What is power (explosive strength)?

In one line

Power (explosive strength) is the ability of muscles to produce a large force quickly; it combines both force and speed.

What is power (explosive strength)?
The ability people call 'explosive strength'
In sports and at the gym you often hear 'he has good power' or 'she is explosive'. People use it for force released in an instant, like jumping high or throwing a ball hard. This post explains exactly what power is and how it differs from strength.
In short
How quickly you produce a large force
Power is the ability of muscles to produce a large force quickly. Even with the same weight, lifting it faster means more power. A Korean dictionary defines the Korean word for it as 'the force made when a muscle contracts very quickly in an instant'. To contract means the muscle shortens and pulls.
A word from physics
The same work in less time
In physics, 'work' is the amount of moving an object by applying force, and power is the amount of work done in a given time. Walking or running up the same stairs takes the same work to lift your body, but running does it in less time, so the power is greater. The unit is the watt (W).
Force x speed
Force multiplied by speed
Power can also be found by multiplying force by speed. So however strong the force, moving very slowly gives small power, and however fast, a very weak force also gives small power. For big power, both force and speed need to be fairly large.
Heavier means slower
Force and speed trade off
Muscles move heavy weights slowly and light weights quickly. The heaviest weight goes up only slowly, while a very light weight flies up. This link, where speed drops as the force you must produce gets larger, is called the 'force-velocity relationship'.
Where power peaks
Not the heaviest, not the lightest weight
So power, which is force times speed, is small with very heavy weights and also with very light ones. Power is greatest at some weight in between. That weight differs from movement to movement; in one jump study, it was greatest when jumping with body weight only, no barbell.
How it is measured
Jumping high or far from standing
A Korean dictionary says this ability is measured with tests like the standing high jump, the standing long jump and running up stairs. All of them push the body hard and fast in a short moment. But jump height or distance is not power itself, which is given in watts. So in labs, people jump on a plate that measures force, and power is calculated in watts.
How it is built
Lift up as hard and fast as you can
The American College of Sports Medicine concluded that training where you deliberately lift up as fast and hard as you can built power. Training with medium weights of about 30 to 70% of the weight you can lift just once, and Olympic lifts that raise the barbell in one quick motion, also increased power. Bouncing moves like jumps are also used for power training.
Common myth
Is power the same as strength?
No. Strength is the greatest force a muscle produces; power also includes how quickly that force is produced. The heaviest weight goes up very slowly, so that is not where power is greatest. Still, strength is the base of power: with weak strength, you cannot produce great power.
Summary
The ability to produce large force quickly
Power (explosive strength) is the ability of muscles to produce a large force quickly, and it equals force times speed. It is not the same as strength, and it peaks not at the heaviest weight but at a weight in between. Related terms: strength, muscular endurance, force-velocity relationship.