In order to explain this section I’ll use the biceps curls exercise (as presented in the following picture).

• First phase when lifting the weight is called concentric (Muscle Actively Shortening). It’s also called the positive phase of movement.
• Second phase when lowering the weight to its original position is called eccentric (Muscle Actively Lengthening). It’s also called negative phase of movement.
• If the weight is being held at a constant position than its called isometric (Muscle Actively Held at a Fixed Length). It’s also called static.

Due to the muscle structure it has least strength in concentric phase. Afterward comes the isometric and eccentric phase is the strongest one. For example: if you can lift (concentric) 50 kg in curls, than means than you can hold statically (isometric) 60 kg and you can use 70 kg for the negative (eccentric, lowering the weight to its original position) phase.
Note: the weights in the previous example are only for explanation purposes and not necessarily reflect the real ratio. Additionally, the numbers came to reflect the “pure strength” of the muscle. They didn’t take into account other parameters (angles).

An exercise can be described with four numbers: ABCD. Each number represents the duration of this phase (in seconds). A – Concentric phase B – Holding the weight in “upper” position C- Eccentric phase D - Holding the weight in “lower” position

If we continue the biceps curl example then 2140 would mean: lift the weight up so it (lifting) would take 2 seconds. Hold it for 1 second in its position. Than bring the weight down so it (lowering) would take 4 seconds. Hold it for 0 seconds in its position, in other words start immediately the next repetition (if needed).

In many cases B and D numbers are omitted. If omitted, they are considered to have zero values unless stated otherwise.

Probably the most common recommendation is: 24 (A=2 and C=4).

Why eccentric phase is longer than the concentric one?

As I already mentioned muscles are stronger in the eccentric phase than in the concentric one. Since both phases in the exercise are made with the same weight and we don’t want to “give a break” to our muscles in the eccentric phase one of the simpler ways to keep intensity is making the eccentric phase slower.

Unfortunately, in reality 24 is almost never kept. It usually takes people 2-3 seconds for repetition (something like: 11 or 21). Eccentric phase is almost always ignored (advanced techniques such as negatives exist, where only the eccentric phase is made).

Note: In exercises with small ranges it’s hard to keep long phase duration. For example: crunches or calf raises are usually not executed with 24 but 22.