Muscle Fibre Types

Muscle Fibre Types

Slow twitch fibres:

Slow Oxidative (Type I)

Fast twitch fibres: Fast Glycolytic (Type IIb) Fast Oxidative Glyc. (Type IIb)

A. Slow Twitch Fibres

• Suited for repeated contractions during activities

requiring a force output of < 20-25% of max force

output

• Examples: lower power activities, endurance events

B) Fast Twitch Fibres

• Significantly greater force and speed

generating capability than slow twitch fibres

• Well suited for activities involving high power

• Examples: sprinting, jumping, throwing

Myoglobin

• Protein that delivers oxygen to muscles

• Slow-twitch muscles are _____ in myoglobin

• Fast-twitch muscles are ______ in myoglobin

Approximate Distribution of Muscle Fibre Types for Different Sports

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

3 Fibre Types Type I or Slow-Oxidative (SO)

Generate energy slowlyFatigue-resistantDepend on aerobic processes

Type IIA or Fast-Oxidative Glycolytic (FOG) Intermediate-type muscle fibresAllow for high-speed energy releaseAllow for glycolytic capacity

Type IIB of Fast-Glycolytic (FG)Store glycogen and high levels of enzymesAllow for quick contraction without the need for oxygen

The Muscle BiopsyUsed to determine muscle fibre type

1. Injection of local anesthetic into the muscle being sampled

2. Incision of approximately 5-7mm is made in the skin and

fascia of the muscle

3. The piece of tissue (250-300mg) removed via the biopsy

needle is imbedded in OCT compound

4. The sample is frozen in isopentane cooled to –180C

Oxidative fibres

Small diameter

Muscle Biopsy

• Muscle stained with myosin ATPase

• Black = Type II

• Light = Type I

• Proportion is genetically determined

Characteristics of Different Muscle Fibre Types

Distribution of Muscle Fibre types

• Tonic muscles– Maintain posture– Type I– Soleus (for dorsi flexion)

• Phasic muscles– Type IIA and IIB– biceps