Tennis ranking related to exercise capacity

Abstract

This is the first 7-year prospective case report on the relationship between VO₂max during preparation and the following year’s entry ranking for a top athlete. The strong relationship between VO₂max and the following year’s ATP entry ranking over time underlines the importance of the preseason training period to optimise cardiorespiratory capacity. The current findings emphasise the relevance and predictive value of continuous performance tests and the need for more elaborate and longitudinal tracking study designs, as well as regression models that include playing style as a covariate.

BACKGROUND

The physical demands upon players in professional tennis have been increasing over the past few years. Currently, average intensities range between 60% and 70% of maximum oxygen uptake.¹ Tennis can be classified as a mainly anaerobic activity with emphasis on glycolysis and glycogenolysis.² However, taking into consideration incomplete physiological regeneration between points, as well as between matches and tournaments, a high cardiorespiratory capacity may help to avoid fatigue³ and aid in recovery, thus promoting continuous success in professional tennis.^1,4 The relative importance of aerobic capacity may depend on an individual athlete’s preferred strategy, as the proportion of playing time versus total match time varies with playing style.⁵ Average point duration may reach more than 15 seconds when baseline players are in control of a rally, as opposed to <5 seconds when attacking players are in control.⁶

Professional players have a cardiorespiratory capacity of 55–65 mL/min/kg.^5–7 Players attend up to 40 tournaments/year, during which athletic training sessions are necessarily reduced in volume and intensity. Thus, the preparation period at the end of the year offers the best, if not the only chance to systematically develop athletic capabilities.⁸ Improving the aerobic capacity in this period may have a strong bearing on tennis performance. This study aimed to examine the relationship between VO₂max during preparation and the following year’s entry ranking, focusing on a single top athlete, to explore the research potential for future systematic evaluation.

CASE PRESENTATION

The athlete (180 cm, 74 kg) has competed at Association of Tennis Professionals (ATP) tour level since 1994. He prefers to play most points from the baseline and to hit ground strokes, rarely coming to the net, and achieves his best results on hard courts. At the beginning of his career, he showed excellent speed and agility capabilities, but his aerobic capacity was average.

INVESTIGATIONS

Between 1999 and 2006, we performed annual tests at the same time in December using the same motor-driven treadmill (Quasar med, HP Cosmos, Germany). The standardised protocol involved a gradient of 0%, an initial speed of 8.5 km/h and 1.5 km/h increments every 4 minutes. Pulmonary gas exchange was measured breath by breath using a mobile indirect calorimetry system (Oxycon Mobile, Viasys Healthcare, Germany) after a sufficient warm-up time of at least 60 minutes. Inspiratory and expiratory gas flows were measured using a bidirectional volume turbine sensor, which was calibrated before exercise testing with 2.0 L/min and 0.2 L/min using the system’s automated calibration unit. The electrochemical sensor of the gas analyser was calibrated using room air and a reference gas of known composition (16% O2/5% CO2). After the calibration procedure was finished, the battery-operated device was strapped to the subject’s back. After 5 minutes’ rest, the treadmill protocol was started. During the test, signals were transmitted telemetrically, and recorded on a personal computer. For data analysis, VO₂max was obtained from the last 30 seconds of the final stage, applying the VO₂max criteria as proposed by Withers et al⁹ Ranking was obtained from the official year-end ATP tour entry ranking list.

Cross-correlation values were computed for pairwise comparisons of the time history of respiratory capacity and ATP entry ranking. A two-sided p value <0.05 was considered significant. Statistical computations were performed using a commercial statistics package (SPSS; SPSS Inc. Chicago, Illinois, USA).

OUTCOME AND FOLLOW-UP

Between 1999 and 2006, the athlete completed 6–7 stages during each treadmill test, reaching maximum speeds of 16–17.5 km/h. During the period that the ATP ranking ranged from 6–97, VO₂max ranged from 55.0–67.4 mL/min/kg, averaging 61.1 mL/min/kg. Cross-correlation analysis indicated a strong inverse relationship between VO₂max and ATP entry ranking over time (fig 1).

Figure 1. Respiratory capacity versus entry ranking over time.

DISCUSSION

Based on these results, the individual cardiorespiratory capacity may explain >80% of an athlete’s ranking position in the following year. However, aerobic capacity is only one of a number of physiological variables. Therefore, its comparably large influence seen in this case might also be explained by psychological mechanisms–for example, feeling fit might raise a player’s confidence. Discrepancies between VO₂max and the ranking, as seen in 2006, were probably due to an illness-caused training reduction of several months.

Despite several limitations, attempts at using parameters of cardiovascular capacity for predicting performance have been made in endurance-related sports.^10–12

It is also known that young elite and non-elite soccer players significantly differ in aerobic endurance.^2,13 Apor¹⁴ showed a rank-order correlation between VO₂max and placing in the Hungarian First-Division Championship. There is also a significant relationship between VO₂max and both the distance covered during a game¹⁵ and the number of sprints attempted by a player.¹⁶

In tennis, such links between endurance capacity and performance have not yet been established. Of the several athletic tests used, only an agility and speed test correlated with the sectional rankings of junior tennis players.¹⁷ Furthermore, in an analysis classifying rankings with performance tests, Roetert et al¹⁸ managed to classify 91% of the cases correctly, but none of the seven variables used contained a measure of endurance.

Even so, fatigue can detrimentally affect players’ mechanics by decreasing proprioceptive aptitude¹⁹ and range of motion,²⁰ which can serve as one explanation why the current data showed individual respiratory capacity to be linked to an athlete’s ranking position in the following year. Thus, it is conceivable that the endurance–performance relationship is masked and might only be detected using more elaborate and longitudinal study designs. Future research might develop regression models including playing style as an additional covariate. The stability of performance throughout the year, using operators for changes in match statistics such as winners and unforced errors, might complement or replace ranking as the dependent variable. Concerning study design, tracking studies hold promise to provide additional advantages as compared to cross-sectional analyses.

Overall, the current findings emphasise the relevance of continuous performance tests to improve the effectiveness of the preseason training period, and to optimise the athletic capabilities of high-class tennis players.

LEARNING POINTS

• In elite tennis, the relative importance of aerobic capacity may depend on an individual athlete’s playing style.

• The preparation period at the end of the year offers the best opportunity to improve aerobic capacity.

• The strong relationship between VO₂max and the following year’s ATP entry ranking over time underlines the importance of the preseason training period to optimise cardiorespiratory capacity.