A large part of the strength required can be attained from
circuit training. A range of press ups, abdominal curls, tricep dips, back
arches etc will provide a good base of strength and strength endurance. Building
good core stability is very important as it helps you keep your posture correct
and your stride length long when you get tired.
Top level middle distance runners now also undertake a weights program - consider
the fact that in international races, the first lap of an 800 is often under
50 seconds, which is a very good performance from heavily muscled strong club
runners. They need to be fast, and for that you need to be strong.
The number of reps for middle distance runners will be high in the gym, sessions
with 5 x 12-15 will help build strength and muscle endurance.
Finally, a range of plyometric work will help produce the power needed for
middle distance running.
Please look at the various other sections of the site for details.