In addition to circulating insulin levels, myriad variables can impact your blood sugar responses to exercise as well. For instance, doing morning exercise lowers your blood glucose levels less than doing the same bout of exercise later in the day due to your being more insulin resistant in the morning. Early morning elevations in naturally-released hormones like cortisol and growth hormone after you go without eating overnight causes most of this resistance. Thus, undertaking morning exercise usually requires you to reduce your insulin doses less and, in some cases, you may even have to take a supplemental dose of insulin to lower your blood glucose levels before or afterwards.
Exercising late in the evening is also most likely to result in nocturnal hypoglycemia (low blood sugars), but exercise earlier in the day can also result in later-onset lows throughout the day and night unless you take precautionary measures, such as eating more or a bedtime snack or lowering your bedtime insulin doses. In addition, if you did a prior session of strenuous exercise, you may experience impaired hormone responses the next time you experience a low or when you do your next workout, meaning that you may be at higher risk for developing hypoglycemia when engaging in successive days of exercise training.
There are many other variables that can affect your blood sugar control during exercise. A short list of them follows:
During a Workout
• What your blood sugars are when you start
• How much insulin is in your system, determined by:
– Types of insulin(s) used
– Timing of prior insulin injection or bolus
– Insulin dosage given
• Type, intensity, and duration of activity
• Carbohydrates that you eat before and during activity
• Activity status (whether it’s a new activity or a usual one)
• Time of day of exercise
• Prior exercise (when you last worked out)
• Type of training (aerobic vs. anaerobic)
• Training status (specific to the activity): whether you’re highly trained or starting out
• Enhancements in insulin sensitivity (how much your insulin action has been enhanced)
• Reductions in your overall insulin doses
• Change in the fuels your body uses (e.g., greater fat use)
• Dietary status (energy balance, fuel intake)
• Body composition (i.e., increased muscle mass)
• Frequency of glycogen-depleting exercise
• Hormonal response to exercise training
In the next blog, I’ll talk more about how your body responds, physiology-wise, to different types of training and activities.