Neuromechanics Weekly: Look to the hammy’s???
“These findings show that while we always consider the tightness of the gastrocnemius/soleus complex and the subsequent restricted ankle motion from this equinus, we also need to consider the role of the hamstrings,” said Jonathan Labovitz, DPM, lead author and associate professor at Western University of Health Sciences, Pomona, CA.
this article from Lower Extremity Review, concludes “After controlling for covariates, participants (86 of 210 feet) with hamstring tightness were 8.7 times as likely to experience plantar fasciitis (p < .0001) as participants without hamstring tightness. Patients with a BMI >35 were 2.4 times as likely as those with a BMI <35 to have plantar fasciitis.”
The question is why?
They go on to say “ If you can’t get dorsiflexion at your talo-crural joint, this often drives dorsiflexion at other joints and that is going to cause collapse of the longitudinal arch of the foot, loading the plantar fascia with increased tensile stress.”
So, loss of ankle rocker leads to increased midfoot pronation, which loads the plantar fascia. That sounds pretty logical to us. We are sure you are thinking a loss of hip extension may do the same thing. Correct. Or you may say ” The calves may be tight so the medial gastroc can invert the rearfoot to correct for too much midfoot pronation and the foot can be supinated"…and you would be correct again.
So why are the tight hammys driving the bus? Or are they?
We remember the hams are a 2 joint muscle, and with the foot in a closed chain position (ie, on the ground); they flex the thigh on the lower leg and tilt the pelvis posteriorly (ie reduce the lordosis). They are FLEXORS which are active from late swing phase, just prior to heelstrike (initial contact) and a little nudge just prior to toe off (preswing) to help extend the thigh.
The tricep surae are FLEXORS and are supposed to be active from loading response till almost pre swing, with a burst of activity at heel lift (terminal stance).
So they take turns, and are not firing (normally) at the same time (or maybe have a small overlap). Going from heel strike to heel strike, the hammys fire 1st.
So IF the two are related, it could be a neurological sequencing issue. How often does that happen? The literature says (and there aren’t many studies) that you can change the order of recruitment of motor units ( the nerve and the muscle fibers it innervates), but not (usually) individual muscles. So probably not.
OK, how about plan B?
The hams and tricep surae are all flexors, correct? What is the innervation to the hamstrings and tricep surae? Hmm….Hamstrings, mostly tibial branch of the sciatic nerve, short head of biceps femoris is the common peroneal: L5-S2. How about the tricep surae? Tibial nerve, mostly S1-S2. I think I see a trend here. Common neurological overlap of FLEXOR muscles.
So are the hams driving the bus? Probably not, but neither are the gastroc/ soleus. The FLEXORS are driving the bus, and excitation of that common neuronal pool is probably causing the tightness
Ivo and Shawn….Uber footgeeks of the web. Dicing and slicing through the literature so you don’t have to.