Having a strong core is good for sports but it is also useful for a good posture and to reduce the risk of back injuries. The following two sets of exercises are my favourites and are suitable for intermediate and advanced practice.
Inclined leg raises
For the first exercises, you will need a weights bench that has a slight angle.
Either lift the legs with the knees straight or knees bent. These exercises work the full length of the abdominal muscles and you can vary the difficulty by adjusting the angle of your knees as well as the angle of the bench.
Try to do 3 sets of 15 repetitions. If you find it easy, make the bench steeper or increase the number of sets or reps! Do not place the feet on the ground until you have completed each set.
Keep the movement slow to avoid tipping the bench up; this is particularly important for cheap benches. You will notice how I raise my hips off the bench to ensure that the upper section of the abdominal muscles are used. Normal leg raises when you are laying on the ground tend to just focus on the lower section and the hip flexors.
Full Leg Raises
These are tougher than the above exercises for two reasons:
1) you’re really working against gravity
2) you’re hanging from a bar which tires out the hands.
You will notice that unlike “normal” leg raises that others do, you have to bring the feet and knees up high. Aim to have the knees reach up to the level of your shoulders; otherwise you are not working the upper section of the abdominal muscles. If you find it tough, just raise the legs up with the knees bent. The trick is to end up lifting up the hips thus working the entire length of the abdominal muscles.
Additionally, try not to swing. This challenges the core even further.
Unlike crunches, the above exercises really work the core and develop it to a level suitable for participating in sports such as rock climbing. Any seasoned rock climber will know how strong the core has to be when tackling massive overhangs, especially if your feet slip away from the roof and you have to control the swing and then bring your feet back up to the holds above you!