There are many factors to consider when purchasing a tennis racquet. Weight. Balance. Celebrity endorsements. But one of the least understood concepts is flex or stiffness in a tennis racquet. What does stiffness mean in a tennis racket? Well, quite a bit as it turns out.

If you had trouble with science when you were in school, you could be surprised to find out that science does play a role in tennis racquet technology. The good news for you is there is no quiz at the end of this discussion. The better news is, you will be better able to decide between a flexible tennis racquet and a stiffer racquet the next time you go to buy a new tennis racquet.

Everyone agrees that the perfect tennis racquet is one that generates enormous power while controlling the ball with spin on demand that always feels good to the arm. The problem is, that one racquet for every player has never been invented. So, every player must find the best combination of these factors for their game and for their budget.

The strings are "dented" by the ball. The racquet frame "bends" just a bit when contact is made. When the racquet springs back to its regular shape, the rebound or trampoline effect can help create power.

All that flex can mean vibrations are created. Those vibrations have to go somewhere and various brands have any number of ways to control vibration so it does not wind up causing tennis elbow or other arm issues. A racket that minimizes any vibration reaching the arm is said to be arm friendly.

Lots of variables come into play in figuring out how much energy is transferred to the ball. The more energy that gets transferred to the ball the more power is exhibited.

How hard do you swing the racquet? It probably varies with every stroke. Your technique. Your physical strength and stamina. These things all count.

There is no one perfect technique to swing the racquet. However, if you like tennis, professional instruction can help you find the technique to improve how you play the game. You will probably also like tennis even more as you will be playing the game with higher skill and less risk of arm issues.

Do you consistently hit right in the sweet spot? Even the pros don't get there every single time. But if your game means you hit off center, or on the frame a great deal, then the tennis racquet stiffness will affect how much energy is actually applied to the ball and how much vibration is created.

If your string tension is at the high end of the recommendations, the strings will give less but it might put more stress on the racquet's frame causing it to flex more. Conversely, lower tension means the string will give more, creating a bigger trampoline effect.

Experimenting with your tension is an excellent idea when pain first shows up when you play. Check the specs to see if your racquet's recommended tension will allow a lower tension. The specs can usually be found on the neck of the racquet's frame.

Stringing professionals (like those at Tennisracquets.com) will also be able to make recommendations for most racquets on the market today. New string might be a great first step.

The differences between relatively stiff strings like synthetic gut or poly and multifilament string or natural gut are real. A softer string will certainly impact power, control, and how much vibration reaches the arm.

Every player who has pain in the elbow, wrist or shoulder should be looking at not just tennis racquet stiffness but string too. An arm friendly tennis racquet frame combined with a softer string could be the answer to tennis elbow for many.

A larger head size should mean a larger sweet spot to contact the ball. But it also means more flex in the head of the frame. This can result in less control if not compensated for in a stiffer racquet. The head size and shape directly influences manufacturers' constructing arm friendly tennis racquets.

Hitting the ball perfectly square will mean more efficient energy transfer. But any tennis player beyond the raw beginner is hitting with spin of many dimensions: topspin, slices, side spin and combinations. The flex in a racquet will influence how much spin is created at contact.

Generally speaking, the longer the ball stays on the strings, the greater the spin. So a softer string with a more flexible racquet ought to help create spin.

A tennis racquet that is head heavy will be somewhat harder to swing. This is where the balance of the racket is nearer the top of the racquet's head than it is to the base of the grip. It is not a description of the overall weight of rackets.

But the payoff should be less vibration reaching the arm and a better transfer of energy. But not all of these tennis racquets are arm friendly so these other factors listed here must also be considered in addressing tennis elbow and other arm issues.

Head light rackets are where the balance is closer to the base than the top of the head. They are easier to swing and are often the best choice for beginners. They will generate less power as a general rule.

The overall weight of a tennis racquet is more about materials than anything else. It is more difficult, however, to make a stiff racquet light in weight. If the objective is to produce a light weight racket that is stiffer than average, the manufacturer will need to employ the latest research and materials.

If however, a more flexible frame is desired, a light weight construction is often used. A flexible frame could, however, result in less power. A flexible frame with a light weight construction may compromise control as well as have less power.

You would think there would be an industry set of specs for stiffness ratings. There are not. Various companies like Wilson have their own specs for determining tennis racquet stiffness. Their Stiffness Index (SI) is a stiffness rating only used for their tennis rackets like the arm friendly Wilson Clash.

The most widely used stiffness ratings are generated off the Babolat RDC (Racquet Diagnostic Center). The Racquet Analysis (RA rating) score is used on their entire lineup including the Babolat Pure Drive on a 1-100 point scale. The higher the number, the stiffer the tennis racket.

You will generally find these ratings in the specs listed in a racquet's description.

While these machines could be hard to find and expensive (perhaps $5000 or so), the specs creating their stiffness rating have become accepted by other tennis racket manufacturers as well. The RA Rating has therefore become a valuable tool in identifying arm friendly tennis racquets in the battle against tennis elbow.

Another complication in comparing a stiffness rating is that some websites (not Tennisracquets.com) publish their own numbers after strings are placed in the tennis racket. When this technique is used their stiffness ratings should be considered proprietary and not comparable to other stiffness ratings.

There is nothing inherently wrong with this method. However, it could lead to confusion if the consumer is not aware of this difference.

There are those who believe that the trampoline effect found in more flexible racquets yields more power. The rebounding of the strings and the frame releases the energy stored in the flex which is then transferred to the ball as it leaves the strings. Therefore, the theory is low stiffness rackets help generate power.

The rub is that the ball does not stay on the strings long enough to actually receive this energy. While the science is not totally settled, the consensus view is that stiff racquets mean more power, and less control and more risk for arm pain including tennis elbow due to vibration.

This does not mean every player ought to buy low RA Rating racquets although the trend toward a more flexible racquet is ongoing. But combinations like high RA Rating frames (a stiff racquet)with softer strings is sometimes adopted to have more power with less vibration thereby reducing the risk of tennis elbow.

The same is true with combinations of lower RA Ratings (a flexible tennis racquet) with stiffer strings. Throw in the option of playing with higher vs lower string tensions and you have a fascinating set of options for those who love the game of tennis. To be sure, tennis elbow only impacts a minority of players, but if it impacts you, finding a solution with arm friendly tennis racquets is a priority.

Deciding on playing with low stiffness rackets is not a simple decision. Hitting with flexible rackets may address elbow issues but have other implications for power, control and spin.

Playing with flexible rackets is not for everyone. But the many new racquets on the market addressing tennis elbow are using innovative materials and construction methods. The stiff vs. flex debate will continue.

One thing that is certain: playing with arm pain whether from tennis elbow or some other cause may be addressed with a new racquet, string type, or even string tension. Of course, you should see your doctor if pain persists or increases.

At tennisracquets.com you have a huge choice of both flexible and stiff racquets. We also have balls, apparel, shoes and accessories making us your one stop shop. Need some advice? Have questions? Call our stellar Customer Service staff. We love to help!