In reply to Shapeshifter:
Hi Shape, to help those replying provide you better guidance a few more bits of info are needed.
- how did you conclude heel hooks are holding you back?
- what number of problems do you try require a heel hook to climb?
Whilst improved flexibility definately helps, I dont think you need embark on a quest for stronger legs.
What you most likely have is a case of being a V6/7 boulderer in crimps, slopers, roofs etc but your heel hooks are not on par. You will need to figure the root cause out yourself to correct this. Your core strength and control also will have alot to do how you facilitate transfer of force into your heel.
The mechanics of successfully performing a heel are complex so I include a couple of practical tips, note that information provided by the rest of the gang above will help in addressing specific areas of weakness, but until you know what they are you cant start working on improving them.
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Like with your football, create a heel hooking drill on easy holds/problems and do this as a warm up. Work up to being able to hook on close, distant, good and bad holds. Include holds that require special attention like pockets with a particular orientation, small slopers.
What you need to build up is being able to identify the best bit to hook and when I say best I mean part of the hold that will keep you hooked throughout the range of motion. For this you will need to think how your body will go into the move and where it will finish at the end of the move.
Check your footwear, got fat baggy heels which your foot freely rotates in when under pressure? Time to ditch the shoes for a pair with a snugger fit.
Review the process, what aspect of heel hooking causes the move to fail? Many people slap a heel on, it sticks and then need do nothing else, at the harder grades you cant get away with this.
You will need to be more active in the pressing, torquing of the heel, paying attention to the angle of your heel to the rock to avoid that sheering point where the force through your heel along the plain of rock exceeds that of force into the rock to keep it on.
Review your core, side plank, back bridge and core control exercises such as controlled twists whilst hanging will help.
Post edited at 18:58