Slow Twitch and Fast Twitch Muscle Fibres Did you eat white meat or dark meat over the holidays?

Slow-Twitch  Most active during: long-distance running, swimming, and cycling  Red or dark in colour  Generate and relax tension slowly; able to maintain a lower level of tension for long durations  Low levels of myosin ATPase and glycolytic enzymes  High levels of oxidative enzymes

Fast-Twitch  Ideal for: short sprints, power lifting, and explosive jumping  Pale in colour  Ability to tense and relax quickly; generate large amounts of tension with low endurance levels  High levels of myosin ATPase and glycolytic enzymes

Fast vs. Slow

Approximate Distribution of Muscle Fibre Types for Different Sports

The Importance of Myoglobin The difference in _____________________ is determined by the amount of ____________ used in energy production Myoglobin: ____________________________

Myoglobin Slow fibres vs. Fast fibres – Slow twitch fibres are __________ in myoglobin – Fast Twitch Fibres have ______________ amounts of myoglobin

3 Fibre Types  Type I or Slow-Oxidative (SO)  Type IIA or Fast-Oxidative Glycolytic (FOG)  Type IIB of Fast-Glycolytic (FG)

Why the Split of Type II Fibres? Studies have shown that there is evidence for changing the type ________to Type ______ muscle fibres with endurance training THERE IS NO WAY ANY TYPE ___ MUSCLE FIBRES CAN BECOME TYPE ____ In other words a fast twitch muscle can _________become a slow twitch muscle

Characteristics of Different Muscle Fibre Types

So how are the fibres distributed? How a muscle works is determined by its fibre type and vice versa TWO categories for basic muscle functions: – Tonic – Phasic

Tonic Muscles These are used on a daily basis for High concentration of _________ twitch fibres (Type I) Great for endurance activities Core and back muscles: constantly contracted

Phasic Muscle Higher percentage of ________ twitch fibres Example: Biceps have a lower amount of Type I fibres and a higher amount of type II because they are used for explosive movement (lifts)

So how do you find where these fibres are? The only true way is to do a _____________to find the percentage of each type of fibre. Muscle biopsy: tissue sample using a needle to take a small amount from the muscle belly

Athletic Performance Elite athletes may have __________% of a specific fibre type in their body

Why does Kenya keep winning in long distance? You are going to read a short article on page 91 Answer the following questions – What has been found regarding the Kenyan’s muscle fibre type? – What social factors have played a large role in Kenyan runners?