Muscle Strength

Original Editor - The Open Physio project.

Top Contributors - Pieter Jacobs, Lucinda hampton, Naomi O'Reilly, Jo Etherton and Alistair James  

Introduction

MMT muscle.jpg
An assessment of muscle strength is typically performed as part of a patient's objective assessment and is an important component of the physical exam that can reveal information about neurologic deficits. It is used to evaluate weakness and can be effective in differentiating true weakness from imbalance or poor endurance. It may be referred to as motor testing, muscle strength grading, manual muscle testing, or many other synonyms. Muscle strength can be assessed by a number of methods: manually, functionally or mechanically. [1]


Function

The function of muscle strength testing is to evaluate the complaint of weakness, often when there is a suspected neurologic disease or muscle imbalance/weakness. It is an important part of the assessment in many client groups including


The Oxford Scale

The most commonly accepted method of evaluating muscle strength is the Oxford Scale (AKA Medical Research Council Manual Muscle Testing scale). This method involves testing key muscles from the upper and lower extremities against the examiner’s resistance and grading the patient’s strength on a 0 to 5 scale accordingly[1]:
  1. Flicker of movement
  2. Through full range actively with gravity counterbalanced
  3. Through full range actively against gravity
  4. Through full range actively against some resistance
  5. Through full range actively against strong resistance

Commonly tested muscles include the shoulder abductors, elbow flexors, elbow extensors, wrist extensors, finger flexors, hand intrinsics, hip flexors, knee extensors, dorsiflexors, great toe extensor, and plantar flexors. These muscle groups are commonly chosen, so that important spinal nerve roots are assessed systematically eg testing the strength of the elbow flexors, elbow extensors, wrist extensors, finger flexors, and hand intrinsics allow for a methodical evaluation of the C5 to T1 nerve roots[1].

This short mute video is a good introduction.

[2]

There are a number of limitations to the usefulness of the Oxford scale.[3] These include:

  • Poor functional relevance;
  • Non-linearity i.e. the difference between grades 3 and 4 is not necessarily the same as the difference between grades 4 and 5;
  • A patient's variability over time i.e. alternating between grades due to fatigue;
  • Intra-rater reliability;
  • Only assesses muscles when contracting concentrically;
  • The difficulty of applying the Oxford Scale to all patient's in clinical practice (so that strength is rarely assessed throughout full range as many patients assessed by physiotherapists do not possess full range due to their respective pathology).

Due to these shortcomings, physiotherapists commonly use modified versions of the Oxford scale in clinical practice. [4]

Performing Manual Muscle Tests

The following links demonstrate Manual Muscle Testing of specific joints and movements:

Upper Extremities Lower Extremities
Shoulder Flexion Hip Flexion
Shoulder Extension Hip Extension
Shoulder Abduction Hip Abduction
Shoulder Horizontal Adduction Hip Adduction
Scapula Elevation Hip External Rotation
Scapular Retraction/ Adduction Hip Internal Rotation
Elbow Flexion Knee Flexion
Elbow Extension Knee Extension
Wrist Flexion Plantarflexion
Wrist Extension Dorsiflexion
Ankle Eversion
Ankle Inversion

Dynamometer

Grip .jpg
Distal strength can be semiquantitatively measured with a handgrip ergometer (or with an inflated BP cuff squeezed by the patient) to record grip strength. Requires specialized equipment, most commonly dynamometers. Dynamometry is a more precise measurement of the force that a muscle can exert and can allow for differences in strength to be recorded over time. Expensive versions exist as do cheap versions as found on internet searches.


Functional Testing

Five Times Sit to Stand Test.jpg
Often provides a better picture of the relationship between strength and disability. As the patient does various maneuvers, deficiencies are noted and quantified as much as possible (eg 30 second sit to stand test, TUG.).
  • Rising from a chair or stepping onto a chair tests proximal leg strength, walking on the heels and on tiptoe tests distal strength.
  • Pushing with the arms to get out of a chair indicates quadriceps weakness.
  • Swinging the body to move the arms indicates shoulder girdle weakness.
  • Rising from the supine position by turning prone, kneeling, and using the hands to climb up the thighs and slowly push erect (Gowers sign and seen in Duchenne gait) suggests pelvic girdle weakness.[5]

Clinical Significance

Muscle strength testing can help diagnose many problems in which weakness is a plays a role. Careful technique is important for ensuring valid and reproducible results. The Oxford Scale is commonly accepted and does not require special equipment, and demonstrates reasonable interrater reliability. More precise methods of measurement, such as hand-grip dynamometry, are less subjective and provide a quantifiable measurement that can be tracked over time[1]. However, a cross-sectional study (2020) shows a lower correlation between the handgrip strength and standard strength measures of the lower limbs (hip, knee, and ankle extensor/flexor muscles), and functional capacity in older women[6]. Functional assessment of strength focuses on how independently patients are able to perform their activities of daily living and whether strength is a limiting factor[1].

References

  1. 1.0 1.1 1.2 1.3 1.4 Naqvi U. Muscle strength grading. InStatpearls [Internet] 2019 May 29. StatPearls Publishing. Available from: https://www.ncbi.nlm.nih.gov/books/NBK436008/ (last accessed 7.1.20)
  2. Vibro56 MMT Available from:https://www.youtube.com/watch?v=gDFhiVCMPm8&t=15s (last accessed 19.12.2019)
  3. Cuthbert SC, Goodheart GJ. On the reliability and validity of manual muscle testing: a literature review. Chiropractic & Osteopathy 2007; 15:4
  4. Porter S. Tidy's Physiotherapy. Edinburgh: Churchill Livingstone, 2013.
  5. Merck Manual How to assess muscle Strength. Feb 2018 Available from:https://www.merckmanuals.com/professional/neurologic-disorders/neurologic-examination/how-to-assess-muscle-strength (last accessed 7.1.2020)
  6. Rodacki AL, Moreira NB, Pitta A, Wolf R, Melo Filho J, Rodacki CD, Pereira G. Is Handgrip Strength a Useful Measure to Evaluate Lower Limb Strength and Functional Performance in Older Women?. Clinical Interventions in Aging. 2020;15:1045.