The significance of resistance training and psychobiology in primary prevention of Type 2 diabetes among people with impaired glucose tolerance

The aim of this thesis was to examine the importance of physical activity in individuals with impaired glucose tolerance (IGT) and, therefore, at risk of developing Type 2 diabetes. Also, factors were identified that could have motivational significance for lifestyle change to improve glucose tolerance and, consequently, reduce the risk of having Type 2 diabetes. Methods were adopted including qualitative and correlational research as well as experimental manipulation. One specific purpose of the study was to compare the effects of maximal resistance training (MRT) versus endurance resistance training (ERT) upon blood glucose and insulin levels as well as cortisol and changes in upper leg skeletal muscle area, overall body fat and body mass index (BMI) in a sample of individuals with IGT. One aspect of the thesis investigated some psychological predictors and consequences of biological and clinical effects due to resistance training.In Paper 1 (Hansen, Landstad, Gundersen, & Svebak, 2012), the aim was to investigate the relative importance of aerobic capacity, physical activity and body weight (BMI) in people with IGT and Type 2 diabetes, and to compare these variables across groups including also healthy controls. The variables counted responses to questions on self-reported physical activity and scores on VO2-max by walking the UKK walking-test (Laukkanen, Oja, Ojala, Pasanen, & Vuori, 1992) (see method section of Paper 1). The participants were recruited into groups of IGT, Type 2 diabetes and controls (total N=64). Statistical analyses were performed by multifactor ANOVA and logistic regression. Obesity, as indicated by BMI (p = .004, OR = > 16.00), was most evident in the IGT and Type 2 diabetes groups. BMI was significantly associated with aerobic capacity in the IGT group. The results supported that primary health care in this area should focus on physical activity and weight reduction to prevent escalation into Type 2 diabetes.Paper 2 (Hansen, Landstad, Hellzen, & Svebak, 2011) aimed at identifying factors that could have motivational significance for lifestyle change to facilitate improved glucose tolerance among individuals with IGT. The qualitative approach reflected assumptions in the Health Belief Model (HBM: Rosenstock, 1974). The HBM assumes that individuals will take health-related actions provided they believe negative health effects can be avoided and they have faith in their own ability to implement relevant actions. Semi–structured interviews started with an open question: What motivated you to consider making health related lifestyle changes by participating in an instructed, controlled, physical strength exercise program? Thereafter follow-up questions probed into rhythm of the day, meals, life in general, social network, reactions from family and friends, physical activity and health and sickness, depending upon the flow of the dialogue. The interviews were analyzed according to a manifest content analysis method. Four motivational factors for the promotion of lifestyle change were identified as (1) structure and rhythm in everyday life, (2) sickness concerns, (3) level of daily activity, and (4) social relations.Paper 3 (Hansen, Landstad, Gundersen, Torjesen, & Svebak, 2012) compared the effects of MRT versus ERT on improvements in blood glucose tolerance, insulin and cortisol levels in overweight individuals at risk of developing Type 2 diabetes. Eighteen participants with baseline values suggesting IGT were randomly assigned to one of two groups. Group 1 engaged in supervised MRT (Bernstein (2007) inverted pyramid system: 5 x 3-4, 60-85% 1 RM), three days/week over four months while members of Group 2 acted as waiting list controls. Later, Group 2 engaged in supervised ERT (3 x 12-15, 45- 65% 1 RM), three days/week over a four months period with the two prebaselines as controls. Both interventions consisted of eight exercises that included the entire body. Glucose (fasting and 2-hour test), insulin and C-peptide measures were assesed from pre to post in both groups. MRT led to reduction in blood levels of 2-hour glucose (p = .044) and fasting C-peptide (p = .023) as well as decreased insulin resistance (p = .040). The ERT caused a significant reduction in the blood levels of insulin (p = .023) and concomitant positive effects on % insulin sensitivity (p = .054) and beta-cell function (p = .020). The findings indicate that both MRT and ERT lead to decreased insulin resistance in people with risk of developing Type 2 diabetes. The MRT appeared to cause a greater increase in glucose uptake capacity (in muscles), whereas ERT led to greater insulin sensitivity, supporting a recommendation of both MRT and ERT as primary intervention approaches for individuals at risk of developing Type 2 diabetes.The purpose of objectives in Paper 4 (Hansen, Landstad, Bronn, Gundersen, & Svebak, 2011) were to compare effects of maximal resistance training (MRT) versus endurance resistance training (ERT) on body fat and muscle mass in overweight people at risk of developing Type 2 diabetes. Dependent variables included changes in body fat after controlling for age and gender, upper leg skeletal muscle area (left + right), BMI and body weight pre-to post intervention. Eighteen individuals, 33-69 years of age, were randomly assigned to one of two groups. Group 1 engaged in MRT three days/week over a four months period while members of Group 2 acted as controls. Later, Group 2 engaged in ERT three days/week over a four months period, and the members acted as their own controls (two pre-baseline reference values). Both interventions consisted of eight exercises. Pre- to post changes were significant for MRT with a reduction in BMI (p = .013) and body weight (p = .010), whereas percentage of body fat was significantly reduced (p = .009) and skeletal muscle area increased (p = .021) with ERT. Again, the results supported both approaches as interventions in primary prevention to reduce the risk among individuals with IGT to develop Type 2 diabetes.Paper 5 (Hansen, Gundersen, & Svebak, submitted for publication) investigated the association of psychological characteristics and changes with biological and clinical effects of resistance training in primary prevention of Type 2 diabetes. Improved quality of life tended to be associated with reduction in percent fat following MRT, whereas changes in quality of life were associated with beneficial changes in fasting glucose, insulin, muscle mass and BMI following ERT. Also, sense of humour tended to increase when BMI was reduced. Moreover, stressrelated psychological changes were associated with biological and clinical changes following ERT. Reduction in fasting glucose was most prevalent among those who increased their positive moods and who also reported small changes in levels of stress from before to after intervention. Interestingly, reduction in perceived stress (PSS) after treatment was relatively marked among those who reduced their blood cholesterol and body fat scores after ERT.In closure, favorable effects of resistance training were observed in the biological, clinical as well as psychological variables. Lasting lifestyle changes rarely result as an immediate consequence of verbal advice from health professionals. Lifestyle changes take time and must be adapted to the individual in light of their social as well as educational and economic settings. Follow-up through coaching, practical support, assistance in the creation of structure in everyday life and facilitation of networks with peers appear to be important if sustainable changes are to take place at all three levels. MRT should be recommended when the target is to reduce BMI and body weight as well as to increase glucose uptake. ERT appeared to be preferable when the target is to reduce corrected % fat and to increase muscle area as well as insulin sensitivity. And ERT yielded the most extensive beneficial psychobiological changes over the treatment period.The conclusions presented here are based upon results related to medical (biological, clinical) and psychological effects of experimental intervention in individuals at risk of developing Type 2 diabetes, and measures included laboratory tests, clinical measures, self-report questionnaires and interviews. The findings should be replicated in larger samples in order to increase the external validity of the findings.