Recently, I've been experimenting at the gym with something I read from Ironman magazine (the best of the muscle magazines in my opinion). The article talked about the relationship between time under tension and muscle growth. Time under tension (also called time under load) is not a new concept, and I remember experimenting with it some years ago.
The Ironman article stated that research shows that the most beneficial time under load is between 35 to 40 seconds for any given exercise. Therefore, one should select the amount of weight that will cause near-failure between 35-40 seconds. Of course, the idea is to keep adding weight over time but also while staying in the 35 to 40 second range.
I've been using this time range for a couple months with some mixed results. I've had very good results with dumbbell rows in this time range. I have increased weight almost every week and am now doing as much weight for this exercise as I probably ever did, along with an increase in muscle size.
On another exercise, shoulder press, I have made zero progress the last couple of months. On the deadlift, my third major exercise, I have made good progress though nothing like the dumbbell row progress.
All this suggests to me that each muscle group (or exercise) has an optimal time under load. For dumbbell rows, I have apparently hit the jackpot with the 35 to 40 second range. For the other exercises, I probably need to try a shorter or longer time under tension.
What determines the optimal time under tension? I haven't looked into it that much, but I'm betting it's the distribution between slow and fast twitch muscle fibers in a muscle group. Beyond getting muscle biopsies, I'm not sure how you can determine the optimal time range besides good old trial-and-error.
Anyone have any other ideas on determining optimal time under tension? Let me know. I will dig around more in this research area when I get some time.