Characterized by short-duration, maximal, high-intensity efforts interspersed with low-intensity or rest periods, rugby union requires the players to perform over the full range of the energy continuum, from anaerobic to aerobic. Fatigue is inevitable; current nutritional recommendations for training, pre, during and post-game aim to enhance performance and recovery.
Characteristics Of Rugby Union
Rugby union is a game of two 40-minute halves. It is characterized by short-duration, maximal, high-intensity efforts (15% game time) interspersed with low-intensity or rest periods.2,5,8,14
The high-intensity efforts last between 5-15 seconds, while the low-intensity or rest periods last up to only 40 seconds. A line-out, maul, ruck or scrum occurs every 33 seconds during a game. Thus, the actual time that the ball is in play is only 25-29 minutes of the 80-minute game duration.2,14
During the game the work to rest (work:rest) ratios for backs is between 1:15 to 1:20, with their rest periods being longer (lasting ~80-100 seconds) than forwards.5
In the study by McLean12, time motion analysis for rugby union forwards and backs showed that half-backs have the longest sprinting time of any of the 15 players on the field (~2.16 minutes), with the average distance covered per sprint being 10-20 meters, with players (backs) maximally covering a total of ~350 meters during a game, and a farther ~550 meters at sub-maximal pace.8
The average running pace of a half-back ranges from 5-8 meters per second when the ball is in play.12,14 Time motion analysis indicates that while sprinting 55% of the efforts are less than 10 seconds, 85% less than 15 seconds, and 5% more than 30 seconds.14
Half-backs only spend ~1.52 minutes with the ball. The greatest amount of their game time is spent in non-purposive running (~51.04 minutes), with half-backs having the longest purposive running time (~21.28 minutes) of any other player on the field12,14; this allows them to cover up to six kilometers per game.8
Therefore, in addition to technical skills, the rugby union player, especially the half-back, needs a high anaerobic capacity in order to produce the speed, power and strength required during a game, as well as aerobic endurance, as they have insufficient time between bouts of high-intensity work to fully recover.2,8
For the body to perform exercise for any given intensity or duration it requires energy. This energy is provided chemically in the form of Adenosine Triphosphate (ATP), a high-energy phosphate stored within skeletal muscle. ATP is the only fuel that can be used directly by the working muscles for contraction.
The body has limited stores (~80-100 grams) of ATP, only enough to supply energy for two seconds of maximal sprinting; therefore ATP must be continually be resynthesized from other sources through different metabolic pathways. The intensity and duration of the event determines the fuel and the energy system that is required to provide energy.10,11
Energy Systems ///
There are three different energy systems in the body: 1) the immediate system - fueled by the intramuscular high-energy phosphates ATP and Phosphocreatine (PCr), 2) the short-term system - the anaerobic glycolysis (glycogenolysis and/or glycolysis) or lactate system, fueled by glycogen, glucose, and the glycerol backbone of triglycerides, and 3) the long-term system - the aerobic glycolysis and oxidative phosphorylation of the macronutrients carbohydrate, lipids and protein.10,11
During a rugby game the total distance covered by players can be broken down into 37% walking, 28% jogging, and 34% sprinting. Thus, "while one energy system will predominate over the other, both aerobic and anaerobic energy systems are always working, regardless of intensity or type of activity".3 The relative contributions of each energy system are dependent upon both the exercise intensity and duration.11
The contribution of energy from each energy system falls along a continuum, and the demands of rugby union require the players to perform over the full range of the energy continuum, from anaerobic to aerobic. At one extreme, during high-intensity, short duration (~10 seconds) exercise, such during the short bursts of play or maximal efforts in a rugby game, the intramuscular high-energy phosphates supply almost all of the energy required.5,11,14
In the middle of the continuum, when there is not enough time for the PCr system to recover between bouts of high-intensity work, and in phases of the game such as accelerations, decelerations, jumping in the line-outs, side-stepping, and scrimmaging, large demands are placed on anaerobic glycolysis to allow the players to sustain high power outputs.5,14
At the other extreme, during less-intense, prolonged exercise, such as during the low-intensity or rest periods of the game, aerobic processes provide almost all of the energy required, and allow the PCr stores to recover.5,11,14
Substrates Used In Energy Production ///
Each energy system uses different substrates for fuel. The immediate system uses the intramuscular high-energy phosphates ATP and PCr, which can be replenished rapidly during the low-intensity or rest periods interspersed between bouts of high-intensity work; 2) anaerobic glycolysis, also called the lactate system, is fueled by different forms of carbohydrate (glycogen, glucose, and the glycerol backbone of triglycerides); and 3) aerobic glycolysis, although fueled by the oxidative phosphorylation of the macronutrients carbohydrate, lipids and protein, is mainly dependent upon the use of carbohydrates for fuel.5,10,11
Research has shown that rugby union players spend a large percentage of game time at intensities greater than 75% of their maximum oxygen uptake capacity (VO2 max) and as it is the intensity that dictates which substrate the body uses for fuel, this suggests that carbohydrate is the primary fuel utilized by players during a game.4
Major Causes Of Fatigue
Fatigue is inevitable during high-intensity exercise. It is defined as "the inability to maintain a given or expected output or force"10, and it is likely to be a multifactoral process during a rugby union game.9,10
Metabolic changes such as lactic acidosis, fuel depletion, impaired excitation-contraction coupling, and product inhibition which occur during a rugby union game can inevitably cause fatigue, thereby reducing the pace/power outputs that the player can maintain for the game duration, which can result in reduced performance.10,11
Lactic Acidosis ///
During the short-duration, high-intensity work efforts, the greater the player's oxygen deficit, the greater their ATP and PCr stores are being depleted, and the greater the accumulation of lactate in their blood.10
Lactate decreases the pH of the tissues in which it accumulates; and studies with isolated muscle preparations have shown that decreasing skeletal muscle pH either 1) impairs muscle contraction by disrupting calcium release, or 2) inhibits ATP resynthesis.1,9,10,15
Studies involving biomechanical analysis of muscle biopsy samples taken from the vastus lateralis at rest and after 10 seconds of maximal sprint exercise show that "ATP is supplied initially by maximal rates of ATP degradation and glycogenolysis, particularly in type-II fibers"7; and that it is the depletion of PCr in those fibers that are primarily responsible for fatigue.7
Glycogen Depletion ///
In a study by Jardine, et. al. (1988), it was found that during an 80-minute rugby union game, the player utilizes a total of 43 mmol/kg wet weight muscle glycogen, which means that glycogen depletion is not a limiting factor in performance (as cited in Nicholas, 1997).
However, if the player's glycogen stores are low or depleted before the game and they do not adequately replenish them, then the muscle glycogen stores could become so depleted that it causes fatigue and impairs performance, especially in the second half of the game.4
The Central Governor Theory ///
There has been suggestion of a 'central governor' in the brain, that subconsciously paces the working muscles so they do not reach complete exhaustion, and that the brain creates sensations interpreted as fatigue to limit exhaustive exercise and prevent maximum lactate accumulation.13
Current Recommendations ///
As carbohydrate is the primary fuel utilized during both training and games, the rugby union player should follow a relatively high carbohydrate diet, with carbohydrates providing 55-65% of their total daily energy intake. This is approximately 7-8 grams per kg of body weight (g/kg/bw). Carbohydrate should form the basis of every meal, and sources should be nutrient dense.4
Protein should contribute 12-15% of the player's total daily energy, coming from high quality sources. This amounts to around 1.4-2.0 g/kg/bw, with those performing three or more resistance sessions consuming the higher amount of protein.4
The rugby union player should try and keep their fat intake down; and as carbohydrate should provide the bulk of their daily energy intake, their fat intake should be around 20-25% of their total daily energy intake.4
Alcohol should provide the minimal amount of energy intake, as it a) dehydrates the body, and b) induces the intake of low-nutrient and high-fat foods. If any alcohol is to be consumed, ensure that it is done at least two hours post exercise, and that 600 grams of carbohydrates are also consumed in the 24 hours after the exercise/game.4
Recommendations for fluids are that the player consumes 1.5-2 liters over and above their training fluid requirements.4
Pre, During, And Post-Game Nutritional Recommendations ///
200-300 grams of carbohydrate 3-4 hours or 50-100 grams of carbohydrate in the two hours before a game ought to be consumed. Meals 3-4 hours before a game should be low in fat, protein and fiber.4
10-15 minutes before the game ~500 ml of fluid of 5-8% glucose concentrate should be consumed. During the game the player should stay well hydrated, drinking 150-200 milliliters (ml) every 10-15 minutes, with at least 300-400 ml at half-time.4
Carbohydrate consumption during the game is important to keep glycogen stores full, and 30-60 grams of glucose per hour of exercise needs to be consumed. The easiest way to do this is via a sports drink that is of a high glucose concentration; this equates to ~500-1000 ml of sports drink per hour of exercise.4
Intake of high glycemic index foods and/or fluids should follow the game. It is important to consume at least 50 grams (this can be as high as 1g/kg/bw) of carbohydrate straight after the game, and a further 50 grams of carbohydrate every two hours after. It is also important for the player to have at least 10-20 grams of protein with their recovery carbohydrates.
In the 24 hours following a game the player needs to consume at least 600 grams of carbohydrates (or ~8 g/kg/bw), while keeping protein and fat intake to a minimum.4
In the first and second hour following the game, the player should drink 500-1000 ml of fluid, ideally of 5-25% carbohydrate concentrate, to aid in glycogen replenishment and recovery.4
Alcohol, if it is to be consumed should only be done at least two hours after the game, when the player is well hydrated and has had their first two hours of carbohydrate intake for recovery.4
- Allen, D. G., Balnave, C. d., Chin, E. R. & Westerblad, H. (1999). Failure of calcium release in muscle fatigue. In M. Hargreaves, & M. Thompson (Eds), Biochemistry of exercise (p. 135-146). United States of America: Human Kinetics.
- Babault, N., Cometti, G., Bernardin, M., Pousson, M. & Chatard, J-C. (2007). Effects of electromyostimulation training on muscle strength and power of elite rugby players. Journal of Strength and Conditioning Research, 21(2). (p. 431-437).
- Brooks, D. (1999). Your personal trainer: The expert training companion for total fitness. United States of America: Human Kinetics.
- Darry, K. (2000). Eating smart (p. 156-194). In A. McKenzie, K. Hodge & G. Sleivert (Eds.). Smart training for rugby: A complete training guide for rugby players and coaches. Auckland, New Zealand: Reed Books.
- Deutuch, M. & Sleivert, G. (2000). Fitness profiling (p. 37-65). In A. McKenzie, K. Hodge & G. Sleivert (Eds.). Smart training for rugby: A complete training guide for rugby players and coaches. Auckland, New Zealand: Reed Books.
- Fogelholm, M. (2006). Vitamin, mineral and anti-oxidant needs of athletes. (p. 313-342). In L. Burke & V. Deakin (Eds.). Clinical sports nutrition (3rd ed.). NSW, Australia: McGraw-Hill.
- Greenhaff, P. L., Casey, A., Constantin-Teodosiu, D. & Tzintzas, K. (1999). Energy metabolism of skeletal muscle fiber types and the metabolic basis for fatigue in humans. In M. Hargreaves, & M. Thompson (Eds), Biochemistry of exercise (p. 275-287). United States of America: Human Kinetics.
- Jenkins, D. & Reaburn, P. (2000). Protocols for the physiological assessment of rugby union players. In Gore, C. J. (Ed.). Physiological tests for elite athletes (p. 327-333). United States of America: Human Kinetics.
- Juel, C. & Pilegaard, H. (1999). Lactate exchange and pH regulation in skeletal muscle. In M. Hargreaves, & M. Thompson (Eds), Biochemistry of exercise (p. 185-200). United States of America: Human Kinetics.
- Maughan, R., Gleeson, M. & Greenhaff, P. L. (1997). Biochemistry of exercise and training. New York, USA: Oxford University Press.
- McArdle, W. D., Katch, F. I. & Katch, V. L. (2007). Exercise physiology: Energy, nutrition, and human performance (6th ed.). United States of America: Lippincott Williams & Wilkins.
- McLean, D. A. (1992). Analysis of the physical demands of international rugby union. Journal of Sports Science, 10. (p. 285-296).
- Noakes, T. D., Peltonen, J. E. & Rusko, H. K. (2001). Evidence that a central governor theory regulates exercise performance during acute hypoxia and hyperoxia. The Journal of Experimental Biology, 204, 3225-3234.
- Nicholas, C. W. (1997). Anthropometric and physiological characteristics of rugby union football players. Journal of Sports Medicine, 23(6). (p. 375-396).
- Ross, A. & Leveritt, M. (2001). Long-term metabolic and skeletal muscle adaptations to short-term sprinting: Implications for sprint training and tapering. Sports Medicine, 31(15), 1063-1082.