The Body’s Main Energy Systems

Energy systems refer to the specific mechanics in which energy is produced and used by your body. Humans generate energy via 3 systems;

  • Phosphogen (APT-PC)
  • Glycolytic
  • Oxidative

The contribution of each energy system is dependent on the duration and intensity of the sport.

The Anaerobic Alactic (ATP-CP) System

This system functions without requiring oxygen, through short duration, bursts of activity to supply the individual with 10-30s of energy for high intensity activity. The ATP-CP system is fuelled by stored ATP and creatine phosphate (CP) which is another high energy substance. This system works without the presence of lactic acid, meaning the intensity of the activity can be repeated after a 20s recovery period.

An example of this system used in a sports setting is any immediate energy source for high-intensity activity, for example: a jump shot in basketball.

The Anaerobic Lactic Glycolytic System

This system again functions without requiring oxygen and uses glucose (carbohydrates) as the energy, through high to medium intensity activity, of which is supplied for 2-3 minutes. During the high-medium intensity activity, pyruvate and H+ (hydrogen ions) accumulate rapidly, lactate (lactic acid) is then formed as a by-product of this system and when this occurs, we are unable to sustain the intensity of the activity and have to reduce or stop the activity due to the cause of muscular cramps, fatigue or performance impairments.

Examples of this system used in sports settings includes any short exertion, high-medium intensity activity, for example: heavy weight training, sprinting over a longer duration (2-3 minutes) and this system is also used in events like the 400m hurdles.

The Aerobic Oxidative System

This system also known as the krebs cycle or the citric acid cycle, requires oxygen during low intensity, long endurance activity, with the primary energy sources being carbohydrates and fats, which are converted into ATP in the mitochondria of they cell. This system begins after 90 seconds to 2 minutes into an activity. This system requires the cardiovascular system to be well trained in order to supply the required amount of oxygen during the activity/sporting event.

A sporting example of when this system is required is: to provide a steady supply of energy throughout a football game.

Fuelling demands for team sports

Nutritional intervention must be sports specific, in order to match the following factors:

The different physiological demands

  • Sport duration
  • Sport intensity
  • Frequency of training
  • Number of players
  • Requirements of team sport

Carbohydrate and fat are the main energy sources for the aerobic and anaerobic energy systems, highlighting the importance of these macronutrients and the inclusion of them within your dietary intake. Additionally, the volume and timing for ingestion of macronutrients is as equally as important to consider pre, post and during team sports.

Maintaining glucose levels throughout team sports and during periods of anaerobic glycolytic work is essential to fuel the brain for optimal attention span and decision making during the activity. During longer duration endurance events there may be an increased risk of glycogen stores depleting and if this occurs the individuals performance is likely to become impaired, fatigue and perhaps ‘hit the wall’. Similarly, hydration status is also important to monitor throughout a sporting event/training, if an individual becomes dehydrated similar side effects can occur.

Research Into Team Sports Nutritional recommendations

  • 5-7 g/kg/day carbohydrate for team sport athletes during competition
  • Research on male team sport athletes demonstrated an average protein intake of 1.2-2.3 g/kg/day
  • Co-ingestion of protein with 1.2 g/kg/day carbohydrate immediately post-football/soccer match for accelerated muscle protein synthesis
  • Some sports teams consume a half time half a litre of sports drinks with sugar in to replenish lost electrolytes through sweat to maintain hydration levels and prevent dehydration

Team sport events…

FOOTBALL

Football is a high intensity, intermittent team sport which requires high aerobic endurance fitness for short bouts of activity (30%) for sprints over 12-30 seconds. Anaerobic episodes only contribute to a small part of a football match, during long duration, low intensity runs.

Muscular glycogen is the most important substrate used as the main energy source during short bursts of activity during a football match.

Typically, players exercise at approximately 80-90% of max HR and 70-80% max oxygen uptake.

RUGBY UNION

Rugby union is a high intensity, intermittent team sport which requires maximal strength and power, interspersed with low intensity aerobic activity. ‘Backs’ position partake in more anaerobic high intensity activity, interspersed with longer recovery periods in the lowest speed zones.

Typically, players exercise at approximately 80-85% VO2max during the course of the game, with the contribution for the anaerobic energy system (phosphocreatine) being larger during periods of high intensity activity.

NETBALL

Netball is a game of intervals of which has more aerobic activity involvement, such as short sprints than it does anaerobic activity. The ATP-CP system is mainly required during short bursts of maximal effort, lasting between 8-10 seconds. The anaerobic glycolysis system would be predominantly used in netball when a centre position works at high intensity for a duration of up to 40 seconds, for example if the team has failed to score (prolonged period of play).

BASKETBALL

Basketball is a game which comprises of explosive speed and power activities, with the ATP-CP system being the immediate source of energy for high intensity activity, such as a jump shot, fast breaks, rebounding and short sprints. During periods of lower intensity and longer duration movements, the aerobic energy system uses oxygen to convert glucose and fat to be used as the main energy source during activity, approximately 65% of the active game time.

Injury mechanisms and prevention

High injury incidence amongst youth athletes has been associated with maturation changes in stature, disproportionate to their strength development and suggested to contribute to greater injury risks. Research has previously shown that female hormonal fluctuations during stages of their menstrual cycle may reduce females neuromuscular control at the knee joint and has caused deficits in thigh musculature, therefore increasing the risk of lower extremity injuries. Supporting research has shown that ACL injuries are greater in females during their mid-cycle ovulatory phase and are reduced during the follicular and luteal phases. Previous research has demonstrated that oestrogen levels have a significant effect on musculotendinous stiffness (MTS) and that MTS decreased significantly during the ovulatory phase of a females menstrual cycle. Therefore, assessment of youth athletes anterior knee laxity (using a knee arthrometer) during their ovulatory phase can help coaches to adapt training loads and interventions during these phases.

Ultimately, coaches should always perform screening with their athletes prior to training/matches/competition to evaluate individual differences between players and to consider any training drills or intensity which may need to be adapted for an individual during the session to prevent injury.

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