No effect of menstrual cycle phase on fuel oxidation during exercise in rowers

The aim of this investigation was to examine the effects of menstrual cycle phase on substrate oxidation and lactate concentration during exercise. Eleven eumenorrheic female rowers (18.4 ± 1.9 years; 172.0 ± 4.0 cm; 67.2 ± 8.4 kg; 27.7 ± 4.8% body fat) completed 1 h rowing ergometer exercise at 70% of maximal oxygen consumption (VO_2max) during two different phases of the menstrual cycle: the follicular phase (FP) and the luteal phase (LP). Resting and exercise measurements of the whole body energy expenditure, oxygen consumption (VO₂), respiratory exchange ratio (RER), substrate oxidation and lactate blood levels were made. Energy expenditure, VO₂ and heart rate during the 1-h exercise were not significantly different (P > 0.05) among menstrual cycle phases. Resting RER and RER during the entire 1 h exercise period were not significantly different among menstrual cycle phases. There was an increase (P < 0.05) in RER in the transition between rest and exercise and a further increase in RER occurred after the first 30 min of exercise at both menstrual cycle phases. Blood lactate concentrations significantly increased in the transition between rest and exercise and remained relatively constant during the whole 1 h of exercise in both menstrual cycle phases. No menstrual cycle phase effect (P > 0.05) was observed for blood lactate concentrations. In conclusion, our results demonstrated no effect of menstrual cycle phase on substrate oxidation and blood lactate concentration during rowing exercise at 70% of VO_2max in athletes. Normally menstruating female rowers should not be concerned about their menstrual cycle phase with regard to substrate oxidation in everyday training.     

The inhibiting effect of atropine on growth hormone release during exercise

Summary The effects of atropine upon changes in the circulating levels of growth hormone (GH), cortisol, lactate, glucose, and free fatty acids (FFA) were studied during exercise using both constant and progressively increasing work loads. At low work loads, atropine had no effect upon the changes in either cortisol or lactate levels, but the normal exercise-induced rise in GH was abolished or markedly reduced. At higher work loads, especially when prolonged, the usual rises in cortisol and lactate were enhanced by atropine, but the rise in GH was diminished and delayed. In no circumstances were the changes in FFA or glucose significantly affected by atropine.We regard the effect of atropine upon changes in cortisol and lactate responses as secondary to its cardiovascular effect, but suggest that the inhibition of GH release may be evidence of a cholinergic mechanism in the control of GH release during exercise.     

Meal palatability, substrate oxidation and blood glucose in young and older men

We investigated the effects of food palatability on the thermic effect of feeding (TEF), substrate oxidation and circulating glucose and insulin. Healthy young men (23.4+/-1.0, SD, years, n=10) and older men (69.4+/-1.3, years, n=9) were resident in a metabolic unit for two 2-day study periods. On the second day of each period, they consumed in random order either a palatable test meal containing 2.93 MJ or a nonpalatable control meal containing the same foods in identical amounts but blended and freeze-dried into biscuit form. TEF and respiratory quotient (RQ) were measured over 6 h and blood samples were taken for measurement of glucose and insulin. Age group had no effect on TEF, RQ or circulating glucose other than to delay the time of peak TEF (P<0.002 for both meals). There was no significant effect of meal type on TEF, but RQ and circulating glucose were higher following consumption of the palatable meal (P<0.001 for both parameters). These results suggest that over 6 h postprandial, consumption of palatable foods does not increase TEF, but is instead associated with increased glycemic response and increased carbohydrate oxidation. These changes, combined with previous work on the glycemic index, predict an accelerated return of hunger and increased energy intake at subsequent meals following consumption of palatable vs. control foods. Further studies are needed to examine the possible mechanism for this previously suggested "second meal" effect of diet palatability on energy intake.     

Salbutamol intake and substrate oxidation during submaximal exercise

In order to test the hypothesis that salbutamol would change substrate oxidation during submaximal exercise, eight recreationally trained men twice performed 1 h at 60% VO₂ peak after ingestion of placebo or 4 mg of salbutamol. Gas exchange was monitored and blood samples were collected during exercise for GH, ACTH, insulin, and blood glucose and lactate determination. With salbutamol versus placebo, there was no significant difference in total energy expenditure and substrate oxidation, but the substrate oxidation balance was significantly modified after 40 min of exercise. ACTH was significantly decreased with salbutamol during the last 10 min of exercise, whereas no difference was found between the two treatments in the other hormonal and metabolic parameters. The theory that the ergogenic effect of salbutamol results from a change in substrate oxidation has little support during relatively short term endurance exercise, but it is conceivable that longer exercise duration can generate positive findings.     

Substrate oxidation during acute exercise and with exercise training in lean and obese women

The purpose of this study was to examine the rates of substrate oxidation in lean and obese women during short-duration, high-intensity exercise and to examine the effects of a 16-week exercise training program on substrate oxidation during 30 min of exercise in lean and obese individuals. Fat and carbohydrate oxidation were measured in 8 non-obese (Non-Ob), 11 lower-body obese (LBO) and 12 upper-body obese (UBO) women at rest and during 30 min of treadmill exercise at 70% of peak oxygen uptake. The obese women participated in 16 weeks of aerobic training (3 times per week at 70% of maximum oxygen uptake). Total fat and carbohydrate oxidation were measured using indirect calorimetry. The respiratory exchange ratio (R) was similar between groups at rest and was found to decrease throughout the exercise session (P<0.01). Fat oxidation was greater at 15 min of exercise than at rest (P<0.01) but did not increase significantly more at 30 min of exercise. Obese women had significantly greater fat oxidation (both absolute concentrations and when expressed per kg of fat free mass, FFM) at 30 min of exercise than the Non-Ob women [Non-Ob 23.5 (3.7) μmol·kg FFM^–1·min^–1, LBO 35.2 (3.1) μmol·kg FFM^–1·min^–1, UBO 33.2 (2.6) μmol·kg FFM^–1·min^–1; P<0.01]. Carbohydrate oxidation also increased (P<0.01) in response to exercise, but no group differences were found. The pattern of fat distribution (LBO vs UBO) did not affect the resting or exercise fat oxidation (P=NS). Sixteen weeks of aerobic exercise did not result in significant changes in resting or exercise fat oxidation in the obese women (n=10; P=NS), but did significantly increase carbohydrate oxidation [pre-training 8.6 (1.4) μmol·kg FFM^–1, post-training 13.6 (2.1) μmol·kg FFM^–1·min^–1; P<0.01]. Unlike earlier studies, this shorter-duration, higher-intensity exercise resulted in a greater whole-body fat oxidation in the obese women than in the Non-Ob women, and exercise training did not result in any changes in fat oxidation, but did increase exercise carbohydrate oxidation. Electronic Publication     

Growth hormone responses during intermittent weight lifting exercise in men

Summary Five normal male volunteers performed two intermittent weight lifting exercises of equal total external work output and duration (20 min) with identical work-rest intervals but different load and frequency of movements. Exercise I consisted of seven sets of seven vertical leg lifts at 85% of the subject's Seven Repetition Maximum (SRM) and, 5 days later, seven sets of 21 vertical leg lifts with one-third of the previously used load (Exercise II). Blood was sampled throughout the exercise and recovery periods for growth hormone, lactate, and glucose analysis. Growth hormone increased after 20 min of Exercise I to a peak during the recovery period. Significantly elevated growth hormone (GH) levels were found 5, 10, and 15 min (P<0.025,P<0.05,P<0.025 respectively) of recovery after Exercise I. No significant elevations of GH occurred in Exercise II. Significant linear correlations (r=0.99,P<0.01) with a time lag of 16 min were found between lactate and GH levels in Exercise I (lactate increases preceded those of GH). No significant differences in plasma glucose concentrations were detected. The results suggests that in intermittent weight lifting exercises of equal total external work output and duration as well as identical work-rest intervals, the load and/or frequency of an exercise are determinant factors in the regulation of plasma GH levels.     

The effect of exercise duration and mode on the growth hormone responses in young women on oral contraceptives

Previous research is conflicting concerning the minimum time duration needed to elicit a growth hormone (GH) response to aerobic exercise; thus, the purpose of this project was to examine the effects of mode and duration on exercise-induced GH responses in young women taking oral contraceptives. Nine healthy young females on oral contraceptives exercised at 75% of their mode-specific peak aerobic power (V̇O₂peak) on the treadmill and cycle ergometer for 10, 15 and 20 min, with serial blood samples taken at rest and every 10 min throughout the entire 5.5 h of the study. Each exercise bout was followed by 70 min of rest. A significant (P<0.02) GH response was observed at the end of exercise regardless of the duration or mode of exercise. The peak GH concentrations were 12.2 (1.8), 10.2 (1.6), and 7.6 (1.5) ng·ml^–1 for the 10-, 15-, and 20-min exercise bouts on the treadmill, respectively. For the cycle ergometer, peak GH concentrations were 9.3 (2.0), 6.3 (1.0), and 9.8 (1.7) ng·ml^–1, respectively. The total integrated area under the curve was not significantly different between the cycle and treadmill exercise for each exercise duration. Moderate-intensity aerobic exercise is sufficient to produce a GH response in as little as 10 min during both treadmill and cycling exercise in young women taking oral contraceptives. Overall, the mode of exercise does not impact the exercise-induced GH response.     

Greater growth hormone and insulin response in women than in men during repeated bouts of sprint exercise

Aim: In a previous study, sprint training has been shown to increase muscle cross‐sectional area in women but not in men [Eur J Appl Physiol Occup Physiol 74 (1996) 375]. We hypothesized that sprint exercise induces a different hormonal response in women than in men. Such a difference may contribute to explaining the observed gender difference in training response. Method: Metabolic and hormonal response to three 30‐s sprints with 20‐min rest between the sprints was studied in 18 physically active men and women. Results: Accumulation of blood lactate [interaction term gender (g) × time (t): P = 0.022], and plasma ammonia (g × t: P < 0.001) after sprint exercise was greater in men. Serum insulin increased after sprint exercise more so in women than in men (g × t: P = 0.020), while plasma glucose increased in men, but not in women (g × t: P < 0.001). Serum growth hormone (GH) increased in both women and men reaching similar peak levels, but with different time courses. In women the peak serum GH level was observed after sprint 1, whereas in men the peak was observed after sprint 3 (g × t; P < 0.001). Serum testosterone tended to decrease in men and increase in women (g × t: P = 0.065). Serum cortisol increased approx. 10–15% after sprint exercise, independent of gender (time: P = 0.005). Conclusion: Women elicited a greater response of serum GH and insulin to sprint exercise. This may contribute to explaining the earlier observed muscle hypertrophy in women in response to sprint training.     

Andrology: Effect of growth hormone administration on circulating levels of luteinizing hormone, follicle stimulating hormone and testosterone in normal healthy men

A new area of growth hormone (GH) therapy in adults is the treatmentof infertility. The aim of this study was to evaluate the effectsof pharmacological GH administration on the secretion of pituitaryand gonadal hormones in normal men. Eight healthy men, 23–32years of age (mean 28.1 years), with a normal body mass indexwere studied in a double-blind, placebo-controlled crossoverdesign. All participants had a normal semen analysis beforeentering the study. Each participant was treated with placeboand GH (12/IU/day, Norditropin; Novo Nordisk, Denmark) duringtwo different 14-day periods, separated by a 6 week washoutperiod. Administration of GH for 14 days resulted in a significantincrease in serum insulin-like growth factor I (IGF-I; P <0.01) but no changes occurred in IGF-I values during placebotreatment. The concentrations of follicle stimulating hormoneand luteinizing hormone displayed no change during the two periodsand did not differ between the GH treatment period and the placeboperiod. The concentration of testosterone was unchanged duringthe placebo/GH periods and there was no difference between theGH treatment period and the placebo period. We conclude thatGH treatment for 14 days in normal healthy men does not affectgonadotrophin or testosterone patterns.     

Thermoregulatory responses of prepubertal boys and young men during moderate exercise

Seven prepubertal boys (aged 10–11 years)?and eleven young men (aged 21–25 years), matched for skinfold thickness and maximal oxygen uptake ( O_2max) per unit of mass, cycled at an intensity of approximately 40% O_2max for 45 min in a warm condition (30?°C, 45% relative humidity). During exercise no age-related differences were observed for the increases in rectal temperature (T _re) and heart rate (HR), although the absolute T _re and HR were significantly greater for the boys because of a higher initial baseline (P??2?·?45 min^?1; P? _sw) on chest, back, and forearm were significantly lower for the boys (P??2; P? _sw in the boys was due to a lower output per activated sweat gland, even though they had a higher activated sweat gland density regardless of site. In contrast, cutaneous blood flow by laser Doppler flowmetry (LDF) in the boys was significantly greater on the chest and back, compared to the men (P?P?P? _sw, compared to the young men. It was concluded that during moderate exercise in an air temperature at 30?°C, prepubertal boys could thermoregulate as efficiently as young men by greater vasodilatation on their trunk despite lower _sw. Furthermore regional differences may exist in the maturation-related modification of vasodilatation.     

The Effect of sex steroid hormones on substrate oxidation during prolonged submaximal exercise in women

In animals, female sex steroid hormones (SS, estrogens-progesterone) influence the energy substrate that is metabolized. Human research on this issue is controversial. This study examined whether changes in circulating SS hormone levels affected the carbohydrate-lipid metabolism during submaximal prolonged (60 min) exercise. Young, physically active females were studied. Four were classified as anovulatory-oligomenorrheic and four were classified as ovulatory-eumenorrheic. Subject responses were pooled to form one group (n = 8) and then their responses under low (L) and high (H) pharmaceutically manipulated SS hormone conditions were examined. During exercise, the mean oxygen consumption levels were 1.70 +/- 0.10/ x min(-1) for L-SS and 1.75 +/- 0.11/ x min(-1) for H-SS (p = 0.07), respectively. The respiratory exchange ratio (RER) responses were significantly different during exercise between the conditions: 0.93 +/- 0.04 for L-SS and 0.90 +/- 0.04 for H-SS (p < 0.05), respectively. RER responses were utilized to calculate substrate oxidation. Significantly less carbohydrate oxidation was found in the H-SS condition as compared to the L-SS condition (p < 0.05). Lipid oxidation was also significantly different, but for this measure, the levels of oxidation were greater in the H-SS than in the L-SS condition (p < 0.05). Finally, total energy expenditure for the 60 min of exercise was not significantly different between the hormonal conditions. Results suggest that sex steroid hormones have an impact upon substrate oxidation in women during exercise. Specifically, high circulating concentrations of the SS hormones result in an enhanced reliance upon the oxidation of lipid as an energy substrate and consequently induce a reduction in carbohydrate oxidation. The mechanism inducing this "metabolism shift" appears due to sex steroid hormones directly and indirectly increasing lipid mobilization and lipolysis.     

Characterizing the profile of muscle deoxygenation during ramp incremental exercise in young men

This study characterized the profile of near-infrared spectroscopy (NIRS)-derived muscle deoxygenation (Δ[HHb]) and the tissue oxygenation index (TOI) as a function of absolute (PO(ABS)) and normalized power output (%PO) or oxygen consumption (%VO(2)) during incremental cycling exercise. Eight men (24 ± 5 year) each performed two fatigue-limited ramp incremental cycling tests (20 W min(-1)), during which pulmonary VO(2), Δ[HHb] and TOI were measured continuously. Responses from the two tests were averaged and the TOI (%) and normalized Δ[HHb] (%Δ[HHb]) were plotted against %VO(2), %PO and PO(ABS). The overall responses were modelled using a sigmoid regression (y = f ( 0 ) + A/(1 + e(-(-c+dx)))) and piecewise 'double-linear' function of the predominant adjustment of %Δ[HHb] or TOI observed throughout the middle portion of exercise and the 'plateau' that followed. In ~85% of cases, the corrected Akaike Information Criterion (AIC(C)) was smaller (suggesting one model favoured) for the 'double-linear' compared with the sigmoid regression for both %Δ[HHb] and TOI. Furthermore, the f ( 0 ) and A estimates from the sigmoid regressions of %Δ[HHb] yielded unrealistically large projected peak (f ( 0 ) + A) values (%VO(2p) 114.3 ± 17.5; %PO 113.3 ± 9.5; PO(ABS) 113.5 ± 9.8), suggesting that the sigmoid model does not accurately describe the underlying physiological responses in all subjects and thus may not be appropriate for comparative purposes. Alternatively, the present study proposes that the profile of %Δ[HHb] and TOI during ramp incremental exercise may be more accurately described as consisting of three distinct phases in which there is little adjustment early in the ramp, the predominant increase in %Δ[HHb] (decrease in TOI) is approximately linear and an approximately linear 'plateau' follows.     

Effect of transdermal nicotine administration on exercise endurance in men

Nicotine is widely reported to increase alertness, improve co-ordination and enhance cognitive performance; however, to our knowledge there have been no attempts to replicate these findings in relation to exercise endurance. The purpose of this study was to determine the effects nicotine might have on cycling endurance, perception of exertion and a range of physiological variables. With local ethics committee approval and having obtained informed consent, 12 healthy, non-smoking men (22 +/- 3 years; maximal O2 uptake, 56 +/- 6 ml kg(-1) min(-1), mean +/- s.d.) cycled to exhaustion at 18 degrees C and 65% of their peak aerobic power, wearing either a 7 mg transdermal nicotine patch (NIC) or a colour-matched placebo (PLA) in a randomized cross-over design; water was available ad libitum. Subjects were exercising at approximately 75% of their maximal O2 uptake with no differences in cadence between trials. Ten out of 12 subjects cycled for longer with NIC administration, and this resulted in a significant 17 +/- 7% improvement in performance (P < 0.05). No differences were observed for perceived exertion, heart rate or ventilation. There were no differences in concentrations of plasma glucose, lactate or circulating fatty acids. In the absence of any effect on peripheral markers, we conclude that nicotine prolongs endurance by a central mechanism. Possible modes of action are suggested.     

The effect of exercise on the production and clearance of testosterone in well trained young men

Summary Tritium-labelled testosterone was infused into four well-trained subjects at rest and during one hour of exercise at about 60% of their maximum aerobic power. This exercise regime led to a mean increase of 27% (range 10–51%) in plasma testosterone concentration. At the same time there were significant decreases in the estimated hepatic plasma flow (EHPF) (45%; range 28–67%), metabolic clearance rate of testosterone (MCR_T) (29%; range 18–37%) and plasma volume (8.2%; range 3–10%). The production rate of testosterone decreased by 10% (range 9–22%) but this was not statistically significant. The ratio MCR_T: EHPF increased in 3 out of 4 subjects in response to exercise but there was considerable inter-subject variation both at rest and during exercise. These findings suggest that the exercise-induced elevation of testosterone level is due solely to the reduction in the rate at which testosterone is cleared from the plasma. The principal cause of the reduction in MCR_T is probably the reduction in EHPF but the variation in the ratio MCR_T: EHPF suggests that changes in the extrahepatic clearance of testosterone may also be involved.     

Responses of young and older men during prolonged exercise in dry and humid heat

Summary Eight young, sedentary men (aged 34 years, SD 3) and six older moderately active, unacclimated men (aged 57 years, SD 2) walked on a treadmill at 30% of their maximum oxygen consumption up to 3.5 h in a thermoneutral [dry bulb temperature (T _db) 21°C, relative humidity (r.h.) 43%)], a warm humid (T _db 30°C, r.h. 80%) and a hot dry (T _db 40°C, r.h. 20%) environment while wearing ordinary working clothes (0.7 c/o). Their oxgen consumption, heart rate (f _c), rectal (T _re) and mean skin temperature (T_sk), sweat rate (SR), and evaporative rate (ER) were measured during the tests. The ratings of thermal sensation (TS) and perceived exertion (RPE) were assessed using standard scales. In the heat stress tests, the number of experiments discontinued did not significantly differ between the two groups. The mean levels and end-exercise values of T _re, T_sk, f _c, TS and RPE were not significantly different between the young and older subjects in any of the environments. In the warm humid environment, however, the T _re and RPE of the older subjects increased continuously (P<0.05) during the test compared to the young subjects. No significant difference between the groups was observed in SR or in ER. In the hot dry environment, however, the ER of older men increased more slowly compared to the young men. In spite of some time-related differences observed in T _re, RPE, and ER, the older subjects did not exhibit higher f _c during exercise in the heat, they were not more hyperthermic and their performance times were similar to the young subjects. Therefore, it was concluded that older calendar age is not necessarily associated with a reduced ability to exercise in a hot environment and other factors, such as physical activity habits and aerobic capacity, may be equally important in determining heat tolerance in the elderly.     

Acute hormone responses to heavy resistance lower and upper extremity exercise in young versus old men

Acute hormone responses of growth hormone (GH), total and free testosterone (TT and FT) and cortisol (C) to heavy resistance isometric exercise were examined in ten young men [YM 26.5 (SD 4.8) years] and ten old men [OM 70.0 (SD 3.7) years]. Loading conditions of the same relative intensity were created for the lower and upper extremity actions separately as well as for both of them together – lower extremity exercise (LE; knee extension), upper extremity exercise (UE; bench press extension), and lower and upper extremity exercise (LUE) performed simultaneously in a seated position. Single voluntary maximal isometric actions lasting for 5 s were performed repeatedly for ten repetitions (with a recovery of 5 s) for a total of four sets. The recovery time between the sets was 1 min. Each exercise led to large acute decreases in maximal isometric force in both YM (P?P?P?P?P?P?P?P?P?P?P?P?P?相似文献   

Differential effect of homeostatic thymus hormone on plasma thyrotropin and growth hormone in young and old rats

There is increasing evidence that the neuroendocrine system is responsive to hormonal signals generated by the immune system. Thus, interleukin-1, hepatocyte stimulating factor and thymosin have been shown to stimulate adrenocorticotropin, beta-endorphin and luteinizing hormone secretion. We report here that homeostatic thymus hormone (HTH), a well-characterized thymic preparation, reduces plasma thyrotropin (TSH) and growth hormone (GH) in young (3 months) Sprague-Dawley male rats, but fails to do so (TSH) or has a significantly weaker effect (GH) in old (26 months) animals. Young and old conscious, free-moving rats carrying an indwelling atrial cannula received the substances to be tested via the cannulas. Plasma samples were taken every 30 min for 5 h and hormones were measured by RIA. In the young rats, HTH (8 mg/kg body wt) induced a marked reduction in plasma TSH which was significantly greater than the normal circadian decline observed in saline-injected young controls. The old rats displayed high basal levels of TSH which showed no circadian rhythmicity and did not respond to HTH. Plasma thyroxine (T4) showed a significant age-related reduction but was not affected by HTH. The above dose of HTH significantly reduced plasma GH in young and old rats, but the effect was greater in the young animals. Mean basal levels of plasma GH were significantly lower in old than in young rats. The present results suggest that HTH, whose production by the thymus is known to be stimulated by TSH and GH, is involved in an inhibitory feedback loop regulating plasma TSH and GH in young rats. Our data also suggest an age-related desensitization of the TSH and GH systems to thymic influence in this species.     

No difference in the skeletal muscle angiogenic response to aerobic exercise training between young and aged men

Ischaemia-induced skeletal muscle angiogenesis is impaired in aged compared with young mice. In humans, vascular endothelial growth factor (VEGF) mRNA and protein following an acute exercise bout are lower in aged compared with young untrained men. We hypothesized that exercise-induced skeletal muscle angiogenesis would be attenuated in aged compared with young men. In eight aged (mean age: 64 years) and six young (mean age: 25 years) sedentary men, muscle biopsies were obtained from the vastus lateralis prior to (Pre), after 1 week and after 8 weeks of an aerobic exercise training program for the measurement of capillarization and VEGF mRNA. Dialysate VEGF protein collected from the muscle interstitial space was measured at rest and during submaximal exercise at Pre, 1 week and 8 weeks. Exercise training increased capillary contacts (CC) and capillary-to-fibre perimeter exchange index (CFPE) of type I and IIA fibres similarly in young and aged. The CC of type IIA and IIB fibres was lower in aged compared with young independent of training status. Exercise-induced interstitial VEGF protein was lower in aged compared with young independent of training status. In untrained, greater exercise-induced interstitial VEGF protein during exercise was associated with greater type I, IIA and IIB CC. Exercise training increased VEGF mRNA similarly in young and aged. These results demonstrate that the angiogenic response to aerobic exercise training is not altered during the ageing process in humans. In addition, muscular activity-associated increases in interstitial VEGF protein may play an important role in the maintenance of skeletal muscle capillarization across the life span.