CHAPTER 7 Energy systems and physical activity

CHAPTER 7

Energy systems and physical activity

CHAPTER 7

The energy for muscular contractions comes from adenosine triphosphate, which is found in several sources including our food and drink. It may be released from carbohydrate, fat or protein, depending on the body's state of activity or health.

The body produces adenosine triphosphate via three energy pathways. Each is the main provider under specific exercise conditions, but all contribute to energy across all degrees of activity. Each energy

system has strengths and weaknesses when compared with the others, and specific sporting performances exemplify each system's majority contribution to the production of adenosine triphosphate. This chapter explores the three basic chemical pathways towards the production of adenosine triphosphate, along with their relative characteristics. The lactate threshold is a major concept in energy system theory.

Assessment tasks Assessment tasks Written report Oral presentation Laboratory reports

Data analysis Case study analysis

Topics

Diet assessment (activity 2)

Multi-stage fitness test (activity 4)

Phosphate recovery times (activity 3) Multi-stage fitness test (activity 4) Step test (activity 5)

Phosphate recovery times (activity 3)

Aerobic power test (activity 7)

Multimedia presentation Activity analysis ? phosphate efforts (activity 6)

Report on participation in physical activity

Test

Basketball analysis (activity 1) Review questions

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CHAPTER 7

After completing this chapter, students should be able to:

? identify the three major energy systems that interplay during physical activity

? describe the various ways in which adenosine triphosphate (ATP) is created within the three energy systems

? explain the advantages and limitations of each of the three energy systems

? analyse how sports performance is controlled and predicted by their reliance on each of the three energy systems

? outline the causes of fatigue including the lactate threshold, energy substrate depletion and inefficient recovery.

Why energy?

Your body needs energy for basic body functions and activity during your whole life -- energy for breathing, sleeping, digesting, sitting in a chair, sprinting for a bus, and everything else you do day and night.

The interaction between muscles and bones keeps the body upright and under control. To allow this teamwork between the muscular and skeletal systems (see chapter 5), the body needs energy sources that will permit muscles to work, for example, the effort needed by the abdominal and back muscles to enable good sitting posture, or by the muscles of the abdominals, back, legs, torso and arms during a softball game.

Adenosine triphosphate

The chemical compound adenosine triphosphate (ATP) provides the energy that allows muscular effort. ATP is the energy source for all muscular effort, whether for a small subconscious movement such as the blinking of an eye or a planned repetitious effort in weight training (see chapter 9, Live It Up 2, second edition).

Sources of ATP

ATP is an end product of your diet. All the food, processed drinks and water that you consume contain nutrients that your body requires for: ? healthy growth ? repair of body `wear and tear' from everyday activities ? energy for all bodily functions.

The components of a healthy diet are carbohydrate, fat, protein, vitamins, minerals and water. ATP can be created from carbohydrate, fat and protein. Chapter 11, Live It Up 2, second edition more fully explores the processes by which the body produces energy from food.

Carbohydrate

When carbohydrate is digested, it is broken down to glucose for blood transportation and then stored as glycogen in the muscles and liver. Glycogen can provide the energy for ATP production under both anaerobic (no oxygen required) and aerobic (oxygen required) conditions.

Fat

Fat provides the major source of energy for long-term physical activity. During a long team game or a marathon, fat (as either triglycerides or free fatty acids) usually contributes to ATP production to meet sub-maximal energy demands. Under special conditions, the athlete may be able to use fat earlier in the activity to `spare' the carbohydrate stores and therefore enable longer high-level effort. During rest conditions, fat produces the majority of the required ATP.

Protein

Protein only minimally contributes to ATP production. In extreme circumstances (such as starvation or ultra triathlon/marathon events) when the body has severely depleted its supplies of carbohydrate and fat, protein can become a viable source of ATP.

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Table 7.1

The body's storage of food fuel

Food fuel Carbohydrate

Fat Protein

Stored as

Glucose Glycogen Adipose tissue (storage of excess carbohydrates) Free fatty acids Triglycerides Adipose tissue

Muscle Amino acids

Site

Blood Muscle and liver Around the body

Blood Muscle Around the body Skeletal muscle Body fluids

Key knowledge

? The cardiorespiratory system: structure of the heart and lungs, mechanics of breathing, gaseous exchange, blood vessels, blood flow around the body at rest and during exercise

? Introduction to aerobic and anaerobic energy systems, including aerobic and anaerobic glycolysis

Key skills

? Use correct terminology to describe the role of the body systems at rest and when undertaking physical activity.

? Observe and record how the body systems function during physical activity.

? Identify and discuss the range of acute effects that physical activity has on the body.

? Perform, observe, analyse, evaluate and report on laboratory exercises related to the body systems.

Activity 1

Report on participation in physical activity

Basketball analysis

As a class, after an appropriate warm-up, play a hard game of basketball or netball. Hand out to-scale court drawings on which player movements can be plotted. 1. Have the class organised into these work groups:

? players ? body parameter recorders; paired off one-on-one with the players ? games analysis recorders; paired off one-on-one with the players. 2. Play a number of 7?10 minute playing segments, each with an intervening 5 minute break. During the play, the games analysis recorders are to plot how far their partner has sprinted, jogged, walked and for how long they stood still in the playing segment. 3. During the breaks, the body parameter recorders are to talk with, assess and record their partners' physical responses, including: ? heart rates (polar heart rate monitors will be useful for this,

or do it manually with 10 second pulse counts) ? respiration rates ? observable perspiration amounts ? verbal reports of fatigue levels (easy, bit puffed, tiring,

struggling, had it . . .). 4. In your work groups, compile your results and address the following issues:

a Present your findings in hard copy tables and/or a multimedia presentation.

b How far did your player sprint, jog and walk? c What percentage of time did he or she spend in each

of sprint/jog/walk, and for how long were they stationary? d Plot their physical responses to the exercise segments

against the other players. e Establish a priority list of perceived fitness among the players. f List the bases for your decisions in question e. g List the information that the class has established from this exercise

that cover fitness, fatigue and energy.

Key knowledge

? Introduction to aerobic and anaerobic energy systems, including aerobic and anaerobic glycolysis

Activity 2

Written report

Diet assessment Record your total diet for three days. Estimate the percentages of carbohydrates, fats and protein by using packet labelling and nutrition guides supplied by your teacher. Have a class discussion to establish how you could improve your diet to meet your energy needs.

CHAPTER 7 ENERGY SYSTEMS AND PHYSICAL ACTIVITY 211

Energy from ATP

ATP is stored in limited quantities within muscle, so each muscle fibre must be able to create its own from the food fuels. Figure 7.1 illustrates how the metabolism of food creates ATP which then provides energy for muscular exertion.

Adenosine

P

P

P

ATP

Food

Energy

Energy

Muscle activity

ADP + P

Adenosine

Figure 7.1:

Energy for muscular activity

P

-- from food to ATP to muscles

P

P

ATP is an adenosine molecule with three phosphate molecules attached. When muscular activity is needed, one of the phosphate molecules breaks off, releasing energy and creating adenosine diphosphate (ADP) (see figure 7.1). This process is reversible: figure 7.2 shows how ADP can become ATP. This reversal can occur continually during the activity as long as sufficient energy substrates are available. Depending on the type of physical activity (see chapter 8), energy substrates include phosphocreatine, glucose, glycogen, lactic acid, fat, protein and oxygen. These are substances the body can use to create ATP.

A muscle fibre stores only a small amount of ATP, so the force and duration of a muscular effort is only as effective as the ATP replenishment process. During and after physical exertion, the body uses several methods of recovery to rebuild used supplies of ATP and food fuels.

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