These differences may be used to prolong or speed up the effect of the injected insulin for special circumstances, but it's better to keep injecting within the same anatomical area all the time. The fatter the area, the slower the absorption. Absorption may also be delayed in areas affected by lipohypertrophy. Exercise of the injection area increases absorption of the insulin in that area. If you exercise the area that was injected, the muscles underneath squeeze the insulin faster.
Local massage can increase the speed of absorption.
Heat increases absorption, cold decreases it. Smoking decreases absorption. Day to day variation up to 50 percent may occur in the same person, with the same dose, in the same area of injection and the same insulin. The same person, using the same technique, may see a 25-50 percent difference in the time of peak action of any insulin on a day to day basis. There are no data on this.