Its the only site I inject IM and practice the following method to make it as painless/easy as possible....
1. I warm the ampoule over hot water.
2. Break the top of the ampoule with a pen cap.
3. Draw the sust with a large gage pin( 20 g should do ).
4. Replace the pin with a 1 1/2 in 27 g pin.
5. Push all the air out of the syringe and let some of the sust out to lubricate the needle then inject into upper thigh( alternate thighs each shot ). Rub vigorously after shot.
This method is pretty easy and the shots are virtually painless each time. However, you may feel that charley horse later on. But I doubt it will stop you from walking or doing anything else.