Body's Responses To Acute Exercise

By Ben Hutchinson

The body reacts in different ways when you exercise. In this document I will describe the responses of the systems in the body. These effects are immediate when taking part in activities of short duration.

Muscoskeletal Response:

The Muscoskeletal System is made up of the muscles, bones, tendons, ligaments and cartilage. This system enables the body to move. These are the responses from within the musculoskeletal system:

Increased Blood Supply:

When you start exercising, working muscles need more oxygen to allow them to keep working at a high rate. The heart pumps faster meaning there is an increased blood supply to deliver more oxygen to the working muscles. This allows the participant to continue to play the sport they are doing for longer periods of time. To test this; I recorded my Heart rate before and after exercise. Because my muscles needed more oxygen as I worked harder, my heart rate increased. I started of with 62 beats per minute as my resting heart rate. After exercising however; my heart rate increased to 105 BPM. This shows a clear increase in my heart rate.

Increase in Muscle Pliability:

When muscles are warm, they are more pliable (stretchy). Before taking part in an activity a warm up should always be carried out because it reduces the risk of muscle injury. This is because the warmer that the muscle is, the more you can stretch without it pulling/snapping. The tissue within the muscle gets warmer from the excess heat that is generated from the increased blood supply. To test the response to exercise; I used the Sit & Reach Test. Before warming up and exercising, my score was 4 CM. After exercising I did the test again and my score was 11 CM which shows a clear improvement due to the muscles becoming more pliable due to exercise.

Increased Range of Movement:

One of the acute responses to the muscoskeletal system is increased range of movement. The response is immediate when you start exercising. The increased movement will make synovial fluid become less vicious (thickness of fluid) making the movement around the joint greater. There is also more synovial fluid being produced which makes the joint more lubricated. This means that the movement is more efficient at the joint, increasing performance levels of the participant.

Muscle Fibre Micro Tears:

Whilst exercising, muscles are put under pressure which makes tiny tears in the muscle occur. Even though this causes moderate soreness and stiffness, the muscles do strengthen and grow bigger after they recover. However the body must rest to allow the tear to repair and refuel before training. Failing to let the muscle fibres repair will cause more muscle pain. The name for muscle growth is Hypertrophy. Muscle Fibre micro tears can be a result of exercises such as, Weightlifting. The muscle then reacts to this by adding more proteins to the muscle.

Energy Systems

There are 3 main energy systems in the body; they generate energy at different times depending on the duration and intensity of the activity involved.

Phosphocreatine (ATP-PC):

Creatine Phosphate (CP) is a high energy compound found in association with ATP. CP is broken down and the spare Phosphate is used to re-synthesize ATP. The ATP-PC system is an only used during high activity movements, between 95% and 100%. This is an anaerobic activity and therefore does not use oxygen when working. Athletes in the events such as 100 Meter spring would use the ATP-PC System as it would allow them to perform at maximum capacity to win the race.

Lactic Acid:

Lactic Acid is a waste product from the Lactate energy system. Lactic Acid hinders nerve meaning muscles lose performance and feel uncomfortable. This lactic acid needs to be flushed away through sweating etc. This is an anaerobic system because oxygen is not used to produce ATP from the muscles. Lactic Acid is produced after working at 60%-95% for up to 3 minutes. The Lactate System would be used in events such as the 400 Meters and 800 Meters. It would work in partnership with the ATP-PC system but would be the primary system.


The Aerobic System uses the Mitochondria to burn Glycogen, Fats, Proteins and Oxygen. This creates the P for ATP. The aerobic system is in use all of the time and gets replaced as the primary energy system when taking part in physical activity. This is because the aerobic system is the main energy stem when intensity is less than 60%. This system uses oxygen to function and create ATP. The aerobic system would be used in long distance events such as the 10,000 Meters and Marathon Running.

Energy Continuum:

The process to say that energy is supplied from the systems constantly. Depending on the intensity of the activity, different energy systems will be the dominant system. The other energy systems will support the dominant one which will be doing most of the work. The systems can interchange on which is the primary system that does most of the work. This allows the other systems to regenerate and be able to be used when needed.

Energy Requirements of Different Sports and Exercise Activities:

As one energy starts to expire whilst taking part in physical activity, another one will take over. This will allow the participant to perform at their maximum ability. For example when running an 800 metre race; you will start by using the ATP-PC system to gain track position and get an initial boost off the line. After around 8 seconds, the ATP-PC system will fade out and the lactate system will be dominant. Lactic Acid will build up as a waste product and after 3 minutes the lactate system will have been replaced as the dominant system by the aerobic system. Whilst the other systems have been working, the ATP-PC system will have replenished and will be able to be used for the last 50-75 metres.

Running 800 metres uses all 3 energy systems however there is some movements/sports that only use one or two systems. One of these is a golf swing which only uses the ATP-PC system because it is a high intensity movement. Diving also only uses the ATP-PC system. An example of using both the ATP-PC and Lactate systems is baseball.

Cardiovascular Response

When exercising; muscles need a constant supply of oxygen and nutrients to keep working. They also need the blood to transport waste products such as; carbon dioxide away from the muscles to the lungs where they can be exhaled. To complete the demands that the muscles set, the heart needs to beat faster to pump more blood around the body. This ensures that oxygen is delivered in larger amounts, quicker and waste products are removed from the body as quickly as possible.

Heart Rate Anticipatory Response:

The rate that the heart reaches before starting to exercise is the Anticipatory Heart Rate. Before starting to exercise, your heart rate begins to increase, in anticipation, as you think about the activity you are about to undertake. This is because the body releases chemicals that makes the heart beat faster in preparation to pump blood around the body to supply the working muscles. This also gives muscles an adequate amount of oxygen before the participant starts the activity. Overall, this would give an increase in Cardiac Output because more blood is being pumped by the heart in 1 minute. This ensures that the participant has enough oxygen to start their initial exercise meaning they can get involved straight away.

Activity Response:

When thinking about physical activity; as well as your heart rate increasing, your brain will send chemicals to the heart, increasing the strength that the heart is beating. This means more blood and therefore more oxygen will be delivered to the working muscles. This response increases the stroke volume of the heart which means there is more blood being ejected by the heart per beat. The result of the increase in activity response means that working muscles will be able to work at a higher level for a longer period of time, increasing performance levels.

Increased Blood Pressure:

Blood pressure is what makes blood flow around the body. When we exercise, blood pressure increases meaning blood is pushed around the body quicker to supply muscles with oxygen when they need it. The systolic reading (when the heart is contracting) should increase from around 110-140 to 190-230 from training vigorously. This could take 10-20 minutes for your blood pressure to return to normal. The diastolic reading shouldn't change as this reading is for when the heart is relaxing (filling up with blood). The result of this on the body is that; the blood will be under more pressure meaning the oxygen gets delivered to the working muscles quicker, keeping high levels of performance.


The narrowing of blood vessels (Arteries, Veins, Capillaries, Arterioles, Venules) to restrict and slow the blood flow. This means that less blood is pumped to the muscles that don’t need it. Therefore more blood can be sent to working muscles that require oxygen. An example of vasoconstriction would be whilst playing football, your arms wouldn’t require as much blood as your legs so the blood vessels leading to the arms would vaso-constrict. This results in your working muscles to function better. Vasoconstriction could also occur if the body temperature is too low. If the body's temperature is below the optimal 37 degrees then the blood vessels will vasoconstrict to reduce heat loss through the skin.


The size of blood vessels increases to allow more blood to flow through. This allows more oxygen and nutrients to be delivered to the working muscles and more waste products to be removed from the muscles and exhaled. Vasodilation can also be used in the blood vessels near the surface of the skin when the temperature of the body is too high. Heat can be carried through the blood to the surface of the skin where it can be lost to the air.


Increase in Breathing Rate (neural and chemical control):

The working muscles demand more oxygen to keep on working whilst exercising. Also more carbon dioxide needs to be exhaled from the body as it is a waste product. These factors mean that faster and deeper breathing is required from the person. Like the Anticipatory Heart Rate, the chemicals are sent to increase breathing rate so your body will be able to perform at maximum capacity. When I tested this; my breathing rate started at 25 BPM, after exercising it had risen to 37 BPM. This tells me that my muscles needed more oxygen when exercising.

Neural Control:

Breathing is voluntary, you make yourself breath. The mechanoreceptors send messages to the brain when they sense a different movement and metabolic status. When exercising, if you are becoming physically tired then you are more likely to breath heavily. Breathing Heavily allows for more oxygen to be inhaled and more waste products to be exhaled.

Chemical Control:

This is involuntary, meaning your body does it without thinking. Chemoreceptors send messages to the brain to tell you that you need to take in more oxygen because you haven’t got enough in your body. Chemoreceptors also tell the brain if the carbon dioxide levels are too high in the body.

Increase Tidal Volume:

Tidal Volume is the amount of air breathed in and out per breath. On average this number is around 500 cm3. However when exercising, tidal volume increases to allow more air to get to the lungs where it can be taken to the heart to get distributed to the working muscles. A bigger tidal volume also means that more carbon dioxide and other waste products can be released from the body when exhaled.