Question: If the act of running induces physiological fatigue, is the term “Recovery Run” an oxymoron?
Answer: Yes, and No.
As I’ve stated numerous times here on the Landice Blog, training stress is relative; a 4 mile run over undulating cross country trails at 7 minute per mile pace may constitute nothing more than a warm up effort for a very fit, high volume marathon runner, whereas that same session may serve as a high stress long run for someone who’s brand new to running. This being said, the concept of the recovery run session is something that we’ll reserve for novice and experienced runners who have established a solid base of run volume, frequency and intensity.
To better understand what causes training related fatigue, we must first understand how running effectively stresses the body. Although there are a variety of physiological factors at play (hormonal, neurological, metabolic, etc.), in today’s training tip, I will focus upon one of the biggest contributors to running related fatigue: Muscular micro-trauma. As runners, our lower body musculature in particular is subjected to high degrees of both concentric and eccentric stress. Movement of the human body is made possible thanks in large part, to the fact that our muscles attach to the skeletal system. When a particular muscle pulls on the bone that it is attached to (concentric/contraction), the bone moves. A good example would be what occurs during the popular weight training exercise, the bicep curl. Note the following diagram:
In order for the object to be lifted upward, the biceps muscle, which attaches to the forearm, contracts/shortens, and effectively pulls the forearm, hand and the object the hand is grasping, upward. This is but a simple example of how the muscular and skeletal systems work in conjunction to allow movement to occur. With running, we have a wide array of muscles, and the bones they attach to, being pulled in order for movement to occur.
Question: But don’t muscles “push?”
Although the skeletal system does in fact exert force against the object we are trying to move, or, in the case of running, move over (the ground), the muscle’s only role in locomotion is to pull upon the particular bone they are attached to in order for said force to occur. Going back to our diagram from above for a moment, in order for the arm to lower the weight back to the relaxed position, the bicep muscle will elongate while the muscle found on the opposite side of the upper arm, the triceps, contracts. Complete movement cannot occur unless all agonist and antagonist muscles are working in unison, much like a pulley system, where one side of the pulley pulls down/elongates while the other shortens and pulls up.
When we run, the musculature of the lower body must exert high degrees of force to overcome gravity and move us forward. In order for this to occur, strong muscular contractions must occur over and over again; most runners will average somewhere between 80 – 90 steps per minute, per leg, while running. Over the course of a 40 minute run, this equates to somewhere around 3,500 muscular contractions, for each muscle group, per leg! When was the last time you went to the gym and executed 3,500 biceps curls with one arm?!?!
It is true that muscular contraction, especially when carried out at relatively higher percentages of one’s maximum capability, can and will lead to muscular fatigue. In the case of running, however, it is not so much the muscular contraction that leads to the soreness and stiffness we experience after a hard race, workout or taxing long run, it is the eccentric loading that the musculature is exposed to every time our feet hit the ground.
During the stride cycle, as the foot makes contact with the surface it is running upon, the body is subjected from anywhere between 3 – >7 times its body weight in force. In order for the body to remain upright and stable, it must counter this force via muscular elongation. Let’s return to our bicep curl example again: If you were handed a very heavy object when the biceps was in the contracted most position, and told to lower it down very slowly, the triceps musculature would not have to work in any way to overcome gravity since gravity was already pulling the weight down towards the ground to begin with. However, in order to keep the weight from dropping out of your hand onto the ground below, the biceps musculature would have to work VERY hard to resist gravity as it elongated slowly while under heavy tension. During the lowering of the weight, the musculature would be subjected to high degrees of eccentric stress; individual muscle fibers would tear and fray very slightly as the weight was lowered down. This micro-trauma would in turn cause the pronounced soreness one might experience 1 – 3 days after the fact.
Now let’s relate this scenario once again to the locomotion that occurs during running: As previously stated, as the foot strikes the ground, the musculature of the lower body is subjected to 3 – >7 times the amount of body weight with each foot strike; for a 150 lb. runner, this means that with every step, the lower body musculature is subjected to anywhere between 450 – 1,050+ lbs. of eccentric force for a split second with every step! No wonder marathon runners struggle to walk for 3 – 4 days after they’ve crossed the finish line!
In the next installment of this training tip, I’ll dive deeper into the science behind muscular fatigue, soreness, and training stress related performance decline. I’ll also discuss the merits of active and passive recovery and how you can best optimize your body’s rate of recovery after hard training sessions and competition. Stay tuned!