Muscle Recruitment refers to the number of muscle fibers that are actually being engaged within a muscle contraction.

For illustration purposes, consider the following example: if a muscle contains 1000 muscle fibers and 500 of them are being engaged, then there is 50% muscle recruitment, but this does not indicate anything about the degree of activation.

The force generated by the individual recruited muscle fibers is how we would define activation, or their ability to contract and generate a given force.

Ideally there would always be 100% muscle recruitment and 100% muscle activation, but in most cases this simply doesn’t happen.