Download Muscle Contractions

Concentric Contractions:
This contraction shortens your muscle as it acts against resistive force (weight). For
example, during a biceps curl, the biceps contract concentrically during the lithe lifting
phase of the exercise.
Eccentric Contractions
During these contractions, the muscles lengthen while producing force—usually by
returning from a shortened (concentric) position to a resting position. The lowering
the weight down during a biceps curl is an eccentric contraction for the biceps.
You're basically slowing the descent of the weight back down instead of allowing the
weight (and gravity) to just pull your arm back down passively.
Isometric Contraction—Muscle Actively Held at a Fixed
Length
Isometric contraction, is one in which the muscle is activated, but instead of being
allowed to lengthen or shorten, it is held at a constant length. An example of an
isometric contraction would be carrying an object in front of you. The weight of the
object would be pulling downward, but your hands and arms would be opposing the
motion with equal force going upwards. Since your arms are neither raising nor
lowering, your biceps will be isometrically contracting. The force generated during an
isometric contraction is wholly dependent on the length of the muscle while
contracting
Frequency and Intensity
Frequency refers to how often you perform something, either the total number of
workouts or a specific movement.
Intensity refers to the level of difficulty of the workout.