In the general population, physical activity reduces with age
[24, 25] and people over the age of 50 represent the most sedentary segment of the adult population
. But with exercise referral the reverse seems to be the case and our finding of an association between older age and adherence in this scheme concurs with other studies
[7, 9, 17, 27]. A number of factors are thought to explain this – older people are less time-constrained, more likely to value the social interaction offered by the group based approaches, and may find it easier to incorporate the scheme exercise activities (such as walking, swimming and cycling) into their everyday life. Whatever the reasons, the finding suggests that age remains a consistent predictor of adherence over both the short and longer term. Other evidence from a study in the Netherlands among older (>50 years) participants found that the occurrence and duration of lapses in attendance, the intention to continue participation, the perceived quality of the exercise programme, and baseline attitude were also important factors in the maintenance of exercise participation
With other social determinants such as gender, ethnicity and deprivation, effects on exercise referral uptake and attendance have yet to be firmly established. In some studies ethnicity was not reported
, while in others the effect of socioeconomic deprivation on referral uptake was inconsistent
[7, 20, 22]. One explanation for the weak evidence may be that schemes operate in different social and environmental contexts and so are not strictly comparable. Our study did not find these factors to have any impact on longer-term adherence.
Another association we identified was with clinical condition. Compared to people with metabolic conditions (diabetes, hyperlipidemia, obesity, hyperthyroidism and hypothyroidism) who were the largest group and used as the reference category, the odds of longer-term adherence were significantly lower for participants referred with orthopaedic (arthritis, back pain, osteoporosis, fibromyalgia and other bone/musculoskeletal disorders), cardiovascular (myocardial infarction, coronary artery bypass graft surgery and coronary angioplasty, angina and silent ischemia, atrial fibrillation, chronic heart failure, peripheral arterial disease and hypertension) and other conditions (neuromuscular, sensory, miscellaneous complaints). Research investigating the association between the clinical reason for referral and attendance at ERS has highlighted higher rates of attendance in participants with serious cardiovascular conditions
 and lower rates in people who were overweight/obese or had a respiratory or mental health condition
[17, 21, 29]. Functional limitation, perceived seriousness of the problem and low self motivation are among the explanations underpinning differing rates of adherence in these groups.
Although our interest was in biosocial explanations for exercise adherence behaviour, the design features of schemes have also been demonstrated to influence adherence. Research has highlighted the link between higher attendance and the flexibility of the scheme, activities tailored to participants’ interests and capabilities, convenient timing, friendly and supportive staff, a wide range of activities, ‘break’ periods and activities that fit easily into everyday life such as such as walking, swimming and cycling
[4, 30, 31]. Characteristics of the referrer are also important as participants referred from cardiac and practice nurses had higher levels of adherence than participants referred by general practitioners