Muscle Responses to Training Objectives: Define key terms hyperplasia, hypertrophy. Explain how training increases muscle strength

Homework: Long Answer Question: A tennis player needs to use their muscles to exert different amounts of force throughout a match. Use your knowledge of muscle contraction to explain how this is possible. (12 marks)

A tennis player needs to use their muscles to exert different amounts of force throughout a match. Use your knowledge of muscle contraction to explain how this is possible. (12 marks) What should be included in a good answer? mechanism of muscle contraction – sliding filament theory different fibre types explanation of motor unit methods of changing amount of force: number of units recruited type of units recruited frequency of stimulation

Mechanism of muscle contraction Action potential arrives at neuromuscular junction ACH released Binds to receptors on sarcolemma wave of depolarisation in muscle t-tubules Sarcoplasmic reticulum releases Ca2+ Ca2+ binds to troponin moves tropomyosin this leaves the binding sites on the actin free Myosin heads attach to actin binding site to form cross bridges ATP required to form cross bridge. Myosin head moves towards the centre/power stroke occurs Actin slides over the myosin/actin moves towards the centre of the sarcomere Cross bridge then broken but can be recreated if calcium ions are still present ATP is also required to allow the myosin to break the cross bridge Muscle shortens and movement generates force Max 7

Different fibre types: Type I / slow twitch fibres are aerobic contract slowly do not fatigue produce low force Type II b / Fast Glycolytic fibres are anaerobic contract quickly produce high / highest force fatigue quickly Type IIa / Fast Oxidative fibres are anaerobic Contract quickly Have some resistance to fatigue Max 5

Explanation of motor unit Each nerve innervates a number of muscle fibres / definition of motor unit Same type of fibre in each motor unit All or None / Nothing law Methods of changing amount of force: more units recruited means more force larger units recruited means more force ST units produce lowest force / FT units produce highest force All units recruited for maximum force. Max 5

Frequency of stimulation: Single nerve impulse produces twitch Wave summation – several impulses in quick succession increases strength of contraction Tetanic contraction – sustained stimulation reaches maximum force of contraction but fatigues quickly Spatial summation – different motor units contracted at different times to maintain level of force without fatigue. Max 6

What happens in / to your muscles when you train? It depends… What does it depend on? Type of training Type of muscle fibre

Nature vs Nurture

Aerobic Training of Type I fibres Muscle fibre hypertrophy (fibres get larger) in mitochondrial size and density in activity of oxidative (aerobic) enzymes in muscle myoglobin triglyceride and glycogen stores capillarisation

Resistance training of Type II fibres Hypertrophy of Type II fibres Hyperplasia (splitting and production of new) of Type II fibres activity of glycolytic (anaerobic) enzymes muscle ATP and PC stores Improved buffering capacity (tolerance of lactic acid)

Aerobic Training of Type II Fibres Conversion of Type IIb fibres to Type IIa fibres through: mitochondrial density capillarisation triglyceride stores myoglobin

CELLULAR ADAPTATION PRODUCED BY AEROBIC TRAINING AFTER SEVERAL WEEKS OF AEROBIC TRAINING BEFORE TRAINING glycogen fats oxygen uptake glycogen fats oxygen uptake = SLOW TWITCH MUSCLE FIBRE (type I) = FAST TWITCH MUSCLE FIBRE (type II) (do not increase in size)

CELLULAR ADAPTATIONS PRODUCED BY STRENGTH TRAINING AFTER SEVERAL WEEKS OF STRENGTH (ANAEROBIC) TRAINING MUSCLE CELL BEFORE TRAINING ATP PC glycogen glycolytic enzymes lactic acid ATP PC glycogen glycolytic enzymes lactic acid = SLOW TWITCH MUSCLE FIBRE (type I) (starts small gets smaller) = FAST TWITCH MUSCLE FIBRE (type II) (starts big gets bigger)

Read the review article on the evidence for hyperplasia Pick out what you think are the 5 most important/interesting/relevant pieces of evidence supporting the occurrence of muscle hyperplasia.

A2 revision guide