Search PubMed⌕ Search

Biomedical subjects

E T Howley

Publications and source records attributed to E T Howley.

At least 37 records · Page 2Linked to original sources
PubMed1995

Criteria for maximal oxygen uptake: review and commentary.

Historically, the achievement of maximal oxygen uptake (VO2max) has been based on objective criteria such as a leveling off of oxygen uptake with an increase in work rate, high levels of lactic acid in the blood in the minutes following the exercise test, elevated respiratory exchange ratio, and achievement of some percentage of an age-adjusted estimate of maximal heart rate. These criteria are reviewed relative to their history, the degree to which they have been achieved in published research, and how investigators and reviewers follow them in current practice. The majority of the criteria were based on discontinuous protocols, often carried out over several days. Questions are raised about the applicability of these criteria to modern continuous graded exercise test protocols, and our lack of consistency in the terminology we use relative to the measurement of maximal oxygen uptake.

Exercise↗
PubMed1994

Adding polylactate to a glucose polymer solution does not improve endurance.

Polylactate (PL), a semi-soluble amino acid/lactate salt, is a newly developed carbohydrate supplement purported to increase endurance. Our purpose was to determine if the addition of PL to a glucose polymer solution (GP) extends exercise time relative to a pure GP solution. In a double blind and random crossover design, 5 subjects exercised twice to exhaustion at 70% of VO2max. During the trials, they consumed GP or a GP/PL mixture at the rate of 0.3 g carbohydrate per kg of body wt in a 7% solution every 20 min until exhaustion. The GP/PL mixture contained 6.25 g GP to 0.75 g PL per 100 ml of water. Mixture composition was critical because PL, as supplied by the manufacturer and under our experimental conditions, produced severe gastro-intestinal efflux in concentrations > or = 2.5%; PL was tolerable in concentrations < or = 0.75%. At 20 min intervals, we measured VO2, respiratory exchange ratio, heart rate, and perceived exertion. At 30 min intervals, we measured serum glucose, insulin, free fatty acids, and glycerol as well as whole blood lactate and pH. We found that the addition of PL to a GP solution had no measurable physiological or performance effects.

Adult↗
PubMed1994

Substrate utilization during prolonged exercise in obese women differing in body fat distribution.

The present investigation compared the pattern of substrate utilization during prolonged walking in obese women with upper (UB) and lower (LB) body fat patterns and the effect of beta-adrenergic receptor blockade on that response. Twenty healthy, premenopausal, obese volunteers (% fat > or = 30%) were characterized by waist-to-hip (WHR) circumference ratios into two distinct groups (UB: WHR > or = 0.85, LB: WHR < or = 0.75). The groups (n = 10 each) were similar for BMI, age, % fat, and maximal aerobic power (VO2max). Subjects participated in two 60-min walk bouts at 55-60% VO2max. The trials (placebo (C) and 80 mg propranolol (PR)) were performed in random order, 110 min after ingestion, with 2-4 days between tests. Open-circuit spirometry was employed to calculate the VO2, VCO2 and respiratory exchange ratio (RER) at 10 min intervals. A significant (P < 0.0001) decline in RER with time was evident in both trials. However, no group differences existed in RER values during either the C trial (RER range = 0.81-0.88) or the PR trial (RER range = 0.86-0.91). The PR trial induced a 23% reduction in the amount of calories utilized as fat compared to C in both WHR groups. Both groups of women showed equal capabilities for performing prolonged exercise with typical and appropriate metabolic shift in fuel mobilization from carbohydrate to fat. Despite the well-defined differences in metabolic activity of adipose cells shown in vitro, this study indicates that women with significantly different regions of adipose tissue stores have similar physiological potentials for substrate use during exercise.

Adipose Tissue↗
PubMed1993

Effect of one- and two-leg training on arm and two-leg maximum aerobic power.

The purpose of this study was to examine the effect of one- and two-leg training on arm and two-leg maximum aerobic power. Seven subjects cycle-trained both legs simultaneously for 30 min.day-1, 4 days.week-1 for 4 weeks. Nine subjects cycle-trained each leg 15 min.day-1, 4 days.week-1 for 4 weeks. Both groups trained at a heart rate equal to that measured at 75% of their two-leg maximum aerobic power. Thus, during each training session the groups performed 30 min of work at the same heart rate intensity. Five subjects served as a non-training control group. Arm and leg maximum oxygen uptake tests were conducted before and after training. Only two-leg training induced significant gains in arm aerobic power (P < 0.0003), whereas both modes of training resulted in significant increases in two-leg aerobic power (P < 0.0008). The data demonstrate that improvements in arm aerobic power were dependent on the quantity of leg muscle mass involved in the training, whereas gains in two-leg aerobic power occurred regardless of whether the legs were trained separately or simultaneously.

Adult↗
PubMed1993

The effect of moderate resistance weight training on peak arm aerobic power.

The purpose of this study was to examine the effect of moderate resistance weight training (MRWT) on peak arm aerobic power as measured by arm cranking ergometry. Fourteen sedentary college age males, divided equally into two groups, served as subjects. The seven subjects in the MRWT group completed 12, 1-hr bouts of weight lifting over a 4 week period, exercising on Monday, Wednesday and Friday of each week. Exercise sessions included 3 sets of 10 repetitions of the following lifts: bench press, overhead dumbbell press, dumbbell arm curl, and behind the neck pull down. The remaining seven subjects served as a non-training control group, whose purpose was to account for possible learning effects on the arm ergometer test that could distort the statistical relevance of the aerobic power data. These subjects did not serve as a control for the weight training exercises, as the procedures used to determine muscular strength may produce a modest training effect. Peak arm aerobic power and muscular strength, as measured by the one-repetition maximum for each lift, were determined before and after the training program. The average increase in strength for all lifts combined for the trained group was 20.0%. They also experienced a 13.4% (p < .005) increase in peak arm aerobic power, whereas there was no significant change in this variable for the control group. It is concluded that peak arm aerobic power is enhanced by the changes in muscular strength produced by 4 wks of MRWT.

Adolescent↗
PubMed1993

Evaluation of the Colin STBP-680 at rest and during exercise: an automated blood pressure monitor using R-wave gating.

The application of automated blood pressure measurement during exercise has been limited by inaccuracies introduced by the effects of accompanying motion and noise. We evaluated a newly developed automated blood pressure monitor for measuring exercise blood pressure (Colin STBP-680; Colin, San Antonio, Texas, USA). The STBP-680 uses acoustic transduction with the assistance of the electrocardiogram R-wave to trigger the sampling period for blood pressure measurement. The automated monitor readings were compared with simultaneous technician mercury sphygmomanometric readings in the same arm. Blood pressure was measured in 18 men at rest and during exercise at 40% VO2 peak, (low intensity), 70% VO2 peak (moderate intensity) and VO2 peak (high intensity) on the cycle ergometer. Mean(s.d.) systolic blood pressure difference between the automated monitor and mercury manometer readings at rest and during exercise at low, moderate and high work intensities were 3(0) mmHg, 3(2) mmHg, 1(1) mmHg, and 0(11) mmHg respectively (analysis of variance; P > 0.05). Resting diastolic blood pressure obtained with the STBP-680 was similar to the mercury manometer readings (78(10) versus 81(7) mmHg (P > 0.05). Exercise diastolic pressure at the low level of work intensity was almost identical between the automated monitor and mercury manometer readings (64(8) versus 65(10) mmHg (not significant)). Diastolic blood pressure readings between the STBP-680 and mercury manometer showed a greater difference at the moderate and high workloads (11 mmHg and 9 mmHg, respectively), but this difference was not significant (P > 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Racial differences in maximal vasodilatory capacity of forearm resistance vessels in normotensive young adults.

This study was performed to determine whether alterations in vascular structure exist in a biracial population of young (age 22.3 +/- 0.6 yrs [mean + SE]) normotensive men. We examined maximal vasodilatory capacity in 21 blacks and 20 whites (average blood pressure = 122/75 and 118/72 mm Hg, respectively). Forearm blood flow was determined at rest and after 10 min of ischemic handgrip exercise using venous occlusion plethysmography. Forearm vascular resistance was computed from blood flow and mean arterial blood pressure determined by auscultation. Minimum forearm vascular resistance was 23% higher in blacks (2.60 +/- 0.60) than in whites (2.11 +/- 0.41) (P = .005), and was unrelated to parental history of hypertension. The regression equation for minimum forearm vascular resistance (Y) and casual blood pressure (X) for blacks was Y = -1.782 + 0.0487X (r = 0.522); for whites it was Y = -1.165 + 0.0367X (r = 0.418). When the data were covaried on resting mean arterial blood pressure, blacks still had a higher minimum forearm vascular resistance (P = .014). The results suggest a racial difference in the vascular structure of the forearm resistance vessels.

Adult↗
PubMed1992

Cardiovascular and plasma catecholamine responses to exercise in blacks and whites.

The purpose of the present study was to assess possible racial differences in cardiovascular and plasma catecholamine responses to dynamic exercise. A biracial group of normotensive college-age men (15 blacks, 15 whites) were tested for maximal oxygen uptake, resting blood pressure, and heart rate. Subjects then rode a cycle ergometer at 25%, 50%, and 75% of peak oxygen uptake (6 minutes at each stage). Blood pressure and heart rate were measured during supine rest, seated rest, and at each stage of exercise with an automated blood pressure monitor. At each stage, venous blood was sampled to allow determination of plasma norepinephrine and epinephrine, and cardiac output was measured with the carbon dioxide rebreathing technique. The results indicated that resting blood pressure was similar for blacks and whites (114/68 versus 115/68 mm Hg, respectively). Blacks exhibited greater systolic and diastolic blood pressures during submaximal dynamic exercise. However, blacks also showed a trend toward a positive parental history of hypertension, which has been associated with an increased pressor response. Racial differences did not exist for heart rate or cardiac output, but blacks had higher values for total peripheral resistance both at rest and during exercise. Although no overall racial differences were seen for plasma catecholamine concentrations at rest, blacks had significantly lower levels of norepinephrine (1,275 versus 1,556 pg/ml) and higher levels of epinephrine (306 versus 216 pg/ml) than whites at the highest work rate. The current study confirms the increased pressor response to exercise in normotensive blacks. Blacks had an elevation in total peripheral resistance that was not accompanied by an increase in plasma norepinephrine levels.

Black or African American↗
PubMed1992

Factors affecting the oxygen cost of stepping on an electronic stepping ergometer.

The purposes of this study were to evaluate (a) the effects of step rate and upper body support on the VO2 and HR responses to fixed work rates on the StairMaster 4000 (SM), (b) the accuracy of the SM settings, and (c) how HR compared with that measured during grade-walking on a treadmill. Six subjects worked at a slow step rate for 6 min and then a faster step rate for the last 6 min of a 12-min test at SM settings of 4, 7, and 10 METs. Gas exchange and HR measurements were made at minutes 4-6 and 10-12. Variations in step rate had no effect on HR (P = 0.45) or VO2 (P = 0.84). The effect of using the arms and hands for support was studied using 6 subjects who worked for 12 min at 4, 7, and 10 METs; the first 6 min without support, and the second 6 min with support. Support resulted in lower HR (P = 0.017) and VO2 (P = 0.002) values at 10 METs. The measured MET values were about 20% lower than those specified by machine settings: True MET values = 0.556 + 0.745 (SM setting). Finally, at the same VO2, systematically higher (7-11 b.min-1) HR values were observed for the SM relative to the treadmill.

Adult↗
PubMed1991

Metabolic responses to drafting during front crawl swimming.

We examined the metabolic responses to front crawl swimming when following directly behind (drafting) another swimmer. Seven trained male swimmers participated as subjects. VO2max (l.min-1) was measured during a progressive tethered swim test and was also estimated from a 20 s sample of expired air collected immediately after an all-out, 549 m (600 yard) swim. On different days, each subject performed two 549 m trials at 95% of his maximal swim velocity, one with drafting and one without drafting, using a counter-balanced design. Underwater pace lights were used to establish the predetermined swim velocity. Drafting significantly reduced post-exercise VO2 (2.85 +/- 0.63 vs 3.12 +/- 0.66 l.min-1), blood lactate (3.4 +/- 0.6 vs 5.0 +/- 0.5 mM), and rating of perceived exertion (11.7 +/- 0.4 vs 14.9 +/- 0.5) (P less than 0.05). A repeated measures ANOVA (condition X distance) also revealed significant reductions in HR during the 549 m swim (137.7 vs 146.8 beats.min-1) (P less than 0.05). The results indicate that drafting results in a decrease in energy expenditure for the range of speeds examined.

Adult↗
PubMed1989

The effects of static stretching and warm-up on prevention of delayed-onset muscle soreness.

It has been suggested in the lay literature that static stretching and/or warm-up will prevent the occurrence of Delayed-Onset Muscle Soreness (DOMS). The primary purpose of this study was to determine the effects of static stretching and/or warm-up on the level of pain associated with DOMS. Sixty-two healthy male and female volunteers were randomly assigned to four groups: (a) subjects who statically stretched the quadriceps muscle group before a step, (b) subjects who only performed a stepping warm-up, (c) subjects who both stretched and performed a stepping warm-up prior to a step test, and (d) subjects who only performed a step test. The step test (Asmussen, 1956) required subjects to do concentric work with their right leg and eccentric work with their left leg to voluntary exhaustion. Subjects rated their muscle soreness on a ratio scale from zero to six at 24-hour intervals for 5 days following the step test. A 4x2x2 ANOVA with repeated measures on legs and Duncan's New Multiple Range post-hoc test found no difference in peak muscle soreness among the groups doing the step test or for gender (p greater than .05). There was the expected significant difference in peak muscle soreness between eccentrically and concentrically worked legs, with the eccentrically worked leg experiencing greater muscle soreness. We concluded that static stretching and/or warm-up does not prevent DOMS resulting from exhaustive exercise.

Adolescent↗
PubMed1988

Aerobic power and cardiovascular response to stress.

The relationship between aerobic fitness as measured by maximal O2 uptake (VO2max) and the cardiovascular response to laboratory stressors was examined in two experiments. First, 34 male college students were screened on the basis of their heart rate (HR) response to a reaction time-shock avoidance (RT-AV) task. The six individuals showing an average HR increase of 45 beats/min (reactives) and the six subjects showing an average increase of 8 beats/min (nonreactives) did not differ in VO2max (47.7 +/- 2 vs. 48.7 +/- 1 ml.kg-1.min-1, respectively). However, a statistically significant association between a reported family history of hypertension and peak HR response to RT-AV was seen. In the second series of experiments, the plasma catecholamine and cardiovascular responses of eight elite endurance-trained athletes (VO2max 70.6 +/- 1 ml.kg-1.min-1) and eight untrained volunteers (VO2max 45.5 +/- 1 ml.kg-1.min-1) were compared on the following: RT-AV, reaction time for monetary reward (RT-AP), cold pressor, isometric handgrip, and orthostatic challenge (standing). The trained group exhibited a significantly lower mean HR at rest (P less than 0.05), otherwise there were no significant differences between the two groups. The results indicate that although individual differences (e.g., family history of hypertension and high resting HR) can be related to the potential for cardiovascular responses to novel laboratory challenges, the contribution of fitness to this characteristic is much less clear. Further exploration of questions pertaining to fitness and stress should focus on individuals with a predisposition to stress reactivity.

Adult↗
PubMed1985

The oxygen requirement for horizontal and grade walking on a motor-driven treadmill.

Oxygen uptake (VO2) was measured in males age 10-59 while they walked at 3 mph at various grades on a motor-driven treadmill. The number of subjects in each age group was as follows: age 10-11, N = 24; age 12-13, N = 46; age 14-15, N = 55; age 16-17, N = 53; age 18-19, N = 30; age 20-24, N = 56; age 25-29, N = 35; age 30-34, N = 32; age 35-39, N = 99; age 40-44, N = 106; age 45-49, N = 78; age 50-54, N = 42; and age 55-59, N = 11. Subjects walked at 3 mph at 0% grade for 3 min; thereafter, the treadmill was raised 3% every third minute with speed maintained. Oxygen uptake was measured continuously but only the values during the last minute at each grade were used in the present analysis. The subjects were in a "steady state," insofar as VO2 was concerned, by the second minute. These data were used to validate formulas for estimating VO2 in horizontal and grade walking published in Guidelines for Graded Exercise Testing and Exercise Prescription (1). The formulas are accurate for estimating the mean oxygen requirement in grade walking from 6-18% in adult males. In horizontal walking and walking at 3% grade, the formulas underestimate VO2 in all age groups. In boys under age 18, the formulas underestimate the energy requirement in walking at all grade levels.

Adolescent↗
PubMed1984

Alcohol, cardiorespiratory function and work performance.

Twelve males (six moderate drinkers and six abstainers) were studied for the influence of varying dosages of alcohol on cardiorespiratory function and work performance. The subjects underwent three separate maximal exercise tests which consisted of progressive workloads on the bicycle ergometer. Prior to each work bout the subject consumed either a placebo (0.0 ml.kg-1), small (0.44 ml.kg-1), or a moderate (0.88 ml.kg-1) dose of a 95 per cent ethanol solution. Analysis of the results indicated that the ingestion of a small or moderate amount of alcohol had no significant effect on heart rate, blood pressure, ventilation, oxygen uptake or work performance.

Adult↗
PubMed1983

Effect of hyperoxia on metabolic and catecholamine responses to prolonged exercise.

The use of inspired gas mixtures with an oxygen fraction in excess of 0.3 has been associated with a decrease in the gas exchange ratio (R) during prolonged work in humans. It had been hypothesized that the lower R was due to a lower plasma catecholamine concentration caused by the hyperoxia (Med. Sci. Sports 10: 167-170, 1978). We tested this hypothesis by measuring changes in plasma epinephrine and norepinephrine when the subjects were switched from breathing air to 60% O2 (and vice versa) during 40 min of cycle ergometer exercise at 67% maximal oxygen uptake (VO2max). The subject breathed one gas mixture for the first 30 min and was switched to the other in the last 10 min. The order was reversed in the second test. The switch in gas mixtures from air to 60% O2 resulted in a significant reduction in R, heart rate, minute ventilation, blood lactate concentration, and plasma epinephrine concentration (P less than 0.05). The plasma norepinephrine concentration (0.1 greater than P greater than 0.05) and the plasma free fatty acid concentration were not significantly changed. Although the direction of the epinephrine change was consistent with the change in R, the epinephrine change was quantitatively small (20 pg/ml) and of questionable physiological significance. This suggests a direct effect of PO2 on cellular metabolism as one cause of the change in R when the subjects were switched from air to 60% O2.

Epinephrine↗