摘要:

Hypothyroidism is a common thyroid disease characterized by exercise intolerance. Both exercise capacity and endurance are compromised in the hypothyroid state. Studies involving rats performing treadmill running have shown that blood flows during exercise to high oxidative, extensor-type muscles are lower in hypothyroid rats compared with those in euthyroid rats. Abnormal cardiac and vascular function appear to contribute to this hxpoperfusion. Experiments involving isolated arterial vessel segments have demonstrated that potential for constriction is normal in vessels from hypothyroid animals; however, reduced vasodilator potential is associated with hypothyroidism. Dysfunction of both endothelium and vascular smooth muscle appear to contribute to blunted potential for vasodilation. Altered ability to generate vasodilatory substances and/or changes in responses to these vasodilators may account for vascular dysfunction. It appears that impaired vascular function interacts with other factors such as poor myocardial function and changes in energy metabolism to compromise exercise tolerance.Key words:blood flow, vasodilation, endothelium, smooth muscle, cGMP

ISSN:1066-7814    

DOI:10.1139/h97-001

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The surface area of contact between capillaries and muscle fibres has been suggested to be the site of greatest oxygen flux density in the movement of oxygen from the capillaries to the muscle fibres. A new measurement of tissue capillarity, designed specifically for use on non-perfusion fixed muscle tissue (i.e., that obtained via needle biopsy) is presented that describes the capillary supply from this perspective. The Capillary-to-Fibre Perimeter Exchange Index (the CFPE Index) is derived as the quotient of the individual capillary-to-fibre ratio (i.e., the capillary-to-fibre ratio calculated for each fibre individually) and the fibre perimeter. This method is suggested to provide a means of quantitating potential alterations in the capacity for oxygen flux (e.g., as may occur in response to a training intervention) and any carrier- or receptor-mediated aspect of blood-tissue exchange between the capillaries and muscle fibres (e.g., insulin or glucose delivery).Key words:capillary supply, muscle fibres, oxygen flux, training, diabetes

ISSN:1066-7814    

DOI:10.1139/h97-002

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The ventilatory response to acute progressive hypoxia below the carbon dioxide threshold using rebreathing was investigated. Nine subjects rebreathed after 5 min of hyperventilation to lower carbon dioxide stores. The rebreathing bag initially contained enough carbon dioxide to equilibrate alveolar and arterial partial pressures of carbon dioxide to the lowered mixed venous partial pressure (≈ 30 mmHg), and enough oxygen to establish a chosen end-tidal partial pressure (50-70 mmHg), within one circulation time. During rebreathing, end-tidal partial pressure of carbon dioxide increased while end-tidal partial pressure of oxygen fell. Ventilation increased linearly with end-tidal carbon dioxide above a mean end-tidal partial pressure threshold of 39 ± 2.7 mmHg. Below this peripheral-chemoreflex threshold, ventilation did not increase, despite a progressive fall in end-tidal oxygen partial pressure to a mean of 37 ± 4.1 mmHg. In Conclusion, hypoxia does not stimulate ventilation when carbon dioxide is below its peripheral-chemoreflex threshold.Key words:peripheral chemoreflex, rebreathing technique, hyperventilati

ISSN:1066-7814    

DOI:10.1139/h97-003

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

We evaluated the effects of short-term, high-intensity exercise training and detraining on resting left ventricular diastolic function (LVDF) and maximal aerobic power (VO2max) in 7 sedentary older (age = 68 ± 4 years) men (n = 5) and women (n = 2). Training consisted of cycling for 60 min with power output set at 70% (Day 1), 80% (Day 2), and 90% (Days 3-5) of the pretraining peak work rate. Detraining consisted of a return to regular exercise habits. LVDF increased 10% in the early (E) flow velocity, decreased 18% in the late (A) flow velocity wave, and decreased 31% in the isovolumic relaxation time. VO2max was increased 12% while plasma volume (PV) increased 10% following, training and returned to baseline after detraining. The exercise-induced change in VO2max was directly related to the change in E/A (r =.52) and indirectly related to the change in IVRT (r = −.62). It was concluded that short-term, high-intensity exercise training improves LVDF and is tolerated well in older subjects, and that the calculated changes in PV and aerobic power are similar to those observed previously in a younger population.Key words:aging, training, cardiac filling

ISSN:1066-7814    

DOI:10.1139/h97-004

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The effectiveness of a new water delivery system (the Water-Del) was examined for maintaining euhydration compared to other fluid replacement strategies. Subjects (N = 10) performed three 60-min cycling trials (@ 50% of VO2max) in an environmental chamber (27 °C; RH = 50%). Trials were randomly assigned from Water-Del (metered: 200 ml water every 15 min), ad libitum every 15 min (ad-lib-15), and ad libitum (ad-lib). Total water intake (TWI), changes in plasma volume (ΔPV), body Weight (ΔBW), thirst, skin temperature (Tsk), and heart rate (HR) were measured. A significant difference (p ≤.05) among trials was observed for TWI, with metered (1.200 ± 0.12 ml) being greater than ad-lib-15 (358 ± 48 ml) and ad-lib (522 ± 106 ml). No significant difference was found for ΔPV. A significant difference (p ≤.05) for ΔHW was observed with metered (0.28 ± 0.16 kg) being different than ad-lib-l5 (−0.63 ± 0.12 kg) and ad-lib (−0.34 ± 0.14 kg). No significant differences (p > .05) were found for thirst, Tsk, or HR. The Water-Del provides for greater fluid intake during exercise compared to other replacement strategies.Key words:hydration, dehydration, plasma volume

ISSN:1066-7814    

DOI:10.1139/h97-005

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Interval samplings uncover blood diurnal oscillations for several hormones, highlighting the importance of short time intervals in the disclosure of subtle pulsatile patterns of some peptide hormones, namely LH. In a study designed to develop new probes against steroid misuse, venous blood was sampled at 5-min intervals for 4 hours from 12 eugonadal adult male athletes, 6 receiving transcutaneous administrations of testosterone propionate and 6 placebo subjects. Brief supraphysiologic serum testosterone peaks were disclosed, the amplitude and frequency of these peaks being larger for the treated group. No solid explanation could be given to explain these bursts. Neither the binding/dissociation kinetics of SHBG molecules with and without increased circulating level of dihydrotestosterone, nor brief testosterone-inducing LH bursts, nor increased Leydig cell release could be invoked to explain these peaks. Their occurrence, although relatively rare, could represent a threat and lead to improper treatment.Key words:blood testosterone, transcutaneous administration

ISSN:1066-7814    

DOI:10.1139/h97-006

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

This study compared the lipid profile of women runners with menstrual cycle irregularities with their normally menstruating counterparts. Relationships among selected steroid hormones and serum lipid levels in 10 eumenorrheic (EU) and 8 oligo-/amenorrheic (O/A) women runners and 6 eumenorrheic controls (CON) were examined. Serum 17 β-estradiol (E2), progesterone (Prog), and dehydroepiandrosterone-sulfate (DHEAS) concentrations were determined in daily blood samples for 21 days, and integrated concentrations were calculated. Fasting blood samples were analyzed far total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), HDL2, HDL3, triglycerides (Trig), and apolipoproteins A-I, A-II, and B. The O/A group had significantly lower E2and Prog than EU or CON groups. Women in the CON group had lower HDL-C and HDL3than the runners. With all women grouped together, E2was not significantly correlated with any measured blood lipid parameters. On the other hand, DHEAS was significantly correlated with HDL-C, HDL2, and apolipoprotein A-I. These data demonstrate that women runners, regardless of menstrual cycle status, exhibit higher HDL-C concentrations than CON and supports previous research reporting a positive association between DHEAS and HDL-C.Key words:estradiol, DHEAS, cholesterol, exercise, amenorrhea

ISSN:1066-7814    

DOI:10.1139/h97-007

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

This investigation examined the relationship between several different aerobic fitness test results and measurements of metabolic recovery from intermittent, high-intensity exercise in 16 male cyclists. No significant correlations were found between maximal oxygen consumption, ventilation threshold, various submaximal endurance measures and the rate of metabolic recovery, net excess postexercise oxygen consumption, or blood lactate removal after intermittent high-intensity exercise except for submaximal heart rate (r = .66,p < .05). These data indicate that aerobic fitness assessments do not indicate the ability to recover after intermittent, high-intensity exercise in endurance-trained cyclists.Key words:maximal oxygen consumption, recovery oxygen consumption, ventilation threshold, lactate, heart rate

ISSN:1066-7814    

DOI:10.1139/h97-008

出版商:NRC Research Press    

年代:1997

数据来源: NRC