MEASUREMENT OF MUSCLE STRENGTH

Muscle strength  can be  evaluated in a number of ways: manually , functionally, or mechanically.

The Oxford Scale

The Oxford scale has been devised to manually assess muscle strength and is widely used by physiotherapists. According to the Oxford scale, muscle strength is graded 0 to 5.

                                                                           

                                                  Summarises the grades

                                                 

     Grade                         Muscle contraction

        0                               No contraction

        1                              Flicker of a contraction


        2                              Full-range active movement with gravity eliminated (counterbalanced)


        3                              Full-range active movement against gravity


        4                              Full-range active movement against light resistance.


        5                              Normal function/full range against strong resistance.

There are limitations to the usefulness of the Oxford scale. These include:

• A lack of functional relevance.

• Non-linearity (the difference between grades 3 and 4 is not necessarily the same as the 

difference between grades 4 and 5).

• A patient's variability with time (rarely falling into a fixed category).

• A degree of subjectivity between assessors.

• Assessment of muscles acting only concentrically

• The  difficulty  of applying  the  scale  to   all  cases  in  clinical practice (so that strength is rarely evaluated throughout full range since many individuals seen by   physiotherapists   do not  possess full range in the first place).

Functional Tools

Functional tools can be used to evaluale strength and can be related to a specific activity or to  one of  its   components . These   tools  are commonly   employed    when   rehabilitating sportsmen back   to   competition .  Sport -  specific   activities   can   be  monitored   by     a physiotherapist with knowledge of the demands of a parlicular sport.



Isokinetic Assessment


Isokinetic  assessment  has  been  used  With  increasing  frequency since it's    inception in the 1970s. IT involves the use of computerized evaluation of movement when  exercising at a preset angular velocity on the isokinetic equipment. This means that the subject can push as hard or as  little  as   desired and the  machine  will  move only at the preset velocity . It is therefore the resistance provided by the machine that varies.

Use  of   isokinetics   has   functional   relevance   since  it  can  evaluate  both eccentric and concentric  activity  through  range.



Drawbacks

The  drawbacks  of  isokinetics  relate to its function , as  natural human  movements  rarely occur at  fixed  velocities . Also  the  machine  operates  on  a fixed axis of movement, which does not  replicate  the  instantaneous axis  of  movement found in most normal joints . The equipment  can  also  be  time - consuming  to  set  up  and not all physiotherapists will have access to it.

Additional limitations have  been  acknowledged by  Lieber (1992). These  include  the  time required to recruit muscle fibres (50-200 milliseconds) making this period of data  obtained unusable. Another drawback is the limb striking the testing bar at the end of the movement, although some isokinetic units employ a damping mechanism to prevent this .