J R Sutton's research while affiliated with The University of Sydney and other places

Publications (221)

Article
Neuromuscular electrical stimulation has grown in popularity as a therapeutic device for training and an ambulation aid to human paralyzed muscle. Despite its current clinical use, few studies have attempted to concurrently investigate the functional and intramuscular adaptations which occur after electrical stimulation training. Six individuals wi...
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Four individuals with a spinal cord injury underwent 16 weeks of isometric electrical stimulation training to both legs for 60 min, five times per week during the first 5 months after injury, while two SCI individuals remained untrained. A baseline biopsy sample of the vastus lateralis muscle was obtained within 1 month of injury, and another biops...
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The effects of sprint training on muscle metabolism and ion regulation during intense exercise remain controversial. We employed a rigorous methodological approach, contrasting these responses during exercise to exhaustion and during identical work before and after training. Seven untrained men undertook 7 wk of sprint training. Subjects cycled to...
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The purpose of this study was to assess the cardiorespiratory responses during arm exercise with and without concurrent electrical stimulation-induced leg cycling in people with paraplegia. On separate days, 10 subjects with spinal cord injuries (T5-T12) performed either arm cranking (ACE), or simultaneous arm cranking + electrical stimulation-indu...
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Electrical stimulation-induced leg muscle contractions provide a useful model for examining the role of leg muscle neural afferents during low-intensity exercise in persons with spinal cord-injury and their able-bodied cohorts. Eight persons with paraplegia (SCI) and 8 non-disabled subjects (CONTROL) performed passive knee flexion/extension (PAS),...
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To examine the effects of a dilutional mediated decrease in arterial O2 content on muscle metabolic and substrate behaviour during exercise, plasma volume was acutely expanded by either 14% (LOW) or 21% (HIGH) using a 6% dextran solution dissolved in saline (Macrodex) and compared with a control (CON) condition. The exercise protocol, performed by...
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The purpose of this study was to compare the oxygen uptake and heart rate responses during submaximal arm cranking to combined arm cranking + electrical stimulation (ES)-induced leg cycling in individuals with spinal cord injury (SCI). Seven subjects with paraplegia (T4-T12) performed combined arm and leg cycling exercise for 5 min, followed by arm...
Article
Electrical stimulation-induced leg muscle contractions provide a useful model for examining the role of leg muscle neural afferents during low-intensity exercise in persons with spinal cord-injury and their able-bodied cohorts. Eight persons with paraplegia (SCI) and 8 non-disabled subjects (CONTROL) performed passive knee flexion/extension (PAS),...
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Full-text available
This study examined the effects of prolonged exercise on human quadriceps muscle contractile function and homogenate sarcoplasmic reticulum Ca2+ uptake and Ca2+-adenosinetriphosphatase activity. Ten untrained men cycled at 75 +/- 2% (SE) peak oxygen consumption until exhaustion. Biopsies were taken from the right vastus lateralis muscle at rest, ex...
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We investigated the effect of acute, graded increases in plasma volume (PV) by use of dextran on substrate turnover and oxidation during exercise. Eight untrained males [peak aerobic power (VO2peak) = 45.2 +/- 2.2 (SE) ml.kg-1.min-1] performed 2 h of cycle ergometry at 46 +/- 4% of VO2peak on three occasions in a randomized order: 0% PV expansion (...
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To investigate the hypothesis that an increase in plasma volume (PV) is obligatory in reducing the cardiovascular drift that is associated with prolonged exercise following training, a plasma expander (Macrodex) was used to acutely elevate PV. Eight untrained volunteers [maximal oxygen consumption; V˙O2max 45.2 (2.2) ml · kg−1 · min−1, mean (SE)] c...
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To characterize the pattern of plasma beta-endorphin throughout the normal menstrual cycle and test the hypothesis that beta-endorphin concentrations are elevated in trained women with amenorrhea compared with trained and sedentary eumenorrheic women. Cohort analytic study. Academic research environment. Healthy female volunteers: 10 eumenorrheic s...
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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 VO2max 4.10 (SEM 0.32) 1.min-1 were infused (10 ml.kg-1) with a 6% dextran (DEX) solution. These responses were also compared to...
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To investigate the effect of acute graded increases in plasma volume (PV) on fluid and regulatory hormone levels, eight untrained men (peak aerobic power 45.2 +/- 2.2 ml.kg-1.min-1) performed prolonged cycle exercise (46 +/- 4% maximal aerobic power on three occasions, namely, with no PV expansion (Con) and after 14% (Low) and 21% (High) expansions...
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To investigate the hypothesis that increases in plasma volume (PV) are crucial to the cardiovascular and thermal adaptations resulting from training, eight moderately active males (Vo2max = 4.10 +/- 0.32 L/min; mean +/- SE) performed prolonged cycle exercise at 60% Vo2max during a control test (CON) and following infusion (10 mL/kg) of a 6% dextran...
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To test the hypothesis that altitude exposure increases glucose utilization and that this increment is mediated by a beta-adrenergic mechanism, the effects of hypobaric hypoxia and beta-blockade on glucose rates of appearance (Ra), disappearance (Rd), oxidation (Rox), and leg uptake [G = 2(arteriovenous glucose difference)(1 - leg blood flow)] were...
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To determine whether nocturnal periodic breathing (PB) at altitude is due primarily to unstable control of ventilation or the inability to maintain stable sleep states, we performed visual and computer analyses of the electroencephalographic and respiratory records of healthy volunteers at simulated altitudes of 4572, 6100 and 7620 m. Transient aro...
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This study investigated forces applied to the pedal of a cycle ergometer by paraplegic subjects undergoing neuromuscular electrical-stimulation-induced leg exercise. The patterns of force application were compared with those of able-bodied subjects cycling under voluntary muscle control in order to investigate the effectiveness of the muscle stimul...
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Previous studies have indicated that native Tibetans have a larger lung capacity and better maintain arterial O2 saturation during exercise than Han ("Chinese") acclimatized lowlanders. To test if differences in ventilation or alveolar-arterial O2 gradient (A-aDO2) were responsible, we compared 10 lifelong Tibetan and 9 Han acclimatized newcomer re...
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Two recently developed methods for measuring the maximal rate of Ca2+ uptake and Ca2+ ATPase activity (EC 3.1.6.38) in vitro use muscle homogenate rather than isolated sarcoplasmic reticulum (SR). In this study we investigated technical aspects of these assays, including specificity and variability of the assays, the effect of different freezing tr...
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The adaptive responses of the cardiovascular system to altitude appear to be dominated by increased sympathetic neural activity. We investigated the combined roles of the sympathetic and parasympathetic nervous systems (SNS and PNS, respectively) in the early (days 4-5) and subsequent (days 11-12) phases of acclimatization on Pike's Peak, CO (4,300...
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The adaptive responses of the cardiovascular system to altitude appear to be dominated by increased sympathetic neural activity. We investigated the combined roles of the sympathetic and parasympathetic nervous systems (SNS and PNS, respectively) in the early (days 4–5) and subsequent (days 11–12) phases of acclimatization on Pike's Peak, CO (4,300...
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To investigate the relationship between motivational factors and physical and biological causes of heat exhaustion in fun run entrants. Case-control study, The Sun-Herald City to Surf fun runs in Sydney in 1991 and 1992. There were 63,732 race entrants who completed the run and received a finishing time; 79 runners with heat exhaustion and 310 age,...
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The interaction between systems regulating acid-base balance (i.e., CO2, strong ions, week acids) was studied in six subjects for 10 min after 30 s of maximal isokinetic cycling during control conditions (CON) and after 3 days of chronic acetazolamide (ChACZ) administration (500 mg/8 h po) to inhibit carbonic anhydrase (CA). Gas exchange was measur...
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To test the hypothesis that native high-altitude residents have less beta-sympathetic and more parasympathetic tone than newcomers, we compared the effects of beta-sympathetic and parasympathetic blockade in 10 Tibetan and 9 Han acclimatized male residents of Lhasa, Tibet Autonomous Region, China (elevation 3,658 m). Each subject was studied during...
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It has been shown that fluctuation of human heartbeat intervals (heart rate variability, HRV) reflects variations in autonomic nervous system activity. We studied HRV at simulated altitudes of over 6000 m from Holter electrocardiograms recorded during the Operation Everest II study (Houston et al. 1987). Stationary, approximately 30-min segments of...
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The reasons for the reduced exercise capacities observed at high altitudes are not completely known. Substrate availability or accumulations of lactate and ammonium could have significant roles. As part of Operation Everest II, peak oxygen uptakes were determined in five normal male volunteers with use of progressively increasing cycling work loads...
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Elevated pulmonary arterial pressure in high-altitude residents may be a maladaptive response to chronic hypoxia. If so, well-adapted populations would be expected to have pulmonary arterial pressures that are similar to sea-level values. Five normal male 22-yr-old lifelong residents of > or = 3,600 m who were of Tibetan descent were studied in Lha...
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To determine whether the working muscle is able to sustain ATP homeostasis during a hypoxic insult and the mechanisms associated with energy metabolic adaptations during the acclimatization process, seven male subjects [23 +/- 2 (SE) yr, 72.2 +/- 1.6 kg] were given a prolonged exercise challenge (45 min) at sea level (SL), within 4 h after ascent t...
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This article outlines the fundamental physiology and pathology of high altitude. It covers the latest findings from the unique experiment Operation Everest II in which eight persons were gradually decompressed to the "summit" of Mt. Everest and extensive physiologic studies done. The article contains an examination of the various high altitude path...
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Operation Everest II was designed to examine the physiological responses to gradual decompression simulating an ascent of Mt Everest (8,848 m) to an inspired PO2 of 43 mmHg. The principal studies conducted were cardiovascular, respiratory, muscular-skeletal and metabolic responses to exercise. Eight healthy males aged 21-31 years began the "ascent"...
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Evidence is reviewed from our recent (1987-1991) investigations which demonstrate better high-altitude adaptation among Tibetans than in acclimatized newcomers or other lifelong high-altitude residents. Characteristics of oxygen transport contributing to the Tibetans' remarkable exercise performance are described.
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We hypothesized that the increased blood glucose disappearance (Rd) observed during exercise and after acclimatization to high altitude (4,300 m) could be attributed to net glucose uptake (G) by the legs and that the increased arterial lactate concentration and rate of appearance (Ra) on arrival at altitude and subsequent decrease with acclimatizat...
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The hypothesis that high-altitude weight loss can be prevented by increasing energy intake to meet energy requirement was tested in seven men, 23.7 +/- 4.3 (SD) yr, taken to 4,300 m for 21 days. Energy intake required to maintain body weight at sea level was found to be 3,118 +/- 300 kcal/day, as confirmed by nitrogen balance. Basal metabolic rate...
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Frequent sleep disturbances and desaturation during sleep are common at high altitude, but few data are available from the highest altitudes at which humans are known to sleep. Because sleep fragmentation at low altitude may impair mental function and oxygen deprivation produces lasting central nervous system abnormalities, a better understanding o...
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This study examined some of the physiological and performance effects of three different tapers in highly trained athletes. After 8 wk of training, nine male middle-distance runners were randomly assigned to one of three different 7-day tapers: a high-intensity low-volume taper (HIT), a low-intensity moderate-volume taper (LIT), or a rest-only tape...
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To investigate the interactions between the systems that contribute to acid-base homeostasis after severe exercise, we studied the effects of carbonic anhydrase inhibition on exchange of strong ions and CO2 in six subjects after 30 s of maximal isokinetic cycling exercise. Each subject exercised on two randomly assigned occasions, a control (CON) c...
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It seems unlikely that oxygen-limited metabolism explains the increased lactate concentrations in blood or muscle during exercise at high altitude compared with sea level values because: 1. Even marked hypoxia equivalent to that at the summit of Mt. Everest may not be sufficiently severe to impair function or to impair muscle oxidative metabolism m...
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An increase in exercise capacity depends on the magnitude of increase in maximum aerobic capacity. Central and peripheral factors may limit oxygen uptake. Central oxygen delivery depends on cardiac output and maximal arterial oxygen content. Peripheral extraction of the delivered oxygen is expressed as a-v̅ O2. With increasing intensities of exerci...
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SUTTON, J. R. VO2max-new concepts on an old theme. Med. Sci. Sports Exerc., Vol. 24, No. 1, pp. 26-29, 1992. This symposium VO2max-new concepts on an old theme" is dedicated to the memory of Hermann Rahn, whose inspiration has led many young investigators to explore new horizons. In the debate on factors limiting VO2max at altitude Hermann Rahn sti...
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To present a case of severe heat stroke after Rugby League football. A 29-year-old Rugby League forward with a mild infection of the upper respiratory tract collapsed while playing football in late March, when the ambient temperature was 24.1 degrees C and the relative humidity up to 73%. He was initially thought to have sustained a head injury and...
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To examine in athletes the effect of long-term amenorrhea on the skeleton, measurements of calcaneal density and whole body retention of 99mTc-imidodiphosphate were made in 42 women who could be allocated to one of 3 groups defined by their level of physical activity and by menstrual status. There was no difference in bone density between eumenorrh...
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Exercise at high altitude is a stress that activates the sympathoadrenal systems, which could affect responses to acute altitude exposure and promote adaptations during chronic altitude exposure. However, catecholamine levels are not clearly described over time at high altitude. In seven male volunteers (23 yr, 72 kg), resting arterial norepinephri...
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Larger chest dimensions and lung volumes have been reported for Andean high-altitude natives compared with sea-level residents and implicated in raising lung diffusing capacity. Studies conducted in Nepal suggested that lifelong Himalayan residents did not have enlarged chest dimensions. To determine if high-altitude Himalayans (Tibetans) had large...
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Alterations in skeletal muscle structure were investigated in 6 male subjects who underwent 40 days of progressive decompression in a hypobaric chamber simulating an ascent to the summit of Mount Everest. Needle biopsies were obtained from vastus lateralis of 5 subjects before and immediately after confinement in the chamber, and were examined for...
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We hypothesized that the increased exercise arterial lactate concentration on arrival at high altitude and the subsequent decrease with acclimatization were caused by changes in blood lactate flux. Seven healthy men [age 23 +/- 2 (SE) yr, wt 72.2 +/- 1.6 kg] on a controlled diet were studied in the postabsorptive condition at sea level, on acute ex...
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To clarify the role of progressive heavy training on vascular volumes and hematologic status, seven untrained males [maximal O2 uptake (VO2max) = 45.1 +/- 1.1 (SE) ml.kg-1.min-1] cycled 2 h/day at an estimated 62% of VO2max. Training was conducted five to six times per week for approximately 8 wk. During this time, VO2max increased (P less than 0.0...
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Arterial O2 delivery during short-term submaximal exercise falls on arrival at high altitude but thereafter remains constant. As arterial O2 content increases with acclimatization, blood flow falls. We evaluated several factors that could influence O2 delivery during more prolonged submaximal exercise after acclimatization at 4,300 m. Seven men (23...
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To evaluate the hypothesis that altitude exposure and acclimatization result in increased dependency on blood glucose as a fuel, seven healthy males (23 +/- 2 yr, 72.2 +/- 1.6 kg, mean +/- SE) on a controlled diet were studied in the postabsorptive condition at sea level (SL), on acute altitude exposure to 4,300 m (AA), and after 3 wk of chronic al...
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In order to determine the effect of short-term training on central adaptations, gas exchange and cardiac function were measured during a prolonged submaximal exercise challenge prior to and following 10-12 consecutive days of exercise. In addition, vascular volumes and selected haematological properties were also examined. The subjects, healthy mal...
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Attention is drawn to the possible distortion of results in randomized trials of exercise‐centered rehabilitation following myocardial infarction, due to a poor compliance of patients with the assigned form of treatment. The possibility of a post‐hoc classification of exercise behavior is explored, with particular reference to data obtained in the...
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Full-text available
To assess the ventilatory adaptation during gradual ascent to extreme altitude, we studied seven healthy males as part of the 40 d simulated ascent of Mt. Everest in a hypobaric chamber. We measured resting ventilation (VE, l.min-1), arterial oxygen saturation (SaO2%), the ventilatory response to oxygen breathing, isocapnic hypoxic ventilatory resp...
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To evaluate the effect of extreme altitude on cardiac function in normal young men, electrocardiograms were recorded at rest and during maximal exercise at several simulated altitudes up to the equivalent of the summit of Mt. Everest (240 torr or 8,848 m). The subjects spent 40 days in a hypobaric chamber as the pressure was gradually reduced to si...
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To examine the relationship between cardiac filling pressures during exercise in man and oxygen transport, we examined sea level data from Operation Everest II. The results showed that, (1) both right atrial and wedge pressures rose with heavy exercise in normal man, (2) the magnitude of the rise in these filling pressures related both to stroke vo...
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The force output of the ankle dorsiflexors was studied during a 40-day simulated ascent of Mt. Everest in a hypobaric chamber; both electrically activated and maximal voluntary contractions (MVCs) were employed. The purpose of this study was to establish whether, under conditions of progressive chronic hypoxia, there was a decrease in muscle force...
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The effects of gender on substrate utilization during prolonged submaximal exercise were studied in six males and six equally trained females. After 3 days on a controlled diet (so that the proportions of carbohydrate, protein, and fat were identical), subjects ran on a treadmill at a velocity requiring an O2 consumption of approximately 65% of max...
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To assess the possibility that climbing to extremely high altitude may result in hypoxic injury to the brain, we performed neuropsychological and physiologic testing on 35 mountaineers before and 1 to 30 days after ascent to altitudes between 5488 and 8848 m, and on 6 subjects before and after simulation in an altitude chamber of a 40-day ascent to...
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The bias and precision of four different methods for determining O2 saturation (SO2) were evaluated during a study of hypobaric hypoxia conducted with seven male subjects exposed progressively over a 40-day period to simulated altitudes from sea level (760 Torr) to 8,840 m (240 Torr). SO2 of arterial and mixed venous blood samples were measured wit...
Article
A cohort of 1680 runners was enrolled through two community road race events and monitored during a 12-month follow-up period for the occurrence of musculoskeletal injuries. Forty-eight percent of the runners experienced at least one injury, and 54% of these injuries were new; the remainder were recurrences of previous injuries. The risk of injury...
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Several studies have found that caffeine improved endurance exercise performance, but the factors which are responsible for this are not fully understood. Possibilities include an increased free fatty acid (FFA) oxidation and a resultant sparing of muscle glycogen as well as an enhancement of neuromuscular function during exercise. In order to furt...
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Five healthy males performed four 30-s bouts of maximal exercise, separated by 4 min of rest, on an isokinetic cycle ergometer. Arterial blood and urine samples were taken from indwelling catheters at rest, immediately postexercise, and for 90 min of recovery. Inulin was continuously infused to measure glomerular filtration rate (GFR). Arterial pla...