Review
Resistance training improves metabolic health in type 2 diabetes: A systematic review

https://doi.org/10.1016/j.diabres.2008.11.024Get rights and content

Abstract

This paper systematically reviews the effect of resistance training (RT) on glycemic control and insulin sensitivity in adults with type 2 diabetes.

Twenty studies were included, with the volume, frequency and intensity of RT varying markedly. Supervised RT improved glycemic control and insulin sensitivity, however, when supervision was removed compliance and glycemic control decreased. Evidence indicates the mechanisms behind the improvements to glucose tolerance require further elucidation.

Although research demonstrates apparent benefits of RT for individuals with diabetes, further research is required to elucidate the minimum effective dose by describing frequency, intensity and the duration of acute and chronic improvements.

Introduction

The world-wide incidence of type 2 diabetes continues to increase [1] however, despite exercise being promoted as a vital part of the treatment process, exercise prescription does not vary between prevention and treatment. For individuals with existing diabetes, specific benefits of exercise include increased insulin sensitivity, improved glycemic control [2], [3], improved lipid profile and lower blood pressure [3]. Importantly, individuals with diabetes completing exercise training using various exercise modes for between 8 weeks and 12 months have experienced decreased HbA1c by clinically significant levels (0.6%), improved insulin sensitivity and reduced serum triglycerides [4].

The American College of Sports Medicine (ACSM) endorses exercise as a treatment method for people with type 2 diabetes and currently recommends expending a minimum cumulative total of 1000 kcal/wk of energy from aerobic activities [5]. The American Diabetes Association (ADA) has similar recommendations for at least 150 min per week of moderate intensity aerobic physical activity and/or 90 min per week of vigorous aerobic exercise [6]. Accordingly, aerobic exercise has been the major focus for exercise-training studies due to consistent findings of improved glucose control [7], [8], however long-term compliance to these recommendations remains low [9] necessitating the investigation of an effective strategy to improve adherence rates.

More recently, resistance training has been the focus of increased research and is suggested to improve glycemic control and insulin sensitivity partially via similar mechanistic pathways to aerobic training [10], and partially through discrete pathways providing additive insulin signalling benefits. The focus on resistance training is in part due to a recognition that individuals with type 2 diabetes, who are also likely to be obese or suffering from other co-morbidities, are likely to struggle to achieve the volume and intensity of aerobic training that is required to be effective [10], [11], and therefore compliance to resistance training may be higher. Both the ACSM and the ADA have now included resistance training in their exercise prescription guidelines for younger individuals with type 2 diabetes and for older individuals with type 2 diabetes free of contraindications. The recommendations are; one set of 10–15 repetitions for 8–10 exercises twice a week [5] and, progressing to three sets of 8–10 repetitions three times a week [6]. These recommendations have largely been based on information regarding healthy individuals and the few [12], [13], [14], [15] randomized controlled trials of resistance training in individuals with type 2 diabetes completed at the time that they were published. However, it should be noted that significant improvements to insulin sensitivity in healthy individuals have been reported only when resistance training was performed three or more days a week [16] and the responses of individuals with diabetes may differ. It is therefore the purpose of this paper to systematically review the literature on the effects of resistance training on the diabetes markers of glycemic control and insulin sensitivity in individuals with type 2 diabetes.

Section snippets

Search strategy

Ovid MEDLINE (1950 to August week 3, 2008), Ovid MEDLINE In-Process (September 02, 2008), OLD MEDLINE (1950–1965), CINAHL (1982 to August week 5, 2008) and EMBASE (1980 to 2008 week 35) electronic databases were searched on September 03, 2008. First, three keyword and categorical searches were performed (i) ‘diabetes’, or ‘diabetes mellitus’, or ‘type 2 diabetes mellitus’; (ii) ‘weight lifting’, or ‘resistance training’, or ‘strength training’, or ‘weight training’, or ‘progressive resistance

Search results

Twenty-four papers from 20 studies met the criteria and are included in this review. Search results are shown in Fig. 1. One doctoral dissertation was excluded, but its related publication identified and also excluded [17]. A paper reporting insulin sensitivity data was excluded [18] as this data had been published previously [19]. A paper reporting phase one of a study [14] was excluded due to having a weight loss diet added to the resistance training, however a paper describing phase two [20]

Resistance training for type 2 diabetes

Within the included studies, RT was almost always completed using machines, including pin-loaded machines (20/24 papers), with some studies incorporating the use of free-weights [15], [23], [24], [25], [30], [32], [37] (Table 2). Two studies varied the delivery of RT using circuit-type training [15], [36]. A whole-body training protocol, mostly progressive in nature where the weight lifted, or sets and repetitions completed increased at varying stages was favoured by most researchers (19/20

Glycosylated haemoglobin

Glycosylated haemoglobin (HbA1c) is considered the optimal way of measuring long-term (120 days) glycemic control [41], with HbA1c values of <7.0% accepted as representing good glucose control [41]. Nine RCT's reported HbA1c data (Table 3), with two studies [13], [22], [24], [26] reporting HbA1c reduced by 1.0–1.2%, from above 8.0% prior to 16 weeks of moderate-high intensity training. Baldi and Snowling [12] showed an improvement over the intervention period which approached significance (P = 

Euglycemic–hyperinsulinemic clamp

Although considered the gold-standard for determining insulin sensitivity levels [42], only two studies used the euglycemic–hyperinsulinemic clamp [19], [30]. Holten et al. [19] reported that despite individuals with diabetes having significantly lower glucose disposal rates (GDRs) and therefore greater insulin resistance than controls, leg glucose clearance rates increased during the second stage of the euglycemic–hyperinsulinemic clamp, showing that improvements are achievable with RT despite

Insulin signalling

Only two studies reported data on glucose transport and insulin signalling in individuals with diabetes [19], [29], [34] with one of these being a RCT [29]. Improved glucose disposal, as measured by incorporation into muscle glycogen, support findings using the euglycemic–hyperinsulinemic clamp [19], [29]. Changes in the glucose transporter-4 (GLUT4) are less clear with an earlier study [19] reporting a 40% increase (P < 0.05) in GLUT4 density compared to a more recent study [29] reporting no

Muscle strength

Ten papers from seven RCT's reported muscle strength data (Table 4), with all but one study [25] reporting improvements of at least 50% after completing RT. The study [25] reporting a decrease (P < 0.05) in strength after RT, reported small losses after 12 months of a home or leisure-centre based maintenance program following on from a 2-month supervised intervention period, although only lower body strength in the home-based group decreased below baseline, and was likely to be due to not being

Lean body mass

Lean body mass (LBM) was measured by dual energy X-ray absorptiometry (DXA) in four studies [13], [20], [22], [30], [40] including two RCT's [13], [20], [22], or estimated after accounting for fat mass in a further six studies [12], [24], [25], [27], [32], [33], [37] including four RCT's [12], [24], [25], [27], with one study [23] not specifying the method used (Table 4). Results varied, with significant LBM increases of 3–6 kg with RT [12], [23], [24] and 2 kg with AT [23]. Two studies reported

Lipid profile

Blood lipids were reported in nine studies with general improvements in total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol and triglycerides reported after RT (P < 0.001; P < 0.01) [24], [36], [40].

Blood pressure

Blood pressure was measured in 10 studies. Three studies reported beneficial changes in systolic blood pressure associated with all forms of training [13], [21], [24]. Improvements to diastolic blood pressure were less frequently observed, but still occurred over

Discussion

Individuals with diabetes are able to complete RT with minimal risk of negative health outcomes or injury, while improving overall glycemic control, insulin sensitivity and muscular strength. Overall, the quality of study design was good with 13 papers reporting on 10 RCT's, of which all but three were published since 2005. The major findings from these studies are that completing RT, and AT over extended durations will result in similar improvements to glycemic control [23], [27]. However, RT

Conflict of interest

The authors declare that they have no conflict of interest.

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