7.4 Health, exercise and sport
Benefits of exercise
- Increasing arterial vasodilation lowers blood pressure and reduces the risk of cardiovascular disease and stroke
- Increases the level of blood HDLs which transport cholesterol to the liver where it is broken down
- Reduces the level of LDLs, reducing the development of atherosclerosis
- Helps maintain a healthy weight – decreases risk of obesity as metabolic rate increases during exercise
- Increased sensitivity of muscle cells to insulin improves blood glucose regulation and reduces the risk of type 2 diabetes
- Increases bone density and reduces its loss during old age – delays the onset and slows the progress of osteoporosis
- Reduces the risk of getting some cancers
- Improves mental well-being
- Moderate exercise – increased number and activity of natural killer cells in blood and lymph. Provide non-specific immunity, recognise glycoproteins on the surface of pathogens and secrete apoptosis-inducing molecules, causing cell lysis
Effects of too little exercise:
- Increased risk of obesity
- High blood pressure and high LDL levels, increasing the risk of CHD and stroke
- High risk of cancer
- Higher risk of type 2 diabetes – decreased sensitivity of liver and muscle cells to insulin – high blood glucose levels not returned to normal as fast as normal
- Higher risk of osteoporosis
Risks of too much exercise
However people who exercise too much can cause damage to their body.
- Joints become abnormally worn e.g. wear of cartilage, swelling of knees and other synovial joints due to a build up of fluid and damaged ligaments
- Strenuous exercise can make the immune system less effective/immune suppression – more likely to suffer infections e.g. of the upper respiratory tract
- High levels decrease the activity of the lymphocytes (phagocytes, B cells and T helper cells) and the ability of the immune system to destroy viruses and other pathogens. They also have increased exposure to pathogens.
- The decrease in T helper cells reduces the amount of cytokines available to activate lymphocytes (B and T cells) so fewer antibodies are produced
- Psychological stress (due to heavy training schedules) and physical stress cause secretion of the hormones adrenaline and cortisol from the adrenal glands which suppress the immune system
- Overtraining à poor athletic performance, chronic fatigue, increased wear and tear on joints, immune syppression resulting in more frequent infections
Exercise and the joints
A common injury is a torn anterior cruciate ligament. This ligament supports the bones at the knee and can be torn due to repeated forces. It is normally treated with keyhole surgery (arthroscopy) – a small incision is made, through which an arthroscope (allows images to be observed by passing light rays along optical fibres) is fed. Surgical instruments are also passed through the holes. Tendons or ligaments taken from elsewhere in the body repair the damaged ligament.
+ Only small incisions – less blood loss and scarring
+ Less pain and recovery time – easier to return to normal activities
If a knee joint is badly damaged, the whole joint must be replaced with a prosthetic (artificial) joint. Prostheses can replace whole limbs or limb parts.
+ Make it possible for people with disabilities to participate in sport
+ Make it possible for people with injuries to play sport again
+ Variations in design for specific activities, can be articulated so they bend
However they are expensive as they must be made of high-quality materials that:
- Are unaffected by body fluids
- Can stand up to the high forces of the knee
- Have the right combination of flexibility and strength for movement and support
Some athletes use performance-enhancing drugs, many of which are now banned from sport and athletes face penalties if found to have used them. There are various types that have different effects on the body:
- Anabolic steroids – increase strength, speed and stamina by increasing muscle size and allowing athletes to train harder and increase aggression
- Stimulants – speed up reactions, reduce fatigue and increase aggression
- Narcotic analgesics – reduce pain so injuries don’t affect performance
Steroids increase protein synthesis so can increase muscle size and strength. Erythropoietin increases the rate at which red blood cells are made, increasing oxygen-carrying capacity of the blood.
Peptide hormones such as erythropoietin are protein chains. They cannot pass through cell membranes easily because they are charged, instead they bind to a receptor on the cell membrane. This activates a second messenger in the cytoplasm which causes chemical changes in the cell by affecting gene transcription.
Steroid hormones are formed from lipids and have complex ring structures. The hormone-receptor complex functions as a transcription factor, switching enzyme synthesis on of off.
Ethical issues of performance-enhancing substances
- Some performance-enhancing drugs are illegal
- Competitions are unfair if some people take drugs – they gain an advantage rather than through training or hard work
- There are serious health risks such as high blood pressure or heart problems
- Athletes may not be fully informed of the health risks
- It is up to each individual – athletes have the right to make their own decisions about drugs and whether they are worth the risk
- Drug-free sport isn’t fair anyway – different access to training facilities, coaches, equipment etc
- Hard to detect every drug so its hard to develop the technology
- No ban on nutritional substances such as vitamins