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5. Fibre Types, Genetics and Muscle Spindles.docx

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Western University
Kinesiology 2230A/B
Glen Belfry

Lecture 5 Bodybuilding: must have balance all over the body Right before competitions, competitors try to deplete the muscle of glycogen because it is stored with water • They will try to burn as much as possible and eat few carbohydrates so they do not get glycogen stores in the body (as well as adipose tissue) Muscle Size and Power • The size of the muscle in an individual differs based on the number of contractions per second they perform  energy system specific • Need more maximal energy when performing one contraction because of increased force produced • Decrease in muscle mass as number of contractions increases (and therefore force decreases) Fibre Types and Increasing Force As the intensity of work increases… • First recruit slow twitch fibres  max them out (maximum amount of tension from them) • Then the 2A fibres increase the force generated  max them out • finally recruit fast twitch b fibres  hit maximum force While training, you must make sure you are recruiting all fibres maximally to get the greatest adaptation of all the fibres Summary of Muscle Fibres Aerobic uses fat for energy All fibres use glycogen Recruitment pattern: how often they are recruited • 2B seldom used Influence of Exercise Bout Intensity on Fibre  Recruitment As the intensity of the exercise increases, initially high oxidative fibres are recruited immediately. You must get to a reasonably intense exercise before you begin to recruit low oxidative fibres • The high oxidative will max out when low oxidative fibres are recruited Summary of Fibre Types Contraction Actin ATPase (slow): increases the strength of the interactions within the actin filaments and to the myosin head in slow twitch fibres. It enables generation of repeated contraction over long time period SDHase: Kreb’s Cycle enzyme – represents oxidative activity Type 1 Fibre • Postural muscles are all slow twitch In skeletal muscle there is no change in the force generated from particular fibres even though they are recruited up to 60 minutes of stimulation • Cannot generate large amounts of force but can generate it for long periods of time 1. Slow Recruitment and relaxation 2. Low myosin ATPase because it does not generate large amounts of force 3. High Actin ATPase to allow for repeated contractions 4. High SDHase because of oxidative capacity 2A Fibre 75% maximum force  can maintain for relatively long periods of time (3-4 minutes of intense movement) • After this point and continuing onto 60 minutes you continually lose force • After 2 minutes you can still generate reasonable power. After about 6 minutes you are starting to become fatigued 2B Fibre Steady decrease in force. By 2 minutes of exercise the force generated is minimal. 1. fast contraction, slower relaxation 2. High Myosin ATPase to break down ATP faster 3. Low in Actin ATPase and SDHase because of short duration and low oxidative capacity 4. Myelinated to create faster contraction Fibre Type Variability Different muscles have different variability of fibre type because of the adaption of the muscle to the function it is used for. Soleus muscle: there is a fair bit of variability in the slow twitch composition of the muscle • In general it still has a very high amount of slow twitch • Small muscle Vastus lateralis: Relatively even distribution of slow and fast twitch Gastronemius: A higher composition of fast twitch Triceps: Fairly high percentage of fast twitch fibres Gender There is greater variability of fibre types in males • There is also generally more fast twitch fibres in males and more slow twitch in females Muscle Fibre Composition and Function • Different muscles have different fibre compositions probably related to function • Typically successful athletes have fibre type profiles that may vary with event Someone with a higher ST
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