Cardiovascular Responses to Exercise

Cardiac Output: amount of blood ejected from left side of the heart (to the body) in L/min

--> determined by heart rate and stroke volume

Heart rate: how quickly the heart is beating (bpm)

Stroke volume: the amount of blood ejected with each contraction ml/beat

Cardiac output = (heart rate x stroke volume) / 1000

Acute

• Increased heart rate

• Increases stroke volume

Both increase until respective max rate and volume achieved

--> max cardiac output is reach (exhaustion)

Prolonged

• Increased heart rate

• Decreased stroke volume

Cardiac output is maintained at the same level throughout

Eventually heart rate increases gradually due to sweat loss and thermoregulation

Stroke volume decreases as a result of cardiovascular drift

Cardiovascular drift: a gradual increase in heart rate and a decrease in stroke volume during prolonged exercise

1. Body participates in prolonged exercise

2. Body temp increase due to heat produced in respiration

3. Sweating decreases blood volume

4. Reduced blood plasma increases viscosity

5. Stroke volume decreases

6. Heart rate increases to maintain cardiac output

VO2 is assessed by measuring the gas concentration and volume of air being breathed out at progressively increasing intensities of exercise

As the oxygen demand increases so does the VO2 max until the person reaches their limit

VO2 max = maximum cardiac output x maximum arteriovenous oxygen difference

Maximal Oxygen Uptake (VO2 max): the max rate at which an individual can take in and use oxygen

Maximum cardiac output: highest volume of blood the heart can pump per minute

Maximum arteriovenous oxygen difference: the amount of oxygen extracted by the muscle from the blood

Fick's law explains that to achieve a higher VO2 max, both maximum cardiac output and the maximum a-VO2 difference must be optimised

Increasing either factor allows for greater oxygen delivery to utilisation by the muscles, supporting higher aerobic performance

Factors that affect cardiac output

Age:

VO2 max increases as people age

Peaks around 20 for males and mid to late teens for females

Steadily declines after peak as the individual ages

The rate of decline in VO2 max is determined by an active healthy lifestyl

Sex:

Relative VO2 max is lower in females compared to makes

Females have a larger percentage of fat

Females have a lower haemoglobin concentration

Females generally have smaller heart, lungs and blood volume

Level of fitness:

Trained individuals will have a higher VO2 max than untrained individuals due to physiological adaptions to training

Increases stroke volume

Increased oxygen carrying capacity

Training leads to a greater area of muscle mass and a higher VO2 max

Type/Intensity of activity:

Dynamic exercise - systolic blood pressure increases and diastolic remains constant

Static exercise - systolic and diastolic blood pressure increases

The type of exercise will limit an individual's highest recorded VO2

--> activities that require more muscle mass usage will result in increase in VO2 max

--> greater number of motor units recruited