3.Blood Lactate, An Important Tool in Predicting and Optimizing Performance in Football

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Aerobic capacity is crucial for the performance in football players, and its assessment is one of the most important ergometric tests in the early stages of pre-season (2,6). In the modern football the distance covered during a match in elite football players range between 10 – 13Km (2,4) and with mean values for VO2max between 55- 75 mL · kg–1 · min (6,2,4), it has been proposed that a VO2max of > 60 mL · kg–1 · min should be the minimum threshold in order to perform in top class contemporary football (6,2,4). However, there many other biochemical factors that should be taken into consideration in football players which their importance and usefulness are crucial to make final conclusions about the fitness levels and the design of a particular training program based on the results. One of the most well know parameters in the athletic world is the anaerobic threshold or lactate threshold. Why this parameter is such of an importance? Because its concentration in the blood is being used as an indicator of aerobic and anaerobic energy production (4,13), it helps to examine the rate of production and its removal from the blood (12), the tolerance to lactate (9), evaluate physical fitness as well as identify any adaptations might occur after following a specific training plan are some of the information can be collected from the test.

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The assessment can be carried out in the laboratory (treadmill) or outdoor (football court). In a laboratory environment the test protocol consists of several incremental stages (4-7, depends on the sport and the athlete) with a small break between the stages in order to collect capillary blood either from the finger (Picture 1) or the ear lobe. Then, the treadmill speed increasing gradually until volitional exhaustion of the athlete where VO2max and vVO2max can be determined as well. After the completion of the test, the anaerobic threshold can be detected with various methods. The diagram bellow shows the determination of 2 thresholds, the LT1 (around 2 mmol L −1) and LT2 (between 3.5 and 4 mmol L −1 ).

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L1 represents the velocity (vLT1) / intensity where the main energy source derived from the aerobic system. L2 shows the velocity (vLT2) / intensity and the transition from aerobic to the anaerobic system and also indicating the upper limit of the steady state between lactate production and removal. Based on these results the sport scientist can develop a training program, monitor the intensity of the players based on the blood lactate results and most importantly work at the right intensities as well as at the right amount of time.

Based on the literature, a football player with high anaerobic threshold would be able to cover more distance in high intensity without accumulating much lactic acid in the blood (6). At the table below, various of velocities at the anaerobic threshold can be seen in professional football players from different leagues and countries.

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Table 1. Mean ± SD values of velocity at LT2 in various studies in football players.

STUDY	COUNTRY	NUMBER OF PARTICIPANTS	LEVEL	VELOCITY AT LT2 (Km/h)
Casajus	Spain	15	Professional	12.4 ± 1.5
Santos et al	Portugal	44	Professional	14.2 ± 1.4
Balikian et al.	Brazil	25	Professional	13.5 ± 0.9
Ziogas et al.	Greece	53	Professional	13.2 ± 0.7

Lactate threshold has shown to strongly correlated to endurance performance, and more emphasis has been placed in comparison to VO2max the recent years. Also, measurement of LT should implemented as a tool during in competitive period for the investigation of aerobic fitness (4,5,1,13). The main reason for this is because LT is associated with peripheral adaptations such as an increase in capillary density and in the ability to transport hydrogen ions and it is more sensitive to changes in training regimens, whereas VO2max is basically limited to central factors (Cardiac Output), where it makes it harder to improve (6). Lastly, LT assessment is one of the gold standard methods to evaluate the aerobic and anaerobic fitness and is a valid as well as reliable tool in monitoring changes in aerobic capacity in football players. However, it should not be a primarily criterion for a player selection as there are other important determinants that should be taken into consideration to define overall a player’s fitness.

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REFERENCES:

1. Al-Hazzaa, H, M., Almuzaini, K, S., Al-Refaee, S, A., Sulaiman, M, A., Dafterdar, M, Y., Al-Ghamedi, A., & Al-Khuraiji, K, N. (2001). Aerobic and anaerobic power characteristics of Saudi elite soccer players. Journal of Sports Medicine and Physical Fitness, 41(1), 54-61.

1. Balikalian, P., Lourencao, A., Riberio, L, F, P., Festuccia, W, T, L., & Neiva, C, M. (2002). Maximal oxygen uptake and anaerobic threshold in professional soccer players: comparison between different positions.

1. Bangsbo, J., Magni, M., & Krustrup, P. (2006). Physical and metabolic demands of training and match-play in the elite football player. Journal of Sports Sciences, 24(7), 665-674.

1. Casajus, J, A. (2001). Seasonal Variation in Fitness Variables in Professional Soccer Players. Journal of Sports Medicine and Physical Fitness, 41(6), 463-469.

5)Chin, M, K., Lo, Y, S., Li, C, T., So, C, H. (1992). Physiological profiles of Hong Kong élite soccer players. British Journal of Sports Medicine, 26(4), 262-266.

1. Edwards, A, M., Clark, N., & Macfadyen, A, M. (2003). Lactate and Ventilatory Thresholds Reflect the Training Status of Professional Soccer Players Where Maximum Aerobic Power is Unchanged. Journal of Sports Science Medicine, 2(1), 23-29

7)Hamilton, A, L., Nevill, M, E., Brooks, S., & Williams, C. (1991). Physiological responses to maximal intermittent exercise: differences between endurance trained runners and games players. Journal of Sports Science, 9(4), 371-382.

8)Jemni, M., Prince, M, S., & Baker, J, S. (2018). Assessing Cardiorespiratory Fitness of Soccer Players: Is Test Specificity the Issue? A Review. Journal of Sports Medicine - Open, 4(1),

9)Nilsson, J., & Cardinale, D. (2015). Aerobic and anaerobic test performance among elite male football players in different team positions. Journal of Sport Science, 6(2), 73-92.

10)Reily, T., Bangsbo, J., & Franks, A. (2000) Anthropometric and Physiological predispositions for elite soccer. Journal of Sports Science, 18(9), 669-683.

11)Strudwick, A, Reily, T., & Doran, D. (2002). Anthropometric and fitness profiles of elite players in two football codes. Journal of Sports Medicine and Physical Fitness, 42(2), 239-242.

12)Tonnessen, E., Hem, E., Leirstein, S., Haugen, T., & Seiler, S. (2013). Maximal aerobic power characteristics of male professional soccer players, 1989-2012. International Journal of Sports Physiology Performance, 8(3), 323-329.

1. Ziogas, G, Patras K, N., Stergiou, N., & Georgoulis, A, D. (2011). Velocity at lactate threshold and running economy must also be considered along with maximal oxygen uptake when testing elite soccer players during preseason. Journal of Strength and Conditioning Research, 25(2), 414-419.