Comparison of laboratory and on-court testing of aerobic fitness in tennis players

Resumen laboratory and on-court testing of aerobic fitness in tennis players

The modern game of tennis is characterised by 200-600 explosive efforts, over a period that may last up to 6hours (Richers, 1995), utilising specific movement patterns depending on the situation and court surface. It is clear that in order for the player to maintain the required speed and power components over such an extended period a range of physiological processes must be optimised. Research has also indicated that in conditions of fatigue, hitting accuracy decreases by as much as 81% (Davey et al., 2003), further illustrating the importance of the physical components of the game upon the potential match outcome. Bergeron et al., (1991) suggested that despite the repeated explosive efforts, the overall metabolic response to tennis match play was comparable to continuous, moderate intensity exercise. Furthermore, literature has suggested that during singles match play plasma lactate values range from 2.3-5.86 mMol.l-1 and % VO2max ranges between 53-73 % (Christmass et al., 1995; Reilly and Palmer, 1995; Bergeron et al., 1991).

This was further supported by Dansou et al. (2001) who suggested that approximately 60% of VO2max was achieved for 80% of the match, and that in spite of the intermittent nature of the sport, the game of tennis induces a moderate aerobic energy expenditure. In light of these findings, it would seem logical that tennis players attempt to quantify the magnitude of their aerobic fitness, as it appears to play a significant role in the energy provision during match play. Furthermore, it could be suggested that the assessment of VO2max may not be the best indicator of aerobic fitness for tennis players, due to the fact that players would rarely achieve VO2 in excess of 75%max. This is supported by Coyle (1995) who suggested that performance in prolonged, continuous aerobic activity was highly related measurements of blood lactate threshold, although VO2max did provide an upper limit of aerobic capacity. Therefore, it could be suggested that measurements of ‘aerobic endurance’ (i.e. anaerobic/ blood lactate threshold) may be more suitable than measurements of ‘aerobic capacity’ (i.e. VO2max) for sports such as tennis where VO2max is rarely reached, and efficiency and economy of movement are more important. Studies in tennis have sought to compare the equivalent on-court and laboratory measures (Ferrauti et al., 2001; Smekal, et al., 2000), but these authors did not utilise intermittent yet sustained sub-maximal testing protocols which more accurately reflect those in a match play environment. Therefore the aim of this study was to produce an intermittent tennis specific test for aerobic fitness that would allow the comparison of sub-maximal physiological responses between laboratory and on-court conditions.

Introduction

The modern game of tennis is characterised by 200-600 explosive efforts, over a period that may last up to 6hours (Richers, 1995), utilising specific movement patterns depending on the situation and court surface. It is clear that in order for the player to maintain the required speed and power components over such an extended period a range of physiological processes must be optimised. Research has also indicated that in conditions of fatigue, hitting accuracy decreases by as much as 81% (Davey et al., 2003), further illustrating the importance of the physical components of the game upon the potential match outcome. Bergeron et al., (1991) suggested that despite the repeated explosive efforts, the overall metabolic response to tennis match play was comparable to continuous, moderate intensity exercise. Furthermore, literature has suggested that during singles match play plasma lactate values range from 2.3-5.86 mMol.l-1 and % VO2max ranges between 53-73 % (Christmass et al., 1995; Reilly and Palmer, 1995; Bergeron et al., 1991).

This was further supported by Dansou et al. (2001) who suggested that approximately 60% of VO2max was achieved for 80% of the match, and that in spite of the intermittent nature of the sport, the game of tennis induces a moderate aerobic energy expenditure. In light of these findings, it would seem logical that tennis players attempt to quantify the magnitude of their aerobic fitness, as it appears to play a significant role in the energy provision during match play. Furthermore, it could be suggested that the assessment of VO2max may not be the best indicator of aerobic fitness for tennis players, due to the fact that players would rarely achieve VO2 in excess of 75%max. This is supported by Coyle (1995) who suggested that performance in prolonged, continuous aerobic activity was highly related measurements of blood lactate threshold, although VO2max did provide an upper limit of aerobic capacity. Therefore, it could be suggested that measurements of ‘aerobic endurance’ (i.e. anaerobic/ blood lactate threshold) may be more suitable than measurements of ‘aerobic capacity’ (i.e. VO2max) for sports such as tennis where VO2max is rarely reached, and efficiency and economy of movement are more important. Studies in tennis have sought to compare the equivalent on-court and laboratory measures (Ferrauti et al., 2001; Smekal, et al., 2000), but these authors did not utilise intermittent yet sustained sub-maximal testing protocols which more accurately reflect those in a match play environment. Therefore the aim of this study was to produce an intermittent tennis specific test for aerobic fitness that would allow the comparison of sub-maximal physiological responses between laboratory and on-court conditions.

Methodology

Eight male university level tennis players (20.9+1.6 yrs, 1.78+0.1 m, 76.7+7.2 kg, 59.5+6.1 ml.kg.min-1) volunteered to participate in two visits to the Laboratories, and two visits to the Tennis Centre, UWIC. During these visits they were required to complete a Maximal Laboratory Test (MLT), and Maximal On-court Test (MCT) which were used to inform the intensities for the Sub-maximal Laboratory Test (SLT), and Sub-maximal On-court Test (SCT). The order of these tests was kept the same for all participants, and each was separated by a minimum of 24 hours. Stature and mass data was collected during the first laboratory visit via a pre-calibrated fixed stadiometer (Holtain, UK) and digital weighing scales (Seca 770, Germany) in minimal clothing. The MLT required the participants to complete an incremental test to exhaustion on a motorised treadmill (H/P/Cosmos, Quasar, Germany), whilst connected to a breath-by-breath Gas Analysis system (Oxycon Pro, Jaeger, Germany) set at a 5 second sampling rate. A resting blood sample was taken from the ear lobe (20 ?l capillary tube) prior to a standardised 3 minute warm up. The test then began at 7 km.h-1 at a 4% gradient for a period of 2 minutes 45 seconds, followed by a 15 second blood sampling period. After each 3 minute stage, the treadmill speed was increased by 1.5 km.h-1 until volitional exhaustion. Heart rate response was recorded via telemetry (Polar S610i, Kempele, Finland) at a 5 second sampling rate throughout the protocol. Blood lactate concentration was determined from these samples using a blood analysis system (Biosen C-Line, EFK Diagnostics, Netherlands). The results were then used to form a lactate profile, with the movement speed (ATms), heart rate (AThr) and percentage maximum heart rate (AT%max hr) equating to the anaerobic threshold determined via the D-max method (Cheng et al., 1992) also recorded. Results from the MLT were utilised the establish three exercise intensities for the SLT. These corresponded to the anaerobic threshold (AT) calculated via D-max (Cheng et al., 1992), a value equivalent to 50% of the difference between the AT and the final lactate value added to AT (AT+50% ?), and a value equivalent to 100% of the difference between AT and the final lactate value minus AT (AT-100%?).

These three intensities were used to determine the run speed for three, 8 minute stages on a motorised treadmill at a consistent 4% gradient. Heart rate telemetry was recorded throughout the protocol and blood samples were taken at 4 minute intervals throughout each 8 minute stage. The participants were then required to complete a MCT. The test comprised of 23 levels, each of which was divided into three stages. Each of these stages comprised of nine specific movements around the court including eight lateral movements across the baseline and one towards the net. A Diagrammatic representation of the movements required for the test are shown in figure 1. Each movement had to be completed in time with a computer generated tone (Test Tone Generator, Timo Esser, Germany) that was played via a CD stereo (JVC RVNB10, UK). At the end of each movement, the participant was instructed to have one foot placed in a specific area in time with the tone, and an appropriate stroke was shadowed. The exact nature of the stroke was not specified, and each participant was instructed to perform a stroke as if in a match play situation, according to the position on the court and the time permitted by the test. Each stage was separated by a 10s rest period. Each level was separated by a 15s rest period before the time allowed for each movement was decreased. The test was incremental until volitional exhaustion. Similar testing principles have been used in an aerobic test for badminton players designed by Hughes et al. (2002). Blood samples were taken at the end of each odd numbered level, and heart rate telemetry was recorded throughout. Following the same process as the laboratory testing, the results from the MCT were used to calculate AT via D-max, AT+50%?, and AT-100%? as the three sub-maximal intensities. These intensities were used to determine the run speed for the three, 8 minute stages of the SCT. This test followed the same format as the MCT with respect to the rest periods, except the intensities were kept the same throughout each of the 8 minutes stages.

Figure 1. A diagrammatic representation of the nine movements that comprise each stage of the test.

For both the SLT and SCT, the movement speed (ATms), heart rate (AThr) and percentage maximum heart rate (AT%max hr) were calculated at AT. This was achieved by plotting the lactate levels from the both the four and eight minute blood samples. This provided a point at which the two lines crossed, which is representative of a modified Maximal Lactate Steady State (MLSS) measurement. An analysis of the relationships and differences between the MLSS data achieved during the sub-maximal laboratory and on court tests was then made using Pearson’s correlation and Paired t-tests, respectively. A 5% level of significance was chosen for the statistical analysis; however significance of 1% and 0.1% were reported where appropriate.

Results

The MLT elicited significantly higher maximum heart rate than the MCT, as shown in table 1. This trend was also demonstrated with the mean heart rate at the AT assessed via D-max, with significantly higher values shown during MLT. The % maximum heart rate at AT was not significantly different between to two conditions.

Table 1. Mean data for the variables assessed during the MLT and MCT, including Maximum Heart Rate (HRmax), Heart Rate at D-max (HR D-max) and % Maximum Heart rate at D-max (%Max HR D-max).

Table 2 illustrates no significant correlation between movement speeds to elicit fatigue in the MLT and MCT. There was also no significant correlation between %Max HR D-max during MLT and MCT. A significant relationship was shown between HR D-max in both conditions. There was a significant correlation (p?0.05) between VO2max and Time to Exhaustion in the MLT, yet no significant correlation existed between VO2max and time to exhaustion in the MCT. Furthermore, no significant correlation existed between the time to exhaustion during MLT and MCT.

Table 2. Mean data for the variables assessed during the MLT and MCT, including Movement Speed at D-max (MS D-max), Heart Rate at D-max (HR D-max) and % Maximum Heart rate at D-max (%Max HR D-max).

Tables 3 demonstrates that the SCT elicited significantly higher mean heart rate at AT and % maximum heart rate at AT. Lactate levels at the AT were not significantly different between the two sub-maximal test conditions. Table 4 illustrates that non-significant relationships were found between all variables assessed during the sub-maximal laboratory and on court testing.

Table 3. Mean data for the variables assessed during the SLT and SCT, including Blood Lactate concentration (Blood [lac]), Heart Rate at the AT (AThr) and % Maximum Heart Rate at the AT (AT%Max hr).

Table 4. Mean data for the variables assessed during the SLT and SCT, including Blood Lactate concentration (Blood [lac]), Heart Rate at the AT (AThr), % Maximum Heart Rate at the AT (AT%Max hr) and Movement speed at the AT (ATms).

Discussion

These data suggest that all of the variables assessed during sub-maximal testing were not significantly correlated between the two conditions. Furthermore, many variables were shown to be significantly different between laboratory and on-court testing protocols. The results from the maximal testing report significantly higher maximum heart rates and heart rate assessed at the AT during MLT compared to the MCT. This result is in contrast to the previous research conducted by Hughes and Fullerton (1995) who suggested that elite badminton players were able to produce significantly higher peak heart rates during specific on court testing versus laboratory testing. However, it is important to note that the playing standard of the subjects used by Hughes and Fullerton (1995) were of a considerably higher level than the subjects in the present study, and it could be argued that elite athletes are better adapted to reproduce maximal effort within their respective performance environments than their non-elite counterparts. VO2max was found to be significantly correlated with time to exhaustion during MLT, yet not significantly correlated to time to exhaustion during MCT. This finding lends support to the work of Coyle (1995) and further suggests that VO2max may not be the best indicator of maximal performance during on court testing. These results could be explained by a combination of factors, including the intermittent nature of the MCT which facilitates recovery during the non-active periods, as well as the participants improved movement technique on the court, and more developed physiological characteristics specific the demands of the on-court protocol. Although the data produced in the current study did not include gas analysis during the court testing, other studies have suggested that VO2 during singles match play ranges between 25.6+2.8ml/kg/min and 29.1+5.6ml/kg/min (Ferrauti et al., 2001; Smekal et al., 2001), equating roughly to 53% VO2max (Reilly and Palmer, 1995). This further supports the notion that VO2max values may play a relatively minor role in tennis performance within the sample populations of the named studies. There was no significant correlation between movement speed at the AT from the MLT and MCT. This result has important implications for this study as it suggests that the movement speed for a given player is not significantly related between laboratory and on-court conditions. This further illustrates the differences between the two testing conditions, and may be explained by the increased economy of the players when performing the movement patterns required during the on-court test and the increased familiarity with the testing environment.

The % maximum heart rates at the AT from the SCT are comparable to those reported by Christmass et al. (1998). They reported an average of 82.8% maximum heart rate (excluding change of ends) during a 90 minute game of singles, compared to 88.3% reported in the current study. In contrast, Reilly and Palmer (1995) reported an average of 76.4 % maximum heart rate; however their testing was performed on wooden courts which are not widely used, and therefore the characteristics of play on the surface may result in a different pattern of physiological loading. This finding suggests the AT assessed during the SCT may also produce a physiological response comparable to singles match play. The sub-maximal testing results elicited significantly different heart rates and % maximum heart rates at the AT, with both values being significantly higher during the SCT. There was also no significant correlation between these values in the different testing conditions. Movement speed at AT was also found to be not significantly correlated between the two sub-maximal conditions. The possible reasons for this relate to the additional physiological loading experienced with intermittent activity that requires multiple changes of direction accompanied with repeated acceleration and deceleration and the eccentric/concentric muscular loading patterns associated with this type of movement pattern. Given that the results showed no significant correlation, it could be suggested that the university level tennis players utilised in this study would be more economical at performing the movement patterns required during the on court test than those required during the laboratory testing. This in turn could allow the participants to maintain higher heart rates, and % maximum heart rates at the AT, whilst the recovery periods would allow the clearance of lactate. This may help to explain the blood lactate results which demonstrated no significant differences between the SLT and SCT. Interestingly, the blood lactate results were not significantly correlated between the two sub-maximal testing conditions.

These results highlight the different physiological responses arising from laboratory and on court testing protocols presented in this paper. The results from the sub-maximal testing are of particular importance due to the specificity of the testing protocol to tennis performance. One must also consider the possibility that the lab and court tests may measure different physiological concepts of the anaerobic threshold, which in part, could be attributed to the continuous nature of the laboratory testing and the intermittent nature of the court testing. Clearly, this is likely to have had an effect upon the results of the study; however it is important to remember that the purpose of the on court test was to expose the subjects to realistic tennis specific physiological stress, and therefore the fact that the protocol is very different in nature to the laboratory tests is an expected consequence. Indeed, the implications of these findings are that the sub-maximal on court test could provide physiological loading which is similar to that reported in the tennis physiology literature, yet is not significantly related to an equivalent sub-maximal laboratory test. The wider implications of this are that the if a sports scientist or coach wishes to assess the aerobic endurance of university level tennis players, then the on court protocol (especially the sub-maximal) presented within this paper may represent a test that produces different results compared to the laboratory measures, and it is therefore recommended that it be integrated into assessment batteries of tennis players, further allowing the sports scientist/coach to gain a better understanding of the physiological characteristics of the participant.

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