study peformed about 5 or so years ago can provide at least a partial answer to this question. In this study, they used ultrasonography to measure the thickness of the fat pad above the deltoid muscle in 220 adults. What they found was that a 5/8 inch needle would not have allowed enough penetration for a true intramuscular injection in 17% of men and around 50% of the women.
The authors concluded that for men weighing 59-118 kg, or 130-260 lb (rounded), and for women weighing 60-90 kg, it may be better to use a 1-inch or 25mm needle. They also suggested that a woman over 90 kg use a needle 1 1/4 inches long, or 38mm.(15)
So, with these data in mind, I think it's safe to assume that a 1-inch needle is sufficient in all types of men for deltoid injections and the same can likely be said for injections in to the thigh. As for the buttocks, I'd say the safest bet is to go with a 1 1/2 inch needle. However, there are going to be plenty of guys who are lean enough to use a 1-inch in the buttocks and a 5/8 inch in the deltoid, and even a 1/2 inch needle in the thigh. To be 100% sure, however, use the lengths suggested above.
I read this and thought it might help.
Topic Author
