2Journal of Epidemiology and Community Health 1996;50:258-263

Physical activity, physical fitness, bloodpressure, and fibrinogen in the NorthernIreland health and activity survey

D MacAuley, E E McCrum, G Stott, A E Evans, B McRoberts, C A G Boreham,K Sweeney, T R Trinick

AbstractStudy objective - To investigate the re-lationship between physical activity, phys-ical fitness, blood pressure, andfibrinogen.Design - This was a cross sectional popu-lation study using a two stage probabilitysample.Setting - Northern Ireland.Participants - A sample of 1600 subjectsaged 16-74 years from the population ofNorthern Ireland.Main outcome measures - Physical ac-tivity profile from computer assisted in-terview using the Allied Dunbar nationalfitness survey scales. Physical fitness usingestimation of VO2 max by extrapolationfrom submaximal oxygen uptake whilewalking on a motor driven treadmill. Sys-tolic and diastolic blood pressure meas-ured with a Hawksley random zerosphygmomanometer. Measurement offibrinogen using the Clauss method.Main results - There were significant re-lationships between both current and pastactivity and blood pressure. These were ofa magnitude that would have been clin-

Department of ically significant, but for the fact that, withEpidemiology and the exception of the relationship betweenPublic Health, The habitual activity and diastolic pressureBelfast, Muihouse (p = 0-03) and past activity and systolicBuilding, Royal pressure (p = 0.03) in men, they were notVictoria Hospital, sustained after adjustment for the effectBelfast BTl2 6BJ of age using analysis of variance. AfterD MacAuleyE E McCrum adjustment for other potentially con-A E Evans founding factors using multiple re-

Policy Planning and gression, there was an inverse relationshipResearch Centre, between systolic blood pressure and pastDepartment of activity in men, so that those with a life-Personnel and Finance(NI), Parliament time ofparticipation compared with a life-Buildings, Stormont, time ofinactivity had a lower systolic bloodBelfast pressure of 6mmHg (p<005). There wasG Stott

a highly significant (p<0 001) inverse as-

sociation between both systolic and dia-Physical Education stolic blood pressure and physical fitnessCentre, The Queen'sUniversity of Belfast, (V02 max) whch was not sustaied afterBelfast adjustment for possible confounding fac-B McRoberts tors. There were relationships betweenC A G Boreham fibrinogen and highest recorded activity

The Laboratory, The (p<0.001), habitual activity (p<0 01), andUlster Hospital, past activity (p<001) in men but no sig-Dundonald, Belfast nificant relationship in women. The re-T R Trinick

lationship between fibrinogen and activityCorrespondence to: was no longer sustained after adjustmentAct forpacAublicati for possible confounding factors. ThereAccepted forpublrcatfonJanuary 1996 was a highly significant (p<0 001) inverse

relationship with physical fitness usingVO2 max. This relationship was sustainedafter adjustment for possible confoundingfactors in both men (p<005) and women(p<O-OOl).Conclusions - There was a relationshipbetween physical activity, physical fitness,and blood pressure but the relationshipwas greatly influenced by age. A reductionof 6mmHg in systolic blood pressure as-sociated with past activity is of clinicalsignificance and supports the hypothesisthat physical activity is of benefit in re-ducing cardiovascular risk. There was alower level offibrinogen in those who weremost active but this relationship was notsignificant after adjustment for possibleconfounding factors. There was also alower level of fibrinogen those who weremost fit (VO2 max) and this relationshippersisted even after adjustment for pos-sible confounding factors.

(J7 Epidemiol Community Health 1996;50:258-263)

There is considerable evidence supporting thebeneficial effect ofphysical activity and physicalfitness on cardiovascular mortality and theeffect on risk factors, such as hypertensionand plasma fibrinogen, may be one possiblemechanism. Epidemiological studies haveshown a reduced risk of developing hy-pertension in physically active persons'2 and ameta-analysis of 25 longitudinal studies3 con-firmed the benefits of aerobic exercise in low-ering raised systolic and diastolic bloodpressures. There is an inverse relationship be-tween vigorous sports participation and hy-pertension4 and the relationship betweenphysical activity and blood pressure has beenshown to be independent of age, body massindex (BMI), and fasting plasma insulin levels.5Blair et al6 found that those with low levels ofphysical fitness have a relative risk of 1 52 forthe development of hypertension when com-pared with those who are very fit. Intervention,including exercise, was shown to reduce therisk of developing hypertension' in a controlledtrial of those with high-normal blood pressureat baseline, and has also been shown to lowersystolic blood pressure by 11 mmHg and dia-stolic blood pressure by 8 mmHg in those withmild to moderate hypertension.3 In general,there has been a linear relationship betweenactivity and blood pressure, but the multiple

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Physical activity and fitness, BP, and fibinogen in N Ireland

risk factor intervention trial study8 and Britishregional heart study9 suggested a "J" shapedcurve.There is also interest in the relationship with

between physical activity, physical fitness, andfibrinogen. Plasma fibrinogen is a well docu-mented risk factor for cardiovascular disease,'0 I'which is independent of hypertension. Fib-rinogen has a role in the clotting mechanismand thus plays an important part in thrombosis.There is evidence from cross sectional'2-16 andlongitudinal'7 studies of reduced fibrinogen inthose undertaking physical activity.

This study offers the opportunity to explorethe relationship between exercise, fitness, andthese two important risk factors. Its aim wasto examine the relationship between physicalactivity, physical fitness, blood pressure, andfibrinogen in a cross sectional population sur-vey of physical activity, other lifestyle para-meters, and cardiovascular risk factors inNorthern Ireland.'8 The particular benefits ofthis study are the detailed measure of physicalactivity and the direct measurement of physicalfitness using oxygen uptake, and the study isparticularly pertinent in a population knownfor its high level of cardiovascular disease."

MethodsThe Northern Ireland health and activity survey(NIHAS), which was designed to yield a rep-resentative sample of adults aged 16 years orover in Northern Ireland, employed two stageprobability sampling. The first stage was asample of 1600 addresses taken from theNorthern Ireland rating and valuation lists,stratified by region to ensure proportional sam-pling across the province. The second stagewas carried out by the interviewers so that oneperson was selected in each household using aKish grid random selection procedure20 toavoid any chance of self selection by membersof the household or bias on the part of theinterviewer.A sample drawn using the Kish grid sampling

method is influenced by the numbers in eachhousehold, thus the sample was weighted totake account of household size and the ap-propriate adjustment was made to the methodof calculating the standard errors.The fieldwork, which was completed be-

tween February and November 1992, com-prised three parts - a computer assistedinterview, a physical appraisal, and fastingblood sample determination. The ques-tionnaire was similar (with some modificationsrelevant to Northern Ireland which did notaffect the meaning ofthe questions; for exampleto allow for the different measures of alcohol),and the physical appraisal was identical to thatused in the Allied Dunbar national fitness sur-vey (ADNFS).2' The questionnaire was carriedout using computer-assisted interviewing anda copy of the questionnaire on disk may beobtained from the Sports Council for NorthernIreland. Those defined as hypertensive in-cluded both those whose blood pressure was160/95 and those who were taking medicationfor high blood pressure.

Physical activity was classified under threeheadings:* The highest level of activity in the four weeks

before the interview (none, light, moderate,vigorous).

* The frequency and intensity of bursts ofphysical activity lasting twenty minutes inthe four weeks before the interview which isa more accurate reflection ofhabitual activity(6 categories: level 0-level 5).

* The years of regular participation in sportand exercise since age 14 years in five cat-egories giving the proportion of life that theperson had been active (0, <0-25, 0-25-0-49,0-50-0-74, 0 75%).The physical appraisal was performed in a

specially designed mobile laboratory at 14 hos-pital sites throughout the province. Height wasmeasured using a Holtain stadiometer and bodyweight was measured to the nearest 0-1 kg usinga Phillips Electronic scale (HP 5320). Bodymass index was used as an index of obesity.Blood pressure was measured with a Hawksleyrandom zero sphygmomanometer. Blood pres-sure measurements were taken after the heightand weight measurements, but before any phys-ical activity. Three readings were taken at oneminute intervals after the subject had beensitting resting for 5 minutes. Blood pressure wasmeasured on the left arm using an appropriatesized cuff and diastolic pressure determinedusing the Korotkoff method.5 The physical ap-praisal team (n = 4) had regular quality as-surance appraisals for technique andinterobserver comparability, and the sphygmo-manometer was subsequently tested for ac-curacy.Aerobic fitness was assessed by oxygen up-

take while walking on a treadmill. Maximumoxygen uptake (V02 max) was calculated byextrapolation from performance at up to 85%of predicted maximum heart rate. Oxygen up-take, in litres per minute corrected for bodyweight, and heart rate were recorded on thetreadmill three times each minute. A leastsquares regression line was drawn through eachrespondent's set of data points. Regression bythe least squares method calculates a straightline through each set of data points. Estimationof V02 max using this method may be limitedby the assumption that each individual has thesame maximum heart rate related to age. Inaddition, the number of data points varied,with some fitter individuals proceeding throughthe whole 16 minute protocol and others onlymanaging a few minutes before their heart raterose above 85% of their predicted maximumfor age (220 beats per minute - age).The more demanding protocol began at a

treadmill speed of 3 km per hour achieving amid range speed of 5 km per hour from the 5thminute to the 14th minute. Gradient changeswere made every minute from the 6th minuteto the 13th minute up to 20 degrees. For fittersubjects, two further speed increments wereincluded to take the subject to target heart rate.The less demanding protocol was at a constantspeed of 3 km per hour with an increase in thegradient. These test protocols were identical tothose used in the ADNFS.2'

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V

MacAuley, McCrum, Stott, Evans, McRoberts, Boreham, Sweeney, Trinick

Table 1 Response to components of Northern Irelandhealth and activity survey

No %

Valid addresses 1456 100Total interviewed, all ages 1020 70 1Attended centre for appraisal 567 38-6Analysable treadmill data 481 33-0Blood tests 633 43-5

A fasting blood sample (30 ml) was takenon a morning during the week preceding thephysical appraisal or not less than two daysafter the physical appraisal at the respondent'shome, place ofwork, or at the physical appraisallaboratory. Participants had been given verbalinstructions and an explanatory letter re-

questing that they fast from all food and alcoholfor 12 hours before the blood test. Samples werecentrifuged at 3000 rpm at room temperature,separated, and analysed on the same day. Thelaboratory is accredited with Clinical PathologyAccreditation UK Ltd. External and internalquality control procedures were used to mon-itor the quality of the laboratory analyses.Measurement of fibrinogen was by the manualClauss method22 (Boehringer Mannheim)using control plasma from Immuno Ltd(Sevenoaks, Kent TN14 5HB, UK).Data were analysed using SPSS on the Mi-

crovax 3100 computer at the Department ofEpidemiology and Public Health, The Queen'sUniversity of Belfast. Analysis of variance was

used for comparison of mean blood pressureand mean fibrinogen between activity groups,and two way analysis of variance was used toadjust for age. The association between bloodpressure and fibrinogen with activity (or fitness)was examined using multiple regression to ad-just for the influence of age, body mass index,alcohol intake (none, 1-9, 10 + units per week),smoking (none, cigars/pipe or <10 cigarettes,10 + cigarettes per day), education (tertiary,secondary, primary), social class (non-manual,

Table 2 Systolic blood pressure (mmHg): men and women

Age groups (y)

All 16-24 25-34 35-44 45-54 55-64 65-74

MenNo 305 57 69 62 61 27 29Mean 122 115 120 117 120 133 142(SD) (16) (10) (13) (13) (15) (19) (18)(SEM) (1 0) (1-5) (1-8) (1 8) (2-2) (4-1) (3 9)WomenNo 299 59 60 58 56 34 31Mean 117 104 106 112 124 135 135(SD) (20) (10) (12) (14) (16) (26) (22)(SEM) (1-3) (1-4) (1-8) (2 1) (2-5) (5-0) (4 5)

Table 3 Diastolic blood pressure (mmHg): men and women

Age groups (y)

All 16-24 25-34 35-44 45-54 55-64 65-74

MenNo 305 57 69 62 61 27 29Mean 76 69 75 75 79 80 79(SD) (11) (8) (10) (11) (9) (15) (13)(SEM) (0 7) (1-2) (1 4) (1.6) (1 3) (3 3) (2 6)WomenNo 299 59 60 58 56 34 31Mean 71 66 65 71 78 78 75(SD) (11) (7) (8) (8) (11) (11) (10)(SEM) (0 7) (1 0) (1 2) (1-2) (1 7) (2-1) (2 0)

manual), and diet (good, bad; based on con-

sumption of dietary fat and fibre by dietaryquestionnaire). The survey was approved bythe Research Ethical Committee of the FacultyofMedicine, The Queens University of Belfast.

ResultsThere were 1456 effective addresses - 145(10%) non-contacts, 285 (20%) refused in-terview, 1020 achieved interviews (70%), and 6missing questionnaires (table 1). The weightedsample (M 474: F 546) was comparable to thepopulation distribution of the 1991 NorthernIreland census in relation to sex and age andthose who attended the physical appraisal wererepresentative of those who completed thequestionnaire in respect of age, height, weight,physical activity, health, and obesity, althoughthey were more likely to be male and non-smokers (p<005). The figures given in thetables are for the weighted sample.Mean systolic and diastolic blood pressures

are shown in tables 2 and 3. There was anincrease in the mean systolic blood pressurewith increasing age in both men (p<0-001) andin women (p<0-001). Overall, 6% of men andwomen were hypertensive using criteria sug-gested in 1992 by the European AtherosclerosisSociety,23 and usingWHO criteria,24 the overallproportions of men and women who were hy-pertensive were 6% and 5% respectively.The relationships between physical activity

and both systolic and diastolic blood pressureswere confounded by age, and after adjustmentfor age only the relationships between habitualactivity and diastolic pressure among men (p =0 03) and past activity and systolic blood pres-sure in men were sustained (p = 0 03).The relationships between habitual activity,

highest recorded activity, past participation,V02 max, and blood pressure were examinedusing multiple regression (table 4). There wasa highly significant positive relationship in bothmen and women between systolic and diastolicblood pressure and age (p<0O001) and BMI(p<0-001). There was an inverse relationshipwith V02 max (p<0001), but this was notsignificant after adjustment for possible con-founding factors (age, BMI, smoking, alcoholintake, education, social class, and diet).There was also a relationship between blood

pressure and habitual activity in men, witha lower mean systolic blood pressure of10 mmHg (p<0-01) and a lower diastolic bloodpressure of 5 mmHg (p<0 05) for level 5 com-pared with level 0. In women there was a lowersystolic blood pressure of 9 mmHg (p<005)and a lower diastolic blood pressure of 5 mmHg(p<001) between levels 3,4 and level 0; com-bining levels 4,5 because of small cell sizesresulted in a lower systolic blood pressure of9 mmHg (p<0 05) and diastolic blood pressureof 7 mmHg (p<0-01) for levels 4,5 comparedwith level 0.Using the highest recorded activity, the sys-

tolic and diastolic blood pressures in men werelower by 15 mmHg (p<001) and 8 mmHg(p<005) respectively and those in women by22mmHg (p<0-01) and 11 mmHg (p<0-01)

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Table 4 Multiple regression analysis of systolic and diastolic blood pressure (BP) and their determinants: men and women (coefficient (SEM))Age BMI V02 max VO2 max Habitual Habitual Highest activity Highest Past Past participation

adjusted activity activity activity participation adjustedadjusted* adjusted

Men LO v L5 None v vigorousSystolic BP § § § NS t NS t NS t t

0-46 1-47 -0-41 -10-07 -15-18 -6-67 -5-64(0-06) (025) (0 10) (3 26) (5 77) (3 04) (2-58)

LO v L3, 4 None v moderatet t-9-16 -11-63(2-97) (5 76)LO v Li, 2t-6-98(3-17)LO v L5 None v vigorous

Diastolic BP § § § NS t NS t NS NS NS0-21 1i11 -0-26 -4-88 -8-02(0-04) (0-17) (0-07) (2-27) (4 00)

Women LO v L3, 4 None v vigorousSystolic BP § § § NS t NS t NS NS NS

0-76 1-23 -0-81 -8-64 -21-86(0-06) (0-26) (0-13) (3-59) (6-81)

None v moderatet- 14-78(6 62)

LO v L3, 4 None v vigorousDiastolic BP § § § NS t NS NS NS NS

0 30 0-76 -0 35 -5-28 -10-59(0-04) (0-13) (0-07) (1 90) (3 64)

LO v LI, 2t-3-82(1-92)

*Adjusted=adjusted for possible confounding variables; t p<OO05; t:p<001; §p<0001.

respectively for those undertaking vigorous ac-tivity compared with no activity. These as-sociations were confirmed when the none/lightcategories were combined due to small cellsizes.There were also lower mean systolic pres-

sures of 7 mmHg (p<0 05) before and 6 mmHg(p<005) after adjustment for possible con-founders between men with a lifetime of par-ticipation compared with those who had beeninactive all their life.There was a highly significant increase in

fibrinogen with age (p<0 001). Fibrinogen waspositively associated with BMI (p<0 001) inboth men and women. There was a relationshipbetween cigarette smoking status in men before(p = 003) and after (p = 0 004) adjustment forage, but there was no relationship in women.In men there was a significantly lower fib-rinogen with habitual activity (p = 0 02), high-est recorded activity (p<0001), and pastactivity (p = 000 1). After adjustment for pos-sible confounding factors, these differenceswere no longer statistically significant. Therewas no significant association between fib-rinogen and habitual activity, highest recordedactivity, or past activity in women (table 5A,B, C).There was a highly significant (p<0001)

inverse association between fibrinogen and fit-ness as measured by V02 max, in both menand women. In men the relationship was suchthat an increase in V02 max of 1 ml/kg/minwas associated with a decrement of 0 03 g/l infibrinogen. This inverse association persistedafter adjustment for possible confounders, withan increase of 1 ml/kg/min in V02 max sug-gesting a decrease in fibrinogen of 0 01 g/l(p<0c05). In women an increase in V02 maxof 1 ml/kg/min was associated with a decrement

of 0-02 g/l in fibrinogen even after adjustmentfor possible confounders (p<0Q001 ).

DiscussionThe age related increase of27 mmHg in systolicblood pressure among men in Northern Irelandwas greater than that found in the cor-responding survey in England25 (the ADNFS;16 mmHg), while the increase of 31 mmHgamong women was comparable (ADNFS;32 mmHg). The rise in diastolic blood pressureof 10 mmHg from age 16-74 years among menwas similar (ADNFS; 8 mmHg) although therise of 9 mmHg among women was less (AD-NFS; 15mmHg).While there were reductions in systolic and

diastolic blood pressures with increasing phys-ical activity of a magnitude that would be ofclinical significance, the association was nolonger significant, with the exception of thereduction in systolic blood pressure with pastactivity in men, when multiple regression wasused to adjust for age, BMI, smoking, alcoholintake, education, social class, and diet. Thissupports the suggestion by Gordon et a12 thatmuch of the relationship between blood pres-sure and physical activity stems from con-founding factors other than physical activityalone. They have pointed out the wide vari-ability in outcome between the studies andsuggested that the blood pressure loweringeffects may be at least partly dependent ongender, BMI, intensity of exercise, duration oftraining, and initial blood pressure. A reductionof 6 mmHg in systolic blood pressure with pastactivity is, however, of clinical significance andsupports the suggestion that lifelong habitualphysical activity is ofbenefit in reducing cardio-vascular risk.

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MacAuley, McCrum, Stott, Evans, McRoberts, Boreham, Sweeney, Trinick

Table 5 Fibrinogen related to highest recorded activity, to habitual activity and to past participation (proportion of lifeactive): men and women(A) Fibrinogen related to highest recorded activity

Highest None Light Moderate Vigorous p Adjusted for age

MenNo 9 18 129 110Mean 3-55 3-62 3-14 2-84 <0 001 0 49(95% CI) (2-81, 4 29) (3-16, 4-07) (2-99, 3 29) (2-71, 2 97)WomenNo 15 16 179 81Mean 3-29 3-60 3-34 3-20 0-41 0 70(95% CI) (2-64, 3-94) (3-17, 4 02) (3-21, 3-48) (3-01, 3-40)

(B) Fibrinogen related to habitual activityHabitual Level 0 Level I Level 2 Level 3 Level 4 Level 5 p Adjusted for age

MenNo 47 47 20 71 24 56Mean 3-39 3-14 3-11 3 03 2-78 2-87 0-02 0-87(95% CI) (3-12, 3-66) (2-91, 3-38) (2-62, 3 61) (2-84, (3-22) (2-60, 2-96) (2-67, 3 08)WomenNo 60 50 49 86 25 20Mean 3-47 3-26 3-36 3-24 3-00 3-55 0-22 0 44(95% CI) (3-22, 3-73) (2-96, 3 57) (3 09, 3 63) (3 09, (3-39) (2-78, 3 22) (2-95, 4-15)

(C) Fibrinogen related to past participation (proportion of life active)

Past 0 <0-25 0-25-0-49 0-50-074 0-75+ p Adjusted for age

MenNo 16 22 35 24 169Mean 3-55 3-23 3-29 3-36 2-91 0-001 0-02(95% CI) (3-13, 3-97) (2-91, 3 54) (2-92, 3 67) (2-96, 3 76) (2-80, 3 02)WomenNo 33 27 38 35 157Mean 304 3-32 3-56 3-18 3-34 0-15 0-19(95% CI) (2-69, 3 38) (2-96, 3 68) (3-23, 3-90) (2-81, 3-54) (3-21, 3-47)

The highly significant inverse association be-tween blood pressure and aerobic fitness, asmeasured by VO2 max, was also eliminatedafter multiple regression was used to adjust forthe confounding factors listed above.There was a relationship between physical

activity and fibrinogen, as would have beenexpected from previous studies, and the marginof difference was both statistically and clinicallysignificant. It is well known that age andsmoking habit confound the relationship withfibrinogen, and the relationship betweenfibrinogen and activity was no longer sustainedafter adjustment for these confounders. This isin keeping with the work of Lee et al,'5 whosuggested that the relationship between activityand fibrinogen could largely be explained bysmoking, while Connelly et al6 found thatthose who were vigorously active had lowerfibrinogen levels, even after adjustment for age,smoking, alcohol, BMI, and occupation.

Ernst17 reviewed the relationship betweenphysical activity and fibrinogen levels in longi-tudinal studies and found evidence of a re-duction of about 0 4 g/l with physical activitywhich is important when we consider that theNorthwick Park heart study27 found that a 0 1 g/ldifference in fibrinogen corresponded to a re-duction of 15% in the risk of coronary heartdisease.While the relationship with physical activity

was no longer sustained after adjustment forage and smoking, the relationship between fib-rinogen and physical fitness was sustained.Lakka et al'8 suggested that the plasma reducingeffect of conditioning physical activity was

largely due to increased fitness. Moller andKristensen" suggested that one possible path-way may be physical activity--physical fit-ness-+fibrinogen, but one would have expectedthat in this model the relationship with physicalactivity would have been sustained.

Physical activity and physical fitness are notthe same, although physical fitness is oftenwrongly used as a surrogate measure of activity.Physical activity is defined as bodily movementproduced by skeletal muscles that results inenergy expenditure while physical fitness is aset of physiological attributes that people haveor achieve that relate to the ability to performphysical activity. The physical fitness com-ponent that has been most frequently studiedin relation to health is aerobic power. Physicalfitness has a large genetic component, althoughit is modified by activity, and it is often difficultto unravel the relationships between physicalactivity which is voluntary and physical fitnesswhich is essentially constitutional. The re-lationship between fibrinogen, physical activity,and physical fitness may suggest a con-stitutional effect.A particular strength of this study is the

detailed measure of physical activity. This in-cluded physical activity at work and 'duringleisure time in a detailed aggregate based onall activities in a four week period. A furtherstrength was the measure of physical fitnessusing a direct measure of oxygen uptake, whichis the most accurate measure of aerobic fitness.A potential weakness is in the sample size whichmay not have been sufficient to detect smalldifferences as statistically significant.

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263Physical activity and fitness, BP, and fibrinogen in N Ireland

ConclusionThere were significant relationships betweenblood pressure, physical activity, and physicalfitness, but with the exception of the re-

lationship between habitual activity and dia-stolic pressure (p = 0 03) and past activity and

systolic pressure (p = 0 03) in men, these were

not sustained after adjustment for age. Whenthe relationships between blood pressure, phys-ical activity, and physical fitness were examinedusing multiple regression to adjust for the in-fluence of potential confounding factors, therelationship between systolic blood pressureand past activity was sustained in men, so

that those who had a lifetime of participationcompared with a lifetime of inactivity had a

systolic blood pressure that was 6 mmHg lower(p<005). A reduction of 6 mmHg in systolicblood pressure is of clinical significance andsupports the hypothesis that it is the exercisehabits of a lifetime, rather than more recent

activity, that offer protection against hy-pertension. There was an inverse associationbetween both systolic and diastolic blood pres-sure and physical fitness (V02 max) whichwas not sustained after adjustment for possibleconfounding factors. This suggests that theprotective effect of activity may be independentof physical fitness level.This study also confirms the relationship

between fibrinogen and physical activity in menbut the relationship was no longer significantafter adjustment for possible confounders.There was, however, a relationship betweenfibrinogen and physical fitness in both men andwomen before and after adjustment for possibleconfounding factors. The relationship betweenphysical activity, physical fitness and both theserisk factors, blood pressure and fibrinogen, ap-pear to have a different pattern, and the benefitsof physical activity and physical fitness mayact through different pathways. Longitudinalstudies of physical activity and fitness may helpfurther clarify these relationships.

We wish to thank Drs Frank Kee and John Yarnell, Departmentof Epidemiology and Public Health, The Queens University ofBelfast, for their helpful advice and criticism.The Northern Ireland Health and Activity was supported by

The Sports Council for Northern Ireland, The Health Pro-motion Agency for Northern Ireland, Northern Ireland Chest,Heart and Stroke Association, The Department of Health andSocial Services (NI), The Department of Education (NI), Saveand Prosper, and a number of local councils.

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