摘要:

Muscle is capable of operating over a wide range of metabolic rates. Most of the metabolic energy for work (ATP), and essentially all of the oxygen consumption of muscle, is due to mitochondrial oxidative phosphorylation. The rate of mitochondrial oxidative phosphorylation is determined by the rate of ATP consumption by the cells (demand) while the metabolic energy level at each metabolic rate is determined by the supply of oxidizable substrate and oxygen (supply). The maximal rate of metabolism is limited by several factors, including the supply of oxidizable substrates (mitochondrial dehydrogenases), of oxygen (blood supply and oxygen diffusion) and the respiratory enzyme capacity (tissue content of mitochondria).

ISSN:0195-9131    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

The symposium, “Mechanisms Which Control &OV0312;O2Near &OV0312;O2max,” led to a general agreement that there is a variable impediment to the movement of O2from the interior of the red cell to the interior of the mitochondrion. By changing the variables associated with O2delivery or by altering the conditions for muscle contractions, the effective O2diffusing capacity for muscle can be altered as well. Because it is often measured as the ratio of &OV0312;O2/PvO2, it was suggested that this be referred to as O2conductance rather than diffusing capacity. In contrast to the wide range of O2conductance values found by the symposium contributors, a very narrow range of O2extraction values was found when &OV0312;O2was graphed against O2delivery. The only experimental values that departed from this relationship to any degree were those where hemoglobin function was altered or if blood flow was forced to extraordinary high levels by a pump. The limits for &OV0312;O2in contracting isolated muscle are set not only by O2supply but by O2demand associated with stimulus patterns. Other intriguing and perhaps useful questions are: 1) What is the relative contribution of such factors as diffusional shunting, flow heterogeneity, red cell transit time, etc., to the apparent O2conductance? 2) How is blood flow to contracting muscle controlled? 3) How is contractile force adjusted to energy supply?

ISSN:0195-9131    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

To compare the physiological response to a cocaine-exercise challenge in cocaine-conditioned animals with that of acute-cocaine animals, rats were injected i.p. with either cocaine (20 mg·kg−1) or saline, twice daily for 14 consecutive days. On the 15th day (test day) cocaine-conditioned rats received an i.v. injection of cocaine (5 mg·kg−1) (chronic group). One-half of the chronic saline rats also received the cocaine injection (acute group), while the other half received saline (saline group). Immediately after injection, all rats were either rested or exercised (22 miming−1, 10% grade) for 30 min. For most parameters there was no difference between the responses of the chronic and acute cocaine groups at rest or to the cocaine-exercise challenge. During exercise, both cocaine groups had similarly higher lactate values than the saline animals (P< 0.05). Both groups had similarly greater reductions in glycogen content of the white and red vastus muscles than occurred in the saline group; and both groups had similar increases in corticosterone. In contrast, cocaine-conditioned animals had a greater rise in norepinephrine (P< 0.059) and epinephrine (P< 0.001) in response to cocaine-exercise than did the acute group. The mechanism responsible for the exaggerated catecholamine response in the chronic cocaine animals is unknown.

ISSN:0195-9131    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

The immune response to acute exercise after long-term training was evaluated in rats. After 10 wk of exercise training on a drum exerciser, both sedentary control and trained groups ran with the intensity of 70% of peak oxygen consumption (&OV0312;O2peak) for 10 min immediately before sacrifice. The mitogenic activity of spleen lymphocytes in trained group to staphylococcal enterotoxin B, a polyclonal T cell activator, decreased as compared to the sedentary control following acute exercise. However, proliferative response to lipopolysaccharide, a B cell mitogen, was augmented. Furthermore, the interleukin-2 production was reduced in the trained group. The lymphocyte subpopulations in the spleen and the peripheral blood lymphocytes were analyzed by flow cytometry. Although the tendency of changes in some populations was observed in trained vs untrained groups, no statistically significant difference was manifested. The serum levels of both norepinephrine and epinephrine increased immediately after acute exercise. The increase in serum lactate concentration was observed following acute exercise in sedentary control, but less prominent in the trained group.

ISSN:0195-9131    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

The purpose of this investigation was to determine the effects of 6 months of endurance training on resting plasma (PV) and blood volume (BV), and resting hormone and electrolyte concentrations in the elderly. Thirty-eight elderly men and women (ages 60–82 yr) were assigned to endurance exercise training (N= 29) or to control (N= 9) groups. Resting plasma levels of adrenocorticotropic hormone, vasopressin, aldosterone, norepinephrine, epinephrine, sodium, potassium, and protein were measured at the start (T1) and end (T2) of 26 wk of training. PV measurement was performed using the Evan's blue dye technique. Endurance training consisted of uphill treadmill walking or stairclimbing exercise 3 times·wk−1, 30–45 min·d−1, at 75–84% of maximal heart rate reserve. The exercise group increased VO2maxby 11.2% (P≤ 0.05) and increased resting PV and BV by 11.2% and 12.7% (P≤ 0.05), respectively. Hormone and electrolyte levels in the exercise group remained unchanged; all variables were unchanged in the control group. These results are similar to findings in younger individuals. Because plasma hormone concentrations were maintained despite a chronically elevated BV, endurance training in healthy, elderly subjects may be associated with a resetting of volume receptors.

ISSN:0195-9131    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Previous investigators reported that peak oxygen uptake (&OV0312;O2peak) could be accurately predicted from nonexercise test variables, and that this score would be suitable for categorizing cardiorespiratory fitness (CRF) within epidemiological studies. However, the accuracy of these models has varied considerably. The purposes of this study were: 1) assess the accuracy of predicting &OV0312;O2peakwith a new nonexerise model, and 2) assess the utility of the predicted &OV0312;O2peakfor categorizing CRF in epidemiological studies. Subjects included 2,350 men and women. Cross-validated multiple regression models revealed that age, sex, resting heart rate, body weight, percentage body fat, smoking, and physical activity were significant predictors (P< 0.001) of &OV0312;O2peak. The multiple regression model for relative &OV0312;O2peak(ml·kg−1.min−1) had R2= 0.733 (SEE = 5.38), whereas the model for absolute &OV0312;O2peak(1.min−1) had R2= 0.773 (SEE = 0.425). The 95% confidence intervals for the predicted &OV0312;O2peakwere large (± 10.6 ml·kg−1.min−1and ± 0.833 1.min−1). These results support the notion that &OV0312;O2peakcan be predicted from a multiple regression model devoid of exercise test variables. However, due to the extreme variability in the predicted scores, the regression models were unable to effectively distinguish CRF categories. Therefore, despite statistical success in predicting &OV0312;O2peakfor the nonexercise test regression models, we conclude that such models fail to provide the accuracy needed for categorizing CRF within large epidemiological cohorts where the purpose is to assess mortality risk.

ISSN:0195-9131    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

The purpose of this project was to determine the effect of changes in stiffness and viscosity of the foot ground interface on the work performed during locomotion. The estimation of the work during locomotion was derived from a mathematical two segment model, representing the foot and the rest of the body. The typical passive elements between the foot and the rest of the body were replaced by a strategic formulation of how a resultant force, F, representing the net effect of all the muscles between the foot and the rest of the body, has to evolve over time in a running situation. The calculations were performed under the assumption that the force F is selected so that the mechanical work performed by F is minimal. The estimations of the work required during a step cycle is generally higher for softer than for harder springs and for low damping compared with high damping. The model calculations demonstrate that specific combinations of material properties may be advantageous or disadvantageous from an energy point of view.

ISSN:0195-9131    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Treadmills are often used in research projects to simulate overground locomotion, assuming that locomotion is similar on a treadmill and overground. The purpose of this investigation was to determine whether a treadmill could be used to simulate overground locomotion. Twenty-two subjects ran on four different surfaces: overground and three treadmills that differed in size and power. The kinematics of the right leg and foot were studied using two high-speed. Locam cameras (lateral and posterior view). The subjects ran in two different shoes at four different speeds (3.0–6.0 m-s−1). The differences in the kinematics between treadmill and overground running could be divided into systematic and subject dependent components. Subjects systematically planted their feet in a flatter position on the treadmill than overground. Most of the lower extremity kinematic variables, however, showed inconsistent trends for individual subjects, depending on the individual subject's running style, running speed, and shoe/treadmill situation. The differences were substantial. It is not-yet understood how the human locomotor system adapts to a particular treadmill running situation. However, it is concluded that individual assessment of running kinematics on a treadmill for shoe or shoe orthotic assessment may possibly lead to inadequate conclusions about overground running.

ISSN:0195-9131    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Physiological and mood state parameters were monitored during a 6-month swimming season in an attempt to determine markers of overtraining and recovery. Fourteen elite male and female swimmers were tested early-, mid-, and late-season and shortly before and after major competition. Training details and subjective ratings of well-being were compiled by the athletes in daily logs. Three swimmers were classified as stale based upon performance deterioration and prolonged, high fatigue levels. Staleness scores were calculated for each athlete using performance change from early- to late-season and daily fatigue ratings for the season. Regression analysis revealed a battery of well-being ratings which predicted staleness scores, accounting for 76% of the variance. The late-season stress ratings and plasma catecholamine levels at rest predicted staleness scores, accounting for 85% of the variance. During tapering, well-being ratings predicted improvement in competitive performance, accounting for 72% of the variance of the improvement in race times from previous best times. It was concluded that self-reported ratings of well-being may provide an efficient means of monitoring both overtraining and recovery; plasma catecholamine levels at rest may provide an additional objective tool for diagnosis.

ISSN:0195-9131    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

This study quantified and compared the cross-sectional and longitudinal influence of age, self-report physical activity (SR-PA), and body composition (%fat) on the decline of maximal aerobic power (&OV0312;O2peak). The cross-sectional sample consisted of 1,499 healthy men ages 25–70 yr. The 156 men of the longitudinal-sample were from the same population and examined twice, the mean time between tests was 4.1 (±1.2) yr. Peak oxygen uptake was determined by indirect calorimetry during a maximal treadmill exercise test. The zero-order correlations between &OV0312;O2peak and %fat (r = −0.62) and SR-PA (r = 0.58) were significantly (P< 0.05) higher that the age correlation (r = −0.45). Linear regression defined the cross-sectional age-related decline in &OV0312;O2peak at 0.46 ml-kg−1·min−1· yr−1· Multiple regression analysis (R = 0.79) showed that nearly 50% of this cross-sectional decline was due to %fat and SR-PA, adding these lifestyle variables to the multiple regression model reduced the age regression weight to −0.26 ml-kg−1·min−1· yr−1· Statistically controlling for time differences between tests, general linear models analysis showed that longitudinal changes in aerobic power were due to independent changes in %fat and SR-PA, confirming the cross-sectional results.

ISSN:0195-9131    

出版商:OVID    

年代:1995

数据来源: OVID