Laurie's Blogs.

Well, this part of the discussion interests me the most.  Mostly because I had the good fortune to get to listen to Dr. Paul Hodges (a motor control & timing / back pain guru from the University of Queensland) lecture on this subject more than once.  

Here’s what I consider to be a good definition of motor timing:  A consistent pattern of anticipatory muscle activity associated with a specific movement task.  I can’t even give you a good source for that.  I just read a bunch of abstracts on muscle timing, muscle activation, and muscle recruitment, and compiled that definition based on the readings.

I have typically thought of motor timing, as it has been described in relation to deficits found in people with back pain, and based on research like the following:

• Patients with low back pain, in contrast to healthy control subjects, demonstrated a significantly different muscle response pattern in response to sudden load release.  These differences may either constitute a predisposing factor to low back injuries or a compensation mechanism to stabilize the back.  (Radebold et al, 2000.)
• Patients with non-specific low back pain demonstrated significantly delayed trunk muscle onset latency and shorter burst and co-contraction durations. (Mehta et al, 2010)
• Changes in trunk muscle recruitment have been identified in people with low-back pain (LBP). These differences may be due to changes in the planning of the motor response or due to delayed transmission of the descending motor command in the nervous system.  While inhibition of the descending motor command cannot be excluded, it is more likely that the change in recruitment of transverse abdominis represents a more complex change in organisation of the postural response. (Hodges PW 2001)

As such, I think of descriptions such as “deficits of the feedforward mechanism for muscle activation” or “improper or altered timing of muscle contractions associated with a certain movement” when I think of motor timing issues.  Interestingly, because the research I had seen and became familiar with was also associated with back pain.  I have always equated motor timing deficits with pain.  But perhaps that is not always so.

We also see altered muscle activation / timing in clinical trials assessing the impact of muscle fatigue:

• Trunk muscle fatigue alters anticipatory postural adjustments in normal subjects. (Allison & Henry, 2002)
• Muscle fatigue yields trunk muscle pattern activation deficits similar to those seen in chronic low back pain patients.  Specifically, a delay of the first burst of muscle activity after impact (a weight suddenly dropped onto a held tray).

Furthermore, when specifically studied to see whether changes in automatic postural control / adjustments were the result of pain interference, Moseley & Hodges (2005) concluded the following:  “The results suggest that altered postural adjustments of the trunk muscles during pain are not caused by pain interference but are likely to reflect development and adoption of an alternate postural adjustment strategy, which may serve to limit the amplitude and velocity of trunk excursion caused by arm movement.”  Okay, so the trouble isn’t pain inhibition, but rather altered postural strategies.

But motor control deficits / abnormal recruitment strategies can happen in muscles and joints other than the trunk, and for reasons other than pain and fatigue.

Recently in the discussion on this topic on the FourLeg Forum (all stemming from the blog: Do Dogs Really Need Core Stability?), there has been a new (to me) finding / theory proposed.  One I had never heard of - that of Latent Myofascial Trigger Points (LMTrPs) and their impact on muscle firing / timing!  Let’s take a look at some research:

• Both hosted and synergistic muscles experience delay in muscle activation and alterations in their recruitment pattern during rapid arm elevation in all planes of movement. These changes may serve as adaptive motor control strategies due to the presence of LMTrPs in upper trapezius muscles. (Bohlooli N et al, 2016)
• MTPs are associated with reduced efficiency of reciprocal inhibition, which may contribute to the delayed and incomplete muscle relaxation following exercise, disordered fine movement control, and unbalanced muscle activation. (Ibarra et al 2011)
• A latent MTP is associated with an accelerated development of muscle fatigue and simultaneously overloading active motor units close to an MTP. (Ge et al, 2012)

Interesting, no?!  Now, the MTP model won’t fit for all types of motor timing / activation deficits, but it would certainly account for some – as the research shows!

What does this mean for you?

There are so many things to look at when evaluating a patient!  And we really do need to look at how we assess for motor timing deficits!  What I’ve come up with is the 3-leg slide of the pelvic limb.  One could do the same with the front limb… but how do we assess for all muscles and joints?!  

I’ll take your ideas and suggestions!  And I’ve love to hear your thoughts and clinical experiences with any of the above as it related to dogs.  Let’s see what we can come up with!

Until your brain settles down for the next time… Cheers!  

Laurie

References:

Radebold, A, et al.  Muscle response pattern to sudden trunk loading in healthy individuals and in patients with chronic low back pain.  Spine. 2000; 25(8): 947-954.

Mehta R et al. Altered trunk motor planning in patients with nonspecific low back pain.  J Mot Behav. 2010; 42(2): 135-144.

Hodges PW.  Changes in motor planning of feedforward postural responses of the trunk muscles in low back pain.  Exp Brain Res. 2001; 141(2): 261-266.

Allison GT, Henry SM. The influence of fatigue on trunk muscle responses to sudden arm movements, a pilot study.  Clin Biomech (Bristol Avon). 2002; 17(5): 414-417.

Moseley GL, Hodges PW.  Are the changes in postural control associated with low back pain caused by pain interference? Clin J Pain. 2005; 21(4): 323-329.

Bohlooli N, et al. Differential activation of scapular muscles, during arm elevation, with and without trigger points.  J Bodyw Mov Ther. 2016; 20(1): 26 – 34.

Ibarra JM, et al. Latent myofascial trigger points are associated with an increased antagonistic muscle activity during agonist muscle contraction. J Pain. 2011; 12(12): 1282-1288.

Ge HY, et al. Accelerated muscle fatigability of latent myofascial trigger points in humans.  Pain Med. 2012; 13(7): 957-964.