Weight lifters and bodybuilders have long debated whether muscle growth is initiated and maintained through maximum lifts, or maximum muscle contractions. There seems to be merit in both theories.
Heavy lifts are necessary to tear muscle fibers and initiate the process of hypertrophy, which is the enlargement of muscle fibers. This growth of type two fast twitch fibers needs adequate force to tear the cross bridging attachment between contracting muscle fibers. The constant reoccurring process of lifting and tearing results in larger muscles, through the growth of muscle cells.
The bodybuilding concept of maximum contraction results in transient hypertrophy, or the increase in blood fluids and a corresponding rise in blood pressure. The contractions also stretch the muscle fascia which is the membranous tissue surrounding muscle bundles. This repeated stretching of the fascia can result in the ability to have a greater “pump “because of the aforementioned stretching of the surrounding tissue around the muscle fibers themselves.
My advice as a personal trainer and a lifter is: Work with heavy weight in a safe fashion to build larger muscles. Work with lighter poundage’s with maximum contractions when the body needs rest to recover from heavy lifting. Older lifters will find they need more “pump” sessions and less heavy lifting to allow the body to recover.
The theory of periodization covers much of these concepts.