5.3.3: Tempo and Time Under Tension

The force‑velocity curve already established that high fiber‑level tension requires slow contraction velocity. The key distinction is between TUT (total time under tension) and TUT under high mechanical tension. A slow 10‑second rep with a 2 kg dumbbell produces long TUT but negligible recruitment and tension in high‑threshold fibers—it is non‑stimulating. A 2‑second eccentric + 1‑second concentric with a heavy load or at the end of a light‑load set to failure produces brief but extremely potent TUT under high tension.

You do not need to write out specific tempos like 3‑0‑1‑0. The practical rule is simple: control the eccentric—a 2–3 second lowering phase is a sensible default that maximizes passive tension and protects tendons and joints by preventing abrupt loading. Let the concentric happen naturally; it will slow on its own as you approach failure. Do not deliberately slow the concentric of light early reps, and do not throw heavy loads ballistically. The body knows what to do when effort is high.