Muscle strength is the ability to exert force against resistance, whereas muscle endurance is the ability to exert sustained effort over a long period of time. Muscle endurance relies on muscle fibers called type 1 (slow twitch). Muscle strength relies on type 2 (fast twitch) muscle fibers. Fast twitch fibers come in two varieties – type A and B. Type A help you pick up a couch and carry it across the room. Type B help you bench press your 1 rep maximum.
It is important to train all types of muscle fibers and systems, as you use them all in your everyday life (e.g. lifting and carrying small children or groceries). It’s also important to keep in mind that genetics play a large part in which types of fibers you will have a larger proportion of; whoever, this shouldn’t hold you back from attempting to improve your weaker areas (e.g. getting stronger if you are actually better with respect to endurance).
Talk to your trainer for more information.