Tennis is a unique sport. Unlike cycling, rowing or running events, the best performances cannot be evaluated based on times posted at world championships or Olympic games. Nor is tennis a team sport like basketball soccer, where complex tactical and technical interactions between units of players are captained and coached from the side-line. In tennis, the player is almost always alone, win or lose.

The tennis athlete that makes it to the professional ranks is one that has invested many years of physical and mental preparation. A top 10 ATP/WTA players demonstrates a complex interaction among talent, motivation, trainability, training, nutrition and supplementation (you decide how you want to order these) that is likely to have been evident from a very young age. Until recently, no standard measure of success/achievement had been published in the scientific literature for tennis. For example, some players achieve top ten ranking only to reduce their physical investment in the sport thereafter. However, a recent study published by INSEP (National Institute of Sports Expertise and Performance, Paris, France) has done an excellent job on analysing the careers of all men and women that have been top 10 players since 1968 i.e. since The Open Era started. In their study, INSEP present a new measure that describes the competitive career of a top 10 ATP & WTA player; the percentage of victories by age.

The data demonstrate that the tennis athlete who makes it to the top 10 is one that enjoys very early success. This statement is true of both male and female professional players, and is unlike athletes involved in track & field, swimming, baseball and golf, who mature physiologically, mentally and tactically in their mid-twenties (Len 2009, Moore 1975, Schulz 1988). The INSEP study highlights the advantage and disadvantage of precocity in tennis: on the one hand, those players who reach world no. 1 status enjoy earlier success than their no. 2-10 rivals i.e. they have a higher victory percentage at their peak age which is 21.5 years. A higher victory percentage goes in hand with more prize money, more sponsorship, and the intangibles of fame and recognition. However, in line with the precocity-longevity theory (McCann 2003), there is no advantage to the duration of playing career in being an early starter and in fact it may be detrimental to the long-term health of the athlete (American Academy of Paediatrics 2000).

 

The professionalisation of tennis: G1 and G2 players

If you take a sneak-peak into any tennis club or academy across North America, in the UK or Australia, you will notice that all the kids (age 5+) turn up for training with bottles of Gatorade, recovery bars, separate tennis and fitness shoes, and multiple rackets. It is a good thing that kids participate in sports early on in their lives so that they can have FUN, but the professionalisation of tennis at a young age allows for the distinction of two generations of players in the INSEP study, named G1and G2 (players from 1968-1985, and players from 1985-2009 respectively). It is likely that the economic environment within tennis (Novak Djokovic has earned $35m aged 24), the superior technical and physical skills of todays’ young athletes, and the advent of sports science including the intensive research into nutrition and recovery over the past 20 years has contributed to tennis academies that invest a lot early on. And the results of this investment are impressive. There are not many sports that can claim that the top 10 female athlete turns pro aged 15, 17 for the males. (Notice that neither female nor male top 10 players reaches adulthood before their professional careers take off?)

 

The INSEP study

The aim of the study was to model the progression of top 10 players as a function of age. The study divided all the top 10 players since 1968, and classified them as G1 who played their first match before 1985 (NF = 47, NM = 69), or G2 (NW = 50, NM = 75) who played their first match after 1985. A total of 50,933 matches were analysed for 97 women and 144 men that were ranked in the top 10 between 1968-2009. The year 1985 was chosen as the median year to divide players that ensured homogenous numbers across the two generations. Variables including gender, best ranking, age of career start and retirement were taken from the ATP, WTA and ITF websites. Each player was defined according to generation (G1 or G2), length of career, age and number of matches played per year.

Once data were collected, the % of victory for each top ten male and female players were calculated per year, and fitted to an exponential curve model. Additional analyses for all no. 1 players were performed and compared with no. 2 – 10 players. The curve model allowed for the peak performance age of top ten players to be calculated. Data are presented as mean and SD, where significance was set at p < 0.05.


The results: career length, age of first professional match, and age of retirement

The following results are presented in a table below

                     

Women

G1

G2

Gap

Sig. p<0.05

First match

16.53 ± 1.85

15.24 ± 1.29

1.29

*

Last match

31.43 ± 5.42

30.22 ± 3.56

1.21

 
Career length

15.89 ± 5.02

15.52 ± 3.19

0.37

 

 

Men

G

G2

        Gap

Sig. p<0.05 

First match

17.88 ± 1.90

17.09 ± 1.32

0.79

*

Last match

33.64 ± 4.42

31.24 ± 2.50

2.40

*

Career length

16.75 ± 4.26

14.68 ± 2.54

2.07

*

Data are presented as mean and standard deviation.  

 

The significant findings can be summarised as follows: G2 women start their professional careers significantly earlier than G1 women and the same finding is true for G2 men. G2 men have significantly shorter careers than G1 men. This is reflected in the age of their last match played ages 31 for G2 man versus 33 for G1 men.

 

The percentage of victories by age

Top 10 women achieve a 69.7 peak win percentage aged 21.5 years, with no. 1’s achieving an 82.5% peak win percentage at the same age. For the men, the top 10 achieve a peak win percentage of 69.4% aged 24.1 years, with no. 1’s increasing their win percentage to 78.5% aged 23.7 years (see Steffi Graf and Pete Sampras two graphs down)

 

 

While the G2 peak-win percentage occurs earlier than that of G1 players, no advantage is offered in terms of achieving a greater win percentage or increase in career length. Similarly for G2 men, the peak-win percentage occurs earlier than G1 players, however G2 players do not achieve a greater percentage of career wins (see graph below). In our graphs, the area under the curve (AUC) is the mathematical modelling that is fitted to the data, and is basically curve that describes the lifetime performance of a player. A greater area under the curve would indicate a longer career and higher percentage of victories, however when analysed this doesn’t happen for G2 v G1 players.

 

 

A very good example of the success of no. 1’s in both the men and women’s game is demonstrated for the careers of Steffi Graf and Pete Sampras:

 

 

 

Tennis capital

The AUC is a description of a tennis players’ career. It considers all of the physical and mental efforts invested by the player, from the age at which they started competing professionally, to their very last professional match. Without going into the complexities of it, the % AUC for some of the top G1 and G2 players goes something like this: Bjorn Borg 12.3, Pete Sampras 12.6, John McEnroe 14.3, Monica Seles 14.3, Steffi Graf 17.0 and Martina Navratilova 24.9.

 

Talented players in high performance environments

The best players peak earlier, this is true for both top 10 men and women. Why this is the case is open to argument, but MY HYPOTHESIS is twofold: 1) they are probably more talented than anybody else the first time they put a racket in their hand and start hitting the ball 2) they are probably highly motivated by their talent, which in turn causes them to being spotted by a high quality coach who in turn convinces them to invest in deliberate practice. Their unique talent and motivation, combined with training within the right coaching environment and parental support probably leads them to peak at a natural point. This could be especially true of G2 players. We have shown here that the most recent generation of players begin their professional careers aged between 15-17, and retiring 14-16 years later. Tennis academies across the world invite kids to pick up a racket aged 5-7 years, which would equate to a 10-12 year period of training prior to a potential future professional starting their career off.

Is there any advantage to kicking off a tennis career at 15 for women, and 17 for men, compared to a year or two later as it was with before 1985? It appears not! In fact, the average career for men has significantly decreased by two years in length compared to pre-1985 with no concomitant increase in win percentage throughout a career. The inherent problem is that in any high performance environment in any sport today, all of the structures are in place for the young athletes who choose to invest their time in a particular sport: sports scientists, fitness coaches, nutritionists, top class coaches, doctors, physiotherapists, facilities including courts, pitches and showers, sports psychologists, partners in clothing and sport-specific accessories. Have a look at The French Tennis Federation ranking profiles for boys starting aged 2002 (aged 10 this year), and what you will notice are HUNDREDS of players born in each of 2002, 2001, 2000, 1999, 1998 with elite level ability by international standards. In other words, the structures are in place within The FFT to produce hundreds of players that have high levels of ability. If they all play 2-3 hours per day with other excellent players and receive to class coaching at the same time, it allows for high levels of competition in training and match play between them, from which the cream will rise to the top. These players are a product of their environment, and delaying their ascension by 2-3 years may be impossible, and would at least be very difficult.

 

The Precocity-Longevity Hypothesis, and tennis

The data here are the first in tennis that have reported that early peaking offers no advantage to players that go on to occupy the top 10 ranking positions. In parallel with this phenomenon is The McCann Precocity-Longevity Hypothesis. This hypothesis has demonstrated a link between early achievement (considered as when an athlete debuts professionally before 23 years) and a shorter life span in professional baseball players (2007) while controlling for factors such as body mass index (BMI), player position and general health. While The McCann Precocity-Hypothesis has not been replicated in other sports, including tennis, it is interesting to note that it has been replicated in politicians who achieve early in their careers. The combination of a long workday, pressure to perform, being available to meet the public, international travel, and stress are all factors involved in the job … could we substitute a politician for a top 10 tennis player here?

A great example of precocity in tennis is Rafa Nadal who has won The French Open aged 19, 20, 21 and 22. He was ranked no. 1 for two years. He has won a total of 10 Grand Slam titles before he turned 25, and for sure his peak has passed him.  Given that the AUC for G2 players is not enhanced by their precocity, it is highly unlikely that Nadal will discover the form he displayed in his early years. Over the past 12 months, we have heard more of Nadal talk about the impact of his tennis on his knees and in his biography, he talks about a chronic foot injury he’s had since adolescence. It will be very interesting to chart his career over the coming years, and if he can post 1-2 more Grand Slam titles he will be doing very well. Later in his life, there is no doubt that he will be in a better position to evaluate the effect of his tennis career on his general physical, and mental health.

Two examples of “late-developers” in the women’s game are Li Na and Francesca Shiavone. Li Na turned professional aged 17, and would be considered a late starter by today’s G2 standards. However, Li Na’s rise to the top 10 has been impressive: she has won over 24 career titles, and has been a finalist twice in Grand Slam events: first in The Australian Open in 2011 which she lost to Kim Clijsters, before taking home The French Open in the same year. She has also been a ¼ finalist at Wimbledon and The US Open. In her career, Li Na has earned close to $8m in prize money. The second example is Francesca Shiavone, who turned professional in her 18th year, and since then has risen to no. 4 in the world. She has appeared twice in The French Open final, winning it in 2010, and has amassed a career total of $8.9m in prize money. Both Li Na and Shiavone are good examples of players who are finding their best form later in their careers. They have become very competitive players that have proved difficult to beat in their mid twenties, both have occupied the top 10 rankings in their mid-twenties, and both are likely to feature prominently in Grand Slam and WTA tournaments for some years to come.

Finally, Caroline Wozniacki turned pro age 15. She occupied the no. 1 ranking at 19 and 20, but aside from Marion Bartoli, she has played more tournaments than any other competitor in the top 10, and this has boosted her ranking to no. 1. However, in peaking so early in her career, she is faced with a big problem. Physically, she is clearly not the strongest player on the circuit, nor is she the fastest. She is tall and very thin, would it have been possible for her to develop physically for an extra 12-18 months? Clearly she has natural talent, but why the rush to make it to no. 1 and compete against women who are clearly bigger, stronger and faster? For > 12 months she has carried the pressure of being no. 1 without a Grand Slam win. Now that the pressure is off, she may perform better in the major events, and according to the numbers here, she should peak next year. Only time will tell, but having been on the pro tour in her 6th year now, she still hasn’t found her best form.

 

Where does tennis go from here?

The INSEP study has demonstrated that the past 20 years has shown an inclination towards precocity in the professional tennis player. This precocity offers no competitive advantage to the players who have made it to the top 10 ranks. We don’t offer any conclusive answer as to the problems posed by precocity. But, perhaps tennis (academies) could decide to delay the entry-level age of players into the professional game, and instead give players 1-2 more years to prepare physically and psychologically for the professional tour. A year or two extra is highly unlikely to adversely affect career development, ranking, prize money accumulation, or sponsorships for any talented and motivated player of international class. It might even help preserve the physical and mental health of young players, which should always be the primary concern of professional sports coaches.