Effects of acute prednisolone intake on substrate utilization during submaximal exercise

We examined the hypothesis that acute therapeutic glucocorticoid intake could change the contribution of fat and carbohydrate (CHO) in energy production during exercise. Nine healthy recreationally-trained male subjects twice performed submaximal exercise (60 min at 60 % VO2max) after ingestion of placebo (Pla) or 20 mg of prednisolone (Pred), according to a double blind and randomized protocol. Respiratory exchange was monitored during exercise and blood samples were collected at rest, every 10 min during exercise and after 5, 10, and 20 min of passive recovery. Pred intake significantly increased total energy expenditure during exercise, but CHO oxidation was lower and fat oxidation higher after Pred vs. Pla. ACTH and IL-6 concentrations were significantly decreased with Pred during exercise, whereas no variations were found in GH, insulin, blood glucose, and lactate between the 2 treatments. In conclusion, it appears that acute prednisolone systemic administration does reduce total carbohydrate oxidation during submaximal exercise. Further studies are necessary to clarify the mechanisms involved and to determine whether this modification in the substrate oxidation balance under glucocorticoid administration in recreationally-trained male subjects could result in a competitive advantage in elite athletes.     

The effect of food matrix on carbohydrate utilization during moderate exercise.

The effect of food matrix on carbohydrate utilization during moderate exercise. Med. Sci. Sports Exerc., Vol. 24, No. 3, pp. 320-326, 1992. To determine the effect of food type and form on the rate of assimilation and utilization of a meal given before exercise, five physically active adult males walked for 4 h on a 10% uphill graded treadmill at 40% VO2max. After a 12-h fast, and 30 min before exercise, subjects ingested 70 g of liquid glucose (G), a refined "hot cereal" (R), a refined "hot cereal" with water-soluble fiber (R/F), an oat bar (O), or placebo (P). Meals R/F, R, and O had significantly lower (P less than 0.05) peak plasma glucose responses than meal G (0.8, 0.9, 1.0, and 2.4 mmol.l-1, respectively). Meals R, O, and R/F had significantly lower (P less than 0.01) peak insulin responses than meal G (135, 150, 190, and 340 pmol.l-1, respectively). All meals except P contained an extrinsic tracer of 200 mg UL-13C-glucose. Mean (+/- SD) total recovery of the administered dose of 13C for all meals was 81 +/- 2%. Both O (34 +/- 4% dose.h-1) and R/F (30 +/- 3% dose.h-1) had significantly lower peak recoveries than did meal G (41 +/- 5% dose.h-1). Meal R/F had a significantly lower (P less than 0.05) rate of exogenous glucose oxidation than meal G during the first hour of exercise. These data suggest that meal R/F slows the rate of assimilation and utilization of exogenous glucose, but does not alter the cumulative 4-h utilization.     

Effect of exercise training on physical activity and substrate utilization in the elderly

This study examined the effect of training on physical activity and substrate utilization in the elderly. Before the start, in week 6 and week 12 (T0, T6 and T12) data on physical fitness, physical activity and substrate utilization were collected in the exercise (11 males, 11 females; 63 +/- 8yrs) and control group (6 males, 5 females; 59 +/- 4yrs). Physical activity was registered with a tri-axial accelerometer and substrate utilization was calculated from resting respiratory exchange ratio (RER) by indirect calorimetry. At T6 physical activity on training days was significantly higher than on non-training days (33.4 +/- 10.3 vs. 26.5 +/- 7.8 counts x min(-1); p<0.001). At T12, after adjusting for training activity, physical activity on training days was significantly lower than on non-training days (23.7 +/- 8.4 vs. 28.2 +/- 9.3 counts x min(-1); p<0.01). RER decreased significantly (0.02 +/- 0.03; p <0.05), indicating a relatively larger fat oxidation. Changes in RER were negatively correlated with pre-training RER. In conclusion, in elderly an increase in structured training (exercise) is compensated for by a corresponding decrease in non-training physical activity. Training increased relative fat utilization in elderly with a high pre-training RER, whereas elderly with a low pre-training RER decreased their relative fat utilization.     

Endocrine regulation of exercise substrate utilization in women compared to men.

During low to moderate intensity exercise, women utilize proportionally more lipid and less carbohydrate compared to men. Estrogen and progesterone may have direct effects on these differences by increasing lipolysis and/or constraining glucose production and utilization. Furthermore, sex steroids may have indirect effects through interactions with other hormones, especially catecholamines.     

Influence of hormonal status on substrate utilization at rest and during exercise in the female population

During exercise, substrate utilization plays a major role in performance and disease prevention. The contribution of fat and carbohydrates to energy expenditure during exercise is modulated by several factors, including intensity and duration of exercise, age, training and diet, but also gender. Because sex hormone levels change throughout a woman's lifetime (in connection with puberty, the menstrual cycle, use of oral contraceptives and menopause), the female population has to be considered specifically in terms of substrate utilization, and metabolic and hormonal responses to exercise. Before puberty, there is no difference between males and females when it comes to substrate oxidation during exercise. This is not the case during adulthood, since women are known to rely more on fat than men for the same relative intensity of exercise. Among adult women, the menstrual cycle and use of oral contraceptives may influence substrate oxidation. While some authors have noted that the luteal phase of the menstrual cycle is connected with greater lipid oxidation, compared with the follicular stage, other authors have found no difference. Among oral contraceptive users, fat oxidation is sometimes increased during prolonged exercise with a concomitant rise in lipolytic hormones, as well as growth hormone. If this result is not always observed, the type of oral contraceptive (monophasic vs triphasic) and hormone doses may be implicated. Menopause represents a hormonal transition in a woman's life, leading to a decline in ovarian hormone production. A decrease in fat oxidation is consequently observed, and some studies have demonstrated a similar respiratory exchange ratio during prolonged exercise in postmenopausal women and in men. As is the case during puberty, no sex difference should thus appear after menopause in the absence of hormonal replacement therapy (HRT). Results concerning women who take HRT remain conflicting. HRT may act on fat loss by increasing lipid metabolism, but this depends on how the treatment is administered (orally vs transdermally). To better understand the role of ovarian hormones in substrate oxidation, studies have made use of animal protocols to investigate cellular mechanisms. Estradiol and progesterone seem to have opposite effects, with greater lipid oxidation when estradiol is used alone. However, the concentrations used (physiological levels or pharmacological doses) may considerably modify fuel selection. In cases where conflicting data are observed in studies of substrate utilization and prolonged exercise in women, methodological reasons must be called into question. Too many parameters, which oftentimes are not specified, may modulate substrate utilization and metabolic and hormonal responses to prolonged exercise. Although information is generally provided about the type of exercise, its duration and the subjects' training level, detailed information is not always given about the subjects' nutritional state and, more specifically, the hormonal status of female subjects. The primary purpose of this review was to identify the impact of hormonal status on substrate oxidation among female subjects at rest and during exercise. A second aim was to describe gender differences in substrate utilization during exercise.     

Effects of reduced ambient temperature on fat utilization during submaximal exercise

PURPOSE: The influence of cold air exposure on fuel utilization during prolonged cycle exercise was investigated. METHODS: Nine male subjects cycled for 90 min in ambient temperatures of -10 degrees C, 0 degrees C, 10 degrees C, and 20 degrees C. External work performed between conditions was constant. Mean oxygen consumption (VO2) over the 90 min in the 20 degrees C trial corresponded to 64 +/- 5.8% VO2peak. RESULTS: Although mean skin temperature was different between trials (P < 0.05), rectal temperatures were not different. At -10 degrees C and 0 degrees C, the respiratory exchange ratio was higher compared with 10 degrees C and 20 degrees C (0.98 +/- 0.01 and 0.97 +/- 0.01 vs 0.92 +/- 0.01 and 0.91 +/- 0.01; P < 0.05). The associated rates of fat oxidation were lower at -10 degrees C and 0 degrees C compared with 10 degrees C and 20 degrees C (0.15 +/- 0.06 and 0.17 +/- 0.06 vs 0.35 +/- 0.06 and 0.40 +/- 0.04 g.min-1; P < 0.05). Blood glycerol was lower at -10 degrees C and 0 degrees C compared with 20 degrees C (P < 0.05); mean values were 0.13 +/- 0.0, 0.13 +/- 0.0, and 0.18 +/- 0.0 mmol.L-1 for the -10 degrees C, 0 degrees C, and 20 degrees C trials, respectively. Mean VO2 was lower in the -10 degrees C trial than the 20 degrees C trial (2.53 +/- 0.06 vs 2.77 +/- 0.09. L.min-1; P < 0.05). Mean blood glucose concentrations were lower at -10 degrees C than 20 degrees C (4.9 +/- 0.2 vs 5.3 +/- 0.1 mmol.L-1; P < 0.05). Although plasma epinephrine concentrations were greater during the 20 degrees C trial compared with all other trials (P < 0.05), plasma norepinephrine did not differ between trials. CONCLUSION: The diminished fat oxidation at colder temperatures potentially reflects a reduction in lipolysis and/or mobilization of FFA or impairment in the oxidative capacity of the muscle.     

Effects of exercise on glycemic control and body mass in type 2 diabetes mellitus: a meta-analysis of controlled clinical trials

Acclimatization to moderate high altitude accompanied by training at low altitude (living high–training low) has been shown to improve sea level endurance performance in accomplished, but not élite, runners. Whether élite athletes, who may be closer to the maximal structural and functional adaptive capacity of the respiratory (i.e. oxygen transport from environment to mitochondria) system, may achieve similar performance gains is unclear. To answer this question, we studied 14 élite men and eight élite women before and after 27 days of living at 2500 m while performing high‐intensity training at 1250 m. The altitude sojourn began 1 week after the USA Track and Field National Championships, when the athletes were close to their season's fitness peak. Sea level 3000‐m time trial performance was significantly improved by 1.1% (95% confidence limits 0.3–1.9%). One‐third of the athletes achieved personal best times for the distance after the altitude training camp. The improvement in running performance was accompanied by a 3% improvement in maximal oxygen uptake (72.1 ± 1.5–74.4 ± 1.5 ml kg^{? 1} min^{? 1}). Circulating erythropoietin levels were near double initial sea level values 20 h after ascent (8.5 ± 0.5–16.2 ± 1.0 IU ml^?1). Soluble transferrin receptor levels were significantly elevated on the 19th day at altitude, confirming a stimulation of erythropoiesis (2.1 ± 0.7–2.5 ± 0.6 μ g ml^‐1). Hb concentration measured at sea level increased 1 g dl^?1 over the course of the camp (13.3 ± 0.2–14.3 ± 0.2 g dl^?1). We conclude that 4 weeks of acclimatization to moderate altitude, accompanied by high‐intensity training at low altitude, improves sea level endurance performance even in élite runners. Both the mechanism and magnitude of the effect appear similar to that observed in less accomplished runners, even for athletes who may have achieved near maximal oxygen transport capacity for humans.     

Effects of a controlled program of moderate physical exercise on insulin sensitivity in nonobese, nondiabetic subjects.

OBJECTIVE: To study the effect of a moderate, aerobic physical exercise program on insulin resistance and its accompanying metabolic changes in a group of healthy, middle-age, nonobese subjects, without modifying oxygen consumption and body weight. DESIGN: The inclusion of subjects was carried out among volunteers from the health personnel of our center, who complied with the inclusion criteria. PARTICIPANTS: Twelve subjects (age 30-60 years, 5 females), nonsmokers, body mass index (BMI) <27 kg/m2 and fasting plasma glucose <6.1 mmol/L. INTERVENTIONS: Insulin resistance was assessed using the Bergmann minimal model modified with insulin, and basal and maximum metabolic rate were measured with standard methods. All subjects completed a 2-month program of aerobic exercise using the American College of Sports Medicine guidelines, consisting of aerobic exercise of moderate, regular, and continual intensity (3 times per week), with a duration of 45 to 50 minutes per session. RESULTS: Following controlled exercise, no significant differences in BMI, waist-hip ratio, blood pressure, lipids, free fatty acids, and leptin plasma values were observed. Plasma glucose and insulin values decreased significantly (-0.37 mmol/L and -16.5 pmol/L, respectively). Insulin sensitivity showed an increase of 2.1 x 10(-4) mU L(-1) min(-1) (P = 0.001). Basal and maximum metabolic rate showed no significant differences after the exercise program. CONCLUSIONS: Moderate aerobic exercise increases insulin sensitivity in nonobese, nondiabetic subjects in the absence of significant changes in weight, BMI, waist-hip ratio, lipid profile, and oxygen consumption.     

Effects of exercise combined with diet therapy on protein utilization in obese children

PURPOSE: Hypocaloric therapy may adversely affect protein utilization in obese children given that metabolic reactions involving protein, a nutrient essential for growth, are energy-dependent. Because physical activity influences nutrient utilization and may modulate the effects of reduced energy intake, exercise combined with diet therapy may be beneficial with regard to protein metabolism. The primary purpose of this study was to evaluate changes in protein utilization in response to sequential addition of an exercise program to dietary intervention in obese children. METHODS: After a 2-wk baseline period, five subjects aged 8-10 yr reduced energy intake [-2092 to -2510 kJ.d(-1)(-500 to -600 kcal.d(-1))] for 12 wk. A walking program [5 d.wk(-1), 3.2-4.8 km.d(-1) (2-3 miles.d(-1))] was implemented during the final 6 wk of diet therapy. At baseline and after phases I (diet only) and II (exercise and diet) of intervention, 15N-glycine was used to assess protein synthesis (PS), protein breakdown (PB), net turnover (NET = PS - PB), and nitrogen flux (Q). RESULTS: Subjects lost 4.2+/-0.4 kg during the 12-wk intervention period (P < or = 0.05). With diet only, NET decreased (P < or = 0.05) due to a reduction in PS (P < or = 0.05) accompanied by no change in PB. Although PS increased with walking (P < or = 0.05), NET did not return to baseline levels due to a concurrent increase in PB (P < or = 0.05). Changes in PS and PB yielded an increase in Q (P < or = 0.05), a measure of amino acid cycling between protein and free amino acid pools. CONCLUSIONS: These results suggest that exercise offers metabolic benefits for obese children during diet-induced weight loss. Longitudinal studies are needed to assess long-term health outcomes associated with the observed changes in protein utilization.     

Effect of exercise on plasma renin substrate

Effects of physical exercise on plasma renin substrate (RS) and plasma renin activity (PRA) levels were studied during short-term and prolonged exercise. Six healthy male volunteers performed a dynamic exercise test with exercise levels of 50, 100, 150, and 200 W for 4 min at each level. Measured with direct radioimmunoassay (RIA), which measures both intact RS and des-angiotensin I-RS (des-A I-RS), a significant increase in RS was seen during short-term exercise. RS measured with indirect (enzymatic) assay, which measures intact RS only, did not change, whereas PRA increased significantly. During prolonged exercise, a 75-km cross-country ski race, PRA increased more than two fold in ten healthy males participating in the study. Measured with direct RIA, RS increased by 22%, the corresponding increase in RS measured enzymatically was 10%. The increases in RS were not significant, however. It is concluded that the increased consumption of RS by rising PRA during exercise is counterbalanced by increased synthesis or release of RS by the liver or extrahepatic tissue. During prolonged exercise, liver production rate of RS apparently reaches a plateau which can be sustained for at least 7-8 h.     

Effects of exercise intensity, duration and recovery on in vitro neutrophil function in male athletes

The aim of the present study was to compare the effects of exercise at 80% VO2max (resulting in fatigue within 1 h) with more prolonged exercise at a lower work rate (55% VO2max for up to 3 h) on blood neutrophil function and plasma concentrations of cortisol, glutamine and glucose. Eighteen healthy male subjects (mean+/-SD age 22.5+/-3.7 yrs, VO2max 60.1+/-6.6 ml x kg(-1) x min(-1)) cycled on an electrically braked ergometer at 80% VO2max to fatigue (37+/-19 min). On another occasion, separated by at least one week, subjects performed exercise on the same ergometer at 55% VO2max for 3 h or to fatigue, whichever was the sooner. Mean exercise time was 164+/-23 min. The order of the trials was randomised. Both exercise bouts caused significant (p<0.05) elevations of the blood leucocyte count and plasma cortisol concentration and reductions in the in vitro neutrophil degranulation response to bacterial lipopolysaccharide and oxidative burst activity. After exercise at the lower work rate for a longer duration, plasma cortisol concentration was higher, blood leucocyte and neutrophil counts were higher, blood lymphocytes, plasma glucose and indices of neutrophil function were lower than those observed at 80% VO2max. Plasma glutamine only fell significantly during recovery after the more prolonged exercise. We conclude that when exercise is very prolonged, the diminution of innate immune function is greater, or at least as great as that observed after fatiguing exercise at higher work rates. Furthermore, reductions in neutrophil function after exercise at 80% VO2max were not related to changes in the plasma glutamine concentration, although both plasma glutamine and neutrophil function were decreased at 1 and 2.5 h post-exercise in the long duration exercise trial.     

Effects of caffeine, fructose, and glucose ingestion on muscle glycogen utilization during exercise

Five competitive cyclists were used to determine the effects of fluid intake (16 ml.kg-1) consisting of: (i) non-nutrient control (CON); (ii) fructose (1 g.kg-1) before exercise (FRU); (iii) caffeine (5 mg.kg-1) before exercise (CAF); (iv) glucose (1 g.kg-1) during exercise (GLU); and (v) fructose/caffeine before and glucose during exercise (CFG) on blood glucose, free fatty acids, muscle glycogen, and other parameters. Exercise consisted of 90 min of cycling at 65 to 70% VO2max. Following exercise, blood glucose was found to be significantly (P less than 0.05) higher for CFG and GLU (117 and 109 mg%) compared to CON, CAF, and FRU (92, 89, and 86 mg%). Blood free fatty acids rose (P less than 0.05) further for CON (1,336), CAF (1,126), and FRU (1,034) over CFG (737) and GLU (714 mumol.l-1). Muscle glycogen utilization was greater (P less than 0.05) for CON (91) vs CAF (63) and GLU (62 mumol/g-1 wet muscle weight). It was concluded that GLU and CAF decrease muscle glycogen utilization, FRU is likely to cause gastric upset, and ingestion of multiple substances produces the greatest variability in muscle glycogen utilization and may provide added endurance benefits in some individuals.     

Influence of exercise duration and hydration status on cognitive function during prolonged cycling exercise

The purpose of the present study was to examine the influence of submaximal aerobic exercise duration on simple and complex cognitive performance. Eight well-trained male subjects agreed to participate in this study (trial group). A control group of eight regularly trained male subjects was included for comparative purposes. For the trial group, the experiment involved a critical flicker fusion test (CFF) and a map recognition task performed before, every 20 min during, and immediately after, a 3-h cycling task at an intensity corresponding to approximately 60 % of VO2max. Data were obtained over two experimental sessions with fluid ingestion (F) or no fluid (NF) ingestion. For the control group the experiment was the same but without exercise and fluid ingestion. In the trial group, a significant effect of hydration status was observed on physiological parameters (p <0.05). No effect was found on cognitive performance. A significant decrease in CFF performance was observed after 120 min of exercise when compared with the first 20 min (respectively for CFFmdi: 2.6 vs. 3.8 Hz), irrespective of experimental condition. A significant improvement in speed of response (respectively: 3291 vs. 3062 msec for 20 and 120 min, respectively) and a decrease in error number (21.5 % vs. 6.0 % for 20 and 120 min, respectively) during the map recognition task were recorded between 80 min and 120 min when compared with the first 20 min of exercise. After 120 min the number of recorded errors was significantly greater indicating a shift in the accuracy-speed trade-off (6.0 % vs. 14.1 % for 120 and 180 min, respectively). These results provide some evidence for exercise-induced facilitation of cognitive function. However this positive effect disappears during prolonged exercise--as evidenced within our study by an increase in errors during the complex task and an alteration in perceptual response (i.e. the appearance of symptoms of central fatigue).     

Effect of exercise intensity and duration on postexercise energy expenditure

The purpose of this study was to examine 1) the effect of two exercise intensities of equal caloric output on the magnitude (kcal) and duration of excess postexercise oxygen consumption (EPOC) and 2) the effect of exercise of equal intensity but varying duration on EPOC. Ten trained male triathletes performed three cycle ergometer exercises: high intensity-short duration (HS), low intensity-short duration (LS), and low intensity-long duration (LL). Baseline VO2 was measured for 1 h prior to each exercise condition. Postexercise VO2 was measured continuously until baseline VO2 was achieved. The duration of EPOC was similar for HS (33 +/- 10 min) and LL (28 +/- 14 min), and both were significantly longer (P less than 0.05) than the EPOC following LS (20 +/- 5 min). However, total net caloric expenditure was significantly more (P less than 0.05) for HS (29 +/- 8 kcal) than for either LS (14 +/- 6 kcal) or LL (12 +/- 7 kcal). The exercise conditions used in this study did not produce a prolonged EPOC. However, the exercise intensity was shown to affect both the magnitude and duration of EPOC, whereas the exercise duration affected only the duration of EPOC. Moreover, the duration of EPOC and the subsequent caloric expenditure were not necessarily related. Based on the resulting magnitude of the postexercise energy expenditure, it is possible that EPOC may be of some value for weight control over the long term.     

Acute effects of moderate exercise on plasma lipoprotein parameters

The acute, transient effects of moderate exercise on plasma lipoprotein parameters were assessed in 12 healthy, normolipidemic male volunteers subjected to a 5.5-km run at a comfortable pace. The course was completed in 31.5 min (range 23-43 min) and elicited a significant increase in pulse rate and plasma lactate levels and a fall in diastolic blood pressure. Of the plasma lipid parameters, total phospholipid, apo B-associated phospholipid, plasma triglyceride, and free fatty acid levels increased substantially immediately after the run and, except for triglyceride, were still raised 2 h later. Lesser but also significant increases were also noted in high-density lipoprotein-cholesterol (HDL-C), HDL3-C, and HDL-phospholipid concentrations after the run. The increase in HDL-phospholipid persisted for 2 h but the others returned to basal levels. Apolipoprotein Al, lecithin: cholesterol acyltransferase activity, total cholesterol, low-density lipoprotein-cholesterol, and the free cholesterol:cholesterol ester ratio remained essentially unaltered by exercise. The results were compatible with an increased secretion of triglyceride and phospholipid-rich VLDL, followed by the rapid clearance of the triglyceride moiety from the plasma and some redistribution of surface components to the HDL fraction.     

The effects of moderate exercise training on immune response

The relationship between moderate exercise training (ET) (five 45-min sessions per week, brisk walking at 60 heart rate reserve for 15 wk) and changes in immune system variables and function was investigated in a group of 36 sedentary, mildly obese women. The study was conducted using a two (exercise (EX) and nonexercise (NEX) groups) by three (baseline, 6 wk, and 15 wk testing sessions) factorial design, with data analyzed using repeated measures ANOVA. The pattern of change over time between groups for number of peripheral blood lymphocytes (total), T cells (CD5), B cells (CD20), and serum IgG, IgA, and IgM levels was significantly different. This was not the case for spontaneous blastogenesis or number of T helper/inducer cells (CD4) or T cytotoxic/suppressor cells (CD8). Within-EX-group changes were characterized by significant decreases in percentage and number of total lymphocytes, and in T cell number after 6 wk, and significant increases in each of the serum immunoglobulins after both 6 and 15 wk of training. B cell number increased significantly in NEX subjects relative to baseline values at both 6 and 15 wk, with no significant changes experienced in EX subjects. In summary, these data suggest that moderate ET is not associated with an improvement in lymphocyte function but is associated with a 20% increase in serum immunoglobulins and several small changes in circulating numbers of immune system variables, highlighted by significant decreases in circulating numbers of lymphocytes, particularly the T cell subpopulation. These changes were especially apparent after 6 wk of training, with some attenuation by 15 wk.