Factors that influence adherence to exercise and their effectiveness: application to cystic fibrosis.

Appropriate, regular exercise is of benefit to patients with cystic fibrosis (CF). As with other segments of the population, it has been difficult to devise exercise programs to which most patients will adhere for long periods of time. In healthy children, factors that are related to positive exercise compliance include social support, perceptions of competency and self-esteem, enjoyment of activity, and availability of a variety of activities. In patients with CF, complications associated with the disease, e.g., time required for other treatment and fatigue, make compliance with recommended exercise activities more difficult. Factors likely to increase compliance in this population include explicit and continued encouragement and support from the family and healthcare team, and the introduction of behavior-changing strategies.

How much activity do youth get? A quantitative review of heart-rate measured activity.

OBJECTIVE: Recommendations for adult physical activity have shifted from 20 to 60 minutes of continuous vigorous activity 3 to 5 times a week to accumulation of 30 minutes of moderate to vigorous physical activity most days of the week. Variations of these guidelines also have been suggested for children, based on the idea of accumulating moderate to vigorous physical activity throughout the day, rather than attaining vigorous physical activity in continuous blocks. The goal of this study was to assess accumulated amounts of physical activity at different intensities in children. METHODS: We reviewed 26 studies (n = 1883) in youth aged 3 to 17 years that used heart-rate recording to measure physical activity in children to determine accumulated daily activity. Included were studies that provided time being active for at least 2 heart rate intensities at or above 120 beats/minute. Descriptive characteristics of the study groups were determined, and the influence of age, gender, and hours and days of observation on the slope of activity time as a function of percentage of heart rate reserve (HRR) was determined using hierarchical linear regression. RESULTS: Youth attained 128.0 +/- 45.6, 47.1 +/- 14.9, 29.3 +/- 13.7, and 14.7 +/- 6.0 minutes/day between 20% to 40%, 40% to 50%, 50% to 60%, and greater than 60% HRR, respectively. Age was a significant predictor of the intercept and slope of the physical activity and %HRR relationship. CONCLUSION: Youth of all ages attain >60 minutes/day of low-intensity physical activity and approximately 30 minutes/day of activity at traditional cardiovascular fitness training levels of 50% or more of HRR. Recommendations for youth activity are discussed.

Asthma and maternal body mass index are related to pediatric body mass index and obesity: results from the Third National Health and Nutrition Examination Survey.

OBJECTIVE: Clinical research has shown an increased prevalence of obesity in children with asthma. This study was designed to assess the relationship between asthma and pediatric body mass index (BMI) in a national database and to examine factors that may modify this relationship. DESIGN: The cross-sectional relationship between asthma and pediatric BMI and obesity (BMI > or = 85th percentile) was studied. Variables that may influence the relationship between asthma and pediatric BMI, such as race/ethnicity and television watching were included in the model for the total sample. A smaller sample of 3,009 white and African American youth were studied in regression models including maternal BMI. STUDY POPULATION: A nationally representative cross-sectional sample of 5154 children and adolescents of 6 to 16 years of age from the Third National Health And Nutrition Examination Survey. RESULTS: In the full sample, asthma and television watching were related to BMI, accounting for 3% of the variance in BMI. When maternal BMI was included in the non-Hispanic sample, television watching, maternal BMI, and the interaction of maternal BMI and asthma were related to youth BMI, accounting for 15% of the variance. The standardized BMI z-score for those youth without asthma and no maternal obesity was 0.06, which increased to 0.33 if the youth had asthma, to 0.70 if the youth did not have asthma but the mother was obese, and to 1.71 if the youth had asthma and the mother was obese. Asthma, television watching, and maternal BMI were independent predictors of youth obesity. CONCLUSIONS: BMI and prevalence of obesity is higher in youth with asthma. Pediatric BMI, but not obesity, is also related to the interaction of asthma and maternal BMI in white and African American youth. Comorbidity of asthma and obesity may complicate treatment of either condition, and prevention of obesity should be encouraged for asthmatic children.

Work and leisure time physical activity and mortality in men and women from a general population sample.

PURPOSE: The purpose of this study was to examine the long-term relationships between total physical activity and mortality from all causes and coronary heart disease (CHD) in the general population. METHODS: A prospective design was used, following participants for 29 years, beginning in 1960. The study population consisted of a randomly selected sample of white male (n = 698) and female (n = 763) residents of Buffalo, New York with a 79.0% participation rate and follow-up rates of 96.0% and 90.2% in males and females, respectively. At baseline, comprehensive information was obtained regarding participants' usual physical activity at work and during leisure time. RESULTS: As of December 31, 1989, three hundred and two (43.3%) men and 276 (41.0%) women died, 109 (15.6%) and 81 (10.6%) from CHD, respectively. In men, a significant interaction was found between activity and body mass index (BMI) for both outcomes. In women, a significant activity by age interaction was observed. In non-obese men (BMI<27.02), activity was inversely associated with all-cause [relative risk (RR) = 0.59; 95% confidence interval (CI), 0.39-0.89] and CHD mortality (RR = 0.39; 95% CI, 0.18-0.83), independent from the effects of age and education. No such associations were found in obese men and increased risks could not be ruled out. Among women, younger participants (age <60 years) had a significantly reduced risk of CHD death with increased activity (RR = 0.26; 95% CI, 0.07-0.99). No other significant associations were observed. CONCLUSIONS: Physical activity favorably influences mortality risks in non-obese men and younger women. Gender-specific factors should be considered for potential effect modification.

Providing sedentary adults with choices for meeting their walking goals.

BACKGROUND: This study was designed to test different ways of meeting the new ACSM/CDC recommendations for physical activity stating that all Americans at least 2 years of age should obtain 30 minutes of moderate intensity activity on most days of the week. METHODS: Thirty-two sedentary 18- to 55-year-old adults were randomly assigned to three groups of brisk walking/6 days per week: 30 continuous minutes, three 10-minute bouts, and 30 minutes in any combination of bouts as long as each bout was at least 5 minutes. Aerobic fitness, blood pressure, body composition, and physical activity were assessed at baseline, at end of program (16 weeks), and at follow-up (32 weeks). RESULTS: All groups significantly (P

Effects of varied vocal intensity on ventilation and energy expenditure in women and men.

This study was completed to determine how ventilatory responses change by means of speech reading at three different sound pressure levels (SPL) as compared to quiet breathing prior to each task. The energy required to alter SPL was also studied and compared to energy expenditures during a quiet breathing condition. Twenty-four adults (12 women, 12 men) were studied while reading a standard passage at low, comfortable, and high SPLs for 7 minutes with quiet breathing periods between each task to achieve respiratory steady state and serve as a control to which the reading tasks were compared. The last 2 minutes of exhaled air for all speaking and quiet breathing tasks were collected using a Hans Rudolph mouth breathing face mask. A Sensor Medics Vmax 29 series diagnostic instrument system measured all ventilatory responses and energy expenditures. Volume and timing alterations in ventilation were characterized by measuring tidal volume (V[T]), inspiratory time (T[I]), inspiratory flow rate (V[T]/T[I]), and expiratory time (T[E]). Average ventilation, energy expenditure, and adequacy of ventilation were measured using minute ventilation (V[E]), oxygen consumption (VO2), carbon dioxide production (VCO2), and partial pressure of end-tidal carbon dioxide (end-tidal PET[CO2]). Results indicated volume, timing, ventilation, and energy expenditure values remained closest to quiet breathing values for the comfortable SPL. Volume, ventilation, and energy expenditure were significantly greater for the high SPL and lower for the low SPL, compared to the baseline steady state, indicating that the low SPL causes a ventilatory deficit that was found to be paid back at the end of the speech task during the quiet breathing period. These results demonstrate that an individual's comfortable SPL is the least energy-requiring way to speech breathe. As SPL rises above or below comfortable SPL, speech breathing requires more energy.

Contractility of the ventilatory pump muscles.

The ventilatory muscles are striated skeletal muscles, and their in situ function is governed by the same relationships that determine the contractile force of muscles in vitro. The ventilatory muscles, however, are functionally distinct from limb skeletal muscles in several aspects, the most notable being that the ventilatory muscles are the only skeletal muscles upon which life depends. Among the muscles that participate in ventilation, the diaphragm is closest to its optimal resting length at functional residual capacity (FRC) and has the greatest capacity for shortening and volume displacement, making it the primary muscle of inspiration. All inspiratory muscles shorten when the lung is inflated above FRC, but interactions among the various inspiratory muscles make for a wider range of high force output than could be achieved by any one muscle group acting in isolation. The velocity of inspiratory muscle shortening, especially diaphragmatic shortening, causes maximal dynamic inspiratory pressures to be substantially lower than maximal static pressures. This effect is especially pronounced during maximal voluntary ventilation, maximal exercise, and maximal inspiratory flow, volume maneuvers over the full vital capacity. During quiet breathing, the ventilatory muscles operate well below the limits of their neural activation and contractile performance. During intense activity, however, the diaphragmatic excursion approaches its limits over the entire vital capacity, and respiratory pressures may near their dynamic maximum. Because the system may operate near its available capacities during increased ventilatory demands, multiple strategies are available to compensate for deficits. For example, if the diaphragm is acutely shortened, it can still generate the required respiratory pressure if it receives more neural drive. Alternatively, other muscles can be recruited to take over for an impaired diaphragm. Thus, the whole system is highly versatile.

Attenuation of contraction-induced skeletal muscle injury by bromelain.

The proteolytic enzyme, bromelain, reportedly has therapeutic effects in the treatment of inflammation and soft tissue injuries. We tested the hypothesis that bromelain attenuates skeletal muscle injury induced by lengthening contractions. The left extensor digitorum longus (EDL) muscle of anesthetized hamsters was injured using a motorized foot pedal which repeatedly flexed/extended the foot through a range of 125 degrees. The EDL muscle was electrically stimulated for 400 ms during plantarflexion. Animals were assigned randomly to either a 0-d group (evaluated 3-h post-injury) or to untreated (UT) or bromelain-treated (T) groups, evaluated 3, 7, or 14 d post-injury. Following injury, T received 5 mg.kg-1 b.w. of bromelain, twice daily. Maximum isometric tetanic force (Po) was measured in vitro, then muscles were fixed, sectioned, and examined for evidence of fiber damage. The Po of injured muscles from T were higher than Po of injured muscles from UT at 3 (18.7 +/- 0.4 vs 16.5 +/- N.cm-2 and 14 d (20.5 +/- 0.6 vs 18.2 +/- 0.6 N.cm-2) (P less than 0.05), but not 7 d (19.5 +/-0.7 vs 17.7 +/- 0.8 N.cm-2). The Po of UT injured muscles were significantly lower than Po of contralateral control muscles at all time periods. Po of injured muscles from T were lower than Po from control muscles at 3 and 7 d (P less than 0.05), but not 14 d. The number of intact fibers of 3-d UT injured muscles was lower than the number of intact fibers in control muscles (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

An organizational model of sports medicine facilities in the United States.

Information on establishing the organizational structure of sports medicine clinics is useful to clinicians intending to start or expand a clinic. The purpose of this study was to identify an organizational model of existing sports medicine facilities in terms of: 1) administration and management, 2) staff qualifications and professional development, 3) location of facility, 4) range of services, 5) availability of services, 6) physician referral base, and 7) fee structure. A survey of 250 sports medicine clinics located in or near urban cities across the United States was conducted by mail. Results of this study indicate that the typical sports medicine facility is corporate-owned. A physical therapist and/or a physician establishes policy, and the physical therapist directs day-to-day operations. On average, the professional staff have four years of athletic team affiliation and seven years of clinical experience with athletes. The staff have attended less than an average of one continuing education course a year over the last five years. The typical facility is located within five miles of a major city, within 10 miles of its primary referral source and competition, and within 10 miles of its clients' homes. Most facilities employ combinations of full-time and part-time physicians, physical therapists, and athletic trainers. The typical sports medicine facility is open 12 hours each weekday. The physician referral base is composed primarily of orthopaedic and family practice physicians who refer an average of 14 new patients a week. J Orthop Sports Phys Ther 1992;15(2):80-86.

Acoustic myography as an indicator of force during sustained contractions of a small hand muscle.

To test the hypothesis that muscle sound amplitudes would remain constant during sustained submaximal isometric contractions, we recorded acoustic myograms from the abductor digiti minimi muscle in 12 subjects at 15, 25, 50, and 75% of a maximum voluntary contraction (MVC). Muscle sounds were detected with an omni-directional electret microphone encased in closed-cell foam and attached to the skin over the muscle. Acoustic amplitudes from the middle and end of the sustained contractions were compared with the amplitudes from the beginning of contractions to determine whether acoustic amplitudes varied in magnitude as force remained constant. Physiological tremor was eliminated from the acoustic signal by use of a Fourier truncation at 14 Hz. The amplitudes of the acoustic signal at a contraction intensity of 75% MVC remained constant, reflecting force production over time. At 50% MVC, the root-mean-square amplitude decreased from the beginning to the end of the contraction (P less than 0.05). Acoustic amplitudes increased over time at 15 and 25% MVC and were significantly higher at the end of the contractions than at the beginning (P less than 0.05). Alterations in the acoustic amplitude, which reflect changes in the lateral vibrations of the muscle, may be indicative of the different recruitment strategies used to maintain force during sustained isometric contractions.

Relative effects of bronchial drainage and exercise for in-hospital care of patients with cystic fibrosis.

Bronchial hygiene therapy is a standard part of the treatment of patients with cystic fibrosis (CF). Coughing alone promotes sputum expectoration and is probably the primary effective component of standard bronchial hygiene therapy. The purpose of this study was to determine whether substituting regular exercise, which also promotes coughing, for two of three daily bronchial hygiene treatments would affect the expected improvements in pulmonary function and exercise response in hospitalized patients with CF. Seventeen patients with CF hospitalized (means length of stay = 13.0 +/- 2.6 days) for an acute exacerbation of their pulmonary disease participated in the study. The patients were randomly assigned to either a group that participated in two cycle ergometer exercise sessions and one bronchial hygiene treatment session per day (EX Group [n = 9]) or a group that participated in three bronchial hygiene treatment sessions per day (PD Group [n = 8]). Pulmonary functions and responses to a progressive, incremental cycle ergometer exercise test were measured on admission and before discharge. Bronchial hygiene therapy consisted of postural drainage, in six positions, with chest percussion and vibration. Therapeutic exercise was of moderate intensity and was individually adjusted based on the patient's heart rate and arterial oxygen saturation response to the admission exercise test. Coughing was encouraged during and after all treatments. Pulmonary function and exercise response were significantly improved over the period of hospitalization in both groups; the improvements were the same in the two groups. These results indicate that, in some hospitalized patients with CF, exercise therapy may be substituted for at least part of the standard protocol of bronchial hygiene therapy.

Resting oxygen consumption and ventilation in cystic fibrosis.

Resting oxygen consumption (VO2) and minute ventilation (VE) were measured on nine control subjects and 13 patients with cystic fibrosis (CF). In patients with CF, VO2 was 20% higher (P less than 0.01) when expressed per m2 and 47% higher (P less than 0.001) when expressed per kg body weight, and VE was 58% higher when expressed per m2 and 94% higher when expressed per kg body weight (P less than 0.001) than in control subjects. Repeated measures of VO2 and VE were highly reproducible over 2 hours (within-subject coefficients of variation: in controls, VO2 = 5.5%, VE = 7.4%; in CF, VO2 = 3.1%, VE = 5.1%). Since the increases in VE were greater than those in VO2, the ventilatory equivalent (VE/VO2) was 32% higher in CF than in controls. We conclude that size-corrected total energy expenditures and VE at rest are higher in patients with CF than in control subjects. Ventilation appears mechanically inefficient but necessary to keep arterial PCO2 from rising and oxygen saturation from falling at rest. Our results are consistent with observations that these patients have an abnormally large physiological dead space (Featherby et al.: Ann Rev Respir Dis 1969; 102:737).

Breathing pattern during exercise in young black and Caucasian subjects.

Lung volumes in sex-, age-, height-, and weight-matched Black subjects are 10-15% lower than those in Caucasians. To determine whether this decreased lung volume affected the ventilatory adaptation to exercise, minute ventilation (VE), its components, frequency (f) and tidal volume (VT), and breathing pattern were observed during incremental cycle-ergometer exercise. Eighteen Caucasian (age 8-30 yr) and 14 Black (age 8-25 yr) subjects were studied. Vital capacity (VC) was lower (P less than 0.001) in the Black subjects [90.6 +/- 8.6 (SD) vs. 112.9 +/- 9.9% predicted], whereas functional residual capacity/total lung capacity was higher (P less than 0.05). VE, mixed expired O2 and CO2, VT, f, and inspiratory (TI), expiratory (TE), and total respiratory cycle (TT) duration were measured during the last 30 s of each 2-min load. Statistical comparisons with increasing power output were made at rest and from 0.6 to 2.4 W/kg in 0.3-W/kg increments. VE was higher in Blacks at all work loads and reached significance (P less than 0.05) at 0.6 and 1.5 W/kg. VE/VO2 was also higher throughout exercise, reaching significance (P less than 0.01) at 1.2, 1.5, and 1.8 W/kg. The Black subjects attained any given level of VE with a higher f (P less than 0.001) and lower VT. TI and TE were shortened proportionately so that TI/TT was not different. Differences in lung volume and the ventilatory response to exercise in these Black and Caucasian subjects suggest differences in the respiratory pressure-volume relationships or that the Black subjects may breathe higher on their pressure-volume curve.

Hospital therapy improves exercise tolerance and lung function in cystic fibrosis.

We studied the benefits of in-hospital therapy on exercise capacity and related these changes to improvements in lung function in 17 patients with cystic fibrosis (CF) of moderate to extreme severity, as defined by results of pulmonary function tests performed at admission and discharge. Tolerance and adaptations to exercise were assessed from measures of peak work capacity (PWC), peak heart rate (PHR), and peak ventilation (PVE) obtained during an incremental exercise test. Treatment lasted from nine to 18 days. All measures of lung function improved; there also were significant increases in PWC, PHR, PVE, and PHR/PWC. Exercise-induced arterial desaturation was less at discharge than at admission. The PWC of the most severely affected patients remained abnormally low, and their adaptations to exercise were abnormal at discharge. We concluded that intensive in-hospital therapy will significantly improve exercise tolerance and lung function in patients with CF with moderate to severe pulmonary dysfunction.

Responses to continuous and intermittent exercise in healthy and insulin-dependent diabetic children.

The hormonal (growth hormone, glucagon, cortisol) and metabolic (glucose, ketone bodies) responses to 30 min of continuous vs 30 min of intermittent exercise were evaluated in five male children with insulin-dependent diabetes mellitus (IDDM) and five healthy male children. Each subject performed both types of exercise. In the healthy children, growth hormone levels rose, and glucose, glucagon, cortisol, and ketone bodies remained unchanged during both continuous and intermittent exercise. In the IDDM subjects, the mean reductions in glucose concentration were 99 mg% and 84 mg% during continuous and intermittent exercise, respectively. The levels of cortisol and ketone bodies in the IDDM subjects were significantly (P less than 0.05) elevated above the values obtained in the healthy subjects irrespective of the type of exercise. The mean concentrations of growth hormone, glucagon, cortisol, and ketone bodies were not significantly different between continuous and intermittent exercise. The study concludes that in healthy children the hormonal and metabolic responses to a continuous and an intermittent exercise protocol are similar. In the IDDM subjects, however, both forms of physical activity are associated with a decline in plasma glucose and no significant differences in hormonal and metabolic responses.

Exercise and Cystic Fibrosis.

In brief: Cystic fibrosis (CF) patients are likely to be less fit than their normal peers, but most can exercise safely. Recent studies show that exercise programs can increase fitness and exercise tolerance. They can also increase the endurance of the respiratory muscles, although pulmonary function will not change. Exercise may be as beneficial as traditional chest physical therapy and postural drainage for getting mucus up from the lungs, but the authors recommend that patients continue therapy until this is confirmed. Because CF patients lose significantly more salt in their sweat than normal people, the authors recommend ample water intake and free access to the salt shaker.

Exercise tolerance and cardiorespiratory adjustments at peak work capacity in cystic fibrosis.

Exercise tolerance and cardiorespiratory adjustments at peak work capacity (PWC) were determined in 20 patients with cystic fibrosis (CF) during progressive cycle ergometry. The results were related to resting lung function tests, expressed by a pulmonary function score (PFS) that ranged from 0 (no pulmonary dysfunction) to 18 (extreme dysfunction). Patients with CF with no (PFS less than 3), mild (PFS 3-7), or moderate (PFS 8-12) pulmonary dysfunction exercised as well as normal subjects. When the PFS exceeded 12, PWC was reduced on the average by 51%, peak heart rate (PHR) was reduced by 15%, and peak ventilation (PVE) was reduced by 39%. Severely affected patients developed arterial desaturation at PWC (-7.3%), CO2 retention (end-tidal PCO2 + 5 mmHg), and an increase in the PHR/PWC ratio. In most patients with CF the PVE/PWC ratio was elevated, suggestion wasted VE and a probable increase in dead space ventilation. The results indicate that whenever pulmonary disease in CF is advanced, there are decreases in exercise tolerance and cardiorespiratory reserves, exercise-induced ventilation-perfusion abnormalities, arterial desaturation, and alveolar hypoventilation. In view of the abnormal physiological adaptations to exercise in patients with CF with advanced lung disease (PFS greater than 12), they should engage in exercise training programs and strenuous physical activity with caution and only after their cardiorespiratory reserves and adjustments to exercise have been objectively evaluated.

Cardiorespiratory adaptations to exercise in cystic fibrosis.

We compared the cardiorespiratory adaptations to exercise of 21 patients with cystic fibrosis (CF) with those of 17 age-, height-, and weight-matched subjects without lung disease. To assess differences in adaptations to exercise in patients with varying severities of pulmonary disease, we grouped them on the basis of their lung function tests results. Exercise consisted of a progressive, incremental cycle ergometer work test. Work load increased every 2 min until the subject could not continue. During exercise, heart rate, and end-tidal and mixed expired O2 and CO2 tensions, minute ventilation (VE), arterial oxygen saturation, and blood pressure were monitored. The patients breathed significantly larger volumes than normal subjects at work loads greater than 0.8 W/kg. Patients with mild, moderate, or seven disease ventilated more per unit of oxygen consumption than did patients with normal pulmonary functions or control subjects. Despite this high total VE, alveolar hypoventilation was observed in the severe groups, as evidenced by elevated end-tidal PCO2, and contributed to aterial desaturation. Resting heart rate was higher in the severe group. The rate of changes in heart rate with increasing work load was the same in all groups. We conclude that the increased VE during exercise was an attempt to maintain alveolar ventilation in the face of increased dead space. The elevated VE was adequate to preserve normal gas exchange in all patients except those with severe lung disease, where CO2 retention and arterial desaturation were observed.

Characteristics of adjustment of lung diffusing capacity to work.

The response of lung diffusing capacity for CO (DLCO) to the onset of exercise or a change in work load was studied in four healthy males. Single-breath DLCO was measured during the transients 1) from rest to 40% of maximum O2 uptake (VO2 max); 2) from rest to 80% VO2 max; and 3) from steady-state exercise at 40 to 80% VO2 max. Protocols 1 and 2 consisted of 8.5 min of exercise while 3 consisted of 10.5 min of exercise at 40% VO2 max followed by 8.5 min at 80% VO2 max. DLCO was measured at 10, 20, 30, 60, 90, 240, and 510 s after onset of change in load. Half times of the responses (1, 39: 2, 43; 3, 56 s) were not statistically different. The percentage of the total response completed at each time interval indicated that 3 was significantly (P less than 0.05) slower than 1 and 2 at 10 and 20 s. The rapid response of DLCO at the onset of exercise may reflect a neural component in pulmonary vascular control during exercise.