Muscles to allow us to do all the functional activities we want to perform, from walking to climbing stairs to typing and doing precise work. Our muscles can deliver huge amounts of power and endurance as well as highly co-ordinated and skilled manipulations. Loss of feeling may be more important in a limb but loss of sufficient muscle power compromises our independence particularly as we get older and find difficulty performing routine actions for ourselves. Muscle power can be reduced by a large number of causes including not using them when ill and forced to rest, pain from injury or operations, stroke or other neurological condition, disease and illness. Muscle power is evaluated using the five step Oxford Scale.
If there is no muscle activity, either visible or with examination of the tendon and muscle belly after several attempts by the patient to perform the muscle action then the muscle is graded as zero. A small muscle contraction such as a twitch, without any joint movement, is rated as one. When the muscle can do its joint action but without the force of gravity resisting the movement then this is graded as two, but the joint needs to be in the right position for correct testing. If the muscle can perform its typical action against the force of gravity then it is rated as three. An example is bending the elbow whilst standing up, where the biceps is working against gravity.
Grade 4 means that the muscle can move the joint through range both against gravity and against resistance such as a weight or the physiotherapist's manual resistance. The amount of resistance is not stated but has to be judged as reasonable for the age, weight, health and normal status of the patient. Grade 5 muscle power is normal power, but this again is a judgment for the patient as a young rugby player will have much greater normal power than an elderly lady, although both might be Grade 5. Some parts of the body cannot have their strength tested manually as the muscles are too strong for the hands to resist appropriately. Bodyweight will need to be the resistance here.