BIOENERGETICS IN SPORTS AND PERFORMANCE

Dr.Punita Adajania

WHAT IS BIOENERGETICS?

Different sports require specific sources of energy.

The body stores energy in a variety of ways—in ATP, PCr, muscle glycogen,etc

In order for this energy to be used,it must undergo certain biochemical reactions in the muscle.

These biochemical reactions serve as a basis for classifying human energy expenditure by three energy systems:

the ATP-PCr system(phosphagen system)

the lactic acid system the oxygen system

ENERGY SYSTEMS

ATP-Pcr SYSTEM Also known as the phosphagen system.

ATP is the immediate source of energy for almost all body processes.

The ATP-PCr system is critical to energy production.

ATP-Pcr SYSTEM The value of the ATP-PCr system is its

ability to provide energy rapidly.

In sport events such as competitive weight lifting or sprinting 100 meters.

Anaerobic power is a term often associated with the ATP-PCr energy system.

LACTIC ACID SYSTEM Cannot be used directly as a source of

energy for muscular contraction.

but it can help replace ATP rapidly when necessary.

Muscle glycogen must be broken down to glucose, which undergoes a series of reactions to eventually form ATP, a process called glycolysis.

LACTIC ACID SYSTEM Aerobic glycolysis.

Anaerobic glycolysis.

Anaerobic glycolysis is the scientific term for the lactic acid energy system.

LACTIC ACID SYSTEM

LACTIC ACID SYSTEM It is used in sport events in which

energy production is near maximal for 30–120 seconds, such as a 200- or 800-meter run.

The lactic acid system has the advantage of producing ATP rapidly.

LACTIC ACID SYSTEM the lactic acid produced as a by- product

may be involved in the onset of fatigue.

OXYGEN SYSTEM Also known as the aerobic system.

Aerobic exercises are designed to stress the oxygen system and provide benefits for the heart and lungs.

The oxygen system cannot be used directly as a source of energy for muscle contraction, but it does produce ATP in large quantities from other energy sources in the body.

PHYSIOLOGICAL PROCESSES INVOLVED IN OXYGEN UPTAKE.

OXYGEN SYSTEM Muscle glycogen, liver glycogen, blood

glucose, muscle triglycerides, blood FFA and triglycerides, adipose cell triglycerides, and body protein all may be ultimate sources of energy for ATP production and subsequent muscle contraction.

Through a complex series of reactions metabolic by-products of carbohydrate, fat, or protein combine with oxygen to produce energy, carbon dioxide, and water.

OXYGEN SYSTEM The whole series of events of oxidative

energy production primarily involves aerobic processing of carbohydrates and fats through the Krebs cycle and the electron transfer system.

OXYGEN SYSTEM

The rate of ATP production is lower.

The major advantage of the oxygen system over the other two energy systems is the production of large amounts of energy in the form of ATP.

This process may be adequate to handle mild and moderate levels of exercise but may not be able to meet the demand of very strenuous exercise.

The oxygen system is used primarily in sports emphasizing endurance, such as distance runs ranging from 5 kilometers (3.1 miles) to the 26.2-mile marathon and beyond.

AEROBIC ENERGY SYSTEMS

Aerobic energy processes take place in the mitochondria of cells.

During steady-state exercise, the pyruvic acid produced is converted to acetyl-CoA in the mitochondria and then undergoes aerobic oxidation.

Fats are another major source of energy during prolonged exercise and can only be used to produce energy using aerobic processes.

ENERGY SYSTEMS & TRAINING

Each of the three energy systems can generate power to different capacities and varies within individuals.

Best estimates suggest that the ATP-PCR system can generate energy at a rate of roughly 36 kcal per minute. Glycolysis can generate energy only half as quickly at about 16 kcal per minute. The oxidative system has the lowest rate of power output at about 10 kcal per minute.

ENERGY SYSTEMS USED IN SPORTS The three energy systems do not work

independently of one another.

From very short, very intense exercise, to very light, prolonged activity, all three energy systems make a contribution however, one or two will usually predominate.

Two factors of any activity carried out affect energy systems more than any other variable they are the intensity and duration of exercise.

CONTRIBUTION OF ENERGY SYSTEMS TO MEET PHYSICAL DEMANDS

A NEW MODEL FOR ENERGY SYSTEMS?

In the year 2000, Noakes and colleagues questioned the classical model of energy systems.

Their argument centered around these key issues: The heart and not skeletal muscle would be affected

first by anaerobic metabolism. No study has definitively found a presence of

anaerobic metabolism and hypoxia (lack of oxygen) in skeletal muscle during maximal exercise.

The traditional model is unable to explain why fatigue ensues during prolonged exercise, at altitude and in hot conditions.

Cardiorespiratory and metabolic measures such as VO2max and lactate threshold are only modest predictors of performance.

In an attempt to produce a more holistic explanation, Noakes developed a model that consisted of five sub-models:

The classical 'cardiovascular / anaerobic' model as it stands now.

The energy supply / energy depletion model.

The muscle recruitment (central fatigue) / muscle power model.

The biomechanical model. The psychological / motivational model.

SOURCES OF ENERGY IN DIFFERENT ACTIVITIES

ATP Any energy requiring processes invariably uses

ATP as the prime source of energy.

At the start of an activity the initial source of energy is from ATP stores at the muscle crossbridges.

The amount of ATP in muscle is rather small.

This amount of ATP in muscle has been estimated to be sufficient to fuel around 3–5 seconds of maximal effort if ATP was the sole energy source.

CREATINE PHOSPHATE The other immediate source of energy for

high intensity exercise is that of creatine phosphate or phosphocreatine (PCr).

Creatine phosphate (PCr) rapidly replaces the ATP and becomes the next major source of energy.

This amount of PCr is sufficient to fuel maximal exercise solely for approximately 6–8 s.

MUSCLE GLYCOGEN An essential store of carbohydrate fuel for

both high- intensity exercise and prolonged activity.

Normal muscle glycogen stores have a concentration of 350 mM kg–1 dry muscle.

Can be increased significantly by a high carbohydrate diet and reduced significantly by repeated bouts of sprinting or a single prolonged bout of exercise or when on a low carbohydrate diet for around 2–4 days.

GLYCOGENOLYSIS AND GLYCOLYSIS

When muscle glycogen breaks down to produce energy, under the influence of the enzyme glycogen phosphorylase.

The process of breaking off glucose molecules from glycogen is known as glycogenolysis.

Glycolysis is a series of processes which takes place in the cytoplasm of cells resulting in the formation of two pyruvic acid molecules and ATP.

If the activity is intense, the pyruvic acid leads to the formation of lactic acid, although during steady-state exercise the majority of the pyruvic acid formed is broken down to produce carbon dioxide and water.

BLOOD GLUCOSE Glucose delivered to the muscle by

blood may also act as a useful energy source during exercise.

ROLE OF NUTRIENTS IN BIOENERGETICS

Proper nutrition forms the foundation for physical performance.

NUTRITION:- MACRONUTRIENTS & MICRONUTREINTS.

MACRONUTRIENTS Six broad categories of nutrients: carbohydrates fats proteins vitamins minerals water

CARBOHYDRATES

Provide a rapid and readily available source of energy.

Found in three forms: monosaccharides, disaccharides, and polysaccharides.

Glucose is the most important simple sugar and is the only form of carbohydrate that can be directly metabolized to obtain energy.

Glycogen is not found in plants and is the polysaccharide form in which animals store carbohydrate.

During exercise, glucose molecules can be removed from glycogen in the liver by glycogenolysis, and released into the bloodstream to provide glucose as a metabolic substrate to other cells of the body.

Glucose and glycogen are the carbohydrates important for metabolism at rest and during exercise.

During exercise, muscle cells can obtain glucose by absorbing it from the bloodstream or by glycogenolysis from intramuscular glycogen stores.

glycogenolysis in the liver can maintain blood glucose levels during exercise and at times of rest between meals.

At rest, carbohydrate is taken up by the muscles and liver and converted into glycogen.

Glycogen can be used to form ATP and in the liver it can be converted into glucose and transported to the muscles via the blood. A heavy training session can deplete carbohydrate stores in the muscles and liver.

Carbohydrate can release energy much more quickly than fat.

FATS Fat is stored predominantly as adipose

tissue throughout the body and is a substantial energy reservoir.

It is less accessible for cellular metabolism as it must first be reduced from its complex form, triglyceride, to the simpler components of glycerol and free fatty acids.

So although fat acts as a vast stockpile of fuel, energy release is too slow for very intense activity.

PROTEIN Protein is used as a source of energy,

particularly during prolonged activity.

however it must first be broken down into amino acids before then being converted into glucose. As with, fat, protein cannot supply energy at the same rate as carbohydrate.

VITAMINS

BIOLOGIC FUNCTIONS OF VITAMINS

MINERALS

MINERALS AND EXERCISE PERFORMANCE Consuming mineral supplements above

recommended levels on an acute or chronic basis does not benefit exercise performance or enhance trainin responsiveness.

Excessive water and electrolyte loss impairs heat tolerance and exercise performance and can trigger heat cramps, heat exhaus- tion, or heat stroke.

During practice or competition, an athlete sweats up to 5 kg of water.

This corresponds to about 8.0 g of salt depletion because each kilogram of sweat contains about 1.5 g of salt (of which 40% represents sodium).

Immediate replacement of water lost through sweating should become the overriding consideration.

ENERGY EXPENDITURE AT REST AND ACTIVITY

Three factors determine the total daily energy expenditure (TDEE):

1. Resting metabolic rate

2. Thermogenic influence of consumed food

3. Energy expended during physical activity and recovery.

BASAL METABOLIC RATE A minimum energy requirement that

sustains the body’s functions in the waking state.

Measuring oxygen uptake under the following three standardized conditions quantifies this requirement called the basal metabolic rate(BMR):

1. No food consumed for a minimum of 12 hours before measurement

2. No undue muscular exertion for at least 12 hours before measurement

3. Measured after the person has been lying quietly for 30 to 60 minutes in a dimly lit, temperature- controlled room.

RESTING METABOLIC RATE It is measured under less strict

conditions (e.g., 3 to 4 hours after a light meal without physical activity.)

Estimates of energy expenditure during rest and during exercise are often based on measurement of whole body oxygen consumption (VO2) and its caloric equivalent.

Under resting conditions, an average person consumes about 0.3 L of O2/min. or 18L of O2/hr. or 432L of O2/day.

One standardized measure of energy expenditure at rest is BMR.

Factors affecting BMR are: Gender Body surface area Age Body temperature Psychological stress Hormones-thyroxine, epinephrine

BMR of a normal individual varies from 1200 to 2400 Kcal/day.

Energy expenditure for athletes engaged in intense training can exceed 10000Kcal/day.

MEASUREMENT OF ENERGY EXPENDITURE

Energy expenditure can be measured using one of the three approaches:

indirect calorimetry direct calorimetry non-calorimetric techniques: Isotope dilution, doubly labelled

water

REFERENCES Essentials of Exercise Physiology, fourth

edition, Victor L. Katch,William D. McArdle, Frank I. Katch.

Exercise Physiology Integrating Theory and Application, William J. Kraemer, Steven J. Fleck, Michael R. Deschenes.