This post was written by my colleague and friend, Cyril Genevois (PhD). Cyril is one of the leading sport scientists in the world, with a focus on high-performance tennis.
His research looks at aerobic contributions in elite tennis, split-step training, groundstroke biomechanics, power protocols and more.
You can follow Cyril on Facebook for research updates, tips, and everything tennis science.
Tennis Demands - A Review
A tennis match is characterized by intermittent exercise, alternating short (4–10 second) bouts of high intensity and short (10–20 second) recovery bouts, interrupted by several periods of longer duration rest (60–90 seconds). The running activities of players encompass high accelerations and decelerations but low velocities reflecting the intermittent play involved in tennis, which does not allow high velocities to be reached (Hoppe et al, 2014).
If the decisive muscle actions (movement and strokes) are explosive by nature and rely mostly on anaerobic breakdown of creatine phosphate for energy production, aerobic power (VO2max) is a variable that promotes better physiological recovery between these actions, matches and tournaments. Thus, tennis could be classified as a predominantly anaerobic activity, requiring high levels of aerobic conditioning to avoid fatigue. Indeed, the aerobic fitness status of players may largely determine their capacity to sustain high-intensity exercise during a match and may even influence a player’s technical and tactical performance by allowing them to make better choices under fatigue.
It has been suggested that VO2max values >50 ml/kg/min for males and > 42 ml/kg/min are generally considered as a minimum standard and preferably a higher value is encouraged for tennis athletes to be able to practice and compete at a high level (Kovacs, 2007). These values are quite similar to those required in most team sports settings - in order to compete at a high level. In recent years, scientific research has shown a growing interest in the development of testing protocols allowing a coupled analysis of aerobic fitness and technical production (Baiget et al, 2014; Brechbühl et al, 2016). The first part of this 2-part series will provide a rationale behind aerobic fitness training for tennis players.
Heart Rate and Physiological Strain During Tennis Play
Heart rate (HR) monitoring is the most popular indirect method of estimating intensity of exercise and it’s used to provide information about the psychophysiological stress associated to match play. During competitive matches, mean HR values range between 60–80% of maximum HR (HRmax), with long and intense rallies eliciting values over 95% of HRmax (Fernandez et al, 2006).
But average HR values should not be the sole measurement of metabolism, as this would not accurately represent the intermittent nature of tennis play and could lead to misinterpretation (figure 1 below). Thus, the HR-based model defining three intensity zones (low intensity < 70%HRmax < moderate intensity < 85% HRmax < high intensity) is commonly used to examine the physiological strain during various types of exercise.
The analysis of relative intensity based on the cumulative time (actual - or effective playing time - with the addition of rest periods) spent in these three metabolic intensity zones during simulated tennis play has revealed that players spend more than 75% of the time in the low-intensity zone, with less than 25% of the time spent at moderate to high intensities (Baiget et al, 2015).
Figure 1. HR variation during tennis match play (adapted from Baiget et al, 2015)
The effective playing time - i.e., the player’s activity during the point - based on this distribution, only accounts to approximately 20 to 30% on clay courts and 10 to 15% on hard court surfaces (Ferrauti et al, 2003). During a 60 minute match or set, that means you’re only playing 12-18 minutes and your active or passive rest accounts for 42-48 minutes.
On top of that, HR values can be affected by several factors during a tennis match. For example, it has been shown that a passive strategy (vs an active one) may place higher cardiovascular demands on the players due to longer times spent at elevated (high) heart rates (Hoppe et al, 2019). This is in line with the high relationship found between HR responses and match activity characteristics such as rally duration and strokes per rally, with serve games being more demanding than return games (Kilit & Arslan, 2017).
In the same vein, playing time on clay courts is higher than on hard courts with a lower exercise to rest ratio leading to higher mean HR (Murias et al, 2007). Moreover, the proportion of time spent in the moderate and higher heart rate zones by elite players during a four-set match were increased following each set indicating increasing stress (Gomes et al, 2011). Thus, not surprisingly, playing style and surface are important factors to take into consideration, in order to better adjust training plans to meet the needs of the player.
In the same way, male tennis professionals performed 50% more total work in Grand Slam matches than juniors due to the best of 5 set format. Thus, junior players transitioning to the professional level must adapt to a field of deeper and higher-quality athletes (Kovalchik & Reid, 2017).
Baiget et al (2015) showed that players with better aerobic fitness played at relatively lower intensities and therefore at a lower level of strain and fatigue. This could be a great advantage when players have to play several matches in a short period of time which has been shown to impair hitting accuracy and stroke positioning (Gescheit et al, 2016).
Finally, when it comes to the performance during an incremental field test specific to tennis, it has been reported that VO2 values - both at submaximal and maximal loads - were moderate predictors of players competitive ranking (Brechbühl et al, 2016 ; Brechbühl et al, 2018), and that better aerobic conditioning of male tennis players at international levels were associated with better technical efficiency at higher exercise intensities compared with male tennis players at national levels (Baiget et al, 2016).
High Intensity Interval training (HIIT) and On-Court Tennis Training (OTT)
Because of the intermittent nature of a tennis match and the alternating demands of energy provision between points and rest, it seems that the training of competitive players should focus on improving their ability to repeatedly perform high-intensity exercise and to recover rapidly from it. For these reasons, tennis training should include physical exercise aimed to enhance both aerobic and anaerobic fitness.
High intensity-interval training (HIIT) consists of repeated, intense exercise bouts separated by passive or active recovery (work and rest intervals ranging from 10 seconds to 4 minutes; 90–100% velocity at the level of VO2max; HR values ≥ 90% of HRmax ; work-to-rest ratios of 1:1–4:1). It is as a time-efficient alternative to moderate- or low-intensity continuous exercise for improving variables related to endurance and anaerobic performance both for young players (Engel et al, 2018) and adults (Wen et al, 2019). HIIT replicates the intermittent nature of tennis play, at higher intensities, and appears a viable exercise programming option because the rest intervals between intense work intervals may contribute to reduced discomfort and inducing a more positive affective response (Thum et al, 2017).
Because training time is premium, tennis coaches are often relying on an integrated approach including technical skills during HIIT sessions (OTT). The primary purpose of OTT is to combine improvement in physical conditioning with the maintenance of technical skills in order to optimize training time. Studies comparing playing (OTT) and non-playing (HIIT) aerobic training in tennis found that the physiological demands (average HR) were greater during the playing session compared to the non-playing session (Fernandez-Fernandez et al, 2011 ; Pialoux et al, 2015 ; Kilit & Arslan, 2019).
This could be related to the involvement of the lower- and upper-limb muscles in hitting the ball. Indeed, It has been reported that running and striking the ball costs 10% more energy than running without striking the ball (Bekraoui et al, 2012). Several studies have shown that OTT protocols are effective in improving aerobic fitness in young tennis players with increases in VO2max of 4.8% (Fernandez-Fernandez et al, 2011), 5.5% (Kilit & Arslan, 2019) and 10.28% (Srihirun et al, 2014). These results are in line with studies using HIIT protocols which showed an increase in VO2max of 6.0% (Fernandez-Fernandez et al, 2012), 5.2% (Kilit & Arslan, 2019), 6.6% (Srihirun et al, 2014).
The main important factor when planning HIIT or OTT is to achieve the required intensity to elicit improvements. For HIIT, using a running-based activity, the speed is calculated as a percentage of the maximal performance obtained during a fitness test - which can vary depending on the test used. For OTT, it is the combination of running distances between every stroke and ball frequency that determines the intensity. It can be assessed during a specific tennis fitness test (Baiget et al, 2014; Brechbühl et al, 2016) or by monitoring the HR response of players.
Repeated Sprint Training (RST)
RST is based on the repetition of « all-out » efforts of short duration (≤ 10 s) interspersed with short & incomplete recoveries (work:rest ratio of 1:4–1:6). This method differs from the traditional HIIT since exercise intensity is maximal, thereby allowing high recruitment of fast-twitch fibers. The goal of RST is to improve the Repeated Sprint Ability (RSA). One study in tennis showed significant correlations between performances in RSA tests and VO2max (Tsiprun et al, 2013). The aerobic energy system is an important determinant in recovery rate from intense activity and assists in power output maintenance during the RST.
Although the main goal of RST is to improve the Repeated Sprint Ability (RSA), it has been shown to improve VO2peak level of 4.9% in tennis (Fernandez-Fernandez et al, 2012). Moreover, the effects of repeated-sprint training in hypoxia (RSH) - low oxygen state - to induce a larger metabolic stimulus have been explored and showed greater improvement in some tennis-specific physical and technical parameters compared with similar training in normoxia with well-trained tennis players (Brechbühl et al, 2018).
The second part of this series will provide coaches with practical testing and training protocols adapted to the specificity of tennis play.
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