Diabetes mellitus is a chronic, metabolic disorder characterized by hyperglycemia as a result of a defect in insulin secretion and/or insulin resistance . In 2000 the worldwide prevalence of diabetes mellitus was 171 million. This is expected to increase up to 366 million in 2030 . Approximately 90% of the people with diabetes mellitus have type 2 diabetes mellitus (T2DM) .
T2DM often results in (severe) micro- and macro-vascular complications, such as cardiovascular problems, retinopathy, neuropathy and kidney failure . Approximately 72% of the people with T2DM have at least one of these complications . Besides the burden for the patient, this also imposes a burden on the health care system: people with one or more micro- and/or macro vascular T2DM complication(s) cost 70-350% as much a year compared to patients without T2DM complications . In addition, global mortality attributable to diabetes was estimated to be 2.9 million people in 2000, 5.2% of all deaths .
Physical inactivity is one of the major risk factors for T2DM and related complications, independent of body mass index (BMI) [6–8]. Increasing physical activity reduces the risk for T2DM and its complications by enhancing metabolic control. Moreover, appropriate levels of physical activity are associated with increased cardio-respiratory fitness, increased health related quality of life and a reduced risk of total- and cardiovascular mortality [9–11]. The American Diabetes Association advises people with T2DM to have at least 150 min/week of moderate-intensity aerobic physical activity (50–70% of maximum heart rate) to maximize the effects of physical activity. In addition, resistance training should be performed three times per week in the absence of contraindications .
Because of its beneficial effects, achieving and/or maintaining an appropriate level of exercise is an important goal in diabetes management . Despite, it is estimated that only 30-40% of people with T2DM are sufficiently active [13, 14]. This percentage appeared to be stable in recent decades  and is significantly lower compared to people without T2DM [13, 16]. Physical activity levels might be increased by means of an exercise intervention. Several intervention elements are thought to increase the success rate of such an intervention. To start with, an exercise intervention should imply more than just education . In addition, a patient-tailored exercise plan optimises the effect of the intervention and can increase adherence to the exercise routine [18, 19]. A gradual increase of physical activity  can avoid injuries. Also, the use of multiple behavioural components such as goal-setting, problem solving and feedback can further increase the (long-term) success of the intervention . In addition, the American College of Sports Medicine and the American Diabetes Association advised in their 2010 joint statement on Exercise & Diabetes to focus exercise interventions on self-efficacy .
Self-efficacy is derived from the Social Cognitive Theory, which states that a behavioural change is made possible by a personal sense of control. Self-efficacy is one of the main constructs of this theory and is the “belief in one’s capabilities to organize and execute the courses of action required to produce given attainments” . Self-efficacy for exercise/physical activity (exercise self-efficacy) is believed to influence physical activity behaviour [22–24]. In people with T2DM a high level of exercise self-efficacy is thought to be predictive of exercise initiation and maintenance over time , and is thought to mediate the relationship between an exercise intervention and physical activity . Also, an increased level of exercise self-efficacy makes it more likely that participants indeed use strategies to improve their physical activity levels .
A patient-tailored exercise intervention with a gradual increase of physical activity and multiple components such as goals setting, has the potential to increase the physical activity level of people with T2DM. This can be provided by means of several individual physiotherapy consultations in which a patient tailored exercise plan is provided and progression evaluated. Because of its important predictive and mediating role, exercise self-efficacy has the potential to discriminate between subjects who can be helped with such individual physiotherapy consultations, and those who are in need of extra support because of their low exercise self-efficacy. Extra support can be given by providing an additional group-based program. A group-based program gives room to verbal persuasion by the physiotherapist and/or group members and vicarious experiences which are sources of self-efficacy  and can therefore increase the level of exercise self-efficacy.
Objectives and hypotheses
The goal of this study is to evaluate a patient-tailored exercise program for people with T2DM that takes levels of exercise self-efficacy into account. If the program succeeds in increasing the amount of physical activity it can be implemented in regular Primary diabetes care.
The primary outcome measure of this study is physical activity. We hypothesize that the intervention will significantly increase the level of physical activity in the intervention groups compared to the control group. In addition, we will examine which determinants contribute to a successful change of the amount of physical activity. Most literature seems to agree that a high age [15, 16, 22, 29, 30], low education [15, 22, 30] and being female [16, 22, 30], are associated with a lower level of physical activity. Although a higher BMI seems to correlate with physical activity among adults , the results of studies on people with T2DM are conflicting [13, 15, 29]. In addition a low exercise self-efficacy , low social support , a depressed mood  and a type D personality  are thought be determinants of a low level of physical activity. We therefore hypothesize that a young age, high education, being male, low BMI, a high level of exercise self-efficacy, a high level social support, the absence of a depressed mood and not having a type D personality contribute to a successful change of the level of physical activity.
Secondary outcome measures are health status, (symptoms of) depression, exercise self-efficacy, BMI, blood pressure and glycemic control.
In line with the Look AHEAD trial  and the DARE study  we hypothesize that our intervention will significantly improve the physical component of health status - but not the mental component-, compared to the control group.
In two systematic reviews [35, 36] on the effects of physical activity on depressive symptoms in elderly people, it was found that increased levels of exercise can lower depression rates and reduce depressive symptoms in the short term. In accordance, we therefore hypothesize that the intervention of the current study will significantly reduce depressive symptoms, compared to the control group.
The intervention is thought to provide participants personal mastery experiences which is a source of self-efficacy . We therefore hypothesize that the intervention will significantly increase exercise self-efficacy, compared to the control group. We additionally hypothesize that the change of exercise self-efficacy will be larger in those with low exercise self-efficacy at baseline as they will receive additional support.
Glycemic control is assessed by means of haemoglobin A1C. As physical activity is thought to improve glycemic control [37–39] we hypothesize that our intervention will significantly reduce haemoglobin A1C, compared to the control group.
Based on literature, an effect of increased physical activity on body mass or BMI can not be expected [37, 38]. We therefore hypothesize that the intervention will not lead to significant decrease in BMI, compared to the control group.
Literature on the effect of physical activity on blood pressure is somewhat ambiguous. In the review of Thomas et al. no effect on diastolic of systolic blood pressure was found. The American College of Sports Medicine and American Diabetes Association concluded in their joint statement on Exercise and Diabetes that only slight reductions of systolic blood pressure can be expected . However, in a meta-analysis by Snowling et al. small to moderate effects of aerobic or a combination of aerobic and resistance exercise on blood pressure were found. We therefore hypothesize that the intervention of the current study will significantly reduce systolic blood pressure in those with an elevated blood pressure, compared to the control group.
Finally, diabetes self-efficacy and quality of sleep are explorative outcome measures. We therefore have no hypotheses regarding these outcome measures.