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Biomedical subjects

J M Pivarnik

Publications and source records attributed to J M Pivarnik.

At least 37 records · Page 2Linked to original sources
PubMed1994

Maternal exercise during pregnancy.

Recent evidence resulting in revised ACOG Guidelines will allow physicians more latitude with their advice for women wishing to exercise during pregnancy. However, there is an increased responsibility for both mother-to-be and her physician to design an individualised activity programme to meet specific goals. The recommendation should continue to be that any woman who chooses to begin, or maintain an exercise routine during pregnancy should do so in consultation and proactive partnership with her obstetrician.

Body Temperature Regulation↗
PubMed1994

Caltrac versus calorimeter determination of 24-h energy expenditure in female children and adolescents.

The purpose of this study was to determine the validity of the Caltrac accelerometer for estimating 24-h energy expenditure (EE) in children and adolescents. EE for 40 girls (13.0 +/- 1.8 yr) was assessed for 24 h via indirect calorimetry in whole-room calorimeters. EE and activity level were estimated concurrently by two Caltrac accelerometers placed on the subjects at each hip. Significant correlations (P < 0.001) resulted between Caltrac estimates and calorimeter values for 24-h total EE (TEE, r = 0.80), sedentary daily EE (SDEE, r = 0.84), and waking EE (WEE, r = 0.85). Nonetheless, the Caltrac significantly (P < 0.001) underestimated EE in all experimental conditions (TEE: -13.3 +/- 8.6%; SDEE: -6.8 +/- 7.3%; WEE: -30.4 +/- 8.5%). A significant multiple correlation between calorimeter values and a combination of Caltrac activity counts and body weight (R = 0.86, P < 0.001) suggested these variables could be useful for daily EE estimation. Additional analyses indicated that as EE increased, the absolute difference between Caltrac and calorimeter values also increased. The significant correlations between Caltrac and calorimeter values suggest the Caltrac may be useful for assessing daily caloric expenditure for groups of children.

Acceleration↗
PubMed1994

A comparison of cardiac index in normal term pregnancy using thoracic electrical bio-impedance and oxygen extraction (Fick) techniques.

OBJECTIVE: To correlate cardiac index in normal late third-trimester pregnancy using the thoracic electrical bio-impedance technique with that obtained from the oxygen extraction technique. METHODS: Eight carefully screened normal pregnant women underwent assessment of cardiac index using both the thoracic electrical bio-impedance technique and the oxygen extraction technique. Measurements were obtained in various positions. RESULTS: The correlation was good between the thoracic electrical bio-impedance and oxygen extraction techniques in the left lateral (r = 0.915) and right lateral (r = 0.863) positions, and the intercepts at the midpoints of the oxygen extraction data in these positions suggested good absolute correlation as well. Correlation between thoracic electrical bio-impedance and the Fick cardiac index was poor in all other positions. CONCLUSIONS: Thoracic electrical bio-impedance cardiac index assessment is influenced by maternal position and must be used with caution in clinical research protocols. This technique appears to be inappropriate for general clinical use during pregnancy.

Adult↗
PubMed1994

Effects of chronic exercise on blood volume expansion and hematologic indices during pregnancy.

OBJECTIVE: To compare blood volumes and hematologic indices between nine aerobically trained, physically active pregnant women who continued to exercise throughout gestation and five healthy yet sedentary gravidas. METHODS: Subjects were tested on three occasions: 25 and 36 weeks of pregnancy and 12 weeks postpartum. Plasma volumes were estimated by dye dilution with Evans blue. Blood samples were taken from the antecubital vein with the subjects resting in a seated, semirecumbent position. In addition to plasma volume estimations, blood samples were analyzed for hematocrit ratio, hemoglobin concentration, red cell count, and plasma protein concentration. Blood volumes and red cell volumes were calculated from plasma volume estimates and hematocrit ratios. RESULTS: Average birth weight and length of gestation did not differ between the subject groups. Analysis of variance indicated that absolute blood volume measures were significantly greater (P < .01) in the physically active compared to sedentary subjects at all three test times. Similar results were found for plasma and red cell volumes (P < .01). Blood volumes relative to body weight were significantly higher in physically active subjects (P < .01) than in their sedentary counterparts at 25 weeks (88.5 versus 75.5 mL/kg) and at 36 weeks (88.4 versus 70.9 mL/kg), as well as at 12 weeks postpartum (72.2 versus 57.6 mL/kg). All vascular volumes were significantly (P < .001) lower at 12 weeks postpartum compared to those seen during pregnancy in both subject groups. Hematologic indices of hematocrit ratio, hemoglobin concentration, red cell count, and plasma protein concentration were all greater (P < .001) at 12 weeks postpartum than during pregnancy. CONCLUSIONS: Physically active women possessed significantly greater vascular volumes than their sedentary counterparts. Although this difference was maintained throughout gestation as the active gravidas continued to exercise, there was no apparent effect on pregnancy outcome.

Adult↗
PubMed1993

Body composition of sedentary and physically active spinal cord injured individuals estimated from total body electrical conductivity.

Reliability and evidence of construct validity of Total Body Electrical Conductivity (TOBEC) for estimating body composition in spinal cord injured subjects was evaluated using 17 males with C6-L2 spinal cord transections. Subjects reporting regular exercise were categorized as active (n = 12); nonexercisers were considered sedentary (n = 5). Measures included body weight, length, circumferences, skinfolds, and three TOBEC readings. Reliability for percent fat of both single and multiple TOBEC trials (t = 3) ranged from .994 to .999. Average percent fat values were significantly (p < .009) higher in sedentary subjects. Sum of seven skinfolds was significantly correlated (r[15] = 0.73, p < .01) with percent fat measured by TOBEC. Results suggest TOBEC is reliable (rtt > 0.99) in estimating body composition in spinal cord injured individuals. High reliability estimates for single and multiple trials indicate use of a single trial will provide reliable body fat estimates. Construct validity evidence infers that TOBEC measured body composition discriminates between active and sedentary paraplegics.

Adult↗
PubMed1993

Aerobic capacity in black adolescent girls.

Our purpose was to determine the aerobic capacities (VO2max) of a group of black female adolescents (age = 11.4-15.8 years) randomly chosen from a single urban school. Of 91 girls selected, 64 performed an incremental treadmill running test to volitional exhaustion and achieved VO2max as determined from expired gas measures. Other measures included height (m), weight (kg), and calf and triceps skinfolds (for % fat estimates). Girls were also asked whether they had achieved menarche. VO2max averaged 37.3 +/- 6.2 ml.kg-1 x min-1 and was significantly correlated (r[62]) with height (-.32, p < .01), body mass index (-.63, p < .001), and % fat (-.65, p < .001) but not with age (-.16, p > .10). Postmenarchal girls were significantly taller and older than premenarchal girls. Contrary to previous studies, the girls' VO2max values were not related to biological age. Our subjects' aerobic capacity values averaged 14% less than those of nonblack U.S. female adolescents previously reported in the literature. This difference in VO2max was primarily a function of body weight. Study implications support the possibility that overweight in adult black women may originate prior to or during early adolescence. Future longitudinal studies should be designed to investigate the effects of aerobic fitness on cardiovascular risk factor reduction in black adolescent girls.

Adolescent↗
PubMed1993

Recent advances in understanding maternal and fetal responses to exercise.

In the past decade, physical health fitness has become increasingly more important in the lives of women of child-bearing age. Many have made regular, and sometimes vigorous commitments to exercise programs. In 1985, the American College of Obstetricians and Gynecologists (ACOG) developed a set of guidelines for women who plan to exercise during pregnancy. Recommendations were based on available, but somewhat limited, scientific data and common sense. Since that time, researchers have learned a significant amount of new information about how a pregnant woman and her fetus respond to aerobic activity. The objective of this communication is to review recent investigations in this area. Specific topics include a) maternal responses to exercise, b) fetal responses to maternal exercise, c) animal research models, and d) pregnancy and physical conditioning. Our objectives are to present information that will a) stimulate new and innovative research designs for exercise and pregnancy studies, and b) add significantly to our knowledge and ability to develop safe and effective exercise programs for women who wish to remain physically active throughout a normal-term pregnancy.

Animals↗
PubMed1993

Effects of maternal aerobic fitness on cardiorespiratory responses to exercise.

We hypothesized that aerobically fit women who continued to exercise throughout pregnancy would have enhanced cardiorespiratory responses to exercise. Physically active (N = 10) and sedentary (N = 6) subjects were compared during steady-state (15 min) semi-recumbent cycle exercise performed at a given heart rate (HR; 140 b.min-1) twice during pregnancy (25 wk, 36 wk) and 12 wk postpartum. Indirect calorimetry was used to measure volumes and fractional concentrations of expired gases. Cardiac output was estimated via CO2 rebreathing. Data were analyzed with repeated measures ANOVA. Caloric expenditure during exercise was significantly (P < 0.001) greater in the physically active (7.2 kcal.min-1) compared with sedentary (4.7 kcal.min-1) subjects. Alveolar ventilation and cardiac output responses to exercise were proportionally greater (P < 0.001) in the aerobically fit subjects. Ventilatory equivalents for O2 and physiological dead space/tidal volume ratios were significantly (P < 0.01) lower in the physically active subjects during exercise. In contrast, ratings of perceived exertion during exercise did not differ between subject groups. It appears that a physically active woman's enhanced cardiorespiratory responses to acute exercise are maintained during pregnancy if she continues her aerobic fitness program throughout gestation.

Adult↗
PubMed1992

Ornithine supplementation and insulin release in bodybuilders.

Ornithine supplementation has gained popularity with athletes because of its alleged potential to release anabolic hormones, factors governing skeletal muscle hypertrophy. Three female and nine male bodybuilders served as subjects in a study to test the effectiveness of oral ornithine in bringing about the release of insulin, an anabolic hormone. After an overnight fast, subjects were administered 40, 100, or 170 mg.kg-1 L-ornithine.HCl by mouth in a random fashion on three consecutive Saturday mornings. Blood samples were drawn at baseline (T = 0), 45, and 90 min afterward. Serum ornithine levels were elevated (p < 0.01) at T = 45 and 90 min for all three dosage levels. However, serum insulin did not change from baseline levels at any dose of ornithine. The present findings show that ornithine is not an insulin secretagogue.

Adult↗
PubMed1992

Menstrual cycle phase affects temperature regulation during endurance exercise.

We investigated whether menstrual cycle phase would affect temperature regulation during an endurance exercise bout performed at room temperature (Ta) of 22 degrees C and 60% relative humidity. Nine eumenorrheic women [age 27.2 +/- 3.7 yr, peak O2 uptake (VO2) 2.52 +/- 0.35 l/min] performed 60 min of cycle exercise at 65% of peak VO2. Subjects were tested in both midfollicular (F) and midluteal (L) phases, although one woman did not show a rise in serum progesterone (P4) that is typically evident 1 wk after ovulation. VO2, rectal (Tre) and skin (Tsk) temperatures, heart rates (HR), and ratings of perceived exertion (RPE) were measured throughout exercise. Sweat loss (SL) was estimated from pre- and postexercise body weight differences. VO2, SL, and Tsk were not affected by menstrual cycle phase. Preexercise Tre was 0.3 degrees C higher during L than during F conditions, and this difference increased to 0.6 degrees C by the end of exercise (P less than 0.01). Compared with F, HRs during L were approximately 10 beats/min greater (P less than 0.001) at all times, whereas RPE responses were significantly greater (P less than 0.01) by 50 min of cycling. No differences in any measured values were found in the subject whose P4 was low in both test conditions. Results indicate that thermoregulation (specifically, regulation of Tre), as well as cardiovascular strain and perception of exercise, was adversely affected during the L phase.

Adult↗
PubMed1992

Maternal respiration and blood gases during aerobic exercise performed at moderate altitude.

We studied whether maternal acid-base status during aerobic exercise performed at moderate altitude is affected by pregnancy. Seven primiparus women were tested at 37 wk gestation and 12 wk postpartum. Subjects were studied at rest, and during two cycle (50 W, 75 W) and two treadmill (67 m.min-1; 2.5% grade, 67 m.min-1; 12% grade) protocols. Exercise bouts lasted 6 min with a 10-min rest between sessions. Minute (VE) and alveolar (VA) ventilation, tidal volume (VT), and ventilatory equivalent for carbon dioxide (VE/VCO2) were significantly (P less than 0.01) greater when exercise was performed during pregnancy. Physiological dead space (VD) was not affected by pregnancy status and did not differ between rest and exercise. Decreases (P less than 0.01) in arterial pH during exercise averaged 0.04 units in both pregnancy and postpartum. Despite similar change in maternal pH, carbon dioxide tension (PaCO2) remained unchanged during exercise at 37 wk gestation but decreased at 12 wk postpartum. Decreases in arterial bicarbonate [HCO3-] associated with exercise were smaller during pregnancy. Our findings indicate that pregnancy did not compromise maternal acid-base status during aerobic exercise.

Acid-Base Equilibrium↗
PubMed1991

Position change and central hemodynamic profile during normal third-trimester pregnancy and post partum.

Central hemodynamic response to position change was assessed in 10 normotensive primiparous patients between 36 and 38 weeks' gestation. Studies were repeated between 11 and 13 weeks post partum. Compared with the left lateral position, we observed a mean 9% fall in cardiac output in the supine position and an 18% fall when patients were standing. When standing, these patients had a 30% increase in pulse and a 21% fall in left ventricular stroke work index. The orthostatic response after pregnancy was much more labile than that during the third trimester. These findings have important descriptive implications for the understanding of the human response to orthostasis during pregnancy, as well as clinical implications for patients at risk of uteroplacental insufficiency and for working women during pregnancy.

Adult↗
PubMed1991

Physiological and perceptual responses to cycle and treadmill exercise during pregnancy.

We compared physiological and perceptual responses to non-weight bearing (cycle) and weight bearing (treadmill) exercise in 16 sedentary women throughout a normal term pregnancy. Subjects were recruited late in the first trimester (less than 13 wk gestation) and were studied at 4 wk intervals throughout pregnancy and 4 wk postpartum (PP). Exercise consisted of four 5 min protocols; two were performed on the cycle (C1 = 50 W; C2 = 75 W) and two on the treadmill (T1 = 66 m.min-1, 2.5% grade; T2 = 66 m.min-1, 12% grade). Measured variables included oxygen consumption (VO2), heart rate (HR), minute ventilation (VE), and ratings of perceived exertion (RPE, 10-point Borg scale). Absolute VO2 (ml.min-1) during cycle exercise increased (P less than 0.001) by 25 wk gestation, while relative VO2 (ml.kg-1.min-1) during treadmill walking was unchanged through late pregnancy and PP. This suggests that cycle exercise is not a true non-weight bearing exercise within a given group of women throughout gestation. Subjects' VO2max values were estimated at each test interval and found to increase (P less than 0.001) by 25-28 wk gestation. Heart rate and RPE responses to exercise remained constant throughout gestation and decreased (P less than 0.01) PP. Although they did not participate in a regular exercise program, it appears that our subjects experienced a mild aerobic training effect during late pregnancy.

Adult↗
PubMed1990

Alterations in plasma volume and protein during cycle exercise throughout pregnancy.

The purpose of this investigation was to determine the effects of cycle exercise on maternal plasma volume (PV) and protein dynamics during pregnancy. Sixteen healthy gravidas (age = 23 +/- 4.6 yr) cycled for 5 min (75 W) at 4 wk intervals throughout term. Venous blood samples were drawn immediately prior to and during the last minute of exercise. Relative (percent) PV changes during exercise were calculated from hematocrit ratios and hemoglobin concentrations. Plasma was analyzed for total protein ([TP]) and albumin ([ALB]) concentrations and colloid osmotic pressure (COP). Resting blood volumes were also estimated (carbon monoxide rebreathing) so that absolute PV (ml) and TP and ALB contents (g) could be determined. COP increases (P less than 0.001) during exercise were similar at all gestational ages. Plasma volume, TP, and ALB decreased during exercise with significantly (P less than 0.001) greater losses occurring from 29-32 wk gestation. This may indicate an increase in capillary permeability to large molecules when vascular volume was highest.

Adult↗
PubMed1990

Responses of aerobically fit men and women to uphill/downhill walking and slow jogging.

Few studies have thoroughly examined metabolic, cardiovascular, and psychophysiological responses to negative treadmill (TM) exercise. We compared oxygen consumption (VO2), heart rate (HR), and perceived exertion (RPE, 0-10 Borg scale) during incremental TM exercise featuring both downhill and uphill stages. Subjects were aerobically trained males (N = 12, VO2max = 61 ml.kg-1.min-1) and females (N = 12, VO2max = 53 ml.kg-1.min-1). On separate occasions, each subject walked (4.8 kph) or jogged (9.6 kph) for 25 min. Five minutes were spent at each of five grades (-10, -5, 0, 5, 10%, or the reverse). TM speed and percent progressions were randomized. VO2 and HR did not differ in the 4.8 kph condition when TM grade was negative. During 9.6 kph, both VO2 and HR significantly (P less than 0.001) increased with progressive increments, but increases were less when TM grade was negative. RPE did not differ in the 4.8 kph condition except at 10% grade, where responses were significantly (P less than 0.001) higher. In 9.6 kph, RPE responses were significantly (P less than 0.001) greater during positive stages. The only gender effect occurred at 10% in the 9.6 kph condition, where women had greater (P less than 0.01) RPE responses than men. Results suggest that both walking and jogging economies differ between negative and positive TM grades. Gender differences appear negligible when comparing aerobically trained men and women.

Adult↗
PubMed1990

Cardiac output responses of primigravid women during exercise determined by the direct Fick technique.

We compared metabolic and cardiovascular responses to aerobic exercise with the direct Fick technique in women during and after pregnancy. Seven subjects were studied at 37 weeks' gestation and again 12 weeks postpartum. All were tested at rest and during four sequential exercise bouts consisting of 5 minutes at each of two cycle (50 and 75 W) and two treadmill (67 m x min-1 at 2.5 and 12% grade) protocols. Oxygen consumption (VO2) and heart rate were measured during the fifth minute of exercise. Arterial and mixed venous oxygen contents, obtained from catheters placed in the radial and pulmonary arteries, respectively, were used to calculate arterial-venous oxygen difference. Cardiac output and stroke volume were calculated from the Fick equation. Responses of VO2, cardiac output, and stroke volume were greater when exercise was performed at 37 weeks' gestation as compared with postpartum. In contrast, heart rate response (during cycling) and arterial-venous oxygen difference (during treadmill walking) were less when exercise was performed during pregnancy. Our results indicate that there is no compromise in maternal cardiac output during either cycle or treadmill exercise performed late in pregnancy as compared with postpartum conditions.

Adult↗
PubMed1989

Urinary 3-methylhistidine excretion increases with repeated weight training exercise.

This investigation examines the effect of progressive resistance weight training exercise on urinary 3-methylhistidine (3-MH) excretions in untrained subjects. For 19 consecutive days, 11 males were fed a weight maintenance, lactovegetarian diet which contained the Recommended Dietary Allowance (0.8g.kg-1.d-1) for protein. No exercise was performed for the first 7 d of the study. Subjects were strength tested on day 8 and performed upper and lower body weight training exercises from days 9-19. Complete, 24-h urine collections were obtained from each subject on a daily basis. Samples were assayed for creatinine and 3-MH. Stable baseline 3-MH values were present during the pre-exercise control period. Significant increases in 3-MH occurred by study day 11, which was the third day of weight training exercise. This was true regardless of whether the data were expressed by daily excretions (microM.d-1; P less than 0.01), per unit of body weight (microM.kg-1.d-1; P less than 0.005), or per unit of creatinine excretion (microM.g Creat-1.d-1; P less than 0.001). Since urinary 3-MH is an index of actin and myosin catabolism, these data support the hypothesis that the rate of skeletal muscle degradation is increased during strength building exercises.

Adult↗