On the determination of ventilatory threshold and respiratory compensation point via respiratory frequency.

This study examined the validity of a quantitative respiratory frequency (f(R)) analysis to detect the ventilatory threshold (theta(Vent)) and respiratory compensation point (RCP). Thirty-six amateur competitive cyclists completed a maximal graded exercise test on an electromagnetically-braked cycle ergometer. theta(Vent) and RCP were determined using multiple gas exchange criteria and by f(R) analysis (theta(Vent)f(R) and RCP(f(R))), employing an iterative least-squares linear regression technique. Fifteen subjects were excluded from the analyses due to a low signal-to-noise ratio and/or high risk for pseudo-threshold resulting from hyperventilation early in the exercise protocol. A Bland-Altman procedure for inter-analysis comparison completed on the remaining participants' data (n=21; age=29+/-7 years; height=177+/-9 cm; weight=76.0+/-15.8 kg; VO(2max)=4.415+/-0.971 lmin(-1); 58.7+/-10.7 ml kg(-1) min(-1)) revealed mean bias+/-95% Limits of Agreement (LOA) of 1.53+/-50.2 W for theta(Vent) and theta(Vent)f(R). The same inter-anlysis comparison (n=21) for RCP and RCP(f(R)) resulted in a mean bias+/-LOA of 12.6+/-26.9 W. The analysis techniques in the present investigation revealed substantial limits of agreement and/or bias for all estimations, and these data indicated f(R) analyses were unsatisfactory to determine theta(Vent) and RCP in trained cyclists.

Thermoregulation in burn patients during exercise.

The purpose of this study was to assess the ability of patients with burns on 30 to 40% and 60% or greater of their BSA to thermoregulate their core temperature during exercise in the heat. Two groups (n = 3 in each) of subjects with healed third-degree burns (34.0 +/- 1.4% and 77.7 +/- 12.4%, respectively) and a group of unburned subjects (n = 2) exercised for 1 hour on a cycle ergometer at 75 Watts in an environmental chamber set at 35 degrees C and 60% relative humidity. Subjects were monitored for rectal and skin temperatures, heart rate, whole body sweat rate, skin blood flow, and active sweat gland density (number per cm ) in unburned, burned, and harvested skin. The results demonstrated that patients with burns on 60% or greater BSA did not show an intolerance to moderate exercise in the heat, as evidenced by only a moderate rise in rectal temperature and heart rate. Furthermore, the responses were similar to those of the unburned subjects.

An inquiry-based learning model for an exercise physiology laboratory course.

We developed an inquiry-based learning model to better stimulate undergraduate students' cognitive development of exercise physiology laboratory concepts. The course core is the two independent research projects that students, working in small groups, complete during the last 9 wk of the semester. Student groups develop their own research question and hypothesis, design the experiment, collect and analyze the data, and report their findings to the rest of the class using presentation software. To help with success of the research projects, students are taken through a series of guided-inquiry laboratory activities during the initial 6 wk of the semester to develop laboratory skills and an understanding of the scientific process. Observations of student behaviors reflected a high level of enthusiasm and engagement in laboratory activities. Surveys, journal entries, and interviews indicated that students felt empowered by having ownership in their projects, which may be the key reason for the success of this model.

Effect of hypohydration on core temperature during exercise in temperate and hot environments.

The purpose of this study was to compare directly the physiological consequences of 5% hypohydration or euhydration during exercise in both temperate (23 degrees C) and hot (33 degrees C) environments. The subjects were eight male volunteers. Each performed four 1-h exercise bouts at 60% maximum oxygen uptake, one in each of the following conditions: hot-hypohydrated, hot-euhydrated, temperate-hypohydrated, and temperate-euhydrated. Heart rate (HR), rectal temperature (Tre), forearm blood flow, and oxygen uptake were measured after 20, 40, and 60 min exercise. Whole-body sweat rate was also determined for each exercise bout. Hypohydration increased Tre significantly (P<0.05) more in the hot environment (0.16 degrees C per 1% decrease in body mass) than in the temperate environment (0.08 degrees C per 1% hypohydration). Furthermore, compared with euhydration, hypohydration decreased forearm blood flow and whole-body sweat rate significantly more during exercise in the hot than in the temperate environment. The reductions in forearm blood flow and whole-body sweat rate appear to have decreased heat loss, thus accounting for the increase in Tre during exercise in the heat while hypohydrated. In conclusion, this study illustrates that the physiological consequences of hypohydration during exercise are exacerbated in the heat.

Sweat ethanol concentrations are highly correlated with co-existing blood values in humans.

This study compared the concentration of ethanol, both absolute and relative to water content, in sweat and blood. Ten male volunteers consumed approximately 13 mmol (kg body weight)-1 of ethanol. Blood and sweat samples were collected approximately 1, 2 and 3 h following ingestion. Sweat was collected following pilocarpine iontophoresis using an anaerobic technique that prevented ethanol evaporation. In addition, the water content of sweat and blood samples was determined. The correlation between sweat and blood ethanol, expressed in mmol l-1, was r = 0.98. The slope of the relationship was 0.81. When corrected for the water content in each sample, and expressed as mmoles per litre of water, the correlation remained very high (r = 0.97) while the slope increased to 1.01. These results suggest that rapid and complete equilibrium of ethanol occurs across the sweat gland epithelium.

Acclimation to humid heat lowers resting core temperature.

The purpose of this study was to test the hypothesis that a reduction in resting rectal temperature (Tre) is partially responsible for the attenuation in the rise of core temperature during the heat exposure following acclimation to humid heat. Nine male volunteers completed 7 days of acclimation, performing 2 h of exercise per day in a hot, humid environment (35 degrees C, 75% relative humidity). Mean (+/- SD) ending Tre significantly (P < 0.05) decreased from 38.9 +/- 0.5 degrees C on day 1 to 38.3 +/- 0.4 degrees C on day 7. Likewise, mean (+/- SD) resting Tre significantly (P < 0.05) decreased from 37 +/- 0.3 to 36.7 +/- 0.4 degrees C. In fact, all nine men showed a decrease in resting Tre from day 1 to day 7, ranging from -0.1 to -0.5 degrees C. In addition, resting Tre and ending Tre were significantly correlated (r = 0.68). However, the mean increases in Tre (ending Tre minus resting Tre) and heat storage that occurred on each of the 7 acclimation days were not significantly different. These results support the hypothesis that a reduction in resting Tre is partially responsible for the attenuation in ending Tre during heat exposure following short-term acclimation to humid heat.

Comparison of mean skin temperature using 'covered' versus 'uncovered' contact thermistors.

The purpose of this study was to compare the mean skin temperature (Tsk) obtained using 'covered' versus 'uncovered' contact thermistors in a variety of environmental conditions. Ten male subjects walked on a treadmill at 6.4 kph for 30 min in three different environments: thermoneutral (23 degrees C/50% RH), hot-humid (35 degrees C/80%), and hot-dry (42 degrees C/20%). Tsk was measured using three 'uncovered' contact thermistors, and three 'covered' thermistors. The 'uncovered' probes were attached using acrylic rings that allowed the outer surface of the thermistors to have free exchange with the environment. The 'covered' probes were affixed to the skin using foam patches and tape. The latter procedure is commonly used in many research and clinical laboratories. The 'covered' probes resulted in a significantly (p < 0.05) higher Tsk under all three environmental conditions. The largest difference occurred in the thermoneutral condition with the 'covered' Tsk being 1.3 degrees C higher than the 'uncovered' Tsk. These results suggest that covering a contact skin thermistor hinders heat loss and results in an artificially high Tsk. It is hoped that the results of this study will encourage the adoption of 'uncovered' contact skin thermistors in the future.

Relationship between blood lactate response to exercise and endurance performance in competitive female master cyclists.

The blood lactate response to graded exercise and its relationship to performance in the field was examined in highly competitive female master cyclists. Thirteen women, age 47.5+/-2.2yr (mean+/-SE), all of whom were United States Cycling Federation (USCF) competitors, underwent laboratory testing for aerobic capacity (VO2max) and lactate threshold (LT), and field testing for performance in 13.5 km and 20 km time-trials. The mean VO2max of the subjects (50.6+/-2.7 ml x kg(-1) x min[-1]) was approximately 10% higher than that previously reported for other age-matched female athletes and correlated moderately (r=-0.67) with age. Maximal heart rate was unrelated to age (r=-0.25, p>0.05). Blood lactate concentration (BLC) while time-trialing was significantly higher than that at the LT (2.86+/-0.17 mmol x l[-1]) for both the 13.5 km (7.59 mmol x l(-1), p < 0.0001), and the 20 km trials (6.99 mmol x l(-1), p<0.002). The LT occurred at a mean power output of 168+/-11.3 W and 66% of VO2max. The VO2 corresponding to a BLC of 4.0 mmol x l(-1) (LT4) was 72% of VO2max. As expected, time-trial performance was highly correlated with VO2max (r=-0.85); however, regression analysis indicated that power output at the lactate threshold was the best laboratory predictor of performance (13.5 km: r2 = 0.83; 20 km: r2 = 0.78). Relative to maximal heart rate, heart rate at LT (88% HRmax) was significantly (p<0.05) lower than time-trial heart rate (92-94% HRmax). The cyclists in this study have higher aerobic capacities and maximal heart rates than those previously reported for other age-matched female athletes and are able to cycle for extended periods at blood lactate concentrations significantly higher than those at the lactate threshold. Traditional methods of exercise prescription, particularly when using age-estimates of maximal heart rate, underestimate training intensities required to be above the LT in female master cyclists.

Oral contraceptives elevate core temperature and heart rate during exercise in the heat.

It is generally believed that the elevated progesterone levels seen during the luteal phase of the menstrual cycle alter thermoregulatory function during exercise. We hypothesized that oral contraceptives (OCs) that contain synthetic progestogen would alter thermoregulation during exercise in a manner similar to that seen during the luteal phase. To test this hypothesis 10 healthy women currently taking OCs were recruited. Subjects performed a 1 h exercise bout in the heat (30 degrees C, 50% relative humidity; RH) at 60% of their maximum oxygen uptake on two occasions: once while on OCs and once during a control trial when the subjects were off OCs. Core temperature, skin temperatures, heart rate, skin blood flow and sweat rate were measured at rest and every 20 min during both exercise bouts. OCs significantly increased core temperature and heart rate over that seen during the control condition. Specifically, after 1 h of exercise, OCs caused a mean 0.3 degrees C and an 8-bpm increase in core temperature and heart rate respectively. Additionally, the differences in core temperature and heart rate during the two trials became more exaggerated as exercise duration increased, as evidenced by significant treatment-by-time interactions. These results suggest that OCs alter thermoregulatory and cardiovascular function during exercise in the heat. Furthermore, the changes in core temperature and heart rate seen during exercise while taking OCs are similar in direction and magnitude to those observed during the luteal phase of the menstrual cycle.

Validity and reliability of a timed 5 km cycle ergometer ride to predict maximum oxygen uptake.

The purpose of this study was to determine the validity and reliability of a timed 5 km cycle ergometer ride to predict maximum oxygen uptake (VO2max). Fifty-two healthy volunteers had their VO2max determined during a maximal treadmill run. They also performed a timed 5 km cycle ergometer ride. The resistance setting for the cycle ride was set at a rate of 0.5 kg/20 kg body weight. A significant inverse relationship was found between the logarithm of cycle time and VO2max (r = -0.83). Furthermore, the test-retest reliability for the 5 km ride was determined to be r = 0.93 (n = 20). These results suggest that a timed 5 km cycle ergometer ride is a valid and reliable predictor of VO2max. Furthermore, the timed cycle ride offers several methodological advantages which makes it potentially useful in clinical, military, and research settings.

Augmented hyperventilation via normoxic helium breathing does not prevent exercise-induced hypoxemia.

The purpose of this study was to determine if augmented hyperventilation produced via normoxic helium breathing would reduce exercise-induced hypoxemia (EIH). Seven highly trained endurance athletes with a mean maximum oxygen uptake of 65 ml.kg-1.min-1, performed two cycle ergometer tests to volitional exhaustion. During one of the tests the subjects breathed ambient air, while during the other they breathed normoxic helium (21% O2, 79% He). Mean maximum expired ventilation significantly (p < .05) increased from 139 L.min-1 during the ambient trial to 168 L.min-1 while breathing normoxic helium. Mean arterial oxygen saturation obtained at maximum exercise, however, was not significantly different for the two trials (ambient = 90%, helium = 89%). These results suggest that significantly augmenting exercise hyperventilation by 21% essentially had no effect on EIH in endurance athletes. Thus, the data do not support the hypothesis that inadequate hyperventilation is an important mechanism for arterial oxygen desaturation during graded exercise to exhaustion in highly trained individuals.

Effect of continuous-wave ultrasound on blood flow in skeletal muscle.

BACKGROUND AND PURPOSE: The purpose of this study was to determine the effect of ultrasound on forearm, skin, and muscle blood flow. SUBJECTS: Twenty volunteers without known vascular problems (10 male, 10 female) participated. METHODS: All subjects received a treatment of continuous-wave ultrasound to the anterior forearm at a dosage of 1.5 W/cm2 for a duration of 5 minutes. The contralateral forearm served as the control and received identical treatment, except the ultrasound output remained at zero. Forearm blood flow was measured using venous occlusion plethysmography, and skin blood flow was measured using cutaneous laser-Doppler flowmetry before and after ultrasound administration, with the difference being muscle blood flow. RESULTS: No differences between the control arm and the ultrasound-treated arm were found for muscle, skin, and forearm blood flow. CONCLUSION AND DISCUSSION: These results suggest that administration of continuous-wave ultrasound at the prescribed dosage had no effect on skeletal muscle blood flow for up to 30 minutes posttreatment. Thus, muscle hyperemia is probably not the primary mechanism responsible for the clinical benefits seen following the use of ultrasound as a therapeutic modality.

Seven-day recall and other physical activity self-reports in children and adolescents.

There is need to develop low cost, practical, and accurate measures of physical activity in children and adolescents, and self-report is a promising methodology for children that is applicable for large studies. The purpose of the present study was to assess the reliability and validity of several self-reports of physical activity. Subjects were 36 fifth-, 36 eighth-, and 30 eleventh-grade male and female students. The test-retest reliabilities were r = 0.77 for the 7-d recall interview, r = 0.81 for the Godin-Shephard self-administered survey, and r = 0.93 for a simple activity rating. For the former two measures, reliability improved with age but was significant at all ages, and for the last measure there were no age effects. Memory skills and obesity status were not related to the reliability of recall, but males were more reliable reporters than females. Validity of the 7-d recall was determined by comparing heart rate monitoring records with recalls of very hard activities on the same day. A correlation of 0.53 (P < 0.001) for the total group supported the validity of the reports. Validity improved with age, but validity coefficients were significant in all age groups. These data indicate that physical activity recalls of children as young as the fifth grade are of adequate reliability and validity to use in research on physical activity in children.

Cholinergic sensitivity of the eccrine sweat gland in trained and untrained men.

The purpose of this study was to compare the cholinergic responsiveness of the human sweat gland in trained and untrained men. Eighteen healthy male volunteers (9 trained, 9 sedentary) served as subjects. Pilocarpine concentration vs. sweat rate dose-response curves were obtained from each subject using iontophoresis. From these measurements, maximal iontophoretic sweat rate (SRmax) was determined and correlated with each subject's maximal oxygen uptake (VO2max). The trained group had a significantly (P less than 0.05) greater mean SR max and their mean dose-response curve was shifted up and to the left, as compared to the sedentary controls. Furthermore, VO2max was significantly correlated with SRmax (r = 0.76). These findings suggest that the modification occurring in the human sweat gland after training may include improvements in both SRmax and cholinergic sensitivity, and support the hypothesis that the potentiation in sweating following training is achieved via a peripheral mechanism.

Effects of ageing and physical training on the peripheral sweat production of the human eccrine sweat gland.

Epidemiological studies suggest that thermoregulatory function declines with ageing. Therefore, it was the purpose of this study to examine the effects of physical training and ageing on the peripheral sweat rate of the human sweat gland. Maximum oxygen uptake and peripheral sweat rate (pilocarpine iontophoresis) were determined in 40 male volunteers (10 sedentary younger men, 10 endurance-trained younger men, 10 sedentary older men, and 10 endurance-trained older men). Maximum oxygen uptake and peripheral sweat rate were significantly (p less than 0.05) greater in the two endurance-trained groups compared to their sedentary counterparts. Furthermore, when matched for maximum oxygen uptake, younger and older men had similar mean peripheral sweat rate values. These results suggest that participation in lifelong aerobic exercise may retard the decrease in peripheral sweat production usually associated with ageing. Further work is needed, however, to determine if such changes can improve overall thermoregulatory function in elderly people.

Blood pressure reactivity to exercise: stability, determinants, family aggregation, and prediction.

Previous studies have shown blood pressure reactivity to exercise predicts future resting blood pressure. Subjects in this study were 206 healthy Mexican-American and Anglo-American families with fifth or sixth grade children. A total of 539 children (mean age = 12 years) and parents (mean age = 37 years) had complete data at baseline, and 79% were remeasured 48 months later. Blood pressure was measured during a submaximal cycle ergometer fitness test. Reactivity measures included systolic blood pressure at 70% of maximal heart rate (SBP70) and slope of the blood pressure-heart rate association during exercise (SLOPE). Stability of reactivity measures over 24 months varied from .22 to .63 (all p less than 0.001). Correlates of blood pressure reactivity in parents included resting heart rate, gender, age, and sodium intake. Correlates of reactivity in children included resting heart rate, body mass index, and age. Modest but significant levels of family aggregation of blood pressure reactivity were observed. In stepwise multiple regression analyses, SBP70 at baseline predicted resting blood pressure 48 months later in parents but not in children. The present results confirm previous studies indicating systolic blood pressure reactivity to exercise is a significant predictor of later resting blood pressure.

Increases in aldosterone precede those of cortisol during graded exercise.

The purpose of this study was to determine the intensity threshold needed to elicit increases in plasma aldosterone and cortisol during graded exercise in humans. Seven male volunteers performed a maximal oxygen uptake (VO2max) test on a cycle ergometer. Plasma levels of aldosterone, cortisol, angiotensin II, ACTH, and potassium were measured at rest and at each 50 W workload of the exercise test. The results showed that aldosterone significantly (p less than or equal to 0.05) increased from a mean (+/- SE) of 231 +/- 22 pmol/L at rest to 464 +/- 22 pmol/L at exhaustion. Cortisol significantly (p less than or equal to 0.05) increased from 284 +/- 38 nmol/L at rest to 311 +/- 39 nmol/L at exhaustion. More importantly, however, was the fact that aldosterone was significantly increased above the resting level at exercise intensities greater than or equal to 60% VO2max. Cortisol, on the other hand, was only significantly increased at exhaustion (i.e. 100% VO2max). These results clearly show that increases in aldosterone precede those of cortisol during graded exercise in humans. Interestingly, potassium (r = 0.79), ACTH (r = 0.55), and angiotensin II (r = 0.54) were all significantly correlated with aldosterone during exercise. Such a finding seems to suggest that all 3 variables may be important stimuli for aldosterone secretion during graded exercise.

BEACHES: an observational system for assessing children's eating and physical activity behaviors and associated events.

An integrated system for coding direct observations of children's dietary and physical activity behaviors was developed. Associated environmental events were also coded, including physical location, antecedents, and consequences. To assess the instrument's reliability and validity, 42 children, aged 4 to 8 years, were observed for 8 consecutive weeks at home and at school. Results indicated that four 60-min observations at home produced relatively stable estimates for most of the 10 dimensions. Interobserver reliabilities during live and videotaped observations were high, with the exception of "consequences" categories that occurred in less than 1% of observed intervals. Evidence of validity was provided by findings that antecedents were associated with respective dietary and physical activity behaviors. The five physical activity categories were validated by heartrate monitoring in a second study. The Behaviors of Eating and Activity for Children's Health Evaluation System is appropriate for studying influences on diet and physical activity in children in a variety of settings.

Reliability of interviewers using the Seven-Day Physical Activity Recall.

The Seven-Day Physical Activity Recall interview is commonly used in epidemiologic research, but the methods of training and certifying interviewers have not been studied or standardized. The purpose of this study was to examine the reliability of the Seven-Day Physical Activity Recall interviews after a structured training program. Twenty-one volunteer interviewers participated in a five-session group training program that targeted standardized interview techniques and scoring procedures. Interviewers scored eight videotaped interviews on two occasions to assess scoring skills. Across all videotapes and interviewers, the test-retest reliability was .99. Two interviewers independently interviewed the same person on the same day, and the reliability of kilocalorie expenditure across interviewers was .86. It was concluded that naive individuals can be taught to reliably conduct and score the Seven-Day Physical Activity Recall interview in a brief training program.