The press-up is the leading exercise to work the chest and can be easily tweaked to make it more or less challenging depending on your fitness level. The most effective way to exercise is to use the 'matrix' method. This involves doing the full range of movement for the exercise and then 2 sets of half the movement, this will become much clearer later! For those who don't know what a press-up is, (do they exist!?) here is a 4 step guide:

Place your hands facing forwards, shoulder width apart, under you shoulders. Keep your upper body and your legs straight.

Bend your arms to a 90^o angle keeping the rest of your body straight and breathing in.

Return your body to the original position breathing out on the way.

Repeat steps 2 + 3.

If you need more of a challenge than the normal press-up, then there are many variations to make it more challenging.

Firstly, as I said earlier the 'matrix' method is very effective. To do this method, do a full set of press-ups and at the end return to the original position and bend your arms half the distance (from 0^o to 45^o) for the same number of repetitions. Then do another set of half the movement this time going from the half the distance to the full distance, (45^o to 90^o).

Secondly, try raising your legs onto something higher such as a chair or your bed.

Thirdly, as this exercises the shoulders and arms you can focus it to the chest by placing your hands further apart.

Alternatively if you need something less challenging you can do the half press-up this is the same movement as the normal press-up except you keep your knees on the floor.

Make sure that after all these exercises you stretch to avoid injury!