The shorter acting stuff works well for site injection/growth...the longer acting (IGF-1LR3) doesn't really matter where you inject.
There are two types of IGF-1 that will typically be used by bodybuilders. One is bio-identical HuIGF-1, a 70 amino acid string. The other is Long R3 IGF-1, which is an 83 amino acid analog of human IGF-I comprising the complete human IGF-I sequence with the substitution of an Arg for the Glu at position 3 (hence R3), and a 13 amino acid extension peptide at the N-terminus (hence the long). Which of these you use depends on your goal.
HuIGF-1 is very short lived in the body (half life of probably around 10 minutes). This type of IGF-1 is very useful if you are seeking local site growth. Since it is so short lived, little of the IGF-1 makes it to other tissues and IGF-1 receptors in the body. The way to inject this is immediately post work out into the muscle that you wish to have local site growth. Use a U100 insulin syringe, and inject 80mcg's bilaterally into the desired muscle immediately post workout. For this type of IGF-1, I would use it workout days only or if desired you could inject on non-workout days first thing in the morning into a muscle group worked the previous day.
For Long R3 IGF-1, it isn't as critical that you inject into a local site as long R3 has a active window of many hours, and is designed specifically to resist being bound. Since it is common to reconstitute this type of IGF-1 with Benzyl Alcohol, Acetic Acid, or Hydrochloric Acid I would still recommend that you inject intra-muscular. It can and probably will leave a nice red irritated spot if you inject Sub-C. I still inject into a muscle just worked to take advantage of increased IGF-1 receptors, but because of the long activity window of this type of IGF-1 any muscle will work well and give you good results,. I would suggest that you inject between 40-80mcg's per day everyday immediately post workout on workout days, and first thing in the morning on non-workout days.
/V