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Biomedical subjects

T W Rowland

Publications and source records attributed to T W Rowland.

At least 37 records · Page 2Linked to original sources
PubMed1993

Accuracy of physical working capacity (PWC170) in estimating aerobic fitness in children.

Physical working capacity, the workload at a heart rate of 170 bpm (PWC170), has been utilized as a marker of maximal oxygen uptake. The precision of PWC170 in predicting VO2max in children has not been fully evaluated. In this study, 35 children (18 boys and 17 girls, mean ages 10.5 and 9.9 years, respectively) underwent maximal cycle testing to assess the relationship between VO2max and PWC170. These measures correlated closely in absolute terms (r = 0.71 and 0.70 for girls and boys, respectively), but the relationship was weaker when both were expressed per kg body weight (r = 0.65 and 0.48, respectively). When VO2max was calculated from the regression equation of VO2max versus PWC170, the mean error from measured VO2max was 3.4 ml.kg-1.min-1 (SD 2.5) for the girls and 2.8 ml.kg-1.min-1 (SD 2.6) for the boys. These findings indicate that although mean predictability of VO2max from PWC170 is good, the variability is wide, with a 10-15% error at one standard deviation. PWC170 provides only a crude estimate of VO2max and should not be used to predict individual maximal aerobic power.

Anaerobic Threshold↗
PubMed1992

The influence of diabetes mellitus on cardiovascular function in children and adolescents.

Early manifestations of non-atherosclerotic cardiomyopathy, a recognized complication of diabetes in adults, have been suggested to contribute to depressed levels of aerobic fitness described in children and adolescents with this disease. This study measured components of aerobic fitness and cardiovascular function during maximal cycle ergometer exercise in 11 insulin-dependent diabetic boys aged 10.2-16.5 years. Mean duration of diabetes was 4.5 years. Eleven non-diabetic subjects matched for age, body size, and regular physical activity served as controls. No differences in maximal oxygen uptake or heart rate were observed between the two groups, nor were any significant differences recorded in submaximal stroke volume, cardiac output, heart rate, and pressure-rate product. This study failed to reveal any evidence of functional myocardial disease in children and young adolescents with diabetes, suggesting that manifestations of diabetic cardiomyopathy should not be expected during the pediatric years. Moreover, these findings indicating normal cardiovascular function in young diabetic subjects imply that regular levels of habitual physical activity are more likely to affect aerobic fitness in these patients rather than influences of the diabetic state itself.

Adolescent↗
PubMed1992

Oxygen uptake plateau during maximal treadmill exercise in children.

The leveling of oxygen uptake at high work loads has been utilized to define maximal VO2 during progressive exercise testing. Exercise studies in children have indicated, however, that a VO2 plateau can commonly be demonstrated in less than one half of subjects. To examine the potential contributions of subject effort, aerobic fitness, and nonaerobic performance to this variability, 15 children ages 7 to 10 years performed progressive treadmill walking to exhaustion with a ramp protocol. The VO2 plateau was defined as a change in VO2 during the final minute of exercise less than 2 SD below the mean of increases between the previous 4 to 5 submaximal minutes. Five subjects (33.3 percent) demonstrated a plateau. No significant differences in mean peak VO2, heart rate, or respiratory exchange ratio were observed between plateau and nonplateau groups. Testing results of speed (50-yard sprint) and leg power (vertical jump) were also similar. These findings suggest that following: (1) subject effort, aerobic fitness, and nonaerobic factors do not explain the presence or absence of a VO2 plateau during exercise testing of children; and (2) a VO2 plateau should not be used as a requirement for defining VO2max during treadmill testing in this age group.

Child↗
PubMed1992

Trainability of the cardiorespiratory system during childhood.

Children have long been suspected of having a diminished capability of responding to endurance training with improvements of maximal oxygen uptake compared to adults. However, studies examining the trainability of children have been beset with methodologic flaws that have precluded firm conclusions about such adult/child differences. Most studies in children that have involved adequate intensity, type, and duration of training have demonstrated the same qualitative changes as would be expected from adult subjects. Some information suggests that children may need a greater exercise intensity than adults to trigger cardiovascular adaptations to training. Other data raise questions regarding differences in autonomic influences on the heart and myocardial function in children that could relate to age-dependent responses to training.

Adaptation, Physiological↗
PubMed1991

Iron deficiency in adolescent girls. Are athletes at increased risk?

Previous studies have indicated a high prevalence of nonanemic iron deficiency in female high school aged endurance athletes. It is not clear, however, whether these adolescents are at more risk for iron depletion than their nonathletic peers. We have previously reported declining serum ferritin levels in response to running but not swimming training in competitive adolescents. In this study we compared these findings with serum ferritin levels and hematologic parameters in a group of nonathletic females from the same community. Mean serum ferritin levels were not significantly different among the groups. A greater percentage of the swimmers and runners had ferritin levels less than 12 ng/ml at the beginning of the season (46.7 and 40%, respectively, compared to 26.7% in the nonathletes), but the differences were not statistically significant. These findings suggest that the high prevalence of hypoferritinemia at the beginning of a competitive season in female high school athletes is similar to that of nonathletes. Other studies have indicated, however, that some sports, particularly running, increase the incidence of iron depletion with training.

Adolescent↗
PubMed1991

Aerobic responses to walking training in sedentary adolescents.

Promotion of physical fitness and an active lifestyle is critical during the formative adolescent years. This study investigated the effect of a school-based, alternative physical education program of walking training on the aerobic fitness of sedentary, predominantly obese teenagers. The subjects trained three days a week for 11 weeks at an average pace of 3.9 mph and heart rate of 151 beats per minute (79.6% of maximum). Physiologic responses during maximal treadmill testing before and after walking training were compared to those during a 3-month control period preceding the program. Weight-relative maximal oxygen uptake improved 9.9 percent (p less than .05), while treadmill endurance time increased by two minutes (23 percent, p less than .05). These findings indicate that small but significant improvements in aerobic function can be expected from walking training in sedentary adolescents.

Adolescent↗
PubMed1991

Effects of obesity on aerobic fitness in adolescent females.

Obesity impairs performance in most athletic events, but the influence of increased body fat on cardiopulmonary function has not been clearly delineated. An understanding of the fatness-fitness relationship is important in the optimal design of exercise programs for obese subjects. In this study, 27 adolescent females with body fat levels ranging from normal to gross obesity were evaluated to determine the impact of adiposity on physiologic factors during maximal and submaximal treadmill walking. Increased skinfold measures correlated significantly with absolute maximal oxygen uptake throughout the range of body fat levels (r = .72), and oxygen consumption per kilogram of body weight and treadmill endurance time both declined as fatness increased (r = -.49 and -.42, respectively). Obesity did not affect submaximal walking economy. These findings indicate that increased fat levels are associated with increased cardiopulmonary exercise capacity, but that functional fitness declines because of the inert load created by excess body fat. Therefore, therapeutic exercise programs for obese adolescents are best designed to increase caloric expenditure and decrease body fat rather than to improve aerobic fitness.

Adolescent↗
PubMed1990

Iron deficiency in the young athlete.

Although overt anemia is uncommon, depletion of body iron stores is common among adolescent female athletes. Poor dietary iron intake, menstruation, and increased iron losses associated with physical training all appear to be important factors. Whether nonanemic iron deficiency can impair exercise performance is uncertain. Nonetheless, athletes with low ferritin levels are at risk for impaired erythropoiesis and should receive therapeutic iron supplementation.

Adolescent↗
PubMed1990

Exercise cardiac contractility in men and boys: a recovery echocardiographic study.

Previous reports have suggested that children possess limited cardiac functional reserve during exercise compared to young adults. In this study, echocardiography was performed immediately after maximal treadmill exercise to measure left ventricular dimensions and shortening fraction (SF) in college men, and these values were compared to previous results in a post-exercise echocardiographic study of prepubertal boys. Post-exercise SF, change in SF from rest, and percent change in SF from rest were all significantly greater in the post-pubertal subjects. In both men and boys changes in SF following exercise were related to reductions in left ventricular end-systolic dimension, with only minor reductions observed in end-diastolic dimension. These findings support the concept that prepubertal subjects may have inferior myocardial function with exercise when compared to young adults.

Adolescent↗
PubMed1990

Mechanical efficiency during cycling in prepubertal and adult males.

Previous studies have indicated that values for mechanical efficiency during cycle exercise in prepubertal subjects are similar to those in adults. Few studies have directly compared these groups, however, and earlier reports did not consider the importance of assessing efficiency at similar relative exercise intensities. Nineteen prepubertal boys and 21 college men underwent cycle exercise testing for determination of delta efficiency (the energy required to increase workload), related to both absolute work load and relative work intensity (percent VO2max). No significant differences in either of these measures were observed between the two groups. Mean delta efficiency between workloads of similar relative intensity was 23.2% for the prepubertal subjects and 22.5% for the adults (p greater than .05). Between equal absolute workloads the values were 23.2 and 26.5%, respectively (p greater than .05). These findings support earlier contentions that the efficiency of muscular contraction during exercise is comparable in pre- and post-pubertal subjects.

Adult↗
PubMed1990

Developmental aspects of physiological function relating to aerobic exercise in children.

The many physiological determinants of exercise performance mature throughout the childhood years. Current research suggests that the improvements in maximal aerobic power which occur as the child ages are an expression of both increased body size and improved function. Absolute VO2max increases during the childhood years in both girls and boys. Average VO2max related to bodyweight, however, remains stable in boys of all ages, while values in girls decline progressively as they grow. VO2 at a given treadmill speed or slope falls during the growing years. This improvement in running economy may explain parallel advances in endurance exercise performance. The explanation for greater running economy with growth is uncertain, but lower step rate, improved running mechanics, and changes in body mass: surface area ratio may play a role.

Body Composition↗
PubMed1989

Iron deficiency in athletes. Insights from high school swimmers.

Previous studies have indicated a high incidence of nonanemic iron deficiency in high school runners, but little is known regarding participants in other sports. The hematologic and iron status of 30 high school swimmers was assessed at the beginning and end of a competitive swim season. Iron depletion (serum ferritin level less than 12 micrograms/L) was initially present in 46.7% of the girls and none of the boys, yet among those subjects with hypoferritinemia there was no evidence of impaired red blood cell production. Serum haptoglobin levels were normal and did not correlate with serum ferritin levels. No significant change was observed in ferritin, hemoglobin, or haptoglobin concentrations during the course of the season. Dietary intake of iron was poor, particularly in the girls, in whom it averaged 43% of the recommended dietary allowance. Menstrual histories suggested an inverse relationship between the amount of menstrual flow and the serum ferritin level. These findings indicate a high prevalence of nonanemic iron deficiency in female high school swimmers that bears no relationship to swim training. Dietary inadequacies and menstrual blood flow appear to be important contributors to the hypoferritinemia observed in these athletes.

Adolescent↗
PubMed1989

Anaerobic threshold and the determination of training target heart rates in premenarchal girls.

The capability of children to respond to endurance training with increased aerobic capacity is unclear. Prepubertal subjects may require higher target heart rates than adults to increase VO2 max, and previous studies failing to demonstrate aerobic trainability in children may have involved inadequate exercise intensity. In this study, heart rates at the anaerobic threshold, measured noninvasively as the ventilatory breakpoint (VBP), were determined during treadmill testing of 12 premenarchal girls to establish a metabolic-based target rate. The mean heart rate at VBP was 171 beats/min (+/- 12 SD) with a range from 147 to 194 beats/min. Although a wide intersubject variability was observed, the rates at VBP exceeded those predicted by standard formulas for calculating target heart rates in adults by over 10 beats/min in a majority of the girls. These data indicated that target heart rate guidelines designed for training older individuals may not adequately stress oxygen delivery systems in prepubertal subjects.

Anaerobic Threshold↗
PubMed1988

The effect of iron therapy on the exercise capacity of nonanemic iron-deficient adolescent runners.

Iron-deficiency anemia impairs exercise capacity, but whether nonanemic iron depletion decreases endurance performance is unclear. In 14 iron-deficient (serum ferritin level, less than 20 micrograms/L [less than 20 ng/L])nonanemic runners, hematologic and treadmill running values were followed up during a competitive season. Following a four-week control period, runners were treated for one month in a double-blind protocol with ferrous sulfate (975 mg/d) or placebo. During treatment, the mean ferritin level rose from 8.7 to 26.6 micrograms/L (8.7 to 26.6 ng/mL) in those patients taking iron and fell from 10.6 to 8.6 micrograms/L (10.7 to 8.6 ng/mL) in the placebo group. Treadmill endurance times improved significantly in the iron-treated runners compared with controls. Endurance time declined in all seven controls (range, 0.07 to 1.30 minutes), while six of seven iron-treated subjects improved their performance (range, 0.03 to 1.92 minutes). No significant differences in maximal or submaximal oxygen consumption, ventilation, or heart rate were observed between the groups except for a 4% increase in maximum oxygen consumption during placebo treatment. These data indicate that nonanemic iron deficiency impairs exercise performance but does not influence gas exchange or cardiac measures.

Adolescent↗
PubMed1988

Submaximal aerobic running economy and treadmill performance in prepubertal boys.

Although the determinants of running economy and its relationship to endurance performance have been evaluated in adults, little data are available in pediatric subjects. Twenty-eight prepubertal boys with diverse athletic abilities underwent progressive maximal treadmill testing. Running economy was defined as (1) VO2 at 9.6 kph and (2) VO2 expenditure for increasing running speed 1.6 kph (delta VO2). Treadmill running times ranged from 12.6 to 23.0 min. Mean VO2 at 6 mph was 48.7 m.kg-1.min-1 (SD 4.3) and delta VO2 averaged 6.8 m.kg-1.min-1 (SD 1.7). VO2max correlated closely to treadmill time. Treadmill endurance times were significantly related to running economy by both definitions; submaximal VO2 levels did not, however, correlate with maximal aerobic power. Delta VO2 was associated with stride frequency, but no other relationships were observed between economy and height, age, respiratory exchange ratio, ventilatory equivalent for oxygen, stride length: leg length ratio, or body surface area: mass ratio. These findings suggest that among older prepubertal boys, greater running economy is associated with superior treadmill endurance performance and that stride frequency may influence submaximal VO2 expenditure in children.

Adolescent↗
PubMed1988

Physiological responses to treadmill exercise in females: adult-child differences.

Physiologic differences between children and adults during treadmill exercise have been defined principally utilizing male subjects. To determine whether these variations are valid in females, responses to treadmill testing to exhaustion in 18 premenarchal girls were compared with an equal number of young adult females (mean age 28.7 yr). Except at the lowest workload, the girls demonstrated significantly higher oxygen consumption and ventilation per body weight at maximal and submaximal speeds. Differences in submaximal running economy disappeared when VO2 was related to body surface area. The children exhibited a greater respiratory rate and lower tidal volume (per kilogram) at a given ventilation as well as inferior breathing efficiency (higher ventilatory equivalent for oxygen). The absolute ventilatory breakpoint was higher in the girls, but there was no significant difference in this parameter between the groups when expressed as percent VO2max. The heart rate at the ventilatory breakpoint was greater in the girls, however. These findings indicate that pre- and post-menarchal females exhibit similar differences in physiologic responses to treadmill running as previously observed in adult and child male subjects.

Adult↗