Strength Testing

by Stephen Holt, MD, MS

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    00:00 So we're going to start with the cervical spine and I always start with the number five because cervical roots 1, 2, 3, and 4 are more involved with muscles around the neck and they're a little bit more tricky to tease apart and more importantly, people rarely get radiculopathy involving those nerve roots, so we'll start with C5 and I'd like to envision that you draw a number five and then if you actually tilt that number five, 90 degrees and have it flat and then put another number five mirroring that on the other side, you actually start to get the shape of a person who's actually flexing their muscles, they're actually showing off their biceps.

    00:42 And at the same time they've got their shoulders abducted which means that they're flexing their deltoid muscles.

    00:49 So it turns out that that simple mnemonic helps us to remember that the C5 nerve root is innervating your biceps muscles and your deltoid muscles.

    00:58 So how about just with your right arm show me you C5s.

    01:01 So by him doing this potion, he's showing me his deltoids, he's showing me his biceps, this is the C5 nerve root.

    01:09 Next up, we'll do C6, where I want him to extend his wrist like so, that's C6 and very simply, the other way, which is lifting your wrist up and that's C7.

    01:20 Now you'll note, by the way, when I say strength you really want to make sure you're isolating one joint at a time.

    01:26 A lot of times I see people when they're testing strength, they'll do something like this — put your hand up like this and now push me away.

    01:33 When he does this, now he's winning because he's stronger than I am.

    01:36 He's testing or I am testing his deltoid muscle, the stabilizing forces around his scapula, his rhomboids.

    01:42 He is doing his biceps or his triceps muscle in this case and his wrist extensors all at the same time — that is not an effective way to assess or to locate a specific area of weakness.

    01:52 So instead — go like up, up this again for me, now I want you to push me away.

    01:57 I'm now testing a single muscle group, just the muscles that work around to extend his arm or extend his elbows, so it's important to really make sure you're isolating your muscle groups by going basically just hold between one joint and the next to make sure that you're not going to get confused.

    02:15 So, again, start off with C5, go like this for me.

    02:18 I'm just going to push down, that's his C5s. Up like this, this is also C5s.

    02:24 Now we'll do C6, put your wrist out like this or flip them over like this, excuse me, and wrist extension, now I'm just going to pull up testing wrist extension that's C6.

    02:34 Now have your wrist go up and I'm going to pull down, that's wrist flexion which is C7.

    02:40 C8 and T1 all involve the interosseous muscles and the muscles of the thumb.

    02:46 It's not important to know exactly which one is which, it's just important to know how to test very quickly the musculature of the hand, so I simply do, I simply do this exercise — put your fingers out like this and we do finger cutting where I just want you to basically squeeze my fingers with your fingers, perfect.

    03:02 Make an okay sign and don't let me pull through, great, I pulled through but that's okay.

    03:08 Already.

    03:10 It's okay. You do the same thing on both sides.

    03:13 Anytime you're comparing, many times you're checking strength you always want to be comparing one side and then the other to makes sure you're able to get an accurate control group in a person who has symptomatology.

    03:23 So as we're about to move on to assessing strength, it's important for us to use the right terminology to describe how strong somebody is or how weak they are, and there's an accepted scale that we use from zero to five, five being full strength and zero meaning we don't feel any muscle activity or whatsoever.

    03:41 So 5 strength. Put your arm up for me like this and he can push me away with ease, he's got full strength in his triceps in this case.

    03:49 4 out of 5 is actually broken up into three parts, 4+, 4, and 4-. 4+ is 75% strength, so he's still going to probably win but I'll be able to fight back.

    04:00 4 is just 50% strength, it's clearly going to be noticeably weaker and then 4- is only 25% strength.

    04:08 From 4 to 3, means that if he was lifting his biceps, he could lift it against gravity so that's at least a 3, but if I pull down on his arm, his no longer able to compete against me with gravity.

    04:23 So it means you can only lift against gravity if you have 3 out of 5 strength, so go ahead and show me a 3 out of 5, and I'm going to resist him and now he can't fight back.

    04:33 2 out of 5 strength is where, while he couldn't lift against gravity, he can still move the arm left and right which is where gravity is not competing with him, so just move your forearm left and right there so that's 2 out of 5 strength, and then lastly, 1 out of 5 strength is where I can feel his biceps tensing, I can feel him trying to move, but he actually doesn't have enough strength to actually move his forearm in space, so that would be 1 out of 5 strength, as opposed to 0 out of 5 strength which is just there's no muscle tone whatsoever.

    05:05 So with that foundation, we're going to go ahead and move on and to start assessing individual muscle groups in his body.

    05:12 Alright, so having discussed the different innervations for the upper extremity and the different cervical roots involved, we're now going to move on to the lower extremities and take a look at the lumbar roots involved.

    05:22 Just like we had a simple mnemonic for remembering that C5 involves your biceps and your deltoids, for the lumbar, for the lumbar nerve roots there's a similar mnemonic that I use and it's simply that we both, we generally have two legs and they start up here at the top at your groin crease around the hips and so the start of the lower extremity exam is going to be L2, two legs.

    05:45 So with that in mind, your hip flexors are L2 your L2 nerve roots so just lift up your knee against resistance, that's L2.

    05:54 Next up, we'll move from one joint to the next, so if this is L2, this is going to be L3, very simple.

    06:00 So I just want you to lift up your leg, great, against resistance, that's L3.

    06:05 Next up, he's going to dorsiflex his foot, that's L4.

    06:09 Next joint, now here is his great toe, lift up your great toe for me, that's L5.

    06:14 And now we're going to wrap around all the way to the back of his heel and I want you to basically plantar flex which is push your foot down, great.

    06:24 So that's S1 in the back there.

    06:27 Keep in mind as I said earlier that generally there's more than one nerve root innervating any particular muscle, this is just a simple way to remember the most dominant nerve root involved in a particular muscle movement.

    About the Lecture

    The lecture Strength Testing by Stephen Holt, MD, MS is from the course Examinations of the Neck and Back Region.

    Included Quiz Questions

    1. C5/biceps and deltoid
    2. C6/wrist flexion
    3. C7/wrist extension
    4. C4/biceps and deltoid
    5. C8/wrist extension
    1. Knee extension/L3
    2. Hip flexors/L4
    3. Knee extension/L5
    4. Hip flexors/L5
    5. Plantar flexion/L4
    1. Can lift against gravity
    2. 25% of normal motor strength
    3. 50% of normal motor strength
    4. Cannot lift against gravity
    5. 75% of normal motor strength

    Author of lecture Strength Testing

     Stephen Holt, MD, MS

    Stephen Holt, MD, MS

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