Exercise Physiology U6

What does ATP stand for?

Adenosine Triphosphate

ATP

ATP contains a high energy bond that is used to provide energy for muscular contraction

Total quantity of ATP in the human body is about 0.1mol/L

Phosphorylation

ATP is converted to ADP and Pi via the enzyme ATPase

Energy produced from this bond breaking is used for muscular contraction

ATPase

Enzyme that speeds up the breakdown of ATP

Resynthesis of ATP

Once the energy has been used for muscular contraction, we are left with ADP. By using energy from our diet, we can join a free phosphate molecule to the ADP to resynthesise ATP.

The daily energy used by the human adult requires the equivalent of each ATP molecule being resynthesised 1000-1500 times.

Macronutrients

The macronutrients in food are broken down in our cells to be used immediately from our bloodstream to resynthesise ATP.

Stored in our muscles, liver and other tissues, ready for when we need additional energy.

Carbohydrates

Blood glucose

Glycogen stored in muscles and liver

Fat

Triglycerides stores in muscles

Adipose tissue fat cells

Protein

Amino acids used for tissue repair and growth

Emergency fuel only

Phosphocreatine PCr

Derived from protein rich foods such as red meat and fish

We synthesise PCr from amino acids in our liver - it’s not something we can directly get from our diet.

Stored in the muscle sarcoplasm

Also known as Creatine Phosphate

3 energy systems

The ATP-PC system

The Lactic Acid system

The Aerobic system

3 energy systems during exercise

During exercise, all the energy systems work concurrently. However, depending on the intensity and duration of the activity, a different system will be predominant.

The ATP-PC system

Fuel source is Phosphocreatine

High intensity, short duration activities

No by-products

Threshold is 10-12 seconds

Time to replenish is 30 secs for 50% and 3 minutes for 100% - O2 is required to replenish PCr stores

ATP-PC system chemical process

PCr → Pi + Cr + energy

ATP-PC system ATP yield

1PCr : 1ATP

ATP-PC system example of predominance

100m sprint

Javelin

85-95%HR max

Type IIb fibres, fast twitch

Lactic acid system

Fuel source is blood glucose and stored glycogen

High intensity, extended short duration activities

Lactate and hydrogen ions are by-products

Threshold is 3 minutes - peak energy output at 1 minute

Time to replenish is 20 mins - 2hours. O2 required for buffering of hydrogen ions and oxidation of lactate

Lactic acid system chemical process

Anaerobic Glycolysis

Glucose → Pyruvic acid + energy → Lactic acid → Lactic acid + H+ ions

Lactic acid system ATP yield

1 glucose : 2ATP

Lactic acid system example of predominance

400m sprint

100m swim

75-85%HR max

Type IIa fibres

Fast Oxidative Glycolytic

Aerobic system

Fuel source is carbs - glucose and glycogen, fats - triglycerides, protein - emergency fuel only

Low intensity, low duration activity

By products are CO2 and H2O

Threshold is infinite

Time to replenish is continual - CO2 exhaled, H2O excreted through sweat, urine or exhaled, food and water required for recovery, mixed GI foods within 30 mins, protein for repair

Aerobic system chemical process

Stage 1 - Aerobic Glycolysis - Glycogen/Glucose → Pyruvic acid + energy → Acetyl Co-A

Beta Oxidation - Fatty acids → Acetyl Co-A

Stage 2 - Krebs cycle - Acetyl Co-A → CO2 + H+ ions + energy

Stage 3 - Electron Transport Chain - H+ ions + e- → H2O + energy

Aerobic system ATP yield

Stage 1 = 1 glucose : 2ATP

Stage 2 = 1 glucose : 2ATP

Stage 3 = 1 glucose : 34ATP, 1 fat : 128 ATP

Aerobic system example of predominance

Marathon steady pace sections

Olympic 2km row mid section

10km swim

60-70HR max

Type I fibres - slow twitch

Muscles fibre types

Type I - slow oxidative

Type IIa - fast oxidative glycolytic

Type IIb - fast twitch glycolytic

Proportion of fibre types

Genetically determined

Athletic differences of fibre types

Successful endurance athletes such as marathon runners and triathletes tend to have predominantly Type I fibres.

Middle distance athletes, such as 800m runners or 400m swimmers tend to have predominantly Type IIa fibres.

Elite power athletes such as 100m sprinters and weightlifters tend to have predominantly Type IIb fibres.

Games players often have an even mixture of fibre types

Characteristics of muscle fibres

Contraction speed

Fatigue resistance

Mitochondrial density

Myoglobin content

Capillary density

Aerobic capacity

Anaerobic capacity

Contraction speed

How quickly the fibres can produce force

Fatigue resistance

How long the fibre can keep contracting without tiring

Mitochondrial density

How many mitochondria the fibre has

Myoglobin content

How much myoglobin the fibre contains

Myoglobin

Stores oxygen ready for aerobic energy production

Capillary density

How many capillaries surround the fibre

Aerobic capacity

How good the fibre is at producing energy using O2

Anaerobic capacity

How good the fibre is at producing energy without O2

Type I muscle fibre characteristics

Slow contraction speed

Very high fatigue resistance

High mitochondrial density

High myoglobin content - red in colour

High capillary density

High aerobic capacity

Low anaerobic capacity

Low force produced

Low PC content

Type IIa muscle fibre characteristics

Fast contraction speed

Medium fatigue resistance

Medium mitochondrial density

Medium myoglobin content - red in colour

Medium capillary density

Medium aerobic capacity

Medium anaerobic capacity

High force produced

High PC content

Type IIb muscle fibre characteristics

Very fast contraction speed

Low fatigue resistance

Low mitochondrial density

Low myoglobin content - white in colour

Low capillary density

Low aerobic capacity

High anaerobic capacity

Very high force produced

Very high PC content

Effects of training on muscle fibres

Research has shown that training can cause physiological adaptations of around 10-20% in muscle fibres.

Regular exercise increases the size and strength of all fibre types - hypertrophy

Fatigue

Limits performance and is dependent on the intensity and duration of exercise

What factors is performance limited by?

Reduced rate of ATP resynthesis

PCr depletion

H+ ion accumulation - lactic acid build up

Glycogen depletion - ‘hitting the wall’

Dehydration

Thermoregulation

Calcium ion shortage - limits muscle contraction

Acetylcholine shortage - limits muscle neurotransmission

Reduced rate of ATP resynthesis

ATP must be continually resynthesised in order to provide energy for body processes, including muscle contraction

If there is insufficient ATP available to sustain muscle contraction then the athlete will start to fatigue

Depletion of Phosphocreatine

Causes fatigue during maximal intensity exercise of about 10-12 seconds

When PCr stores run out, the muscles are no longer able to contract with the same degree of speed and force

PCr stores will begin to replenish if the intensity of activity drops

Hydrogen ion accumulation

During intense exercise lactic acid starts to accumulate in the muscles

Hydrogen ions dissociate from the lactic acid and decrease the pH of the muscle and the blood leading to acidosis.

This interferes with muscle contraction and causes pain

The decreased pH also inhibits the action of phosphofructokinase and therefore energy can no longer be released from carbohydrates. 

Phosphofructokinase

An enzyme used in the breakdown of glycogen

Glycogen depletion

Glycogen is the main fuel source for the lactic acid and aerobic energy systems

The rate at which glycogen is depleted is dependent on the intensity of the exercise undertaken - the high the intensity, the faster glycogen is used and therefore depleted.

When glycogen stores are depleted, athletes are said to ‘hit the wall’ as the body tries to metabolise fat but is unable to use fat as a duel on its own.

Why do some athletes reach fatigue sooner?

Depends on:

VO2 max and lactate threshold

VO2 max

The maximum amount of oxygen you can uptake and utilise in one minute per kg of body weight

Factors that can limit VO2 max

Genetics

Lifestyle choices e.g. smoking

Age

Gender

Volume of training

Lactate threshold

The exercise intensity at which lactate starts to accumulate in the blood to a critical level

This happens when lactic acid is produced faster than it can be removed

This point is referred to as OBLA

OBLA

Onset of blood lactate accumulation

The point at which blood lactate reaches a concentration of 4 mmol per litre of blood

Relationship between lactate threshold and VO2 max

The more oxygen that can be brought in and utilised (good VO2 max), the longer a performer can work without reaching the lactate threshold (OBLA).

OBLA occurs at a percentage of VO2 max

An untrained person can work at about 55-60% of their VO2 max without reaching OBLA

Endurance training can increase this to 70-80% VO2 max

Recovery

Recovery takes place when physical activity stops or lowers in intensity

The main aim of the recovery process is to restore the body to its pre-exercise state

Recovery involves the removal of waste products produced during exercise and replenishment of fuels used up during exercise

EPOC

The recovery process requires additional oxygen to make up for the deficit generated during exercise

Minute ventilation and heart rate remain above resting levels post-exercise to deal with the effects of fatigue - a cool-down helps this process

Intake of additional oxygen is known as Excess Post-exercise Oxygen Consumption

EPOC depends on the duration and intensity of exercise undertaken and has 2 components:

Alactacid component - fast recovery - phosphocreatine

Lactacid component - slow recovery - lactic acid

The fast component requires 2-3L of O2 and takes about 3 mins to complete

The slow component requires 5-8L of O2 and takes about 20 mins to 2 hrs to complete, dependent on the fatigue level

Fate of lactate

Lactic acid is removed and resynthesised during the lactacid of EPOC

It is initially converted back into pyruvic acid

The majority (50%) is oxidised into CO2 and H2O via the Krebs cycle and Electron Transport Chain

20% is converted to blood glucose or protein in the liver via a series of chemical reactions called the Cori cycle

The remaining lactic acid (10%) is converted to urine and sweat

Methods to speed up the recovery process

Active cool down - to remove lactic acid and re-saturation of myoglobin and haemoglobin

Ice baths

Sports massage

Cryotherapy

Compression clothing

Nutrition and supplements - mixed GI meal immediately after exercise, protein supplements for growth and repair and fluid intake to prevent dehydration and aid recovery

Whole body cryotherapy

An extreme cold temperature treatment that can help to speed up recovery

Requires expensive, specialist equipment

Causes vasoconstriction of blood vessels which helps to reduce inflammation around muscle micro tears post exercise

Compression clothing

Can reduce the severity and duration of DOMS, increase venous return from the lower legs, and enhance lactate removal

The pressure exerted from compression clothing reduces tissue swelling and helps to increase venous return by squeezing the nearby blood vessels which enhances recovery.

Long term adaptations to the cardiovascular system from aerobic training

Bradycardia - resting heart rate lowers

Cardiac hypertrophy

Increased stroke volume

Increased cardiac output

Increased RBC Improved vasomotor control

Decreased risk of hypertension, CHD and atherosclerosis

Long term adaptations to the musculoskeletal system from aerobic training

Increased capillarisation

Increased oxygen diffusion rate

Increased myoglobin

Increased mitochondria

Hypertrophy of Type I and IIa fibres

Increased calcium deposits and bone strength

Increased synovial fluid

Long term adaptations to the respiratory system from aerobic training

Increase minute ventilation, tidal volume and vital capacity

Increased capillarisation

Increased Pulmonary diffusion

Increased strength of respiratory muscles

Performance gains from aerobic training

Increased anaerobic/lactate threshold, conservation of glycogen stores

Decreased recovery times

Faster replenishment of PC and glycogen stores

Increased VO2 max

Faster re-saturation of haemoglobin and myoglobin with O2

Exercise for longer at a higher intensity without fatigue

Long term adaptations to the cardiovascular system from anaerobic training

Cardiac hypertrophy

Thicker and more elastic myocardium

Increased ejection fraction

Long term adaptations to the musculoskeletal system from anaerobic training

Muscular hypertrophy

Increased phosphocreatine stores

Increased bone density and tendon strength

Development of Type IIb muscle fibres and utilisation of Type IIa

Increased motor neurones firing speed

Increased speed of contraction

Performance gains for anaerobic training

Increased lactate threshold

Increased force, power, speed, strength output

Decreased response time

Functions of the skeleton

Support

Protection

Movement

Blood production

Mineral storage

Axial skeleton

Made up of the vertebral column, rib cage and cranium

Appendicular skeleton

Made up of the shoulder girdle, hip girdle, arms and legs

Types of bones

Long bones

Short bones

Irregular bones

Flat bones

Sesamoid bones

Long bones

Cylindrical shape, found in limbs

Acts as levels for movement

E.g. femur, humerus, phalanges

Short bones

Compact shape, designed for weight bearing

E.g. carpals, tarsals

Irregular bones

Complex shape, designed for protection and multiple muscle attachments

E.g. vertebrae

Flat bones

Smooth, even surface designed for muscle attachment and protection of organs

E.g cranium, ileum (part of pelvis)

Sesamoid bones

Small, oval bones situated with tendons

Designed for injury prevention

E.g. patella

Soft tissue

Ligaments

Tendons

Cartilage

Ligaments

Strong, fibrous tissue that connects bone to bone

Stabilises joints to allow specific movements

Tendons

Strong, elastic tissue made of collagen that connects muscle to bone

Transmits force to cause movement

Cartilage

Firm, resilient matrix of connective tissue with no blood supply

Cartilage types

Yellow elastic cartilage

White fibrous cartilage

Articular (hyaline) cartilage

Yellow elastic cartilage

Pliable, flexible tissue that forms structures such as the nose and ears

White fibrous cartilage

Tough, thick tissue that acts as a shock absorber e.g. knee meniscus/vertebral discs

Articular cartilage

Surround surface of articulating bones, reducing friction at the joint. Exercise thickens articular cartilage