Strong adductors (inner thigh) are important running, particularly as you move from one leg to the other.
The adductors work as a force couple with the gluteus medius.
If they’re not strong enough it can contribute to a degree of hip collapsing, and in turn demand excess load upon the knees, hips and back.
Squeeze for 10 to 30 seconds at 80% strength, before releasing pressure without dropping the ball.
If you’re an endurance runner, a good goal would be to hold each squeeze for 1 minute, with the ability to repeat 4 times.