1. Muscles pairs
And other things

2. Three Main Types of Muscel Fibers
Slow Twitch oxidative fibers (I)
Fast Twitch A (II-A)
Fast Twitch B(II-B)

3. Slow Twitch Oxidative Fibers (I)
Oxidative (uses oxygen to create energy)‏
Very fatigue resistant
Posture muscles

4. Fast twitch A (II-A)‏ oxidative rapid contractions
relatively fatigue resistant
sprinter's legs

5. Fast twitch B (II-B)‏ >glycolytic rapid contractions
easily fatigued
>arm muscles

6. The diagram shows the structure of the muscles
The diagram shows the structure of the muscles. The inset picture (brown colored) shows you the fast and slow twitch fibers. Lighter = fast twitch / darker = slow twitch.

7. Muscles have opposing pairs
Muscles can only pull not push
So they can only move a bone or joint in one direction.
It requires another muscle to move it back

8. Who are some common pairs?
Triceps and Biceps -bending and straightening the elbow
deltoids and lattisimus dorsi - lifting the arm and lowering the arm
abdominals and erector spinae- bending the spine forward and backward

9. A few more groups
hip abductors and adductors - moving the legs apart and together
quadriceps and hamstrings - bending and straightening of the knee
gastrocnemius and tibialis anterior - standing on your toes or pulling your toes up toward your shin

10. A couple more
pectorals and trapezius - moving the arms/shoulders forward and backward (arms are held horizontal and shoulder high for this movement)‏
iliopsoas and gluteals- lifting the knee or moving the knee backward

11. Natural muscle imbalances
Daily use tends to strengthen one part of the pair more than the other
Ex:
Biceps – lift against gravity, therefore they are stronger than triceps.
Turning your head in one direction, or using one arm more strengthens one set of muscles, but can weaken or shorten others

13. How can this hurt us? Imbalances can lead to muscle pain
Most lower back problems are from muscle imbalances
one way is abdominal muscles become weak but erector spinae becomes too strong, pulling the pelvis into the wrong position

15. So, let's work those muscles...
But don't forget to work both parts of the pair.
You might also need to work a weaker member of a pair to strengthen it or to stretch it.
If you carry heavy groceries or kids, you might need to work on your triceps.