IB Sports, exercise and health science A.3.2.2 Effects of Physical Activity on the Muscular and Immune Systems Notes

How physical activity affects the muscular system

Exercise improves strength, endurance, and muscle size

Regular physical activity increases muscle strength, improves endurance, and can cause hypertrophy.

Muscle Strength

1. Muscle strength refers to the ability of a muscle or group of muscles to exert force against resistance.
2. Regular resistance training and weight-bearing exercises (such as lifting weights) stimulate muscle fibers, leading to increased strength.

Muscle Endurance

1. Muscle endurance is the ability of a muscle to perform repeated contractions over an extended period without fatigue.
2. Exercises such as running, cycling, and swimming enhance endurance by improving the oxidative capacity of muscle fibers.

Muscle Hypertrophy

1. When muscles are exposed to resistance or stress, such as lifting heavy weights, they adapt by increasing in size.
2. This is the result of muscle fiber repair after microscopic damage incurred during exercise.
3. Hypertrophy is most effectively achieved with moderate to high resistance and repetitions (typically 6-12 reps per set).

Excessive or improper exercise can damage muscle tissue

Improper or excessive exercise can harm the muscular system.

Overtraining

1. Overtraining occurs when an individual exceeds the body's ability to recover from intense physical activity.
2. This can lead to muscle breakdown, fatigue, and a decrease in performance. Signs include persistent soreness, reduced strength, and poor sleep.

Muscle Fatigue

This happens when the body's energy stores (such as glycogen) are depleted, leading to muscle exhaustion and a decline in performance.

Muscle Injuries

1. Muscle injuries such as strains, tears, or sprains are common, especially when exercise is done improperly or without a warm-up.
2. Overuse injuries, such as tendinitis, are common in athletes who perform repetitive movements.

How physical activity affects the immune system

Moderate exercise strengthens immune function

1. Moderate exercise improves immune function.

Enhanced Circulation of Immune Cells

1. Regular moderate physical activity boosts immune system function by improving the circulation of immune cells such as T-cells, B cells and macrophages, which play a crucial role in fighting infections.
2. Exercise increases blood flow, helping immune cells travel through the body more efficiently to detect and combat pathogens.

Reduction in Chronic Inflammation

1. Chronic low-level inflammation has been linked to conditions such as cardiovascular diseases, diabetes, and arthritis.
2. Exercise helps to reduce chronic inflammation, a key factor in the development of many diseases.
3. Regular moderate physical activity can decrease the production of pro-inflammatory cytokines and increase anti-inflammatory cytokines, improving overall immune function.

Improved Immune Responses

1. Moderate exercise enhances the overall responsiveness of the immune system.
2. Exercise increases the production of antibodies and enhances the activity of macrophages, which are important in detecting and destroying pathogens.

Excessive exercise can suppress immune function

1. Excessive or intense exercise without adequate recovery can negatively affect the immune system.
2. This increases the risk of infections and illness.

Suppressed Immunity from Intense Exercise

1. Intense or prolonged exercise (e.g., marathon running, long-distance cycling) can lead to immune suppression.
2. This is particularly true when recovery time is insufficient.
3. During periods of intense exercise, the body's stress hormones, like cortisol, are elevated, which can suppress the activity of immune cells.

Increased Susceptibility to Infections

1. Athletes who engage in excessive training or competition without adequate recovery often experience a period of immune suppression.
2. This is why athletes are more prone to upper respiratory tract infections (URTIs), such as the common cold, after periods of intense training.

Chronic Stress and Immune Function

1. Chronic stress from overtraining can impair immune function by increasing levels of cortisol, a hormone that suppresses immune responses.
2. When cortisol remains elevated for extended periods, it can reduce the number of immune cells available to fight off infections.

The J-Shaped Curve

1. The J-shaped curve illustrates the relationship between physical activity and the incidence of upper respiratory tract infections (URTI), such as the common cold, sinus infections, and other upper respiratory illnesses.
2. It shows that exercise has both beneficial and detrimental effects on immune function depending on its intensity and volume.
3. At low levels of exercise, individuals may not stimulate their immune system enough.
4. Conversely, at high volumes of exercise, such as intense training, the immune system can become suppressed, increasing the risk of infections.
   1. Moderate Exercise: Involves regular physical activity that is neither too intense nor too light, such as jogging or swimming, which boosts immune function.
   2. Excessive Exercise: Involves training that is prolonged or highly intense, such as long-distance running or extreme endurance activities, which may lead to immune suppression.

Low to Moderate Exercise: Enhancing Immune Function

Positive Effects on Immunity

1. Low to moderate exercise enhances immune function by stimulating the circulation of immune cells, such as T-cells and macrophages.
2. This helps the body fight infections more effectively.

Chronic Inflammation Reduction

1. Regular exercise also helps to reduce chronic inflammation, which has been linked to numerous health problems, including cardiovascular diseases and autoimmune disorders.
2. This is achieved by the body's production of anti-inflammatory cytokines during moderate physical activity.

High Exercise Volume (Excessive Exercise)

Negative Impact on Immunity

1. Prolonged or intense physical activity (e.g., long-distance running, excessive endurance training) can negatively affect the immune system.

Cortisol and Immune Suppression

1. Excessive training increases cortisol levels (a stress hormone), which has a suppressive effect on the immune system by reducing the efficiency of immune cells like T-cells and B-cells.
2. This leads to a temporary period of weakened immunity.

Maintaining Immune Health in Athletes

Balanced Training

1. Training programmes should include periods of rest and recovery.
2. These periods allow the immune system to recover from the strain of exercise, preventing overtraining and immune suppression.
3. When the body is not allowed adequate recovery time, immune cells like T-cells and B-cells become less effective at responding to infections.
4. Rest periods allow these immune cells to regenerate and function at optimal levels.

Nutrition

1. Adequate intake of macronutrients (proteins, fats, carbohydrates) and micronutrients (vitamins and minerals) is essential for maintaining immune function.
   1. Protein: Crucial for tissue repair and the production of antibodies and cytokines, which help fight infections.
   2. Carbohydrates: Provide energy for sustained activity. Adequate carb intake helps prevent immune suppression during prolonged exercise.
   3. Fats: Healthy fats, particularly omega-3 fatty acids, have anti-inflammatory effects and help support immune function.
   4. Vitamins such as Vitamin C, Vitamin D and zinc are essential for immune health.

Sleep

1. Sufficient and quality sleep is crucial for immune function.
2. During sleep, the body produces immune cells such as T-cells, which help combat infections.
3. Sleep deprivation can lead to lower levels of immune cells and increased inflammation, making the body more susceptible to infections.

Stress Management

1. Psychological stress from intense training, competition, or daily life can negatively impact immune function.
2. High stress levels lead to elevated cortisol, which suppresses immune responses and increases the risk of infections.
3. Practices such as meditation, yoga, mindfulness, and deep breathing can help manage stress and improve immune health.

Hydration

1. Hydration is vital for supporting all bodily functions, including immune function.
2. Proper hydration helps transport immune cells and nutrients throughout the body and prevents dehydration-induced immune suppression.
3. Dehydration can impair circulation and reduce the efficiency of immune cell function, making it harder for the body to fight infections.
4. The open window of immunodepression is the 3 to 72-hour period after prolonged intense exercise when natural killer cells, salivary IgA, and neutrophil activity are suppressed.
5. During this window, athletes are most vulnerable to infection, so heavy training blocks must be paired with careful recovery.