If you take a look at the stringing instruction label in the picture above, you'll see that for that particular day, Roger Federer has requested that both his main and cross strings undergo a process called pre-stretching.
But what is this process, and what are the benefits of doing so? Are there any negatives? Do all pros have their string pre-stretched? Should you tell your stringer to pre-stretch your strings next time? Let's take a look.
What Does Pre Stretching Tennis Strings Mean?
Pre stretching refers to the practice of stretching a tennis string before you start to string a racquet with it.
Rather than just cutting the string off the reel, threading it through the first grommet hole and starting to pull tension with the stringing machine, pre-stretching means you apply some tension to the string to change its properties.
The reason strings are sometimes pre-stretched is to slow down the initial tension loss that occurs as soon as a racquet is strung.
All tennis strings have a certain level of elasticity, so by stretching them beforehand, you are essentially removing elasticity from the string, which will result in less tension loss across the string bed over time
This is used so your string bed will maintain a consistent feel through the life of the strings. A significant drop in tension (through tension loss) can affect the accuracy of your shots, which in the pro game where the margins are small can be the difference between winning and losing.
How To Pre Stretch Tennis Strings
There are two ways you can pre-stretch a tennis string:
The first is the old school method which involves looping the string around a fixed object like a door handle, walking to the other side of the room with both ends of the string until it's under tension and using your body weight to stretch it. Just make sure it's a fairly round object that won't kink or cut into the string.
The second is to use the pre-stretching feature found on several modern stringing machines. This built-in feature lets you pull strings at a higher tension before dropping down to your preferred tension. You can then clamp off, weave the next string and pre-stretch again.
The pre-stretch function on these machines can usually be set to pull at a fixed percentage above the desired tension.
For example, if you set 10% pre-stretch on the machine and want to string your racket at 50 lbs, the machine will initially pull the string to 55 lbs (10% above 50 lbs) before reducing it to the desired 50 lbs.
This makes the string less elastic, and along with a good tie-off knot (I prefer the Parnell knot), it should help reduce tension loss.
You can also achieve a similar effect on crank or drop-weight stringing machines. However, the process for pre-stretching is slightly different.
Many stringers using a crank machine will opt to pre-stretch by double-pulling tension. This means they pull the set tension, release the string, then pull it again. You could manually adjust the tension before each pull but considering this is done by adjusting a spring; it's both tiresome and easy to forget between each string pull.
Stringers using a drop-weight machine usually pull tension once but leave the weight applied to the pull for a specified amount of time.
Which is Better: Machine Pull or Manual Pre Stretch?
In terms of which is better, I don't think there is a right or wrong answer.
For removing elasticity, the machine pre-stretch is more effective as it pulls an increased tension on a shorter area of the string, immediately before the string is pulled again to the correct tension.
However, for making the string more comfortable to work with (reducing coil memory) and applying some pre-stretch, the manual method does a better job.
I prefer the manual method as it makes natural gut easier to string with, and your bodyweight does a good enough job at pre-stretching. This is also the method used by Roger Federer's stringers, Priority 1.
As for which you should choose, I would say if you are looking to significantly reduce tension loss or want a deader feeling stringbed, using pre-stretch from the machine is a good option.
If you just want to reduce the liveliness of a natural gut string and give it a little pre-stretch, the looping round an object is fine. The more bodyweight and muscle you put into the string, the more it's stretched.
Why Do Some Players Request Pre Stretching?
Tension loss typically isn't a massive concern for pro players as they get their racquets strung so frequently and play with them just a few hours after they were freshly strung.
However, a racquet starts to lose some tension as soon as it's off the stringing machine, and for players who want that feeling of ultra-consistent tension, then pre-stretching is a way to minimise tension loss.
The other reason some players will opt for a pre-stretch (usually 10%) is that they prefer the slightly deadened feeling that strings at higher tension offer.
Take, for example, Venus Williams, who has been know to string as high as 80lbs, along with a 10% pre-stretch. She enjoys that board like string bed because the strings have had some of their elasticity removed.
As for Federer, in the main image of this post, he has requested both his main strings (natural gut) and his cross strings (polyester) to be pre-strung.
Typically Federer will only have his mains pre-stretched, so I'm not sure why this changed for the Laver Cup. Indoor conditions, the time accrued before he would use the racquet and just personal preference on the given day could all play a part.
Federer's usual preference for just having his mains pre-stretched will be for tension maintenance and perhaps ever so slightly reducing the liveliness natural gut offers.
In terms of a rough estimate, I'd say around 40-50% of players will ask for pre-stretching.
None of the tournament stringing rooms offers pre-stretching as a default option, so it's up to the players to request it alongside any other non-standard tweaks required like using around the world stringing method, 2 knots instead of 4, power pads or string savers that aren't part of the stringing room's default set up.
Are There Any Types of String You Shouldn't Pre Stretch?
The general line of thinking is that pre-stretching polyester strings is not advisable. You are taking a string that already has little elasticity to it and making it even less so.
While this will have a benefit to tension maintenance (poly strings lose tension quicker), you are taking away some of the playability of the string and also reducing its overall shelf life in the racquet.
From my experience, polyester strings at high tensions (or pre-stretched) will go dead quicker. Considering they don't last long anyway, I can't see the benefit.
For recreational players, I don't see that making too much sense either. It's quite rare for your average club player to hit the ball big enough to see many benefits from polyester in its normal state, so to make it even deader by pre-stretching isn't a logical move.
Still, many players do request for their polyester strings to be pre-stretched. As for the reasoning, it's a combination of wanting increased tension maintenance and enjoying that ultra dead feeling that allows them to take massive cuts at the ball and still find the court.
Why Do Stringers Sometimes Pre Stretch Strings?
Even if a player hasn't requested a pre-stretch, or you are stringing your own racquets but don't want to do a full pre-stretch, it can be beneficial to give the string a slight stretch to make the job easier.
When strings come off a reel, they have a coil memory which makes them rather annoying to handle and more likely to kink which is bad for the string.
Whenever I'm stringing my racquet, I tend to give all strings a very light pre-stretch by looping them around a door handle and pulling them tight to reduce those coils and make them easier to string with.
This has little to no effect on the playability of the string as I'm not applying a ton of weight, but it makes the job easier and reduces the chance of kinks which can lead to premature breakage of a string.
Should You Pre Stretch Your Strings?
Like most things with racquets, pre-stretching is purely a preference thing. Many pros do it through force of habit as it is likely what their coaches suggested when they first started playing the game at a more serious level.
So while it might be worth testing if you feel like tension loss affects your game, I recommend that, instead of pre-stretching, simply string your racquet a few pounds higher than your desired tension.
Do you pre-stretch your tennis strings? If so, why do you do it? Let me know in the comments.