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Biomedical subjects

K J Stewart

Publications and source records attributed to K J Stewart.

At least 55 records · Page 3Linked to original sources
PubMed1990

Effects of diltiazem or propranolol during exercise training of hypertensive men.

This was a prospective, randomized, double-blind, placebo-controlled trial to establish whether beta blockers or calcium-channel blockers limit exercise capacity and training responses in men with mild hypertension. Circuit weight and aerobic training was used to assess the effects of drugs on cardiovascular fitness and muscle strength. Fifty-two sedentary men, ages 25-59 yr, with a diastolic blood pressure of 90-105 mm Hg off drugs, without significant ST depression during maximal stress testing, received diltiazem, propranolol, or placebo. Maximal oxygen uptake (VO2max) and exercise duration during treadmill testing, as well as one-repetition maximal strength, were assessed on eight weight machines after a single-blind placebo baseline, after 2 wk of drug run-in, and after 10 wk of exercise training. Total daily doses were 240 mg for propranolol and 360 mg for diltiazem. Propranolol decreased VO2max after drug run-in (P less than 0.05). Exercise training increased VO2max (P less than 0.05) in the diltiazem and placebo groups. After training VO2max in the propranolol group increased (P less than 0.05) from run-in but not beyond baseline levels. Thus, the reduction of VO2max consequent to propranolol therapy limited the overall benefits of training. Exercise duration did not change with run-in and increased (P less than 0.05) with training by 22%, 19%, and 10% for the diltiazem, placebo, and propranolol groups, respectively. Strength after run-in was unchanged, and exercise training increased strength (P less than 0.0001) on all weight machines in all groups. The results show an advantage of diltiazem to propranolol, particularly among physically active patients engaged in aerobic exercise who require antihypertensive therapy.

Adolescent↗
PubMed1989

Resistive training effects on strength and cardiovascular endurance in cardiac and coronary prone patients.

Resistive training using heavy loads with few repetitions increases strength but does little to improve cardiovascular endurance. Circuit weight training, a form of resistive training using moderate loads with frequent repetitions, is used to improve both cardiovascular and strength fitness. Studies of circuit weight training in healthy adults and athletes have shown increases of 20-45% and cardiovascular improvement from 0 to 15%. An increasing number of exercise programs for cardiac and coronary prone populations have introduced circuit weight training. The few reported studies have shown that high risk patients can attain increases in fitness similar to those seen in healthy populations. Furthermore, the hemodynamic responses to circuit weight training suggest that it is a clinically safe and acceptable form of exercise.

Blood Pressure↗
PubMed1989

Introduction to the symposium: resistive weight training: a new approach to exercise for cardiac and coronary disease prone populations.

This symposium is concerned with the use of resistive exercise in cardiac and coronary prone populations. In the past, these populations have been refrained from resistive exercise. However, recent studies suggest that this form of exercise is safe and has favorable effects on physical fitness, cardiac risk factors such as hypertension and hyperlipidemia, and psychological status.

Coronary Disease↗
PubMed1988

Suckling and lactational anoestrus in wild gorillas (Gorilla gorilla).

The present observations of wild gorillas demonstrate that lactation has a major influence on birth spacing. The frequency of suckling declined as infants matured, from greater than 1/h during the first year to about 1/2 h by 30-36 months when mothers usually resumed sexual cycling. In contrast, the length of suckling bouts remained relatively constant throughout lactation, averaging between 2.6 and 3.2 min per bout. Within infant age categories, suckling frequencies of less than or equal to 0.5 bouts/h were associated with mothers who had resumed cycling, whereas higher frequencies were associated with mothers who were still anoestrous. These results complement those obtained from studies of breast-feeding in humans, and support the suggestion that the frequency of suckling is a critical factor in the contraceptive effects of lactation.

Anestrus↗
PubMed1986

Usefulness of self-efficacy in predicting overexertion during programmed exercise in coronary artery disease.

Overexertion during group jogging was evaluated in relation to self-perceived functional capacity and ability to self-monitor exertional heart rate in 40 men, mean age 55 +/- 9 years, with documented coronary artery disease. Patients' confidence in their ability to jog various distances was measured with a jog self-efficacy (SE) scale before a group exercise program was begun. Depression, type A personality, and performance of symptom-limited treadmill exercise were also assessed. Later, each patient was monitored with ambulatory (Holter) electrocardiography during programmed group jogging. Ambulatory monitoring disclosed significant noncompliance with exercise prescriptions: 33% of patients exceeded their prescribed range of 70% to 85% of maximal treadmill heart rate for at least 10 minutes of the 20-minute exercise bout. Another 25% spent 10 minutes or longer exercising below the prescribed range. Pretest jog SE predicted the number of minutes patients exercised above or below the prescribed intensity, but depression, type A and treadmill performance measures did not. Self-monitoring accuracy (the amount of agreement between exercise heart rate recorded by the electrocardiogram and by the patient) was also related to the number of minutes patients exercised outside the prescribed range. Comparison of SE and self-monitoring accuracy variables revealed that "overachievers" were patients who overestimated their ability to jog, while "underachievers" were those who overestimated their heart rate during exercise. Self-perceptions and self-monitoring skills appear to be important independent predictors of behavioral compliance to exercise guidelines.

Adult↗
PubMed1986

Circuit weight training in cardiac patients.

This was a prospective, randomized evaluation of the safety and efficacy of 10 weeks of circuit weight training in patients, aged 35 to 70 years, with documented coronary artery disease. Circuit weight training refers to the performance of a series of weight-lifting exercises using a moderate load with frequent repetitions. Patients had participated in a supervised cardiac rehabilitation program for a minimum of 3 months before the study. Control patients (n = 20) continued with their regular exercise consisting of a walk/jog and volleyball program, while the experimental group (n = 20) substituted circuit weight training for volleyball. No sustained arrhythmias or cardiovascular problems occurred. The experimental group significantly increased treadmill time from 619 to 694 seconds while the treadmill time of the control group did not change. Strength in the experimental group increased by an average of 24% while there was no change in the control patients. Circuit weight training appears to be safe, and to result in significant increases in aerobic endurance and musculoskeletal strength compared with traditional exercise used in cardiac rehabilitation programs.

Adult↗
PubMed1986

Self-efficacy mediates strength gains during circuit weight training in men with coronary artery disease.

Motivation to engage in health-promoting exercise has been ascribed to global personality traits such as self-esteem or athletic self-confidence. Self-Efficacy Theory challenges this view by proposing that highly specific estimates of personal capabilities mediate adoption of new or difficult behavior patterns. We tested this assumption by measuring self-efficacy perceptions in 40 men with coronary artery disease who participated in an experiment evaluating effects of circuit weight training (CWT). Specific self-efficacy estimates were assessed during baseline strength/endurance testing and after 10 wk participation in CWT or volleyball. Correlational analyses of self-efficacy in relation to performance on strength/endurance tests strongly supported the contention that adoption of novel activities is governed by highly specific self-perceptions. Participation in CWT produced greater strength and endurance gains than did volleyball, and these changes were accompanied by increased self-efficacy in CWT subjects for activities resembling the training tasks. The assertion that self-efficacy perceptions directly mediate involvement in challenging physical activities was supported by multiple regression analyses. These revealed that pre-training self-efficacy judgments predicted post-test strength gains even after controlling for baseline strength, type of training and frequency of participation in exercise sessions.

Adult↗
PubMed1983

The effects of family disruption on adolescent males and females.

Given the rapidly increasing rate of marital dissolution, a staggering number of children are experiencing family disruption. The purpose of this study was to ascertain the possible effects of separation and divorce on the formation of adolescents' self-image. Additionally, this study sought to determine if adolescents from disrupted homes differed from those from intact homes with regard to anxiety levels, locus of control, and perception of their family. A total of 217 subjects participated in the study by completing a battery of questionnaires. Results indicated that males from disrupted homes had better self-concepts and better perceptions of their family environment than those from intact homes. The opposite results were found among females, emphasizing the difference between the sexes in adjusting to family disruption.

Adaptation, Psychological↗
PubMed1980

Reproduction in wild gorillas and some comparisons with chimpanzees.

Information was collected over a period of almost 12 years on the gorillas of the Virunga Volcanoes region of Rwanda and Zaire, most of it collected since September 1972. Comparisons were made with the Gombe Stream chimpanzee population (values in parentheses). Gorilla females matured at about 8 years (compared with 9-10 years for the chimpanzee) and first bred at 10-11 years (11-12 years). Males started to breed later, possibly at 15 years (about 13 years). Oestrous periods of female gorillas lasted for about 2 days (10 days) and oestrous cycles for about 30 days (36 days). Gestation in the gorilla lasts 255 days (228 days). Intervals between surviving offspring in the Virunga study groups was about 4 1/2 (5 1/2 years) but in the whole Virunga population was nearer 8 years. Lactational amenorrhoea lasted about 2 1/2 years (3 1/2 years). In gorillas and chimpanzees there were about 3 cycles to conception after parturition and females probably produce in their lifetime about 3 offspring that survive to adulthood. A successful male's productivity is greater. Mortality of immature gorillas was about 40% (50%). Initiation of courtship is generally by the female in gorillas but the male in chimpanzees. Copulation in gorillas lasts for about 1 1/2 min (7 sec) and occurs at a rate of once every 3 h when a female is in oestrus (once in 2 h). Interference in copulation is more common in the chimpanzee than the gorilla, but competition between individual males is more intense in gorilla populations. Females of both species can clearly exercise their preferences for particular males. The observed differences between the species in courtship and mating behaviour can be related to differences in the number of males available to and competing for oestrous females: in the loose multi-male chimpanzee community there is more advantage to males in initiating copulation and mating frequently and efficiently, and to females in advertising oestrus, than in the relatively stable one-male mating system of the gorilla.

Animals↗
PubMed1977

Physiological and morphological factors associated with successful fencing performance.

The relation between fencing success during a season of intercollegiate competition and various physiological and morphological variables were determined in 14 fencers. Bivariate and multiple regression analysis was used to determine the extent to which the independent variables, individually and collectively, accounted for the variance in two measures of fencing success. The fencing scores correlated significantly with VE max, Vo2 max, the 2 km run, and weight, while there was no significant correlation between the fencing scores and submaximal heart rate at 6 mph, and 1 min steptest score, or other morphological measurements. Cardiorespiratory fitness variables of Vo2 max and VE max accounted for the greatest variance in each of the two fencing scores (57.7 and 58.1%, respectively). Although morphological factors play a role in fencing success, their influence is small when physiological factors are accounted for. Future energy-cost studies are suggested to determine the physiological basis for the relationship between cardiorespiratory fitness and fencing success.

Adipose Tissue↗
PubMed1976

Cardiorespiratory mobilization and endurance performance.

Twenty subjects performed for 11 min on a bicycle ergometer 30 sec following 5 min of prior exercise (PE) at each of four different intensities. PE was adjusted to maintain a heart rate of 110, 140, and 170 beats/min. The 4th treatment was no PE. Heart rate was an estimate of the mobilization of the cardiorespiratory system during exercise. The criterion task (CT) included cycling for 10 min against 3 kg resistance at 68 rpm followed by 1 min of an all-out work bout where subjects tried to complete as many rpm's as possible against 3 kg. The 11th minute was used to assure the complete exhaustion of energy reserves following the paced part of the task. Overall performance following PE-170 was significantly worse than that following no PE, PE-110, and PE-140, which was probably due to a build up of anaerobic metabolites such as lactate during the PE. Total work appeared to be greatest following PE-110, which showed a slight tendency toward better performance especially after the 6th minute. However, no clear cut evidence was produced to support the hypothesis that light to moderate PE would sufficiently improve performance by mobilizing the cardiorespiratory system, thereby reducing the initial oxygen deficit in the CT and thus allowing more work to be performed.

Adult↗
PubMed1975

The prediction of maximal oxygen uptake before and after physical training in children.

Maximal oxygen consumption (V O2 max) expressed in ml/kg/min and predicted V O2 max were determined before and after 8 weeks of training in 24 boys 10-12 years. Training involved 13 of them while 11 were controls. Predicted V O2 max was based on submaximal cycling heart rate according to the Astrand-Rhyming procedure. Pre-training, V O2 max was underpredicted by 12 per cent. This resulted mainly from an apparently low cycling efficiency in these subjects compared to that implicit in the prediction equation. Although adjustments in the prediction equation could equalize the means for V O2 max and predicted V O2 max, the rather low correlation (r = .55) between these measures precluded the accurate prediction of individual scores. V O2 max remained unchanged with training while submaximal heart rate during bicycle and treadmill exercise showed a significant decrease, resulting in predicted increases in V O2 max in children. Since V O2 max was actually unchanged, the prediction falsely indicated an improvement. Furthermore, despite a significantly lower heart rate in the trained group, there was no difference in predicted V O2 max between the groups post-training. These findings indicate that if V O2 max is the parameter of interest, it would seem to be more satisfactory to measure it directly until more reliable methods of prediction are developed.

Analysis of Variance↗