I'm an amateur who has played for a couple of years. In the beginning I bought just a random racket - "for beginners", they say. Then I saw some Big Helmet tournaments and got curious about players who punch their rackets and change the behavior.
How exactly does the tension affect the game? And if the tension really matters, then how will I know if I need to restring?
Does it make sense to try to play with a different racket - will I "feel" the difference?
I'll try my best to answer your question - I don't quite understand what you're asking when you say
punches their racquet's strings and changes the racquet after that
If you are a beginning tennis player, the rule of thumb is that you should restring your racquet as many times in a year as you play in a week. So if you play twice a week, you should get your racquet restrung every 6 months. Some people play with the same strings for years or until the strings break.
The reason some players get the strings replaced before they break is because of tension loss. It depends on the string material used - but all strings lose tension after being used for a while.
For professional players, they get their racquets restrung constantly because any amount of tension loss can potentially affect their shots, so they try to minimize how much that can happen. A single player could get anywhere from 2-10 racquets restrung for a tournament. The very top players (like Federer, Nadal, Djokovic, Murray, etc.) can get about 8 racquets restrung for them before every match they play. They pay a professional racquet stringing company to travel with them to various tournaments to restring their racquets for them.
Unless you are a fairly advanced player, you are not likely to notice a little difference in the amount of tension in strings - like 3-5 kg difference. But for advanced players, they will notice because they have a better feel for the tension.
Tension typically affects the amount of power (or control) you get from the strings. The lower the tension - the more power you get. The higher the tension, the less power (thus control) you get. It's just like a trampoline - a loose trampoline will bounce you higher in the air than a tight one will.
Not sure where anyone got the information that higher/lower tension changes the size of a sweet spot. It's the racquet head size and the number of strings. (Definition of a sweet spot is the most efficient power generated with the least amount of vibration)
That said, I found an interesting article published by a Dr. at the University of Sheffield (http://www.tennisindustrymag.com/articles/2005/01/does_higher_string_tension_giv.html) which shows the correlation between low tension - 40lbs and high tension - 70lbs and their effects on spin. (Seeing as we know that more power will be generated with lower tension)
If you don't want to read - it summarises that with higher tension you are more likely to execute a shot correctly as the ball does not travel along the stringbed as much as it would at a lower tension.
The conclusion: "Changing racquet tension does not affect spin, but it does affect string movement, dwell time, and ball contact distance. These latter parameters all can affect the ball trajectory as well as the player’s feel of the impact. The main advice is that high string tensions make your shot more consistent and make it easier to hit topspin shots." - Dr. Simon Goodwill
The tension of a racket really matters !!
All has to do with the so called sweet spot. The higher the tension, the smaller the sweet spot, the less likely for you to hit optimally.
After a racket has been restrung, tension usually drops a bit (0.5 - 1.0 kg), maintaining a steady tension afterwards. Restringing a racket (for me at least) only happens when one of the strings snap.
Only experienced players or (semi)-professional players will notice a decline in racket tension. You shouldn't be worrying about that.
Yes, the tension on your racket matters. A loosely strung racket will act like a trampoline. When you hit the ball, your strings will generate more speed on your shots. But with a higher tension, this rebound effect is reduced, giving you a smaller sweet spot but more control.
