摘要:

The purpose of this study was to examine serum and salivary cortisol responses to cycling exercise in male children, 10.6 ± 0.2 yr (mean ± SE). Each child performed a graded exercise test on a cycle ergometer to determine &OV0312;O2max. On a separate day, a 30-min bout of exercise at 70% of &OV0312;O2maxwas performed. Blood, obtained from a venous catheter, and saliva samples were collected at rest, at 15 and 30 min of exercise, and 15 min post-exercise. The mean serum cortisol level at 15 min (7.94 ± 1.43 μg·dl−1) and 30 min (8.72 ± 1.77 μg·dl−1) of exercise and at 15 min post-exercise (8.21 ± 1.59 μg·dl−1) were significantly greater than rest (5.54 ± 0.86 μg·dl−1). The increase in salivary cortisol levels over time approached (P= 0.08), but did not reach significance. However, effect size analyses indicated that the increase in salivary cortisol at 30 min of exercise (0.64) and 15 min post-exercise (0.62) was similar to the change in serum cortisol at these same two time points (0.72 and 0.66, respectively). Serum and salivary cortisol were correlated (P< 0.05) at 15 min of exercise (r = 0.77), 30 min of exercise (r = 0.90), and 15 min post-exercise (r = 0.84), but not at rest (r = 0.46). In conclusion, 30 min of submaximal exercise at 70% of &OV0312;O2maxsignificantly increased serum cortisol level; and salivary and serum cortisol are correlated during and after exercise.

ISSN:0195-9131    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Nonsteroidal anti-inflammatory drugs (NSAID) are frequently used in sports medicine but few studies have documented their potential importance in modifying exercise-induced changes in renal function. The effects of indomethacin (50 mg orally every 8 h for 36 h) on renal blood now (RBF) and glomerular filtration rate (GFR) were investigated in eight fit healthy males (age 21–42) before and after 30-min treadmill exercise at 80% &OV0312;O2maxand during 120-min recovery. Each volunteer served as their own control. There were no differences between control and indomethacin for the resting values of RBF, GFR, or renal vascular resistance (RVR). Using analysis of variance for repeated measures, indomethacin produced a significant reduction in RBF compared with control (P= 0.009) that was associated with a significant elevation in RVR (P= 0.027). Changes in GFR mirrored the changes in RBF but differences failed to reach statistical significance. These results suggest that with sustained exercise indomethacin can compromise renal function and potentiate the risk of developing acute renal failure. Indomethacin and other NSAID are widely used in the sports arena, and athletes should be warned of the potential danger of their use when renal function may be compromised.

ISSN:0195-9131    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Comparable effects of diet and exercise on body composition and lipoproteins in older men.Med. Sci, Sports Exerc., Vol. 26, No. 11, pp. 1307–1315, 1994. Changes in body composition, fat distribution and lipoprotein lipids in response to weight loss elicited by a 10-month program of hypocaloric diet (HD) therapy alone or combined with aerobic exercise training (AEX+HD) were examined in sedentary obese older males. Body composition was assessed by hydrodensitometry and fat distribution was evaluated with skinfold thickness and circumference measures. The HD group underwent a dietary/behavioral modification program to reduce caloric intake. The AEX+HD group underwent a similar dietary modification program combined with aerobic exercise training. Following completion of the study, 15 subjects from each group were individually pair matched based on age (57.1 ± 1.7 vs 61.3 ± 2.4 yrs) and their reduction in body mass (−7.6 ± 1.3 vs −8.0 ± 1.1 kg). Reductions in fat and fat-free mass and skinfold thickness and circumferences were similar in both groups. In both the AEX+HD and HD groups there were significant reductions in the ratio of low-density lipoproteins to high-density lipoproteins (HDL-C) and triglycerides and a significant increase in HDL2-C. There were no differences in final values or absolute and relative changes in the various lipoprotein values between the two groups. These results suggest weight loss induced by diet alone or combined with aerobic exercise cause similar changes in body composition and lipoprotein lipids.

ISSN:0195-9131    

出版商:OVID    

年代:1994

数据来源: OVID

ISSN:0195-9131    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

During constant-load exercise of moderate intensity, pulmonary O2uptake (&OV0312;O2) is characterized by two temporal response components. The first occurs during the transit delay from the exercising limbs and is mediated predominantly by increased pulmonary blood flow. Thereafter, this response is supplemented by the influence of increased O2extraction, causing &OV0312;O2to increase monoexponentially to its steady state, with a time constant that does not vary appreciably with work rate, at this intensity. At work rates that engender a lactic acidosis, however, an additional slow phase of &OV0312;O2is superimposed upon the underlying kinetics: this is of delayed onset and prolongs the time to steady state over the range within which the increases in blood lactate and [H+] stabilize or even decrease (heavy exercise). At higher work rates (severe exercise) a steady state is unattainable, with the &OV0312;O2trajectory resulting in &OV0312;O2maxprogressively earlier the higher the work rate: it is therefore a fundamental determinant of exercise tolerance. Although the kinetic features of this slow &OV0312;O2component (other than its delay) remain to be determined, current evidence suggests that it is manifest predominantly in the exercising limbs, with the recruitment profile and metabolic features of fast-twitch fiber activation being the major contributor.

ISSN:0195-9131    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Characterizing oxygen uptake (&OV0312;O2) kinetics yields valuable information regarding both a) the effectiveness of the coupling of O2delivery to tissue metabolic demands, and b) the ability of the muscle itself to utilize O2for oxidative phosphorylation. During moderate exercise &OV0312;O2reaches a new steady state within 3 min in normal subjects, with little or no sustained rise in blood lactate. The steady state &OV0312;O2increases linearly with work rate. The time constant for &OV0312;O2in Phase 2 (after first 15–20 s) is constant across work intensities, and appears to reflect muscle oxygen utilization kinetics. However, when heavier exercise is performed, which elevates blood lactate throughout the exercise, the &OV0312;O2response becomes more complex. The predominant, Phase 2 response continues to rise exponentially with about the same time constant as for moderate exercise, and the amplitude continues to be linearly related to work rate. However, an additional, slowly developing rise in &OV0312;O2is also usually observed, beginning 100–200 s into exercise. This additional &OV0312;O2delays attainment of a steady state, increases the overall O2“cost” of the exercise, and is statistically associated with the rate and magnitude of increase in blood lactate. Interestingly, in children, neither the slow component nor blood lactate rise as much during heavy exercise.

ISSN:0195-9131    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

This paper: 1) Reviews evidence for the location of the slow component of &OV0312;O2kinetics either within the exercising limbs or alternatively at some site in the rest of the body, e.g., ventilatory, cardiac or accessory muscles. 2) Presents evidence in support of both the fast and slow components (i.e., <3 min and >3 min from exercise onset, respectively) of the exercise &OV0312;O2response residing predominantly in the exercising muscle. For a pulmonary &OV0312;O2slow component in excess of 600 ml O2·min−1, more than 80% could be attributed to an augmented &OV0312;O2across the exercising limbs. 3) Assesses the potential for the lactate ionper seto exert a metabolic stimulatory effect in exercising muscle in the absence of the potentially confounding influences of changes in muscle temperature, H+, blood flow or O2delivery. Within the surgically isolated, electrically stimulated canine gastrocnemius, square wave infusions that increased arterial blood [lactate] by ∼10 mM and intramuscular [lactate] to in excess of 9 mM did not increase muscle &OV0312;O2. In summary, these investigations demonstrate that the exercising muscle is the predominant site of the &OV0312;O2slow component. However, despite the close temporal association between changes in blood lactate and &OV0312;O2during intense exercise, lactate itself does not mandate an additional &OV0312;O2demand in exercising dog muscle.

ISSN:0195-9131    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

For constant-load, heavy exercise (i.e., above the lactate threshold (TLac.)), a slow component of oxygen uptake (&OV0312;O2) is observed. Endurance training reduces the magnitude of the slow component and, hence, end-exercise &OV0312;O2. Reductions in exercise &OV0312;O2have been reported after 7–8 wk of training; unpublished observations suggest that the &OV0312;O2slow component may be attenuated after just 2 wk of training. A minimum training intensity for eliciting reductions in constant-load exercise &OV0312;O2has not been established; however, in the elderly, training at an intensity below TLacresulted in similar reductions in exercise &OV0312;O2as did training above TLac. Mechanisms responsible for the reduced slow component of &OV0312;O2after training remain to be firmly established. Evidence both for and against blood lactate concentration ([L−]) as a mediator of the slow component has been published; high correlations between [L−] and the slow component, and between the training-induced reductions in these variables, appear to be more coincidental than causal. Decreased pulmonary ventilation after training may account for between 14% and 30% of the reduction in the slow component of &OV0312;O2. Epinephrine infusion does not augment exercise &OV0312;O2, nor does β-adrenergic blockade diminish the magnitude of the slow component of &OV0312;O2.

ISSN:0195-9131    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Maximal rates, coupling, and control of oxidative phosphorylation were studied in isolated skeletal muscle mitochondria from rat and rabbit. Mitochondria were incubated under various conditions of temperature, pH, and substrate availability. A 20% decrease in coupling (ADP/O) was observed at 43°C as compared to 37°C in rat mixed skeletal muscle mitochondria. Changes in pH from 7.00 to 6.20 affected neither coupling nor maximal (state 3) respiration rates. Changing the substrate supply from pyruvate to palmitoyl-carnitine (+ malate) did not alter ADP/O, but markedly degraded the energy state sustained at submaximal ATP turnover. Thus, carbohydrate depletion may be associated with inhibition of contractile function and the recruitment of less economical higher threshold motor units. State 3 respiration of mitochondria from rabbit Type IIb fibers oxidizing pyruvate + malate + α-glycerophosphate was 27% higher than that of mitochondria from Type I rabbit skeletal muscle. However, the ADP/O ratio in the Type IIb preparation was 18% lower. The experimental findings suggest that temperature, substrate supply, and energetic differences between slow twitch and fast twitch motor units may impact the economy of mitochondrial oxygen utilization during heavy aerobic exercise, and thus contribute to the slow component of oxygen uptake.

ISSN:0195-9131    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

This paper offers a brief synopsis of the five preceding papers which constitute the proceedings of the symposium “Mechanistic basis of the slow component of &OV0312;O2kinetics during heavy exercise.” The key features have been taken from each paper and a coherent position regarding the site and potential underlying mechanisms for the “excess” &OV0312;O2is presented. The hypothesis is developed that some aspect of fiber type recruitment patterns might be responsible for this phenomenon. Elucidation of the precise determinants of &OV0312;O2during heavy exercise is fundamental to our understanding of muscle energetics. Furthermore, certain patient populations, whose exercise tolerance is limited by impaired cardiovascular and/or respiratory capacity, may benefit from interventions designed to constrain the magnitude of the &OV0312;O2slow component.

ISSN:0195-9131    

出版商:OVID    

年代:1994

数据来源: OVID