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N Gledhill

Publications and source records attributed to N Gledhill.

35 records · Page 2Linked to original sources
PubMed1995

A study to validate the modified Canadian Aerobic Fitness Test.

This study evaluated the predictive ability of the modified Canadian Aerobic Fitness Test (mCAFT) on an independent sample of subjects and compared it to the original Canadian Aerobic Fitness Test (CAFT). Male and female subjects (n = 154), 15-69 yrs of age, performed the mCAFT and a maximal treadmill test. VO2max scores predicted from the mCAFT equation did not differ significantly from those measured during the treadmill test, whether the sample was analysed overall or categorized by sex, whereas the CAFT (Jetté) equation resulted in VO2max scores that were significantly lower than either the measured values or those predicted using the mCAFT. The strength of the linear relationship between predicted and measured VO2max scores is the same for both the mCAFT (r = 0.88) and CAFT (r = 0.89). However, the mCAFT results in a lower mean square error (37.0 for mCAFT vs. 63.3 for CAFT) and thus is an improvement over the CAFT prediction.

Adolescent↗
PubMed1995

Determining power outputs for cycle ergometers with different sized flywheels.

A number of cycle ergometers are presently being used in a variety of laboratory applications for which the quantification of power output is required. To calculate the power output of cycle ergometers with varying sized flywheels, the circumference of the resistance track on the flywheel is multiplied by the number of flywheel revolutions produced with one complete revolution of the pedal. This provides the "effective distance travelled," and by selecting an appropriate combination of pedalling rate plus flywheel resistance, any desired power output can be produced.

Ergometry↗
PubMed1994

Endurance athletes' stroke volume does not plateau: major advantage is diastolic function.

Left ventricular function was examined during incremental work rates to maximum using simultaneous determinations of stroke volume, left ventricular ejection time (LVET), and diastolic filling time (DT). Seven endurance trained and seven untrained young adult males were studied on a cycle ergometer at matched heart rates of 90, 120, 140, 160, 180, and 190 bpm (+/- 1 bpm). Stroke volume of the untrained subjects reached a plateau at 120 bpm, but stroke volume of the trained subjects continued to increase to their maximum heart rate with no plateau. Throughout incremental work rates, LVET was significantly longer and DT was significantly shorter in the trained subjects. At a heart rate of 190 bpm, the corresponding rates of ventricular emptying and ventricular filling of the trained versus the untrained subjects were 20% and 71% greater, respectively (P < 0.01). We conclude that during incremental work rates the stroke volume of endurance trained athletes increases progressively to maximum with no plateau. In addition, although trained athletes rely on enhancements in both ventricular filling and ventricular emptying to augment stroke volume, by far their major advantage over untrained subjects is in ventricular filling.

Adult↗
PubMed1992

Development and validation of a fitness screening protocol for firefighter applicants.

It is imperative that fitness screening protocols for firefighter applicants embody the specific physical requirements of fighting fires. Based on the physiological characterization of experienced firefighters performing essential tasks, a test battery was developed that includes both job related performance tests and a combination of health related and performance related laboratory tests of physical fitness. Fifty-three firefighters with an average of 5.4 years of experience completed the battery and provided Likert scale comparisons of the tests with actual firefighting operations for criterion validation. "Acceptable" through "maximum" times were established for the job related performance tests, and "minimum" through "optimum" standards were developed for the physical fitness tests. Guidelines for the medical screening of firefighter applicants are also described. In addition, an overall scoring procedure was formulated for the ranking of acceptable applicants.

Adult↗
PubMed1992

Characterization of the physical demands of firefighting.

To characterize the physical demands associated with on-the-job use of current firefighting equipment and the performance of essential firefighting operations, an initial task analysis of all firefighting operations was followed by an in-depth physical and physiological characterization of those tasks deemed to be physically demanding. The most commonly encountered applications of strength and endurance were lifting and carrying objects (up to 80 lbs), pulling objects (up to 135 lbs), and working with objects in front of the body (up to 125 lbs). The most demanding firefighting operations required a mean VO2 of 41.5 ml/kg.min-1 with peak lactate concentrations of 6 to 13.2 mM. Ninety percent of the demanding firefighting operations that were studied required a mean VO2 of 23 ml/kg.min-1. These aerobic energy requirements corresponded to 85 and 50% VO2max, respectively. Therefore a minimum VO2max standard for firefighter applicants of 45 ml/kg.min-1 is recommended.

Adult↗
PubMed1992

Development of fitness screening protocols for physically demanding occupations.

The fitness screening of applications to physically demand occupations has become increasingly complex with the advent of Equal Opportunity legislation and Affirmative Action initiatives. A comprehensive study was conducted of the physical demands and associated physiological responses of workers in strenuous jobs at a large multifaceted natural gas company. Based on these findings, an applicant fitness screening protocol was developed and validated. The protocol was implemented for an 18-month period, after which the results were examined with regard to gender differences in success rates and other influencing factors. Because of ongoing changes in attitudes and practices in the workplace, fitness screening for applicants was interrupted and a review was initiated of all strenuous jobs with the aim of reducing their physical demands.

Humans↗
PubMed1986

Effect of graded erythrocythemia on cardiovascular and metabolic responses to exercise.

The effects of graded induced erythrocythemia on cardiovascular and metabolic responses to intense treadmill running were studied in four highly trained endurance runners. Three autologous infusions of 1 unit (U) whole blood (450 ml/U) were administered sequentially 2-7 days apart. Maximal O2 consumption (VO2max) increased from 5.04 l/min at control (C) to 5.24 l/min after 2 U (R2) and 5.38 l/min after 3 U (R3). Cardiac output during treadmill running at 91% control VO2max was 28.2 l/min at C, 29.8 l/min at R2, and 33.1 l/min at R3. Corresponding heart rates were unchanged, and stroke volume was increased at R3. Peak lactate concentration was reduced, and arterial acid-base status improved at R2 and R3 after standardized bouts of intense exercise. Arterial blood pressures and electrocardiograms during exercise were not affected by erythrocythemia. We conclude that the reinfusion of up to 3 U of autologous blood into highly trained endurance runners who have normal hematology does not adversely affect their cardiovascular response to maximal exercise. In addition, the increases in VO2max following reinfusion of 2 U, and again after 3 U, suggest that the aerobic power of the working muscles was not surpassed at these levels of erythrocythemia.

Acid-Base Equilibrium↗
PubMed1984

Validation of noninvasive maximal cardiac output measurement.

Due to the invasiveness of direct techniques and problems that constrain the use of popular indirect techniques during very heavy (non-steady-state) exercise, measurements of maximal cardiac output are seldom included in studies of exercise. The acetylene-rebreathing technique is well-suited for maximal exercise; however, until recent technological advances, difficulties involved in collecting and measuring alveolar acetylene samples have restricted its use. We compared cardiac output values measured via the acetylene-rebreathing technique (QA) (modified for use with a mass spectrometer) and the dye-dilution technique (QD) at rest and during light to maximal exercise in six moderately active males. Although QA consistently underestimated QD, the two techniques showed a significant correlation of 0.87 throughout all levels of exercise. During maximal exercise, QA and QD values were not significantly different (24.7 and 26.7 l X min-1, respectively). Modifications in the QA technique that reduce potential sources of error were also examined. We conclude that the acetylene-rebreathing technique, modified for use with a mass spectrometer, is a simple and valid procedure for measuring maximal cardiac output.

Adult↗
PubMed1983

Effect of acute induced metabolic alkalosis on 800-m racing time.

Six trained middle-distance runners wer studied under alkalotic (NaHCO3 ingestion), placebo (CaCO3 ingestion), and control conditions to determine the effect of an acute induced metabolic alkalosis on time to run an 800-m race. Pre-exercise, following NaHCO3 ingestion, pH and standard [HCO3-] were significantly higher. In the alkalotic condition, subjects ran faster (2.9 s) and the corresponding post-exercise values for blood [lactate] and extracellular H+ were higher than in the control and placebo conditions, suggesting an increased anaerobic energy contribution. These results support the speculation that the increase in extracellular buffering following NaHCO3 ingestion facilitated H+ efflux from the cells of working muscle, thereby delaying the decrease in intracellular pH and postponing fatigue. It is concluded that the ingestion of NaHCO3 by trained middle-distance runners prior to an 800-m race has an ergogenic benefit.

Bicarbonates↗
PubMed1982

Blood doping and related issues: a brief review.

The intent of blood doping is to increase maximal aerobic power by increasing the capacity of blood to carry oxygen. This manipulation gained notoriety in the sports world because of rumors of blood doping by competitors in endurance events. Researchers also have become interested in induced erythrocythemia because its study provides insight into the limiting factor(s) of maximal aerobic power (Vo2max). It is concluded in this review that to increase Vo2max, it is necessary to elevate significantly the hemoglobin concentration by infusing at least 900 ml of blood. The use of inadequate reinfusion volumes, premature reinfusion of the blood following withdrawal, and storage of the blood by refrigeration rather than by freezing are major reasons for the contradictory findings from earlier studies of blood doping. Changes in blood volume and 2,3-diphosphoglycerate following blood doping are transient and, other than during the first 24 h post infusion, appear to be inconsequential. In addition, this review also examines related issues such as attendant hemodynamic and lactate changes, the need of controls, and ethical considerations in blood doping.

2,3-Diphosphoglycerate↗
PubMed1980

Effect of induced erythrocythemia on aerobic work capacity.

The aerobic work capacity of 11 highly trained runners was studied employing a double-blind design 1) before phlebotomy (C1), 2) following restoration of normocythemia (C2), 3) after a sham reinfusion of 50 ml of saline (sham), 4) following autologous reinfusion of approximately 900 ml of freeze-preserved blood (reinfusion), and 5) upon reestablishment of control hematologic levels after erythrocythemia (C3). There were no hematologic differences among C1, C2, sham, and C3, but following reinfusion, hemoglobin was significantly elevated (15.7-16.7 g . 100 ml-1). Maximum O2 consumption (VO2max) and running time to exhaustion were significantly increased 24 h postreinfusion (5.11-5.37 l . min-1 and 7.20-9.65 min, respectively) and 7 days postreinfusion. When sham preceded reinfusion, VO2 max and time to exhaustion were the same as control. However, 16 wk postreinfusion, despite the return to normal hematologic values, VO2max remained significantly above control levels at sham and C3. These findings indicate that there is a distinct increase in VO2max following induced erythrocythemia and suggest that oxygen transport limits maximal aerobic capacity.

Adult↗
PubMed1978

VA/Q inhomogeneity and AaDO2 in man during exercise: effect of SF6 breathing.

Pulmonary gas exchange was studied in five normal subjects both at rest and during moderate steady-state exercise on a bicycle ergometer while breathing a) room air and b) a mixture of 20.9% O2-balance sulfur hexafluoride (SF6). The alveolar-arterial oxygen pressure differences (AaDO2) widened significantly from rest to exercise. Breathing the O2-SF6 mixture reduced the AaDo2 significantly from 10.9 to 4.2 Torr at rest and from 15.5 to 10.1 Torr during exercise (P less than or equal to 0.01). There were no concurrent changes in metabolism, cardiac output, or heart rate during the SF6 breathing. Possible changes in the anatomic shunt fraction, alveolar-end-capillary equilibration, or the distribution of blood flow cannot account for these observations. We conclude that the AaDO2 increase during exercise reflects an inhomogeneity of ventilation-perfusion ratios (VA/Q) most probably arising within regions of the lung (intraregional inhomogeneity) rather than between regions (interregional inhomogeneity).

Adult↗
PubMed1975

Renal response to short-term hypocapnia in man.

This study examines the renal response to moderate hyperventilation in healthy man. Eight men hyperventilated for 26 hr (PaCO2 approximately 30 to 32 mm Hg) in normoxia (barometric pressure, PB approximately 740 mm Hg) and hypobaric hypoxia (PB approximately530 mm Hg). Anaerobic samples of arterial blood and urine were studied at two-hour intervals. Plasma [HCO3-] fell with time during sustained hypocapnia and after 26 hr was reduced 2.5 mEq/liter, with plasma pH compensated approximately 60%. Statistically significant changes in renal H+ handling were observed within the initial 2 hr of hyperventilation and were evident over the first 12 hr. Over 26 hr, mean total HCO3-excretion in hypocapnia was 10.2 mEq above control and mean total acid excretion (UVTA + UVNH4+) was 17.5 mEq below control. An increased urinary excretion of cations, especially sodium, accompanied the decrease in acid excretion. Plasma lactic acid accumulation was negligible. We conclude that renal mechanisms contribute significantly and relatively quickly to plasma pH compensation during the early phase of adaptation to hypocapnia in man.

Acid-Base Equilibrium↗
PubMed1975

Effects of moderate hypoxemia and hypocapnia on CSF [H+] and ventilation in man.

The effects of 26 h of normoxic hypocapnia (PaCO2, 31 MMHg) vs. 26 h of hypocapnia plus hypobaric hypoxia (PaCO2 32, PaO2 57 mmHg) were compared with respect to: a) CSF acid-base status; and b) the spontaneous ventilation (at PIO2 145 mmHg) which followed the imposed (voluntary) hyperventilation. For each condition of prolonged hypocapnia, PaCO2 was held constant throughout and pHa and [HCO3-]a were constant over the final 6-10 h. We assumed that measured changes in lumbar CSF acid-base status paralleled those in cisternal CSF. Spontaneous hyperventilation followed both normoxic and hypoxic hypocapnia but was significantly greater following hypoxic hypocapnia. In the CSF, pH compensation after 26 h of hyperventilation was incomplete (similar to 45-50%), was similar to that in arterial blood, and was unaffected by a superimposed hypoxemia. These data were inconsistent with current theory which proposes the regulation of CSF [HCO2] via local mechanisms and, in turn, the mediation of ventilatory acclimatization to hypoxemia and/or hypocapnia via CSF [H+]. Alternative mediators of ventilatory acclimatization were postulated, including mechanisms both dependent on and independent of "chemoreceptor" stimuli.

Acid-Base Equilibrium↗