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Biomedical subjects

W M Kohrt

Publications and source records attributed to W M Kohrt.

84 records · Page 5Linked to original sources
PubMed1990

Endurance training decreases plasma glucose turnover and oxidation during moderate-intensity exercise in men.

To assess the effects of endurance training on plasma glucose kinetics during moderate-intensity exercise in men, seven men were studied before and after 12 wk of strenuous exercise training (3 days/wk running, 3 days/wk cycling). After priming of the glucose and bicarbonate pools, [U-13C] glucose was infused continuously during 2 h of cycle ergometer exercise at 60% of pretraining peak O2 uptake (VO2) to determine glucose turnover and oxidation. Training increased cycle ergometer peak VO2 by 23% and decreased the respiratory exchange ratio during the final 30 min of exercise from 0.89 +/- 0.01 to 0.85 +/- 0.01 (SE) (P less than 0.001). Plasma glucose turnover during exercise decreased from 44.6 +/- 3.5 mumol.kg fat-free mass (FFM)-1.min-1 before training to 31.5 +/- 4.3 after training (P less than 0.001), whereas plasma glucose clearance (i.e., rate of disappearance/plasma glucose concentration) fell from 9.5 +/- 0.6 to 6.4 +/- 0.8 ml.kg FFM-1.min-1 (P less than 0.001). Oxidation of plasma-derived glucose, which accounted for approximately 90% of plasma glucose disappearance in both the untrained and trained states, decreased from 41.1 +/- 3.4 mumol.kg FFM-1.min-1 before training to 27.7 +/- 4.8 after training (P less than 0.001). This decrease could account for roughly one-half of the total reduction in the amount of carbohydrate utilized during the final 30 min of exercise in the trained compared with the untrained state.

Adult↗
PubMed1990

Exercise and recovery ventilatory and VO2 responses of patients with McArdle's disease.

This study was designed to determine whether patients with McArdle's disease, who do not increase their blood lactate levels during and after maximal exercise, have a slow "lactacid" component to their recovery O2 consumption (VO2) response after high-intensity exercise. VO2 was measured breath by breath during 6 min of rest before exercise, a progressive maximal cycle ergometer test, and 15 min of recovery in five McArdle's patients, six age-matched control subjects, and six maximal O2 consumption- (VO2 max) matched control subjects. The McArdle's patients' ventilatory threshold occurred at the same relative exercise intensity [71 +/- 7% (SD) VO2max] as in the control groups (60 +/- 13 and 70 +/- 10% VO2max) despite no increase and a 20% decrease in the McArdle's patients' arterialized blood lactate and H+ levels, respectively. The recovery VO2 responses of all three groups were better fit by a two-, than a one-, component exponential model, and the parameters of the slow component of the recovery VO2 response were the same in the three groups. The presence of the same slow component of the recovery VO2 response in the McArdle's patients and the control subjects, despite the lack of an increase in blood lactate or H+ levels during maximal exercise and recovery in the patients, provides evidence that this portion of the recovery VO2 response is not the result of a lactacid mechanism. In addition, it appears that the hyperventilation that accompanies high-intensity exercise may be the result of some mechanism other than acidosis or lung CO2 flux.

Adult↗
PubMed1990

Effect of exercise on glucose disposal: response to a maximal insulin stimulus.

We used the euglycemic clamp to assess the effects of exercise on maximally insulin-stimulated glucose disposal. In 11 young men, a 60-min bout of exercise had no significant effect on the rate of glucose disposal during a euglycemic clamp performed approximately 30 min postexercise in which plasma insulin was raised to approximately 2,500 microU/ml (a maximal insulin stimulus). The maximal rate of glucose disposal attained during the clamp averaged 15.7 +/- 1.0 mg.kg lean body mass-1.min-1 after exercise vs. a control value of 15.4 mg.kg lean body mass-1.min-1. In a second experiment, eight men performed supine cycle exercise during the 3rd h of a 4-h euglycemic clamp with a plasma insulin concentration of approximately 2,500 microU/ml. Exercise during the hyperinsulinemic clamp resulted in a 70% increase in glucose disposal rate. There was no measurable increase in glucose 6-phosphate in the quadriceps muscle during the insulin infusion at rest. We conclude that prior exercise does not enhance maximally insulin-stimulated glucose disposal in young healthy men. Our results are compatible with the interpretations that glucose availability rather than glucose metabolism limits the rate of glucose disposal in response to a maximal insulin stimulus in resting subjects and that the increase in glucose uptake in response to superimposed exercise is primarily due to an increase in glucose availability.

Adult↗
PubMed1990

Exercise training enhances leg vasodilatory capacity of 65-yr-old men and women.

To determine whether extremity vasodilatory capacity may be augmented in older persons by endurance exercise training, lower leg blood flow and conductance were characterized plethysmographically at rest and during maximal hyperemia in 9 men and 10 women aged 64 +/- 3 (SD) yr before and after 31 +/- 6 wk of walking and jogging at 70-90% of maximal oxygen uptake for 45 min 3-5 days/wk. Maximal oxygen uptake expressed as milliliters per kilogram per minute improved 25% in men and 21% in women (P less than 0.01). Maximal leg blood flow and conductance increased in all nine men by an average of 39 +/- 33 (P less than 0.001) and 42 +/- 44% (P less than 0.004), respectively. Results were more variable in women and achieved unequivocal statistical significance only for maximal blood flow (+33 +/- 54% for blood flow and +29 +/- 55% for conductance; P less than 0.02 and P = 0.05, respectively). Body weight and skinfold adiposity declined in both sexes (P less than 0.05). Enhancement of vasodilatory capacity was related to weight loss in men and adipose tissue loss in women (r = 0.61 and 0.51, respectively; P less than 0.05). There were no significant changes in exercise capacity, body weight, or maximal blood flow in four male and three female controls aged 66 +/- 4 yr. Thus adaptability of the lower limb circulation to endurance exercise training is retained to at least age 65 yr.

Aged↗
PubMed1989

Measurement of fat distribution by magnetic resonance imaging.

Because of the important role of intra-abdominal fat in predicting increased risk for diabetes, hypertension, and heart disease, methods to quantify intra-abdominal fat are needed. Computed tomography defines quantity of intra-abdominal fat but is associated with significant radiation risk. We explored using magnetic resonance imaging (MRI) to measure amount and distribution of intra-abdominal fat. Because MRI has no known risk, the same subject can be studied repeatedly. Six subjects with percent body fat ranging from 14% to 44% had MRI scans of the chest, abdomen, and thigh on two separate occasions. Total abdominal fat and subcutaneous abdominal fat correlated with percent total body fat as determined from hydrostatic weighing (r = .99, P less than .001). Intra-abdominal fat correlated with the ratio of widest abdominal to widest hip circumference (r = .85, P less than .05). Reproducibility of the MRI measurements of fat was less than 3% for total body areas, less than 5% for subcutaneous fat areas, and less than 10% for internal fat areas. Reproducibility was better in individuals with higher percent total body fat. We conclude that MRI can reliably measure fat areas with no radiation risk to the patient.

Abdomen↗
PubMed1989

Ten kilometer performance and predicted velocity at VO2max among well-trained male runners.

Previous research (study 1) has shown that a significant relationship exists between 10 km run time (RT) and predicted running velocity at VO2max (vVO2max) among well-trained males heterogeneous in VO2max. Since competitive runners often display a homogeneous fitness profile, the purpose of this study was to determine the association between 10 km RT and vVO2max among a group of trained runners exhibiting nearly identical VO2max values (study 2). Running economy (RE), vVO2max, and velocity at a 4 mM blood lactate concentration (v at 4 mM BL) were calculated in both studies. Correlations were obtained as shown in Table 2. The relationship between VO2max and 10 km RT achieved statistical significance only in study 1, while RE explained a greater amount of performance variation in study 2. In both studies, variation in 10 km RT attributable to vVO2max was similar and exceeded that due to either VO2max or RE. vVO2max also accounted for essentially the same amount of variation in 10 km RT as did v at 4 mM BL. It was concluded that, among well-trained subjects homogeneous in VO2max, a strong relationship exists between 10 km RT and vVO2max that appears to be mediated to a large extent by RE.

Adult↗
PubMed1989

Longitudinal assessment of responses by triathletes to swimming, cycling, and running.

Fourteen triathletes (eight male, six female) were tested four times (in February, May, August, and October) to monitor adaptations to training for a triathlon (1.9-km swim, 90.3-km bike, 21.1-km run). VO2max was measured during treadmill running (TR), cycle ergometry (CE), and tethered swimming (TS). Lactate threshold (LT), defined as the VO2 at a lactate concentration of 4 mM, was determined during TR and CE. In all sessions, TS VO2max was less than TR and CE (P less than 0.05), and CE was less than TR (P less than 0.05). Means for Session I were 57.4, 53.4, and 48.3 ml.min-1.kg-1 for TR, CE, and TS, respectively. Corresponding values for Session IV were 58.4, 56.0, and 47.8 ml.min-1.kg-1. The only significant increase in VO2max was for CE (5%). VO2 at the LT increased from Session I to IV for both TR (6%) and CE (10%); the LT for TR was at a higher VO2 than for CE in all sessions. The percent VO2max at LT for TR in Sessions I and IV was 80 and 85%, respectively. Analogous values for CE were 72 and 76%. The minimal increases in VO2max suggest that subjects had reached their potential in this parameter. Improvements in race performance were probably attained through peripheral adaptations, as suggested by increases in the VO2 at LT. The occurrence of the LT at a lower percent VO2max in cycling than in running suggests that the triathletes had greater potential for improvement in cycling.

Adult↗
PubMed1987

Effects of respiratory muscle endurance training on ventilatory and endurance performance of moderately trained cyclists.

This study examined the effects of respiratory muscle endurance training (RMET) on ventilatory and endurance performance among moderately trained, male cyclists. Nine subjects initially completed two cycling VO2 max tests, two endurance cycling tests for time at 95% VO2 max, a 15-s MVV test, and an endurance breathing test for time at 100% MVV. Four subjects then underwent 3 weeks of strenuous RMET while five served as controls. Mean posttest 15-s MVV and endurance breathing time were significantly higher in the RMET group (243 +/- 14 l X min-1 and 804 +/- 94 s) than in the control group (205 +/- 6 l X min-1 and 48 +/- 8 s). No significant group differences in VO2 max or endurance cycling time at 95% VO2 max were observed following RMET. Results of this exploratory study indicated that RMET improved ventilatory power and endurance, but did not alter VO2 max or endurance cycling performance among moderately trained, male cyclists.

Adult↗
PubMed1987

Fluid shifts with successive running and bicycling performance.

Seven men and five women triathletes ran 10 km and bicycled 40 km at race pace for the purpose of studying changes in plasma, blood, and red blood cell volumes. A second trial followed 1 wk later with the order of exercise counterbalanced (running first-cycling second; cycling first-running second). Water consumption was measured by providing water bottles on the bike phase, at 3.2 and 6.7 km on the run phase, and at the transition area. Body weight was obtained at the start and end of each phase. A 10-ml blood sample was obtained just before starting and immediately upon finishing each phase. Changes in plasma volume, blood volume, and red cell volume were calculated from hematocrit and hemoglobin values. Changes in blood volume, plasma volume, and red cell volume did not differ between the sexes; therefore, results were combined. Sequential cycling and running caused significant hemoconcentration (-6 to -8% blood volume; -8 to -10% plasma volume) with moderate dehydration (-3 to -4% body weight) despite ad libitum fluid replacement. More severe fluid compartment shifts occurred on the initial phase regardless of exercise mode. Blood volume and plasma volume changes during the second mode of exercise were minor in extent with the major differences occurring in red cell volume. When fluid changes were calculated on a per hour basis, shifts were greater during running than during cycling.

Bicycling↗
PubMed1987

Physiological responses of triathletes to maximal swimming, cycling, and running.

The objectives of this study were to: (a) develop a physiological profile for a group of trained triathletes and (b) determine whether multiple modes of training result in general or specific adaptations. VO2max of 13 trained triathletes (mean = 29.5 yr) was measured during treadmill running (TR), cycle ergometry (CE), and tethered swimming (TS) over a 6-wk period encompassing a half-triathlon (1.2 mile swim/56 mile bike/13.1 mile run). Most subjects performed two tests in each mode. Since test-retest reliability coefficients for TR, CE, and TS VO2max were 0.97, 0.93, and 0.97, respectively, results were averaged: formula; see text The mean TR VO2max indicated that the subjects were well-trained, but not of elite caliber. Mean CE VO2max was 95.7% of the TR value, which is greater than the value typically found in non-cyclists (88 to 92%) but less than that of highly trained cyclists (98 to 105%). Mean TS VO2max was 86.6% of the TR value. As in cyclists, this percentage is greater than that of recreational swimmers (78 to 82%) but less than that of elite swimmers (93 to 95%). Running and cycling times in the triathlon were significantly (P less than 0.01) related to the corresponding VO2max values (r = -0.68 and r = -0.78, respectively), but swimming times were not (r = -0.50). It is concluded that these triathletes were well-trained in all events, but not to the same extent as athletes who train in only one sport. Running and cycling performance were associated with VO2max.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Effects of shoes and foot orthotics on VO2 and selected frontal plane knee kinematics.

The objective of this study was to investigate the effects of shoes and foot orthotics on running economy and selected frontal plane knee kinematics during the support phase of running. Twenty-one male runners who had been fitted with orthotics served as subjects. Subjects participated in three submaximal runs on a treadmill under the following conditions: barefoot, shoes, and shoes plus orthotics. A run consisted of 1 min at 161 m . min-1, 2 min at 180 m . min-1, and 4 min at 201 m . min-1. VO2 was calculated for the last 3 min of each test. Frontal plane motion was filmed during the sixth min of each submaximal run, and linear and angular displacement of the knee were then calculated from film data. Results from the mechanical aspect of this study indicate that there were no significant differences among the means for linear displacement of the knee. Angular displacement of the knee during barefoot running was significantly (P less than 0.05) less than shoe and shoe-plus-orthotic conditions. There was no difference, however, between shoes and shoes plus orthotics. The economy results revealed that the aerobic cost of running increased as the amount of mass added to the foot increased. In absolute terms (1 . min-1), running in shoes plus orthotics was significantly (P less than 0.05) more costly than running barefoot. It appears that if orthotics do, in fact, improve running economy by improving running mechanics, the amount of improvement is negated by the additional cost of running associated with the mass of the orthotics.

Energy Metabolism↗