Neuromechanics Weekly: No video this week, but check this out….

a little neuro that is, at least, peripherally related to running, for this beautiful Saturday Morning…

A question from one of our readers.

Dr Ivo

I am a runner and often get fatigued and tired, even after a short run. I have had a complete blood work up which was negative, as was my physical exam. My Dr prescribed Zanaflex for muscle spasms and I take ibuprofen prn

The short answer: Stop taking Zanaflex (Tizanidine)

The long answer…

Hmmm. Let’s see. Tizanidine ( mm relaxant ) is a alpha 2 adrenergic agonist (ie they promote activity of alpha 2 receptors). This means it acts on adrenergic receptors (ones that respond to epinephrine and norepinephrine) as opposed to cholinergic receptors (which use acetylcholine as a neurotransmitter). Adrenergic agents usually causes a sympathetic response, like pupil dilation, or increased heart rate.

Adrenergic receptors are usually either alpha or beta subtypes. Alpha receptors usually cause vasoconstriction of arteries to the heart, vasoconstriction of veins, and slowing of the GI tract.

There are 2 classes of alpha adrenergic agonists,

alpha 1: Alpha-1 adrenergic agonists stimulate alpha-1 receptors coupled to G proteins and phospholipase C. They cause vasoconstriction (contraction of blood vessels) and mydriasis; they are used as vasopressors, nasal decongestants and in eye exams. They can be classified in two groups: those which do not cross the blood-brain barrier and have peripheral effects and those which penetrate into the brain and have mainly central effects.

alpha 2: inhibit adenylyl cyclase activity.  alpha 2 adrenoceptors are often located on the sympathetic nerve terminals that inhibit the release of norepinephrine and therefore act as a feedback mechanism for modulating the release of norepinephrine. In other words , they inhibit release of epinephrine and norepinephrine (or slow sympathetic activity). Sympathetic activity (like increased heart rate with exercise and vasodilation of capillaries in muscle, to provide more oxygen supply and remove metabolites) is necessary for us to function during exercise performance. Tizanidine falls into this category.

Aren’t you glad you asked?

We remain, undisputedly, Gait AND Neuro Geeks…The Gait Guys