By Shelby Stoner, PHASE IV Exercise Physiologist
Other articles in the Hormone Series:
Hormones are the special chemical messengers in our bodies that are created in our endocrine glands. These messengers control most major bodily functions, from basic needs like hunger to complex systems like reproduction, and even emotions and mood! Hormones control a number of physiological reactions in the body including energy metabolism and muscle growth. Understanding which hormones are released with exercise and the physiological functions they influence gives us a deeper look into exactly what happens in the body as a result of exercise.
As many of us know, insulin is produced by the pancreas in order to help control blood sugar levels. It does this by regulating carbohydrate and fat metabolism through promoting the storage or absorption of glycogen (stored form of carbohydrate) and glucose (simple form of carbohydrate). In resting conditions, insulin helps facilitate the uptake of glucose into the cell by promoting the insertion of glucose carriers in the cell membrane. It is important to note that insulin can cause fat storage in adipose (fat) tissue instead of being used to fuel our activities. At the onset of exercise, the release of insulin is suppressed; therefore it is important to avoid foods with lots of sugar or a high glycemic index immediately prior to exercise as this will cause a spike in insulin levels which promotes glycogen STORAGE rather than allowing it to FUEL physical activity. In this case, it is better to wait until the body has started sweating before using any sports drinks or energy gels.
Considering plasma insulin levels fall during exercise, insulin is not responsible for the increased transport of glucose into the cell. With insulin out of the picture, and therefore a lack of glucose carriers in the plasma membrane, the muscle cell will compensate by creating more glucose carriers as a response to exercise. Why does this matter? By increasing the number of glucose carriers in the plasma membrane, the affinity (aka degree of attraction) and receptor sites that specifically bind to insulin increase, improving overall insulin sensitivity. Therefore, the cells are now more receptive to circulating levels of insulin.
This particular response of regular aerobic training is vital to the treatment and prevention of diabetes, more specifically Type II diabetes. By increasing the cell’s responsiveness to the limited amount of insulin available, exercise helps drive the glucose into the cells where it can be used for energy production rather than staying in the bloodstream (where it can lead to detrimental consequences for the body).
Numerous studies have shed light on physical activity and exercise in improving insulin sensitivity. In a study of sedentary, young adult women (ages 18–35), 6 months of 3x/week aerobic training and 3x/week resistance training improved glucose uptake in the body. In another study, sedentary, insulin-resistant, middle-aged adults who engaged in 30 minutes of moderate walking 3-7 days/week for 6 months succeeded in reversing their insulin resistance. No matter what your age, weight, or current fitness level is, studies have shown that exercise training can significantly improve your insulin sensitivity and improve overall health.
Stay tuned in the upcoming weeks for more info on hormone responses to exercise including Cortisol, Human Growth Hormone, and more!
Whether your goals are related to weight loss or improved performance, PHASE IV science has the answers. Call us to schedule a complimentary 30-minute health and fitness consultation at our facility in Santa Monica. 310-582-8212