One of the most overlooked areas in the equipment tennis players’ use is the string they play with.
I have found that a common mistake junior players’ make is focusing too much on the racket model they use and not paying enough attention to the string and tension of the racket. Although the right racket is important and should be selected based on the players’ size, strength, ability and age, the string a player uses is just as crucial as it is directly linked to power, spin, control and injury prevention. An error most players are prone to is using the same string as the pros and then following the recommended tension for the particular racket. This is often not the best decision.
For example:
Polyester is the most common string in a junior racket and is often strung too tightly. If you choose to use a full polyester string it is recommend dropping the tension by at least three – five pounds. This will help with reducing the risk of injury as it limits the stress and shock incurred by your arm and shoulder at impact along with taking away some of the vibration. Many injuries can occur because of the string or tension in the racket. If you insist on using full Polyester, a quick tip is to start by dropping the tension. 
Another area to focus on when choosing suitable string to use, especially for younger players, is not only how you hit the ball, but also how much you are practicing. In younger players who are still developing and growing the recommendation would be to use a softer synthetic string or blend the polyester with a synthetic string. You should also lower the tension on the polyester if you blend your string, as a guide the polyester should be on average at least two pounds less than the synthetic string.
I have seen junior players and pros go both ways with blending the string. A couple of examples being polyester mains with synthetic crosses, which is the most common, or synthetic mains with polyester crosses. How you choose to blend the string is completely based on your preference.
Lots of players today are stringing their rackets lower than the recommended tension for that racket. At first you may feel like you have less control and more power but that consistency will improve the more you play with it.
Additional information:
The tension in your racket will vary based on the conditions in which you are competing in or practicing. The rule of thumb is that if you are playing indoors, at altitude or on a fast court surface you should increase the tension anywhere from two to four pounds. 
If you are playing on a slow damp clay court or a gritty slow hard court and it is humid or damp outside you ought to lower your tension by two to four pounds.
Finally, all your rackets should never be strung at the same tension. For example, if you have 3 rackets, one racket should have a different tension two to four pounds less or more depending on the surface, weather or overall conditions you are playing in. This is because the conditions can often change during the course of a match.
In conclusion, having a greater awareness about the string and tension you use in your rackets is important for improving your game, reducing the risk of suffering injury and giving you an extra edge. Hopefully this article is helpful and gives you an insight into how best to go about choosing the strings and tension you play with.
Best of luck to you all!
Frank Salazar (JTCC Senior Director of High Performance)
