Endurance can be broken into two categories; muscular endurance and metabolic endurance. In the previous blog we discussed how range of motion can have a direct impact upon endurance - which is what we will discuss today. To better understand how range of motion and muscular endurance relate we need to define workspace. The work space of a joint is the range of motion that you can actively achieve. Check out the video below for an example.
Muscles are recruited (used) through the activation of the spindle cell. The spindle cell is a stretch receptor that is housed within the muscle belly - there are thousands of spindle cells in each muscle. As the muscle is loaded the muscle spindle will stretch to match the extent of the load, the spindle will then send a signal to the spinal cord which will send a signal to the same muscle to contract.
The Sensory Fibers and Intrafusal Fiber make up the Muscle Spindle. The extrafusal fiber is the contractile muscle that we are familiar with
Multiple muscle spindles must be stretched to create a meaningful muscle contraction - the activation of multiple spindles is called summation. Temporal summation is the time based increase of stretched muscle spindles. When a muscle is under load for a prolonged period it will fatigue allowing more stretch of spindles resulting in more muscular contraction. Spatial summation is the simultaneous stimulation of multiple spindle cells - this can happen due to an increase in load or moving through a greater range of motion.
We can look at walking/running to get a better understanding of the relationship between range of motion and muscular endurance. In walking or running gait the glute muscle group (butt cheek) is one of the main muscles pushing us forward and stabilizing the leg while it’s on the ground. If we are lacking flexion, extension, or rotation range of motion within our hips the force the glutes will be able to generate is greatly diminished (decreased opportunity for spacial summation). As the glute fatigues stability of the limb will be lost and the hamstring, calves, and/or low back will take over the job of moving us forward.
If you feel beat up after your long runs or part way through your morning walk your knees or back start getting a little spicy this is a mechanism worth looking into. I’m not saying that all muscular endurance is contingent upon having healthy ranges of motion - this is just some low hanging fruit when it comes to building more endurance in movement.
There you have it, another reason to plan and make time for recovery and mobility work. Get in the habit of checking on how well your body is moving and developing mobility and flexibility. You won’t just feel better - you’ll perform better.