A double hump (M shape) will often be seen (see below) in people with meniscal dysfunction. 

This is probably due to impingement during normal joint motion and reflex inhibition. 

Think of it like this:

The joint surfaces rotate around within the menisci.

As the knee is extended / flexed a point is reached where the damaged meniscus is under alot of pressure from the joint surfaces. Of not the dip is normally seen in concentric results in one contraction cycle only.

The meniscus reacts with pain inhibition which temprarily turns off the muscles.

This gives the dip (and is often only seen ever third repetition).

Generally the peak torque will be lower. 

It must be stressed that normal isokinetic test results do not exclude meniscal pathology.