Saliva flow and composition in humans exposed to acute altitude hypoxia

Summary The effects of acute hypoxia (2 days at 4350 m) on whole saliva flow and composition were studied on 12 sea-level natives, at rest and following a maximal exercise. Exercise, performed in normoxia and hypoxia, did not induce variations in saliva flow rate, saliva potassium or α-amylase concentrations. In contrast, acute hypoxia did lead to an increase in mean saliva flow rate both at rest (0.63 ml·min⁻¹ to 0.93 ml·min⁻¹,P<0.01) and after exercise (0.56 ml·min⁻¹ to 1.06 ml·min⁻¹,P<0.05) and a decrease in mean saliva potassium concentration at rest (20.8 mmol·1⁻¹ to 14.7 mmol·1⁻¹,P<0.01) as well as after exercise (21.7 mmol·1⁻¹ to 16.5 mmol·1⁻¹,P<0.05). This effect might be the consequence of a hypoxia-induced stimulation of the parasympathetic nervous system.     

Substrate utilisation during exercise and shivering

It is generally assumed that exercise and shivering are analogous processes with regard to substrate utilisation and that, as a consequence, exercise can be used as a model for shivering. In the present study, substrate utilisation during exercise and shivering at the same oxygen consumption (V˙O₂) were compared. Following an overnight fast, eight male subjects undertook a 2-h immersion in cold water, designed to evoke three different intensities of shivering. At least 1 week later they undertook a 2-h period of bicycle ergometry during which the exercise intensity was varied to match the V˙O₂ recorded during shivering. During both activities hepatic glucose output (HGO), the rate of glucose utilisation (Rd), blood glucose, plasma insulin, free fatty acid (FFA) and beta-hydroxybutyrate (B-HBA) concentrations were measured. The V˙O₂ measured during the different levels of shivering averaged 0.49 l · min⁻¹ (level 1: low), 0.6 l · min⁻¹ (level 2: low-moderate), and 0.9 l · min⁻¹ (level 3: moderate), and corresponded closely to the levels measured during exercise. HGO and Rd were greater (P < 0.05) during exercise than during shivering at the same V˙O₂ (9.5% and 14.7%, respectively). The average (SD) HGO during level 3 exercise was 3.0 (0.91) mg · kg⁻¹ . min⁻¹ compared to 2.76 (1.0) mg · kg⁻¹ . min⁻¹ during shivering. The values for Rd were 3.06 (0.98) mg · kg⁻¹ · min⁻¹ during level 3 exercise and 2.68 (0.82) mg · kg⁻¹ · min⁻¹ during shivering. Blood glucose levels did not differ between conditions, averaging 5.4 (0.3) mmol . l⁻¹ over all levels of shivering and 5.2 (0.3) mmol · l⁻¹ during exercise. Plasma FFA and B-HBA were higher (P < 0.01) during shivering than during corresponding exercise (12.3% and 33.3%, respectively). FFA averaged 0.61 (0.2) mmol · l⁻¹ over all levels of shivering and 0.47 (0.16) mmol · l⁻¹ during exercise. The figures for B-HBA were 0.44 (0.13) mmol · l⁻¹ during all levels of shivering and 0.32 (0.1) mmol · l⁻¹ during exercise. Plasma insulin was higher (P < 0.05) during level 2 and 3 shivering compared to corresponding exercise; at these levels the average value for plasma insulin was 95.9 (21.9) pmol · l⁻¹ during shivering and 80.6 (16.1) pmol · l⁻¹ during exercise. On the basis of the present findings it is concluded that, with regard to substrate utilisation, shivering and exercise of up to 2 h duration should not be regarded as analogous processes. Accepted: 12 February 1997     

Blood metabolite and catecholamine responses to prolonged exercise following either acute plasma volume expansion or short-term training

 To determine the effect of acute plasma volume (PV) expansion on substrate utilization, blood metabolites and catecholamines to prolonged, moderate intensity cycle exercise, eight untrained men mean maximal oxygen uptake,O_2max 4.10 (SEM 0.32) l · min⁻¹ were infused (10 ml·kg⁻¹) with a 6% dextran (DEX) solution. These responses were also compared to those elicited using a short-term training (TR) protocol involving cycling for 90 to 120 min · day⁻¹ at 60% O_2max for 3 consecutive days. In general DEX, which resulted in a calculated expansion of PV by 23.9%, was without effect in modifying exercise oxygen uptake or the reduction in the respiratory exchange ratio (R) observed during prolonged exercise. In addition, the concentrations of blood glucose, glycerol, alanine and serum free fatty acids, although altered (P < 0.05) by exercise, were not altered by DEX. Blood lactate concentration was only higher (P < 0.05) at 30 min of exercise during DEX compared to the control. With the exception of blood lactate concentration, which was reduced (P < 0.05), TR did not change R or the concentrations of other blood metabolites. The concentrations of nonadrenaline and adrenaline, were depressed (P < 0.05) by DEX and TR at 60 and 90 min of exercise. These results would suggest that mechanisms as yet undefined can compensate for the estimated 10% reduction in arterial oxygen content mediated by acute PV expansion and enable prolonged exercise to be performed without adjustments in substrate selection and substrate mobilization. Accepted: 23 August 1996     

Effect of short-term endurance training on exercise capacity,haemodynamics and atrial natriuretic peptide secretion in heart transplant recipients

Exercise tolerance of heart transplant patients is often limited. Central and peripheral factors have been proposed to explain such exercise limitation but, to date, the leading factors remain to be determined. We examined how a short-term endurance exercise training programme may improve exercise capacity after heart transplantation, and whether atrial natriuretic peptide (ANP) release may contribute to the beneficial effects of exercise training by minimizing ischaemia and/or cardiac and circulatory congestion through its vasodilatation and haemoconcentration properties. Seven heart transplant recipients performed a square-wave endurance exercise test before and after 6 weeks of supervised training, while monitoring haemodynamic parameters, ANP and catecholamine concentrations. After training, the maximal tolerated power and the total mechanical work load increased from 130.4 (SEM 6.5) to 150.0 (SEM 6.0) W (P < 0.05) and from 2.05 (SEM 0.1) to 3.58 (SEM 0.14) kJ · kg⁻¹ (P < 0.001). Resting heart rate decreased from 100.0 (SEM 3.4) to 92.4 (SEM 3.5) beats · min⁻¹ (P < 0.05) but resting and exercise induced increases in cardiac output, stroke volume, right atrial, pulmonary capillary wedge, systemic and pulmonary artery pressures were not significantly changed by training. Exercise-induced decrease of systemic vascular resistance was similar before and after training. After training arterio-venous differences in oxygen content were similar but maximal lactate concentrations decreased from 6.20 (SEM 0.55) to 4.88 (SEM 0.6) mmol · 1⁻¹ (P < 0.05) during exercise. Similarly, maximal exercise noradrenaline concentration tended to decrease from 2060 (SEM 327) to 1168 (SEM 227) pg · ml⁻¹. A significant correlation was observed between lactate and catecholamines concentrations. The ANP concentration at rest and the exercise-induced ANP concentration did not change throughout the experiment [104.8 (SEM 13.1) pg · ml⁻¹ vs 116.0 (SEM 13.5) pg · ml⁻¹ and 200.0 (SEM 23.0) pg · ml⁻¹ vs 206.5 (SEM 25.9) pg · ml⁻¹ respectively]. The results of this study suggested that the significant improvement in exercise capacity observed after this short-term endurance training period may have arisen mainly through peripheral mechanisms, associated with the possible decrease in plasma catecholamine concentrations and reversal of muscle deconditioning and/or prednisone-induced myopathy.     

Effects of a 24-h carbohydrate-poor diet on metabolic and hormonal responses during prolonged glucose-infused leg exercise

Summary Extant literature dealing with metabolic and hormonal adaptations to exercise following carbohydrate (CHO) reduced diets is not sufficiently precise to allow researchers to partial out the effects of reduced blood glucose levels from other general effects produced by low CHO diets. In order to shed light on this issue, a study was conducted to examine the effects of a 24-h CHO-poor diet on substrate and endocrine responses during prolonged (75 min; 60% ) glucose-infused leg exercise. Eight subjects exercised on a cycle ergometer in the two following conditions: 1) after a normal diet (CHO_N), and 2) after a 24-h low CHO diet (CHO_L). In both conditions, glucose was constantly infused intravenously (2.2 mg · kg⁻¹ · min⁻¹) from the 10th to the 75th min of exercise in relatively small amounts (10.4±0.8 g). No significant differences in blood glucose concentrations were found between the two conditions at rest and during exercise although a significant increase (p<0.01) in glucose level was observed in both conditions after 40 min of exercise. The CHO_L as compared to the CHO_N condition, was associated with significantly (p<0.05) lower resting concentrations of insulin, muscle glycogen (8.7 vs 10.6 g · kg⁻¹), and triacylglycerol, and greater concentrations of Β-hydroxybutyrate (0.5 vs 0.2 mmol · L⁻¹), and free fatty acids. During exercise, the CHO_L condition as compared to the CHO_N condition, was associated with significantly (p<0.05) lower insulin and R values, as well as greater free fatty acid (from min 20 to 60) and epinephrine (min 60 to 75) concentrations. Norepinephrine and glucagon concentrations also showed a net tendency (p<0.06) to be higher in the CHO_L condition. There were no significant differences at rest and during exercise in blood lactate and cortisol concentrations between the two conditions. These results demonstrate that blood glucose is not the sole determinant of the metabolic and hormonal responses during prolonged exercise following a low CHO intake and indicate that other factors may be involved in the regulatory mechanism.     

Effects of angiotensin II on arterial pressure,renin and aldosterone during exercise

Summary To evaluate the effect of isotonic exercise on the response to angiotensin II, angiotensin II in saline solution was infused intravenously (7.5 ng · kg⁻¹ · min⁻¹) in seven normal sodium replete male volunteers before, during and after a graded uninterrupted exercise test on the bicycle ergometer until exhaustion. The subjects performed a similar exercise test on another day under randomized conditions when saline solution only was infused. At rest in recumbency angiotensin II infusion increased plasma angiotensin II from 17 to 162 pg · ml⁻¹ (P<0.001). When the tests with and without angiotensin II are compared, the difference in plasma angiotensin II throughout the experiment ranged from 86 to 145 pg · ml⁻¹. The difference in mean intra-arterial pressure averaged 17 mmHg at recumbent rest, 12 mmHg in the sitting position, 9 mmHg at 10% of peak work rate and declined progressively throughout the exercise test to become non-significant at the higher levels of activity. Plasma renin activity rose with increasing levels of activity but angiotensin II significantly reduced the increase. Plasma aldosterone, only measured at rest and at peak exercise, was higher during angiotensin II infusion; the difference in plasma aldosterone was significant at rest, but not at peak exercise. In conclusion, the exercise-induced elevation of angiotensin II does not appear to be an important factor in the increase of blood pressure. It is suggested that the vasodilating mechanisms in the working muscles and the vasoconstricting mechanisms in the non-working vascular beds are powerful and dominant during isotonic exercise and attenuate the opposing or additive vasoconstrictor effects of angiotensin II. The negative feedback effect of angiotensin II on renal renin secretion, however, is not inhibited by exercise.     

An acute oral dose of caffeine does not alter glucose kinetics during prolonged dynamic exercise in trained endurance athletes

This study investigated the possible influence of oral caffeine administration on endogenous glucose production and energy substrate metabolism during prolonged endurance exercise. Twelve trained endurance athletes [seven male, five female; peak oxygen consumption ( ) = 65.5 ml·kg^–1·min^–1] performed 60 min of cycle ergometry at 65% twice, once after oral caffeine administration (6 mg·kg^–1) (CAF) and once following consumption of a placebo (PLA). CAF and PLA were administered in a randomized double-blind manner 75 min prior to exercise. Plasma glucose kinetics were determined with a primed-continuous infusion of [6,6-²H]glucose. No differences in oxygen consumption ( ), and carbon dioxide production ( ) were observed between CAF and PLA, at rest or during exercise. Blood glucose concentrations were similar between the two conditions at rest and also during exercise. Exercise did lead to an increase in serum free fatty acid (FFA) concentrations for both conditions; however, no differences were observed between CAF and PLA. Both the plasma glucose rate of appearance ( ) and disappearance ( ) increased at the onset of exercise (P<0.05), but were not affected by CAF, as compared to PLA. CAF did lead to a higher plasma lactate concentration during exercise (P<0.05). It was concluded that an acute oral dose of caffeine does not influence plasma glucose kinetics or energy substrate oxidation during prolonged exercise in trained endurance athletes. However, CAF did lead to elevated plasma lactate concentrations. The exact mechanism of the increase in plasma lactate concentrations remains to be determined. Electronic Publication     

The effect of prolonged submaximal exercise on gas exchange kinetics and ventilation during heavy exercise in humans

This study compared ventilation, gas exchange (oxygen uptake, V̇O₂) and the surface electromyogram (EMG) activity of four major lower limb muscles during heavy exercise before (Pre-Ex) and after (Post-Ex) a sustained 90-min cycling exercise at 60% V̇O_2peak. The 90-min exercise was incorporated under the hypothesis that sustained exercise would alter substrate availability in the second exercise bout causing differences in fibre recruitment patterns, gas exchange and ventilation. Nine trained male subjects [V̇O_2peak=60.2 (1.7) ml·kg⁻¹·min⁻¹] completed two identical 6-min bouts of cycling performed at high intensity [~90% V̇O_2peak; 307 (6) W, mean (SE)]. Ventilation and gas exchange were measured breath-by-breath and the EMG was recorded during the last 12 s of each minute of the two 6-min bouts. EMG signals were analysed to determine integrated EMG (iEMG) and mean power frequency (MPF). V̇O₂ at min 3 and min 6 in Post-Ex were significantly higher (i.e., +201 and 141 ml·min⁻¹, respectively, P<0.05) than in Pre-Ex but there was a ~25% decrease of the slow component, taken as the difference between min 6 and min 3 [187 (27) vs 249 (35) ml·min⁻¹, respectively, P<0.05]. The greater whole-body V̇O₂ after 3 min of exercise in Post-Ex was not accompanied by clear alterations in the iEMG and MPF of the examined leg muscles. Ventilation and heart rate were elevated (~12–16 l·min⁻¹ and ~10 beats·min⁻¹, respectively, P<0.05) as were the ratios V̇ _E/O₂ and V̇ _E/V̇CO₂ in the Post-Ex tests. It was concluded that the V̇O₂ and ventilation responses to high-intensity exercise can be altered following prolonged moderate intensity exercise in terms of increased amplitude without associated major changes in either iEMG or MPF values among conditions.     

Substrate utilization in boys during exercise with [13C]-glucose ingestion

The influence of glucose ingestion on substrate utilization during prolonged exercise in children and adolescents is currently unknown. In the present study we determined the effect of intermittent exogenous glucose (GLU_exo) ingestion on substrate utilization during prolonged exercise, in adolescent boys ages 13–17 years. Healthy untrained volunteers performed four 30-min exercise bouts on a cycle ergometer, separated by 5-min rest periods (≅60% maximum O₂ consumption), on two occasions spaced 1–4 weeks apart. Two trials were performed, a control trial (CT), in which subjects ingested water intermittently during the exercise, and a glucose trial (GT), in which subjects ingested a ¹³C-enriched GLU_exo drink (≅3 g glucose · kg body mass⁻¹), also intermittently during the exercise. Total free fatty acids (FAT_total), glucose (GLU_total) and carbohydrate (CHO_total) oxidation was determined from indirect calorimetry, while GLU_exo oxidation was calculated from the ¹³C/¹²C ratio in expired air after 5–10 min and 25–30 min of exercise in each bout. Heart rate and rating of perceived exertion (RPE) were determined at the same time intervals. The oxidation of CHO_total was 169.1 (12.9) g · 120 min⁻¹ and 203.1 (15.9) g · 120 min⁻¹ (P < 0.01) and that of FAT_total was 31.0 (4.2) g · 120 min⁻¹ and 17.1 (2.5) g · 120 min⁻¹ (P < 0.01) in CT and GT, respectively. GLU_exo oxidation in GT was 57.8 (4.3) g · 120 min⁻¹, or 34.2 (2.2)% of that ingested. Endogenous glucose oxidation was 169.1 (12.9) g · 120 min⁻¹ and 145.3 (11.9) g · 120 min⁻¹ (P < 0.01) in CT and GT, respectively. Insulin and glucose concentrations were higher in GT than in CT by 226% and 37%, respectively (both P < 0.05). Free fatty acids and glycerol concentrations were lower in GT than in CT, by 27% and 79%, respectively (both P < 0.05). Heart rate was similar between trials, but RPE was lower in GT vs CT at both 115 and 135 min. Thus, under these experimental conditions, GLU_exo intake spares endogenous carbohydrate and fat by 16% and 45%, respectively, contributes to approximately 25% of the total energy demand of exercise, and lowers the RPE. Accepted: 21 May 2000     

Oxygen uptake kinetics during treadmill running across exercise intensity domains

The purpose of the present study was to examine comprehensively the kinetics of oxygen uptake ( ) during treadmill running across the moderate, heavy and severe exercise intensity domains. Nine subjects [mean (SD age, 27 (7) years; mass, 69.8 (9.0) kg; maximum , , 4,137 (697) ml·min^–1] performed a series of "square-wave" rest-to-exercise transitions of 6 min duration at running speeds equivalent to 80% and 100% of the at lactate threshold (LT; moderate exercise); and at 20%, 40%, 60%, 80% and 100% of the difference between the at LT and (Δ, heavy and severe exercise). Critical velocity (CV) was also determined using four maximal treadmill runs designed to result in exhaustion in 2–15 min. The response was modelled using non-linear regression techniques. As expected, the amplitude of the primary component increased with exercise intensity [from 1,868 (136) ml·min^–1 at 80% LT to 3,296 (218) ml·min^–1 at 100% Δ, P<0.05]. However, there was a non-significant trend for the "gain" of the primary component to decrease as exercise intensity increased [181 (7) ml·kg^–1·km^–1 at 80% LT to 160 (6) ml·kg^–1·km^–1 at 100% Δ]. The time constant of the primary component was not different between supra-LT running speeds (mean value range = 17.9–19.1 s), but was significantly shorter during the 80% LT trial [12.7 (1.4) s, P<0.05]. The slow component increased with exercise intensity from 139 (39) ml·min^–1 at 20% Δ to 487 (57) ml·min^–1 at 80% Δ (P<0.05), but decreased to 317 (84) ml·min^–1 during the 100% Δ trial (P<0.05). During both the 80% Δ and 100% Δ trials, the at the end of exercise reached [4,152 (242) ml·min^–1 and 4,154 (114) ml·min^–1, respectively]. Our results suggest that the "gain" of the primary component is not constant as exercise intensity increases across the moderate, heavy and severe domains of treadmill running. These intensity-dependent changes in the amplitudes and kinetics of the response profiles may be associated with the changing patterns of muscle fibre recruitment that occur as exercise intensity increases. Electronic Publication     

Maintenance of testosterone status in fitness joggers after increased training mileage

The primary objective was to evaluate the early effect of increased training mileage on testosterone (T) status in recreational joggers. Serum total (T_tot) and free (T_free) concentrations at rest, overnight urinary T_tot excretion, and the T_tot and T_free responses to maximal exercise were used as indicators of T status. A group of 13 male [mean (SD) age 24.5 (2.5) years] fitness joggers [maximal oxygen consumption, , 52.9 (4.9) ml·kg^–1·min^–1] qualified as subjects. The training intervention consisted of a 100% increase in the habitual distance run [12 (3) miles·week^–1] for 2 consecutive weeks, while maintaining the customary training intensity. Blood samples were obtained at rest and after maximal exercise tests, at the beginning and end of a control week of habitual jogging (baseline) and also following the 1st and 2nd weeks of the intervention. The and treadmill exercise endurance time were unchanged across sampling times. Serum T_tot and T_free concentrations averaged 565 (62) and 24 (2.6) ng·dl^–1, respectively, at baseline and did not change significantly. Urinary T_tot excretion averaged 1.5 (0.21) ng·min^–1 at baseline, and also remained unchanged during the intervention. Relative increases in T_tot (23%) and T_free (22%) were observed following maximal exercise compared to rest (P<0.05). However, the exercise-related increases in serum T_tot and T_free were not evident after adjustment for the change in plasma volume. It was concluded, that the training intervention did not alter T status in these fitness joggers. Electronic Publication     

Pituitary–adrenal responses to arm versus leg exercise in untrained man

The purpose of this study was to examine pituitary–adrenal (PA) hormone responses [beta-endorphin (β-END), adrenocorticotropic hormone (ACTH) and cortisol] to arm exercise (AE) and leg exercise (LE) at 60 and 80% of the muscle-group specific VO₂ peak. Eight healthy untrained men (AE VO₂ peak=32.4±3.0 ml kg⁻¹ min⁻¹, LE VO₂ peak=46.9±5.3 ml kg⁻¹ min⁻¹) performed two sub-maximal AE and LE tests in random order. Plasma β-END, ACTH and cortisol were not different (P>0.05) between AE and LE at either exercise intensity; the 60% testing elicited no changes from pre-exercise (PRE) values. For 80% testing, plasma β-END, ACTH and cortisol were consistently, but not significantly, greater during LE than AE. In general, plasma β-END and ACTH were higher (P<0.05) during 80% exercise, than PRE, for both AE and LE. Plasma cortisol was elevated (P<0.05) above PRE during 80% LE, and following 80% for both AE and LE. Plasma ACTH was higher (P<0.05) during 80% LE and AE versus 60% LE and AE, respectively. Plasma β-END and cortisol were significantly higher during and immediately after 80% LE than 60% LE. Thus, plasma β-END, ACTH and cortisol responses were similar for AE and LE at the two relative exercise intensities, with the intensity threshold occurring somewhere between 60 and 80% of VO₂ peak. It appears that the smaller muscle mass associated with AE was sufficient to stimulate these PA axis hormones in a manner similar to LE, despite the higher metabolic stress (i.e., plasma La^-) associated with LE.     

Intramyocellular lipid stores increase markedly in athletes after 1.5 days lipid supplementation and are utilized during exercise in proportion to their content

Intramyocellular lipids (IMCL) and muscle glycogen provide local energy during exercise (EX). The objective of this study was to clarify the role of high versus low IMCL levels at equal initial muscle glycogen on fuel selection during EX. After 3 h of depleting exercise, 11 endurance-trained males consumed in a crossover design a high-carbohydrate (7 g kg⁻¹ day⁻¹) low-fat (0.5 g kg⁻¹ day⁻¹) diet (HC) for 2.5 days or the same diet with 3 g kg⁻¹ day⁻¹ more fat provided during the last 1.5 days of diet (four meals; HCF). Respiratory exchange, thigh muscle substrate breakdown by magnetic resonance spectroscopy, and plasma FFA oxidation ([1-¹³C]palmitate) were measured during EX (3 h, 50% W _max). Pre-EX IMCL concentrations were 55% higher after HCF. IMCL utilization during EX in HCF was threefold greater compared with HC (P < 0.001) and was correlated with aerobic power and highly correlated (P < 0.001) with initial content. Glycogen values and decrements during EX were similar. Whole-body fat oxidation (Fat_ox) was similar overall and plasma FFA oxidation smaller (P < 0.05) during the first EX hour after HCF. Myocellular fuels contributed 8% more to whole-body energy demands after HCF (P < 0.05) due to IMCL breakdown (27% Fat_ox). After EX, when both IMCL and glycogen concentrations were again similar across trials, a simulated 20-km time-trial showed no difference in performance between diets. In conclusion, IMCL concentrations can be increased during a glycogen loading diet by consuming additional fat for the last 1.5 days. During subsequent exercise, IMCL decrease in proportion to their initial content, partly in exchange for peripheral fatty acids.     

Effect of a 1 year combined aerobic- and weight-training exercise programme on aerobic capacity and ventilatory threshold in patients suffering from coronary artery disease

Weight-training is recommended as a complement to conventional aerobic-training for most low to moderate risk patients suffering from coronary artery disease (CAD). The purpose of this study was to evaluate the effect of a 1 year exercise programme combining weight- and aerobic-training on peak oxygen uptake (VO_2,peak) and ventilatory threshold (VT). We studied 40 men suffering CAD who were divided into three groups: 14 subjects to weight-training plus aerobic-training [mean (SD] [combined exercise group, age 55 (10) years], 14 to aerobic-training only [aerobic-training group, age 57 (11) years], and 12 to a control group [standard care, age 57 (11) years]. A symptom-limited graded exercise test using the standard Bruce protocol was performed using a 12-lead electrocardiogram, and gas analysis techniques. Muscle strength was determined only in the combined exercise group using the one-repetition maximum method on each of eight weight exercises. Arm and leg strength increased by 21.9% and 27.8% respectively (P<0.0001) from pre to post-tests. The VO_2,peak did not differ between the combined and aerobic-training groups but their adjusted means were greater than those of the control group [39 (1.8) and 35.3 (1.8) compared to 26.2 (2.7) ml·kg^–1·min^–1 (P<0.001)]. The oxygen uptake at VT was higher in the combined group [24.7 (1.4) ml·kg^–1·min^–1] compared to aerobic [18.7 (1.4) ml·kg^–1·min^–1] and control [13.6 (1.7) ml·kg^–1min^–1] groups (P<0.001). Similar results were found for exercise tolerance (treadmill time to peak and at VT). Combined exercise training increased the VT more than aerobic-training alone. Combined exercise training did not improve the VO_2,peak or the functional capacity more than aerobic-training alone. Electronic Publication     

Effect of altered pre-exercise carbohydrate availability on selection and perception of effort during prolonged cycling

This study assessed the effect of altered carbohydrate (CHO) availability on self-selected work rate during prolonged time-trial cycling. Eight endurance-trained men undertook two experimental cycling time-trials after glycogen-depleting exercise and 2 days of: (a) high (9.3 ± 0 g CHO kg⁻¹ day⁻¹) (HC) and (b) low CHO intakes (0.6 ± 0.1 g CHO kg⁻¹ day⁻¹) (LC), via a double-blinded crossover design. All feedback regarding performance was removed during both exercise trials. Self-selected external power output was not different during the first 2 h of exercise between experimental conditions (P > 0.05), despite reported sensations of increased tiredness before and during exercise, significantly reduced whole body CHO oxidation (P < 0.05), plasma lactate concentrations (P < 0.05) and earlier onset of fatigue during exercise in LC versus HC. Perceived exertion was not different throughout exercise between conditions (P > 0.05). Mean power output declined significantly in LC versus HC (P < 0.05) after ∼ 2 h of exercise, and was associated with significant reductions in cadence, heart rate and plasma glucose concentration (P < 0.05). These results demonstrate that when compared with time-trial cycling performed after a HC diet, reduced CHO availability does not initially alter self-selected work rate in endurance athletes who are deceived of their CHO status prior to exercise. This finding suggests that reduced work rate during exercise following lowered CHO intake may, in part, be a consequence of the subject’s awareness of dietary CHO restriction rather than solely a physiologically mediated action. Further research is required to distinguish the influence of circulating glucose and peripheral glycogen availability on pacing strategy during prolonged exercise.     

Energy cost of treadmill and floor walking at self-selected paces

Summary Oxygen uptake-velocity regression equations were developed for floor and level treadmill walking by having two groups of men, aged 19–29 years (n=20) and 55–66 years (n=22), walk at four self-selected paces, from “rather slowly” to “as fast as possible”. A two-variable quadratric model relating VO₂ (ml·kg⁻¹·min⁻¹) to velocity (m·s⁻¹) was adopted for prediction purposes. However, age and fatness significantly (p<0.05) interacted with treadmill walking speed, while age alone significantly interacted with floor speed. In addition, a significant difference was found between the energy cost of floor and treadmill walking. For example at the normal walking speed of 1.33 m·s⁻¹, the energy cost for the treadmill (age 55–66 years) was 10.58 ml·kg⁻¹·min⁻¹ and for the floor, 11.04 ml·kg⁻¹·min⁻¹ (p<0.05). Four quadratic equations are therefore presented, one each for floor and treadmill in each of the two age-groups. The percent variance explained was between 87 and 95% for each of these equations. Supported by a grant from the Ontario Ministry of Health (DM449)     

Plasma vasopressin,renin activity,and aldosterone responses to maximal exercise in active college females

Summary The effect of maximal treadmill exercise on plasma concentrations of vasopressin (AVP); renin activity (PRA); and aldosterone (ALDO) was studied in nine female college basketball players before and after a 5-month basketball season. Pre-season plasma AVP increased (p<0.05) from a pre-exercise concentration of 3.8±0.5 to 15.8±4.8 pg · ml⁻¹ following exercise. Post-season, the pre-exercise plasma AVP level averaged 1.5±0.5 pg · ml⁻¹ and increased to 16.7±5.9 pg · ml⁻¹ after the exercise test. PRA increased (p<0.05) from a pre-exercise value of 1.6±0.6 to 6.8±1.7 ngAI · ml⁻¹ · hr⁻¹ 5 min after the end of exercise during the pre-season test. In the post-season, the pre-exercise PRA was comparable (2.4±0.6 ngAI · ml⁻¹ · hr⁻¹), as was the elevation found after maximal exercise (8.3±1.9 ngAI · ml⁻¹ · hr⁻¹). Pre-season plasma ALDO increased (p<0.05) from 102.9±30.8 pg · ml⁻¹ in the pre-exercise period to 453.8±54.8 pg · ml⁻¹ after the exercise test. In the post-season the values were 108.9±19.4 and 365.9±64.4 pg · ml⁻¹, respectively. Thus, maximal exercise in females produced significant increases in plasma AVP, renin activity, and ALDO that are comparable to those reported previously for male subjects. Moreover, this response is remarkably reproducible as demonstrated by the results of the two tests performed 5 months apart.     

Exercise training induces similar elevations in the activity of oxoglutarate dehydrogenase and peak oxygen uptake in the human quadriceps muscle

During exercise involving a small muscle mass, peak oxygen uptake is thought to be limited by peripheral factors, such as the degree of oxygen extraction from the blood and/or mitochondrial oxidative capacity. Previously, the maximal activity of the Krebs cycle enzyme oxoglutarate dehydrogenase has been shown to provide a quantitative measure of maximal oxidative metabolism, but it is not known whether the increase in this activity after a period of training reflects the elevation in peak oxygen consumption. Fourteen subjects performed one-legged knee extension exercise for 5–7 weeks, while the other leg remained untrained. Thereafter, the peak oxygen uptake by the quadriceps muscle was determined for both legs, and muscle biopsies were taken for assays of maximal enzyme activities (at 25°C). The peak oxygen uptake was 26% higher in the trained than in the untrained muscle (395 vs. 315 ml min⁻¹ kg⁻¹, respectively; P < 0.01). The maximal activities of the Krebs cycle enzymes in the trained and untrained muscle were as follows: citrate synthase, 22.4 vs. 18.2 μmol min⁻¹ g⁻¹ (23%, P < 0.05); oxoglutarate dehydrogenase, 1.88 vs. 1.54 μmol min⁻¹ g⁻¹ (22%, P < 0.05); and succinate dehydrogenase, 3.88 vs. 3.28 μmol min⁻¹ g⁻¹ (18%, P < 0.05). The difference between the trained and untrained muscles with respect to peak oxygen uptake (80 ml min⁻¹ kg⁻¹) corresponded to a flux through the Krebs cycle of 1.05 μmol min⁻¹ g⁻¹, and the corresponding difference in oxoglutarate dehydrogenase activity (at 38°C) was 0.83 μmol min⁻¹ g⁻¹. These parallel increases suggest that there is no excess mitochondrial capacity during maximal exercise with a small muscle mass.     

Muscle blood flow and flow heterogeneity during exercise studied with positron emission tomography in humans

Blood flow is the main regulator of skeletal muscle's oxygen supply, and several studies have shown heterogeneous blood flow among and within muscles. However, it remains unclear whether exercise changes the heterogeneity of flow in exercising human skeletal muscle. Muscle blood flow and spatial flow heterogeneity were measured simultaneously in exercising and in the contralateral resting quadriceps femoris (QF) muscle in eight healthy men using H¹⁵ ₂O and positron emission tomography. The relative dispersion (standard deviation/mean) of blood flow was calculated as an index of spatial flow heterogeneity. Average muscle blood flow in QF was 29 (10) ml · (kg muscle)⁻¹ · min⁻¹ at rest and 146 (54) ml · (kg muscle)⁻¹ · min⁻¹ during exercise (P=0.008 for the difference). Blood flow was significantly (P < 0.001) higher in the vastus medialis and the vastus intermedius than in the vastus lateralis and the rectus femoris, both in the resting and the exercising legs. Flow was more homogeneous in the exercising vastus medialis and more heterogeneous (P < 0.001) in the exercising vastus lateralis (P=0.01) than in the resting contralateral muscle. Flow was more homogeneous (P < 0.001) in those exercising muscles in which flow was highest (vastus intermedius and vastus medialis) as compared to muscles with the lowest flow (vastus lateralis and the rectus femoris). These data demonstrate that muscle blood flow varies among different muscles in humans both at rest and during exercise. Muscle perfusion is spatially heterogeneous at rest and during exercise, but responses to exercise are different depending on the muscle. Accepted: 16 June 2000     

The oxygen consumption with unloaded walking and load carriage using two different backpack designs

The purpose of this study was to assess the energy expenditure associated with load carriage using both a traditional rucksack and a new rucksack design, the AARN rucksack, which incorporates front balance pockets. Nine volunteers walked at 3 km h⁻¹ at various uphill and downhill gradients on a treadmill without a load and carrying a load of 25.6 kg in each of the rucksacks. The oxygen consumption associated with both of the loading conditions was significantly (P < 0.001) higher than that associated with unloaded walking at all downhill gradients tested, although there was no significant difference between the two loading conditions. During the uphill gradients the oxygen consumption associated with the AARN pack was significantly (P < 0.05) lower than that associated with the traditional pack at the 0%, 5%, 10% and 20% gradients. The mean (%) differences at these gradients, expressed in ml · kg⁻¹ · min⁻¹ were 1.18 (9%), 1.45 (8%), 1.76 (8%) and 1.88 (6%), respectively. On average for the whole protocol, the oxygen consumption associated with the AARN rucksack was 5% lower than that associated with the traditional rucksack [mean (SD) 17.28 (7.46) ml · kg⁻¹ · min⁻¹ for the AARN pack and 18.20 (7.84) ml · kg⁻¹ · min⁻¹ for the traditional pack]. The findings of the present study suggest that a load carriage system that allows the load to be distributed between the back and font of the trunk is more appropriate for carrying relatively heavy loads than a system that loads the back only. Accepted: 22 November 1999