By Nick Pereira, MSc. Sports and Exercise Physiotherapy Candidate, University of Cape Town. Division of Physiotherapy & Exercise Science and Sports Medicine Division, Sport Science Institute of South Africa.
Diabetes type 2 (DM 2) is a non-communicable lifestyle disease which affects more than 422 million people worldwide (Seib et al., 2018). The global prevalence is 8.3% and is expected to rise to 10.1% by 2030 (Namadian, Presseau, Watson, Bond, & Sniehotta, 2016). Diabetes is a chronic metabolic condition, characterized by elevated blood glucose levels. DM 2 results from the body’s ineffective production, or use of insulin which is a mechanism by which blood glucose levels become elevated. If the blood glucose remains chronically high and uncontrolled, a state of hyperglycemia occurs which can have detrimental long term effects for the heart, blood vessels, eyes and nerves (Namadian et al., 2016). There are modifiable and non-modifiable risk factors for DM 2 with known genetic predispositions being affected by obesity, smoking, physical inactivity and poor dietary choices (Sbroma Tomaro et al., 2017). The term “Exercise Resistance” is another genetic contributor to the condition of DM 2. It has been described in the literature as the lack of clinical improvement in DM 2 patients after exercise intervention, due to inefficient cellular oxidative capacity, and mitochondrial content (Dutton, Provost, Tan, & Smith, 2008). It is evident that there is a genetic predisposition to the disease, as well as a genetically predetermined response to potential treatment. These examples highlight the complexity of considerations for clinicians when treating individuals with this non-communicable disease.
There are numerous comorbidities associated with DM 2 which have varying severity including: cardiovascular disease, kidney and nerve damage, amputation due to diabetic neuropathy and premature death (“Exercise and type 2 diabetes: American College of Sports Medicine and the American Diabetes Association: Joint Position Statement,” 2010). The economic burden of DM 2 is estimated to be $1.3 Trillion USD in 2015 and has been ranked in the top four non-communicable diseases to be addressed by the World Health Organization’s (WHO) global action plan for the prevention and control of non-communicable diseases (NCD) (Seib et al., 2018).
The diagnosis of DM 2 is recommended by the American Diabetes association with the following four clinical markers: Gylcated Hemaglobin; Fasting plasma glucose; 2-h plasma glucose; and the classic symptoms of polyuria, polydipsia and unexplained weight loss (“Exercise and type 2 diabetes: American College of Sports Medicine and the American Diabetes Association: Joint Position Statement,” 2010). Many of the studies reviewed in this paper refer to glycated hemoglobin as a direct clinical marker for measuring response to various exercise modes due to its relationship to long term glucose control. Other clinical markers noted in the literature, although sometimes indirect include: Maximum oxygen capacity (VO2 Max), abdominal fat, lean muscle mass, body mass index and fasting insulin levels (Seib et al., 2018).
There is large evidence to show that the burden this lifestyle disease carries is immense. There is growing emphasis on treating chronic diseases early to avoid associated sequalae (Reed & Pipe, 2016). Exercise prescription coupled with lifestyle interventions, behavior modification, education and have been shown to manage this disease in the individual (Seib et al., 2018). However, prescriptions and educational mediums that show the greatest improvements have not been agreed on unanimously (“Exercise and type 2 diabetes: American College of Sports Medicine and the American Diabetes Association: Joint Position Statement,” 2010). Treating DM2 is a multifaceted approach and requires structured physical activity, education, medication, self-efficacy and exercise prescription – this paper will explore current considerations relating to exercise prescription in the management of DM 2.
The Role of Exercise in the management of DM 2:
It has long been established in the literature that medication, lifestyle changes and exercise are all components of treating DM 2 (Zanuso, Jimenez, Pugliese, Corigliano, & Balducci, 2010). DM 2 is a disease of lifestyle and adults with this pathology often report low levels of physical activity with little to no participation in exercise. Adults with DM 2 also report more barriers to exercise and have greater risk of relapse to sedentary behavior than adults without DM 2 when involved in exercise programs (Schneider et al., 2016). Adherence of the DM 2 population to exercise interventions has been shown to be poor because of variables such as self-efficacy, motivation and other psychological parameters (Wisse et al., 2010). These are generally not accounted for by the literature researching exercise adherence in this population, although it is a key element to the success of the intervention (Dutton et al., 2008).
Aerobic Exercise and DM 2:
Aerobic exercise is a long-standing exercise mode which operates on the premise of improving cardiovascular fitness by increasing the body’s capacity to use oxygen. It performs this by improving the hearts capacity to send blood by essentially strengthening it, allowing for improved efficiency of blood moved by the heart as a pump – this is often referred to as cardiorespiratory fitness. This efficiency can be seen by the heart rate being lowered at rest or lowered during exercise at previously challenging intensities. In DM 2, the link between aerobic exercise and insulin sensitivity increasing has been made in the literature and it is widely accepted that aerobic exercise improves Diabetes Melitus (DM) markers such as glycated hemoglobin and fasting glucose levels (Zanuso et al., 2010). During moderate exercise intensity, individuals with DM 2 exhibit blood glucose uptake in the muscles which exceeds the rate of hepatic glucose production – this causes blood glucose levels to decline. Plasma insulin levels also lower during this imbalance which makes the risk of plasma induced hypoglycemia minimal in patients not using exogenous insulin. Aerobic exercise has been shown to increase insulin effect and glucose tolerance for more than 24h but less than 72h (“Exercise and type 2 diabetes: American College of Sports Medicine and the American Diabetes Association: Joint Position Statement,” 2010)
It has been shown that DM 2 patients have the potential to improve at the same rates to aerobic exercise as matched control patients without DM 2, with regards to improvements in VO2 Max capacity and cardiorespiratory or aerobic fitness (Boulé, Kenny, Haddad, Wells, & Sigal, 2003). The discussion around the benefits of aerobic exercise, leans more towards the intensity of exercise being beneficial in showing positive changes in DM 2 markers. A 2010 meta-analysis concluded that aerobic exercise, when performed at higher intensities, showed reduced glycated hemoglobin, increases in VO2 max, and improved insulin sensitivity (Zanuso et al., 2010). The following study protocol has shown significant improvements in markers of DM 2, and can be used as a guideline in aerobic exercise prescription which encompasses both moderate and vigorous intensity aerobic exercise.
(Mourier et al., 1997).
Pre-training period of 2 weeks with 3 training sessions per week erg cycle at 75% VO2
Training period of 8 weeks of aerobic and interval training.
Aerobic consisting of 45 mins of erg cycling at 75% VO2 Max (twice per week)
Interval training alternating 5 sets of 5 minutes 85% VO2 max and 3 minutes of 50% V02 max. (once per week)
This protocol resulted in a clinically and statistically significant improvement of glycated hemoglobin, VO2 max and decrease in abdominal fat measurements.
Resistance Exercise and DM 2:
There are various types of resistance exercise studied and compared in the literature, namely: “circuit training”, “progressive resistance training” and “resistance training”. Resistance exercise has been studied in relation to DM 2 for several years, with initial results not showing changes to glycated hemoglobin, but rather to the comorbidities of DM 2, such as Low-density lipoprotein (LDL) cholesterol and fasting triglycerides. There have been links from various studies connecting increase in insulin sensitivity with an increase in lean muscle mass, brought on by resistance training (Ibañez et al., 2005). There is debate though whether the improved glucose markers seen with resistance training is due to decrease of subcutaneous adipose, increase of lean muscle (thus improved glucose uptake) or the change in quality of skeletal muscle (short term) (Zanuso et al., 2010). Three major randomized control trials suggest that the effects of resistance training are comparable to aerobic training with regards to changes in glucose control in DM 2 individuals.
The advised prescription of resistance training in DM 2 based on current evidence is as follows:
(Baldi & Snowling, 2003)
10 exercises to be performed at three supervised sessions per week: 10 Repetition Maximum (RM) Upper body; 15 RM lower body. Weight progressions of 5% increases per week for 10 weeks.
(Dunstan et al., 2002)
9 exercises to be performed at three non-consecutive sessions per week: Weeks 1-2, 50%-60% of 1RM; Weeks 3-26, 75%-80% 1RM, 8-10 reps for 26 weeks
(Castaneda et al., 2002)
5 exercises to be performed three times per week:
Week 1-8, 50-70% of 1RM 3 x 10-15.
Week 9-16, 70-80% 1RM 3-5 reps.
The next step would be to take the merits of aerobic exercise and resistance training, and combine them into an intervention. With regards to the best evidence based prescription of the combination of these exercise modalities, the protocol used by Balducci et al showed most significant improvements in metabolic, lipidic profiles, adiposity and blood pressure and it took place over an entire calendar year. In the study, glycated hemoglobin had significant reductions and fat free mass increased. Fasting blood glucose, LDL cholesterol and total cholesterol decreased while High Density Lipoprotein cholesterol increased.
(Balducci, Leonetti, Di Mario, & Fallucca, 2004).
56 Weeks, 6 exercises (including resistance and aerobic exercises) were performed three times per week.
Resistance training 40-60% of 1RM 3 sets of 12 reps. Aerobic training at 40%-80% of Heart Rate Reserve.
Clinical considerations for prescribing exercise:
The prescription of exercises for individuals or groups who require intervention is challenging. Though some of the most significant studies in this field have been highlighted above, the art of prescription is often matching the evidence to the needs or situation of the individual. There are no blanket fixes or recipes for results. This NCD is one of lifestyle and it therefore makes sense that an intervention of the lifestyle is needed to address the disease. Management approaches are multifactorial and although the exercises prescribed above show clinically significant results in research, there is often no mention of diet, or psychological determinants like self-efficacy and motivation to adhere to exercises and lifestyle interventions in the literature.
Measurements of exercise intensity are important to ensure that the intervention is in line with evidence based guidelines for exercise prescription. In the literature, HR and VO2 Max are the gold standards for measuring exercise intensity. The equipment required to have these monitored in everyday practice is impractical. The following tools are recommended when monitoring exercise intensity. Rate of perceived exertion (using the Borg scale of exertion); the talk test; and wearable technology (activity trackers, smart watches with heart rate monitoring function). (Reed & Pipe, 2016). Heart rate targets can be set using the Fox formula of 220-age to gauge maximum heart rate and subsequent training zones can be calibrated from that figure. It is important to recognize the various external and internal factors which will affect the heart rate seen such as caffeine ingestion, humidity, stress and medication (Reed & Pipe, 2016). The Borg scale is a validated measure of perceived exertion which scores exercise intensity from 6 (no exertion at all) to 20 (very, very hard) (Reed & Pipe, 2016). The talk test is another practical way to measure exercise intensity. When literature describes exercise intensity as ‘moderate’ or ‘vigorous’ the talk test suggests that when a comfortable conversation cannot be maintained during exercise the individual has entered the state of vigorous exercise (Reed & Pipe, 2016).
There may be multiple barriers to be addressed before the actual physical intervention may take place. Barriers to exercise such as cultural beliefs, social and economic factors and psychological considerations need to be viewed in context to approach the individual with the greatest efficacy (Namadian et al., 2016).The physical condition of the DM individual needs to be considered when prescribing exercise – many of them will not have undertaken regular exercise and it is important to conduct screening tests before the prescription of exercise can be undertaken. The American Heart association recommend a treadmill stress test for anyone who has comorbidities of heart disease, and the American diabetes association recommend pre-exercise stress test for any individuals who have had diabetes for ten years or longer (“Exercise prescription for diabetes,” 2009).
It has been shown in the literature that compliance to prescribed exercise regimes is poor even with what would be deemed ‘sufficient’ support (Wisse et al., 2010). The authors performed a two-year study, with a supervised exercise program which involved a structured exercise program with telephonic and supervised follow ups by therapists yielded non-significant outcomes for physical activity levels, glycated hemoglobin and insulin sensitivity.
The psychological component of adherence and consequent considerations for exercise prescription should include behavior and comorbidities such as depression (Schneider et al., 2016). Motivation towards exercise and the nature of a lifestyle change can cause poor compliance to any intervention. Behavioral activation can be used as a strategy that teaches awareness of daily activities on mood and can be applied to create lasting changes in attitudes towards exercise and lifestyle modifications in the management of DM 2. (Schneider et al., 2016).
The lifestyle interventions required to have a significant impact on the disease process in the DM 2 individual includes education, modifications to diet, beliefs on exercise, self-efficacy and insight into the progression of the disease if not managed appropriately (Chen et al., 2015). This requires more than just one professional in isolation to address all the components of the disease. Exercise and its prescription is a well-researched intervention for DM 2 and has multiple positive effects in the life of a DM 2 individual. Although the intervention is multi-faceted, with thoughtful consideration, support and collaboration with other health care and exercise professionals, this NCD can be addressed and positive, long-term changes can be made to the health and lives of individuals with DM 2.
Nick is a exercise and health advocate ,a contributor to Men’s Health Magazine, South Africa – as well clinical practitioner and lifelong student of exercise and nutrition.
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