Consistent aerobic exercise has many physiological effects on the cardiorespiratory system. The heart like any other muscle needs exercise, this exercise comes in the form of aerobic exercise. In this assignment I am going to illustrate the changes

Increased muscle mass in the ventricle can lead to a more forceful contraction. Increased contractibility coupled with the increased elastic recoil increases the ejection from the trained heart. More blood enters the left ventricle and a greater percentage of what enters is pushed out in a single contraction.

Heart rate

The heart rate is one of the easiest ways to measure cardiovascular activity. H.R. reflects the amount of work the heart has to do to meet demands of the body. To measure H.R. the pulse is taken at the radial artery on the wrist.

During exercise the heart rate must increase to meet demands of the active muscles. When exercise is complete your heart rate does not instantly return to resting level (60-80bpm average for adult) but takes a period of time known as heart rate recovery period. Heart rate can be as low as 40bpm in a trained individual.

Following a period of training as shown in the graph below the heart rate returns to resting level quicker after exercise than it does before prior to training.

Resting heart rate usually decreases substantially following aerobic endurance training (more than 10bpm).

E.C.G.

The effects on a person's rhythm strip are clearly evident as we can see from the two strips on page three.

Rhythm strip 1 is a normal sinus rhythm at 80bpm, if we compare this to rhythm strip 2 we can see that is faster. Rhythm strip 2 is a normal sinus bradycardia, which is a slow but regular heartbeat that is common to people with a good level of aerobic fitness.

It is clearly evident that in a person with good aerobic fitness that the heart is not having to work as hard and fast to meet the demands of the body.

Cardiac output

H.R. and stroke volume are the two main factors that affect cardiac output. When at rest or during sub-maximal exercise at a steady rate of work, cardiac rate does not change much following a period of endurance training, however, cardiac output increases considerably at maximal rates of work. This increase results primarily from the increase in stroke volume.

Maximal cardiac output can range from 14-20litres/min in an untrained person to 40L/min or more in a highly conditioned endurance athlete like Paula Radcliffe.

Myocardium

Cardiac muscle is collectively called the myocardium. The thickness of the myocardium varies directly with stress placed on the heart. The left ventricle's power is reflected by the greater size of its muscular wall (hypertrophy) compared with other chambers of the heart.

* Increase in muscle RNA content

* Myofibrils thicken

* Number of contractile filaments within the muscle fibre increases

Comparative Cardiac Dimensions in College Athletes vs Sedentary Students

Dimension

Runners

Swimmers

Wrestlers

Normals

LVmass,g

302

308

330

211

Septum, mm

0.9

0.7

3

0.3

LV wall, mm

1.3

0.6

3.7

0.3

LV volume

60

81

10

01

LV internal dimension at end diastole

54

57

48

46

Table showing differences between athletes and untrained hearts.

With more vigorous aerobic exercise, the demands on the left ventricle are greatly increased and therefore over time it adapts its size in order to meet demands.

Blood flow

The increase of blood flow to muscles is one of the most important factors for increased aerobic endurance capacity and performance.

As the cardiovascular system becomes better trained it adapts to allow increased blood flow to the muscles. Four factors account for this increased blood supply to muscle following training:

. Increased capillarization of trained muscle.

2. Greater opening of existing capillaries in trained muscles.

3. More effective blood redistribution.

4. increased blood volume.

groups

Capillaries per mm2

Muscle to fibre ratio per mm2

Capillary to fibre ratio

Trained individual

640

440

.5

Untrained individual

600

557

.1

This table shows that the trained man has larger muscle fibres and therefore fewer for a given area. They also have approx 50% higher capillary to fibre ratio than the untrained man.

The existing capillaries in trained muscles can open up more, which increases blood flow through the capillaries and into the muscles. A more effective redistribution of blood can also increase flow to active muscles. Blood flow can be redirected to the active muscles and pulled away from the areas that have less demand.

Organ

Percentage

Volume (ml/min)

Hepatic-splanchnic

27

350

Kidneys

22

100

Muscles

20

000

Brain

4

700

Skin

6

300

Heart

4

200

Other

7

350

Total

00

5000

The table above shows the distribution of 5 litres of cardiac output to the organs of the body. During exercise this can change and the muscle receive the most of the supply, almost 85% of blood is redistributed to the muscles.

Fatty deposits

A healthy cardiovascular system may aid sporting performance but it also has substantial health benefits. Benefits of aerobic exercise:

. Reduced risk of coronary heart disease

2. Reduction of percentage body fat (weight loss)

3. Improved circulation

4. Reduced risk of cancer

5. Reduced risk of diabetes

6. Improved immune system