Strength Testing: Manual Muscle Testing and Dynamometry

MMT is appropriate for some cases, but it’s generally less sensitive and less specific than dynamometry. Objective measurement with instruments brings greater validity and reliability to your test.

Let’s talk about strength testing! Measuring isometric strength is one of the first assessments we perform on a patient or injured athlete. This process is performed daily in almost any rehabilitation setting, including Physicians’ offices. Strength testing is a vital part of our job and the services we provide to our patients and referral sources.

We have two options for measurement: manual or with instruments. Manual Muscle Testing (MMT) is appropriate for some cases, but it’s generally less sensitive and less specific¹. Objective measurement with instruments brings greater validity and reliability to your test. In this article we’ll analyze five methods of measuring strength, including MMT and dynamometry. First, let’s start with a history of manual measurement.

History of MMT

Manual Muscle Testing measures the maximum force a muscle or muscle group can produce. This type of evaluation likely began centuries ago in China. However, the Royal Central Institute of Gymnastics in Sweden formed the first school devoted to studying manual therapy, physical therapy, massage, and medical gymnastics in 1860.²

This early group produced important research and literature that paved the way for today’s clinical practice. For example, American Physician Dr. George H. Taylor published “Exposition of the Swedish Movement-Cure” in 1860, a key precursor to work by Harvard’s Dr. Robert Lovett in the early 1910s. Further studies and books by Physical Therapists Henry and Florence Kendall (founding member of APTA in Maryland), Catherine Worthingham, Lucille Daniels, and Marian Williams form the basis of today’s MMT techniques².

Performing MMT

Manual Muscle Testing is best in the prone and supine positions, but you can also do it with the patient seated or standing. Typically, you won’t use any strapping that would minimize contributory muscle activation. MMT can help isolate and identify the injured muscle. It can also help determine whether there is a neurological impairment from injury, aging, or another factor.

Make or Break MMT

Two types of MMT are the ‘make’ and ‘break’ tests. The make test assesses the full maximum voluntary isometric contraction they can produce. In a purely manual test, the patient pushes against your body, usually your hands. Without a dynamometer, the clinician estimates the amount of force and compares it bilaterally. The key to this test is that the clinician is stronger than the patient³.

In a break test, the patient resists the increasing pressure that you apply.  During this eccentric phase, you are looking for the muscle / muscle group to eventually break away, especially if there is acute injury or chronic pain.

We are very familiar with how to grade break testing with a scale of zero to five. A five represents “strong” or “facilitated” and a zero represents “weak” or “functionally inhibited.”⁴ You can also use the terms “none” to “normal.”⁴ We can agree that it is pretty easy to grade a 0 or a 5 but achieving specificity within that range is difficult, and quite subjective. If you want to learn more about make and break testing and their cited literature, I recommend this study from the Journal of Chiropractic Medicine.

Objective Strength Testing

The demand for objective measurement in rehab is growing day by day. If you receive reimbursement for your services, you are likely required to provide specific information about a patient’s status.  If you’re preparing an athlete to return to full sports participation, you would likely be asked to provide objective documentation on their functional abilities.  The better documentation you provide, the more transparent you can be to your payers and patients.

Objective measurement goes beyond these documentation benefits. Think about the impression it makes for patients who can see their strength gains quantified with real numbers. That’s indisputable data showing the progress they’ve made. Say goodbye to early dropouts or complaints of not making progress. Objective measurement may be the key to keeping patients motivated and demonstrating the value of your sessions.

Strength Testing With Dynamometry

Using a dynamometer is the best way to measure strength objectively. Also known as quantitative muscle testing, this technique of measuring force is both reliable and valid. There are three types of dynamometers: fixed, portable fixed, and hand-held.

Fixed Dynamometers

Fixed dynamometers are particularly well-suited for measuring isometric strength. Regardless of the strength of the patient or the clinician, the fixed position provides the most accurate way to measure force.  Better yet, the values it produces are meaningful and it clearly demonstrates the symmetry between limbs or between the agonist and antagonist muscles surrounding a joint.

Fixed dynamometers like those found in BTE’s PrimusRS, Simulator II, and EvalTech, are the most consistent way to measure strength. Especially for research purposes, strength tests must be reproducible between tests. If you test the joint one way during an initial evaluation and in a different manner later, what is the point?  You have wasted your time as the data is not meaningful. The ability to set up a device and know that you or another clinician can replicate the same test is paramount to the test’s reliability.

Portable Fixed Dynamometers

A fixed dynamometer works wonders in the clinic, but you may need a portable solution. Consider the ability to measure joint strength in various places around the clinic, on the playing field, at a work site, or even in a patient’s home.

Portable fixed dynamometers can be affordable, easy to use and reproducible in any setting. They’re especially helpful where clinics and clinicians are limited on space, time, and resources.  Doing more with less is something that we have likely all encountered at some point in our careers (and maybe even still do now).

Portable fixed dynamometers allow you to quickly assess strength in an objective, valid, and reliable way, anywhere you need it. Take our newest evaluation product, the EVJ for example. The key to its precise measurement is a load cell that is fixed at both ends or a wall or table to provide a stable testing anchor point. This small unit measures force of push or pull and is flexible enough to measure isolated movements and functional activities.

Hand-held Dynamometers

As a low-tech option, simple hand-held dynamometers are inexpensive, easy to use, and they can move from location to location. While these devices are still objective, research shows significant limitations. First, they lack consistency of patient positioning, which impacts the nature of the movement⁵. Second, there is no clear way to see rates of force production⁵. Third, these tools have been shown to widely underestimate force⁶.

Hand-held dynamometry is also less applicable to the entire body and functional activity. You have probably used a hand grip or pinch gauge to measure these isolated movements, but there aren’t many standardized methods for other joints.

Research Comparing Three Types of Dynamometry

A 2013 study compared the test-retest reliability and validity of isometric knee-flexion and extension using three different methods⁷.  Researchers tested each subject using a fixed isometric dynamometer (specifically, the EvalTech), a portable fixed dynamometer, and a hand-held dynamometer. The following day, the examiner performed the same tests.

Test-retest reliability is expressed as a rating between 0 and 1. Anything above 0.9 has excellent reliability, and anything below 0.5 has poor reliability. Analyzing the results, the researchers considered the EvalTech fixed dynamometer the “gold standard” of measurement with a reliability of 0.93. The portable fixed dynamometer came in close second at 0.92. In contrast, the hand-held dynamometer showed poor reliability of 0.49⁷. According to the study, fixed dynamometry is a near-perfect test for muscle strength.

Conclusion

Doing a MMT or break test allows you to feel an obvious discrepancy between limbs.  However, even to an experienced clinician, the ability to quantify that value and quickly identify the difference between the two limbs is very difficult. There are multiple ways of reporting and quantifying muscle strength with objective dynamometry, and we owe it to ourselves and to our patients to give them as much information as possible.

 

Jeff Johnson, MA, ATC
Clinical Specialist
BTE

 

References

1. Baschung Pfister P, de Bruin ED, Sterkele I, Maurer B, de Bie RA, et al. 2018. Manual muscle testing and hand-held dynamometry in people with inflammatory myopathy: An intra- and interrater reliability and validity study. PLOS ONE 13(3): e0194531.
2. Manual Muscle Testing. Kinesiology.com. https://www.kinesiology.com/manualmuscletesting/
3. Rarick L., Gross K., Mohns M. Comparison of two techniques of measuring strength of selected muscle groups in children. Res Q. 1955;26:76–79.
4. Kendall F.P., Kendall McCreary E., Provance P.G. 1993. Muscles—testing and function.4th ed. Williams and Wilkins. pp. 179–190.
5. Stark T, Walker B, Phillips JK, Fejer R, Beck R. 2011. Handheld dynamometry correlation with the gold standard isokinetic dynamometry: a systematic review. PM R.3(5):472–479. https://pubmed.ncbi.nlm.nih.gov/21570036
6. Martin HJ, Yule V, Syddall HE, Dennison EM, Cooper C, Aihie Sayer A. 2006. Is hand-held dynamometry useful for the measurement of quadriceps strength in older people? Gerontology 52(3):154–159. https://pubmed.ncbi.nlm.nih.gov/16645295/
7. Toonstra J, Mattacola CG. Test-Retest reliability and validity of isometric knee-flexion and –extension measurement using 3 methods of assessing muscle strength. J Sport Rehabil. 2013; Feb 18; Technical Notes(7). pii:2012-0017. https://pubmed.ncbi.nlm.nih.gov/22951307/