Why the eccentric matters most

The lowering or returning phase produces more force per unit of effort and more adaptation than the lifting phase. On a reformer that is the carriage returning home, and it is the phase almost everyone rushes.

Doubling the duration of that phase doubles the work done in it, at no change in load and no cost to technique.

A concrete prescription

Push or pull for two counts, return for four. On footwork that turns a set of ten from about twenty seconds of work into about sixty.

It will feel like a substantially harder set at the same spring setting, because it is.

Tempo and time under tension, ten repetitions
Tempo (out : back)Seconds per repTotal set
1 : 1220 s
2 : 2440 s
2 : 4660 s
3 : 5880 s

Where slow tempo is most valuable

Anywhere control is the limiting factor rather than strength: footwork, strap work, knee stretches, and any exercise where the carriage returns under spring tension.

It is less useful in exercises that are already isometric, such as plank variations, where duration is already the variable.

Do not slow everything

Jumpboard work and dynamic sequences depend on rhythm and rebound, and slowing them removes the point of the exercise.

Use tempo deliberately on control-focused work and leave the dynamic work dynamic.