Isotonic contraction (iso-same, tonweight/ resistance) 
1. In isotonic contraction the length of the muscle changes but the tension remains constant.
2. Here, the force produced is unchanged.
3. Eg: Lifting dumbbells and weight lifting.

Types of movement: The different types of movements that occur in the cells of our body are amoeboid, ciliary, flagellar and muscular movement.
1. Amoeboid movement:
Cells such as macrophages exhibit amoeboid movement for engulfing pathogens by pseudopodia formed by the streaming movement of the cytoplasm.
2. Ciliary movement:
This type of movement occurs in the respiratory passages and genital tracts which are lined by ciliated epithelial cells.
3. Flagellar movement:
This type of movement occurs in the cells which are having flagella or whip-like motile organelle. The sperm cells show flagellar movement.
4. Muscular movement:
The movement of hands, legs, jaws, tongue are caused by the contraction and relaxation of the muscle which is termed as the muscular movement.

The muscle contracts when the myosin shifts. The lack of ATP after death prevents it from relaxing and the muscle remains contracted. Such process occurs in all muscles and the body becomes rigid.

Skull bones.

A. I Bands.

Cranium, facial bone, Bones of middle, ear, and Hyoid bone.

(i) Exercise and physical activity fall into four basic categories. Endurance, strength, balance and flexibility.
(ii) Endurance or aerobic activities increase the breathing and heart rate. They keep the circulatory system healthy and improve overall fitness.
(iii) Strength exercises make the muscles stronger. They help to stay independent and carry out everyday activities such as climbing stairs and carrying bags.
(iv) Balance exercises help to prevent falls which is a common problem in older adults. Many strengthening exercises also improves balance.
(v) Flexibility exercises help to stretch body muscles for more freedom of joint movements.
(vi) Regular exercises can produce the following beneficial physiological changes:
(vii) The muscles used in exercise grow larger and stronger.
(viii) The resting heart rate goes down.
(ix) More enzymes are synthesized in the muscle fibre.
(x) Ligaments and tendons become stronger.
(xi) Joints become more flexible.
(xii) Protection from heart attack.
(xiii) Influences hormonal activity.
(xiv) Improves cognitive functions.
(xv) Prevents Obesity.
(xvi) Promotes confidence, esteem.
(xvii) Aesthetically better with good physique.
(xviii) Overall well-being with good quality of life.
(xix) Prevents depression, stress and anxiety.
(xx) During muscular exercise, there is an increase in metabolism. The O₂ need of the muscles is increased. This requirement is met with more oxygen rich RBCs available to the active sites.
(xxi) There is an increase in heart rate and cardiac output. Along with balanced diet, physical activity plays a significant role in strengthening the muscles and bones.

The Rib cage:

(i) There are 12 pairs of ribs.
(ii) Each rib is a thin flat bone connected dorsally to the vertebral column and ventrally to the sternum.
(iii) It has two articulation surfaces on its dorsal end hence called bicephalic.
(iv) The first seven pairs of ribs are called 'true ribs' or vertebro-sternal ribs.
(v) Dorsally they are attached to the thoracic vertebrae and ventrally connected to the sternum with the help of hyaline cartilages.
(vi) The 8^th, 9^th and 10^th pairs of ribs do not articulate directly with the sternum but joined with the cartilaginous (hyaline cartilage) part of the seventh rib.
(vii) These are called 'false ribs' or vertebrochondral ribs.
(viii) The last 11^th and 12^th pairs of ribs are not connected ventrally. Therefore, they are called as 'floating ribs' or vertebral ribs.
(ix) Thoracic vertebrae, ribs and sternum together form the ribcage.