Short answer: Yes. The Humalog, NovoLog and Humulin N labels say the rate of insulin absorption is affected by the injection site, exercise and other factors. In a 1978 study, cycling sped up absorption of insulin injected into the leg by 135% in the first 10 minutes, but not from the arm. Heat does something similar: a sauna more than doubled absorption speed in another study.
The Humalog and NovoLog labels (section 12.2) say "the rate of insulin absorption and onset of activity" is affected by the site of injection, exercise and other variables. The Humulin N label says the same with "physical activity level." The Lantus label (section 5.3) says the time course depends on the area of injection, the injection site's blood supply and its temperature.
All four labels also say changes in physical activity can raise the risk of low blood sugar, and that dose changes may be needed when activity changes. Exercise can work on two fronts: it can speed up how fast insulin leaves the injection site, and it lowers blood sugar on its own.
Koivisto and Felig (1978) injected labeled fast-acting insulin into the leg, arm or abdomen of people with type 1 diabetes, then had them do an hour of on-and-off cycling. They compared this with a resting day.
| Injection site | What happened with leg exercise |
|---|---|
| Leg | Absorption up 135% in the first 10 minutes, still 50% above resting at 60 minutes |
| Arm | No change in absorption |
| Abdomen | Absorption slower during the recovery period |
Compared with a leg injection, an arm injection cut the blood-sugar-lowering effect of the exercise by 57% and an abdominal injection by 89%. The authors concluded that injecting in the arm or abdomen avoids the speed-up during leg exercise and reduces exercise-related lows.
In a second study (Koivisto 1980), eight people with type 1 diabetes sat in a sauna twice for 25 minutes at 85 °C. Insulin absorption from the injection site was 110% faster than at room temperature, and blood sugar afterward was 3.0 to 3.3 mmol/L (about 54 to 60 mg/dL) lower than on a control day.
For pumps, the Humalog label says insulin exposed to temperatures above 98.6 °F (37 °C) should be thrown away, and that the insulin can get hotter than the air when the pump or tubing sits in sunlight or near heat.
MedlinePlus advises not injecting insulin into a part of the body you are about to exercise, such as the shoulders or thighs, and says exercise can lower blood sugar for up to 12 hours afterward. The NIDDK says more activity than usual can lower blood glucose for up to 24 hours. Both suggest checking blood sugar before and after exercise and asking the care team how to adjust insulin or snacks.
Where you inject also matters for rotation. The labels warn that repeated injections into thickened skin (lipodystrophy) can change absorption. See injection site rotation. Logging the site with each dose, as Dose Track does, makes it easier to match a low after a workout to where the insulin went.
Read more on Dose Track: Injection site rotation · Why injection site rotation matters · Lipohypertrophy · How to store Humalog