EXERCISE PHYSIOLOGY (Human Physiology 2) Physiotherapy Dr. Waheeb Alharbi

References (1) Physiological basis of medical practice By; John B. West (2) Textbook of Medical physiology By; Arthur C. Guyton & John E. Hall

Exercise and your body During ex, the body is trying to tell you something to do. There has to be a purpose to these changes (occurred during ex) or else the body would not bother. So simply your body is saying "If you are going to be doing this, I need extra resources".

How does our body response to exercise The following changes may occur; - Your heart beats become faster - Your breathing become more deeply and more frequently - You start sweating and feeling hot - You start feeling thirsty - Your skin become flushed - You can feel your pulse beating - Your muscles may begin to ache - You may feel light headed.

(1) Faster heart beats & stronger pulse feeling : - The heart is a muscle and its function is to pump blood around your body. - Blood is the transport system for your body and carries the fuel and nutrients your body requires. - The heart size is like the size of a clenched fist and weighs about 300g. At rest the HR averages about bpm in a healthy adults. At rest the HR averages about bpm in a healthy adults. During moderate ex your heart will respond to the ↑ demands for resources by slightly enlarging → thus allowing more blood to enter your heart, and by ↑ the No. of bpm. This allows more blood to be pumped around your body (i.e. 80 x 130 = 10.4 L). As the intensity of your ex ↑ (e.g. you have to sprint) HR increases still further so more blood can be circulated (e.g. 80 x 170 = 13.6 L). During moderate ex your heart will respond to the ↑ demands for resources by slightly enlarging → thus allowing more blood to enter your heart, and by ↑ the No. of bpm. This allows more blood to be pumped around your body (i.e. 80 x 130 = 10.4 L). As the intensity of your ex ↑ (e.g. you have to sprint) HR increases still further so more blood can be circulated (e.g. 80 x 170 = 13.6 L).

(2) Deeper and more frequent breathing - Because your body is asking for more O 2 to cope with the demand for a greater fuel supply to your working muscles. - The O 2 you require is breathed in through your nose and mouth and passes down your bronchial tubes and into your lungs which are made up of over 300 million tiny air sacs called Alveoli. It is here the O 2 transfers itself to your blood to be transported around your body. - At rset, you usually breathe in about 500ml/b and you do this 12 times/min. This would give you 6 L of air. When you are exercising it is quite reasonable to take in 2300ml/b and your BR could ↑ 2 or 3 times. - Slow deep breathing is more efficient than rapid shallow breathing in increasing air flow to your lungs.

(3) Sweating, feeling hot & flushed - When you exercise the muscles are used more and as a result produce heat. This heat needs to be dissipated and your body loses heat in 2 principal ways. A) Your sweat glands are stimulated to secrete fluid, which then evaporates on the surface of your body to produce a cooling effect. B) Your small BV near to the surface of your skin enlarge to allow more blood to flow closer to the surface where cooling can take place. This is what makes you feel "flushed". Your body is telling you it wants to cool down so you should help it. - On a hot day you should try and wear a short- sleeved shirt, or at least have the sleeves rolled up, to allow more skin surface to be exposed to the air.

(4) Feeling thirsty - Ex will ↑ the temp of your body which will try to reduce it by secreting fluids. These fluids come from the reservoir of fluids contained in your body. If the fluids are not replaced, the level in the reservoir will go down and eventually this will trigger a feeling of thirst. - Prolonged periods of intensive ex can result in fluid losses of up to 2-3 L → dehydration which will not only adversely affect performance but can also be dangerous. - Fluid, esp H 2 O, should be regularly consumed before, during and after training or matches to continually top up your reservoir and prevent you feeling thirsty.

(5) Muscle Ache - In moderate ex your body may be able to remove the waste materials as they are produced, but as the intensity or length of the activity ↑, the build up of these waste products occurs faster than they can be removed. - The waste materials occupy space previously available to the fuel and nutrients in your blood, so as they build up, your blood supply to carry them away ↓. Without O 2 and nutrients the efficiency of your muscles diminishes, waste products swell your muscle, and muscle soreness ensues. - The waste materials occupy space previously available to the fuel and nutrients in your blood, so as they build up, your blood supply to carry them away ↓. Without O 2 and nutrients the efficiency of your muscles diminishes, waste products swell your muscle, and muscle soreness ensues. - When such soreness occurs, stretching the muscles involved will assist in reducing the pain and discomfort.

(5) Feeling light headed - Normally blood is circulating to all parts of your body. When demand ↑ for more fuel to be taken to working muscles, your body responds by reducing your blood supply to some organs not immediately involved in the activity. It is then redistributed to the areas in need. This means that organs such as your liver and stomach will have their blood supply reduced so that more blood can be taken to your muscles. - Your brain is another part of your body that finds itself having to deal with a reduced BF and the diminished O 2 supply may well make you feel light-headed and cause your conc to lapse. In severe cases it could cause you to collapse. - Your brain is another part of your body that finds itself having to deal with a reduced BF and the diminished O 2 supply may well make you feel light-headed and cause your conc to lapse. In severe cases it could cause you to collapse.

Respiration in exercise VO 2 & V E in exercise; - Normal VO 2 for a young man at rest is about 250ml/min. However, under maximal conditions, this can be ↑ 8-20 times, such as in untrained average male may reach 3600 ml/min in trained average male may reach 4000 ml/min in male marathon runner may reach 5100 ml/min - This ↑ is reflected in a similar ↑ in V E, which ↑ from 5600 ml/min to as much as ml/min. This ↑ is due to the ↑ in both V T & fr (figure 18-B). V T can be as much as 50% of the VC and is mostly taken from inspiratory reserve. - ↑ in V E → ↑ the elastic and flow-resistive work of breathing → ↑ the total energy requirement for breathing.

Figure 18-B

- Ex ↑ the diffusion capacity of the lungs. The ↑ results from the greater expansion of the lungs and also from improvement of the VE/Perf ratio, which results from ↑ BF through the lungs. - O 2 diffusing capacity is a measure of the rate at which O 2 can diffuse from the pulmonary alveoli into the blood. This is expressed in terms of ml of O 2 that will diffuse each min for each mmHg difference between P A O 2 and pulmonary blood O 2 pressure. - The normal diffu capac in a nonathlete at rest is 23 ml/min, nonathlete during max ex is 48 ml/min. This amount may ↑ to 64 ml/min in speed skater during max ex, 71 ml/min in swimmers during max ex and 80 ml/min in oarsman during max ex. - These results mainly from the fact that BF through many of the pulm cap is sluggish or even dormant in the resting state, whereas in max ex, ↑ BF through the lungs causes all the pulm cap to be perfused at their max rate, thus providing a far greater surface are through which O 2 can diffuse into the pulm cap blood.

- There is a linear relation between VO 2 & total V E (fig 84-6). Both VO 2 & V E ↑ approx 20-fold between the resting state and maximal intensity of ex in the well-trained athlete.

Figure 84-6

Blood gases during exercise; - BG do not always have to become abnormal for resp to be stim in ex. Instead, resp is stim mainly by neurogenic mech during ex. Part of this stim results from direct stim of the respiratory center by the same nervous signals that are transmitted from the brain to the muscles to cause the ex. An additional part is believed to result from sensory signals transmitted into the respiratory center from the contracting muscles and moving joints. All this extra nervous stim is normally sufficient to provide almost exactly the necessary ↑ in V E required to keep the blood respiratory gases very near to normal.

CVS in exercise - CVS serves 5 important functions during exercise; 1) Delivers O 2 to working muscles 2) Oxygenates blood by returning it to the lungs 3) Transports heat from the core to the skin 4) Delivers nutrients and fuel to active tissues 5) Transports hormones - Ex places an ↑ demand on the CVS. O 2 demand by the muscles ↑ sharply. Metabolic processes speed up and more waste is created. More nutrients are used and body temp ↑. To perform as efficiently as possible the CVS must regulate these changes and meet the body’s increasing demands.

- A key requirement of CV func in ex is to deliver the required O 2 and other nutrients to the exercising muscles. For this purpose, the muscle BF can ↑ a maximum of approx 25-fold during strenuous ex. Almost one half this ↑ in flow results from intramuscular vasodilation caused by the direct effectof ↑ muscle metabolism. The remaining ↑ results from multiple factors, the most important of which is probably the moderate ↑ in arterial BP that occurs in ex, usually about a 30% ↑. - The ↑ in pressure not only forces more blood through the BV but also stretches the walls of the arterioles and further reduces the vascular resistance. Figure 84-9 shows the interrelations among work output, VO 2 & Q during ex. All these parameters are related directly to one another (linear function), because the muscle workout ↑ VO 2 and VO 2 in turn dilates the muscle BV → ↑ venous return and Q.

Fig 84-9

- Normal Q at rest is approx 5-6 L/min, and may ↑ to L/min during heavy ex (table 21-2). This ↑ is achieved by ↑ of both SV & HR. - Fig shows the approx changes in SV & HR as the Q ↑ from its resting level to a marathon runner. The SV ↑ from 105 to 162 ml, whereas HR ↑ from 50 to 185 bpm. Therefore, the HR accounts by far for a greater proportion of the ↑ in Q than does the ↑ in SV during strenuous ex. - The SV normally reaches its maximum by the time Q has ↑ only half way to its maximum. Any further ↑ in Q must occur by ↑ HR.

Table 21-2

Fig 84-10

- During max ex, both SV & HR are ↑ to about 95% of their max level. - CVS is normally much more limiting on VO 2 max than is the RS, because O 2 utilization by the body can never be more than the rate at which the CVS can transport O 2 to the tissues. VO 2 max is the rate of O 2 under max aerobic metabolism.

- Due to light ex the following changes take place; 1) Extensive vasodilation occurs as the rate of VO 2 in skeletal muscle ↑. Peripheral resistance drops, BF through the cap ↑, and blood enters the venous system at an accelerated rate. 2) The venous return ↑ as skeletal muscle contraction squeeze blood along the peripheral veins and an ↑ BR pulls blood into the venae cavae via the respiratory pump. 3) Q ↑, primarily in response to; a- the ↑ in venous return b- atrial stretching (the atrial reflex).

This regulation by venous feedback produces a gradual ↑ in Q to about double resting levels. Over the range of ↑, the BF to skeletal muscles, cardiac muscles and skin rises. The ↑ flow to the muscles reflects the dilation of arterioles and precapillary sphincters in response to local factors; the ↑ flow to the skin occurs in response to the rise in body temp. At higher level of exertion, other physiological adjustments occur as the cardiac and vasomotor centers call for the general activation of the SNS. Q ↑, toward maximal levels, and major changes in the peripheral distribution of blood take place, facilitating the BF to active skeletal muscle.

- During ex at max level, your blood essentially races between the skeletal muscles and the lungs and heart. Although BF to the most tissues is diminished, skin perfusion ↑ further, because the body temp continues to climb. Only the blood supply to the brain remains unaffected.

Exercise, CV fitness & health - CV performance improves sig with training. Table 21-3 compares the cardiac performance of athletes with non athletes. Trained athletes have bigger hearts and larger SV than do non athletes and these are important functional differences.

Table 21-3

Exercise and CV disease - Regular ex has several beneficial effects. Even moderate ex routine can lower total blood cholesterol levels. - A high cholesterol level of the major risk factors for atherosclerosis, which leads to CV disease and stroke. - A regular ex, a healthy lifestyle, a balanced diet, weight control and not smoking → reduces stress, lowers BP and slows the formation of plaque. - A regular moderate ex may cut the incidence of heart attack almost in half. - Ex is also beneficial in accelerating one’s recovery after a heart attack. - Regular light to moderate ex coupled with a low fat diet and a low stress lifestyle, not only reduces symptoms of CAD, such as angina, but also improves one’s mood and overall quality of life.