Why Manual Muscle Testing is Eroding the Physical Therapy Profession
Manual Muscle Testing (MMT) never made sense to me in school. Its utility further baffled me during my clinicals and early years as a clinician when I would routinely notice other clinicians dishing out the same strengthening exercises regardless of the patient’s MMT scoring. Today, I consider MMT to be nothing more than a screen rather than a true assessment of strength.
At one time, MMT was a useful tool when it was first developed during the pre-World War I poliomyelitis epidemic when portable dynamometers weren’t even a thing. But, even by the mid-1900’s, researchers knew the reliability of MMT was suspect. Fast-forward 100 years, and even with the incredible advancement of technology and research, we’re still doing the same thing.
MMT has evolved into a silent, profession-eroding problem because of the nearly unanimous use by therapists to justify their entire Plans of Care and insurance reimbursements on the results of a flawed testing system.
Simply put, MMT is not sensitive enough. A shoulder grade of 5/5 still cannot detect a 11-28% strength deficit when measured with isokinetic testing. Similar findings have shown that side-to-side differences could only be detected manually if there was greater than a 15-25% strength deficit.
As a profession, we are already not challenging our patients enough. Even in elderly populations, our APTA knows this to be true and has made a campaign to address this.
MMT just poisons the well by enabling us to justify substandard care.
Why are we staking our reputations on a flawed and antiquated form of objective measuring?
Here’s a scenario that occurs almost monthly in my clinic: We get a referral from one of our surgeons to strength test an athlete after they have been ‘cleared’ by another hospital system to return to sport. Isokinetic dynamometry shows a 40% strength deficit between sides. Because they were discharged from their previous PT, insurance will not cover additional sessions to actually strengthen them because this other therapist deemed the athlete ‘strong’ based off of 5/5 MMT.
MMT has been shown to be unsuitable for use with patients who have MMT scores of 4 and higher. So, why do we depend on this for our athletes and higher level orthopedic patients especially if the scoring can be easily biased?
Charlatans are the best at biasing MMT results especially when justifying the magical powers of a copper/magnet/ion bracelet.
“OK Dustin, just like we practiced.”
Well, What Are Our Alternatives?
Max Strength Testing
An estimation of a patient’s 1 repetition maximum (1RM) is a low-tech option to determine a patient’s strength. However, inaccuracies of strength have been documented.
In a recent JOSPT article, it was found that leg press and leg extension 1RM measures overestimated strength by 23.6% and 5.4% respectively with an ICC of <.70.
However, in a clinical setting, traditional 1RM testing is unrealistic. Therefore, 1RM calculations are a safer alternative, but they may not always produce accurate results and usually underestimate the actual 1RM.
In research, isokinetic dynamometry has established itself as the gold standard in strength testing. We know that a quadriceps strength deficit of >10% increases ACL re-injury by 4 times per isokinetic standards. MMT is not that sensitive to detect these deficits. Even closed kinetic chain strength testing fails to capture 23-26% quad strength deficits compared to OKC isokinetic testing.
The price tag of a refurbished unit will run your clinic about $15,000. In our clinic of two full-time therapists we can recoup the costs after 6 months of using the unit 2-4x/day. If you still can’t sway your clinic owner to purchase one, make it a priority to collaborate with a clinic in your area who does.
If this is all still too unrealistic, every clinic should have, at the very least, a hand-held dynamometer.
Hand-held dynamometers (HHD) have been around for decades and today a device will run you about $1,000 which is most certainly a more budget friendly and practical proposal.
But, is it worth getting? Let’s check out the validity/reliability studies.
A 2011 systematic review examined the validity of HHD compared to isokinetic dynamometry. In their review of 19 studies, the authors concluded that there was minimal differences between HHD and isokinetic testing. The authors do note in their limitations that there continues to be a fundamental lack of consensus for patient/practitioner positioning as well as force application.
In general, the reliability research of HHD has shown its clinical relevance to be favorable. However, a 2014 systematic review of HHD and upper extremity strength testing in 54 studies showed 26 of these studies had an ICC of >.90. Due to the risk of bias in these studies, the authors concluded that PT’s should not rely on HHD for the evaluation of upper extremity disorders. However, again there was no consensus on the testing procedure in this report which may explain the variability in the findings.
We know that the strength of the examiner matters. In general, it was found that the reliability of HHD was excellent if the force output of the patient was <120N (27lbs). This study showed that reliability correlates with the strength of the examiner.
In the aforementioned 2017 JOSPT article comparing HHD, 1RM, and isokinetic testing, the authors concluded that 1RM leg extension (from 90° and 45°) and HHD (fixated at 90°) provide the best alternatives to Biodex testing in measuring quad strength.
In an ideal orthopedic setting, an isokinetic dynamometer would be in every clinic with MMT only utilized in the most limited of situations. As a compromise between science-based medicine and practicality, HHD and 1RM should be the minimal standard in strength testing.
Below we have put together clinic friendly charts to use as a reference if you decide to utilize HHD.
HHD Normative Data Charts
Clink on the links below to download the PDFs