Study guide: Muscular System in Sport

📋 Course Outline

1. Muscle Types and Their Functions
2. Major Skeletal Muscles
3. Muscle Roles and Antagonistic Pairs
4. Types of Muscle Contraction
5. Muscle Fibre Types and Performance
6. Acute Muscular Responses to Exercise
7. Long-Term Muscular Adaptations
8. Additional Factors Affecting Muscles

📖 1. Muscle Types and Their Functions

★ Must-know

📌 The body contains cardiac, skeletal, and smooth muscle; cardiac and smooth muscle are involuntary, while skeletal muscle is voluntary.

• Cardiac muscle forms the walls of the heart chambers, contracts involuntarily, and, when the heart is healthy, does not fatigue.

• Skeletal muscles attach to bones and enable conscious movement, strength, and power; they also maintain posture and generate heat that helps maintain normal body temperature.

• Smooth muscles work involuntarily in and around organs such as the intestines and blood vessels, and help move substances around the body to supply cells with oxygen and nutrients.

Further detail

• Fitness training strengthens cardiac muscle and makes the heart more efficient at pumping blood around the body.

📖 2. Major Skeletal Muscles

📝 Essential Points

• The major skeletal muscles named in the course are deltoids, biceps, triceps, wrist flexors, wrist extensors, supinators, pronators, pectorals, abdominals, obliques, quadriceps, hip flexors, tibialis anterior, erector spinae, trapezius, latissimus dorsi, gluteals, hamstrings, gastrocnemius, and soleus.

📖 3. Muscle Roles and Antagonistic Pairs

🔑 Key Concepts & Definitions

• Agonist: The prime mover responsible for the movement, including when it controls a lowering phase while lengthening.
• Antagonist: Relaxes and produces the opposite movement to the agonist; antagonistic partners lie on opposite sides of a joint or bone.
• Synergist: Works with the agonist to control direction and make movement more efficient.
• Fixator: Prevents unwanted movement by stabilizing a joint and controlling the muscle's origin for effective contraction.

★ Must-know

• In an antagonistic pair, one muscle contracts and shortens while its partner relaxes and lengthens; the muscles swap actions to reverse the movement because muscles pull but cannot push.

Further detail

• The tendon at the moving end of a muscle is the insertion, while the tendon at the fixed end is the origin.

💡 Memory Hook

Agonist drives or controls movement; antagonist opposes it.

📖 4. Types of Muscle Contraction

🔑 Key Concepts & Definitions

• Concentric contraction: Generates force while the muscle shortens, as when raising or lifting a weight.
• Eccentric contraction: Generates force while the muscle lengthens, as when lowering a weight.
• Isometric contraction: Generates force while the muscle remains the same length, as when holding a load.

💡 Memory Hook

Concentric shortens, eccentric lengthens, isometric holds length.

📖 5. Muscle Fibre Types and Performance

★ Must-know

📌 Skeletal muscle fibres are broadly classified as Type I slow-twitch or Type II fast-twitch, with Type II including Type IIa and Type IIx fibres.

• Type I fibres contract slowly with less force, resist fatigue, have high aerobic capacity, and suit long-duration aerobic activities such as distance running and swimming.

• Type IIa fibres contract quickly and produce high force while resisting fatigue more than Type IIx fibres; they suit speed, power, and strength activities such as repeated weight-training sets of 10–12 repetitions and 400-metre running.

• Type IIx fibres contract rapidly and produce high force but fatigue faster than Type IIa fibres; they suit short, high-intensity anaerobic activity, including 100-metre running and stop–go sports such as rugby or football.

Further detail

• Muscle-fibre proportions vary between individuals and between muscle groups within one individual; the mix is largely inherited, although training can affect fibre efficiency.

• The course gives an average human muscle-fibre mix of 60% fast-twitch and 40% slow-twitch fibres.

📖 6. Acute Muscular Responses to Exercise

★ Must-know

📌 Acute muscular responses occur during or immediately after a single exercise session, whereas chronic responses develop over a longer period.

• Exercise increases muscular metabolic activity and oxygen and glucose demand, which is met by increased blood supply to working muscles.

• Resistance-training stress can cause microtears in muscle fibres, producing tissue swelling and pain; rest allows proteins to repair the tissue so it becomes stronger.

Further detail

• Exercise-related chemical reactions that break down carbohydrates and fats release heat, and the heat produced is directly related to the amount of muscular work performed.

• Warming makes muscles more pliable and flexible, helping them stretch further, improving joint flexibility, and reducing susceptibility to muscle strains.

• During high-intensity exercise, anaerobic work produces lactate, which the course associates with a burning sensation and rapid fatigue that can impair muscle contraction if it is not removed.

• Delayed onset muscle soreness (DOMS) is muscle pain occurring 24–48 hours after strenuous exercise that can last up to 3 days and is associated with exercise-related microtears, particularly in people inexperienced with the intensity.

💡 Memory Hook

Exercise raises muscle work → oxygen demand, heat, and fatigue responses increase.

📖 7. Long-Term Muscular Adaptations

🔑 Key Concepts & Definitions

• Hypertrophy: An increase in muscle size caused by muscle fibres enlarging as their muscle-cell protein content increases, following regular overloaded resistance training.
• Myoglobin: A muscle protein that binds and stores oxygen in skeletal muscle and transports it to mitochondria, supporting energy production.

★ Must-know

• Muscle hypertrophy provides more room for mitochondria, and an increase in mitochondrial number and size improves the muscle's ability to produce aerobic energy and can improve aerobic performance.

• Endurance training increases capillarisation, improving blood delivery of oxygen and nutrients and removal of waste; improved use of fat and oxygen lets muscles work at higher intensity with less lactate, delaying onset of blood lactate accumulation (OBLA) and fatigue.

Further detail

• Regular exercise overload strengthens tendons; regular exercise also increases the flexibility and strength of ligaments and tendons around joints, while cartilage becomes thicker.

• Long-term exercise adaptation increases muscle glycogen storage, allowing training at higher intensities for longer; muscle glycogen can produce energy without oxygen.

• Well-trained athletes can use fat stores more efficiently by breaking fat down into fatty acids and using oxygen to produce energy, including when carbohydrate becomes scarce.

💡 Memory Hook

Regular overload → larger, stronger muscle fibres.

📖 8. Additional Factors Affecting Muscles

🔑 Key Concepts & Definitions

• Cramp: A sudden, involuntary muscle contraction that can be painful and may be associated with exercise, dehydration, or inadequate blood supply.

★ Must-know

📌 Under the all-or-none law, a nerve impulse must be sufficient to activate at least one motor unit; once activated, all muscle fibres in that unit contract, or none do.

• Age-related muscle loss, called sarcopenia, begins around age 50; physically inactive people can lose 3% to 5% of muscle mass per decade after age 30, and active people also experience some muscle loss.

Further detail

• Most muscle cramps develop in the leg muscles, particularly the calf; drinking plenty of fluid during physical activity, especially in hot weather, and stretching can help prevent cramp.