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We have detailed elsewhere why we feel handheld dynamometry is important. We feel that, definitively, these device can provide more valid, reliable results than MMT alone. However, just because you have a better tool doesn't mean that it is being used correctly. 

We have made a useful chart to help guide you on what is a good test and what isn't. Let's break it down. 

Is it repeatable?

Do what you can to standardize the test. You will likely want to come back and re-measure at some point, you need to make sure you are measuring it the same way each time. Measuring shoulder flexion? Is you dynamometer at the wrist or elbow? I see people test hip abduction in sidelying all the time. I think this is a remnant of our manual muscle test training where a 3/5 is against gravity. But anyone who has ever done this knows it can be tough to get a patient into the perfect testing position. Wouldn't it be more repeatable to test in supine? 

Have you isolated what you want to test?

Before testing, you need to decide what your goal is. If you want to know how strong a specific muscle is, make sure there isn't anything else that contribute force to your test. If you are more interested in a movement, i.e. shoulder internal rotation, that's fine too. Just make sure you set up for that. 

Is it comfortable?

This one is pretty simple. If your test hurts, they wont push into it as hard as they can. Make sure you have adequate padding. 

Are you testing in mid-rage?

Rememebr the length-tension relationship? To crudely summarize, most muscles are strongest when they are in their mid-range of motion. You wouldn't want to measure hip flexion strength at 120* of hip flexion if you are interested in how strong hip flexors are. This wont give you an accurate picture of how much force these muscles can generate. We see this get messed up with hip extension all the time. 

If you test in prone, pictured here, your hip is within a few degrees of maximal extension. You just cant produce much force in this position.

Compare that to the example below.  

We would call this a much more appropriate test to determine the force producing capacity of the hip extensors.

Don't take our word for it though, lets look at the data. 

When testing hip extension at multiple different positions, Bazett-Jones found the following average hip force values. Notice that -10* of hip extension is about 1/4 the force of the hip in 90* of hip flexion. Test in mid-range.

Unless you have a specific reason not to...

The obvious example here would be shoulder external and internal rotation at 90/90. Or maybe you have a swimmer and would like to measure the shoulder at full flexion? Go for it. We certainly think this can be valuable information that can guide your decision making. 

How high are the forces?

It's important to know how much force the tester can resist versus how force the subject can create. 

Let me give you an example. Knee extension is the obvious place to start. It is not breaking news that dynamometers can be useful for testing quad strength. For one, the research has estabilshed that quad strength is an important outcome for many populations (ACLR, knee OA). We also know that quads are very strong. 3.0 Nm/Kg is a commonly used benchmark which roughly equates to about 100% of your bodyweight in freedom units (ft*lbs/lbs). So, an athlete that is 180 pounds, should be able to produce about 180 ft*lbs of torque. Making some assumptions on limb length, that's around 135 pounds of force through the dynamometer (remember handheld dynamometers measure linear force, electromechanical dynamometers measure rotational torque: you need to multiply by limb length to compare directly). We use dynamometers to be more reliable with our testing. This amount of force CANNOT be reliably resisted with your hands alone. See the picture below. We contend that this is a reeeeaaaaly good way to get kicked in the chin. External fixation MUST be used in this situation. 

For weaker muscles, it's absolutely fine to use true handheld set-ups for testing. A good check is to determine what the tester's maximum is for a given position: push into a wall as hard as you can and see what the dynamometer says. If your test is showing over 50% of your push-into-the-wall-max, you should use external fixation (straps in pull mode or holster in push mode).  

Follow these rules and you will be well on your way to performing better strength tests. Look for a preferred testing position document coming soon. Until then, #testdontguess, y'all.