In climbing, there is an old adage stating that "climbing is the best training for climbing," an adage used by many to make excuses for not training outside of climbing. I personally disagree with this philosophy as I will explain.
When we are speaking of the exact skills needed in climbing, how and when to step, climbing techniques and mental skills, there is no substitute for the activity of climbing itself.
However, in order to develop strength levels specific to the sport of climbing such as improving grip strength and upper body strength and endurance climbing will produce very limited or even no results or improvements.
One of the main reasons climbing isn’t good for strength training is because in climbing failure is not an option. If you have muscular failure while climbing, it may very well prove fatal. So the goal while climbing id to avoid this completely.
Alternatively, when one is strength training for climbing, one wants to reach and even pass the point of muscular failure as it is this very act that causes the body to respond with an increase in strength to adapt to the stress being place on it. So the two methods are mutually exclusive and you will never achieve maximum strength by climbing alone.
Another example that reinforces the disparity between climbing and strength training for climbing is the way in which you grip the rock. In climbing, the rock demands the climber to use a random variety of many different grip positions and, at times, you may even deliberately vary the way you grip the rock. As a result, it's unlikely that any single grip position will ever get worked maximally and, therefore, the individual grip positions (e.g. crimp, open hand, pinch, etc.) are slow to increase strength.
This should help you understand why a full season of climbing may indeed improve your anaerobic endurance (i.e. endurance of strength), but do little to increase you absolute maximum grip strength.
Therefore, varying grip positions is a great strategy for maximizing endurance when climbing for performance, but it will never work for training maximum grip strength. Effective finger strength training demands you target a specific grip position and work it until failure, which can only be done safely in a non climbing environment.
Finally, it could be better for some climbers to participate in cross training with other activities that are not particularly sport-specific. As an example someone who needs to lose weight should spend the majority of their non-climbing time performing aerobic activity to burn off the excess body fat as it is essential that a climber be as lean as possible for optimum performance.
If someone is totally devoid of at least some modicum of fitness, they would be better off doing some circuit training that will give them both strength and aerobic benefits.
In closing I will say that regardless of your experience level in climbing, you will see a huge improvement by including specialized strength training in your regimen.
