Humans are made to move. However, the structure of modern-day life makes it easy to minimize movement. In fact, with the availability of the drive-thru, you don’t even have to get out of your car to get an unhealthy meal. No wonder chronic disease rates are so high! But humans need more movement in the form of aerobic exercise and strength training.
Aerobic exercise has so many health benefits. It improves heart health and oxygen delivery to your muscles and tissues, and over time you develop greater endurance. Everyone needs some form of exercise that raises their heart rate, especially diabetics, and people with prediabetes since exercise helps with blood sugar control. However, a new study finds that elevated blood sugars or prediabetes may interfere with some of the health benefits you get from aerobic exercise.
Adaptations to Aerobic Exercise
According to researchers at Joslin Diabetes Center, having blood sugars above normal could make it harder to get the healthy adaptations we associate with aerobic exercise. When you exercise in a manner that elevates your heart rate for a sustained period, your heart must work harder to deliver oxygen to muscle tissues. Over time, the heart adapts and becomes a more efficient pump. In addition, other changes take place that enhances oxygen delivery to tissues such as an increase in capillary density around muscle tissue, and a boost in mitochondrial enzymes that make ATP, a cell’s energy currency. These changes lead to an increase in aerobic capacity.
Based on studies in mice and humans with prediabetes, these adaptations are lessened in people with chronically higher blood sugars. In other words, a person with a high blood sugar level might not boost their aerobic capacity as much as someone metabolically healthy even if they exercise consistently.
What a Study Showed about Aerobic Exercise and Blood Sugar
In the study, researchers artificially raised the blood sugar in mice and had them take part in an aerobic exercise that involved running in an exercise wheel. What they found was mice with higher blood sugar levels didn’t experience the same improvements in aerobic capacity relative to the mice that had normal blood glucose levels. In fact, the mice with higher blood sugar levels experienced training adaptations similar to what happens with strength training – an increase in muscle fibers and a decline in blood vessels carrying blood to the muscle.
How can we explain these findings? There’s a signaling pathway called the JNK pathway. It’s this pathway that tells muscle cells how to respond to exercise training, whether to make aerobic or strength-training adaptations. In response to aerobic exercise, you should get an increase in capillaries surrounding the muscle to boost oxygen delivery, whereas with strength training you should see an increase in muscle fiber size and a reduction in the number of capillaries that surround the muscles. The mice with elevated blood sugar who did aerobic exercise, strangely enough, got adaptations that usually occur with strength training.
The explanation? Scientists believe signals get crossed in mice with higher blood sugar levels. Muscle cells didn’t get the message to adapt in a manner conducive to aerobic fitness but instead to adapt in a way consistent with strength training. You might think these adaptations are unique to mice, but early clinical studies in humans show similar findings. In studies, people with higher blood glucose levels didn’t improve their aerobic capacity as much as those with normal blood glucose readings. The same phenomenon may occur in humans: those with elevated blood sugars are having signals from the JNK pathway crossed and making muscle adaptations consistent with strength training rather than aerobic training. The poor response to aerobic training seems to be independent of body weight and insulin levels in the blood.
Aerobic Exercise Still Has Health Benefits
Although you might not get the same improvements in aerobic capacity with aerobic exercise if you have higher blood sugar readings, it doesn’t mean you won’t get health benefits. Aerobic exercise improves insulin sensitivity and that can lead to healthier blood glucose levels. It’s possible that regular aerobic exercise may lower blood sugar readings enough to make greater gains in aerobic capacity. Combining aerobic exercise with strength training is also effective for lower elevated blood glucose.
Another benefit of aerobic exercise, beyond improving aerobic capacity, is its effect on weight control and the risk of obesity. It’s no secret that aerobic exercise and strength training enhances body composition, burns calories, and lower the risk of obesity. In turn, losing weight improves blood glucose control. People who lose weight also have a reduced risk of developing prediabetes or type 2 diabetes.
Aerobic exercise benefits the heart in other ways too. For most people, even people with hypertension, blood pressure drops for several hours after an aerobic workout, but over time, the drop in blood pressure becomes more sustained. Studies show aerobic exercise can lower systolic blood pressure between 4 and 9 millimeters of mercury, comparable to some blood pressure medications.
In addition, regular aerobic exercise can improve blood lipids by lowering triglycerides and increasing HDL-cholesterol, the “good” form of cholesterol particle linked with a lower risk of cardiovascular disease.
Exercise Has Mental Health Benefits Too
Then there are the mental health benefits of an aerobic workout. Studies show aerobic exercise improves the symptoms of depression and anxiety. There are several ways exercise may boost mood. One is by increasing blood flow to the brain. Research also suggests that exercise alters the connection between the hypothalamus in the brain and the pituitary gland that releases key hormones. Its effects on this circuit may improve the stress response.
Aerobic exercise also boosts endorphins, natural chemicals produced in the brain that have a positive impact on mood and sense of well-being. You are probably already familiar with endorphins if you’re a runner. Some experts believe they explain the runner’s high that runners get after taking a run or jog.
The Bottom Line
Having elevated blood sugars could interfere with some of the adaptations to aerobic exercise. However, you still get health benefits and aerobic exercise helps with blood sugar control. Plus, if you lose weight in response to aerobic exercise, it’s possible to reverse prediabetes. So, aerobic exercise is still a heart-healthy activity and one that every person with prediabetes and diabetes should take advantage of.
References:
- Tara L. MacDonald, Pattarawan Pattamaprapanont, Prerana Pathak, Natalie Fernandez, Ellen C. Freitas, Samar Hafida, Joanna Mitri, Steven L. Britton, Lauren G. Koch, Sarah J. Lessard. Hyperglycaemia is associated with impaired muscle signaling and aerobic adaptation to exercise. Nature Metabolism, 2020; DOI: 10.1038/s42255-020-0240-7.
- Prim Care Companion J Clin Psychiatry. 2006; 8(2): 106.doi: 10.4088/pcc.v08n0208a.
- Mayo Clinic.com. “Exercise: A drug-free approach to lowering high blood pressure”
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