Many studies have shown that stretching a muscle can increase IGF-1 levels. That rise is desirable because IGF-1 has been shown to slow the process of protein breakdown. Bodybuilders have also been told to stretch before, during, and after workouts to stretch the connective tissue surrounding muscle cells. Some trainers have advocated that the muscle connective tissue is like a pillow cover. If the pillow cover is tight, the pillow can’t expand to its full size. Stretching is thought to expand the muscle sheaths, which will allow the connective tissue to expand and allow for more growth of the muscle bellies.
Researchers put the stretching theory to the test and examined muscle IGF-1 responses. Thirty people were randomly assigned into one of three training groups: a) static stretching before strength training, b) static stretching before each training set, and c) no stretching before or during exercise. Strength and IGF-1 levels were collected at the beginning (pre-test) and end (post-test) of the entire experimental procedure.
Here is the real blow for stretching before or during exercise. The group that did not stretch showed a significant increase in strength with all exercises, whereas the groups that stretched before or during exercise had increas es in strength for only certain exercises. And here’s the good stuff about muscle growth and IGF-1. Researchers found that the group that did not stretch showed higher values of IGF-1 when compared with the other groups. It has been concluded that not stretching can more effectively increase muscle strength as well as basal serum IGF-1 levels.
So despite what you have been taught for years, stretching is not good before or during exercise. If you decide to stretch, make sure it’s afterward.