Unit 4 option C: Human health & fitness C.2 Exercise physiology; exercise & the musculo- skeletal system. By Mr. Wilson

ATP & contracting muscles 3 ways ATP is generated for contracting muscles: 3 ways ATP is generated for contracting muscles: Lactic acid system - medium bursts of vigorous exercise (400m sprints). Lactic acid system - medium bursts of vigorous exercise (400m sprints). Aerobic respiration – prolonged exercise (marathon). Aerobic respiration – prolonged exercise (marathon). ATP-PCr (phosphocreatine) system – short sharp bursts of vigorous exercise (100m sprint). ATP-PCr (phosphocreatine) system – short sharp bursts of vigorous exercise (100m sprint).

ATP-PCr system

Muscle spindles Intrafusal muscle or muscle spindles have attached sensory neurones. Intrafusal muscle or muscle spindles have attached sensory neurones. Information about muscle contraction from all over the body is sent to the brain for processing via action potentials. Information about muscle contraction from all over the body is sent to the brain for processing via action potentials.

Motor units A motor neurone & its motor fibres (muscle fibres). A motor neurone & its motor fibres (muscle fibres). Few fibres per neurone = precise finely co-ordinated movements Few fibres per neurone = precise finely co-ordinated movements Many fibres per neurone = not so precise movement. Many fibres per neurone = not so precise movement. What is the neurotransmitter here? What is the neurotransmitter here?

Types of muscle contraction

Muscle strength Depends on cross-sectional area. Depends on cross-sectional area. Wider muscles have more myofibrils (as more protein is laid down). These generate greater shortening forces and are thus considered stronger. Wider muscles have more myofibrils (as more protein is laid down). These generate greater shortening forces and are thus considered stronger. These muscles, however, fatigue quicker through depletion of ATP (and glycogen stores & accumulation of lactic acid). These muscles, however, fatigue quicker through depletion of ATP (and glycogen stores & accumulation of lactic acid).

More on fatigue… Continual stimulation of muscle over an extended time decreases its ability to contract with the same strength! Continual stimulation of muscle over an extended time decreases its ability to contract with the same strength! Seen as – Low O 2 availability, increased lactic acid accumulation, depletion in K + ions. Seen as – Low O 2 availability, increased lactic acid accumulation, depletion in K + ions. Caused by – Excessive activity, malnutrition, cardiovascular problems, pulmonary problems, excessive alcohol consumption Caused by – Excessive activity, malnutrition, cardiovascular problems, pulmonary problems, excessive alcohol consumption

Anaerobic respiration & the oxygen debt If anaerobic respiration is required in exercise lactic acid will be produced from the reduction of pyruvate. If anaerobic respiration is required in exercise lactic acid will be produced from the reduction of pyruvate. This is cleared from muscle by the blood to the liver to be re- oxidised to pyruvate & then glycogen. This is cleared from muscle by the blood to the liver to be re- oxidised to pyruvate & then glycogen.

Summary of effect of exercise on muscle (short term). Blood flow increase of up to x 25. Blood flow increase of up to x 25. Creation of an oxygen debt (after PCr depleted & AR commences). Creation of an oxygen debt (after PCr depleted & AR commences). Fatigue – Inability to maintain muscle contraction of the same force. Caused, in part, by toxicity of lactic acid. Also caused by depletion of ATP & glycogen stores. Then…. Fatigue – Inability to maintain muscle contraction of the same force. Caused, in part, by toxicity of lactic acid. Also caused by depletion of ATP & glycogen stores. Then…. Exhaustion – depletion of K + ions in muscle cells. Exhaustion – depletion of K + ions in muscle cells.

Summary of effect of exercise on muscle (short term). Cramp – powerful sustained contractions after heavy over exercise. Made worse by lactic acid, cold & low concentrations of salt. Cramp – powerful sustained contractions after heavy over exercise. Made worse by lactic acid, cold & low concentrations of salt. Damage – Tearing/straining – common when not ‘warmed up’. Shorter tighter muscles more prone (heavy exercise). Muscle soreness caused by tissue inflammation. Damage – Tearing/straining – common when not ‘warmed up’. Shorter tighter muscles more prone (heavy exercise). Muscle soreness caused by tissue inflammation. Glycogen & K+ depletion – May take several days of recovery to restore. Glycogen & K+ depletion – May take several days of recovery to restore.

Summary of effect of exercise on muscle (long term). Muscle size – Genes/testosterone influence. Exercise may increase diameter of fibres by up to 60%. Muscle size – Genes/testosterone influence. Exercise may increase diameter of fibres by up to 60%. Co-ordination – improves responses. Co-ordination – improves responses. Blood supply – more extensive. Blood supply – more extensive. Muscle cell mitochondrial efficiency increases up to double. Increased numbers increase enzyme activity. Energy stores increased & fatty acid stores released more readily. Muscle cell mitochondrial efficiency increases up to double. Increased numbers increase enzyme activity. Energy stores increased & fatty acid stores released more readily.