Intensity:
The physiological stress on the body during exercise. Your level of intensity can be readily determined by measuring your pulse rate (heart rate) immediately following an exercise bout.

Interval Training:
Training made up of successive bouts of exercise at near maximal intensity alternated with periods of rest or lighter exercise such as brisk walking or slow jogging.

Isometric:
This is a type of muscle contraction in which the muscle generates force but does not undergo significant shortening, such as pushing against a wall.

Isotonic:
This is a type of muscle contraction in which the muscle generates force against a constant resistance resulting in movement, such as curling a 40-pound barbell.

Illness Symptoms that upset your health.

Incomplete Proteins Proteins which are low in one or more of the essential amino acids.

Iso kinetic Exercise Isotonic exercise in which there is ACCOMMODATING RESISTANCE. Also refers to constant speed. Nautilus and Cybex are two types of iso kinetic machines, where machine varies amount of resistance being lifted to match force curve developed by the muscle.