PubMed Health⌕ Search

Biomedical subjects

J Stray-Gundersen

Publications and source records attributed to J Stray-Gundersen.

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

The effect of running on serum and red cell ferritin. A longitudinal comparison.

It is unclear whether running can affect iron stores. Results using the serum ferritin assay (SER FER) have been conflicting. Decreased red cell ferritin (RBC FER) values (< or = 4 ag/RBC) occur in iron depleted or inflammatory states. We compared the longitudinal changes of hemoglobin (Hb), SER FER, RBC FER, % saturation of total iron binding capacity (% sat TIBC), and daily dietary intake in 27 runners during a training program. These parameters were measured at days 0, 49 (range 48-52), and 115 (range 85-120). No significant changes occurred in the SER FER, % sat TIBC and Hb determinations throughout the study. Overall the RBC FER values trended down (mean values 11.7 ag/RBC to 7.7 ag/RBC; p = 0.06). Fifteen runners (56%) acquired RBC FER values in the iron deficient range (mean 6.8 ag/RBC to 2.4 ag/RBC; p < 0.05). These values differed significantly from the remaining 12 runners (mean 17.3 ag/RBC to 14.7 ag/RBC). The decline in RBC FER into the iron deficient range was primarily seen in a subset of runners who began with a RBC FER value < or = 10 ag/RBC (positive predictive value 0.79) and was independent of iron intake. We conclude that ferritin can be affected by running as recognized by the red cell ferritin assay. Moreover our results suggest that this decrease in red cell ferritin is likely a function of defective iron utilization rather than total body iron deficiency. A potential consideration is that this fall may occur as a result of repetitive running-associated injury and inflammation.

Erythrocytes↗
PubMed1995

Relationships of generalized and regional adiposity to insulin sensitivity in men.

The relative impacts of regional and generalized adiposity on insulin sensitivity have not been fully defined. Therefore, we investigated the relationship of insulin sensitivity (measured using hyperinsulinemic, euglycemic clamp technique with [3-3H]glucose turnover) to total body adiposity (determined by hydrodensitometry) and regional adiposity. The latter was assessed by determining subcutaneous abdominal, intraperitoneal, and retroperitoneal fat masses (using magnetic resonance imaging) and the sum of truncal and peripheral skinfold thicknesses. 39 healthy middle-aged men with a wide range of adiposity were studied. Overall, the intraperitoneal and retroperitoneal fat constituted only 11 and 7% of the total body fat. Glucose disposal rate (Rd) and residual hepatic glucose output (rHGO) values during the 40 mU/m2.min insulin infusion correlated significantly with total body fat (r = -0.61 and 0.50, respectively), subcutaneous abdominal fat (r = -0.62 and 0.50, respectively), sum of truncal skinfold thickness (r = -0.72 and 0.57, respectively), and intraperitoneal fat (r = -0.51 and 0.44, respectively) but not to retroperitoneal fat. After adjusting for total body fat, the Rd and rHGO values showed the highest correlation with the sum of truncal skinfold thickness (partial r = -0.40 and 0.33, respectively). We conclude that subcutaneous truncal fat plays a major role in obesity-related insulin resistance in men, whereas intraperitoneal fat and retroperitoneal fat have a lesser role.

Adipose Tissue↗
PubMed1993

Uremic myopathy limits aerobic capacity in hemodialysis patients.

Eleven end-stage renal disease patients trained by stationary cycling during their hemodialysis treatments. After a 6-week control period, 12 weeks of training began and was increased to 30 to 60 minutes at > or = 70% of peak heart rate. Baseline, pretraining and, posttraining exercise tests were performed. Workload (WL), oxygen uptake (VO2peak), cardiac output (Q), heart rate (HR), and arterial oxygen content (CaO2) were measured. Stroke volume (SV), arteriovenous oxygen difference ((a-v)O2), and mixed-venous oxygen content (CvO2) were calculated. Rectus femoris biopsies were obtained pretraining and posttraining. At peak exercise, WL increased from 60 +/- 4 to 70 +/- 6 W (P < 0.05), VO2peak showed an upward trend from 14.8 +/- 0.9 to 16.8 +/- 1.3 mL/kg/min (P < 0.1), and Q, HR, SV, CaO2, CvO2, and (a-v)O2 were unchanged. Ten of the 11 patients increased WL, but only six increased VO2peak (five of 11 patients decreased VO2peak). The difference between groups (P < 0.02) was attributable to (a-v)O2, which increased in those who increased VO2peak (P < 0.02). There was an upward trend for succinate dehydrogenase activity (P < 0.06), and phosphofructokinase activity increased (P < 0.05). However, the rectus femoris capillary to fiber ratio, type I and II fiber areas, and fiber area variability were unchanged, and neither histomorphologic nor enzymatic activity changes were related to change in VO2peak. We conclude that not all dialysis patients increase VO2peak after training, but most can improve exercise capacity. Patients who improved VO2peak widened their (a-v)O2 difference, increasing oxygen extraction and showing that oxygen delivery is not always the limiting factor. Thus, the limitation of VO2peak in dialysis patients is a complex interaction of central and peripheral factors. Muscle therapies, such as exercise training, are needed in addition to increased oxygen delivery in rehabilitation of dialysis patients.

Adult↗
PubMed1993

The effect of tyre pressure on the economy of cycling.

Cycling requires power generation to overcome gravity, air resistance, and rolling resistance. When rolling surface and rolling speed are constant for a given tyre, rolling resistance is determined by tyre inflation pressure and the combined weight (CW) of the bicycle and rider. In this study, the oxygen uptake per unit CW (VO2 x CW-1) of seven trained bicycle racers (5 men, 2 women, 24 +/- 2 years) was measured while each cycled up a 4% incline at 19.3 km.h-1 and 75 revolutions.min-1 on a motor-driven treadmill, using randomly-ordered tyre pressures of 552, 690, 827, and 965 kPa. Subjects (55.8-78.4 kg) rode their racing bicycles equipped with the same set of sew-up tyres and wheels. VO2.CW-1 was averaged over the last 3 min of a 5 min ride at each pressure. A repeated measures analysis of variance was performed and significance set at p < 0.05. VO2.CW-1 ranged from 28.1 +/- 0.6 to 28.9 +/- 0.5 ml.kg-1 x min-1 and was not significantly different between tyre pressures. We conclude that differences in rolling resistance caused by varying tyre pressure between 552 and 965 kPa, are too small to be detected physiologically.

Adult↗
PubMed1993

Adaptations in the elbow flexors of elderly males after heavy-resistance training.

The structural and functional characteristics of the elbow flexors in five elderly males were studied before and after 12 wk of heavy-resistance training. Muscle volume and cross-sectional area of two of the elbow flexor (biceps brachii and brachialis) muscles were determined by magnetic resonance imaging. Mean muscle fiber area, percent fiber distribution, and collagen and noncontractile tissue densities were determined on histological sections from needle biopsies. Isokinetic strength of the elbow flexors was measured at velocities between 60 and 300 degrees/s. Muscle volume and cross-sectional area of the biceps brachii and brachialis significantly increased by 13.9 and 22.6%, respectively, after the training program. A preferential hypertrophy of type II fibers (37.2%) was observed. Significant increases in peak torque were observed at all the tested velocities. The amount of work a subject could perform during a 25-repetition test at 240 degrees/s increased by 41% after training. These results demonstrate that the skeletal muscles of elderly individuals can adapt to heavy-resistance exercise and do so by increases in both muscle size and strength.

Adaptation, Physiological↗
PubMed1993

Determinants of VO2peak in patients with end-stage renal disease: on and off dialysis.

Peak oxygen uptake (VO2peak) of patients on maintenance hemodialysis is very low. Exercise training performed during, or "on" dialysis, and at other times, "off" dialysis, both improve VO2peak. Equivalence of these approaches has not been shown, nor have the physiologic factors limiting VO2peak been clarified in these patients. We hypothesized that hemodialysis does not acutely alter the cardiovascular response to peak exercise, and further that anemia and a low peak heart rate limit VO2peak. Ten patients with end-stage renal disease (ESRD) performed cycle ergometry to peak exercise. Peak oxygen uptake measured immediately prior to dialysis was compared with predicted values, and with measurements obtained during the second 30 min of dialysis. The determinants of VO2peak were compared with previously reported norms. "Off" dialysis, VO2peak for nine of 10 patients was below the 95% confidence limit for normals. Their cardiovascular response to peak exercise was unchanged by 30-60 min of hemodialysis. Stroke volume was similar to that of normals; however, peak heart rate was 77% of predicted, and hematocrit was 27% (at rest). Peak exercise mixed-venous oxygen content was 3.6 ml O2 ml.dl-1 blood, similar to values reported for athletes. These findings show that up to 1 h of dialysis minimally effects VO2peak, and imply that low oxygen delivery limited VO2peak in these patients.

Adult↗
PubMed1992

Left ventricular dimensions and mass using magnetic resonance imaging in female endurance athletes.

Few published studies of left ventricular (LV) mass in female endurance athletes have been performed with M-mode echocardiography, which involves assumptions of LV geometry. Therefore, magnetic resonance imaging, a 3-dimensional technique, was used to examine LV mass, LV end-diastolic volume and mean wall thickness in female long distance runners (n = 13; mean age 29 years), cyclists (n = 12; mean age 26 years) and cross-country skiers (n = 11; mean age 24 years), and the findings were compared with sedentary control subjects (n = 10; mean age 27 years) matched for height and body weight. The physical characteristics for all subjects included height (mean 166 cm, and body weight (mean 56 kg). The percent body fat (mean 11.7) and maximal oxygen uptake (VO2max, mean 63 ml.kg-1.min-1) were similar (p greater than 0.05) among all athletic groups, but significantly different from the control group (body fat, mean 22.5%; VO2max, mean 35 ml.kg-1.min-1). LV mass (mean 159 kg), LV end-diastolic volume (mean 122 ml), and mean wall thickness (mean 11.5 mm) were also similar among the athletic groups and significantly larger than the following control values: LV mass (mean 115 g), LV end-diastolic volume (mean 93 ml) and mean wall thickness (mean 9.8 mm). Ratios of LV mass to lean body weight were similar among all athletic groups, although athletic groups had larger ratios (p less than 0.05) than the sedentary control subjects. LV mass/LV end-diastolic volume ratio was similar (p greater than 0.05) among all groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1992

A practical approach to altitude training: where to live and train for optimal performance enhancement.

Altitude training may improve performance by a number of mechanisms. Acclimatization may improve both oxygen delivery and extraction. Hypoxic exercise may increase the training stimulus thus magnifying the effects of endurance training. Conversely, high altitude decreases VO2max and reduces the workloads at which training occurs. At altitude, base training is performed at a slower velocity and lower oxygen uptake (lower absolute workload) compared to sea level, though heart rate is similar and lactate is higher (probably greater relative workload). Interval workouts are performed at a lower absolute workload at altitude and are associated with lower peak heart rates and blood lactate concentrations. Red cell volume is increased during altitude training, as long as iron stores are normal. We suggest that for performance at altitude, acclimatization and/or hypoxic exercise is preferable; for performance at sea level, living at altitude (acclimatization) with sea level training may be the optimal strategy. However neither approach is a substitute for a carefully designed training program including appropriate rest and nutrition.

Acclimatization↗
PubMed1992

MR imaging-guided muscle biopsy for correlation of increased signal intensity with ultrastructural change and delayed-onset muscle soreness after exercise.

To determine if there is a correlation between the degree of delayed increase in signal intensity (SI) of muscle after exercise on magnetic resonance (MR) images and the amount of ultrastructural (ULS) injury and delayed-onset muscle soreness (DOMS), MR imaging-guided muscle biopsy was performed to obtain tissue from the legs of nine sedentary subjects 48 hours after downhill running on a treadmill. The degree of soreness was subjectively graded. T1-weighted, spin-density, T2-weighted, and short inversion time inversion-recovery images were obtained before and after biopsy, at 48 and 96 hours after exercise, respectively. The delayed SI increase of muscle on images obtained before biopsy was subjectively graded and measured. The degree of ULS injury was determined with electron micrographs. Serum creatine kinase levels were obtained before and up to 144 hours after exercise at 24-hour intervals. The measured SI, SI grades, and DOMS grades were correlated with the degree of ULS injury. Linear regression analysis revealed poor correlation between the DOMS grades and the degree of ULS injury and good correlation between the SI grade and the degree of ULS injury.

Adult↗
PubMed1992

Effects of resistance training on elbow flexors of highly competitive bodybuilders.

The influence of gender on muscular adaptation of the elbow flexors to 24 wk of heavy resistance training was studied in five male bodybuilders (MB) and five female bodybuilders (FB) who were highly competitive. Muscle cross-sectional area (CSA), fiber area, and fiber number were determined from the biceps brachii, and voluntary elbow flexor torque was obtained at velocities of contraction between 0 and 300 degrees/s. Biceps and flexor CSA was 75.8 and 81% greater, respectively, in MB than in FB, but muscle CSA was not significantly altered by the training program in either group. Because estimated fiber number and the volume density of nonmuscle tissue were similar in MB and FB, most of the gender difference in muscle CSA appeared to be due to greater absolute mean fiber areas in MB (10.51 and 10.68 x 10(3) microns 2 pre- and posttraining, respectively) than in FB (5.33 and 5.96 x 10(3) microns 2 pre- and posttraining, respectively). In neither MB nor FB did fiber type achieve further hypertrophy during the 24-wk training program. These data suggest that the extent of any change in muscle mass or muscle fiber characteristics is minimal after a bodybuilder of either gender has attained a high degree of muscle mass and a highly competitive status.

Adaptation, Physiological↗
PubMed1991

Influence of lifetime cross-country skiing on plasma lipids and lipoproteins.

Low concentrations of total and LDL cholesterol are associated with minimal risk of atherosclerosis. Aerobic exercise has been similarly associated with a low risk of heart disease. The literature is inconclusive as to whether there is an association between total and LDL cholesterol and exercise. Further, previous work has, almost exclusively, examined male runners. Therefore, we examined 176 male and female cross-country skiers, participating in the National Master's Championships, for body composition, dietary habits, exercise habits, and serum lipid levels. Our results show markedly low concentrations of serum LDL cholesterol and total cholesterol, as well as the expected high concentrations of HDL cholesterol and low concentrations of triglycerides, in these lean skiers. Their diets contained 30% fat, and they exercised 9 h weekly. Although it is difficult to separate the effects of diet, leanness, and exercise on the lipid profile, it is apparent that the lifestyle led by these people is associated with a lipid profile that confers an extremely low risk of atherosclerotic disease.

Adult↗
PubMed1991

The effect of body position on the energy cost of cycling.

Energy expenditure during bicycling on flat terrain depends predominantly on air resistance, which is a function of total frontal area (bicycle and rider), coefficient of drag, and air speed. Body position on the bicycle may affect energy expenditure by altering either frontal area or coefficient of drag. In this study, oxygen uptake (VO2) was measured for each of four body positions in 10 cyclists (8 males, 2 females, 24 +/- 2 yr, 67.7 +/- 3.3 kg, VO2max = 65.8 +/- 1.5 ml.kg-1.min-1) while each bicycled up a 4% incline on a motor-driven treadmill (19.3 km.h-1), thereby eliminating air resistance. Positions studied included: 1) seated, hands on brake hoods, cadence 80 rev.min-1; 2) seated, hands on dropped bar (drops), 80 rev.min-1; 3) standing, hands on brake hoods, 60 rev.min-1; and 4) seated, hands on brake hoods, 60 rev.min-1. Subjects rode their own bicycles, which were equipped with a common set of racing wheels. Energy expenditure, expressed as VO2 per unit combined weight, was not significantly different between drops and hoods positioning (30.2 +/- 0.6 vs 29.9 +/- 0.9 ml.kg-1.min-1) but was significantly greater for standing compared with seated cycling (31.7 +/- 0.4 vs 28.3 +/- 0.7 ml.kg-1.min.-1, P less than 0.01). These results indicate that body posture can affect energy expenditure during uphill bicycling through factors unrelated to air resistance.

Adipose Tissue↗
PubMed1990

Muscle cross-sectional area and torque in resistance-trained subjects.

Eight elite male bodybuilders (MB), five elite female bodybuilders (FB), eight male control (MC), and eight female control recreational weight-trainers (FC) performed maximal elbow flexions on an isokinetic dynamometer at velocities between 1.02 and 5.24 rad.s-1, from which peak torque (PT) was measured. Elbow flexor cross-sectional area (CSA) was measured by computed tomographic scanning. Flexor CSA.lean body mass-1 ratios were greater in MB than in other subject groups. Correlations of PT were positively related to CSA but negatively to CSA.lean body mass-1 and to PT.CSA-1. PT.CSA-1 at low-velocity contractions were greater in MC and FC than in MB and FB groups, suggesting a training effect. The velocity-associated declines in torque between velocities of 1.02 and 5.24 rad.s-1 averaged 28.4 +/- 0.9% and were statistically identical in men and women among the subject groups, suggesting that neither gender nor training had affected this variable.

Female↗
PubMed1990

Maximal inspiratory pressure following maximal exercise in trained and untrained subjects.

Previous investigators have demonstrated that 5-10 min of fatiguing exercise would lead to respiratory muscle fatigue in normal subjects. The purpose of this study was to determine if there was a differential inspiratory pressure response to maximal cycle ergometer exercise in trained and untrained subjects. Six highly trained cross country skiers and five untrained college students were studied prior to and 10, 60, and 120 s postexercise (incremental VO2max to exhaustion). On each occasion, maximal inspiratory pressure (MIP) was measured at the mouth from residual volume. Prior to exercise, the two groups had similar MIP values. After exercise, the sedentary subjects experienced significant decreases in MIP compared to the preexercise values. These decreases averaged 10%, 17%, and 13% at 10, 60, and 120 s postexercise, respectively. The skiers, on the other hand, showed no evidence of a decrease in MIP postexercise, with the postexercise values being slightly, but not significantly, higher than the preexercise values. From these results, we conclude that maximal exercise results in inspiratory muscle dysfunction in normal subjects but not in athletes training at or near elite levels. Thus, it appears that endurance exercise training induces an adaptive change in the inspiratory muscles that protects them from the acute loss of strength seen following exercise in normal subjects.

Adolescent↗
PubMed1989

Effects of 100% oxygen on performance of professional soccer players.

Supplemental oxygen is currently widely utilized in conjunction with athletic competition. To assess the utility of this practice, 12 professional soccer players performed two bouts of exhaustive exercise separated by 5 minutes of rest ("recovery period"). During the recovery period, the subjects breathed either room air or 100% oxygen, assigned by randomized, double-blind design. The entire procedure was repeated on each subject using the opposite gas. The administration of enriched oxygen during the recovery period had no effect on plasma lactate levels or on performance during the second period of exercise. The subjects were unable to identify which gas they received. In conclusion, data from this study indicate that using 100% oxygen applied for short periods offers no advantage on recovery from exhaustive exercise or on subsequent exercise performance.

Adult↗
PubMed1989

Contrasts in muscle and myofibers of elite male and female bodybuilders.

Muscle cross-sectional area (CSA), fiber area, and fiber number were determined from the biceps brachii of eight elite male bodybuilders (MB) and five elite female bodybuilders (FB) who had similar training characteristics. Biceps CSA was obtained from computer tomographic scanning and corrected for noncontractile tissue. Biceps CSA was twofold greater in MB relative to FB and strongly correlated to lean body mass (R = 0.93). Biceps CSA expressed per kilogram lean body mass (LBM) or per centimeter body height (BH) was 35% greater in MB compared with FB. Most of the gender difference in muscle CSA was because of greater absolute mean fiber areas in MB (9,607 microns2) relative to FB (5,386 microns2); however, MB also had a significantly greater population of small type II fibers (less than 2,000 microns2) compared with FB. Type II fiber area/LBM averaged 1.6-fold greater in MB compared with FB; however, type I fiber area/LBM was similar between groups. Biceps CSA was positively correlated to fiber CSA (R = 0.75) and fiber number (R = 0.55). This suggests that adaptations to resistance training may be complex and involve fiber hypertrophy and fiber number (e.g., proliferation). Alternatively, since the muscle characteristics before training are not known, these apparent adaptations might be genetically determined attributes.

Adult↗
PubMed1989

Sustained maximal ventilation after endurance exercise in athletes.

Although impaired respiratory muscle performance that persists up to 5 min after exercise is stopped has been demonstrated during exhaustive exercise in normal young men, it is not known whether impaired respiratory muscle function follows endurance exercise to exhaustion in highly trained athletes. To study the effects of exercise on sustained maximal voluntary ventilation immediately after exercise, eight elite cross-country skiers performed a 4-min maximal sustained ventilation (MSV) test before and immediately after exhaustive exercise. Subjects were encouraged to maintain maximal ventilation (VE) throughout the MSV test. To encourage greater effort, rapid visual feedback of VE was provided on a computer terminal along with a target VE based on their 12-s maximum voluntary ventilation (MVV). The subjects (7 males, 1 female) were 18.5 +/- 0.9 yr old (mean +/- SD) and exercised for 62.5 +/- 16.7 min at 77 +/- 5% of their maximum oxygen consumption during which average VE was 106.7 +/- 24.2 l/min BTPS. The mean MVV was 196.0 +/- 29.9 l/min or 107% of their age- and height-predicted MVV. Before exercise the MSV was 86% of the MVV or 176.7 +/- 30.5 l/min, whereas after exercise the MSV was 90% of the MVV or 180.3 +/- 28.9 l/min (P = NS). The total volume of gas expired during the 4-min MSV was 706.7 +/- 121.9 liters before and 721.2 +/- 115.5 liters after exercise (P = NS). In this group of athletes, exhaustive exercise produced no deleterious effects on the ability to perform a 4-min MSV test immediately after exercise.

Adolescent↗