5.2.1 User Manual Isoforce
REV 5
01st July 2014
page 7 von 77
TUR Therapietechnik GmbH | Grubenstr. 20 | 18055 Rostock | Germany
1.1 About contractions
1.1.1 Concentric
Concentric, when literally translated, means towards the middle. This type of contraction occurs when
the tension generated within the muscle is sufficient to overcome a resistance (in most cases at least
gravity) to move a body segment (or the attachment of the muscle on that body segment) towards
another segment (or the origin of the muscle in question) or vice versa. This type of contraction is
dependent on one end of the muscle having more stability than the opposite end. The term dynamic
shortening seems to be a more appropriate way of describing concentric contractions.
1.1.2 Eccentric
Eccentric, when literally translated, means away from the middle. Whenever a muscle lengthens it
generates a contractile force meaning all movements in the body occur with some muscular activity
(this is absolute). The term lengthening is actually misleading as in most instances the muscle does not
actually lengthen. In reality it returns from its shortened condition to its normal resting length. In most
instances in which muscles contract eccentrically they actually act as a brake or resistive force against
the moving force of gravity or other external force (like a weight). This work is often referred to as
negative work for reasons I do not understand. Eccentric actions produce greater loading of the elastic
musculoskeletal components and are used during many dynamic movements (like walking down stairs
or hitting a ball). As the majority of muscle tears are thought to occur during eccentric motions
improvements in this performance may be beneficial for injury prevention. However, eccentric motions
produced by active dynamometers are not considered to be like those seen during functional activities.
Short and rapid eccentric motions are normally produced during daily and sporting activities,
isokinetically this is not seen as the movements are usually long and through full range of motion.
1.1.3 Isometric
Isometric, when literally translated, means equal length. When a muscle is contracted without any
appreciable change in length this is referred to as isometric contraction. This term is abused by
researchers, exercise scientists and physiotherapists to describe many different situations in which a
muscle is contracted but cannot be said to be acting either concentrically or eccentrically.
1.2 Exercise Types
Different type exercise programs are available that apply Davis’ Law to produce better integrity of the
joint. There are three basic types outlined: isometric, isotonic, and isokinetic. Isotonics can be divided
into a concentric (positive) movement, an eccentric (negative) movement, and variable resistance. The
isokinetic type can also be divided into a concentric or eccentric movement or both.
These types of exercises can be defined and contrasted in terms of the speed of movement and the
resistance applied. In isometrics, we know that the speed of movement is zero and the resistance is
fixed. In isotonics, on the other hand, the speed is variable, generally fluctuating around 60° as
demonstrated in weight lifting where there often is a slowing of movement at the weak points in the
range of motion (ROM). The resistance in isotonics is fixed (the amount of weight lifted). In isokinetics,
