Chronic adaptations to aerobic exercise

Chronic adaptations to aerobic exercise

1. Favourable autonomic balance

   • lower resting HR, quicker HRR, higher HRV
     • associated with improved arterial baroreflex sensitivity

2. Cardiovascular adaptations

   • Increases
     • VO2 peak
     • cardiac output
     • stroke volume
     • plasma volume
       • increased water retention - role of kidneys
         • increased plasma volume >> more blood returning to heart >> higher EDV >> stretches heart wall >> heart contracts harder due to frank starling mechanism >> increased SV (and lower HR)
         • notable increase within 24hrs
         • 12-20% increase after 3-6 sessions without changes in RBC
   • Decreases
     • heart rate
     • a-vO2 difference
   • Remodelling of myocardium
     • left ventricular hypertrophy
       • increased Q >> increased venous return >> increased EDV and SV >> remodelling >> LVH >> increased Q...
     • HYPERTROPHY
       • Eccentric hypertrophy
         • aerobic/ endurance trained
         • thickening of myocardium and ventricles increase in size
           • increased EDV, lower HR
       • Concentric hypertrophy
         • strength trained
         • increased mass but left ventricle not as large
   • Remodelling of vasculature
     • increased cross sectional area of coronary and peripheral arteries
     • increased capillary network
       • develop new arterioles
       • 10-20% increase in capillarisation per g of muscle
       • increased perfusion to support increased blood flow and energy demands
     • improved elasticity to vasodilator blood vessels
     • increased size of lumen and reduced blood pressure
     • Other blood vessel adaptations
       • increased anti-oxidant defence
       • increased nitric oxide availability
       • reduced inflammation
       • reduced sympathetic nervous activity
       • reduced vascular tone

3. Respiratory adaptations

   • More alveoli and capillaries activated
   • Diaphragm and intercostal muscles strengthened
     • increases force and ability to expand (vital capacity) - less work, reduces energy demands
   • Increased oxidative enzyme activity and capacity of respiratory muscles
     • enhanced ventilatory function
     • efficiently metabolise lactate as fuel
   • Ventilatory muscular endurance improved by 16% after 20 weeks running training

4. Metabolic adaptations

   • Increased mitochondrial content and function >> deliver more ATP
   • Increased oxidative enzyme capacity to accelerate electron transport
     • citrate synthase - marker of mitochondrial content
     • succinate dehydrogenase (ET chain)
     • cytochrome C oxidase (ET chain)
   • PGC1a gene activated in skeletal muscle in response to endurance exercise
     • master regulator of mitochondrial biogenesis
     • most influenced by oxygen free radicals, glycogen & ATP depletion, exercise duration
   • REDUCED CHO METABOLISM
     • decreased/ slower utilisation of muscle glycogen
     • increased muscle glycogen storage
     • decreased glucose production as reduced need for CHO as fuel
     • decreased use of plasma glucose
   • INCREASED FAT OXIDATION
     • increased blood flow in trained muscle
     • increased fat metabolising enzymes
     • increased muscle mitochondrial respiratory capacity
     • decreased catecholamine release for same power output

5. Muscular adaptations

   • Muscle fibre type
     • limited change
     • fast twitch glycolytic can change to fast twitch oxidative state
       • maximises aerobic potential
   • Muscle fibre size
     • selective hypertrophy
     • increase type 1 size
     • increases ATP generation
   • Myoglobin
     • increased type 1 sfibres >> increase MB stores and enhance O2 extraction

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