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

Summary 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<0.001) and decreased type I fibres (–6.3±2.0%,p<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 m²,p<0.05), IIa (+652±207 m²,p<0.001) and IIb (+773±196 m²,p< 0.001) fibres. During fixed term maximal incremental exercise the mean carbon dioxide output ( ) and mean respiratory exchange ratio ( ) were significantly increased (p<0.01) after training. The R-time relationship was at all times shifted to the left after training, being significantly (p<0.01) so over the final five min of exercise. No changes in mean exercise oxygen uptake ( ), maximum oxygen uptake ( ) and maximum heart rate (FHR_max) were observed between tests. These results indicate that high intensity training can significantly affect respiratory exchange during fixed term progressive exercise.     

Effect of high intensity interval training on 2,3-diphosphoglycerate at rest and after maximal exercise

Summary The purpose of this study was to examine the effect of intense interval training on erythrocyte 2,3-diphosphoglycerate (2,3-DPG) levels at rest and after maximal exercise. Eight normal men, mean ± SE=24.2±4.3 years, trained 4 days·week^–1 for a period of 8 weeks. Each training session consisted of eight maximal 30-s rides on a cycle ergometer, with 4 min active rest between rides. Prior to and after training the subjects performed a maximal 45-s ride on an isokinetic cycle ergometer at 90 rev·min^–1 and a graded leg exercise test (GLET) to exhaustion on a cycle ergometer. Blood samples were obtained from an antecubital vein before, during and after the GLET only. Training elicited significant increases in the amount of work done during the 45-s ride (P<0.05), and also in maximal oxygen uptake ( max: Pre=4.01±0.13; Post=4.29±0.07 l·min^–1;P<0.05) during exercise and total recovery (Pre=19.14±0.09; Post=21.45±0.10 l·30 min^–1;P<0.05) after the GLET. After training blood lactate was higher, base excess lower and pH lower during and following the GLET (P<0.05 for all variables). Training caused no significant differences in erythrocyte 2,3-DPG levels at rest (Pre=11.8±0.7; Post=12.1±0.7 mol·g^–1 hemoglobin (Hb);P>0.05), at exhaustion (Pre=12.0±0.8; Post=11.2±0.8 mol·g^–1 Hb;P>0.05) or during 30 min of recovery from the GLET. Additionally, acute exercise (pre-training GLET) did not effect any change in 2,3-DPG at exhaustion or during recovery from exercise compared to resting values. The higher max and total recovery values observed after training appear to be unrelated to 2,3-DPG levels. Under the present conditions, the role, if any, of 2,3-DPG in enhancing tissue oxygenation during increased metabolic demand remains obscure.Supported by grants from Miles Laboratories, Elkhart, Indiana, and the Ball State Graduate Student Research Fund     

Human corticotropin-releasing factor (hCRF) is a potent respiratory analeptic

Summary During intravenous corticotropin-releasing factor stimulation tests we observed a deepening of the tidal volume in 35 patients. To investigate this presumed respiratory stimulation we measured respiratory parameters in 12 healthy male volunteers in a single-blind placebo-controlled trial. The intravenous 60-s infusion of 100 µg of human corticotropin-releasing factor induced a very potent respiratory stimulation in every subject: respiratory minute volume (mean ± S.D.) increased by 81% from 6.319±0.577 to 11.464±1.264 liters per min (P<0.001), whereas there was only a slight rise in the mean respiratory rate from 12.4±3.0 to 14.7±2.7 breaths per min (P<0.001). Mean tidal volume increased from 531±105 to 809±175 ml (P<0.001). Mean end-tidal partial pressure of carbon dioxide decreased (P<0.001) from 40.3±1.2 to 33.4±1.2 mmHg, whereas mean end-tidal partial pressure of oxygen increased (P<0.001) from 93.2±5.4 to 113.5±5.4 mmHg. After 10 to 20 min both end-tidal carbon dioxide and oxygen partial pressures returned to the baseline values. The placebo had no measurable effects.We conclude that human corticotropin-releasing factor is a potent respiratory stimulant. With 100 µg the resting respiratory minute volume increases by 81%. These data point to the possible importance of the corticotropin-releasing factor as a useful adjunct in the management of patients with alveolar hypoventilation.Abbreviations hCRF human corticotropin-releasing factor - P_ETCO₂ end-tidal partial pressure of carbon dioxide (the last portion of the V_T during expiration, called end-tidal volume, contains CO₂ from the alveolar region) - P_ETO₂ end-tidal partial pressure of oxygen - minute volume - V_T respiratory tidal volume     

Expiratory muscle fatigue impairs exercise performance

High-intensity, exhaustive exercise may lead to inspiratory as well as expiratory muscle fatigue (EMF). Induction of inspiratory muscle fatigue (IMF) before exercise has been shown to impair subsequent exercise performance. The purpose of the present study was to determine whether induction of EMF also affects subsequent exercise performance. Twelve healthy young men performed five 12-min running tests on a 400-m track on separate days: a preliminary trial, two trials after induction of EMF, and two trials without prior muscle fatigue. Tests with and without prior EMF were performed in an alternate order, randomly starting with either type. EMF was defined as a ≥20% drop in maximal expiratory mouth pressure achieved during expiratory resistive breathing against 50% maximal expiratory mouth pressure. The average distance covered in 12 min was significantly smaller during exercise with prior EMF compared to control exercise (2872 ± 256 vs. 2957 ± 325 m; P = 0.002). Running speed was consistently lower (0.13 m s⁻¹) throughout the entire 12 min of exercise with prior EMF. A significant correlation was observed between the level of EMF (decrement in maximal expiratory mouth pressure after resistive breathing) and the reduction in running distance (r ² = 0.528, P = 0.007). Perceived respiratory exertion was higher during the first 800 m and heart rate was lower throughout the entire test of running with prior EMF compared to control exercise (5.3 ± 1.6 vs. 4.5 ± 1.7 points, P = 0.002; 173 ± 10 vs. 178 ± 7 beats min⁻¹, P = 0.005). We conclude that EMF impairs exercise performance as previously reported for IMF.     

Glomerular hypertrophy after subtotal nephrectomy: relationship to early glomerular injury

Structural adaptations in response to approx. 70% nephrectomy were studied in male Sprague-Dawley rats. Rats developed systemic hypertension as well as progressive albuminuria after nephrectomy. At 18–26 weeks after nephrectomy (n=6) or sham treatment (n=6) kidneys were perfusion-fixed and examined by light and electron microscopy. Glomerular tuft volume (+140%), capillary volume (+151%) and length (+77%), mesangial volume (+115%), podocyte volume (+96%), glomerular basement membrane surface area (+107%) and filtration slit length (+85%) were all significantly greater in nephrectomized rats. The incidence of segmental glomerular sclerosis was low and variable among these rats, but was significantly higher than in controls (P=0.037). Urinary albumin excretion was elevated in the nephrectomized rats (89±72 SD mg/day vs 11±11 mg/day in control rats, P=0.01) and correlated significantly with the incidence of sclerosis (r=+0.8311, P<0.05). The relationships of the level of albuminuria and the sclerosis rate to various morphometric parameters were examined by regression analysis for the nephrectomy group. A significant negative correlation was found between albuminuria and average tuft volume (r=–0.8136) and glomerular basement membrane surface area (r=–0.8168). Both sclerosis rate and albuminuria showed negative correlations with filtration slit length (r=–0.8180 and r=–0.8598). These findings suggest that under some circumstances, glomerular hypertrophy may prevent or ameliorate the early stages of glomerular injury after subtotal nephrectomy.     

Ventilatory responses to exercise training in obese adolescents

The aim of this study was to examine ventilatory responses to training in obese adolescents. We assessed body composition, pulmonary function and ventilatory responses (among which expiratory flow limitation and operational lung volumes) during progressive cycling exercise in 16 obese adolescents (OB) before and after 12 weeks of exercise training and in 16 normal-weight volunteers. As expected, obese adolescents' resting expiratory reserve volume was lower and inversely correlated with thoraco-abdominal fat mass (r=-0.74, p<0.0001). OB presented lower end expiratory (EELV) and end inspiratory lung volumes (EILV) at rest and during submaximal exercise, and modest expiratory flow limitation. After training, OB increased maximal aerobic performance (+19%) and maximal inspiratory pressure (93.7±31.4 vs 81.9±28.2cmH(2)O, +14%) despite lack of decrease in trunk fat and body weight. Furthermore, EELV and EILV were greater during submaximal exercise (+11% and +9% in EELV and EILV, respectively), expiratory flow limitation delayed but was not accompanied by increased V(T). However, submaximal exertional symptoms (dyspnea and leg discomfort) were significantly decreased (-71.3% and -70.7%, respectively). Our results suggest that exercise training can improve pulmonary function at rest (static inspiratory muscle strength) and exercise (greater operating lung volumes and delayed expiratory flow limitation) but these modifications did not entirely account for improved dyspnea and exercise performance in obese adolescents.     

Effects of aerobic exercise training on cognitive function and cortical vascularity in monkeys

This study examined whether regular exercise training, at a level that would be recommended for middle-aged people interested in improving fitness could lead to improved cognitive performance and increased blood flow to the brain in another primate species. Adult female cynomolgus monkeys were trained to run on treadmills for 1 h a day, 5 days a week, for a 5 month period (n=16; 1.9±0.4 miles/day). A sedentary control group sat daily on immobile treadmills (n=8). Half of the runners had an additional sedentary period for 3 months at the end of the exercise period (n=8). In all groups, half of the monkeys were middle-aged (10–12 years old) and half were more mature (15–17 years old). Starting the fifth week of exercise training, monkeys underwent cognitive testing using the Wisconsin General Testing Apparatus (WGTA). Regardless of age, the exercising group learned to use the WGTA significantly faster (4.6±3.4 days) compared to controls (8.3±4.8 days; P=0.05). At the end of 5 months of running monkeys showed increased fitness, and the vascular volume fraction in the motor cortex in mature adult running monkeys was increased significantly compared to controls (P=0.029). However, increased vascular volume did not remain apparent after a 3-month sedentary period. These findings indicate that the level of exercise associated with improved fitness in middle-aged humans is sufficient to increase both the rate of learning and blood flow to the cerebral cortex, at least during the period of regular exercise.     

Pulmonary function in normal subjects following exercise at cold ambient temperatures

Summary We measured pulmonary function in 12 healthy volunteers before and at 5-min intervals for 30 min following treadmill exercise of 30 min duration performed under control (20° C) and cold (–11 ° C) ambient temperatures. Post-run changes in forced vital capacity (FVC), residual volume (RV) and peak expiratory flow rate were similar between the two temperature conditions. FVC decreased slightly but significantly 5 min post-run (–0.25 ±0.201 and –0.21–0.201, for control and cold conditions respectively) and returned to baseline by 30 min. RV increased significantly post-exercise (+ 0.07 ± 0.091 and + 0.14 ± 0.11, control and cold respectively) and remained elevated for 30 min. Forced expired volume in 1 s was not significantly different following either run. Post-exercise, maximum mid-expiratory flow rate and flows at 50% and 25% of vital capacity were not significantly different between warm and cold conditions. These data suggest that changes in lung volumes following exercise under cold ambient conditions are similar to changes seen following warm exercise of similar duration. In non-asthmatics, moderate exertion under cold ambient conditions does not appear to cause clinically significant decreases in expiratory flow rates as compared to similar exertion under warm conditions.     

Effect of exercise training on aortic collagen content in spontaneously hypertensive rats (SHR)

Summary We investigated the effects of exercise training on the amount of aortic collagen and systolic blood pressure in spontaneously hypertensive rats (SHR). Ten-week old SHR were trained either by forced treadmill running (26.8 m·min^–1 h·day^–1, five times a week, 0% incline) or by voluntary running in revolving wheels (7,800 m·day^–1 at peak) for 8 weeks. Succinate dehydrogenase (SDH) activity measured as a marker of an endurance training effect was 13% higher (P<0.01) in the soleus of forced-exercised animals than in that of sedentary ones. (6.56±0.17 mol·g^–1·min^–1; mean ± SEM), whereas SDH activity in that of voluntarily-exercised group was found to be at the same level as in sedentary animals. The systolic blood pressure after training increased by 26.4 in sedentary, 21.1 in voluntarily-exercised, and 33.9 mm Hg in forced-exercised rats, when compared with the value of each group at the beginning of the training programm. A significant difference was observed in the increment of blood pressure only between the voluntarily- and forced-exercised groups (P<0.05). The amount of aortic collagen in voluntarily-trained rats (96.5±2.0 mg·g tissue^–1, 39.8±0.7 mg·100 mg protein^–1) was significantly less than that in forced-trained rats (P<0.05). These results suggest that voluntary, mild exercise training may be more effective in the reduction of collagen accumulation in the aorta associated with the suppression of blood pressure increase than forced, vigorous exercise training in SHR.     

A comparison of inspiratory muscle fatigue following maximal exercise in moderately trained males and females

Exercise-induced inspiratory muscle fatigue (IMF) has been reported in males but there are few reports of IMF in females. It is not known if a gender difference exists for inspiratory muscle strength following heavy exercise, as is reported in locomotor muscles. Therefore, the relationship between fatigue and subsequent recovery of maximal inspiratory pressure (MIP) following exercise to maximal oxygen consumption was examined in a group of moderately trained males and females. Eighteen males (23±3 years; mean ± SD) and 16 females (23±2 years) completed ten MIP and ten maximal handgrip (HG) strength maneuvers to establish baseline. Post-exercise MIP and HG were assessed successively immediately following a progressive intensity test on a cycle ergometer and at 1, 2, 3, 4, 5, 10, and 15 min. relative to fat-free mass was not statistically different between males (62±7 ml kg^–1 min^–1) and females (60±8 ml kg^–1 min^–1). Males had higher absolute MIP values than females at all time intervals (P<0.05). Immediately following exercise, MIP was significantly reduced in both genders (M=83±16%; F=78±15% of baseline) but HG values were not different than resting values. MIP values remained depressed for both males and females throughout the 15 min (P<0.05). Differences for MIP between males and females were not statistically significant at any measurement time (P>0.05). The findings in this study conclude that IMF, observed immediately following maximal exercise, demonstrated the same pattern of recovery for both genders.     

Predictors of sweat loss in man during prolonged exercise

Summary Nineteen healthy male subjects, differing in training status and (52±1 ml · min^–1 · kg^–1, mean ±SEM; 43–64 ml · min^–1 · kg^–1, range), exercised for 1 h at an absolute workload of 192±8 W (140–265 W); this was equivalent to 70±1% (66–74%). Each exercise test was performed on an electrically braked cycle ergometer at a constant ambient temperature (22.5±0.0° C) and relative humidity (85±0%). Nude body weight was recorded prior to and after each exercise test. Absolute sweat loss (body weight loss corrected for respiratory weight loss) during each test was 910±82 g (426–1665 g); this was equivalent to 1.3±0.1% (0.7–2.2%) of pre-exercise body weight (relative sweat loss). Weighted mean skin temperature and rectal temperature increased after 5 min of exercise from 30.5±0.3° C and 37.2±0.1° C respectively to 32.5±0.2° C and 38.8±0.1° C respectively, recorded immediately prior to the end of exercise. Bivariate linear regression and Pearson's correlation demonstrated absolute sweat loss was related to (r=0.72,p<0.001), absolute exercise workload (r=0.66,p<0.01), body surface area (r=0.62,p<0.01), weight (r=0.60,p<0.01) and height (r=0.53,p<0.05). Relative sweat loss was related to (r=0.77,p<0.001) and absolute exercise workload (r=0.59,p<0.01). There was no relationship between sweat loss (absolute or relative) and heart rate, skin temperature or rectal temperature. In addition, there was no relationship between rectal temperature or absolute exercise workload or . Stepwise multiple linear regression indicated to be the most important predictor of absolute (r=0.72,F=18.27,p<0.001) and relative (r=0.77,F=24.58,p<0.001) sweat loss in man during prolonged exercise.     

Effects of inspiratory impedance on hemodynamic responses to a squat–stand test in human volunteers: implications for treatment of orthostatic hypotension

Recent studies in our laboratory demonstrated that spontaneous breathing through an inspiratory impedance threshold device (ITD) increased heart rate (HR), stroke volume (SV), cardiac output (Q), and mean arterial blood pressure (MAP) in supine human subjects. In this study, we tested the effectiveness of an ITD as a countermeasure against development of orthostatic hypotension, provoked using a squat-to-stand test (SST). Using a prospective, randomized blinded protocol, 18 healthy, normotensive volunteers (9 males, 9 females) completed two-counterbalanced 6-min SST protocols with and without (sham) an ITD set to open at 0.7 kPa (7-cm H₂O) pressure. HR, SV, Q, total peripheral resistance (TPR), and MAP were assessed noninvasively with infrared finger photoplethysmography. Symptoms were recorded on a 5-point scale (1=normal; 5=faint) of subject perceived rating (SPR). The reduction in TPR produced by SST (–35±5 %) was not affected by the ITD. Reduction in MAP with ITD during the transient phase of the SST (–3.6±0.5 kPa or –27±4 mmHg) was less (P=0.03) than that measured while breathing through a sham device (–4.8±0.4 kPa or –36±3 mmHg) despite similar (P<0.926) elevations in HR of 15±2 bpm. SV (+2±4 %) and Q (+22±5 %) with the ITD were higher (P<0.04) than SV (–8±4 %) and Q (+10±6 %) without the ITD. SPR was 1.4±0.1 with ITD compared to 2.0±0.2 with the sham device (P<0.04). This reduction in orthostatic symptoms with application of an ITD during the SST was associated with higher MAP, SV and Q. Our results demonstrate the potential application of an ITD as a countermeasure against orthostatic hypotension.     

Dissociation between\dot V_{O_2 \max } and ventilatory threshold responses to endurance training

Summary The purpose of this investigation was to determine whether the ventilatory gas exchange threshold (T_vent) changes significantly during the first 1–3 weeks of endurance training. Six men were studied during 3 weeks of training, which consisted of pedaling on a cycle ergometer 6 d·wk 30 min per session at 70% of pretraining . At the end of each week, T_vent, and maximal and submaximal heart rates were determined during an incremental exercise test on the cycle ergometer. Constant-load submaximal exercise blood lactate concentrations were determined during training sessions on Monday, Wednesday, and Friday of each week of training. T_vent did not change significantly during the 3 weeks of training (+ 0.09 l·min^–1;P>0.05). In contrast, significant changes occurred in all other training indexes measured. increased by 0.36 l·min^–1 (P<0.05) after just 2 weeks of training and did not change further after 3 weeks. Significant reductions (40–45%;p<0.05) in blood lactate levels during training sessions occurred by the middle of the 2nd week of training. Decreases in maximal (~ 11 bt·min^–1) and submaximal (~ 14 bt·min^–1) exercise heart rates after 1 week of training were significant (P<0.05). The results demonstrate that changes in T_vent lag behind alterations in several other cardiovascular and metabolic parameters in response to endurance training. The dissociation between the significant improvement in and the lack of a significant increase in T_vent during the first 3 weeks of training indicates that the exercise-induced changes in these two parameters are regulated by different mechanisms.     

The effect of training on responses of Β-endorphin and other pituitary hormones to insulin-induced hypoglycemia

Summary We studied whether the previously reported intensified -endorphin response to exercise after training might result from a training-induced general increase in anterior pituitary secretory capacity. Identical hypoglycemia was induced by insulin infusion in 7 untrained (Skeletal muscle enzyme activity, fiber composition and in relation to distance running performance 49±4 ml · (kg · min)^–1, mean and SE) and 8 physically trained (Skeletal muscle enzyme activity, fiber composition and in relation to distance running performance 65±4 ml · (kg · min)^–1) subjects. In response to hypoglycemia, levels of -endorphin and prolactin immunoreactivity in serum increased similarly in trained (from 41±2 pg · ml^–1 and 6±1 pg · ml^–1 before hypoglycemia to 103±11 pg · ml^–1 and 43±9 pg · ml^–1 during recovery, P<0.05) and untrained (from 35±7 pg · ml^–1 and 7±2 pg · ml^–1 to 113±18 pg · ml^–1 and 31±8 pg · ml^–1 P<0.05) subjects. Growth hormone (GH) was higher 90 min after glucose nadir in trained (61±13 mU · l^–1) than in untrained (25±6 mU · l^–1) subjects (P<0.05). Levels of thyrotropin (TSH) changed in neither of the groups. It is concluded that, in contrast to what has been formerly proposed, training does not result in a general increase in secretory capacity of the anterior pituitary gland. TSH responds to hypoglycemia neither in trained nor in untrained subjects. Finally, differences in -endorphin responses to exercise between trained and untrained subjects cannot be ascribed to differences in responsiveness to hypoglycemia.     

Respiratory muscle training improves swimming endurance in divers

Respiratory muscles can fatigue during prolonged and maximal exercise, thus reducing performance. The respiratory system is challenged during underwater exercise due to increased hydrostatic pressure and breathing resistance. The purpose of this study was to determine if two different respiratory muscle training protocols enhance respiratory function and swimming performance in divers. Thirty male subjects (23.4 ± 4.3 years) participated. They were randomized to a placebo (PRMT), endurance (ERMT), or resistance respiratory muscle training (RRMT) protocol. Training sessions were 30 min/day, 5 days/week, for 4 weeks. PRMT consisted of 10-s breath-holds once/minute, ERMT consisted of isocapnic hyperpnea, and RRMT consisted of a vital capacity maneuver against 50 cm H₂O resistance every 30 s. The PRMT group had no significant changes in any measured variable. Underwater and surface endurance swim time to exhaustion significantly increased after RRMT (66%, P < 0.001; 33%, P = 0.003) and ERMT (26%, P = 0.038; 38%, P < 0.001). Breathing frequency (f _b) during the underwater endurance swim decreased in RRMT (23%, P = 0.034) and tidal volume (V _T) increased in both the RRMT (12%, P = 0.004) and ERMT (7%, P = 0.027) groups. Respiratory endurance increased in ERMT (216.7%) and RRMT (30.7%). Maximal inspiratory and expiratory pressures increased following RRMT (12%, P = 0.015, and 15%, P = 0.011, respectively). Results from this study indicate that respiratory muscle fatigue is a limiting factor for underwater swimming performance, and that targeted respiratory muscle training (RRMT > ERMT) improves respiratory muscle and underwater swimming performance.     

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

Summary The purpose of this study was to examine the effects of pre-exercise glucose and fructose feedings on muscle glycogen utilization during exercise in six well-trained runners ( =68.2±3.4 ml·kg^–1·min^–1). On three separate occasions, the runners performed a 30 min treadmill run at 70% . Thirty minutes prior to exercise each runner ingested 75 g of glucose (trial G), 75 g of fructose (trial F) or 150 ml of a sweetened placebo (trial C). During exercise, no differences were observed between any of the trials for oxygen uptake, heart rate or perceived exertion. Serum glucose levels were elevated as a result of the glucose feeding (P<0.05) reaching peak levels at 30 min post-feeding (7.90±0.24 mmol·l^–1). With the onset of exercise, glucose levels dropped to a low of 5.89±0.85 mmol·l^–1 at 15 min of exercise in trial G. Serum glucose levels in trials F and C averaged 6.21±0.31 mmol·l^–1 and 5.95±0.23 mmol·l^–1 respectively, and were not significantly different (P<0.05). There were also no differences in serum glucose levels between any of the trials at 15 and 30 min of exercise. Muscle glycogen utilization in the first 15 min of exercise was similar in trial C (18.8±8.3 mmol·kg^–1), trial F (16.3±3.8 mmol·kg^–1) and trial G (17.0±1.8 mmol·kg^–1), and total glycogen use was also similar in trial C (25.6±7.9 mmol·kg^–1), trial F (35.4±5.7 mmol·kg^–1) and trial G (24.6±3.2 mmol·kg^–1). In contrast to previous research, these results suggest that pre-exercise feedings of fructose or glucose do not affect the rate of muscle glycogen utilization during 30 min of treadmill running in trained runners.     

The effects of dietary manipulation upon the respiratory exchange ratio as a predictor of maximum oxygen uptake during fixed term maximal incremental exercise in man

Summary This study examined the effects of dietary manipulation upon the respiratory exchange ratio ( ) as a predictor of maximum oxygen uptake ( ). Seven healthy males performed fixed term maximal incremental treadmill exercise after an overnight fast on three separate occasions. The first test took place after the subjects had consumed their normal mixed diet (45±5% carbohydrate (CHO)) for a period of three days. This test protocol was then repeated after three days of a low CHO diet (3±2% CHO), and again after three days of a high CHO diet (61±5% CHO). Respiratory gases were continuously monitored during each test using an online system. No significant changes in mean exercise oxygen uptake ( ), or maximum functional heart rate (FHR_max) were found between tests. Mean exercise carbon dioxide output ( ) and R were significantly lower than normal after the low CHO diet (bothp<0.001) and significantly higher than normal after the high CHO diet (bothp<0.05). Moreover, compared with the normal CHO diet, the R-time relationship during exercise was at all times significantly (p<0.001) shifted to the right after the low CHO diet, and shifted to the left, being significantly so (p<0.05) over the final 5 min of exercise, after the high CHO diet. As a result, predictions of based on the R-time relationship were similar to recorded after the normal CHO dietary condition (-1.5±1.9%), but higher after the low CHO diet (+14.8±3.9%,p<0.001) and lower after the high CHO diet (–7.0±4.5%,p<0.01). These results indicate that dietary manipulation can significantly affect respiratory gas exchanges during fixed term maximal incremental exercise, and by doing so can significantly influence predictions of based on R.     

Blood lactate production and recovery from anaerobic exercise in trained and untrained boys

Summary Blood lactate production and recovery from anaerobic exercise were investigated in 19 trained (AG) and 6 untrained (CG) prepubescent boys. The exercises comprised 3 maximal test performances; 2 bicycle ergometer tests of different durations (15 s and 60 s), and running on a treadmill for 23.20±2.61 min to measure maximal oxygen uptake. Blood samples were taken from the fingertip to determine lactate concentrations and from the antecubital vein to determine serum testosterone. Muscle biopsies were obtained from vastus lateralis. Recovery was passive (seated) following the 60 s test but that following the treadmill run was initially active (10 min), and then passive. Peak blood lactate was highest following the 60 s test (AG, 13.1±2.6 mmol·l^–1 and CG, 12.8±2.3 mmol·l^–1). Following the 15 s test and the treadmill run, peak lactate values were 68.7 and 60.6% of the 60 s value respectively. Blood lactate production was greater (p<0.001) during the 15s test (0.470±0.128 mmol·l^–1·s^–1) than during the 60s test (0.184±0.042 mmol·l^–1·s^–1). Although blood lactate production was only nonsignificantly greater in AG, the amount of anaerobic work in the short tests was markedly greater (p<0.05-0.01) in AG than CG. Muscle fibre area (type II%) and serum testosterone were positively correlated (p<0.05) with blood lactate production in both short tests. Blood lactate elimination was greater (p<0.001) at the end of the active recovery phase than in the next (passive) phase. It is concluded that blood lactate production in prepubescent boys is related to serum testosterone level and muscle type II fibre area, indicating the role of maturation and training. Submaximal exercise is likely to increase blood lactate removal during recovery.     

A single open sea air dive increases pulmonary artery pressure and reduces right ventricular function in professional divers

After decompression from dives, bubbles are frequently observed in the right ventricular outflow tract and may lead to vascular damage, pulmonary arterial hypertension and right ventricular overload. No data exist on the effect of open sea diving on the pulmonary artery pressure (PAP). Eight professional divers performed an open sea air dive to 30 msw. Before and postdive a Doppler echocardiographic study was undertaken. Systolic pulmonary artery pressure (SPAP) was estimated from measurement of peak flow velocity of the tricuspid regurgitant jet; the ratio between pulmonary artery acceleration times (AccT) and right ventricular ejection time (RVET) was used as an estimate of the mean PAP. No evidence of either patent foramen ovale or intra-pulmonary shunt was found in any subject postdive after performing a Valsalva maneuver. SPAP increased from 25 ± 3 to 33 ± 2 mmHg and AccT/RVET ratio decreased from 0.44 ± 0.04 to 0.3 ± 0.02 20 min after the dive, respectively. Pulmonary vascular resistance increased from 1.2 ± 0.1 to 1.4 ± 0.1 Woods Units. Postdive right ventricle end-diastolic and end-systolic volumes were increased for about 19% (P = 0.001) and 33% (P = 0.001) and right ejection fraction decreased about for 6% (P = 0.001). Cardiac output decreased from 4.8 ± 0.9 (l min⁻¹) to 4.0 ± 0.6 at 40 min postdive due to decreases in heart rate and stroke volume. This study shows that a single open sea dive may be associated with right heart overload due to increased pressure in the pulmonary artery.     

Influence of intense exercise on saliva glutathione in prepubescent and pubescent boys

Intense aerobic exercise has been found to prompt changes in oxidative stress, but in children remains almost unexplored. The aim was to investigate the effect of intense physical exercise on reduced glutathione (GSH as a biomarker of oxidative stress) and adrenocortical response (to verify a certain level of stress after exercise) in 38 prepubescent and 32 pubescent non-athlete boys. Four subgroups were established as puberty stage and physical fitness. Saliva samples were taken before and after incremental exercise testing to measure GSH, and cortisol levels. Saliva reduced glutathione levels were lower in all subgroups after exercise except in the prepubescent average fit group, significance being greater in the pubescent (P < 0.001) than in the prepubescent group (P < 0.01). Saliva cortisol increased after exercise in all except in the prepubescent “average fit” group. Physical exercise may give rise to oxidative stress and adrenocortical response in pubescent and prepubescent boys, depending on the duration and intensity of the test.