Showing papers on "Exercise physiology published in 1993"
TL;DR: In face of a considerable reduction in the contribution of anaerobic glycogenolysis to ATP production, power output was supported by energy that was mainly derived from PCr degradation and an increased aerobic metabolism.
Abstract: Eight male subjects volunteered to take part in this study. The exercise protocol consisted of ten 6-s maximal sprints with 30 s of recovery between each sprint on a cycle ergometer. Needle biopsy samples were taken from the vastus lateralis muscle before and after the first sprint and 10 s before and immediately after the tenth sprint. The energy required to sustain the high mean power output (MPO) that was generated over the first 6-s sprint (870.0 +/- 159.2 W) was provided by an equal contribution from phosphocreatine (PCr) degradation and anaerobic glycolysis. Indeed, within the first 6-s bout of maximal exercise PCr concentration had fallen by 57% and muscle lactate concentration had increased to 28.6 mmol/kg dry wt, confirming significant glycolytic activity. However, in the tenth sprint there was no change in muscle lactate concentration even though MPO was reduced only to 73% of that generated in the first sprint. This reduced glycogenolysis occurred despite the high plasma epinephrine concentration of 5.1 +/- 1.5 nmol/l after sprint 9. In face of a considerable reduction in the contribution of anaerobic glycogenolysis to ATP production, it was suggested that, during the last sprint, power output was supported by energy that was mainly derived from PCr degradation and an increased aerobic metabolism.
933 citations
TL;DR: Through physical exercise and training, especially resistance training, it may be possible to prevent sarcopenia and the remarkable array of associated abnormalities, such as type II diabetes, coronary artery disease, hypertension, osteoporosis and obesity.
Abstract: Advancing adult age is associated with profound changes in body composition. One of the most prominent of these changes is sarcopenia, defined as the age-related loss in skeletal muscle mass, which results in decreased strength and aerobic capacity and thus functional capacity. Sarcopenia is also closely linked to age-related losses in bone mineral, basal metabolic rate and increased body fat content. Through physical exercise and training, especially resistance training, it may be possible to prevent sarcopenia and the remarkable array of associated abnormalities, such as type II diabetes, coronary artery disease, hypertension, osteoporosis and obesity. Using an exercise program of sufficient frequency, intensity and duration, it is quite possible to increase muscle strength and endurance at any age. There is no pharmacological intervention that holds a greater promise of improving health and promoting independence in the elderly than does exercise.
517 citations
TL;DR: The findings suggest that FFA uptake in exercising muscle is a saturable process and that the transport capacity is enhanced by training, and that a shift towards a larger fat combustion occurred with endurance training.
Abstract: 1. The influence of training-induced adaptations in skeletal muscle tissue on the choice between carbohydrates (CHO) and lipids as well as the extra- vs. intracellular substrate utilization was investigated in seven healthy male subjects performing one-legged knee-extension exercise. In each subject one of the knee extensors was endurance trained for eight weeks, whereafter the trained (T) and non-trained (NT) thighs were investigated a week apart. 2. The activity of beta-hydroxy-acyl-coenzyme A dehydrogenase (HAD) and capillary density in the knee extensors were significantly larger in T than in NT. 3. During dynamic knee-extension exercise, performed at the same absolute intensity for 2 h, femoral venous blood flow was lower in T than in NT (P < 0.05), but oxygen uptake was similar. 4. Respiratory quotient (RQ) values over the exercising thigh, averaging 0.81 (T) vs. 0.91 (NT; P < 0.05) indicated that a shift towards a larger fat combustion occurred with endurance training. 5. Both free fatty acids (FFA) and serum triacylglycerol contributed to the utilization of fat in NT and T muscles with no significant contribution from muscle fibre triacylglycerol. 6. At high plasma FFA concentrations net uptake of FFA plateaued in NT but not in T muscles. 7. The findings suggest that FFA uptake in exercising muscle is a saturable process and that the transport capacity is enhanced by training. The lower CHO utilization in the T leg was mainly a function of the glycogenolysis of the muscle being reduced. Hormones such as insulin, noradrenaline and adrenaline are unlikely to play a role in this shift as differences in plasma levels during T and NT leg exercise were small and insignificant, implying that local structural and functional adaptations of the training muscle are crucial for the observed shifts in the metabolic response to exercise.
462 citations
TL;DR: The adaptations in aging skeletal muscle to exercise training may prevent sarcopenia, enhance the ease of carrying out the activities of daily living, and exert a beneficial effect on such age-associated diseases as Type II diabetes, coronary artery disease, hypertension, osteoporosis, and obesity.
Abstract: There is an approximate 30% decline in muscle strength and a 40% reduction in muscle area between the second and seventh decades of life Thus, the loss of muscle mass with aging appears to be the major factor in the age-related loss of muscle strength The loss of muscle mass is partially due to a significant decline in the numbers of both Type I and Type II muscle fibers plus a decrease in the size of the muscle cells, with the Type II fibers showing a preferential atrophy There appears to be no loss of glycolytic capacity in senescent skeletal muscle whereas muscle oxidative enzyme activity and muscle capillarization decrease by about 25% Vigorous endurance exercise training in older people, where the stimulus is progressively increased, elicits a proliferation of muscle capillaries, an increase in oxidative enzyme activity, and a significant improvement in VO2max Likewise, progressive resistive training in older individuals results in muscle hypertrophy and increased strength, if the training stimulus is of a sufficient intensity and duration Since older individuals adapt to resistive and endurance exercise training in a similar fashion to young people, the decline in the muscle's metabolic and force-producing capacity can no longer be considered as an inevitable consequence of the aging process Rather, the adaptations in aging skeletal muscle to exercise training may prevent sarcopenia, enhance the ease of carrying out the activities of daily living, and exert a beneficial effect on such age-associated diseases as Type II diabetes, coronary artery disease, hypertension, osteoporosis, and obesity
437 citations
TL;DR: Recommendations for training monitoring can be made, but their relevance in the practice must still be clarified; changes in blood chemistry variables, hormone levels, and nocturnal urinary catecholamine excretion are required.
Abstract: Overtraining is an imbalance between training and recovery, exercise and exercise capacity, stress and stress tolerance. Stress is the sum of training and nontraining stress factors. Peripheral (short-term overtraining, STO) or peripheral and central fatigue may result (long-term overtraining, LTO). STO lasting a few days up to 2 wk is termed overreaching. STO is associated with fatigue, reduction, or stagnation of the 4 LT performance capacity (performance at 4 mmol lactate or comparable criterion), reduction of maximum performance capacity, and brief competitive incompetence. Recovery is achieved within days, so the prognosis is favorable. LTO lasting weeks or months causes overtraining syndrome or staleness. The symptomatology associated with overtraining syndrome has changed over the last 50 yr from excitation and restlessness (so-called sympathetic form) to phlegmatic behavior and inhibition (so-called parasympathetic form). Increased volume of training at a high-intensity level is likely the culprit. The parasympathetic form of overtraining syndrome dominates in endurance sports. Accumulation of exercise and nonexercise fatigue, stagnation, or reduction of the 4 LT performance capacity, reduction in maximum performance capacity, mood state disturbances, muscle soreness/stiffness, and long-term competitive incompetence can be expected. Complete recovery requires weeks and months, so the prognosis is unfavorable. Other optional or further confirmation requiring findings include changes in blood chemistry variables, hormone levels, and nocturnal urinary catecholamine excretion. Based on the findings reported, recommendations for training monitoring can be made, but their relevance in the practice must still be clarified.
366 citations
Book•
09 Dec 1993
TL;DR: This manual provides evidenced-based coverage of the major studies in this area, including a discussion of treadmill scores and expired gas measurements and their ability to enhance the diagnostic capabilities of the exercise test.
Abstract: This is the definitive guide to the clinical aspects of exercise testing and training/research. It offers complete coverage of basic exercise physiology and exercise lab methodology, including proper procedures for expired gas measurement, the computerized ECG, hemodynamics, and more! This manual also provides evidenced-based coverage of the major studies in this area, including a discussion of treadmill scores and expired gas measurements and their ability to enhance the diagnostic capabilities of the exercise test.
275 citations
TL;DR: The results indicate: 1) the LM speed in test 1 corresponds to a maximum lactate steady state speed during constant load exercise; 2) only a slight speed increase above theLM speed results in continuous marked [Lac-]B increase and earlier exhaustion.
Abstract: During an incremental exercise test after a preceding bout of maximum exercise, blood lactate initially decreases to an individual minimum and then increases again. To determine whether this minimum represents an individual equilibrium between lactate production and catabolism during constant load exercise, the following field tests were performed: in 25 runners and five basketball players (series 1) the speed corresponding to the individual lactate minimum (LM) was measured in test 1 (incremental test after exercise induced lactic acidosis). On two occasions, two constant speed runs over 8 km were performed, one using the LM speed (LMS) (test 2), and another at a running speed of 0.2 m.s-1 above the LMS (test 3). Results of runners/basketball players: blood lactate concentration ([Lac-]B) in test 2 changed from 3.6/4.9 mmol.l-1 to 4.0/4.9 mmol.l-1 during the last 4.8 km, in test 3 from 4.6/4.6 mmol.l-1 to 6.5/6.9 mmol.l-1. These results indicate: 1) the LM speed in test 1 corresponds to a maximum lactate steady state speed during constant load exercise; 2) only a slight speed increase above the LM speed results in continuous marked [Lac-]B increase and earlier exhaustion. Variation of the increment duration in 13 males (series 2) shows no change of the LMS using 800-m and 1200-m increments (4.49 and 4.44 m.s-1) but a marked shift to higher speed using 400-m increments (4.96 m.s-1). Effects of low muscle glycogen stores on the LMS were determined in 10 males (series 3).(ABSTRACT TRUNCATED AT 250 WORDS)
257 citations
TL;DR: The training-induced augmentation of early diastolic filling at rest and during exercise may be an important adaptation to allow an increase in stroke volume at rest, cardiac output, and maximal oxygen consumption during exercise.
Abstract: Background. Diastolic filling atrest isaltered markedly withadvancing age. Whether exercise training canimprove diastolic filling atrest orduring exercise ineither healthy older orhealthy youngmenhas notbeendetermined. Thepurpose ofthis study wastodetermine if6months ofaerobic exercise training improves diastolic filling. Methods andResults. Radionuclide diastolic filling parameters weremeasured atrestandduring exercise in14older (age, 60to82years) and17young(age, 24to32years) rigorously screened healthy malesbefore exercise training andin13older and11youngmenafter 6monthsofendurance exercise training. Diastolic filling rates wereexpressed intwoways, asabsolute milliliters ofblood(mL*s'lm-2) andnormalized totheend-diastolic volume. Atbaseline, thepeakearly filling rates werelower intheolder groupcompared withtheyounggroupasexpressed inabsolute milliliters ofblood(older, 85±7 mL *solm-2; young, 173+10mL *s'lm-2; P<.0001) andinend-diastolic volume persecond (1.66+0.11 versus2.55±0.08, P<.0001), whereas thepeakatrial filling rates weregreater inabsolute milliliters of blood(85±5 versus56±7mL-s'lm-2,P=.003) andinend-diastolic volumepersecond(1.70±0.12 versus 0.80+0.06, P<.0001). During exercise, atanygiven heart rate, theolder grouphadalower peak filling ratethantheyounggroup. Also, atpeakexercise, thesingle peakfilling ratewasdecreased inthe older groupinmL.S m-2(384±19 versus565±36 mL-s'm-2, P=.0002) andinend-diastolic volume persecond (6.01±0.25 versus 7.91+0.28 end-diastolic volume persecond, P<.0001). Sixmonths ofintensive aerobic exercise training hadsimilar effects intheoldandyounggroups overall. Maximal oxygenconsumption increased 19%(ANOVAtraining effect, P<.0001) andechocardiographic left ventricular massincreased 8%(ANOVAtraining effect, P=.002). Training increased theresting peak early filling rateinabsolute milliliters ofblood by+14%(ANOVAtraining effect, P=.02). During exercise, thepeakeariy orsingle peakfilling rateatanygiven heart ratewasincreased. Atpeakexercise, thesingle peakfilling ratewasincreased by14%inmL s1 - mI2(ANOVAtraining effect, P=.0004). Theonly age-related differential effect oftraining wasonthepeakatrial filling rateinend-diastolic volume per second, which decreased by27%intheolder group butwasunchanged intheyoung(+5%)(ANOVA young versusolder, P=.001). Theindependent predictors ofa greater maximaloxygenconsumption by multivariate analysis wereahigher peakexercise heart rate, agreater resting peak early filling rate, the exercise trained state, andayounger age. Conclusions. Healthy older menhavereduced early diastolic filling atrest andduring exercise compared withyoungmen.Endurance exercise training enhances early diastolic filling atrestandduring exercise inboththeoldandtheyoung. Training reduces theelevated resting atrial filling rateintheold, whereas theyoungwereunchanged. Thetraining-induced augmentation ofearly diastolic filling atrestandduring exercise maybeanimportant adaptation toallow anincrease instroke volume atrestandanincrease in stroke volume, cardiac output, andmaximaloxygenconsumption during exercise. (Circulation 1993;88:116-126)
256 citations
TL;DR: The results suggest that the most rapid increase in muscle glycogen content during the first 24 h of recovery is achieved by consuming foods with a high GI.
Abstract: The effect of the glycemic index (GI) of postexercise carbohydrate intake on muscle glycogen storage was investigated Five well-trained cyclists undertook an exercise trial to deplete muscle glycogen (2 h at 75% of maximal O2 uptake followed by four 30-s sprints) on two occasions, 1 wk apart For 24 h after each trial, subjects rested and consumed a diet composed exclusively of high-carbohydrate foods, with one trial providing foods with a high GI (HI GI) and the other providing foods with a low GI (LO GI) Total carbohydrate intake over the 24 h was 10 g/kg of body mass, evenly distributed between meals eaten 0, 4, 8, and 21 h postexercise Blood samples were drawn before exercise, immediately after exercise, immediately before each meal, and 30, 60, and 90 min post-prandially Muscle biopsies were taken from the vastus lateralis immediately after exercise and after 24 h When the effects of the immediate postexercise meal were excluded, the totals of the incremental glucose and insulin areas after each meal were greater (P < or = 005) for the HI GI meals than for the LO GI meals The increase in muscle glycogen content after 24 h of recovery was greater (P = 002) with the HI GI diet (106 +/- 117 mmol/kg wet wt) than with the LO GI diet (715 +/- 65 mmol/kg) The results suggest that the most rapid increase in muscle glycogen content during the first 24 h of recovery is achieved by consuming foods with a high GI
239 citations
TL;DR: Overall results showed that the physically active group had significantly higher fitness levels, which were associated with significantly higher levels of heart rate variability, when compared with their sedentary counterparts (p < 0.001), which provides suggestive evidence for habitual aerobic exercise as a beneficial modulator ofheart rate variability in an aging population.
236 citations
TL;DR: There was a close linear relationship between the rates of anaerobic ATP production in muscle and the value estimated for the whole body by the O2 deficit, which suggests that the accumulated O1 deficit is a valid measure of the an aerobic energy release during bicycling.
Abstract: To examine the anaerobic energy release during intense exercise, 16 healthy young men cycled as long as possible at constant powers chosen to exhaust the subjects in approximately 30 s, 1 min, or 2-3 min. Muscle biopsies were taken before and approximately 10 s after exercise and analyzed for lactate, phosphocreatine (PCr), and other metabolites. O2 uptake was measured for determination of the accumulated O2 deficit (a whole body measure of the anaerobic energy release), and this indirect measure of the anaerobic energy release was compared with a direct value obtained from measured muscle metabolites. Muscle lactate concentration rose by 30.0 +/- 1.2 mmol/kg and muscle PCr concentration fell by 12.4 +/- 0.9 mmol/kg during the 2-3 min of exhausting exercise. The anaerobic ATP production was consequently 58 +/- 2 mmol/kg wet muscle mass, which may be the maximum anaerobic energy release for human muscle during bicycling. Because the anaerobic ATP production was 6 and 32% less for 1 min and 30 s of exercise, respectively, than for 2 min of exercise (P < 0.03), 2 min of exhausting exercise may be required for maximal use of anaerobic sources. Lactate production provided three times more ATP than PCr breakdown for all three exercise durations. There was a close linear relationship between the rates of anaerobic ATP production in muscle and the value estimated for the whole body by the O2 deficit (r = 0.94). This suggests that the accumulated O2 deficit is a valid measure of the anaerobic energy release during bicycling.
TL;DR: Strenuous resistive exercise may elevate PEMR for a prolonged period and may enhance postexercise lipid oxidation.
Abstract: Two separate experiments were performed to determine the effect of acute resistive exercise on postexercise energy expenditure in male subjects previously trained in resistive exercise. In experime...
TL;DR: Long-term exercise training had little, if any, effect on improving cognitive function in this older adult sample, but a positive change in self-reported morale was found for the exercise condition.
Abstract: The effect of long-term aerobic training on psychological function was examined in 87 sedentary older adults who engaged in a year-long endurance exercise training program compared with a nonexercising control group. In addition to improved cardiovascular fitness, a positive change in self-reported morale was found for the exercise condition. Of the cognitive functions measured, a significant effect was noted for the Wechsler Memory Scale (WMS) Logical Memory subtest; however, this effect was caused by a decline in performance from pre- to posttesting in the control group. Long-term exercise training had little, if any, effect on improving cognitive function in this older adult sample.
TL;DR: The intervention was not effective in re ducing the number of running injuries; it proved signifi cantly effective (P < 0.05) in improving specific knowl edge of warm-up and cool-down techniques in the intervention group.
Abstract: The purpose of this study was to evaluate the effect of a health education intervention on running injuries. The intervention consisted of information on, and the subsequent performance of, standardized warm-up, cool-down, and stretching exercises. Four hundred twenty-one male recreational runners were matched for age, weekly running distance, and general knowledge of preventing sports injuries. They were randomly split into an intervention and a control group: 167 control and 159 intervention subjects participated throughout the study. During the 16-week study, both groups kept a daily diary on their running distance and time, and reported all injuries. In addition, the intervention group was asked to note compliance with the standardized program. At the end of the study period, knowledge and attitude were again measured. There were 23 injuries in the control group and 26 in the intervention group. Injury incidence for control and intervention subjects was 4.9 and 5.5 running injuries per 1000 hours, respectively. The intervention was not effective in reducing the number of running injuries; it proved significantly effective (P < 0.05) in improving specific knowledge of warm-up and cool-down techniques in the intervention group. This positive change can perhaps be regarded as a first step on the way to a change of behavior, which may eventually lead to a reduction of running injuries.
TL;DR: The topics presented here include brief discussions of the role of exercise in the prevention of weight gain, the effect of exercise on weight loss and maintenance, and exercise and health risks in overweight persons.
Abstract: Physically active men and women may be less likely than their sedentary peers to become overweight. Caloric restriction in overweight persons produces larger weight losses than does exercise, although more of the weight loss by dieting is from lean body mass. The addition of exercise to diet intervention produces more weight loss than does dieting alone. Exercise has a favorable effect on body fat distribution, with a reduction in waist-to-hip ratio with increased exercise. Exercise is especially important in maintaining weight loss in overweight persons. Several prospective studies have shown that overweight men and women who are active and fit have lower rates of morbidity and mortality than overweight persons who are sedentary and unfit. Therefore, exercise is of benefit to overweight persons, even if it does not make them lean. Exercise is recommended as an important part of a weight control program.
TL;DR: Observed increases in GSH oxidation indicate the presence of oxidant stress during prolonged submaximal exercise and similar redox changes on consecutive days of exercise, with recovery to preexercise values within 15 min, indicate no evidence of persistent or cumulative exercise effects on blood glutathione redox status.
Abstract: We tested whether consecutive days of prolonged submaximal exercise would result in oxidant stress sufficient to alter blood antioxidant profiles, progressively change and exhaust blood and plasma antioxidants, and damage RNA. Eleven moderately trained males (24.3 +/- 1.1 yr) exercised 90 min at 65% peak O2 uptake on a cycle ergometer for 3 consecutive days. During day 1 exercise, blood reduced glutathione (GSH) declined 55 +/- 10% and oxidized glutathione (GSSG) increased 28 +/- 7% within 15 min. Total blood glutathione did not significantly change during exercise. GSH levels returned to baseline after 15 min of recovery. On day 3, preexercise GSH and GSSG levels were not significantly different from day 1 preexercise values; essentially similar results were obtained during exercise and recovery. During day 1 exercise, plasma total ascorbate (ascorbate + dehydroascorbate) increased from 53.8 +/- 9.3 to 59.0 +/- 11.3 microM, and percent reduced ascorbate increased from 77.6 +/- 9.3 to 87.3 +/- 9.7%. During day 3 exercise, plasma ascorbate changes were similar to those on day 1. Plasma vitamin E did not change due to exercise on either day 1 or 3. RNA adducts, urinary 8-hydroxyguanosine, did not change significantly due to exercise. Observed increases in GSH oxidation indicate the presence of oxidant stress during prolonged submaximal exercise. Similar redox changes on consecutive days of exercise, with recovery to preexercise values within 15 min, indicate no evidence of persistent or cumulative exercise effects on blood glutathione redox status.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: The results suggest that the guidelines issued by the American College of Obstetricians and Gynecologists may be too stringent for well-conditioned, low-risk, prenatal patients.
Abstract: The value of exercise during pregnancy is controversial; both benefits and risks have been hypothesized. As empiric evidence is scant, the issue was investigated in a prospective study that assessed the impact on fetal growth of maternal exercise in each trimester of pregnancy. A cohort of over 800 prenatal patients was recruited from obstetric practices in Pennsylvania and New York between January 1987 and June 1989. Subjects were interviewed at entry into care and recontacted at 28 and 36 weeks of gestation. In women with prior adverse outcomes or a lack of conditioning, the associations between maternal exercise and fetal growth were equivocal. In fit, low-risk, prenatal patients, exercise was positively associated with fetal growth. With low-moderate exercise levels, the adjusted mean birth weights were about 100 g higher than in nonexercisers (117 g; 95% confidence interval 17 to 217 g). With heavier exercise, larger birth weight increments were seen, close to 300 g in those who exercised throughout pregnancy at levels of about 2,000 kcal/week in energy expenditure (276 g; 95% confidence interval 54 to 497 g). These results suggest that the guidelines issued by the American College of Obstetricians and Gynecologists may be too stringent for well-conditioned, low-risk, prenatal patients. Additional research to define safe limits more precisely seems warranted.
TL;DR: The energetic profile of the exercising bottlenose dolphin resembles that of a relatively sedentary mammal if the exercise variables defined for terrestrial mammals are used, however, the energetic cost of swimming for this cetacean is low in comparison to that of other aquatic and semi-aquatic mammals.
Abstract: Despite speculation about the swimming efficiency of cetaceans, few studies have investigated the exercise physiology of these mammals. In view of this, we examined the physiological responses and locomotor energetics of two exercising adult Tursiops truncatus. Oxygen consumption, heart rate, respiratory rate and post-exercise blood lactate concentration were determined for animals either pushing against a load cell or swimming next to a boat. Many of the energetic and cardiorespiratory responses of exercising dolphins were similar to those of terrestrial mammals. Average heart rate, respiratory rate and oxygen consumption for dolphins pushing against a load cell increased linearly with exercise levels up to 58 kg for a female dolphin and 85 kg for a male. Oxygen consumption did not increase with higher loads. Maximum rate of oxygen consumption (VO2max) ranged from 19.8 to 29.4 ml O2 kg-1 min-1, which was 7-11 times the calculated standard metabolic rate (VO2std) of the dolphins. Blood lactate concentration increased with exercise loads that exceeded VO2max. The maximum lactate concentration was 101.4 mg dl-1 (11.3 mmol l-1) for the male, and 120.6 mg dl-1 (13.6 mmol l-1) for the female. When swimming at 2.1 m s-1, heart rate, respiratory rate and post-exercise blood lactate concentration of the dolphins were not significantly different from values at rest. The cost of transport at this speed was 1.29 +/- 0.05 J kg-1 min-1. The energetic profile of the exercising bottlenose dolphin resembles that of a relatively sedentary mammal if the exercise variables defined for terrestrial mammals are used. However, the energetic cost of swimming for this cetacean is low in comparison to that of other aquatic and semi-aquatic mammals.
TL;DR: The postexercise hypotension results from a persisting peripheral vasodilation despite an increase in renin activity: the persistent sympathetic activity and reduced vagal tone are probably reflex responses to this vasodilatation.
Abstract: Hemodynamics (by aortic Doppler), autonomic factors (power spectrum analysis of heart rate and blood pressure variabilities and baroreceptor sensitivity), and plasma renin activity during the hypotension after maximal exercise were studied in 10 normal subjects on two separate days: a nonexercise (control) day (30 min of upright rest followed by 60 min of supine rest) and an exercise day (maximal upright bicycle exercise followed by 60 min supine) in random order. After exercise, diastolic pressure was reduced for the entire hour, cardiac output increased (+33.8%, P < 0.05), stroke volume was unchanged, and systemic vascular resistance fell (-28.6%, P < 0.01). Indexes of vagal activity were reduced for 60 min, whereas the sympathetic indexes were elevated. Baroreflex sensitivity was also reduced for the first 10 min after exercise. Renin activity increased threefold after exercise. The postexercise hypotension results from a persisting peripheral vasodilation despite an increase in renin activity: the persistent sympathetic activity and reduced vagal tone are probably reflex responses to this vasodilatation.
TL;DR: In spite of a significantly higher blood flow during active recovery, the lactate release was the same whether the leg was resting or performed low‐intensity exercise in the recovery periods, and a variety of factors affect muscle lactate transport, including arterial lactate concentration, muscle perfusion, muscle contraction pattern and muscle morphology.
Abstract: 1. Lactate and H+ efflux from skeletal muscles were studied with the one-legged knee extension model under conditions in which blood flow, arterial lactate and the muscle-blood lactate concentration gradient were altered. Subjects exercised one leg twice to exhaustion (EX1, EX2), separated by a 10 min recovery and a period of intense intermittent exercise. After 1 h of recovery the exercise protocol was repeated with the other leg. Low-intensity exercise was performed with one leg during the recovery periods, while the other leg was passive during its recovery periods. 2. Prior to, and immediately after, EX1 and EX2 and then 3 and 10 min after EX1, a biopsy was taken from the vastus lateralis of the exercised leg for lactate, pH, muscle water and fibre-type determinations. Measurements of leg blood flow and venous-arterial differences for lactate (whole blood and plasma), pH, partial pressure of CO2 (PCO2), haemoglobin, saturation and base excess (BE) were performed at the end of exercise and regularly during the recovery period after EX1. 3. The lactate release was linearly related (r = 0.96; P < 0.05) to the muscle lactate gradient over a range of muscle lactate from 0 to 45 mmol (kg wet wt)-1. The muscle lactate transport was evaluated from the net femoral venous-arterial differences (V-Adiff) for lactate. This rose with increases in the muscle lactate gradients, but as the gradient reached higher levels the V-Adiff lactate responded less than at smaller gradients. Thus, the lactate transport over the muscle membrane appears to be partly saturated at high muscle lactate concentrations. 4. The percentage of slow twitch (%ST) fibres was inversely related to the muscle lactate gradient, but it was not correlated to the lactate release at the end of the exercises. In spite of a significantly higher blood flow during active recovery, the lactate release was the same whether the leg was resting or performed low-intensity exercise in the recovery periods. In several other conditions the muscle lactate and H+ gradients would have predicted that the V-Adiff lactate would have been greater than it actually was. Thus, a variety of factors affect muscle lactate transport, including arterial lactate concentration, muscle perfusion, muscle contraction pattern and muscle morphology. 5. The muscle and femoral venous pH declined during EX1 to 6.73 and 7.14-7.15, respectively, and they increased to resting levels during 10 min of either passive or active recovery.(ABSTRACT TRUNCATED AT 400 WORDS)
TL;DR: Patients with CFS have normal fatigability and metabolism at both the intracellular and systemic levels, normal muscle membrane function and excitation-contraction coupling, and an inability to fully activate skeletal muscle during intense, sustained exercise.
Abstract: We studied whether muscle fatigue, metabolism, or activation are abnormal in the chronic fatigue syndrome (CFS). Subjects performed both an intermittent submaximal and a sustained maximal voluntary isometric exercise protocol of the tibialis anterior muscle. The extent of fatigue, metabolic response, and changes in both M-wave amplitude and twitch tension during exercise were similar in patients and controls. The response to systemic exercise was also normal in the patients. However, voluntary activation of the tibialis was significantly lower in the patients during maximal sustained exercise. The results indicate that patients with CFS have (1) normal fatigability and metabolism at both the intracellular and systemic levels, (2) normal muscle membrane function and excitation-contraction coupling, and (3) an inability to fully activate skeletal muscle during intense, sustained exercise. This failure of activation was well in excess of that found in controls, suggesting an important central component of muscle fatigue in CFS.
TL;DR: Several topics for future research are suggested, including methods to achieve higher aerobic/cardiovascular fitness, reduce secondary cardiovascular/pulmonary disabilities and related health care costs, and promote health, wellness, and an active lifestyle.
Abstract: The purpose of this paper is to review the exercise physiology literature on spinal cord injured individuals with quadriplegia performing voluntary arm exercise and/or electrically stimulated leg exercise The effects of level of injury, active muscle mass, and sympathetic dysfunction on acute physiologic adjustments during exercise testing and chronic training adaptations are discussed Several topics for future research are suggested, including methods to achieve higher aerobic/cardiovascular fitness, reduce secondary cardiovascular/pulmonary disabilities and related health care costs, and promote health, wellness, and an active lifestyle
TL;DR: In heavy-resistance exercise, it appears that the duration of the force production and the length of the rest periods between sets are key exercise variables that influence increases in plasma beta-EP and serum cortisol concentrations.
Abstract: To examine the changes of plasma beta-endorphin (beta-EP) concentrations in response to various heavy-resistance exercise protocols, eight healthy male subjects randomly performed each of six heavy-resistance exercise protocols, which consisted of identically ordered exercises carefully designed to control for the repetition maximum (RM) resistance (5 vs. 10 RM), rest period length (1 vs. 3 min), and total work (joules). Plasma beta-EP, ammonia, whole blood lactate and serum cortisol, creatine kinase, urea, and creatinine were determined preexercise, midexercise, immediately postexercise, and at various time points after the exercise session (5 min-48 h), depending on the specific blood variable examined. Only the high total work-exercise protocol [1 min rest, 10 RM load (H10/1)] demonstrated significant increases in plasma beta-EP and serum cortisol at midexercise and 0, 5, and 15 min postexercise. Increases in lactate were observed after all protocols, but the largest increases were observed after the H10/1 protocol. Within the H10/1 protocol, lactate concentrations were correlated (r = 0.82, P < 0.05) with plasma beta-EP concentrations. Cortisol increases were significantly correlated (r = 0.84) with 24-h peak creatine kinase values. The primary finding of this investigation was that beta-EP responds differently to various heavy-resistance exercise protocols. In heavy-resistance exercise, it appears that the duration of the force production and the length of the rest periods between sets are key exercise variables that influence increases in plasma beta-EP and serum cortisol concentrations. Furthermore the H10/1 protocol's significant challenge to the acid-base status of the blood, due to marked increases in whole blood lactate, may be associated with mechanisms modulating peripheral blood concentrations of beta-EP and cortisol.
TL;DR: To test the hypothesis that differences in left ventricular diastolic performance contribute to the heterogeneity of VO2 max seen in healthy subjects, 57 normal sedentary volunteers and 9 endurance athletes were studied.
Abstract: Previous studies have established that most of the heterogeneity in exercise capacity seen with sedentariness, aging, or physical training can be accounted for by individual differences in the maximal rate of total body oxygen consumption (VO2 max) during dynamic exercise. However, the factors that limit VO2 max in normal subjects remain disputed. To test the hypothesis that differences in left ventricular diastolic performance contribute to the heterogeneity of VO2 max seen in healthy subjects, 57 normal sedentary volunteers (36 +/- 13 yr, range 20-76 yr) and 9 endurance athletes (37 +/- 8 yr, range 26-51 yr) were studied. Aerobic capacity was estimated as VO2 max during a multistage dynamic cycle exercise protocol, whereas resting left ventricular systolic and diastolic function was assessed by two-dimensional and Doppler echocardiography. The relationship of the left ventricular functional indexes with VO2 max was investigated by stepwise multiple regression analysis. VO2 max ranged from 25 to 58 ml.kg-1 x min-1 in sedentary subjects and from 44 to 60 ml.kg-1 x min-1 in athletes. With univariate analysis, significant correlations were observed between VO2 max and age (r = -0.60), maximal heart rate (r = 0.48), maximal work load (r = 0.80), left ventricular volumes at both end diastole (r = 0.51) and end systole (r = 0.62), peak early transmitral filling velocities (r = 0.80), and the ratio of early to late transmitral filling velocities (r = 0.87).(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: The results conform to the idea that a reflex originating in contracting muscle is essential for the normal blood pressure response to dynamic exercise, and that other neural, humoral and haemodynamic mechanisms cannot govern this response.
Abstract: 1 Nine subjects performed dynamic knee extension by voluntary muscle contractions and by evoked contractions with and without epidural anaesthesia Four exercise bouts of 10 min each were performed: three of one-legged knee extension (10, 20 and 30 W) and one of two-legged knee extension at 2 x 20 W Epidural anaesthesia was induced with 05% bupivacaine or 2% lidocaine Presence of neural blockade was verified by cutaneous sensory anaesthesia below T8-T10 and complete paralysis of both legs 2 Compared to voluntary exercise, control electrically induced exercise resulted in normal or enhanced cardiovascular, metabolic and ventilatory responses However, during epidural anaesthesia the increase in blood pressure with exercise was abolished Furthermore, the increases in heart rate, cardiac output and leg blood flow were reduced In contrast, plasma catecholamines, leg glucose uptake and leg lactate release, arterial carbon dioxide tension and pulmonary ventilation were not affected Arterial and venous plasma potassium concentrations became elevated but leg potassium release was not increased 3 The results conform to the idea that a reflex originating in contracting muscle is essential for the normal blood pressure response to dynamic exercise, and that other neural, humoral and haemodynamic mechanisms cannot govern this response However, control mechanisms other than central command and the exercise pressor reflex can influence heart rate, cardiac output, muscle blood flow and ventilation during dynamic exercise in man
TL;DR: To determine whether the ergogenic benefits of carbohydrate (CHO) feedings are affected by preexercise muscle glycogen levels, eight cyclists performed four self-paced time trials on an isokinetic ergometer over a simulated distance of 70 km.
Abstract: To determine whether the ergogenic benefits of carbohydrate (CHO) feedings are affected by preexercise muscle glycogen levels, eight cyclists performed four self-paced time trials on an isokinetic ...
TL;DR: It is suggested that regular exercise does not increase the resistance to stress‐related disease by influencing psychological make‐up or acute psychophysiologic reactivity.
Abstract: This study assessed the association of aerobic fitness with psychological make-up and physiological stress-reactivity in a group of untrained men, as well as the effects of 4 and 8 months of exercise training on these parameters. Psychological assessment included questionnaires on personality (Neuroticism, Type A, Hostility), coping styles (Anger In, Anger Out), negative affect (Depression, Anxiety), and self-esteem. Stress reactivity was measured as the cardiovascular and urinary catecholamine response to two competitive reaction time tasks and the cold pressor test. No cross sectional relationships were found between aerobic fitness, defined as the maximal oxygen consumption during an exhaustive exercise test, and any of the psychological variables. In addition, psychological make-up did not change as a consequence of exercise training. In further contrast to our hypothesis, aerobic fitness was associated with high, rather than low, cardiovascular reactivity. Longitudinal effects of training were limited to a reduction in the overall levels of heart rate and diastolic blood pressure. This suggests that regular exercise does not increase the resistance to stress-related disease by influencing psychological make-up or acute psychophysiologic reactivity.
TL;DR: In this article, the validity of the oxygen debts (alactic and total), maximal blood lactate, and oxygen deficit as measures of anaerobic capacity was examined and the evidence supporting or challenging these measures and providing research foci for future investigations.
Abstract: Anaerobic capacity is defined as the maximal amount of adenosine triphosphate resynthesized via anaerobic metabolism (by the whole organism) during a specific mode of short-duration maximal exercise. This review focuses on laboratory measures which attempt to quantify anaerobic capacity; it examines the evidence supporting or challenging the validity of these measures and provides research foci for future investigations. Discussion focuses on anaerobic capacity measured during running and cycling, since almost all data reviewed were collected using these exercise modes. The validity of the oxygen debts (alactic and total), maximal blood lactate and oxygen deficit as measures of anaerobic capacity was examined. The total oxygen debt, now termed the excess post-exercise consumption, was used in investigations in the 1920s and 1930s to quantify anaerobic energy production; it has since been shown to be an invalid measure of anaerobic capacity, since its magnitude is known to be influenced by factors (e.g. temperature, catecholamines, substrate cycling, lactate glycogenesis) other than those directly involved in anaerobic metabolism. Maximal blood lactate, a measure also used in some of those early investigations, is often used in exercise and sports physiology. Opinion on the utility of maximal blood lactate as an estimate of anaerobic (lactic) capacity is, however, divided. Despite problems interpreting the physiological meaning of maximal blood lactate levels (due primarily to acute changes in blood volume), this measure is still used in both research and athletic settings to describe anaerobic capacity. Its use is supported by (a) the high correlations observed between maximal blood lactate and short-duration exercise performance presumably dependent upon anaerobic capacity, and (b) the higher maximal blood lactate values observed in sprint and power athletes (who would demonstrate higher anaerobic capacities) compared with endurance athletes or untrained people. However, training-induced changes in other performance, physiological and biochemical markers of anaerobic capacity have not always been paralleled by changes in maximal blood lactate; its relatively high variability also diminishes its usefulness to athletic populations, since relatively small changes in anaerobic capacity may not be detected by a measure with such high variability. These latter findings may be partially related to the confounding influence of blood volume which often changes in response to short and long term exercise demands. Maximal blood lactate is known to be influenced by the intensity and duration of the preceding exercise bout; therefore, it is plausible that these factors may also influence the degree to which maximal blood lactate accurately reflects anaerobic capacity.(ABSTRACT TRUNCATED AT 400 WORDS)
TL;DR: It is suggested that CHO supplementation can enhance prolonged continuous variable-intensity exercise by reducing dependency on muscle glycogen as a fuel source.
Abstract: Effects of carbohydrate (CHO) supplementation on muscle glycogen utilization and endurance were evaluated in seven well-trained male cyclists during continuous cycling exercise that varied between low [45% maximal O2 uptake (VO2 max)] and moderate intensity (75% VO2 max). During each exercise bout the subjects received either artificially flavored placebo (P), 10% liquid CHO supplement (L; 3 x 18 g CHO/h), or solid CHO supplement (S; 2 x 25 g CHO/h). Muscle biopsies were taken from vastus lateralis during P and L trials immediately before exercise and after first (124 min) and second set (190 min) of intervals. Subjects then rode to fatigue at 80% VO2 max. Plasma glucose and insulin responses during L treatment reached levels of 6.7 +/- 0.7 mM and 70.6 +/- 17.2 microU/ml, respectively, and were significantly greater than those of P treatment (4.4 +/- 0.1 mM and 17.7 +/- 1.6 microU/ml) throughout the exercise bout. Plasma glucose and insulin responses of S treatment were intermediate to those of L and P treatments. Times to fatigue for S (223.9 +/- 3.5 min) and L (233.4 +/- 7.5 min) treatments did not differ but were significantly greater than that of P treatment (202.4 +/- 9.8 min). After the first 190 min of exercise, muscle glycogen was significantly greater during L (79 +/- 3.5 mumol/g wet wt) than during P treatment (58.5 +/- 7.2 mumol/g wet wt). Furthermore, differences in muscle glycogen concentrations between L and P treatments after 190 min of exercise and in time to fatigue for these treatments were positively related (r = 0.76, P < 0.05). These results suggest that CHO supplementation can enhance prolonged continuous variable-intensity exercise by reducing dependency on muscle glycogen as a fuel source.
TL;DR: Investigation determined that the y-intercept is related to the ability to perform exercise of this nature, and the Wlim-Tlim relationship, VO2max, and total work completed in five 60-s exercise bouts on the cycle ergometer were determined.
Abstract: When exercise to exhaustion is performed using at least two different intensities, work to fatigue (Wlim) can be expressed as a linear function of time to fatigue (Tlim). Whereas the slope of this function is related to endurance ability, the y-intercept is associated with the potential to perform high intensity interval exercise. The purpose of the present investigation was to determine the influence of 8-wk intermittent high-intensity exercise training on the y-intercept derived from the Wlim-Tlim relationship. Eight healthy, untrained male students (19.1 +/- 0.6 yr) completed five 60-s bouts of maximal exercise on the cycle ergometer, three times a week, for 8 wk. Seven controls avoided regular activity for the same period. Prior to and immediately following the training period, the Wlim-Tlim relationship, VO2max, and total work completed in five 60-s exercise bouts on the cycle ergometer were determined. Correlational analysis established relationships between the y-intercept and total work accomplished in the interval test pre- (r = 0.90; P < 0.01; N = 15) and post-training (r = 0.92; P < 0.01; N = 15), confirming that the y-intercept is related to the ability to perform exercise of this nature. Moreover, the "anaerobic" energy yield, calculated from total work and oxygen consumed during the interval exercise, was also related to the y-intercept (r = 0.78; P < 0.01). Interval training significantly increased both the y-intercept (P = 0.0015) and total work accomplished in the interval test (P = 0.001), while the slope of the Wlim-Tlim relationship (critical power) remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)