Two rules about string tension get passed from player to player: string it tighter for control, looser for power. A player who has been missing long asks for a few more pounds. A player who wants more pace asks for a few less. Both expect to feel the difference on the first ball.
Tension does matter, but the research suggests it matters in quieter ways than the rules imply. A lower tension does not make a racket weaker. It does not make it much more powerful either, and most players cannot feel small changes at all.
What the physics says
The basic mechanism is simple. When ball and strings meet, both deform, and the ball is the poor performer. According to a review written at the ITF, “the majority of energy loss during racket/ball contact is in the ball, which returns up to about 50% of its pre-impact energy, whereas the strings are much more efficient, being 90-95% energy efficient.” A softer string bed takes more of the deformation, the ball takes less, and a little less energy is lost.
A little is the important word. Using a physics model of the racket, Rod Cross concluded that “Racket power can also be increased by stringing the racket at a lower tension, but the effect is almost negligible.” His estimate: “if the string tension in a tennis racket is decreased from 60 to 50 lb, the increase in serve speed will be only about 0.7%. In the case of a forehand or backhand, the corresponding increase in ball speed is about 1.1%.”
What happens on court
On court, the effect was a little larger. In a study of 41 advanced players who hit 1312 forehands with rackets strung with nylon at 180, 230 and 280 newtons (about 40, 51 and 62 lb), “low string tensions (180 N) produced greater rebound speeds (108.1+/-9.9 km.h-1) than high string tensions (280 N, 105.3+/-9.6 km.h-1; P<0.05).” The difference between low and high tension was “approximately 3%, a value that is consistent with theoretical estimates.”
The same study found a change in direction that matters more than the speed. Looser strings sent the ball on a path “approximately 2° higher” with a topspin stroke. The authors give an example: “For a ball struck at 20 m·s-1 with an angle of inclination of 14°, a 2° increase would result in a 2.5-m increase in the range of the ball and a 0.36-m increase in the maximum height of its flight path.” The error pattern followed: “High string tension was more likely to result in a net error, whereas low string tension was more likely to result in the ball travelling long.”
Real players complicate the physics further. When 18 elite men hit with rackets at different tensions, the very loose racket did not produce faster balls. The researchers noted that this was “contrary to previous laboratory-based tests” and suggested the cause “may be attributable to lower swing speeds from participants as they were not familiar with such a low string tension.” Recent studies with polyester strings have not found a simple rule either. One, with 15 players at 48, 54 and 60 lb, found “A significantly higher ball speed was observed at 54lbs compared to both 48lbs and 60lbs”. Another, with 27 trained players between 40 and 60 lb, found that “String tension did not significantly affect ball speed, whereas accuracy differed significantly across tensions”.
The fair summary is that, as far as the physics goes, lower tension does not cost power and may add a little. On court, with real swings and modern strings, the gain is small and can disappear, and in one study the middle tension was the fastest.
Control, or launch angle?
What about control? The ITF review is frank: “The reason for higher string tension generating more control is not as well established.” The on-court study suggests one part of the answer. If tighter strings send the ball out at a slightly lower angle, a player who has been hitting long will see more balls land in, and will call that control. A player who has been hitting into the net will see the opposite.
So the error pattern is useful information. Mostly long can mean the string bed is too soft for that swing, and mostly in the net can mean it is too firm, although technique and the type of shot still matter more than either.
The number on the machine is not the tension you play with
The tension a stringer sets is a pull tension, and it is not what ends up in the racket. Measurements in strung rackets found that “the tension immediately after stringing with a nylon string is about 30% lower than the pull tension, and the tension immediately after stringing with a polyester string is about 40% lower than the pull tension.” The same authors went further: “string tension by itself is not an important parameter in a tennis racket. The important parameter is the string-bed stiffness, which depends on factors such as head size and string type as well as string tension.”
Strings also relax. In laboratory tests on 90 strings, “if a racket is strung at a tension of 28 kg, the tension will drop typically to about 24 kg within 20 min, which is about the time it takes to string a racket. After 24 h, the tension is typically about 20 kg.” String types differ: “Natural gut has one of the lowest rates of tension loss (some kevlar strings are lower) while all polyester strings lose tension rapidly.” Exact figures depend on the string and the test, but the message is the same: the same number on two machines, or on two kinds of string, does not mean the same string bed.
Can players feel it?
Most cannot feel small changes. In one study, “Only 11 (27%) of those tested could correctly identify a tension difference of 5 kg (11 lb) or less. Fifteen (37%) could not pick a difference of 10 kg (22 lb).” The authors also noted that “impact sound was an important factor”. Elite players did not do much better: “Eleven participants (61%) could not correctly detect a 75 N (17 lb) difference between rackets. Only two participants (11%) could correctly detect a 25 N (6 lb) difference.” A request for two pounds more or less is, for most players, a request they will not be able to feel.
What about the elbow?
Lower tension is often recommended for sore elbows, and there is some laboratory support for the idea. With 20 recreational players holding a racket still while a machine fired balls at it, average peak acceleration at the elbow was 5.58 m/s² at 200 N, 6.83 at 222 N and 7.45 at 245 N. But the same study found that “an off-centred shot produced an acceleration amplitude that was almost three times that of a shot on the defined target location”, and its authors wrote that “Future observational studies are required to assess string tension and subsequent development of tennis elbow.”
A review of racket properties and injury listed the location of impact on the racket head, racket stiffness and grip force as influences on “shock and vibration to the arm”, and an early study of more than 500 players found that “age and amount of playing time per day were contributing factors” to tennis elbow. Neither abstract mentions tension. Lowering tension is a reasonable thing to try, but there is no evidence that it prevents tennis elbow, and anyone with elbow pain should have it checked by a doctor or physiotherapist.
How to test tension properly
The research points to a simple way to choose:
- Change in large steps. Most players cannot feel 5 kg, so small adjustments mostly change the label.
- Test blind. Ask someone to string two or three rackets with the same string at different tensions and label them with codes.
- Watch where the misses go. Mostly long suggests trying a firmer string bed, and mostly in the net a softer one.
- Measure, not only feel. Count balls in a target zone and, if possible, measure ball speed. As one recent study put it, “Perceived comfort provides complementary information but should not replace objective performance testing”.
- Compare like with like. The same tension in polyester and in nylon or gut is a different string bed, and polyester loses tension fastest.
Lower is not weaker, and tighter is not automatically more controlled. Tension changes the launch angle and the feel a little, and the string, the frame and the swing change them more. A careful test in practice will say more about the right tension than any rule.
Sources
- Miller (2006). Modern tennis rackets, balls, and surfaces. British Journal of Sports Medicine, 40(5), 401-405. doi.org/10.1136/bjsm.2005.023283
- Cross (2000). Flexible beam analysis of the effects of string tension and frame stiffness on racket performance. Sports Engineering, 3(2), 111-122. doi.org/10.1046/j.1460-2687.2000.00046.x
- Bower and Cross (2005). String tension effects on tennis ball rebound speed and accuracy during playing conditions. Journal of Sports Sciences, 23(7), 765-771. doi.org/10.1080/02640410400021914
- Bower and Cross (2008). Elite tennis player sensitivity to changes in string tension and the effect on resulting ball dynamics. Sports Engineering, 11(1), 31-36. doi.org/10.1007/s12283-008-0006-z
- Zhao, Li and Liu (2025). Effects of different tennis racket string tension on forehand stroke effect and racket dynamic impact. PLoS ONE, 20(1), e0317442. doi.org/10.1371/journal.pone.0317442
- Yang, Sun and Ren (2026). Subjective-objective fit in tennis racket string-tension selection: perceived comfort, hitting performance, and fastest swing-speed associations. Frontiers in Psychology, 17, 1889737. doi.org/10.3389/fpsyg.2026.1889737
- Cross and Bower (2001). Measurements of string tension in a tennis racket. Sports Engineering, 4(3), 165-175. doi.org/10.1046/j.1460-2687.2001.00082.x
- Cross, Lindsey and Andruczyk (2000). Laboratory testing of tennis strings. Sports Engineering, 3(4), 219-230. doi.org/10.1046/j.1460-2687.2000.00064.x
- Bower and Cross (2003). Player sensitivity to changes in string tension in a tennis racket. Journal of Science and Medicine in Sport, 6(1), 120-131. doi.org/10.1016/s1440-2440(03)80015-4
- Mohandhas, Makaram, Drew, Wang, Arnold and Abboud (2016). Racquet string tension directly affects force experienced at the elbow: implications for the development of lateral epicondylitis in tennis players. Shoulder and Elbow, 8(3), 184-191. doi.org/10.1177/1758573216640201
- Hennig (2007). Influence of racket properties on injuries and performance in tennis. Exercise and Sport Sciences Reviews, 35(2), 62-66. doi.org/10.1249/JES.0b013e31803ec43e
- Gruchow and Pelletier (1979). An epidemiologic study of tennis elbow. American Journal of Sports Medicine, 7(4), 234-238. doi.org/10.1177/036354657900700405
