Aerobic training leads to adaptations across multiple body systems that improve cardiorespiratory endurance. Key adaptations include increased heart size and stroke volume, lower resting and submaximal heart rate, greater pulmonary ventilation and oxygen extraction, increased muscle capillarization and mitochondria, and an elevated maximal oxygen uptake (VO2max). The magnitude of improvement in VO2max depends on an individual's training status and genetics.

1. Adaptations to
Aerobic Training

2.  Adaptations to aerobic training
 Cardiorespiratory endurance
 Endurance training
 Major Cardiovascular Changes
 Respiratory Changes
 Muscle Changes
 Metabolic Changes

3.  Cardiorespiratory endurance
◦ Ability to sustain prolonged, dynamic exercise
◦ Improvements achieved through multisystem
adaptations (cardiovascular, respiratory, muscle,
metabolic)
 Endurance training
–  Maximal endurance capacity =  VO2max
–  Submaximal endurance capacity
 Lower HR at same submaximal exercise intensity
 More related to competitive endurance performance

5.  Heart size
 Stroke volume
 Heart rate
 Cardiac output
 Blood flow
 Blood pressure
 Blood volume

6.  O2 transport system and Fick equation
◦ VO2 = SV x HR x (a-v)O2 difference
–  VO2max =  max SV x max HR x  max (a-v)O2
difference
 Heart size
◦ With training, heart mass and LV volume 
– Target pulse rate (TPR)  cardiac hypertrophy   SV
–  Plasma volume   LV volume   EDV   SV
◦ Volume loading effect

8.  SV  after training
◦ Resting, submaximal, and maximal
◦ Plasma volume  with training   EDV   preload
◦ Resting and submaximal HR  with training   filling
time   EDV
–  LV mass with training   force of contraction
◦ Attenuated  TPR with training   afterload
 SV adaptations to training  with age

11.  Resting HR
–  Markedly (~1 beat/min per week of training)
–  Parasympathetic,  sympathetic activity in heart
 Submaximal HR
–  HR for same given absolute intensity
◦ More noticeable at higher submaximal intensities
 Maximal HR
◦ No significant change with training
–  With age

13.  HR-SV interactions
◦ Does  HR   SV? Does  SV   HR?
◦ HR, SV interact to optimize cardiac output
 HR recovery
◦ Faster recovery with training
◦ Indirect index of cardiorespiratory fitness
 Cardiac output (Q)
◦ Training creates little to no change at rest, submaximal
exercise
◦ Maximal Q  considerably (due to  SV)

16. •  Blood flow to active muscle
•  Capillarization, capillary recruitment
–  Capillary:fiber ratio
–  Total cross-sectional area for capillary exchange
•  Blood flow to inactive regions
•  Total blood volume
◦ Prevents any decrease in venous return as a result of
more blood in capillaries

18.  Blood pressure
–  BP at given submaximal intensity
–  Systolic BP,  diastolic BP at maximal intensity
 Blood volume: total volume  rapidly
–  Plasma volume via  plasma proteins,  water and
Na+ retention (all in first 2 weeks)
–  Red blood cell volume (though hematocrit may )
–  Plasma viscosity

21.  Pulmonary ventilation
–  At given submaximal intensity
–  At maximal intensity due to  tidal volume and
respiratory frequency
 Pulmonary diffusion
◦ Unchanged during rest and at submaximal intensity
–  At maximal intensity due to  lung perfusion
 Arterial-venous O2 difference
–  Due to  O2 extraction and active muscle blood flow
–  O2 extraction due to  oxidative capacity

22.  Fiber type
–  Size and number of type I fibers (type II  type I)
◦ Type IIx may perform more like type IIa
 Capillary supply
–  Number of capillaries supplying each fiber
◦ May be key factor in  VO2max
 Myoglobin
–  Myoglobin content by 75 to 80%
◦ Supports  oxidative capacity in muscle

23.  Mitochondrial function
–  Size and number
◦ Magnitude of change depends on training volume
 Oxidative enzymes (SDH, citrate synthase)
–  Activity with training
◦ Continue to increase even after VO2max plateaus
◦ Enhanced glycogen sparing

26.  High-intensity interval training (HIT): time-
efficient way to induce many adaptations
normally associated with endurance training
 Mitochondrial enzyme cytochrome oxidase
(COX)  same after HIT versus traditional
moderate-intensity endurance training

28.  Lactate threshold
–  To higher percent of VO2max
–  Lactate production,  lactate clearance
◦ Allows higher intensity without lactate accumulation
 Respiratory exchange ratio (RER)
–  At both absolute and relative submaximal intensities
–  Dependent on fat,  dependent on glucose

30.  Resting and submaximal VO2
◦ Resting VO2 unchanged with training
◦ Submaximal VO2 unchanged or  slightly with training
 Maximal VO2 (VO2max)
◦ Best indicator of cardiorespiratory fitness
–  Substantially with training (15-20%)
–  Due to  cardiac output and capillary density

33.  Long-term improvement
◦ Highest possible VO2max achieved after 12 to 18
months
◦ Performance continues to  after VO2max plateaus
because lactate threshold continues to  with training
 Individual responses dictated by
◦ Training status and pretraining VO2max
◦ Heredity

35.  Training status and pretraining VO2max
◦ Relative improvement depends on fitness
◦ The more sedentary the individual, the greater the 
◦ The more fit the individual, the smaller the 
 Heredity
◦ Finite VO2max range determined by genetics, training
alters VO2max within that range
◦ Identical twin’s VO2max more similar than fraternal’s
◦ Accounts for 25 to 50% of variance in VO2max

37.  Sex
◦ Untrained female VO2max < untrained male VO2max
◦ Trained female VO2max closer to male VO2max
 High versus low responders
◦ Genetically determined variation in VO2max for same
training stimulus and compliance
◦ Accounts for tremendous variation in training
outcomes for given training conditions

40.  Endurance training critical for endurance-based
events
 Endurance training important for non-
endurance-based sports, too
 All athletes benefit from maximizing
cardiorespiratory endurance