Sunday, 4 November 2012

Physical Capacity of Top Class Soccer Players

Top-class football players are characterized by moderate-to-high maximum oxygen uptake (VO2max), that is 57 to 75 ml kg/min.17 However, due to the intermittent nature of the game, fitness-specific evaluations are more appropriate to accurately describe the physical capacity of the players. In this regard, performance in the yo-yo intermittent recovery (YYIR) test better reflects the ability to perform repeated intense exercise than VO2max per Se. Indeed, YYIR performance is well correlated with the amount of high-intensity running during a match. In addition, YYIR tests provide more sensitive measures of changes in performance in sports of intermittent nature than VO2max: performance in the YYIR test level 2 of Australian football players was 37% better than for the substitutes, whereas no differences were observed in VO2max between starters and nonstarters. World-class players cover approximately 2400 m in the YYIR test level 1 and 1300 m in the YYIR test level which is 10% to 20% higher than moderate professional players. Elite European top-league division players exhibit greater sprint and repeated sprint performances compared with amateur players. For example, higher level players have both faster 6 into 40-m (20 + 20-m sprints with 180° turns separated by 20 s of passive recovery; professional 7.12 s vs. amateur 7.55 s) shuttle sprints, and single 20 + 20-m shuttle sprint (professional 6.88 s vs. amateur 7.08 s) performance than amateur players. The percent decrements during this repeated sprint test was smaller for top-class players compared with moderate professional and amateur players (3.3%, 5.1%, and 6.1%, respectively).

Physiological Adaptation to High-Intensity Training

Amateur footballer

Based on the contribution of the predominant energy system, high-intensity exercises can be divided into aerobic high-intensity and anaerobic (speed and speed endurance) training, which represents the intensities below, close to, and above VO2max, respectively. This section provides an overview of the major physiological adaptations that occur in response to aerobic high intensity and speed endurance training and their relevance for football. Aerobic high-intensity training elicits increases in cardiovascular parameters such as heart size, blood flow capacity, and artery distensibility. These changes improve the capacity of the cardiovascular system to transport oxygen, resulting in faster muscle and pulmonary VO2 kinetics and higher VO2max.Thus, a greater amount of energy can be supplied aerobically, allowing a player to both sustain intense exercise for longer duration and also recover more rapidly between high-intensity phases of the game.

   Anaerobic training involving speed-endurance drills increases the activity of

some anaerobic enzymes, such as creatine kinase, phosphofructokinase, myokinase, and glycogen phosphorylase. A higher rate of anaerobic energy turnover may improve the ability to produce power rapidly and continuously during short maximal bouts. A period of speed-endurance training increases the number of muscle membrane transport proteins involved in pH regulation, such as Na+/H+ exchange isoform 1 (NHE1) and monocarboxylate transporters (MCT1 and MCT4), and in some cases enhances muscle buffering capacity.31 These changes may reduce the inhibitory effects of H+ within the muscle cell and form part of the explanation for the improved performance during repeated intense exercises that are observed after a period of speed-endurance training. Anaerobic training also increases the expression of the Na+,K+ transport pump, which, by reducing the contraction-induced net loss of K+ from the working muscles, preserves the cell excitability and force development. This sequence of events should improve a player’s ability to sustain very intense exercise for longer duration and perform high-intensity efforts more frequently during the game.

   A large number of other muscular adaptations also occur with high-intensity
training. For example, both aerobic high-intensity and speed-endurance training up-regulate several mitochondrial oxidative proteins and increase the muscle glycogen content—the most important substrate for energy production in football. The overall effect is pronounced changes in muscle metabolism with an increased fat oxidative capacity and reduced glycogenolysis, carbohydrate oxidation, and energy expenditure at a given exercise intensity. These adaptations may be beneficial in football, where an improved capacity to use muscle triglycerides, blood free fatty acids, and glucose as substrates for oxidative metabolism could spare the limited muscle glycogen stores, thus allowing a player to exercise at a higher intensity toward the end of the game.

   Muscle capillarization is also enhanced in response to speed-endurance training.  An enriched capillary network may lead to a shorter diffusion distance between capillaries and muscle fibers, and a larger area available for diffusion. Collectively, the enhanced capillarization may favor the release of compounds from muscle interstitium and delay fatigue development during intense exercise. In support of this contention, a higher capillary density is associated with performance improvements in an approximately 3-min exhaustive bout, and related to muscle force maintenance (during and in recovery period) from short-term intense exercise.
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