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ABSTRACT: These experiments examined the influence of exercise intensity and duration on antioxidant enzyme activity in locomotor muscles differing in fiber type composition. Nine groups of female Sprague-Dawley rats (age 120 days) exercised 4 days/wk on a motor-driven treadmill for 10 wk. The impact of three levels of exercise intensity (low, moderate, and high: approximately 55, approximately 65, and approximately 75% of maximal oxygen consumption, respectively) and exercise duration (30, 60, and 90 min/day) was assessed. Sedentary animals served as controls. Oxidative capacity in the soleus and white and red gastrocnemius was assessed by measurement of citrate synthase (CS) activity, and antioxidant capacity was evaluated by assay of total superoxide dismutase, catalase, and total glutathione peroxidase (GPX) activities. In all muscles, CS activity increased as a function of exercise duration. Furthermore, in the soleus and white gastrocnemius, the magnitude of the training-induced increase in CS activity was directly related to exercise intensity. In contrast, the peak increase in CS activity in the red gastrocnemius was relatively independent of exercise intensity. Catalase activity was not increased (P > 0.05) in any muscle with training. Training-induced changes in superoxide dismutase and GPX activities were muscle specific; specifically, exercise training significantly (P < 0.05) increased superoxide dismutase activity in the soleus as a function of exercise duration up to 60 min/day. Conversely, training-induced significant (P < 0.05) increases in GPX activity occurred in red gastrocnemius only; the magnitude of the GPX increase was directly related to exercise duration but relatively independent of intensity. These data demonstrate that exercise training-induced changes in muscle antioxidant enzymes are muscle specific.
The American journal of physiology 02/1994; 266(2 Pt 2):R375-80.
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ABSTRACT: We examined the relationship between the intensity and duration of exercise training and the up-regulation of diaphragmatic oxidative and antioxidant enzyme activities. Nine groups of rats exercised for 10 weeks (4 days/week). Groups of animals exercised at three intensities (low, moderate, and high); at each exercise intensity, a group of animals ran at one of three exercise durations (30, 60, and 90 min/day). Sedentary animals served as controls. Muscle oxidative capacity was assessed by citrate synthase (CS) activity while antioxidant capacity was evaluated by total superoxide dismutase (SOD) and total glutathione peroxidase (GPX) activities. All intensities and durations of exercise training promoted significant (P < 0.05) increases in costal diaphragmatic CS, SOD, and GPX activities. Increases in costal CS, SOD, and GPX activity were independent of the exercise intensity and duration. High and moderate intensity exercise of 90 min duration significantly elevated (P < 0.05) crural diaphragm CS activity. Further, high and moderate intensity exercise of durations > or = 60 min promoted significant (P < 0.05) increases in crural diaphragm SOD activities. Exercise did not influence (P > 0.05) crural diaphragm GPX activity. We conclude that the training threshold for up-regulation of oxidative and antioxidant enzyme activities differs between the costal and crural diaphragm.
Respiration Physiology 02/1994; 95(2):227-37.
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ABSTRACT: Controversy exists as to the effect of endurance training on myocardial antioxidant enzyme activity. These experiments sought to clarify this issue by examining antioxidant enzyme activities in the rat ventricular myocardium in response to different intensities and durations of exercise training. Female Fischer-344 rats (120 days old) were assigned to either a sedentary control group or one of nine exercise training groups. Animals were exercised on a motorized treadmill for 10 wk; combinations of three durations (30, 60, and 90 min/day), and three levels of exercise intensity (low, moderate, and high) were studied. Exercise training did not alter (P > 0.05) citrate synthase, catalase, or glutathione peroxidase activities in the right or left ventricle. In contrast, high-intensity exercise (all durations) and moderate-intensity exercise (90 min/day) resulted in a significant increase (P < 0.05; +28-30%) in right ventricular superoxide dismutase (SOD) activity. Similarly, high-intensity exercise training (all durations) resulted in a significant elevation (P < 0.05; +14-26%) of left ventricular SOD activity. Furthermore, low- and moderate-intensity exercise training of long duration (i.e., 60-90 min/day) resulted in significant increases (P < 0.05; +10-23%) in left ventricular SOD activity. These data support the hypothesis that high-intensity exercise (> or = 30 min/day) or moderate-intensity exercise of long duration (> or = 60 min/day) is effective in upregulating SOD activity in the ventricular myocardium.
The American journal of physiology 01/1994; 265(6 Pt 2):H2094-8.
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ABSTRACT: This article reviews the principles of pulse oximetry and assesses the accuracy of pulse oximeter measurements obtained during exercise, based on reports of 10 studies that evaluated 24 pulse oximeters. Nine of the studies used cycle exercise, and 1 study utilized treadmill running for mode of activity. Subject populations included patients with cardiovascular or pulmonary disorders, nondisabled individuals, and athletes. Studies were performed under normoxic and hypoxic conditions, and 5 of the 10 studies validated 18 pulse oximeters at arterial oxyhemoglobin saturation (%HbO2) levels of < or = 78%. Sixteen of the 24 pulse oximeters (67%), from 7 of the 10 studies, observed pulse oximeter estimates (%SpO2) during exercise to be accurate, at least when %HbO2 was > or = 85% in nonsmokers. However, the degree of accuracy of the pulse oximeters was variable, even among the same models. Recent studies suggest the current generation of finger-probe-equipped pulse oximeters may be more accurate than ear-probe-equipped models. We recommend that clinicians carefully secure the probe; monitor signal strength; be wary of %SpO2 values of < or = 68% to 78% to avoid undetected severe hypoxemia; and be alert to whether a patient is a smoker, in which case %SpO2 will likely be overestimated. Researchers interested in using pulse oximeter estimates should validate their particular pulse oximeter(s) via arterial blood sampling.
Physical Therapy 01/1994; 74(1):40-9. · 3.11 Impact Factor
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ABSTRACT: These experiments tested the hypothesis that high intensity (interval) training is superior to moderate intensity (continuous) exercise training in the upregulation of antioxidant enzyme activity in skeletal muscle. To test this postulate, we examined changes in oxidative and antioxidant enzyme activities in rat skeletal muscle following 12 wk of either interval (6 x approximately 5-min intervals at approximately 80-95% VO2max) or continuous (45 min at approximately 70% VO2max) exercise training. Both continuous and interval training resulted in significantly elevated (P < 0.05) succinate dehydrogenase (SDH) and 3-hydroxyacyl-CoA-dehydrogenase (HADH) activities in the gastrocnemius (G) and soleus (S) muscles compared with controls. SDH and HADH activities in the G and S muscles did not differ between the two exercise groups. Glutathione peroxidase (GPX) activity exceeded controls (P < 0.05) in only the interval trained S muscle. Soleus superoxide dismutase (SOD) activity was higher (P < 0.05) in both exercise groups compared with controls. No differences in SOD activity existed between interval and continuous trained animals. We conclude that when matched for oxygen cost, interval and continuous exercise training result in similar increases in SOD activity. However, high intensity interval exercise is superior to moderate intensity continuous exercise in the promotion of GPX activity in the S.
Medicine & Science in Sports & Exercise 11/1993; 25(10):1135-40. · 4.43 Impact Factor
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ABSTRACT: Limited information exists concerning the effects of high intensity interval exercise training (HIET) on metabolic alterations in both inspiratory and expiratory muscles. To test the hypothesis that HIET will improve the oxidative capacity of the diaphragm and major expiratory muscles, we examined Krebs cycle and beta oxidation enzyme activities in the diaphragm and three groups of expiratory (abdominal) muscles in rats subjected to 12 weeks (5 days.wk-1) of treadmill exercise. Two groups of female Sprague-Dawley rats (age ca 120 days) were studied: (1) HIET group (n = 10; animals performed 6 x ca 5-min running intervals.day-1 at ca 90-95% VO2max); (2) sedentary control group (n = 7). When compared to controls, HIET resulted in significantly elevated (P less than 0.05) activities of 3-hydroxy-acyl-Co-A dehydrogenase (HADH) and citrate synthase (CS) in the costal diaphragm, rectus abdominus, external obliques, and the plantaris muscles. In contrast, training did not increase (P greater than 0.05) the activities of CS or HADH in the crural diaphragm or the internal obliques/transversus abdominus muscles. By comparison, the training-induced increases in oxidative capacity (e.g., CS activity) in the costal diaphragm, rectus abdominus, and external obliques were relatively small (ca 23, 10, 12%, respectively) when contrasted to the exercise-induced increase in CS activity in the plantaris muscle (ca 47%). We conclude that HIET results in small but significant improvements in the oxidative and beta oxidation capacities of the costal diaphragm and at least two abdominal expiratory muscles.
Respiration Physiology 09/1992; 89(2):169-77.
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ABSTRACT: Limited data exist concerning exercise training-induced alterations in skeletal muscle oxidative and antioxidant enzyme activity in senescent animals. Therefore, the purpose of this study was twofold: 1) to examine the exercise training-induced changes in oxidative and antioxidant enzyme activity in skeletal muscle of old rats; and 2) to critically analyze the relationship between oxidative and antioxidant enzyme activities in skeletal muscle in both trained and untrained senescent rats. Female Fischer-344 rats (approximately 24-mo-old) were divided into 1) exercised trained (ET; n = 10) and 2) sedentary (S; n = 6) groups. The ET rats performed a 10-week training program of treadmill exercise (approximately 60 min, 5 days/wk). Training significantly (p less than 0.05) improved VO2max (delta 22.8%) in the ET rats above their age-matched controls. Further, the ET group had significantly elevated (p less than 0.05) activities of succinate dehydrogenase (SDH) in the soleus and red gastrocnemius (RG) muscles as well as greater (p less than 0.05) 3-hydroxyacyl-CoA dehydrogenase (HADH) activity in the RG when compared to the S group. However, training did not alter (p greater than 0.05) HADH activity within the white gastrocnemius (WG) or soleus muscles. Activity of the antioxidant enzyme, glutathione peroxidase (GPX) was higher (p less than 0.05) in the soleus and RG in ET rats when compared to the S rats; in contrast, training did not alter (p less than 0.05) GPX activity in the WG. Finally, the correlation coefficients between SDH and GPX activities (combined ET and S groups) for the RG, WG, and soleus muscles were r = .73, .17 and .36, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
International Journal of Sports Medicine 08/1992; 13(5):412-6. · 2.43 Impact Factor
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ABSTRACT: We investigated age-related changes in antioxidant, glycolytic, beta-oxidation, and tricarboxylic acid cycle enzyme activity in the diaphragm and plantaris muscle of female Fischer 344 rats. Tissue samples from the costal and crural diaphragm and plantaris muscle were obtained from 30 animals in the following age groups: 1) 6 mo old (n = 10), 2) 26 mo old (n = 10), and 3) 30 mo old (n = 10). Aging had no effect (P greater than 0.05) on the activities of citrate synthase (CS) and 3-hydroxyacyl-CoA dehydrogenase (HADH) in the costal or crural diaphragm. Similarly, no age-related differences existed (P greater than 0.05) in the crural diaphragm in lactate dehydrogenase (LDH) or glutathione peroxidase (GPX) activity. In contrast, the activities of LDH and GPX were significantly (P less than 0.05) higher in the costal diaphragm in the 30- than in the 6-mo old animals. In addition, the ratio of LDH to CS activity increased (P less than 0.05) as a function of age in the costal diaphragm. Conversely, the ratio of CS to GPX activity in the costal diaphragm was lower (P less than 0.05) in the 30- than in the 6-mo old animals. No significant (P greater than 0.05) age-related differences existed in LDH-to-CS or CS-to-GPX activity ratios in the crural diaphragm. Finally, aging resulted in a significant decrease (P less than 0.05) in the activities of LDH, CS, and HADH in the plantaris muscle. These data demonstrate that, unlike many hindlimb locomotor muscles, the oxidative capacity of the Fischer 344 rat diaphragm does not decrease in old age.
Journal of Applied Physiology 07/1992; 72(6):2317-21. · 3.75 Impact Factor
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ABSTRACT: Recent evidence demonstrates that endurance exercise training improves the oxidative capacity of the major mammalian inspiratory muscle (e.g., costal diaphragm). In contrast, no data exist concerning the effects of exercise training on abdominal expiratory muscles. We tested the hypothesis that 12 wk of endurance exercise training would significantly increase the activity of selected beta oxidation and Krebs cycle enzymes of abdominal expiratory muscles of the rat. To test this hypothesis two groups of female Sprague-Dawley rats were studied: group 1, continuous exercise training (n = 13); and group 2, sedentary control (n = 6). Exercise trained animals ran 5 d.wk-1 on a motorized treadmill for 45 min.d-1 at approximately 75-80% VO2max. When compared with controls, exercise training resulted in elevated (P less than 0.05) activities of 3-hydroxy-acyl-Co-A dehydrogenase (HADH) and citrate synthase (CS) in two abdominal expiratory muscles (rectus abdominus and external obliques). In contrast, training did not alter (P greater than 0.05) CS or HADH activity in the internal obliques/transversus abdominus muscles. In general, the training-induced increases in expiratory muscles CS activity were relatively small (approximately 10-13%) when compared with the training-induced increase in CS activity in the plantaris muscle (approximately 44%). These data demonstrate that continuous exercise training results in small but statistically significant improvements in the oxidative and beta oxidation capacities of expiratory muscles.
Medicine & Science in Sports & Exercise 06/1992; 24(5):551-5. · 4.43 Impact Factor
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ABSTRACT: We examined the oxidative and antioxidant enzyme activities in respiratory and locomotor muscles in response to endurance training in young and aging rats. Young adult (4-mo-old) and old (24-mo-old) female Fischer 344 rats were divided into four groups: 1) young trained (n = 12), 2) young untrained (n = 12), 3) old trained (n = 10), and 4) old untrained (n = 6). Both young and old endurance-trained animals performed the same training protocol during 10 wk of continuous treadmill exercise (60 min/day, 5 days/wk). Compared with young untrained animals, the young trained group had significantly elevated (P less than 0.05) activities of 3-hydroxyacyl-CoA dehydrogenase (HADH), glutathione peroxidase (GPX), and citrate synthase (CS) in both the costal diaphragm and the plantaris muscle. In contrast, training had no influence (P greater than 0.05) on the activity of lactate dehydrogenase within the costal diaphragm in young animals. In the aging animals, training did not alter (P greater than 0.05) activities of CS, HADH, GPX, or lactate dehydrogenase in the costal diaphragm but significantly (P less than 0.05) increased CS, HADH, and GPX activities in the plantaris muscle. Furthermore, training resulted in higher activities of CS and HADH in the intercostal muscles in the old trained than in the old untrained animals. Finally, activities of CS, HADH, and GPX were significantly (P less than 0.05) lower in the plantaris in the old untrained than in the young untrained animals; however, CS, HADH, and GPX activities were greater (P less than 0.05) in the costal diaphragm in the old sedentary than in the young untrained animals.(ABSTRACT TRUNCATED AT 250 WORDS)
Journal of Applied Physiology 04/1992; 72(3):1068-73. · 3.75 Impact Factor
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ABSTRACT: Much of the previous research efforts aimed at determining those physiological characteristics that contribute to distance running success have centered around distances greater than 1500 meters with little attention to events such as the 800 meter run. Therefore, this investigation examined the relationship between selected physiological and body composition, characteristics and performance in an 800 meter run. Measurements of body composition, VO2max, running economy, and performance times for 100 and 300 meter dashes were obtained on 11 male track athletes. Stepwise multiple regression analysis was performed using 800 meter race time as the dependent variable. Although the combination of 300 and 100 meter run times, percent body fat, running economy and VO2 max as independent variables accounted for the greatest amount of total variance (r2 = .89), the additional variance explained by the model did not increase significantly (p greater than 0.05), when VO2max, percent body fat, and running economy were added to a model which contained 300 and 100 meter run time (r2 = .85) as the explanatory variables. These data offer additional support for the notion that much of the intramuscular ATP produce and utilized during an 800 meter run comes from anaerobic metabolic pathway.
The Journal of sports medicine and physical fitness 01/1992; 31(4):499-504. · 0.85 Impact Factor
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ABSTRACT: This study compared the efficacy of a 7% glucose polymer beverage containing electrolytes (GP) versus a nonnutrient, nonelectrolyte placebo (P) in maintaining blood homeostasis during recovery from football and determined whether consumption of the GP beverage improved anaerobic performance immediately after football competition when compared with the placebo. Forty-four high school football players participated in a 50-play scrimmage designed to simulate game conditions. At each of six periods before and during the scrimmage, players consumed 170 ml of the GP or P beverage. Eight maximal-effort 40-yd sprints (40-sec rest intervals) were performed before and after the scrimmage to assess the decrement in anaerobic performance from the scrimmage. Venous blood samples were drawn before and after the scrimmage and analyzed. The pre- to postscrimmage differences in mean and peak sprint velocities did not differ between treatments, nor did body weight and plasma. In contrast, the percent decrease in plasma volume was significantly greater in the P group. Postscrimmage increases in glucose and insulin were greater in the GP group. These data suggest that CHO-electrolyte drinks do not prevent a decline in anaerobic performance when compared to water, but a CHO-electrolyte drink is more effective in maintaining PV than water during recovery from anaerobic exercise.
International journal of sport nutrition 07/1991; 1(2):178-91.
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ABSTRACT: Examination of the alveolar-to-arterial O2 tension (A-a PO2 difference) provides a method of examining the efficiency of pulmonary gas exchange during exercise. At present, considerable confusion exists as to the exact pattern of the A-a PO2 difference during incremental exercise. We tested the hypothesis that the A-a PO2 difference during incremental exercise is alinear with respect to metabolic rate. Measurements of the A-a PO2 difference were made on six healthy male subjects during incremental exercise under sea level conditions (PIO2 = 149 torr). An alinear model best described the relationship between the A-a PO2 difference and metabolic rate; only small increases in the A-a PO2 difference occurred at low work rates followed by a rapid increase at higher work rates. The existence of a "A-a PO2 difference threshold" was mathematically confirmed by the use of a computer algorithm to define inflection points. These data provide evidence that the relationship between the A-a PO2 difference and metabolic rate is alinear and that a metabolic threshold exists for a rapid increase in the A-a PO2 difference. We conclude that the efficiency of pulmonary gas exchange during exercise is unaltered from rest during low-to-moderate power outputs, however, high intensity exercise compromises pulmonary gas exchange efficiency as evidenced by a significant widening of the A-a PO2 difference.
International Journal of Sports Medicine 07/1991; 12(3):313-8. · 2.43 Impact Factor
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ABSTRACT: Limited data exist concerning the effect of growth and aging on the metabolic properties of the diaphragm. Therefore, we investigated age-related changes in protein concentration and glycolytic and Krebs cycle enzyme activity in the diaphragm as well as the plantaris muscle of female Sprague-Dawley rats ranging in age from 1 to 12 months. Samples from the costal and crural diaphragm and the plantaris muscle were obtained from 38 animals in the following age groups: (1) 1 month old (N = 7); (2) 4 month old (N = 6) (3) 6 month old (N = 13); and (4) 12-month-old (N = 12). Body weight and diaphragm weight increased rapidly by a factor of 6 and in parallel during 1-4 months postpartum before reaching a plateau at 6 months of age. No significant difference (P greater than 0.05) existed in the ratio of diaphragm weight to body weight among age groups. Protein concentration was significantly higher (P less than 0.05) in the costal diaphragm and plantaris at 4 and 6 months when compared to 1 and 12 months of age. In the crural diaphragm, protein concentration was significantly lower (P less than 0.05) at 1 month postpartum when compared to all other age groups. Succinate dehydrogenase (SDH) activity was significantly higher (P less than 0.05) at 1 month of age in the plantaris, the costal diaphragm and the crural diaphragm when compared to older animals. In contrast, the activity of lactate dehydrogenase (LDH) in the plantaris, the costal diaphragm and the crural diaphragm was significantly lower (P less than 0.05) in the 1-month-old animals when compared to all other ages.(ABSTRACT TRUNCATED AT 250 WORDS)
Respiration Physiology 02/1991; 83(1):1-9.
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ABSTRACT: This study characterized the biochemical properties of the rat diaphragm by measuring the activities of selected citric acid cycle and glycolytic enzymes. The diaphragm was removed from 10 female Sprague-Dawley rats (180 days old) and dissected into five discrete anatomic regions: crural (region 1), left posterior costal (region 2), left anterior costal (region 3), right anterior costal (region 4), and right posterior costal (region 5). Sections were assayed for total protein concentration and the activities of succinate dehydrogenase (SDH) and lactate dehydrogenase (LDH). The SDH activity in the crural region was approximately 18% lower (P less than 0.05) than that in any costal region. Furthermore, protein concentration was significantly lower (P less than 0.05) in the crural region compared with all costal regions. In contrast, costal regions 2-5 did not significantly differ from each other in protein concentration or SDH activity. LDH activity did not differ significantly (P greater than 0.05) between regions. Finally, the LDH-to-SDH activity ratio was significantly higher (P less than 0.05) in the crural diaphragm compared with all costal regions. We conclude that the crural region of the rat diaphragm is significantly lower in oxidative capacity than all the costal regions. Investigators who use a rodent model to study diaphragmatic function and plasticity should consider the oxidative heterogeneity of the diaphragm when designing experiments.
Journal of Applied Physiology 09/1990; 69(2):648-50. · 3.75 Impact Factor
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ABSTRACT: Controversy exists concerning the adaptability of mammalian respiratory muscles in response to endurance training. We examined the effects of 8 wk of progressive treadmill exercise (45 min/day 5 days/wk) on the biochemical adaptations of rat diaphragm and intercostal muscles. Female Sprague-Dawley rats were randomly assigned to a sedentary control (n = 10) or an exercise-training group (n = 10). Endurance training resulted in an enhanced oxidative capacity in the anterior costal diaphragm as evidenced by a 29% increase (P less than 0.05) in the activity of succinate dehydrogenase (SDH) in trained animals compared with controls (4.15 +/- 0.13 vs. 3.21 +/- 0.17 mumol.g-1.min-1). Similarly, SDH activity in the intercostal muscles was 32% greater (P less than 0.05) in the trained animals than in the untrained animals (1.72 +/- 0.11 vs. 1.30 +/- 0.06 mumol.g-1.min-1). In contrast, the crural region of the diaphragm showed no significant increase (P greater than 0.05) in oxidative capacity as a result of the training program (3.28 +/- 0.12 vs. 3.13 +/- 0.18). Furthermore, training did not alter (P less than 0.05) lactate dehydrogenase activity in the intercostals or in the crural or the costal diaphragm. These data demonstrate that the oxidative capacity of the costal diaphragm and the intercostal muscles can be enhanced by increasing respiratory loads via regular endurance exercise. We speculate that the lack of metabolic adaptation in the crural region of the diaphragm was not due to limited plasticity of the fibers in this area but to failure to the exercise-training program to provide the appropriate stimulus for cellular adaptation.
Journal of Applied Physiology 06/1990; 68(5):2114-8. · 3.75 Impact Factor
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ABSTRACT: The purpose of these experiments was to examine the influence of various fluid replacement drinks on exercise-induced disturbances in homeostasis during heavy exercise. Nine trained cyclists performed constant load exercise on a cycle ergometer to fatigue on three occasions with 1-week separating experiments. The work rate was set initially at approximately 85% of VO2max (range 82-88%) with fatigue being defined as a 10% decline in power output below the initial value. During each experiment subjects consumed one of the following three beverages prior to and every 15 min during exercise: (1) non-electrolyte placebo (NEP; 31 mosmol.kg-1); (2) glucose polymer drink containing electrolytes (GP; 7% CHO, 231 mosmol.kg-1), and (3) electrolyte placebo drink without carbohydrate (EP; 48 mosmol.kg-1). Both the GP and EP beverage contained sodium citrate/citric acid (C) as a flavoring agent while C was not contained in the NEP drink. Although seven of nine subjects worked longer during the GP and EP treatment when compared with the NEP trial, the difference was not significant (P greater than 0.05). No differences (P greater than 0.05) existed between the GP and EP treatments in performance time. Exercise changes in rectal temperature, heart rate, delta % plasma volume and plasma concentrations of total protein, free fatty acids, glucose, lactate, potassium, chloride, calcium, and sodium did not differ (P greater than 0.05) between trials.(ABSTRACT TRUNCATED AT 250 WORDS)
European Journal of Applied Physiology and Occupational Physiology 02/1990; 60(1):54-60.
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ABSTRACT: Recent evidence suggests that heavy exercise may lower the percentage of O2 bound to hemoglobin (%SaO2) by greater than or equal to 5% below resting values in some highly trained endurance athletes. We tested the hypothesis that pulmonary gas exchange limitations may restrict VO2max in highly trained athletes who exhibit exercise-induced hypoxemia. Twenty healthy male volunteers were divided into two groups according to their physical fitness status and the demonstration of exercise-induced reductions in %SaO2 less than or equal to 92%: 1) trained (T), mean VO2max = 56.5 ml.kg-1.min-1 (n = 13) and 2) highly trained (HT) with maximal exercise %SaO2 less than or equal to 92%, mean VO2max = 70.1 ml.kg-1.min-1 (n = 7). Subjects performed two incremental cycle ergometer exercise tests to determine VO2max at sea level under normoxic (21% O2) and mild hyperoxic conditions (26% O2). Mean %SaO2 during maximal exercise was significantly higher (P less than 0.05) during hyperoxia compared with normoxia in both the T group (94.1 vs. 96.1%) and the HT group (90.6 vs. 95.9%). Mean VO2max was significantly elevated (P less than 0.05) during hyperoxia compared with normoxia in the HT group (74.7 vs. 70.1 ml.kg-1.min-1). In contrast, in the T group, no mean difference (P less than 0.05) existed between treatments in VO2max (56.5 vs. 57.1 ml.kg-1.min-1). These data suggest that pulmonary gas exchange may contribute significantly to the limitation of VO2max in highly trained athletes who exhibit exercise-induced reductions in %SaO2 at sea level.(ABSTRACT TRUNCATED AT 250 WORDS)
Journal of Applied Physiology 07/1989; 66(6):2491-5. · 3.75 Impact Factor
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ABSTRACT: Evidence exists to indicate that prolonged ventilatory work fatigues respiratory muscles and may limit exercise tolerance. However, the effects of short-duration, high-intensity ventilatory work on subsequent exercise remains in question. We tested the hypothesis that intense short-term volitional hyperpnea would result in respiratory muscle fatigue and would therefore hinder subsequent exercise tolerance. Pulmonary function was determined in ten healthy, male subjects before and after two constant load exercise tests to exhaustion on a cycle ergometer. Test 1 was a preliminary test to determine VO2max, peak exercise VE, and peak exercise power output. Test 2 was a constant load (85% peak power output) exercise test to exhaustion. Test 3 was identical to test 2 but was preceded by 10 min of volitional, isocapnic hyperpnea (85% of peak exercise V.E) at a controlled frequency and tidal volume. Pulmonary function measures (FVC, FEV1, FEV1/FVC, and peak flow) were not significantly (P less than 0.05) altered by the volitional hyperpnea. Ventilation and gas exchange variables (VO2, VE, f, end-tidal PO2 and PCO2, VE/VO2, VE/VCO2, %SaO2) during exercise and time to exhaustion were not significantly (P less than 0.05) different between treatments. These experiments failed to show any effect of short-term ventilatory work on pulmonary function or subsequent exercise performance.
International Journal of Sports Medicine 03/1989; 10(1):48-52. · 2.43 Impact Factor
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ABSTRACT: The purpose of these experiments is to test the hypothesis that exercise-induced hypoxemia at sea level in highly trained athletes might be exacerbated during acute hypoxia and therefore result in correspondingly larger decrements in maximal O2 uptake (VO2max) compared with less trained individuals. Thirteen healthy male volunteers were divided into two groups according to their level of fitness: 1) trained endurance athletes (T) (n = 7), with a VO2max range of 56-75 ml.kg-1.min-1 and 2) untrained individuals (UT) (n = 6), with a VO2max range of 33-49 ml.kg-1.min-1. Subjects performed two incremental cycle ergometry tests to determine VO2max under hypoxic conditions [14% O2-86% N2, barometric pressure (PB) = 760 Torr] and normoxic conditions (21% O2-79% N2, PB = 760 Torr). Tests were single blind, randomly administered, and separated by at least 72 h. Mean percent oxyhemoglobin saturation (%SaO2) during maximal exercise under hypoxic conditions was significantly (P less than 0.05) lower in the T group (77%) compared with the UT group (86%). Furthermore, the T group exhibited larger decrements (P less than 0.05) in VO2max (normoxic-hypoxic) compared with the UT group. Finally, a significant linear correlation (r = 0.94) existed between normoxic VO2max (ml.kg-1.min-1) and delta VO2max (normoxic-hypoxic). These data suggest that highly T endurance athletes suffer more severe gas exchange impairments during acute exposure to hypoxia than UT individuals, and this may explain a portion of the observed variance in delta VO2max among individuals during acute altitude or hypoxia exposure.
Journal of Applied Physiology 05/1988; 64(4):1486-92. · 3.75 Impact Factor
