When I work on blocker mechanics with my players there are a couple of key points I try to get them to focus on in their execution. One of them is what they do with their hands. The tendency among blockers is to just put their hands up above their heads. Maybe they get a bit of penetration over the net. If you’re a massive player and/or have a huge jump, then this might work just fine. Most mere mortal volleyball players, though, need something a bit more to execute good blocks.
What I have my players work on is pointing their thumbs up such that rather than the fingers extending the line of the forearms, it is the thumb that does so. This rotates the fingers outward, thereby broadening the block in the area of the hands.
The act of pointing the thumbs up also tends lock the elbows. Many newer blockers have the problem of never actually getting their arms fully extended. This thumb pointing can help correct that problem. If you really get them to focus on pushing their thumbs up and not just turning the hand it will help get the shoulder shrug into their block that gives them that little bit more length in their arms which could make all the difference.
See also blocking visual cues.
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