How do you develop super strong grip? Like being able to tear the phonebook type of grip? Serious.
Try some towel pull ups. I used to regularly do sets of 5-15 reps for a total of 100 reps daily (earlier on you might possibly do more than 15 reps, but as you get to the higher numbers, your grip goes).
Try buying Captains of Crush grippers. I started with a #1 years ago. Then, I advanced to doing 20-30 reps with the #1 and jumped to the #2. Once you are able to do about 20 reps with the #2, proceed to the #3. From the #3 on, it becomes logarithmically difficult to bang out double digit reps.
You can also try regular & reverse wrist curls while standing and using exercise bands with heavy resistance. I like the bands over the barbells, because it gives your wrist better range of motion and you can just manipulate angles a little better.
Now, none of these on their own or even in combination of each other will guarantee your ability to tear through a phone book. To be quite honest, I don't think I've ever met anyone capable of such a feat. Nonetheless, those exercises will give you a very strong grip.
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