/- 0% CHO) was consumed. Subjects were fasted each day until after the completion of the walk. Blood samples were obtained at rest prior to exercise and after completion of each of three laps of 12.3 km. Exercise intensity corresponded to approximately 17% of VO2max. The first day of each walk demonstrated that the pattern of substrate mobilisation in response to this type of exercise is highly reproducible, there being no difference in any of the parameters measured between the two walks. Circulating glucose, lactate, insulin and triglyceride levels remained essentially unchanged; alanine fell progressively and glycerol, free fatty acid (FFA) and 3-hydroxybutyrate (BHB) rose progressively. After the first day there was a general tendency for the blood glucose concentration to decline as exercise progressed; by the end of the walk on Day 2, blood glucose was lower on the low CHO diet than on the high CHO diet. On Day 4 plasma insulin was higher (p less than 0.05) on the high CHO diet than on the low CHO diet and declined progressively on both diets. Blood lactate and alanine concentrations were generally higher at rest on the high CHO diet, but fell so that no differences existed by the end of exercise.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of dietary manipulations on blood glucose and hormonal responses following supramaximal exercise

The effects of supramaximal exercise on blood glucose, insulin, and catecholamine responses were examined in 7 healthy male physical education students (mean +/- SD: age = 21 +/- 1.2 years; VO2max = 54 +/- 6 ml X kg-1 X min-1) in response to the following three dietary conditions: a normal mixed diet (N); a 24-h low carbohydrate (CHO) diet intended to reduce liver glycogen content (D1); and a 24-h low CHO diet preceded by a leg muscle CHO overloading protocol intended to reduce hepatic glycogen content with increased muscle glycogen store (D2). Exercise was performed on a bicycle ergometer at an exercise intensity of 130% VO2max for 90 s. Irrespective of the dietary manipulation, supramaximal exercise was associated with a similar significant (p less than 0.01) increase in the exercise and recovery plasma glucose values. The increase in blood glucose levels was accompanied by a similar increase in insulin concentrations in all three groups despite lower resting insulin levels in conditions D1 and D2. Lactate concentrations were higher during the early phase of the recovery period in the D2 as compared to the N condition. At cessation of exercise, epinephrine and norepinephrine were greatly elevated in all three conditions. These results indicate that the increase in plasma glucose and insulin associated with very high intensity exercise, persists in spite of dietary manipulations intended to reduce liver glycogen content or increase muscle glycogen store.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of diet on muscle pH and metabolism during high intensity exercise

Five healthy male subjects exercised for 3 min at a workload equivalent to 100% VO2max on two separate occasions. Each exercise test was performed on an electrically braked cycle ergometer after a four-day period of dietary manipulation. During each of these periods subjects consumed either a low carbohydrate (3 +/- 0%, mean +/- SD), high fat (73 +/- 2%), high protein (24 +/- 3%) diet (FP) or a high carbohydrate (82 +/- 1%), low fat (8 +/- 1%) low protein (10 +/- 1%) diet (CHO). The diets were isoenergetic and were assigned in a randomised manner. Muscle biopsy samples (Vastus lateralis) were taken at rest prior to dietary manipulation, immediately prior to exercise and immediately post-exercise for measurement of pH, glycogen, glucose 6-phosphate, fructose 1,6-diphosphate, triose phosphates, lactate and glutamine content. Blood acid-base status and selected metabolites were measured in arterialised venous samples at rest prior to dietary manipulation, immediately prior to exercise and at pre-determined intervals during the post-exercise period. There was no differences between the two treatments in blood acid-base status at rest prior to dietary manipulation; immediately prior to exercise plasma pH (p less than 0.01), blood PCO2 (p less than 0.01), plasma bicarbonate (p less than 0.001) and blood base-excess (p less than 0.001) values were all lower on the FP treatment. There were no major differences in blood acid-base variables between the two diets during the post-exercise period.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of inspiratory threshold loading on ventilatory kinetics during constant-load exercise

Humoral factors play an important role in the control of exercise hyperpnea. The role of neuromechanical ventilatory factors, however, is still being investigated. We tested the hypothesis that the afferents of the thoracopulmonary system, and consequently of the neuromechanical ventilatory loop, have an influence on the kinetics of oxygen consumption (VO2), carbon dioxide output (VCO2), and ventilation (VE) during moderate intensity exercise. We did this by comparing the ventilatory time constants (tau) of exercise with and without an inspiratory load. Fourteen healthy, trained men (age 22.6 +/- 3.2 yr) performed a continuous incremental cycle exercise test to determine maximal oxygen uptake (VO2max = 55.2 +/- 5.8 ml x min(-1) x kg(-1)). On another day, after unloaded warm-up they performed randomized constant-load tests at 40% of their VO2max for 8 min, one with and the other without an inspiratory threshold load of 15 cmH2O. Ventilatory variables were obtained breath by breath. Phase 2 ventilatory kinetics (VO2, VCO2, and VE) could be described in all cases by a monoexponential function. The bootstrap method revealed small coefficients of variation for the model parameters, indicating an accurate determination for all parameters. Paired Student's t-tests showed that the addition of the inspiratory resistance significantly increased the tau during phase 2 of VO2 (43.1 +/- 8.6 vs. 60.9 +/- 14.1 s; P < 0.001), VCO2 (60.3 +/- 17.6 vs. 84.5 +/- 18.1 s; P < 0.001) and VE (59.4 +/- 16.1 vs. 85.9 +/- 17.1 s; P < 0.001). The average rise in tau was 41.3% for VO2, 40.1% for VCO2, and 44.6% for VE. The tau changes indicated that neuromechanical ventilatory factors play a role in the ventilatory response to moderate exercise.     

Effect of glucose polymer diet supplement on responses to prolonged successive swimming, cycling and running

Fifteen male endurance athletes were studied to determine the effect of a glucose polymer (GP) diet supplement on physiological and perceptual responses to successive swimming, cycling and running exercise. Thirty min of swimming, cycling and running at 70% VO2max, followed by a run to exhaustion at 90% VO2max was performed after one week of training under two dietary conditions: 1) GP (230 g of GP consumed daily) and 2) placebo (P, saccharin-sweetened supplement consumed daily). During GP, daily carbohydrate (CHO) intake was higher (p less than 0.05) by 173 g or 14% of energy intake than during P, but total energy intake was not significantly different. During 90 min of exercise, CHO utilization and blood glucose were significantly higher under GP than P by an average of 20.2% and 14.5%, respectively, but heart rate, ventilation, oxygen uptake, ratings of perceived exertion, and plasma lactate were not different. Run time to exhaustion at 90% VO2max was significantly longer by 1.2 min (23%) under GP. The results suggest that a GP diet supplement may be of value during endurance exercise by increasing the availability of CHO.     

Maximal aerobic capacity for repetitive lifting: comparison with three standard exercise testing modes

A multi-stage, repetitive lifting maximal oxygen uptake (VO2max) test was developed to be used as an occupational research tool which would parallel standard ergometric VO2max testing procedures. The repetitive lifting VO2max test was administered to 18 men using an automatic repetitive lifting device. An intraclass reliability coefficient of 0.91 was obtained with data from repeated tests on seven subjects. Repetitive lifting VO2max test responses were compared to those for treadmill, cycle ergometer and arm crank ergometer. The mean +/- SD repetitive lifting VO2max of 3.20 +/- 0.42 l.min-1 was significantly (p less than 0.01) less than treadmill VO2max (delta = 0.92 l.min-1) and cycle ergometer VO2max (delta = 0.43 l.min-1) and significantly greater than arm crank ergometer VO2max (delta = 0.63 l.min-1). The correlation between repetitive lifting oxygen uptake and power output was r = 0.65. VO2max correlated highly among exercise modes, but maximum power output did not. The efficiency of repetitive lifting exercise was significantly greater than that for arm cranking and less than that for leg cycling. The repetitive lifting VO2max test has an important advantage over treadmill or cycle ergometer tests in the determination of relative repetitive lifting intensities. The individual curves of VO2 vs. power output established during the multi-stage lifting VO2max test can be used to accurately select work loads required to elicit given percentages of maximal oxygen uptake.     

Rectal and rectal vs. esophageal temperatures in paraplegic men during prolonged exercise

This study investigated the rectal (Tre), esophageal (Tes), and skin (Tsk) temperature changes in a group of trained traumatic paraplegic men pushing their own wheelchairs on a motor-driven treadmill for a prolonged period in a neutral environment. There were two experiments. The first experiment (Tre and Tsk) involved a homogeneous group (T10-T12/L3) of highly trained paraplegic men [maximum O2 uptake (VO2max) 47.5 +/- 1.8 ml.kg-1.min-1] exercising for 80 min at 60-65% VO2max.Tre and Tsk (head, arm, thigh, and calf) and heart rate (HR) were recorded throughout. O2 uptake (VO2), minute ventilation (VE), CO2 production (VCO2), and heart rate (HR) were recorded at four intervals. During experiment 1 significant changes in HR and insignificant changes in VCO2, VE, and VO2 occurred throughout prolonged exercise. Tre increased significantly from 37.1 +/- 0.1 degrees C (rest) to 37.8 +/- 0.1 degrees C after 80 min of exercise. There were only significant changes in arm Tsk. Experiment 2 involved a nonhomogeneous group (T5-T10/T11) of active paraplegics (VO2max 39.9 +/- 4.3 ml.kg-1.min-1) exercising at 60-65% VO2max for up to 45 min on the treadmill while Tre and Tes were simultaneously recorded. Tes rose significantly faster than Tre during exercise (dT/dt 20 min: Tes 0.050 +/- 0.003 degrees C/min and Tre 0.019 +/- 0.005 degrees C/min), and Tes declined significantly faster than Tre at the end of exercise. Tes was significantly higher than Tre at the end of exercise. Our results suggest that during wheelchair propulsion by paraplegics, Tes may be a better estimate of core temperature than Tre.     

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.     

Enhanced protein breakdown after eccentric exercise in young and older men

The effects of eccentric exercise on whole body protein metabolism were compared in five young untrained [age 24 +/- 1 yr, maximal O2 uptake (VO2max) = 49 +/- 6 ml.kg-1.min-1] and five older untrained men (age 61 +/- 1 yr, VO2max = 34 +/- 2 ml.kg-1.min-1). They performed 45 min of eccentric exercise on a cycle ergometer at a power output equivalent to 80% VO2max (182 +/- 18 W). Beginning 5 days before exercise and continuing for at least 10 days after exercise, they consumed a eucaloric diet providing 1.5 g.kg-1.day-1 of protein. Leucine metabolism in the fed state was measured before, immediately after, and 10 days after exercise, with intravenous L-[1-13C]leucine as a tracer (0.115 mumol.kg-1.min-1). Leucine flux increased 9% immediately after exercise (P less than 0.011) and remained elevated 10 days later, with no effect of age. Leucine oxidation increased 19% immediately after exercise and remained 15% above baseline 10 days after exercise (P less than 0.0001), with no effect of age. In the young men, urinary excretion of 3-methylhistidine per gram of creatinine did not increase until 10 days postexercise (P less than 0.05), but in the older men, it increased 5 days after exercise and remained high through 10 days postexercise (P less than 0.05), averaging 37% higher than in the young men. These data suggest that eccentric exercise produces a similar increase in whole body protein breakdown in older and young men, but myofibrillar proteolysis may contribute more to whole body protein breakdown in the older group.     

The effects of a glycogen loading regimen on acid-base status and blood lactate concentration before and after a fixed period of high intensity exercise in man

Six healthy male subjects exercised after an overnight fast for a fixed 3 min period at a workload equivalent to 100% of their maximal oxygen uptake ( ) on 3 separate occasions. The first test took place after subjects had consumed a mixed diet (43±3% carbohydrate (CHO), 41±5% fat and 16±3% protein) for 3 days, and was followed 2 h later by prolonged cycling to exhaustion at 77±3% to deplete muscle glycogen stores. Following this, subjects consumed a low CHO diet (4±1% CHO, 63±5% fat and 33±6% protein) for the remainder of the day and for the subsequent 2 days; on the morning of the next day a second high intensity test took place. Finally subjects followed a 3 day high CHO diet (73±7% CHO, 17±6% fat and 10±1% protein) before their last test. Acid-base status and selected metabolites were measured on arterialised-venous blood at rest prior to exercise and at intervals for 15 min following exercise. Prior to exercise, plasma pH and blood lactate concentration were higher (p<0.05) after the high CHO diet when compared with the low CHO diet. Pre-exercise plasma bicarbonate, blood PCO₂ and blood base excess were all higher after the high (p<0.001,p<0.01,p<0.01 respectively) and normal (p<0.05,p<0.05,p<0.05 respectively) CHO diets when compared with the low CHO diet. During the post-exercise period there were no differences in plasma pH or blood base excess between the three experimental situations; plasma bicarbonate was higher (p<0.05) at 2 min post-exercise after the high CHO diet when compared with the low CHO diet; blood PCO₂ was higher throughout the post-exercise period after the high CHO diet when compared with the low CHO diet and at 2 min post-exercise was higher after the normal CHO diet than after the low CHO diet (p<0.5). The post-exercise blood lactate concentration after the high CHO diet was at all times higher than the corresponding values recorded after the normal CHO diet and until 15 min post-exercise was significantly higher than the values recorded after the low CHO diet. The present experiment further substantiates the view that a pattern of dietary and exercise manipulation can significantly influence the acid-base status of the blood and by doing so may influence high intensity exercise performance.     

Metabolic and sarcoplasmic reticulum Ca2+ cycling responses in human muscle 4 days following prolonged exercise

This study investigated the effects of prolonged exercise on muscle sarcoplasmic reticulum (SR) Ca2+ cycling properties and the metabolic responses with and without a session of exercise designed to reduce muscle glycogen reserves while on a normal carbohydrate (CHO) diet. Eight untrained males (VO(2peak) = 3.81 +/- 0.12 L/min, mean +/- SE) performed a standardized cycle-to-fatigue at 55% VO(2peak) while on a normal CHO diet (Norm CHO) and 4 days following prolonged exercise while on a normal CHO diet (Ex+Norm CHO). Compared to rest, exercise in Norm CHO to fatigue resulted in significant reductions (p < 0.05) in Ca2+ uptake (3.17 +/- 0.21 vs. 2.47 +/- 0.12 micromol.(g protein)-1.min-1), maximal Ca2+ ATPase activity (Vmax, 152 +/- 12 vs. 119 +/- 9 micromol.(g protein)-1.min-1) and both phase 1 (15.1 +/- 0.98 vs. 13.1 +/- 0.28 micromol.(g protein)-1.min-1) and phase 2 (6.56 +/- 0.33 vs. 4.91 +/- 0.28 micromol.(g protein)-1.min-1) Ca2+ release in vastus lateralis muscle. No differences were observed between Norm CHO and Ex-Norm CHO in the response of these properties to exercise. Compared with Norm CHO, Ex+Norm CHO resulted in higher (p < 0.05) resting Ca2+ uptake (3.17 +/- 0.21 vs. 3.49 +/- 0.24 micromol.(g protein).min-1 and higher ionophore ratio, defined as the ratio of Vmax measured with and without the Ca2+-ionophore A23187, (2.3 +/- 0.3 vs. 4.4 +/- 0.3 micromol.(g protein).min-1) at fatigue. No differences were observed between conditions in the concentration of muscle glycogen, the high-energy phosphates (ATP and PCr), or metabolites (Pi, Cr, and lactate). Ex+Norm CHO also failed to modify the exercise-induced changes in CHO and fat oxidation. We conclude that prolonged exercise to fatigue performed 4 days following glycogen-depleting exercise while on a normal CHO diet elevates resting Ca2+ uptake and prevents increases in SR membrane permeability to Ca2+ as measured by the ionophore ratio.     

Physical fitness of blind and sighted children

Twenty-seven children (age 7-17 years) with varying degrees of blindness but with no other known disorder were assessed for physical fitness. Twenty-seven randomly selected children with normal eyesight were also assessed. Maximum oxygen uptake (VO2max) was measured directly during a progressive exercise test on a treadmill. There was a significant and substantial reduction in VO2max in totally blind children (mean +/- standard deviation 35.0 +/- 7.5 ml X min-1 X kg-1) compared with normal children (45.9 +/- 6.6 ml X min-1 X kg-1). Partially sighted children had a significant but smaller reduction in VO2max. Fitness assessed by a step-test was significantly reduced in the visually impaired children, and skin-fold thickness was also significantly greater in totally blind children. The level of habitual physical activity for each child, as assessed by a questionnaire, correlated with VO2max (r = 0.53, p less than 0.0001). Blind children were significantly less active than normal children, and the difference between mean VO2max for blind and normal children became non-significant when their different activity levels were taken into account. It is concluded that totally blind children are less fit than other children at least partly because of their lower level of habitual activity.     

Maximum O2 uptake, O2 debt and deficit, and muscle metabolites in Thoroughbred horses

This study determined maximal O2 uptake (VO2max), maximal O2 deficit, and O2 debt in the Thoroughbred racehorse exercising on an inclined treadmill. In eight horses the O2 uptake (VO2) vs. speed relationship was linear until 10 m/s and VO2max values ranged from 131 to 153 ml.kg-1.min-1. Six of these horses then exercised at 120% of their VO2max until exhaustion. VO2, CO2 production (VCO2), and plasma lactate (La) were measured before and during exercise and through 60 min of recovery. Muscle biopsies were collected before and at 0.25, 0.5, 1, 1.5, 2, 5, 10, 15, 20, 40, and 60 min after exercise. Muscle concentrations of adenosine 5'-triphosphate (ATP), phosphocreatine (PC), La, glucose 6-phosphate (G-6-P), and creatine were determined, and pH was measured. The O2 deficit was 128 +/- 32 (SD) ml/kg (64 +/- 13 liters). The O2 debt was 324 +/- 62 ml/kg (159 +/- 37 liters), approximately two to three times comparative values for human beings. Muscle [ATP] was unchanged, but [PC] was lower (P less than 0.01) than preexercise values at less than or equal to 10 min of recovery. [PC] and VO2 were negatively correlated during both the fast and slow phases of VO2 during recovery. Muscle [La] and [G-6-P] were elevated for 10 min postexercise. Mean muscle pH decreased from 7.05 (preexercise) to 6.75 at 1.5 min recovery, and the mean peak plasma La value was 34.5 mmol/l.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.