Eccentric (n)  ec·cen·tric is a term used to describe a type of movement or exercise.

Eccentric Definition:

The word concentric is most commonly used in sports science and medicine. In these settings eccentric defines a type of exercise or movement.

Translated literally eccentric means away from the centre. 

Concnetric (n)  con·cen·tric is a term used to describe a type of movement or exercise.

Concentric Definition:

The word concentric is most commonly used in sports science and medicine. In these settings concentric defines a type of exercise or movement.

Translated literally concentric means towards the centre. 

Isotonic (n) literally means equal tension. In exercise science isotonic contraction is a contraction in which the tension remains constant as the muscle shortens or lengthens. i·so·ton·ic (adj.) (s-tnk)
 

Isotonic is fixed resistance variable speed movement.

The term isometric (n) comes from the Greek "ios" which means the same, and "metric" which means distance. i·so·met·ric (s-mtrk) Combined together they make a static contraction where there is no perceivable motion. There are two types of isometric resistance:-
  • An immovable force (overcoming isometric)
  • An opposing resistance (yielding isometric) which is what isokinetics machines produce

Isometric is variable effort against an immovable force

Isokinetic (n)  is a term used to describe a type of movement or exercise.
 
Isokinetic or Isokinetics Definition:
 
The word isokinetic is most commonly used in sports science and medicine. In these settings isokinetic defines a type of exercise or movement.
 
Translated literally isokinetic (i·so·ki·net·ic pronounced ī'sō-kə-nĕt'ĭk) means movement at a constant speed. 
 
The key to isokinetic movement or exercise is this:
 
The speed of the motion is always kept the same even as the resistance alters.