1. Muscle Speed and Tone

2. Muscle Fibres Muscles are made up of cells called fibres.
Muscle contract (shorten) because the fibres do.
All the fibres do not contract at once.
The number contracting depends on how much force is needed.
You use more muscle fibres to lift 100kg than 10kg.

3. Two types of muscle fibres
Slow twitch – contract slowly, and without much force. But they do not tire easily. They are suited to endurance activities.
Fast twitch – contract much faster than slow twitch fibres, and with much more force. But they do tire quickly. They are suited to activities that require short bursts of strength and power.

4. Every muscle contains a mixture, but:
The mixture is different in different muscles.
Your gastrocnemius contains a lot of fast twitch fibre. Standing on your toes gets tiring.

5. The mixture is different for different people.
Some distance runners have 80% slow twitch fibres while some weight lifters have 80% fast twitch fibres.

6. Why the difference?
It’s your parents fault!!
You inherited the mixture from them and it’s too late to change it now.
Can you train your muscles to react differently?

7. How muscle speed affects performance
The more fast twitch fibres you have, the more suited you are to sports that need bursts of strength and power.
Think About!!
“Suppose two sprinters X and Y are competing. They are the same age and weight and at the same level of fitness. But X has 75% fast twitch fibre in her leg muscles and Y has only 55%. So X should be able to start faster, accelerate faster and sprint faster than Y. She has a better chance of winning!”

8. Muscle Tone
Even when a muscle is relaxed, a small number of its fibres are contracted – enough to keep the muscle taught but not enough to cause movement. This state of partial contraction is muscle tone.
Without muscle tone you would not be able to stand up straight, keep your head up.
Poor muscle tone leads to poor posture. That is why it is important to also train your muscles by doing resistance exercises.

9. Think about!!
What muscles are being worked in the following exercises:
Press up
Chin up
Bench Press
Leg extension/curl
Step ups
Sit ups