The game of water polo requires the activation of both aerobic and anaerobic metabolism for energy provision (19,22,25), and match analysis has shown that dynamic body contacts between opponents frequently occur throughout a water polo match-play, requiring adequate muscle strength (21). For these reasons, water polo training aims at enhancing both aerobic and anaerobic power together with muscular strength. Platanou and Geladas (22) found that the overall water polo game mean heart rate corresponds to lactate threshold intensity. Because of this fact, training at or above lactate threshold with incomplete recovery between bouts is often performed by water polo players, aiming to improve their ability to cope with the game demands. Training at intensities above the lactate threshold activates both aerobic and anaerobic metabolism and may produce important adaptations that improve swimming performance indices (17). Recently, D'Ercole et al. (6) observed that HIIT with relatively short resting intervals (10–20 seconds) in nonelite water polo players resulted in significant improvements in swimming performance. Moreover, high-intensity interval training (HIIT) of long duration (>1 minute) interspersed with long resting intervals (>1 minute) is a training practice that increases exercise performance parameters in already trained athletes, with a concomitant increase in the maximal oxygen uptake (V[Combining Dot Above]O2max) or the speed at the lactate threshold (7,9,10,14,26).
In swimming, the physiological responses of long (4 × 400-m) and short work duration (16 × 100-m) HIIT at intensity between the lactate threshold and V[Combining Dot Above]O2max have been found to be similar (3). However, Libicz et al. (15) reported slightly greater V[Combining Dot Above]O2 and heart rate responses with the longer duration efforts compared with the shorter ones in 2 training sessions performed at the velocity corresponding to V[Combining Dot Above]O2max. Whatever the case, the long-term effects of HIIT with different work and rest intervals on specific performance parameters of elite water polo players are still unknown. Moreover, a comparison between HIIT of different work duration and rest interval is of great importance providing evidence as to which type of HIIT is more beneficial to use in the preseason conditioning.
In real training conditions, HIIT is concurrently performed with strength and specific water polo training, including technical preparation, tactical training drills, and short sprint training. The influence of concurrent strength and endurance training on exercise performance has shown controversial results (2,10–12,16). More recently, it was shown that strength training, together with water polo training performed in-season, produced positive effects on performance qualities, such as 20-m swim sprint, jumping, throwing velocity, and strength level of water polo players (29). To date, the effects of a combined program of strength training and HIIT, together with specific water polo training, on swimming endurance performance indices of elite players remains to be elucidated. Thus, the aim of the present study was to compare the effects of long duration with sufficient rest HIIT (HIIT4 × 4) and short duration with incomplete rest HIIT (HIIT16 × 100), concurrently performed with maximal strength and specific water polo training, on swimming endurance performance indices of elite water polo players.
Experimental Approach to the Problem
To compare the effects of an 8-week concurrent maximal strength and overload endurance training of long duration and long rest intervals (HIIT4 × 4) with concurrent maximal strength and high-intensity interval training of short duration and short rest intervals (HIIT16 × 100) on specific performance indices, 2 water polo clubs were randomly assigned to either HIIT4 × 4 or HIIT16 × 100 group. No effort was made to randomize players' participation within each group because this would not be approved by the coaches and players at the elite level and would be impractical in team training planning, control, and application. A test for the measurement of maximal strength and an incremental swimming performance test were used to detect changes between pretraining to posttraining. The speed corresponding to blood lactate concentration of 4.0, 5.0, and 10.0 mmol·L−1 (V4, V5, V10) was calculated before and after the training period to test any swimming endurance changes. In addition, the lactate tolerance ability, defined as the differential speed between blood lactate concentrations of 5.0 and 10.0 mmol·L−1, was calculated (23). A noncontrolled study was conducted because coaches normally include strength training in the preseason period and it would be unethical to persuade elite players to follow a “noncomplete” training schedule. The players applied HIIT programs (HIIT4 × 4 or HIIT16 × 100) twice a week. Maximal strength training (twice a week), sprint training (once a week), technical and tactical skills (5–6 days per week), and a friendly match-play (once a week) were similar between groups. With the present experimental setting, the effect of different swimming endurance training protocols (HIIT4 × 4 vs. HIIT16 × 100) performed concurrently with strength and specific water polo training could be examined.
Two water polo clubs participating in men's top-level division Greek championship took part in the study. All players recruited from the first club (n = 7, age: 29.9 ± 5.1 years, stature: 187.6 ± 7.1 cm, body mass: 90.2 ± 11.6 kg) were members of the finalist team in the Greek championship top-level division in the year 2011–2012, who had also competed in the European champions league tournament. The players of the second club (n = 7, age: 28.9 ± 4.9 years, age range: 22–35 years, stature: 182.4 ± 7.2 cm, body mass: 88.6 ± 13.1 kg) were experienced water polo players who had been playing at top-level division for more than 5 years. All players trained on a daily basis. Written informed consent was obtained from all players before the commencement of the study. The study was approved by the faculty review board and conformed to the Declaration of Helsinki. The compliance rate of 80% for both the HIIT and the strength training was the criteria for the completion of the study.
Training Content of HIIT4 × 4 and HIIT16 × 100 Groups
Players of HIIT4 × 4 group performed 4 × 4-minute bouts of freestyle swimming at an intensity that corresponded to ∼106% of V4, interspersed with 3 minutes of active recovery at self-selected intensity. This set of repetitions was performed twice a week: Monday and Wednesday mornings at 10:00 AM (Table 1). The total swimming distance covered in each session was approximately 1,770 m (swimming bouts: 1,170 m, active recovery: 600 m).
The training intensity of HIIT16 × 100 group corresponded to ∼106% of the V4 and consisted of 2 series of 8 × 100 m (16 × 100 m). Each effort was interspersed with 20 seconds of passive rest. Two minutes of passive rest was given between each series. The HIIT16 × 100 sessions were conducted on Tuesday and Thursday mornings at 10:00 AM (Table 1).
Every 2 weeks, the players of both groups were asked to attempt a slight increase of their training speed, maintaining a similar subjective perception while completing the HIIT session. Any speed improvement was recorded and used for the adjustment of training pace during subsequent HIIT.
Strength Training and Specific Water Polo Training
A specific 10-minute warm-up procedure using 10–15 repetitions of 50–60% of 1RM and stretching exercises was followed before the initiation of the strength training program. This consisted of 4 sets of 4–5 repetitions at 85–90% 1RM with emphasis on maximal speed of movement in the concentric phase. When the participants were able to perform 6 repetitions, the load was increased by 2.5 kg. A 3-minute rest was allowed between each set. The exercises (bench press, seated pull-down, triceps press, shoulder press, and leg press) targeted specific muscles that are mainly used in water polo: pectoralis major, latissimus dorsi, triceps, deltoids, and quadriceps. The training sessions lasted approximately 50–60 minutes. All strength training sessions were supervised by the same experimenter and were performed on separate days for each group (Table 1).
Specific training included (a) sprint training (i.e., 10 × 25-m all-out swimming efforts with 2 minutes of active recovery; once a week), (b) technical training (passes for 10–15 minutes, shots for 10–15 minutes; 5–6 days a week), and (c) tactical training (counterattacks, “extra-man player” training, 20–25 minutes; 5–6 days a week). All players were instructed to perform technical and tactical exercises at low to moderate intensity. Throughout the intervention period, strength training characteristics and training time for sprint, technical and tactical training, remained similar for both groups (Table 1). The 2 training programs were used before the commencement of the competition period (precompetition season). The baseline test was conducted at the end of August, and the posttraining test was performed at the end of October. All players had returned from ∼45 days off-season holidays in which they participated in basic endurance and fitness training twice a week (resistance training at low-medium intensities and 10 repetitions, basketball, handball). Five days before the baseline tests, players of both clubs followed a low-intensity swimming training with similar characteristics as an introductory microcycle in the beginning of the preseason training period. During the intervention period, players were receiving daily instructions and recommendations for their diet according to training intensity and duration. An expert dietician was responsible for the nutritional recommendations in both groups.
Pretraining and Posttraining Testing Procedures
The week before commencement and the week after the experimental training period, the players' fitness level was evaluated through an incremental swimming test (5 × 200 m) as previously described by Tsekouras et al. (27). After a 10-minute standardized warm-up, participants swam 5 repetitions of 200 m, in an outdoor 25-m pool, at intensities corresponding to 60, 70, 80, 90, and 100% of maximum speed, with a 5-minute passive recovery between each effort. Fingertip blood samples were taken after each 200-m repetition and were immediately analyzed using the reflectance photometry-enzymatic reaction method (Accusport, Boehringer, Germany). The speed corresponding to lactate concentrations of 4.0, 5.0, and 10.0 mmol·L−1 (V4, V5, and V10) were calculated from the speed-lactate curve by interpolation of a second-order polynomial function. The lactate tolerance ability was defined as the differential velocity between blood lactate concentrations of 5.0 and 10.0 mmol·L−1 (V10-V5) (23). The reliability of using a speed-lactate test for detection of the V4 has been reported to be high (intraclass correlation coefficient = 0.847, p ≤ 0.05) (28).
The week before and after the experimental period and 2 days after the 5 × 200-m test, the 1 repetition maximum (1RM) on bench press was measured for the evaluation of maximal strength. A 2-minute recovery between each effort and 2.5 kg increments, respectively, were used. The players were familiar with bench press exercises as part of their regular strength training program in the previous season.
Data are expressed as mean ± SD or 90% confidence limits. A 2-way analysis of variance for independent samples and repeated measures was used to identify changes between pretraining and posttraining values in V4, V5, V10, and V10-V5. Significant differences between groups were observed on the pretraining values of V4, V5, and V10. To control for these differences, an analysis of covariance was applied using the pretraining values as a covariate. The absolute change scores of V4, V5, V10, and V10-V5 were used as a dependent variable in each analysis. A Tukey's post hoc test was used to locate the differences between mean values. Effect size (ES) for changes of performance parameters was calculated as described by Rhea (24). Pearson's correlation coefficients were used to detect associations in the percentage changes between strength and specific performances indices. The level of significance was set at p ≤ 0.05.
The players were adapted to both training modes and increased their speed every 2 weeks. Swimming speed during training was increased from the first to the eighth week (HIIT4 × 4: 1.22 ± 0.04 to 1.39 ± 0.07 m·s−1, p < 0.01, ES = 4.6, HIIT16 × 100: 1.37 ± 0.03 m·s−1 to 1.46 ± 0.05 m·s−1, p < 0.01, ES = 2.7). The percentage change of training speed was higher for HIIT4 × 4 (HIIT4 × 4: 14 ± 5% vs. HIIT16 × 100: 7 ± 3%, p = 0.01). The greater part of this change was achieved after 4 weeks of HIIT4 × 4 or HIIT16 × 100 training (8 ± 2% vs. 4 ± 2%, p = 0.01).
The changes from pretraining to posttraining in the speed-lactate curve of each group are presented in Figure 1. Swimming speed corresponding to V4, V5, and V10 was significantly increased from pretraining to posttraining only in the HIIT4 × 4 group (V4: 9 ± 5%, ES = 3.6, p = 0.00; V5: 8 ± 3%, ES = 3.5, p = 0.00; V10: 7 ± 2%, ES = 2.0, p = 0.00). No changes were observed in HIIT16 × 100 group regarding V4, V5, and V10 (V4: 4 ± 5%, p = 0.08, ES = 2.1; V5: 3 ± 3%, p = 0.07, ES = 1.9; V10: 1 ± 1%, ES = 0.3, p = 0.62; Table 2).
Pretraining values for the above parameters were significantly greater in HIIT16 × 100 group than HIIT4 × 4 group (p < 0.01), and analysis of covariance was used on the performance change scores of all variables. Analysis of covariance using the pretraining values as a covariate showed that V4 but not V5 and V10 baseline values are significant covariates. However, this analysis showed no difference in performance change scores between groups regarding V4 and V5 (V4: p = 0.12, V5: p = 0.69). Adjusted V10 change was greater in HIIT4 × 4 group (V10: p = 0.05). Adjusted performance score changes of V4, V5, and V10 are shown in Table 2.
HIIT16 × 100 training decreased V10-V5 (19 ± 20%, ES = 0.7, p = 0.03; Table 2), whereas HIIT4 × 4 training had no impact on this parameter (2 ± 18%, ES = 0.2, p = 0.96; Table 2). Analysis of covariance showed that pretraining value is not a significant covariate and posttraining percentage change values are not different between groups (p = 0.15).
Significant maximum strength gains were observed after training for both groups (HIIT4 × 4: 14 ± 4%, ES: 1.0, p < 0.01; HIIT16 × 100: 19 ± 10%, ES = 2.0, p < 0.01; Table 2). Analysis of covariance showed that the pretraining value is not a significant covariate and posttraining values are not different between groups (p = 0.18). The body mass remained unchanged (p > 0.05) for both groups (HIIT4 × 4 pretraining: 88.6 ± 13.07 kg, posttraining: 88.3 ± 12.2 kg; HIIT16 × 100 pretraining: 90.2 ± 11.6 kg, posttraining: 91.4 ± 12.3 kg). No significant correlations were detected between percentage changes in maximum strength level and the swimming performance variables (r = 0.02 to −0.37, p > 0.05).
The present study compared the effects of 2 different high-intensity interval training programs performed concurrently with maximum strength and specific water polo training during the precompetition period on performance indexes of elite water polo players. With a realistic training setting approach in water polo, we were able to demonstrate for the first time that both training programs improved swimming endurance parameters together with maximum strength level. Despite differences in the initial fitness level, it seems that HIIT4 × 4 is more effective in enhancement of V4, V5, and V10, whereas HIIT16 × 100 is superior in lactate tolerance (V10-V5) development within each respective group.
Of note, we observed that the concurrent strength training and HIIT during the precompetition season is an effective regimen that enhances swimming performance parameters. In terms of endurance performance, greater improvements were induced by HIIT4 × 4 than HIIT16 × 100. Although the 2 groups demonstrated different baseline training status, the analysis of covariance using the pretraining values as a covariate demonstrated no difference between groups in the posttraining values of V4, V5, and V10-V5. However, V10 was improved more in the HIIT4 × 4 group (p = 0.05), and we cannot overlook the within-group specific improvements, which probably indicate that this was the result of different HIIT modes. Although a different initial fitness status may be critical for the training effect, this should have been partly counterbalanced by a faster and overall greater adjustment of the training speed in the HIIT4 × 4 compared with the HIIT16 × 100 group (increased by 14 vs. 7% within 8 weeks). Considerable increments in aerobic performance were also detected by previous studies on team sports that used concurrent strength training and HIIT4 × 4 (10) or HIIT4 × 4 training in isolation (9,18). It has been suggested that high-intensity training of long work intervals is more efficient for increasing aerobic capacity than HIIT of short work intervals (4). Besides, Billat (5) reported that when the rest interval between efforts is longer, the velocity during work intervals is greater than that obtained by shorter rest. Likewise, in the present study, greater gains in swimming speed were reached for HIIT4 × 4 compared with HIIT16 × 100 as the training intervention (0–8 weeks) progressed. Although in well-trained athletes, the underlying mechanisms behind these adaptations are still under investigation, the improvements in swimming endurance might be linked to the HIIT characteristics (i.e., the long work duration in combination with sufficient active recovery between bouts). It has been suggested that long work intervals are related with specific cardiovascular and muscular adaptations, such as increased content and activation of aerobic enzymes, greater muscle glycogen content (20), increased work economy, and greater ability to buffer H+ ions (30).
Moreover, the insignificant development in aerobic fitness parameters and the large (∼20%) increment in the lactate tolerance ability (i.e., V10-V5) observed in HIIT16 × 100 group might be related to the specific HIIT characteristics. The overload endurance swimming training slightly above the V4 is a training method during which the athlete activates both aerobic and anaerobic metabolisms. However, it seems that the frequent and long-term training at velocities greater than V4 with incomplete rest intervals may not improve the parameters related to aerobic fitness (i.e., swimming economy). A basic physiological reason that may explain this suggestion is related to the increased lactate production, which reduces muscle pH and probably leads to muscle fatigue as the training set progresses. Indeed, the players of HIIT16 × 100 group exhibited a progressive inability to retain high exercise intensity throughout the training session and as such the exercise time from effort to effort showed 3- to 4-second increases. Therefore, the improvement in V10-V5 seems to be associated with the work to rest ratio. The shorter rest interval that was given in HIIT16 × 100 group might have proven inadequate for lactate removal and probably have led to lactate tolerance adaptation. Along this line, the HIIT with 16 × 100 m repetitions and inadequate rest interval may be appropriate when a short period and limited time before a tournament is available. In this case, a fast improvement of anaerobic ability may be accompanied with a meaningful (i.e., 4%) endurance improvement, concurrently with strength gain. In this group (HIIT16 × 100), the actual 4% in V4 improvement corresponds to 12% when the baseline values were equalized for the 2 groups (extracted from the analysis of covariance). Whatever the case, players in the HIIT16 × 100 group started the 8-week training period with high V4, V5, and V10 speed values comparable with those reported for long distance competitive swimmers (V4: 1.18–1.20 m·s−1) (8) and possibly any further speed improvement was very difficult to achieve. At the elite level, these small changes in performance may be important for the in-game efficiency.
With regard to maximum strength gain, all players exhibited a significant posttraining increment in muscular strength compared with baseline values. Strength level was approximately increased by 14 and 19%, for HIIT4 × 4 and HIIT16 × 100 groups, respectively (Table 2). Similar gains were observed after 11 weeks of combined strength and endurance training in competitive young swimmers (2). Kraemer and Ratamess (13) suggested that moderately trained athletes exhibit such high increments in strength level. The strength training protocol applied in the present study (twice per week 85–90% of 1RM) is equally beneficial in strength gains to resistance training programs of lower load (60–80% 1RM) and longer duration (18 weeks) (29). The elite players who participated in the present study were familiarized with strength endurance but not with maximal strength training and were tested during the precompetition season. Therefore, the observed high strength gain is not surprising. In addition, the unchanged body mass possibly indicates that the improvement in maximal strength level is mainly attributed to specific neuromuscular adaptations induced after high-load, high-speed (90% 1RM, 4–5 repetitions) strength training and no increments in muscle hypertrophy (1). Hence, it seems that the setting in the present study (maximal strength and endurance training on separate days; 2 training sessions were devoted on each component) was adequate and effective to elicit significant strength and endurance increments.
High-intensity interval training is a training method that enhances exercise performance in well-trained water polo players. Different work to rest ratio intervals affects the physiological adaptations occurring after HIIT. It seems that greater gains in aerobic performance parameters can be obtained with long work intervals (4 minutes) and exercise intensity that exceeds 100% of V4. However, HIIT of shorter work duration (16 × 100 m), similar exercise intensity, and incomplete recovery time in between may induce small but practically significant endurance gains. The HIIT16 × 100 training seems to be superior for lactate tolerance improvements. The above results seem to have a great practical importance because water polo requires both aerobic and anaerobic demands (19,22,25). Although a direct comparison between groups is not justified with the present experimental setting, it seems that long interval training with a long resting interval between efforts is beneficial in high-level water polo players, whereas HIIT with shorter work intervals and incomplete recovery in between is adequate to induce meaningful gains to a higher ability group of players (i.e., players who possess a high pretraining endurance capacity). Moreover, the present data support the opinion that strength, HIIT, and specific water polo training, performed concurrently, positively affects exercise performance. It is noteworthy that both group of players showed significant improvement within a short period of training and reach competitive readiness with this type of concurrent training. It seems that these improvements are comparable with strength or endurance training programs when performed in isolation. Additionally, it seems that the order of training components applied in the present study is appropriate for meaningful strength gain, allowing time for the required specific water polo training. Future studies are necessary to explore the underlying factors that stimulate benefits from concurrent training in elite water polo players.
In conclusion, high-intensity swimming training concurrently performed with maximal strength training improves muscle strength and allows specific adaptations leading to enhancement of swimming performance indices of elite water polo players. Relative to players' initial ability level, both training modes seem effective for the improvement of endurance ability when they are applied concurrently with strength training.
The authors gratefully acknowledge the cooperation of coaches T. Vlachos, N. Karamanis, and the water polo players for their contribution. The authors have no professional relationships with companies or manufacturers that might benefit from the results of the study. There is no financial support for this project and no funds were received for this study. The results of this study do not constitute endorsement of any product by the authors or the National Strength and Conditioning Association.
1. Aagaard P, Simonsen EB, Andersen JL, Magnusson P, Dyhre-Poulsen P. Increased rate of force development and neural drive of human skeletal muscle following resistance training. J Appl Physiol (1985) 93: 1318–1326, 2002.
2. Aspenes S, Kjendlie PL, Hoff J, Helgerud J. Combined strength and endurance training in competitive swimmers. J Sports Sci Med 8: 357–365, 2009.
3. Bentley DJ, Roels B, Hellard P, Fauquet C, Libicz S, Millet GP. Physiological responses during submaximal interval swimming training: Effects of interval duration. J Sci Med Sport 8: 392–402, 2005.
4. Billat V, Slawinsky J, Bocquet V, Demarie A, Lafitte L, Chassaing P, Koralsztein JP. Intermittent runs at the velocity associated with maximal oxygen uptake enables subjects to remain at maximal oxygen uptake for a longer time than intense but submaximal runs. Eur J Appl Physiol 81: 188–196, 2000.
5. Billat VL. Interval training for performance: A scientific and empirical practice. Part 1: Aerobic interval training. Sports Med 31: 13–31, 2001.
6. D'Ercole C, Gobbi M, D'Ercole A, Iachinim F, Gobbi F. High intensity training for faster water polo. J Sports Med Phys Fitness 52: 229–236, 2012.
7. Denadai BS, Ortiz MJ, Greco CC, De Mello M. Interval training at 95% and 100% of the velocity at VO2max: Effects on aerobic physiological indexes and running performance. Appl Physiol Nutr Metab 31: 1–7, 2006.
8. Fernandes RJ, Sousa M, Machado L, Vilas-Boas JP. Step length and individual anaerobic threshold assessment in swimming. Int J Sports Med 32: 940–946, 2011.
9. Helgerud J, Engen LC, Wisloff U, Hoff J. Aerobic endurance training improves soccer performance. Med Sci Sports Exerc 33: 1925–1931, 2001.
10. Helgerud J, Rodas J, Kemi OJ, Hoff J. Strength and endurance in elite football players. Int J Sports Med 32: 677–682, 2011.
11. Hickson RC. Interference of strength development by simultaneously training for strength and endurance. Eur J Appl Physiol 45: 255–263, 1980.
12. Kraemer WJ, Patton JF, Gordon SE, Harman EA, Deschenes MR, Reynolds K, Newton RU, Triplett NT, Dziados JE. Compatibility of high-intensity strength and endurance training on hormonal and skeletal muscle adaptations. J Appl Physiol (1985) 78: 976–989, 1995.
13. Kraemer WJ, Ratamess NA. Hormonal responses and adaptations to resistance exercise and training. Sports Med 35: 339–361, 2005.
14. Laursen PB, Shing CM, Peake JM, Coombes JS, Jenkins DG. Interval training program optimization in highly trained endurance cyclists. Med Sci Sports Exerc 34: 1801–1807, 2002.
15. Libicz S, Roels B, Millet GP. VO2 responses to intermittent swimming sets at velocity associated with VO2max. Can J Appl Physiol 30: 543–553, 2005.
16. Losnegard T, Mikkelsen K, Ronnestad BR, Hallen J, Rud B, Raastad T. The effect of heavy strength training on muscle mass and physical performance in elite cross country skiers. Scand J Med Sci Sports 21: 389–401, 2011.
17. Maglischo EW. Swimming Even Faster. Mountain View, CA. Mayfield Publishing Company, 1993.
18. McMillan K, Helgerud J, Macdonald R, Hoff J. Physiological adaptations to soccer specific endurance training in professional youth soccer players. Br J Sports Med 39: 273–277, 2005.
19. Melchiorri G, Castagna C, Sorge R, Bonifazi M. Game activity and blood lactate in men's elite water-polo players. J Strength Cond Res 24: 2647–2651, 2010.
20. Perry CG, Heigenhauser GJ, Bonen A, Spriet LL. High-intensity aerobic interval training increases fat and carbohydrate metabolic capacities in human skeletal muscle. Appl Physiol Nutr Metab 33: 1112–1123, 2008.
21. Platanou T. Time motion analysis of the international level water polo players. J Hum Mov Stud 46: 319–331, 2004.
22. Platanou T, Geladas N. The influence of game duration and playing position on intensity of exercise during match-play in elite water-polo players. J Sports Sci 24: 1173–1181, 2006.
23. Pyne DB, Lee H, Swanwick KM. Monitoring the lactate threshold in world-ranked swimmers. Med Sci Sports Exerc 33: 291–297, 2001.
24. Rhea MR. Determining the magnitude of treatment effects in strength training research through the use of the effect size. J Strength Cond Res 18: 918–920, 2004.
25. Smith HK. Applied physiology of water polo. Sports Med 26: 317–334, 1998.
26. Smith TP, Coombes JS, Geraghty DP. Optimising high-intensity treadmill training using the running speed at maximal O2 uptake and the time for which this can be maintained. Eur J Appl Physiol 89: 337–343, 2003.
27. Tsekouras YE, Kavouras SA, Campagna A, Kotsis YP, Syntosi SS, Papazoglou K, Sidossis LS. The anthropometrical and physiological characteristics of elite water polo players. Eur J Appl Physiol 95: 35–41, 2005.
28. Turner AP, Smith T, Coleman SGC. Use of an audio-paced incremental swimming test in young national-level swimmers. Int J Sports Physiol Perform 3: 68–79, 2008.
29. Veliz RR, Requena B, Suarez-Arrones L, Newton RU, Saez de villarreal E. Effects of 18-weeks in-season heavy resistance and high-intensity training on throwing velocity, strength, jumping and maximal sprint swim performance of elite male water polo players. J Strength Cond Res 28: 1007–1114, 2014.
30. Weston AR, Myburgh KH, Linday FH, Dennis SC, Noakes TD, Hawley JA. Skeletal muscle buffering capacity and endurance performance after high-intensity interval training by well-trained cyclists. Eur J Appl Physiol 75: 7–13, 1997.