0895-4356/90$3.00+ 0.00 Copyright 0 1990Pergamon Press plc
J ClinEpidemic4 Vol. 43, No. 6, pp. 569-577,1990 Printed in Great Britain. All rights reserved
LEISURE TIME PHYSICAL ACTIVITY HOSPITAL-BASED POPULATION
IN A
P. BOFFETTA,“’J. BARONE’ and E. L. WYNDER”* ‘Mahoney Institute for Health Maintenance, American Health Foundation, 320 East 43rd Street, New York, NY 10017 and 2Cattedra di Epidemiologia dei Tumori, Universita di Torino, Italy (Received in revised form 22 September 1989)
Abstract-The epidemiology of self-reported leisure time physical activity (LTPA) has been studied among 3381 men and 1664 women enrolled in a hospital-based case-control study. 51% of men and 36% of women reported LTPAs during a lifetime, and 23% of men and 22% of women reported LTPAs after 44 years of age. Brisk walking, swimming, cycling and tennis accounted for the majority of LTPAs after 44 years of age. Only 13% of men and 9% of women reported LTPA practice for more than 20 years and more than 3 hours/week; and 0.6% of men and 0.1% of women reported running or jogging for the same duration. LTPA practice was related to age, education, smoking status, and body mass index. Specifically, ex-smokers reported more frequently LTPA practice than current smokers. Despite the effort to identify aerobic exercise, results from the present analysis suggest that LTPA practice might be over-reported, as a result of a “wish” bias. Problems arising from the use of data on
self-reported LTPA practice are discussed in detail. Leisure time activity
Physical activity
INTRODUCTION
The possible role of physical activity in the etiology of chronic diseases such as cardiovascular disease, hypertension, osteoporosis, and breast and colon cancer has been widely considered [l-5]. Leisure time physical activity (LTPA) is a complex behavior, measured by a variety of methods [6], and it is likely to be influenced by biases in reporting [7]. Whether individuals report exercise or not is affected by a host of variables including age, education, sex, body weight and smoking [8]. Some of these behaviors are also influenced by exercise: therefore, a complex confounding relationship arises between LTPAs and chronic disease risk factors. In order to determine what affects participation in regular LTPA at different ages throughout life and what health behaviors are *Author for correspondence
Aerobic exercise
Report bias
associated with regular physical activity, it is necessary to assess frequency, duration, intensity, type of activity and demographic/ behavioral variables. The purpose of the present report is to describe the epidemiology of reported LTPAs in a large hospital population, as a basis for further analyses looking at the association between LTPA practice and specific cancer risks. MATERIAL AND METHODS
This analysis is based on data collected in an on-going hospital-based case-control study on tobacco-related diseases. Subjects were enrolled in 8 different hospitals in Philadelphia, Detroit, Chicago, New York City and Long Island, N.Y. For the purpose of this descriptive analysis, cases and controls were combined together. In 1985, a section on LTPAs was added to the questionnaire, which also included information 569
570
P.
kXFETTA
on demographic variables, occupational history, smoking, drinking, and dietary habits, medical history and vitamin intake. The term physical activity is not a uniformly defined behavior. In the present analysis, subjects were asked about regular, strenuous activity, specifically defined as “exercise carried out for at least 20 minutes, 3 times a week, for 1 year or more, during which you perspire and become short of breath”, which they had engaged in since the age of 15. This definition was aimed to identify subjects performing aerobic exercise and corresponds to the 1990 goal established by the Department of Health and Human Services for the U.S. adult population [9]. Twenty-six activities were coded separately: basketball, tennis, paddleball or racquetball, squash, football, soccer, volleyball, hunting, field hockey, ice hockey, karate, judo, boxing, wrestling, swimming, running, brisk walking, cycling, aerobic dancing, cross-country skiing, jogging, rope skipping, rowing, gymnastic, downhill skiing and mountain climbing. Professional physical activity as an athlete or dancer was also recorded. Up to 2 LTPAs were recorded for 3 different age periods: 15-21, 22-24, and 45 + years. Therefore, each subject might report a maximum of 6 LTPAs. In the analysis, each reported LTPA was accounted for separately: therefore, the total proportion of subjects reporting LTPAs is smaller than the sum of the proportions for each activity, the difference corresponding to the proportion of subjects reporting more than one LTPA. The number of hours per week, months per year, and total years engaged in the activity were also recorded. The average weekly caloric expenditure (WCE) from reported LTPAs was calculated according to the formula WCE
=
i
xijhXmi112)Yi
iYi
’
where i ranges from 1 to 6 (the maximum number of reported LTPAs was 6), hi = hr/week, mi = months/year, yi = number of years, and xij is a hourly caloric expenditure estimate for LTPA =j. These estimates ranged from 300 kcal/hr for aerobic dancing and gymnastic, to 1200 kcal/hr for running. The number of cigarettes smoked per day was derived by multiplying the average quantity of each smoked brand of cigarette by the amount
et al.
of years the brand was smoked, summing these products and dividing the sum by the total number of years of smoking; Quetelet Index (QI) was calculated according to the formula: QI = weight [kg]/height [ml*. The direct method of standardization [lo] was used for rate adjustment, using males and females as standard populations; t-test for the difference between two means, chi-square test for the difference among proportions [lo], and chi-square test for linear association among proportions [l l] were used. RESULTS
This analysis is based on 3381 men and 1664 women enrolled between January 1985 and October 1987. 71% of subjects (68.6% of men and 75.7% of women) had a diagnosis of cancer, of whom 22.5% were cancers of the digestive system, 20.6% cancers of the respiratory tract, and 14.7% cancers of the genito-urinary system. Among non-cancer cases, 7.0% of subjects had a circulatory disease, 4.1% a digestive disease, and 2.8% of subjects suffered from injuries. Fifty-one percent of men and 36% of women reported some LTPA (Tables 1 and 2); men practise LTPAs more frequently during their youth, while women are more likely to participate before 22 or after 44 years of age. The most frequently reported sports among men include basketball and football, but both are rarely practised after 22 years of age; also swimming, running, brisk walking, tennis, and cycling. Among women, brisk walking, swimming, cycling, aerobic dancing and tennis were the most frequently reported activities. In both sexes, group LTPAs are more frequently practised early in life, while individual activities, such as brisk walking, are more frequently reported after 44 years of age. 11 men (0.3%) and 4 women (0.2%) reported professional physical activity. Only 13% of men and 9% of women reported more than 20 years of total duration and more than 3 hours/week. Brisk walking, tennis, and swimming are the LTPAs reported for longer periods of time, while well defined aerobic activities, such as running and jogging, are rarely practised for more than 20 years and more than 3 hours/week: only 9 runners (0.3%) and 9 joggers (0.3%) among men, and 1 jogger (0.1 O/o)among women fall into this category. The reduction in the proportion of subjects reporting LTPAs, when only adequate duration of practice is taken into
571
Epidemiology of Leisure Time Physical Activity Table 1. LTPAs among men,* by age period Subjects reporting LTPAs while aged >20yr > 3 hr/week
LTPAt
Any period (NJ (%I
15-21 (%I
2244 (%I
45+ (%)
Basketball Football Swimming Walking brisk Running Tennis Bicycling Jogging Gymnastics Soccer Paddleball/racquetball Aerobic dancing Boxing
480 472 328 278 242 208 175 141 138 97 88 82 55
14.2 14.0 9.7 8.2 7.2 6.2 5.2 4.2 4.1 2.9 2.4 2.4 1.6
13.7 13.7 5.4 1.0 5.5 2.3 1.7 0.9
0.5 0.0
:4 1.3 0.9 1.4
3.3 1.4 4.8 3.5 1.8 4.2 1.6 2.5 1.8 0.9 1.3 1.2 0.5
4.3 7.5 1.2 3.3 3.5 1.9 1.9 0.1 0.8 1.1 0.0
0.9 0.1 1.9 2.5 0.3 1.8 0.6 0.3 0.6 0.2 0.6 0.2 0.1
1724
51.0
38.5
24.8
22.8
13.0
Any LTPA
*N = 3381. TOnly LTPAs reported by 50 or more subjects are listed separately. Table 2. LTPAs among women,* by age period Subjects reporting LTPAs while aged LTPAt
Any period (NJ (%I
15-21 (%)
2244 (“/J
45+ (%I
>20yr > 3 hr/week
Walking brisk Swimming Aerobic dancing Bicycling Tennis Basketball Gymnastics Volleyball Running Field hockey Jogging
194 168 107 107 92 69 58 29 24 16 15
11.7 10.1 6.4 6.4 5.5 4.1 3.5 1.7 1.4 1.0 0.9
2.8 6.9 1.6 3.1 2.8 4.1 1.4 1.6 0.8 0.9 0.0
4.5 4.7 3.4 2.3 3.2 0.2 1.6 0.2 0.4 0.1 0.5
10.0 5.1 3.2 2.9 2.2 0.0 1.6 0.0 0.3 0.0 0.5
3.0 2.2 0.5 0.6 1.3 0.0 0.3 0.0 0.0 0.0 0.1
Any LTPA
591
35.5
20.0
17.8
21.6
9.0
*N = 1664. tOnly LTPAs reported by 15 or more subjects are listed separately.
account, is shown in detail in Fig. 1. This effect is even stronger among subjects reporting well defined aerobic activities, namely runners and joggers (Fig. 1). The average WCE was 2854 kcal for men and 1660 kcal for women (Table 3). A trend of decreasing WCE with age is clear in both sexes, but it is stronger among men, corresponding to the shift from highly caloric LTPAs, such as running or football, to less energetic LTPAs, such as swimming or brisk walking. If subjects not reporting any LTPA are included, the average WCEs are 1456 kcal for men and 589 kcal for women, respectively. About 30% of men and 16% of women had a caloric expenditure over 2000 kcal/week, the level associated with a decrease in coronary disease risk [2].
Table 4 shows the age and education-adjusted proportion of men reporting LTPA practice by age, education, smoking habit, and body mass index. The proportion of men reporting LTPAs declines with increasing age, and strongly increases with increasing level of education Table 3. WCE by sex and age period WCE’ Overall
Men 2854 f 3242
Women 1660 k 2189
While aged 15-21 2244 45f
3426 f 3810 2406 + 2875 2027+2190
1761 + 2665 1577 + 1989 1492 f 1201
*Mean + SD. excluded.
Subjects
not
reporting
any
LTPA
are
P. BOF~~A et al.
Practice 1449(46.5%0) 279(9.3%)..
f-20 Yrs 1054 ( 35.3%). 261(6.70/o) **
l-3H/WfI) 54 (l.B%o)* 14 (0.596)** (I
1 Hours /
4+H/W iOOOU3.5%)* 247(9.3%).’
*
2ltYrs 395(13.2%)* 16 (0.6%)
I-3n/w 6 (0.2%). 0 1o.oO/o)**
504 (33.2%).
*
??
4t H/W 369(13.0%) 16(0.6%)
??
*
??
week
All LTPA’s ??* Running and jogging ??
Fig. 1. Subjects 45 + years old reporting practice of LTPA and of running and jogging by sex and duration.
Table 4. LTPAs and selected characteristics; men Any LTPA reported Number of subjects
No LTPA reported W1
Any period Wl
while aged 15-21 W)
2244 W1
45+ (“/I
Running and jogging (“/I
115 603 933 1140 589
40.1 41.3 50.8 52.4 48.9 *
59.9 52.1 49.2 47.6 51.1 *
48.3 42.4 36.7 34.7 30.6 **
38.8 26.9 21.6 19.5 30.2 *
20.8 24.3 21.1 32.3 **
21.3 11.8 9.5 8.3 6.3 **
393 723 1289 833 142
77.1 61.1 56.5 41.0 28.8 **
22.9 32.3 43.5 59.0 71.2 **
16.3 23.0 32.7 45.3 55.0 **
8.2 14.2 17.7 30.1 38.6 **
8.8 10.4 16.2 24.1 32.2 **
3.9 4.2 1.4 12.8 21.1 **
575 494 700 686 706 193
45.7 48.6 55.0 45.3 50.1 47.0 *
54.3 51.4 45.0 54.7 49.9 53.0 *
39.4 42.5 37.3 38.3 36.2 36.9
27.8 22.7 21.6 25.9 24.9 29.6
21.9 16.4 11.5 27.4 21.6 21.5 *
12.7 10.6 8.9 13.9 11.9 9.5
656 654 730 643 691
51.6 45.3 48.9 48.0 51.5
48.4 54.7 51.1 52.0 48.5
35.9 39.9 38.8 41.2 36.4
24.8 28.6 24.5 25.0 21.5
21.2 21.6 20.7 21.5 16.3 **
11.2 13.5 11.5 10.2 9.7
Agea
18-44 45-54 5564 65-14 15+ Test for trendf Education (yr)b O-8 9-11 12 13-16 17+ Test for trend’ Smoking habits’
Nonsmoker CCd 1-20/day CCd 21 +/day EC’ I-20/day EC’ 21 +/day Cigar/pipe only Test for differencea Quetelet Index’
10.1-23.0 23.1-24.9 25.0-26.6 26.7-29.1 29.2 + Test for trend’
“Adjusted for education. bAdjusted for age. cAdjusted for age and education. dCurrent cigarette smoker. ‘Ex-cigarette smoker. ‘Chi-square test for trend: *p < 0.05 for difference among proportions, **p -z 0.05 for trend. rChi-square test for difference among proportions: *p < 0.05.
no significant trend;
Epidemiology
of Leisure
(23, 32, 44, 59 and 71% among men with O-8, 9-11, 12, 13-16, and 17+ years of education, respectively). Current smokers report less frequent (48%) LTPA practice than non-smokers (54%), the difference being larger among those aged 45 and over. Ex-smokers, on the other hand, report little LTPA practice until 44 years of age, when they were presumably still smokers, and show a later increase in reported LTPAs. Subjects in the highest body mass quintile (QI > 29.1) report LTPAs less frequently (48%) than other subjects, but no clear trend is suggested among the remaining quintiles, whose proportions range between 49 and 55%. Table 4 also shows the relationship between personal characteristics and running and jogging. Their practice decreases with age, increases with education, and Table
5. LTPAs
Time Physical
513
Activity
is associated with never or ex-smoker status and low body mass. Among women (Table 5), there is a decline in the proportion of subjects reporting LTPAs with increasing age, and an increase with increasing level of education. The findings on the association between smoking habit and reported LTPAs among women partially parallel the results among men: ex-smokers tend to increase LTPAs over age, presumably after quitting smoking, while current light (l-20 cigarettes/day) smokers, but not current smokers with heavier consumption, report LTPAs in a similar proportion to nonsmokers. No consistent relationship with QI is suggested among women. Very few women reported running or jogging, but results suggest that runners and joggers are more likely to be young, highly educated, never or ex-smokers, and thin.
and selected characteristics;
women
Any LTPA reported while aged
Running and
Number of subjects
No LTPA reported W)
Any period (Xl
15-21 (%l
2244 (X1
45+ (%l
Agea 1844 45-54 5564 65-14 15f Test for trend’
146 325 659 453 80
50.0 58.8 64.9 70.1 75.3
50.0 41.2 35.1 29.9 24.1 **
28.8 20.6 19.6 18.1 19.2 **
40.4 22.0 14.8 14.0 9.8 **
21.5 22.4 23.1 9.6 **
9.6 3.0 1.6 1.0 1.6 **
Education (~r)~ O-8 9-11 12 13-16 17+ Test for trend’
29 302 691 496 145
89.7 11.1 69.1 47.1 46.1
10.3 22.3 30.9 52.3 53.9 **
6.9 10.8 16.5 28.2 29.6 **
3.4 8.3 15.5 24.2 25.3 **
3.4 14.4 16.6 21.5 26.5 **
0.0 1.1 1.2 3.3 6.1 **
Smoking habit’ Nonsmoker CCd l-20/day CCd 2 1+/day EC’ I -2O/day EC’ 21 f/day Test for differences
594 351 262 300 142
62.8 64.5 75.9 59.8 61.8
37.2 35.5 24.1 40.2 38.2 *
18.0 24.0 14.9 21.4 21.8 *
18.0 17.7 12.0 23.2 11.2 *
21.8 16.1 10.4 25.3 26.8 *
3.2 1.8 0.0 3.9 1.9
Quetelet Index’ 10.1-21.2 21.3-23.2 23.3-25.6 ?5.7-29.0 29.1+ Test for trend’
303 348 314 341 344
63.8 61.7 62.1 65.4 67.5
36.2 38.3 31.3 34.6 32.5
20.8 19.4 23.2 20.9 16.8
20.1 20.7 16.6 16.7 14.8 **
19.6 22.9 19.6 18.8 19.1
3.3 2.1 3.6 1.5 1.6
“Adjusted for education. hAdjusted for age. ‘Adjusted for age and education. dCurrent cigarette smoker. eEx-cigarette smoker. ‘Chi-square test for trend: *p < 0.05 for difference **p < 0.05 for trend. YChi-square test for difference among proportions:
among
proportions,
*p < 0.05.
jogging W)
-
no significant
trend;
P. bFF!ZlTAet ai.
514
Reports of LTPA do not show any consistent association with marital status, ethnic group or religion in either sex (data not shown). The results of the present analysis consistently suggest that educational level is the most important determinant of reported LTPA practice, as well as of true aerobic exercise. A more detailed analysis on the association between education and most frequently reported LTPAs indicates that basketball, football, swimming, brisk walking, running, tennis, jogging, gymnastics, aerobic dancing and paddleball/racquetball practice among men show a significant positive trend with education; one (boxing) shows a borderline significant negative trend, and two (cycling and soccer) show no association. Results for women are remarkably similar: cycling and aerobic dancing show no association with education, while the remaining LTPAs show or suggest a positive trend. DISCUSSION
The hospital population on which the study is based is highly educated. Even if this aspect could reduce the generalizability of our results, controlling for education via direct standardization ensures a correct interpretation of internal comparisons. Participation in physical activity is not a uniformly defined concept: the definition of “active” varies from mere participation in one or more sports to rigid criteria of number of calories expended or hours spent exercising per week. The present analysis attempted to identify well defined aerobic activity on the basis of self-reported information on LTPAs carried out for at least 20 minutes, 3 times a week, for at least 1 year, causing dyspnea and sweating. It was not possible to estimate the actual caloric expenditures, nor to specifically certify the individuals’ practices into aerobic and non-aerobic exercise. No information was available on baseball, as well as on sports with low caloric expenditure, such as golf and fishing and on LTPAs related to hobbies. A major problem in the epidemiology of weak associations, such as that suggested between physical activity and cancer risk [4], is that of bias, in this case of report or “wish” bias. It is possible that physical exercise during leisure time is reported in excess of its actual occurrence, even if the questionnaire was specifically designed to identify aerobic activity. It seems unlikely that over 7% of men and 10% of
women over 45 in this population actually do walk briskly and long enough to produce aerobic benefits, i.e. not less than 4 miles/hr. Similarly, it is unknown how many of those who reported exercise as swimmers, tennis players, or cyclists performed these activities vigorously and continuously. Furthermore, only about 10% of men and women (Tables 1 and 2) reported a practice of these LTPAs for more than 20 years and more than 3 hours/week, which corresponds to the amount recommended by the American College of Sports Medicine [ 121. Running and jogging, which are more likely to be well defined aerobic activities, are reported by only about 3% of men and less than 1% of women over 44 years of age, and very few subjects (0.6% of men, 0.1% of women) practised them for more than 20 years and more than 3 hours/week (Fig. 1). The validity (agreement between reported LTPAs and a more objective measure of exercise or physical fitness) of self-reported LTPA practice was recently evaluated by several investigators (Table 6): it seems that a generic report of physical activity does not consistently represent a good indicator of aerobic activity or physical fitness, whereas detailed indices, which carefully quantify caloric expenditure in the practice of LTPAs, are more valid measures of actual physical activity. The present study has an intermediate level of detail in the assessment of LTPA practice: the possibility of report bias cannot be ruled out. A “wish” or report bias could affect the estimated prevalence of subjects performing LTPAs, and, if individuals with a specific disease reported LTPA differently than controls, could produce differential misclassification in case-control comparisons. In the present analysis, 51% of men and 36% of women reported some LTPA during their lifetime, and 23% of men and 22% of women reported some LTPA after the age of 44. A comparison of these results with other studies is difficult, because of differences in the definition and the measure of LTPA, and in the likelihood of a report bias. Stephens et al. [20] reviewed eight U.S. and Canadian surveys, and reported that the proportion of active subjects ranged between 17 and 26% for men and 13 and 15% for women if rigorous definitions of LTPA were applied, but it might be as high as 70-80% if less rigorous definitions were used. Results of recently published studies confirm the importance of report bias: in a U.S. survey by Brooks 181, 29% of men and 33% of women reported no
*SAQ: Self-administered
questionnaire:
375 men, mean age 47, who underwent a clinical examination at a preventive medicine clinic, Dallas
in past 4
and F
IAQ: Interviewer-administered
questionnaire;
SAQ (past 3 months, F and D of strenuous racquet and non-racquet sports, cycling, swimming; F, D and S of walking, running, or jogging; F of El sweating) and recall SAQ (7 days, D of vigorous and moderate LTPAs)
LTPAs
IAQ (F of vigorous months, 6 levels)
yr,
61 volunteers, 48% women, Montreal area
1966
Overall index (combination of climbing, walking, and LTPAs), of EI sweating, from SAQ
of level of fitness
36 men and 32 women, volunteers, 20-70 yr, Pawtucket, Rhode Island
appraisal
Personal
204 employees, 70% women, volunteers, Houston
EI
SAQ (I day, all activities) and IAQ (7 days, D of sleep, light, moderate, hard, very hard activity)
18-64 yr,
studies
LTPA*
12 males, 3469 yr, volunteers, 8 of whom post-myocardial infarction patients, Stanford
of self-reported
SAQ (D and F past 12 months, sweating and dyspnea)
Measure
from selected
I75 males, 36-59 yr, population sample, Minneapolis
Population
Table 6. Results
exercise test
exercise test
EI: Exercise-induced;
Treadmill
D: Duration;
practice Results
fitness in
with all validation
F: Frequency;
S: Speed.
Positive association with sweating, walking, running, or jogging, vigorous non-racquet sports. No association with racquet sports, cycling
Positive association measures
Agreement between the 2 measures, sweating index correlates better with oxygen uptake than the more complex index
Self report overestimates both sexes
Agreement of overall energy expenditure among validation and 2 measures, over report of duration of hard and very hard activities in SAQ (no data on IAQ)
Positive association with light, heavy, and total LTPA, no association with moderate LTPA or sweating/dyspnea
LTPAs
on a
Maximum oxygen intake, body fat, muscular endurance (2 1;vels)
uptake,
exercise test
Maximum oxygen cycle ergometer
Treadmill
Heart rate and body movement detector
Treadmill
of self-reported
Validation
on the validity
I191
1181
[I71
1161
iI51
[13, 141
Reference
576
P. BOF~TTAet al.
LTPA, and 13% reported heavy intensity LTPAs; in a Canadian population-based survey 54% of men and 62% of women were sedentary, and 28 and 21% respectively were adequately active [21]; a Louis Harris survey recently showed that up to 79% of men and women reported regular exercise, either at work or elsewhere; 29% of men and 37% of women stated walking several days per week, and 44% of men and 28% of women reported strenuous exercise [22]. Stephens et al. [20] also listed specific LTPAs from 7 out of 8 surveys they reviewed: walking, swimming, and cycling were among the most frequently reported LTPAs in the studies with a less rigorous definition of exercise: these activities are therefore more likely to contribute to the overall report bias. The rank of jogging, on the other hand, was higher in one study with more rigorous definition. The comparison of these results with the present analysis confirms the possibility of a report bias in our study, and supports the choice to specifically analyze runners and joggers as characterizing aerobic activity. The average WCE in LTPAs was 1450 kcal/week for men and 590 kcal/week for women. 25% of men and 8% of women had a caloric expenditure higher than 2000 kcal/week. These data are similar to the results of a population-based study in MinnesotaJ231, in which 34% of men and 17% of women reported more than 2000 kcal/week, and the average expenditures were 1350 and 780 kcal/week, respectively. The expected decline in physical activity with age has been shown in other surveys, with the drop especially noted between the teen years and early adulthood [20,21,23]. An increase in LTPA practice among young cohorts, independent from the effect of aging, has been suggested [24]: in the present analysis, such a trend is clearly present among women, but not among men (Tables 4 and 5). The relationship between sport practice and income and education has been noted in other surveys [7,20,23,25]: a higher frequency of LTPA practice is to be expected among wealthier subgroups of the population. The relation between smoking status and LTPAs is a negative association in the present and some other studies [2,.26]. Some investigations have shown that non-smoking men aged 25-44 have a greater participation in high intensity exercise than smokers [23], while other
studies have shown no association [26]. The fact that reported LTPA is higher among exsmokers than among current smokers, perhaps in an attempt not to gain weight, represents an original finding of the study. The trend towards less physical activity in subjects with greater body mass shown by the present analysis has been previously reported [2,23,26]: one study, on the other hand, found an inverse relationship [25]. It must be noted that in the present study this trend does not include very thin subjects. The purpose of this study was to determine baseline data on reported LTPA practices. Further analyses will address the role of LTPA practice in the etiology of specific cancers. A further important result of this analysis was the suggested need of a more detailed questionnaire to identify actual aerobic activity. Specific questions on distance, time and speed should be asked with regard to brisk walking, swimming, tennis and cycling, which are the most frequently reported LTPAs after 44 years of age. Results of the present descriptive analysis confirmed the relationship between LTPA practice and age, education level and obesity that have been found in other surveys. An important original finding regarded ex-smokers: their LTPA practice was more similar to never smokers’ than to current smokers’, suggesting that quitting of tobacco smoking may be related to other health promoting habits. Acknowledgements-This research was supported by National Cancer Institute Program Project Grant CA32617 and Center Grant CA17613, and American Cancer Society Special Institutional Grant SIG-8. We would like to acknowledge the valuable contributions of the following cooperating institutions and individuals: Memorial Hospital (New York), Dr David Schottenfeld; Long Island Jewish Hillside Medical Center (New York), Dr Ranti R. Rai; Queens General Hospital (New York), Dr Hans Grunwald: Hines Veterans Hosnital (Chicano. Ill.), Dr John Sharp; Loyola University Hosiital (Chicaio; Ill.), Dr Edward k. Garrity; Hospital of- the ‘Unive&ity of Pennsylvania (Philadelnhia. Penn.). Dr Paul Stollev; Thomas Jefferson University’Hospital(Philadelphia, Penn:), Dr James E. Colberg; Henry Ford Hospital (Detroit, Mich.), Dr Robert M. O’Bryan. We would also like to thank Marion Moore for review of hospital records, Pao Huan Chung and Chuen Lan Liang for programming assistance, Verna Harrison and Laurie Marmelstein for preparation of the manuscript.
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specific benefits and risks of physical activity and exercise. Public Health Rep 1985; 100: 180-188. 2. Paffenbarger RS, Wing AL, Hyde RT. Physical activity as an index of heart attack risk in college alumni. Am J Epidemiol 1978; 108: 161-175.
Epidemiology of Leisure Time Physical Activity 3. Paffenbarger RS, Hyde RT, Wing AL. Physical activity and incidence of cancer in diverse populations: a preliminary report. Am J Clin Nutr 1987; 45: 312-317. 4. Frish RE, Wyshak G, Albright NL et al. Lower prevalence of breast cancer and cancers of the reproductive system among former college athletes compared to non-athletes.-Br J Cancer 1985; 52: 885-891. 5. Vena JE. Graham S. Zieleznv M et al. Occupational exercise and risk of cancer. k J Clin Nutr 1987; 45: 318-327. 6. Caspersen CJ, Powell KE, Christenson GM. Physical activity, exercise, and physical fitness: definitions and distinctions for health-related research. Public Health Rep 1985; 100: 126131. I. Dishman RK, Sallis JF, Orenstein DR. The determinants of physical activity and exercise. Public Health Rep 1985; 100: 158-171. 8. Brooks CM. Leisure time physical activity assessment of American adults through an analysis of time diaries collected in 1981. Am J Public Health 1987; 77: 455-460. 9. U.S. Department of Health and Human Services. Surgeon General’s Report: Promoting Health-Preventing Disease, 1990 Objectives for the Nation. Washington, D.C.: Public Health Service, National Institutes of Health; 1980. IO. Fleiss JL. Statistical Methods for Rates and Proportions. New York: Wiley; 1981. II. Armitage P. Tests for linear trends in proportions and frequencies. Biometrics 1955; 11: 375-385. 12. American College of Sports Medicine. Guidelines for Exercise Testing and Prescription. Philadelphia: Lea & Febiger; 1986. 13. Taylor HL, Jacobs DR, Schucker B et al. A questionnaire for the assessment of leisure time physical activities. J Chron Dii 1978; 31: 741-755. 14. Leon AS, Jacobs DR, DeBacker G et al. Relationship of physical characteristics and life habits to treadmill exercise capacity. Am J Epidemiol 1981; 113: 653660. 15. Taylor CB, Coffey T, Berra K et al. Seven-day activity
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17. 18. 19.
20. 21.
22.
23.
24.
25. 26.
571
and self-report compared to a direct measure of physical activity. Am J Epidemiol 1984; 120: 818-824. Optenberg SA, Lairson DR, Slater CH et al. Agreement of self-reported and physiologically estimated fitness status in a symptom-free population. Prev Med 1984; 13: 349-354. Siconolfi SF, Lasater TM, Snow RCK et al. Selfreported physical activity compared with maximal oxygen uptake. Am J Epidemiol 1985; 122: 101-105. Godin G, Jobin J, Bouillon J. Assessment of leisure time exercise behavior by self-report: a concurrent validity study. Can J Public Health 1986; 77: 359-362. Kohl HW, Blair SN, Paffenbarger RS et al. A mail survey of physical activity habits as related to measured physical fitness. Am J Epidemiol 1988; 127: 1228-1239. Stephens T, Jacobs DR, White CC. A descriptive epidemiology of leisure-time physical activity. Public Health Reii985; 100: 147-158.. Stephens T, Craig CL, Ferris BF. Adult physical activity in Canada: findings from the Canada Fitness Survey I. Can J Public Health 1986; 77: 285-290. Genevie L, Taylor H, Kagay M. Prevention in America V: Steos Peoole Take-or Fail to Take-for Better Health, 1987. New York: Louis Harris; 1987. Folsom AR, Caspersen CJ, Taylor HL et al. Leisure time physical activity and its relationship to coronary risk factors in a population-based sample. The Minnesota Heart Survey. Am J Epidemiol 1985; 121: 570-579. Powell KE, Paffenbarger RS. Workshop on epidemiologic and public health aspects of physical activity and exercise: a summary. Public Health Rep 1985; 100: 118-126. Sallis JF, Haskell WL, Wood PD et al. Physical activity assessment methodology in the Five-city project. Am J Epidemiol 1985; 121: 91-106. Blair SN, Jacobs DR, Powell KE. Relationships between exercise or physical activity and other health behaviors. Public Health Rep 1985; 100: 172-180.
J ClinEpidemic4 Vol. 43, No. 6, pp. 569-577,1990 Printed in Great Britain. All rights reserved
LEISURE TIME PHYSICAL ACTIVITY HOSPITAL-BASED POPULATION
IN A
P. BOFFETTA,“’J. BARONE’ and E. L. WYNDER”* ‘Mahoney Institute for Health Maintenance, American Health Foundation, 320 East 43rd Street, New York, NY 10017 and 2Cattedra di Epidemiologia dei Tumori, Universita di Torino, Italy (Received in revised form 22 September 1989)
Abstract-The epidemiology of self-reported leisure time physical activity (LTPA) has been studied among 3381 men and 1664 women enrolled in a hospital-based case-control study. 51% of men and 36% of women reported LTPAs during a lifetime, and 23% of men and 22% of women reported LTPAs after 44 years of age. Brisk walking, swimming, cycling and tennis accounted for the majority of LTPAs after 44 years of age. Only 13% of men and 9% of women reported LTPA practice for more than 20 years and more than 3 hours/week; and 0.6% of men and 0.1% of women reported running or jogging for the same duration. LTPA practice was related to age, education, smoking status, and body mass index. Specifically, ex-smokers reported more frequently LTPA practice than current smokers. Despite the effort to identify aerobic exercise, results from the present analysis suggest that LTPA practice might be over-reported, as a result of a “wish” bias. Problems arising from the use of data on
self-reported LTPA practice are discussed in detail. Leisure time activity
Physical activity
INTRODUCTION
The possible role of physical activity in the etiology of chronic diseases such as cardiovascular disease, hypertension, osteoporosis, and breast and colon cancer has been widely considered [l-5]. Leisure time physical activity (LTPA) is a complex behavior, measured by a variety of methods [6], and it is likely to be influenced by biases in reporting [7]. Whether individuals report exercise or not is affected by a host of variables including age, education, sex, body weight and smoking [8]. Some of these behaviors are also influenced by exercise: therefore, a complex confounding relationship arises between LTPAs and chronic disease risk factors. In order to determine what affects participation in regular LTPA at different ages throughout life and what health behaviors are *Author for correspondence
Aerobic exercise
Report bias
associated with regular physical activity, it is necessary to assess frequency, duration, intensity, type of activity and demographic/ behavioral variables. The purpose of the present report is to describe the epidemiology of reported LTPAs in a large hospital population, as a basis for further analyses looking at the association between LTPA practice and specific cancer risks. MATERIAL AND METHODS
This analysis is based on data collected in an on-going hospital-based case-control study on tobacco-related diseases. Subjects were enrolled in 8 different hospitals in Philadelphia, Detroit, Chicago, New York City and Long Island, N.Y. For the purpose of this descriptive analysis, cases and controls were combined together. In 1985, a section on LTPAs was added to the questionnaire, which also included information 569
570
P.
kXFETTA
on demographic variables, occupational history, smoking, drinking, and dietary habits, medical history and vitamin intake. The term physical activity is not a uniformly defined behavior. In the present analysis, subjects were asked about regular, strenuous activity, specifically defined as “exercise carried out for at least 20 minutes, 3 times a week, for 1 year or more, during which you perspire and become short of breath”, which they had engaged in since the age of 15. This definition was aimed to identify subjects performing aerobic exercise and corresponds to the 1990 goal established by the Department of Health and Human Services for the U.S. adult population [9]. Twenty-six activities were coded separately: basketball, tennis, paddleball or racquetball, squash, football, soccer, volleyball, hunting, field hockey, ice hockey, karate, judo, boxing, wrestling, swimming, running, brisk walking, cycling, aerobic dancing, cross-country skiing, jogging, rope skipping, rowing, gymnastic, downhill skiing and mountain climbing. Professional physical activity as an athlete or dancer was also recorded. Up to 2 LTPAs were recorded for 3 different age periods: 15-21, 22-24, and 45 + years. Therefore, each subject might report a maximum of 6 LTPAs. In the analysis, each reported LTPA was accounted for separately: therefore, the total proportion of subjects reporting LTPAs is smaller than the sum of the proportions for each activity, the difference corresponding to the proportion of subjects reporting more than one LTPA. The number of hours per week, months per year, and total years engaged in the activity were also recorded. The average weekly caloric expenditure (WCE) from reported LTPAs was calculated according to the formula WCE
=
i
xijhXmi112)Yi
iYi
’
where i ranges from 1 to 6 (the maximum number of reported LTPAs was 6), hi = hr/week, mi = months/year, yi = number of years, and xij is a hourly caloric expenditure estimate for LTPA =j. These estimates ranged from 300 kcal/hr for aerobic dancing and gymnastic, to 1200 kcal/hr for running. The number of cigarettes smoked per day was derived by multiplying the average quantity of each smoked brand of cigarette by the amount
et al.
of years the brand was smoked, summing these products and dividing the sum by the total number of years of smoking; Quetelet Index (QI) was calculated according to the formula: QI = weight [kg]/height [ml*. The direct method of standardization [lo] was used for rate adjustment, using males and females as standard populations; t-test for the difference between two means, chi-square test for the difference among proportions [lo], and chi-square test for linear association among proportions [l l] were used. RESULTS
This analysis is based on 3381 men and 1664 women enrolled between January 1985 and October 1987. 71% of subjects (68.6% of men and 75.7% of women) had a diagnosis of cancer, of whom 22.5% were cancers of the digestive system, 20.6% cancers of the respiratory tract, and 14.7% cancers of the genito-urinary system. Among non-cancer cases, 7.0% of subjects had a circulatory disease, 4.1% a digestive disease, and 2.8% of subjects suffered from injuries. Fifty-one percent of men and 36% of women reported some LTPA (Tables 1 and 2); men practise LTPAs more frequently during their youth, while women are more likely to participate before 22 or after 44 years of age. The most frequently reported sports among men include basketball and football, but both are rarely practised after 22 years of age; also swimming, running, brisk walking, tennis, and cycling. Among women, brisk walking, swimming, cycling, aerobic dancing and tennis were the most frequently reported activities. In both sexes, group LTPAs are more frequently practised early in life, while individual activities, such as brisk walking, are more frequently reported after 44 years of age. 11 men (0.3%) and 4 women (0.2%) reported professional physical activity. Only 13% of men and 9% of women reported more than 20 years of total duration and more than 3 hours/week. Brisk walking, tennis, and swimming are the LTPAs reported for longer periods of time, while well defined aerobic activities, such as running and jogging, are rarely practised for more than 20 years and more than 3 hours/week: only 9 runners (0.3%) and 9 joggers (0.3%) among men, and 1 jogger (0.1 O/o)among women fall into this category. The reduction in the proportion of subjects reporting LTPAs, when only adequate duration of practice is taken into
571
Epidemiology of Leisure Time Physical Activity Table 1. LTPAs among men,* by age period Subjects reporting LTPAs while aged >20yr > 3 hr/week
LTPAt
Any period (NJ (%I
15-21 (%I
2244 (%I
45+ (%)
Basketball Football Swimming Walking brisk Running Tennis Bicycling Jogging Gymnastics Soccer Paddleball/racquetball Aerobic dancing Boxing
480 472 328 278 242 208 175 141 138 97 88 82 55
14.2 14.0 9.7 8.2 7.2 6.2 5.2 4.2 4.1 2.9 2.4 2.4 1.6
13.7 13.7 5.4 1.0 5.5 2.3 1.7 0.9
0.5 0.0
:4 1.3 0.9 1.4
3.3 1.4 4.8 3.5 1.8 4.2 1.6 2.5 1.8 0.9 1.3 1.2 0.5
4.3 7.5 1.2 3.3 3.5 1.9 1.9 0.1 0.8 1.1 0.0
0.9 0.1 1.9 2.5 0.3 1.8 0.6 0.3 0.6 0.2 0.6 0.2 0.1
1724
51.0
38.5
24.8
22.8
13.0
Any LTPA
*N = 3381. TOnly LTPAs reported by 50 or more subjects are listed separately. Table 2. LTPAs among women,* by age period Subjects reporting LTPAs while aged LTPAt
Any period (NJ (%I
15-21 (%)
2244 (“/J
45+ (%I
>20yr > 3 hr/week
Walking brisk Swimming Aerobic dancing Bicycling Tennis Basketball Gymnastics Volleyball Running Field hockey Jogging
194 168 107 107 92 69 58 29 24 16 15
11.7 10.1 6.4 6.4 5.5 4.1 3.5 1.7 1.4 1.0 0.9
2.8 6.9 1.6 3.1 2.8 4.1 1.4 1.6 0.8 0.9 0.0
4.5 4.7 3.4 2.3 3.2 0.2 1.6 0.2 0.4 0.1 0.5
10.0 5.1 3.2 2.9 2.2 0.0 1.6 0.0 0.3 0.0 0.5
3.0 2.2 0.5 0.6 1.3 0.0 0.3 0.0 0.0 0.0 0.1
Any LTPA
591
35.5
20.0
17.8
21.6
9.0
*N = 1664. tOnly LTPAs reported by 15 or more subjects are listed separately.
account, is shown in detail in Fig. 1. This effect is even stronger among subjects reporting well defined aerobic activities, namely runners and joggers (Fig. 1). The average WCE was 2854 kcal for men and 1660 kcal for women (Table 3). A trend of decreasing WCE with age is clear in both sexes, but it is stronger among men, corresponding to the shift from highly caloric LTPAs, such as running or football, to less energetic LTPAs, such as swimming or brisk walking. If subjects not reporting any LTPA are included, the average WCEs are 1456 kcal for men and 589 kcal for women, respectively. About 30% of men and 16% of women had a caloric expenditure over 2000 kcal/week, the level associated with a decrease in coronary disease risk [2].
Table 4 shows the age and education-adjusted proportion of men reporting LTPA practice by age, education, smoking habit, and body mass index. The proportion of men reporting LTPAs declines with increasing age, and strongly increases with increasing level of education Table 3. WCE by sex and age period WCE’ Overall
Men 2854 f 3242
Women 1660 k 2189
While aged 15-21 2244 45f
3426 f 3810 2406 + 2875 2027+2190
1761 + 2665 1577 + 1989 1492 f 1201
*Mean + SD. excluded.
Subjects
not
reporting
any
LTPA
are
P. BOF~~A et al.
Practice 1449(46.5%0) 279(9.3%)..
f-20 Yrs 1054 ( 35.3%). 261(6.70/o) **
l-3H/WfI) 54 (l.B%o)* 14 (0.596)** (I
1 Hours /
4+H/W iOOOU3.5%)* 247(9.3%).’
*
2ltYrs 395(13.2%)* 16 (0.6%)
I-3n/w 6 (0.2%). 0 1o.oO/o)**
504 (33.2%).
*
??
4t H/W 369(13.0%) 16(0.6%)
??
*
??
week
All LTPA’s ??* Running and jogging ??
Fig. 1. Subjects 45 + years old reporting practice of LTPA and of running and jogging by sex and duration.
Table 4. LTPAs and selected characteristics; men Any LTPA reported Number of subjects
No LTPA reported W1
Any period Wl
while aged 15-21 W)
2244 W1
45+ (“/I
Running and jogging (“/I
115 603 933 1140 589
40.1 41.3 50.8 52.4 48.9 *
59.9 52.1 49.2 47.6 51.1 *
48.3 42.4 36.7 34.7 30.6 **
38.8 26.9 21.6 19.5 30.2 *
20.8 24.3 21.1 32.3 **
21.3 11.8 9.5 8.3 6.3 **
393 723 1289 833 142
77.1 61.1 56.5 41.0 28.8 **
22.9 32.3 43.5 59.0 71.2 **
16.3 23.0 32.7 45.3 55.0 **
8.2 14.2 17.7 30.1 38.6 **
8.8 10.4 16.2 24.1 32.2 **
3.9 4.2 1.4 12.8 21.1 **
575 494 700 686 706 193
45.7 48.6 55.0 45.3 50.1 47.0 *
54.3 51.4 45.0 54.7 49.9 53.0 *
39.4 42.5 37.3 38.3 36.2 36.9
27.8 22.7 21.6 25.9 24.9 29.6
21.9 16.4 11.5 27.4 21.6 21.5 *
12.7 10.6 8.9 13.9 11.9 9.5
656 654 730 643 691
51.6 45.3 48.9 48.0 51.5
48.4 54.7 51.1 52.0 48.5
35.9 39.9 38.8 41.2 36.4
24.8 28.6 24.5 25.0 21.5
21.2 21.6 20.7 21.5 16.3 **
11.2 13.5 11.5 10.2 9.7
Agea
18-44 45-54 5564 65-14 15+ Test for trendf Education (yr)b O-8 9-11 12 13-16 17+ Test for trend’ Smoking habits’
Nonsmoker CCd 1-20/day CCd 21 +/day EC’ I-20/day EC’ 21 +/day Cigar/pipe only Test for differencea Quetelet Index’
10.1-23.0 23.1-24.9 25.0-26.6 26.7-29.1 29.2 + Test for trend’
“Adjusted for education. bAdjusted for age. cAdjusted for age and education. dCurrent cigarette smoker. ‘Ex-cigarette smoker. ‘Chi-square test for trend: *p < 0.05 for difference among proportions, **p -z 0.05 for trend. rChi-square test for difference among proportions: *p < 0.05.
no significant trend;
Epidemiology
of Leisure
(23, 32, 44, 59 and 71% among men with O-8, 9-11, 12, 13-16, and 17+ years of education, respectively). Current smokers report less frequent (48%) LTPA practice than non-smokers (54%), the difference being larger among those aged 45 and over. Ex-smokers, on the other hand, report little LTPA practice until 44 years of age, when they were presumably still smokers, and show a later increase in reported LTPAs. Subjects in the highest body mass quintile (QI > 29.1) report LTPAs less frequently (48%) than other subjects, but no clear trend is suggested among the remaining quintiles, whose proportions range between 49 and 55%. Table 4 also shows the relationship between personal characteristics and running and jogging. Their practice decreases with age, increases with education, and Table
5. LTPAs
Time Physical
513
Activity
is associated with never or ex-smoker status and low body mass. Among women (Table 5), there is a decline in the proportion of subjects reporting LTPAs with increasing age, and an increase with increasing level of education. The findings on the association between smoking habit and reported LTPAs among women partially parallel the results among men: ex-smokers tend to increase LTPAs over age, presumably after quitting smoking, while current light (l-20 cigarettes/day) smokers, but not current smokers with heavier consumption, report LTPAs in a similar proportion to nonsmokers. No consistent relationship with QI is suggested among women. Very few women reported running or jogging, but results suggest that runners and joggers are more likely to be young, highly educated, never or ex-smokers, and thin.
and selected characteristics;
women
Any LTPA reported while aged
Running and
Number of subjects
No LTPA reported W)
Any period (Xl
15-21 (%l
2244 (X1
45+ (%l
Agea 1844 45-54 5564 65-14 15f Test for trend’
146 325 659 453 80
50.0 58.8 64.9 70.1 75.3
50.0 41.2 35.1 29.9 24.1 **
28.8 20.6 19.6 18.1 19.2 **
40.4 22.0 14.8 14.0 9.8 **
21.5 22.4 23.1 9.6 **
9.6 3.0 1.6 1.0 1.6 **
Education (~r)~ O-8 9-11 12 13-16 17+ Test for trend’
29 302 691 496 145
89.7 11.1 69.1 47.1 46.1
10.3 22.3 30.9 52.3 53.9 **
6.9 10.8 16.5 28.2 29.6 **
3.4 8.3 15.5 24.2 25.3 **
3.4 14.4 16.6 21.5 26.5 **
0.0 1.1 1.2 3.3 6.1 **
Smoking habit’ Nonsmoker CCd l-20/day CCd 2 1+/day EC’ I -2O/day EC’ 21 f/day Test for differences
594 351 262 300 142
62.8 64.5 75.9 59.8 61.8
37.2 35.5 24.1 40.2 38.2 *
18.0 24.0 14.9 21.4 21.8 *
18.0 17.7 12.0 23.2 11.2 *
21.8 16.1 10.4 25.3 26.8 *
3.2 1.8 0.0 3.9 1.9
Quetelet Index’ 10.1-21.2 21.3-23.2 23.3-25.6 ?5.7-29.0 29.1+ Test for trend’
303 348 314 341 344
63.8 61.7 62.1 65.4 67.5
36.2 38.3 31.3 34.6 32.5
20.8 19.4 23.2 20.9 16.8
20.1 20.7 16.6 16.7 14.8 **
19.6 22.9 19.6 18.8 19.1
3.3 2.1 3.6 1.5 1.6
“Adjusted for education. hAdjusted for age. ‘Adjusted for age and education. dCurrent cigarette smoker. eEx-cigarette smoker. ‘Chi-square test for trend: *p < 0.05 for difference **p < 0.05 for trend. YChi-square test for difference among proportions:
among
proportions,
*p < 0.05.
jogging W)
-
no significant
trend;
P. bFF!ZlTAet ai.
514
Reports of LTPA do not show any consistent association with marital status, ethnic group or religion in either sex (data not shown). The results of the present analysis consistently suggest that educational level is the most important determinant of reported LTPA practice, as well as of true aerobic exercise. A more detailed analysis on the association between education and most frequently reported LTPAs indicates that basketball, football, swimming, brisk walking, running, tennis, jogging, gymnastics, aerobic dancing and paddleball/racquetball practice among men show a significant positive trend with education; one (boxing) shows a borderline significant negative trend, and two (cycling and soccer) show no association. Results for women are remarkably similar: cycling and aerobic dancing show no association with education, while the remaining LTPAs show or suggest a positive trend. DISCUSSION
The hospital population on which the study is based is highly educated. Even if this aspect could reduce the generalizability of our results, controlling for education via direct standardization ensures a correct interpretation of internal comparisons. Participation in physical activity is not a uniformly defined concept: the definition of “active” varies from mere participation in one or more sports to rigid criteria of number of calories expended or hours spent exercising per week. The present analysis attempted to identify well defined aerobic activity on the basis of self-reported information on LTPAs carried out for at least 20 minutes, 3 times a week, for at least 1 year, causing dyspnea and sweating. It was not possible to estimate the actual caloric expenditures, nor to specifically certify the individuals’ practices into aerobic and non-aerobic exercise. No information was available on baseball, as well as on sports with low caloric expenditure, such as golf and fishing and on LTPAs related to hobbies. A major problem in the epidemiology of weak associations, such as that suggested between physical activity and cancer risk [4], is that of bias, in this case of report or “wish” bias. It is possible that physical exercise during leisure time is reported in excess of its actual occurrence, even if the questionnaire was specifically designed to identify aerobic activity. It seems unlikely that over 7% of men and 10% of
women over 45 in this population actually do walk briskly and long enough to produce aerobic benefits, i.e. not less than 4 miles/hr. Similarly, it is unknown how many of those who reported exercise as swimmers, tennis players, or cyclists performed these activities vigorously and continuously. Furthermore, only about 10% of men and women (Tables 1 and 2) reported a practice of these LTPAs for more than 20 years and more than 3 hours/week, which corresponds to the amount recommended by the American College of Sports Medicine [ 121. Running and jogging, which are more likely to be well defined aerobic activities, are reported by only about 3% of men and less than 1% of women over 44 years of age, and very few subjects (0.6% of men, 0.1% of women) practised them for more than 20 years and more than 3 hours/week (Fig. 1). The validity (agreement between reported LTPAs and a more objective measure of exercise or physical fitness) of self-reported LTPA practice was recently evaluated by several investigators (Table 6): it seems that a generic report of physical activity does not consistently represent a good indicator of aerobic activity or physical fitness, whereas detailed indices, which carefully quantify caloric expenditure in the practice of LTPAs, are more valid measures of actual physical activity. The present study has an intermediate level of detail in the assessment of LTPA practice: the possibility of report bias cannot be ruled out. A “wish” or report bias could affect the estimated prevalence of subjects performing LTPAs, and, if individuals with a specific disease reported LTPA differently than controls, could produce differential misclassification in case-control comparisons. In the present analysis, 51% of men and 36% of women reported some LTPA during their lifetime, and 23% of men and 22% of women reported some LTPA after the age of 44. A comparison of these results with other studies is difficult, because of differences in the definition and the measure of LTPA, and in the likelihood of a report bias. Stephens et al. [20] reviewed eight U.S. and Canadian surveys, and reported that the proportion of active subjects ranged between 17 and 26% for men and 13 and 15% for women if rigorous definitions of LTPA were applied, but it might be as high as 70-80% if less rigorous definitions were used. Results of recently published studies confirm the importance of report bias: in a U.S. survey by Brooks 181, 29% of men and 33% of women reported no
*SAQ: Self-administered
questionnaire:
375 men, mean age 47, who underwent a clinical examination at a preventive medicine clinic, Dallas
in past 4
and F
IAQ: Interviewer-administered
questionnaire;
SAQ (past 3 months, F and D of strenuous racquet and non-racquet sports, cycling, swimming; F, D and S of walking, running, or jogging; F of El sweating) and recall SAQ (7 days, D of vigorous and moderate LTPAs)
LTPAs
IAQ (F of vigorous months, 6 levels)
yr,
61 volunteers, 48% women, Montreal area
1966
Overall index (combination of climbing, walking, and LTPAs), of EI sweating, from SAQ
of level of fitness
36 men and 32 women, volunteers, 20-70 yr, Pawtucket, Rhode Island
appraisal
Personal
204 employees, 70% women, volunteers, Houston
EI
SAQ (I day, all activities) and IAQ (7 days, D of sleep, light, moderate, hard, very hard activity)
18-64 yr,
studies
LTPA*
12 males, 3469 yr, volunteers, 8 of whom post-myocardial infarction patients, Stanford
of self-reported
SAQ (D and F past 12 months, sweating and dyspnea)
Measure
from selected
I75 males, 36-59 yr, population sample, Minneapolis
Population
Table 6. Results
exercise test
exercise test
EI: Exercise-induced;
Treadmill
D: Duration;
practice Results
fitness in
with all validation
F: Frequency;
S: Speed.
Positive association with sweating, walking, running, or jogging, vigorous non-racquet sports. No association with racquet sports, cycling
Positive association measures
Agreement between the 2 measures, sweating index correlates better with oxygen uptake than the more complex index
Self report overestimates both sexes
Agreement of overall energy expenditure among validation and 2 measures, over report of duration of hard and very hard activities in SAQ (no data on IAQ)
Positive association with light, heavy, and total LTPA, no association with moderate LTPA or sweating/dyspnea
LTPAs
on a
Maximum oxygen intake, body fat, muscular endurance (2 1;vels)
uptake,
exercise test
Maximum oxygen cycle ergometer
Treadmill
Heart rate and body movement detector
Treadmill
of self-reported
Validation
on the validity
I191
1181
[I71
1161
iI51
[13, 141
Reference
576
P. BOF~TTAet al.
LTPA, and 13% reported heavy intensity LTPAs; in a Canadian population-based survey 54% of men and 62% of women were sedentary, and 28 and 21% respectively were adequately active [21]; a Louis Harris survey recently showed that up to 79% of men and women reported regular exercise, either at work or elsewhere; 29% of men and 37% of women stated walking several days per week, and 44% of men and 28% of women reported strenuous exercise [22]. Stephens et al. [20] also listed specific LTPAs from 7 out of 8 surveys they reviewed: walking, swimming, and cycling were among the most frequently reported LTPAs in the studies with a less rigorous definition of exercise: these activities are therefore more likely to contribute to the overall report bias. The rank of jogging, on the other hand, was higher in one study with more rigorous definition. The comparison of these results with the present analysis confirms the possibility of a report bias in our study, and supports the choice to specifically analyze runners and joggers as characterizing aerobic activity. The average WCE in LTPAs was 1450 kcal/week for men and 590 kcal/week for women. 25% of men and 8% of women had a caloric expenditure higher than 2000 kcal/week. These data are similar to the results of a population-based study in MinnesotaJ231, in which 34% of men and 17% of women reported more than 2000 kcal/week, and the average expenditures were 1350 and 780 kcal/week, respectively. The expected decline in physical activity with age has been shown in other surveys, with the drop especially noted between the teen years and early adulthood [20,21,23]. An increase in LTPA practice among young cohorts, independent from the effect of aging, has been suggested [24]: in the present analysis, such a trend is clearly present among women, but not among men (Tables 4 and 5). The relationship between sport practice and income and education has been noted in other surveys [7,20,23,25]: a higher frequency of LTPA practice is to be expected among wealthier subgroups of the population. The relation between smoking status and LTPAs is a negative association in the present and some other studies [2,.26]. Some investigations have shown that non-smoking men aged 25-44 have a greater participation in high intensity exercise than smokers [23], while other
studies have shown no association [26]. The fact that reported LTPA is higher among exsmokers than among current smokers, perhaps in an attempt not to gain weight, represents an original finding of the study. The trend towards less physical activity in subjects with greater body mass shown by the present analysis has been previously reported [2,23,26]: one study, on the other hand, found an inverse relationship [25]. It must be noted that in the present study this trend does not include very thin subjects. The purpose of this study was to determine baseline data on reported LTPA practices. Further analyses will address the role of LTPA practice in the etiology of specific cancers. A further important result of this analysis was the suggested need of a more detailed questionnaire to identify actual aerobic activity. Specific questions on distance, time and speed should be asked with regard to brisk walking, swimming, tennis and cycling, which are the most frequently reported LTPAs after 44 years of age. Results of the present descriptive analysis confirmed the relationship between LTPA practice and age, education level and obesity that have been found in other surveys. An important original finding regarded ex-smokers: their LTPA practice was more similar to never smokers’ than to current smokers’, suggesting that quitting of tobacco smoking may be related to other health promoting habits. Acknowledgements-This research was supported by National Cancer Institute Program Project Grant CA32617 and Center Grant CA17613, and American Cancer Society Special Institutional Grant SIG-8. We would like to acknowledge the valuable contributions of the following cooperating institutions and individuals: Memorial Hospital (New York), Dr David Schottenfeld; Long Island Jewish Hillside Medical Center (New York), Dr Ranti R. Rai; Queens General Hospital (New York), Dr Hans Grunwald: Hines Veterans Hosnital (Chicano. Ill.), Dr John Sharp; Loyola University Hosiital (Chicaio; Ill.), Dr Edward k. Garrity; Hospital of- the ‘Unive&ity of Pennsylvania (Philadelnhia. Penn.). Dr Paul Stollev; Thomas Jefferson University’Hospital(Philadelphia, Penn:), Dr James E. Colberg; Henry Ford Hospital (Detroit, Mich.), Dr Robert M. O’Bryan. We would also like to thank Marion Moore for review of hospital records, Pao Huan Chung and Chuen Lan Liang for programming assistance, Verna Harrison and Laurie Marmelstein for preparation of the manuscript.
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