Funny thing about jargon, you only understand it if it's your jargon. I realize that I throw some phrases out there that are self-explanatory to me, but may be completely indecipherable to everyone else. Like when a DJ friend asks me about uptempo and I'm like, "Wtf is uptempo?" Or when my training partner is talking computer stuff with another nerd and all I can hear is, "My computer is really fast and cool--literally!" It happens in the gym too. "Mind-muscle connection," "positive nitrogen balance," "working weight." We all throw these kinds of terms out there and expect others to understand them without explanation. Maybe we bodybuilders, as a community, are just trying to make it sound more complicated than "Me lift heavy thing! Me grow strong!" At any rate, today I will be explaining the time-under-tension principle.
I hate to beat a dead horse, but the adaptive response your body deploys in reaction to training is only as great as the amount of stress you place on the target muscle. This means not only heavy weight, but also plenty of time lifting that weight. Ideally you want to apply stress to the entire muscle--this means using a complete range of motion in addition to meticulous form. But even once you've done that, you still need to spend some srs quality "time under tension".
This means maximizing the amount of stress you are applying during a set by using that time efficiently. Nice slow reps, consciously lowering the weight during the eccentric phase of the movement, and resisting locking out the joints at the apex of the motion. Example: During chest presses, locking out the elbows at the "top" in order to finish the rep has zero significance from a bodybuilding perspective--when I say this, I mean a perspective which prescribes only techniques which maximize muscular growth. In this case, locking out the elbows would release tension from the pectorals and instead allow the weight to rest on the connective tissue and bones in your arms and shoulders. Thus, each time you "lock out" you not only risk injury to tendons and ligaments, you also lose tension in the target muscle, and precious seconds out of your set during which the target muscle is not being stressed. Given a true high intensity approach, with only one working set per exercise, this is not time you can afford to lose. This is why you won't see curls all the way into the chest, rests between squats, or dumbbells clicking together on chest press or flyes--these are complete losses of tension at the point where your maximal contraction is taking place. Don't waste that squeeze!
Additionally, training with too much weight can also minimize the positive effects of time-under-tension, usually because only a few reps are being performed. At worst, a set of three partial and/or cheat reps, for example, would not only fail to produce gains due to the lack of adequate overload in the muscle as a whole because of poor form and range of motion, it would also fail to produce gains due to the inadequate duration of the set. The body is slow moving and lazy--a 15 second set is not going to be properly motivating!
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