Strength is a slightly misleading word here as there is
not much need for being able to lift a huge weight slowly, it is all about
the powerful movements at speed, requiring large elastic strength - the ability
to contract muscles at speed.
This kind of strength is developed in two ways - firstly in the gym and
secondly by the performance of plyometric exercises.
As stated in the speed section the profile for a high jumper differs from other
jumpers as the amount of speed required isn't as high. All jumpers need to
develop their explosive power, high jumpers more so than others.
In the gym a range of exercises are important. Early in the training
period sets of between 6 and 12 reps are used to build strength and muscle mass.
Once this strength has been worked on the key is to turn this into power.
The number of reps will vary according to the exercise, but generally, you'll
try to do a mixture of high weight low rep activity where your pure strength
is improved and, more importantly, lower weight fast reps for developing power.
This might be 3 x 6 at just 40% of 1 lift maximum for bench press, whilst
for the key leg exercises of power cleans, snatch and squats you might do
3 x 3 at 80% as these involve faster movements anyway.