Tennis technique: does the wrist really have to be LOOSE at impact? 

I would say this: 100% tightness means that all muscles are activated. 100% looseness means that no muscles are activated. If all muscles are activated at near full strength, then you will not be able to hit a good shot. If you are "loose" then you can more easily choose which muscles to activate at what time(s)-this is coordination. The vast majority of players are over-activating the muscles of their arms. They assume that because the direction and speed of the ball is determined by muscle, that more activation will get them more of both. If a coach tells a player to be "loose" and they deactivate a lot of the muscles in their arms, manage to hit the ball, and the racquet doesn't fly out of their hands, then the player has clearly activated their muscles appropriately to at least prevent the racquet from slipping. We are not good a literal instruction since we don't think in terms of muscles and muscular activation (for instance, we don't think: ramp up activation of extensor carpi radialis longus from 3% to 17% and as it approaches 9%, drop activation of the tires major from 22% to 5%, then activate the extensor carpi ulnaris sharply from 15% to 45%), we think in movement and we use real world feedback to subconsciously inform what we do. So what am I saying. I agree, the “loose” terminology is literally wrong. However, I would argue that it is metaphorically correct. The purpose of instruction is to induce a better stroke in your player. I personally find it helpful to use both literal and metaphorical descriptors in my coaching. I tend to explain what is actually happening to the best of my ability/understanding, and then, I apply whatever metaphorical instruction helps them make sense of the stroke and gets them to better coordinate their bodies.

Hi there, very helpful. The mental image of being really loose and then firm on contact helped me nearly instantly. Thank you. I like your accent; not wanting to come across as a smart ass, and not having English as my mother tongue myself, still, one simple improvement tip for you: The „ed“, which changes verbs to the past tense (eg improve -> improved ) is not a spoken syllable. The e is silent, phonetically only a “d“ gets added to the end of the verb. Improv[e]d; discuss[e]d; confirm[e]d etc (Of course with some exceptions, like in the above used verb “added”:)

When you accelerate you should be relaxed as possible but at the moment you hit the ball you should tighten up and then realease the tension again. It is the exact same principle as in karate.

can you make a video of your take on the dominant eye's role in tennis??

Non credo Mouratoglou suggerisca a Rune di tenere la mano rilassata. Empiricamente, possiamo però dire che contribuire a far sì che principianti e amatori non tengano praticamente tutti i muscoli vicino al polso, attivati per tutta l'azione, li aiuta a sperimentare accelerazioni maggiori. L 'evoluzione, per poter cacciare lanciando, ci ha consegnato un polso così fatto, ma un tennista molto scarso lo avverte principalmente come un fattore di perdita di controllo

Limp wrist. Just about sums up this video.

Devi stare sciolto anche quando parli inglese