Introduction

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Regular physical activity protects against cardiovascular diseases, obesity, diabetes, and osteoporosis¹ and helps promote mental health.² In the United Kingdom, 70% of men and 80% of women are insufficiently active to benefit their health.³ Over 200 "exercise on prescription" schemes have been identified in England⁴ but few have been rigorously evaluated. ^{5 6} We present results from a randomised controlled trial evaluating the effectiveness of promoting physical activity in primary care.

	Methods

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Participants
Participants were recruited from one general practice (list size 11 400) situated in a socioeconomically disadvantaged area of Newcastle. ^{7 8} All patients aged 40 to 64 years who satisfied our inclusion criteria were eligible to participate. Patients unable to complete a submaximal exercise test were excluded (patients with cardiovascular or respiratory disease causing raised risk), as were patients undertaking regular vigorous exercise at least three times a week over the previous six months. Exclusion criteria are described in more detail on the BMJ's website.

Recruitment
Between March 1995 and March 1996 the researcher (JH) approached all patients aged 40-64 attending routine surgeries. Patients completed a recruitment card, signed by their general practitioner, which they returned to the researcher before leaving. Postal recruitment was introduced between March and August 1996 to boost declining opportunistic recruitment. Patients not previously approached opportunistically were identified from the practice register, checked for eligibility, and sent a postal invitation to participate.

Data collection
Data were collected in three phases: baseline assessment; post-intervention follow up, 12 weeks after baseline (postal questionnaire); and repeat assessment one year after baseline, at which assessors were blind to allocated group (see figure 1). Baseline and follow up assessments lasted 75 minutes and included a structured interview questionnaire, physical measurements, and exercise test (cycle ergometer). Participants who refused the one year assessment were sent a follow up questionnaire. All non-respondents received one telephone reminder and two written reminders as required. Our null hypothesis was that changes in self reported physical activity at follow up would be the same in the intervention and control arms.

View larger version (52K): [in this window] [in a new window]   Flow of participants

Outcome measures
Self reported physical activity was assessed by using a shortened version of the National Fitness Survey questionnaire that included questions on the type, frequency, duration and intensity of different activities in the previous four weeks. ^{3 9} Activities were categorised as moderate, expending 5-7.5 kcal/min (0.209-0.314 MJ/min), or vigorous, expending >7.5 kcal/min (>0.314 MJ/min). ^{3 10 11} A physical activity score was based on the number of sessions of moderate and vigorous activity lasting a minimum of 20 minutes in the previous four weeks. The score included all walking, cycling, and other sports or leisure activities but excluded home based activities (housework, gardening, and "do it yourself"). Scores were computed for respondents with complete physical activity data at each time period. Anthropometric, physiological, and other related outcomes, including changes in the variables of the exercise test, will be reported separately.

Randomisation
After their baseline assessment, participants were randomised in blocks of 10. They chose blind from a set of 10 randomly ordered cards (two for each number from one to five, corresponding to the control group and four intervention groups) and were allocated to the corresponding group.

Interventions
All participants received their baseline results (blood pressure, weight for height, activity level and aerobic capacity, smoking, and alcohol consumption) and a pack containing information on the benefits of physical activity, other lifestyle factors (smoking, alcohol, weight, and diet), recommended activity levels for men and women of different ages,³ and 19 leaflets on leisure facilities and activities available locally. Brief advice was given, comparing individual's results with recommended levels and highlighting details in the information pack. Those in the control group received no further intervention.

Motivational interviewing
Motivational interviewing is a technique for negotiating behaviour change¹² that uses the stages of change model of behaviour change.^13-16 A health visitor (LF), who was trained in motivational interviewing, delivered the motivational interviews. Interviews were scheduled to last 40 minutes and took place at the practice or local leisure centre. They aimed to promote safe, effective physical activity but did not prescribe particular activities. A structured record was completed at each interview, a copy of which was given to participants; this was used to review progress for those attending more than one interview.

Financial incentive
Vouchers were non-transferrable, valid during the intervention period, and could be exchanged for one episode of most aerobic activities in any local authority leisure centre, swimming pool, or other voluntary or community leisure activity in Newcastle. Date, place of use, and activity were recorded.

Analysis
A successful outcome was defined as moving up one or more levels of physical activity score from baseline to follow up. We calculated that 107 participants per group would be required to detect a difference between success rates of 40% to 60% at 80% power and 5% significance level.

	Results

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Recruitment and response rates
In all, 2974 patients were approached (96% of those aged 40-64 years): 1308 opportunistically and 1666 by post. Of these, 477 (16%) were excluded and 734 agreed to participate. In total, 217 men and 306 women were enrolled. Baseline characteristics were evenly distributed in control and intervention groups (table 1).

Uptake of interventions
Among participants in the intervention group, 341 (82%) attended at least one interview. Attendance was higher in the interventions that included vouchers than the other interventions, (86% (180) v 77% (161)). Among participants offered six interviews, the median number of interviews attended was three.

Main outcomes

At 12 weeks
The proportions with improved physical activity scores differed significantly in the four intervention groups combined, compared with the controls (38% (123) v 16% (13), P=0.001) (table 2). Within the intervention groups, no significant effect was due to the introduction of vouchers (P=0.84) or more than one interview (P=0.26), but there was a significant interaction between these interventions (P=0.01): the highest proportion of participants with increased physical activity scores (55%) was in the group offered both multiple interviews and vouchers. This was 39% (95% confidence interval 25% to 53%) more than in the control group.

At one year
Increases in physical activity reported at 12 weeks by participants in the intervention group were not maintained at one year, regardless of the intensity of intervention. Only the increase in vigorous activity in the intervention groups was close to statistical significance. The data were consistent with small positive or negative effects of intervention groups compared with controls.

	Discussion

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Interpretation
Adoption of physical activity (initiation of increased physical activity in previously sedentary individuals) and adherence to physical activity (long term maintenance of increased physical activity) have been described as distinct phases of activity behaviour influenced by different factors. ^{19 20} This trial evaluated interventions to promote adoption of physical activity in socioeconomically disadvantaged, middle aged adults. The most effective intervention was the most intensive, apparently due to synergy between motivational interviewing and financial incentive. A comparatively brief intervention (one motivational interview) was effective for only a third of participants in the short term. Results at one year showed that short term increases in physical activity were not maintained. Even the most intensive intervention was ineffective in promoting adherence to exercise in the absence of further incentives to maintain changes in lifestyle.

Limitations
The study was experimental, ^{21 22} with most of the recruitment, intervention, and evaluation functions undertaken by research staff. Our recruitment rate (17%) was considerably higher than other exercise on prescription schemes, which have typically involved less than 1% of the patient base from which they were drawn⁴; this may have been facilitated by the researcher being in the practice to initiate recruitment daily.

Implications
The results of this trial have important implications for the organisation and effectiveness of physical activity promotion in primary health care.^4-6 In light of our findings, primary healthcare teams need to assess critically the interventions that are currently used to promote physical activity, and they should reconsider the use of scarce resources to fund "exercise prescription" schemes. Further research is needed to develop interventions that promote long term adherence to exercise in addition to adoption of exercise and to identify less costly ways of delivering these.