Question

Define isotonic and isometric contractions.

Answer 1

Hint: Isotonic, iso means same and tonic means tension so isotonic literally refers to the same tension. Similarly, isometric, iso means same and metric means a measure of length so isometric refers to the same length.

Complete answer
Muscles work in different ways depending on the types of activities which require muscle contraction. The action of actin and myosin cross-bridge cycling generates tension in the muscle fiber. The muscle may lengthen, shorten, or remain the same when under tension.
Isotonic Contractions: Isotonic contractions maintain constant tension as they contract or shorten. Tension will develop up to a certain level. After this level, the tension is constant. This occurs when maximal force of contraction of muscle exceeds the total load on the muscle.
Examples of isotonic exercise include stair climbing, bicep curls, push-ups and squats.
Isometric Contractions: The force during isometric contractions is produced without change in the length of the muscle. The muscle itself does not change in length while the tension never exceeds the opposing force. Example: the muscles found in the hands and forearm: these muscles do not change length, and joints are not moved, so force for grip is sufficient.
An example is when the muscles of the hand and forearm grip an object; the joints of the hand do not move, but muscles generate enough force to prevent the object from being dropped.

Note:
When referring to the muscular system, the term contraction implies shortening. Isometric exercises can help to strengthen a muscle. A third type of muscle contraction is also there known as isokinetic meaning same motion i.e. the muscle shortens at a consistent rate throughout the motion.