After passing 100kg/220lbs on deadlift my double overhand grip started to feel weaker. What do you recommend to increase grip strength?
Your double overhand deadlift is always and forever going to be limited by grip strength. If you want to continue deadlifting heavier, learn the hook grip or use a mixed grip.
If you try hook grip now it wont be nearly as painful or hard to adjust to than if if you first try it when you pull 440.
If someone has no aspirations of competing, can’t tolerate the hook grip, and isn’t interested in using the mixed grip, they can use straps.
I personally own and use the IronMind - Strong Enough straps.
Personally, I don’t compete either. But I would still recommend using some sort of modified grip with your standard, lower rep, lower set deadlifts. Usually, people will use straps for the higher volume pulling exercises, like RDL’s and rack pulls. If you decide to try the hook grip, start with your warmup sets. Slowly work your way up to your worksets over multiple workouts to help desensitize it. Some people use athletic tape over their thumb. Personally, it makes it more unstable for me due to sweat. It’s more of a discomfort than painful. Otherwise, the mixed grip does not hurt at all. It is just a little akward. It also requires a lot more attention to keeping the bar from twisting laterally. For the first time, you may want to use it on all of your warmups. After that, you should just use it on the last warmup and all work sets.
I will say that trying to put the straps on and maintaining the proper position in a deadlift is challenging.