Estimation of aerobic capacity from submaximal cycle ergometry in women.

Simple, valid, and reliable methods of estimating maximal oxygen uptake (VO2max) are needed for epidemiologic studies of physical activity, to evaluate fitness for job performance, and to assist in prescription of exercise. Such estimations in women have not received due research attention. Heart rate responses to submaximal cycle ergometry and VO2max during maximal treadmill and cycle ergometer testing were measured in 37 healthy women aged 19-47 yr (X = 31.7 +/- 7.9). The submaximal test was very reliable on retest (r = 0.92), but overestimated measured treadmill VO2max (X = 2.42 vs 2.23 l.min-1; r = 0.76, SEE = 0.229). The submaximal test also greatly overestimated maximal cycle ergometer VO2max (X = 2.42 vs 2.06 l.min-1; r = 0.70, SEE = 0.340). Similar 8.5% (treadmill) and 18.5% (cycle ergometer) overestimation by the submaximal test were found for VO2max relative to body weight. A simple submaximal exercise test is highly reliable as an estimate of VO2max when used for women. It also provides a reasonably good estimate of treadmill measured VO2max.

Bone mineral content in Hawaiian, Asian, and Filipino children.

Os calcis bone mineral content (BMC) was measured by single photon absorptiometry in 86 children, ages 6 to 13 years from Hawaiian, Oriental, Caucasian, and Filipino ethnic groups. Pearson correlations indicated significant positive correlations between BMC and age, height, and weight. However, there were no significant differences in age, height or weight between ethnic groups. ANOVA revealed a significant effect of ethnic group on BMC with the Hawaiian group having a significantly higher BMC than the Asian or Caucasian groups. When age, height and weight were controlled for, ANCOVA still showed a significant effect of ethnicity on BMC. The current findings suggest that ethnic differences can develop early in life.

Comparison of treadmill exercise testing protocols for wheelchair users.

The reduced early mortality and the increased life span of persons with spinal cord injury (SCI) and other chronically disabling conditions which result in loss of use of the legs places them at increased risk of coronary heart disease, diabetes, and hypertension. Exercise testing in this population is becoming more common, but there is a need for assessment of protocols in order to determine the best method to elicit a maximal response in a reasonable time without endangering the patient. Three wheelchair treadmill protocols were compared in seven men with paraplegia aged 21-44 years (five SCI, two post-polio). Subjects repeated each protocol to estimate reliability. Protocol G consisted of increasing treadmill grade at a constant speed (4.8 km.h-1); in protocol S, the speed was increased at a constant grade (0%), and in protocol C, speed and grade were increased. Two-minute stages were used in all protocols. Peak oxygen uptake [VO2max; mean (SD): 23.6 (5.8) ml.kg-1 x min-1; 1.66 (0.37) l.min-1], VCO2 production [1.98 (0.46) l.min-1], ventilation volume [83.0 (25.6) l.min-1], respiratory exchange ratio [1.2 (0.12)], and heart rate [173 (18)] were determined. Over all trials none of the variables was significantly different among the three protocols, but all were highest in C and lowest in S. Reliability coefficients for absolute and relative VO2max ranged from 0.76 and 0.81 in G to 0.95 and 0.98 in C (all P < 0.05). These data suggest that an incremental treadmill test similar to the C protocol may be the optimal method to use when evaluating the exercise capacity of wheelchair users.

On the use of oxygen to facilitate decompression.

Oxygen is widely used at elevated partial pressures to facilitate decompression, yet the optimum dosage and the magnitude of the beneficial effects are poorly known. This is because oxygen enhancements, expressed as increases in the allowed pressure reductions, are small and easily masked by individual variation. Furthermore, oxygen can also produce detrimental results, and the range from a therapeutic to a toxic dose is narrow. Berhage and McCracken recently reported two massive investigations involving 1185 rats and 60 experimental conditions. These authors suggest that the conventional concept of an "equivalent air depth" (EAD) is untenable and that oxygen must be considered in calculating the totat tissue gas tension. We find instead that the observations of Berghage and McCracken are compatible with a model in which the tensions of oxygen and carbon dioxide dissolved in tissue are taken into account, and that this model, in turn, agrees with EAD predictions of oxygen enhancements for subtoxic oxygen pressures.

Respiratory volume-time relationships during resistive loading in the cat.

The first-breath (neural) effects of graded resistive loads added separately during inspiration and expiration was studied in seven anesthetized cats before and after bilateral vagotomy. Additions of airflow resistance during inspiration reduced the volume inspired (VI) and increased inspiratory duration (TI). The duration of the ensuing unloaded expiration (TE) was unchanged. Vagotomy eliminated the TI modulation with inspiratory loads. Tracheal occlusion at the onset of inspiration yielded TI values similar to the fixed values observed following vagotomy. Resistive loads added during expiration produced similar results. Expired volume (VE) decreased and (TE) increased approaching the values obtained after vagotomy. Unlike the inspiratory resistive loads, loading during expiration results in an upward shift in the functional residual capacity (FRC). The FRC shift produces a time lag between the onset of diaphragmatic (EMG) activity and the initiation of airflow of the next (unloaded) inspiration. These studies suggest separate volume-time relationships for the inspiratory and expiratory phases of the breathing cycle. Both relationships are dependent upon vagally mediated volume feedback.