At the medical clinic where I work as an exercise physiologist, a patient came to see me; let’s call him John. He was healthy, but his fasting blood glucose levels were high. He was in his mid-40s and had low muscle mass. John was not on medication and wanted to avoid it. He asked my advice.
John was like 54 million U.S. adults aged 40–71 who have prediabetes and/or insulin resistance. His muscles were resisting the action of insulin, which regulates blood sugar in the body. And if he stayed the course, he was on his way to full-on type 2 diabetes.
It’s a global challenge. One projection says that type 2 diabetes will affect 600 million people worldwide by 2035 (Pesta et al. 2017). And it’s no surprise that this estimate is so high. We lead sedentary lifestyles, with rising rates of obesity and an aging population—the three primary risk factors for type 2 diabetes (Colberg et al. 2010). We can’t fix the age factor, but we can modify lifestyles to reduce the risks.
This upcoming epidemic obliges personal trainers to prepare for more clients at risk of type 2 diabetes. Fortunately, a growing body of evidence supports resistance training as a way to manage or prevent the disease. Read on for tools and tips that will give you the confidence to explain the importance of resistance training and to design an exercise routine for a client with diabetes or prediabetes.
Type 2 Diabetes: The Basics
Type 2 diabetes represents 90%–95% of diabetes cases. People with prediabetes may not feel that anything is wrong, and even with full-blown diabetes, early symptoms can be mild enough that they go unnoticed. Thus, a lot of cases of diabetes and prediabetes are undiagnosed. Diabetes has to be determined by a blood test (ADA 2016).
With type 1 diabetes, the body produces no insulin, so it must be injected. With type 2, the body produces insulin but still has trouble controlling blood sugar, also called glucose.
To confirm a diabetes diagnosis, doctors look for one of these four criteria:
- glycated hemoglobin A1c (HbA1c) at 6.5%
- fasting blood sugar over 126 milligrams per deciliter (7.0 millimoles per liter)
- 2-hour oral glucose tolerance test over 200 mg/dL (11.1 mmol/L)
- symptoms of high blood glucose, which can confirm the diagnosis (ADA 2016)
Research has found that the skeletal muscles of people with type 2 diabetes have metabolic dysfunctions like insulin resistance, lipid accumulation, impaired glucose synthesis and weakened mitochondrial function. The good news is that exercise—especially resistance training—can reverse these dysfunctions (Strasser & Pesta 2013).
Progress Requires a Proper Diet
You must make this clear to clients: Just as they cannot lose weight without good eating habits, they cannot get their blood sugar under control without managing their carbohydrate intake. Consider this extreme example: Tim Noakes is an ultramarathon runner and coach who wrote the book Lore of Running (Oxford University Press 1985), which suggested using a high-carb diet to replenish energy stores. At one point, he realized he was gaining weight despite his training. (Note that we tend to overestimate the number of calories burned by exercise.) Noakes was soon diagnosed with type 2 diabetes. If he could not outrun his carb-heavy diet, who can?
For people with type 1 diabetes, insulin injections regulate blood glucose. For those with type 2, the insulin is there, but it’s failing at one of its most important duties: clearing the blood of excess glucose. The problem appears to be that muscle tissue becomes unresponsive to insulin. And since 70%–75% of insulin-stimulated glucose clearance happens at the skeletal muscle level, that seems like a good place to start examining this topic more closely (Jensen et al. 2011).
See also: Mindful Eating and Type 2 Diabetes
How Muscle Loses Insulin Sensitivity
Let’s look at what decreases a muscle’s sensitivity to insulin. Most glucose gets into muscle cells with the help of a glucose transporter (GLUT4). The stored form of glucose is glycogen, which has an inverse correlation to insulin sensitivity: The fuller our glycogen stores get, the more our muscles resist the action of insulin. Muscles basically act like Jack Nicholson’s character in the movie As Good As It Gets: “Go sell crazy somewhere else; we’re all stocked up in here.”
So, the first step to improving insulin sensitivity is reducing glycogen levels in muscle fibers (Jensen et al. 2011). And how do we make this happen? Muscle contraction.
Black, Swan & Alvar (2010) looked at the acute effect of one session of resistance training to observe how intensity and volume influenced insulin sensitivity. They compared four exercise bouts of varying volumes and intensities:
- Moderate Intensity, Single Set: 1 set at 65% of 1-RM (12–15 reps)
- Moderate Intensity, Multiple Sets: 4 sets at 65% of 1-RM (12–15 reps)
- Higher Intensity, Single Set: 1 set at 85% of 1-RM (6–8 reps)
- Higher Intensity, Multiple Sets: 4 sets at 85% of 1-RM (6–8 reps)
All the exercise bouts reduced fasting blood glucose 24 hours after training. Four sets at higher intensity had the best results. So, the more fibers you recruit and the more work you do, the bigger the effect.
Cassidy et al. (2017) reviewed the literature on how high-intensity interval training affects glucose control. They found that even one session of HIIT was slightly better at glucose control than energy-matched, moderate-intensity endurance exercise. That’s more evidence that higher intensities have a bigger effect on glucose control—probably because more muscle fibers need to be recruited.
How about the long-term effects of resistance exercise? The testing level of HbA1c represents average blood glucose for 3 months. Thus, long-term resistance training should reduce HbA1c.
An Australian study looked at the effects of 6 months of resistance training. Scientists found that a combination of weight loss and weight training reduced HbA1c three times more than weight loss alone (Dunstan et al. 2002). Weight loss does help create storage space in muscle fibers, but not as much as resistance training can. The answer lies in working the muscles hard enough to deplete glycogen stores.
Some studies have found that resistance training improves glycemic control more effectively than low-intensity endurance training. A review paper from Australia reported that lower-intensity activities may help mobility, but higher-intensity activity levels have a stronger influence on HbA1c levels (Scott, de Courten & Ebeling 2016). It makes sense, because resistance training uses more fibers.
Aging and Muscle Loss
Aging brings sarcopenia—gradual loss of muscle mass. As sarcopenia advances, lean tissue decreases, reducing the body’s capacity to store glucose and fuel physical activity. While lower muscle mass decreases physical activity, declining muscle quality contributes to insulin resistance, one of the prime symptoms of type 2 diabetes (Scott, de Courten & Ebeling 2016).
However, the sarcopenia process should not be considered definitive. Even though aging tends to reduce muscle mass, resistance training can counter this loss (Strasser & Pesta 2013). It’s possible that an increase in muscle mass is linked to improved glycemic control. It makes sense, since a muscle will store more glucose as it adapts to training demands.
Exercises to Fight Type 2 Diabetes
Let’s get back to John for a minute. I asked him about his exercise routine. He said he was on and off with it. At the gym, he did cardio and lifted weights, but only for his upper body. He felt the treadmill did enough for his legs. John was basically ignoring his biggest muscle mass. I suggested he add lower-body exercises to his routine, because that area has the largest glucose stores.
Another problem with type 2 diabetes is that it compromises the oxidative capacity of mitochondria, thereby reducing fat oxidation. This causes lipids to accumulate in muscle cells and interferes with insulin signaling, thus increasing insulin resistance (Strasser & Pesta 2013).
Though oxidative capacity is usually linked to aerobic activities, resistance training has been shown to improve mitochondrial oxidative capacity and mitochondrial content. Pesta et al. (2017) found that 14 weeks of resistance training significantly increased the mitochondria’s enzymatic activity. Additionally, Strasser & Pesta (2013) saw an improvement in fatty-acid metabolism after only one training session. We have to acknowledge that most of these results are from healthy subjects—the data on people with type 2 diabetes is limited. But Little et al. (2011) found that only 2 weeks of HIIT improved the mitochondrial capacity of subjects with type 2 diabetes.
The younger you are, the easier it is to gain lean tissue. John was in his 40s and already had low muscle mass. To create more glucose storage capacity, his workout needed to focus on big, compound movements that would increase his muscle mass.
Some drugs counter the effects of type 2 diabetes, but nothing works as well as lifestyle modifications. In a study of people with prediabetes, drug treatment reduced the incidence of diabetes by 31% (compared with a placebo), but lifestyle changes lowered the rate by 58% (Knowler et al. 2002).
The American Diabetes Association’s Standards of Medical Care in Diabetes 2018 says adults with diabetes should engage in 2–3 sessions a week on nonconsecutive days. The ADA also suggests reducing sitting time and breaking it up every 30 minutes. Sedentary activities have been linked to a decrease in insulin sensitivity.
Exercise selection is important. When training a client with diabetes, pick exercises that use lots of muscles, so you involve plenty of fibers. Switch the training program every 6–8 weeks. Using higher intensities (85% of 1-RM) will maximize strength gains and improvements to insulin sensitivity, but remember that most clients with type 2 diabetes may be deconditioned and not yet suited for this kind of intense work. Lower-intensity training (65% of 1-RM) will still improve insulin sensitivity and increase oxidative capacity (see “Basic Circuit: Sample Routine,” below).
Always tailor the program to the individual. To get a higher return on time, use a circuit approach. It will let a muscle group fully recover before the next set. This approach may also be more enjoyable to clients. A study published in 1997 explored the effect of 5 months of circuit-type resistance training in subjects with type 2 diabetes. The researchers reported a significant decrease in HbA1c levels with 2 sets of 12–15 repetitions (Honkola, Forsén & Eriksson 1997).
Pro Tip: “Exercise Snacks”
What else can you do for clients with type 2 diabetes? Encourage them to give “exercise snacking” a try. An exercise snack is not a cookie or piece of candy. Rather it’s a short, intense bout of exercise, shortly before a meal, that can quickly add glucose-storage capacity in muscle tissue and increase insulin response.
How does it work? The “snack” primes muscle tissue to the effect of insulin. A research paper published in 2014 looked into the effects of six 1-minute bouts of incline walking a half-hour before each meal. The study found that brief, intense “exercise snacks” before main meals are a time-efficient and effective approach to improving glycemic control for people with insulin resistance. Researchers also found that these short bouts were as efficient as 30 minutes of activity at a moderate intensity (Francois et al. 2014).
Medication and Type 2 Diabetes
You will probably encounter prospective clients who take type 2 diabetes medication, such as metformin. The effects of metformin on the energy system of muscle fibers are not fully understood. In their review, Pesta et al. (2017) reported that the drug may interfere more with aerobic training adaptations than with adaptations to resistance training. The researchers concluded that resistance training would be a better fit for clients on metformin.
Following Up With John
So what happened with John? I saw him 3 months later. He signed up with a trainer and got serious about resistance training. He made sure to add lower-limb exercises, such as squats and leg presses. Also, he met with a dietitian to improve his eating habits. Today, his blood sugar is under control, with no need for medication.
Basic Circuit Sample Routine
If your assessment shows that a client is ready to do a basic circuit, try the following routine. Perform 8–12 repetitions of each move (body weight only or loaded) and go through the entire circuit 3–5 times, based on ability. Here’s the “formula”:
Spend at least 8–12 minutes doing a full-body, multiplanar, functional warmup.
Pick one exercise for the lower body (squat, leg press, step-up or lunges).
Follow the lower-body move with a pulling exercise (chinup, pulldown, rowing).
Next, do a pushing exercise (pushup, chest press or shoulder press).
Cool down with total-body stretches and check in with the client.