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Being active is one of the key ways to help manage diabetes, stay healthy, and lower high blood sugar. Yet, navigating changes in blood glucose when you're active can seem daunting, especially if you are on insulin or other blood-sugar-lowering medications. Knowing how and why your blood sugar changes can go a long way to help you recognize what's normal and what's not. And just how great of a management tool physical activity can be.
Let's get down to the nitty gritty to help you move more and keep your blood sugar under control.
Your blood sugar before exercise
At rest, two hormones from your pancreas—insulin and glucagon—play opposing roles to keep your blood sugar stable: insulin moves sugar into your cells and glucagon shuttles sugar out of cells. After you eat, sugar and other nutrients are released into your blood from your intestines. Insulin levels rise to move that sugar into your cells, including muscle and liver cells, to be used or stored. Between meals, glucagon levels rise to maintain your blood sugar by releasing that stored glucose back into your bloodstream—preventing lows.
Your blood sugar during exercise
It's time to get your heart pumpin': As you start to move, your muscles use their own stored sugar as well as sugar from the bloodstream to make an energy compound (called ATP) that helps them contract. And soon, your hungry muscles need more sugar to make that fuel. So your body gradually lowers insulin levels and raises glucagon levels to release more stored sugar (from your liver) into your bloodstream for muscles to use.
At rest, muscles require insulin to absorb glucose, so how does that released sugar enter active muscle cells with only a small amount of insulin? First, working muscles place more transporters on the surface of their cells that act like doors for insulin to deposit sugar into. The more doors, the more sensitive cells are to insulin, even with less of it floating around. And second, active muscles can also absorb glucose on their own without insulin, so less insulin is needed. Both pathways prompt muscles to absorb excess glucose, helping to lower high blood sugar.
Now you're in the swing of your activity, be it dancing, walking, swimming, or a body-weight circuit. To keep your muscles happy, your body releases other hormones, like adrenaline, that free even more stored glucose from the liver. How much sugar is released depends on how long and how hard you go. During intense activities (think: short sprints with little downtime or a hard lifting session), adrenaline may release more sugar than your muscles can use, which can raise blood sugar for up to two hours post-exercise. This temporary spike is common and typically does not impact your A1C, though it may need to be balanced through food or medicine post-workout (see Workout Out with Insulin, below).
Your blood sugar after exercise
While you cool down, catch your breath, and sip water, your muscles and liver are still hard at work absorbing sugar out of the blood to replenish their stores for next time. And those good effects that happened during exercise—improved insulin activity and sensitivity—may remain enhanced for up to 48 hours post-sweat! Heart-pumping aerobic activities aren't the only form of exercise that's beneficial: resistance training can also increase glucose uptake and reduce insulin resistance. That's why combo workouts (think: water aerobics, body-weight circuits, or even walk-then-lift sessions) may be the most effective for blood glucose management.
Workouts and insulin
How muscles use glucose during exercise is the same for all people. But people with type 1 diabetes or those who take insulin often need to take extra steps to avoid swings and lows during activity. This often means adjusting insulin or eating a source of glucose before or during exercise. If blood sugar levels rise after a hard effort, it may seem intuitive to treat raised levels with an insulin dose, but this rise is temporary and taking insulin could increase increase the risk for a delayed low.
Navigating your body's response to physical activity when on insulin can be frustrating, but finding a regular exercise routine that works for you is possible. Have patience with yourself and take the necessary precautions: check your blood sugar before working out, pack a source of glucose, and listen to your body for symptoms of hypoglycemia (e.g., shakiness, weakness, abnormal sweating, tingling of mouth and fingers, anxiety, and hunger).
Supporting research by Mary E. Sanders, Ph.D., ACSM-RCEP, CDE, FACSM