Aerobic Capacity

A2

AEROBIC CAPACITY

AEROBIC CAPACITY• the ability to take in, transport and use oxygen to sustain

prolonged periods of aerobic/sub-maximal work.

• Aerobic capacity is dependent upon the efficiency of the following systems:

• Pulmonary ventilation and external respiration• Internal transport via the heart, blood and blood vessels• Muscle cells to use oxygen for energy production

VO2 Max• This is closely linked to aerobic capacity but there is a difference:• VO2 max is defined as the highest rate of oxygen consumption

attainable during maximal/exhaustive work.• VO2 is thought to be the best indicator of aerobic endurance.

VO2max• mean values are :• males (20 yo) = 40 ml kg-1 min-1

• (for average male body mass 87.5 kg)• females (20 yo) = 35 ml kg-1 min-1

• (for mean female body mass 66 kg)• endurance athletes = 75 ml kg-1 min-1

• (for mean body mass 66 kg)

VO2 example

Factors affecting VO2 Max

• Individual Physiological Make-up• Efficiency of:• Respiratory system to consume O2• Heart to transport O2• Vascular system to transport O2• Muscle cells to use O2• An increase in VO2 max would be linked to all of these

systems. The higher VO2 max the greater potential to work at that level, just below the anaerobic threshold, increasing work intensity and delaying fatigue.

Factors affecting VO2 Max

• Heredity/Genetics• This can account for variation in VO2 max:• If an athlete has a greater percentage of type I

or type IIa fibres. This may affect how much they can improve by.

• However, heredity only indicates an individuals potential to have a high VO2 max. It is ultimately the aerobic training they undertake that helps them achieve their potential.

Factors affecting VO2 Max

• Training• A programme of aerobic training will increase

VO2 max. A maximum level of aerobic conditioning can be reached within approximately 8-19 months of heavy endurance-based training.

• Aerobic training can cause VO2max to be improved by 10 - 20%

Factors affecting VO2 Max

• Age• The limitation in oxygen transport to the

muscles and a decreased a-VO diff are the main causes of a reduced VO2 max. It is thought that VO2max reduces at about 10% per decade (1 per cent per year) during ageing - for sedentary people.

• VO2max reduces less for active sportspeople as they age

Age and VO2 max

• The decrease is thought to have 2 main causes:• Cardiovacular – maximum HR, cardiac output

(Q), stroke volume (SV) and blood circulation to muscle tissues decrease due to a decreased left ventricular contractility/elasticity.

• Respiration – lung volumes, for example max VE (minute ventilation), decrease linearly after maturation due to a decrease in elasticity of lung tissues and thoracic cavity walls.

Factors affecting VO2 Max• Gender• VO2 max values for woman are generally 20-25% lower than males.

Woman are disadvantaged by having a greater body fat percentage, since this decreasesVO2 max when measured per kilogram of body weight.

• Women’s smaller body size also means:• A smaller lung volume – decreases external respiration and oxygen intake• A smaller heart – increases resting HR, lowering SV and Q at maximal

rates of work• Lower blood/haemoglobin levels decrease oxygen transport and blood

volume.

• women have greater reductions in VO2max from late teens onwards probably because of the tradition of less physical activity for women

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AEROBIC CAPACITY

IMPORTANCE OF AEROBIC CAPACITY TO ENDURANCE PERFORMERS

• useful as an indicator showing athletes’ maximal physiological capacity

• repeated tests would show the effects of endurance training on VO2max

EXAMPLE OF SPORTING ACTIVITIES• swimming (>200m)• running (>800m)• cross country skiing• games lasting longer than a few

minutes

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AEROBIC CAPACITY

AEROBIC FITNESS TESTS

There are many tests that vary in validity and reliability. Two tests that you are required to know are both ‘indirect’ which estimate and predict a VO2 max value based on test results.

• PWC 170 test– A submaximal test on a cycle ergometer. The performer cycles at 3

progressive low-moderate work intensities (100-115bpm, 115-130bpm and 130-145bpm) and their HR values are recorded. As HR increases linearly with work load a line can be drawn through these 3 points to predict level of work at a HR of 170 bpm

• Multistage shuttle run test (bleep test)– the subject runs a progressively quicker shuttle run to exhaustion– each level and shuttle in the progression is numbered– the level reached by the subject is correlated to the VO2max

Aerobic Training• To enable you to plan a training programme you will be required

to know continuous, fartlek, interval training and repetition running. It is important to measure the intensity. Training zones and target heart rates are often used as they are more practical.

• A simple formula to calculate the appropriate HR percentage, often termed the critical threshold and based on Karvonen’s principle (220-age = max HR) is below:

• Critical Threshold = resting HR + %(max HR-resting HR)• EG: for 60% HR for a 17 year old with a resting HR of 72:• CT = 72 + (0.60 x 131) 79 = 151 (203 – 72 = 131) = (max HR –

resting HR)• Individuals working at the top end of the training threshold

would get greater adaptations.

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MONITORING EXERCISE INTENSITYTARGET HEART RATE• a specific heart rate (HR) to be achieved and

maintained during exercise• if aerobic adaptations are to occur, training

must take place at a HR above the aerobic threshold

• this theory is based on the fact that VO2 is proportional to HR

AEROBIC TRAINING ZONE• this is shown on graph• which shows a range of HR values

at which aerobic training should occur

• this will enable adaptations to occur which improve VO2max

HR ESTIMATION• HR will depend on fitness of athlete• maximum HR

HRmax = 220 - age• aerobic threshold (Karvonen)

HR = HRrest + 0.6(HRmax - HRrest)

• example :– age = 20, HRrest = 70

bpm– HRmax = 220 - 20 = 200 bpm– aerobic threshold HR

= 70 + 0.6(200 - 70)= 70 + 0.6 x 130 = 70 +

78 = 148 bpm

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AEROBIC CAPACITY

ADAPTATIONS PRODUCED BY AEROBIC TRAINING• cardiovascular system becomes more efficient• heart becomes bigger and stronger and pumps more blood per pulse• more haemoglobin is available in blood for oxygen transport• capillary system in muscle bed is utilised better and developed

• pulmonary systems become more efficient• musculature of torso becomes stronger and more efficient• lung volumes increase slightly, greater volumes of air can be

breathed per breath• efficiency of alveoli improves, and more alveoli are utilised

• more myoglobin and mitochondria are created in muscle cells

Aerobic Training Methods

• This involves whole body activities like running, cycling, rowing and swimming, and is aimed at overloading the cardio-vascular/respiratory systems to increase aerobic capacity/VO2 max.

• Overload is achieved by applying the principle of FITT.• F – Frequency – a minimum of 3-5 times per week for a

minimum of 12 weeks• I – Intensity – measured using HR% within a critical

threshold/training zone• T – Time/duration – a minimum of 3-5 minutes to 40+ minutes• T – Type – overloading the aerobic energy systems

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TYPES OF TRAINING USED TO DEVELOP AEROBIC CAPACITY

CONTINUOUS TRAINING• exercise regimes lasting longer than 3

minutes• involving low forces• where breathing is comfortable and the

activity is aerobic• examples :

– jogging, swimming, step aerobics

INTERVAL TRAINING (repetition running)

• characterised by sets, repetitions and rest relief

• example :– swimming :

• 2 sets of 10 at 50m at 70% effort

• with 30 seconds rest relief between repetitions, and 3 minutes rest between sets

– circuit training, weight training

FARTLEK TRAINING• fartlek means ‘speed play’• pace is varied from sprinting to

jogging• this is a combined form of

continuous and interval training

• normally performed in the countryside

• over 45 minutes or longer• can include all round body

exercises between running bouts• helps develop VO2max and the

recovery process

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FOOD FUEL USAGE FOR AEROBIC ACTIVITYFOOD FUEL USAGE• this depends on :

– EXERCISE INTENSITY– EXERCISE DURATION

AT REST• ATP utilisation is slow• a mixture of fats and carbohydrates is

used to resynthesise ATP

FOR LOW INTENSITY LONG DURATION AEROBIC ACTIVITY

• usage of a variety of fuels• but mainly the oxidation of a mixture of

CHO and fats• the longer the exercise the bigger the

proportion of ATP resynthesis provided by fats

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FOOD FUEL USAGE FOR AEROBIC ACTIVITYSOURCES OF FUELS• main source of CHO for muscular energy during exercise is glucose• derived from stored muscle and liver glycogen• lack of CHO fuel is the limiting factor for aerobic endurance

performance

• main source of fat for muscular energy during exercise is free fatty acids (FFA)

• derived from triglycerides stored as adipose tissue under the skin and in muscle tissue

• triglycerides break down into FFA for entry into the aerobic energy system

• proteins become a significant source of energy only in extreme conditions

• when CHO and fats are depleted

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FOOD FUEL UTILISATION DURING AEROBIC EXERCISEGLYCOGEN SPARING AS A LONG-TERM

ADAPTATION TO AEROBIC TRAINING

• for the person who has undertaken sustained aerobic training

• an adaptation is produced where fats are used earlier on in exercise

• thus conserving glycogen stores (respiratory exchange ratio (RER) indicates greater use of fats)

• the graph shows a higher proportion of fats utilised by the trained person

• thereby releasing CHO for higher intensity work

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AEROBIC CAPACITY

ADAPTATIONS PRODUCED BY AEROBIC TRAININGCARDIAC RESPONSE• blood plasma volume increases with training• therefore increased blood plasma volume enters left ventricle• increasing the stretch of the ventricular walls by the Frank-Starling

mechanism

• cardiac hypertrophy – heart becomes bigger and stronger (mainly left ventricle)

• increased ventricular muscle mass and stronger elastic recoil of the myocardium

• causes a more forceful contraction during ventricular systole• therefore stroke volume increases and HR decreases (bradycardia)• and hence providing more oxygen per pulse• the net effect is up to 20% bigger stroke volume and greater oxygen

delivery to muscles

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AEROBIC CAPACITY

ADAPTATIONS PRODUCED BY AEROBIC TRAINING• cardiovascular system becomes more efficient

VASCULAR RESPONSE• more haemoglobin is created and is available in blood for oxygen

transport• capillary system in muscle bed is utilised better and developed• there is increased capillarisation of trained muscle• and improved dilation of existing capillaries due to increased blood

volume• increased elasticity and thickness of smooth muscle of arterial

walls makes walls tougher and therefore less likely to stretch under pressure

• hence a more effective blood distribution• this maintains blood pressure forcing blood through capillary network• during ageing arteries lose muscle and hence stretch more under

pressure• hence greater BP required to force blood through capillary system• heart has to work harder

BLOOD VESSELS IN THE HEART • blood flow to heart decreases because heart muscle is more

efficient• hence decrease in resting HR• and increase in diastolic HR during maximal workloads

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AEROBIC CAPACITYADAPTATIONS PRODUCED BY AEROBIC TRAINING• pulmonary systems become more efficientRESPIRATORY RESPONSE• musculature of torso becomes stronger and more efficient• lung volumes increase slightly, greater volumes of air can be

breathed per breath• increase in VC at the expense of RV• hence decrease in breathing rate (f) at submaximal workloads• and increase in breathing rate (f) at maximal workloads• hence large increase in volume of air breathed per minute (VE)

• increase in pulmonary blood flow and plasma volume• efficiency of alveoli improves, and more alveoli are utilised• hence increased gaseous exchange and VO2max

RECOVERY• improved oxygen recovery• with better muscle capillarisation and efficient cool-down, lactic acid

removal is improved• hence reduction in DOMS

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CELLULAR ADAPTATION PRODUCED BY AEROBIC TRAINING

glycogenfatsoxygen uptake

glycogenfatsoxygen uptake

AFTER SEVERAL WEEKS OF AEROBIC TRAINING

= SLOW TWITCH MUSCLE FIBRE (type I)= FAST TWITCH MUSCLE FIBRE (type II) (do not increase in

size)

BEFORE TRAINING

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AEROBIC CAPACITYADAPTATIONS PRODUCED BY AEROBIC TRAINING

MUSCLE CELL RESPONSE• more myoglobin is created in muscle cells• more and bigger mitochondria in muscle cells• increased oxidative enzymes glycogen phosphorylase,

phosphofructokinase, lipoprotein lipase• hence increased activity of Kreb’s cycle and electron transport chain• and increase in stores and utilisation of fat• increase in stores of glycogen in muscle• which enables more fuel to be available for aerobic work

• conversion of type IIb to type IIa fibres

NEURAL RESPONSE• better recruitment of slow twitch fibre motor units making muscle

usage more efficient