Hypotonic
Hypotonic: Diminished tone of skeletal muscles; diminished resistance of muscles to passive stretching. May be related to inhibition, reciprocal inhibition, arthrokinematics inhibition and/or increased resting length of muscle.
For example, if your knees bow-in (functional knee valgus) during a squat, running, or jumping it is likely that your gluteus medius is hypotonic.