Breaking It Down: Physiology, Running and Recovery

By Dana Riederer • Triathlete Magazine

For many of us, our first important race of the season is quickly approaching, and many athletes are engaged in steady training to improve on last year's performances, set a PR or simply go the distance. But as you crank up the volume and intensity of training, it's important to understand (and mitigate to the extent possible) the orthopedic stress that working out—and especially running—places on the body.

Muscles are among the most metabolically active tissues in our body. They are always trying to tailor their structural and functional properties to the level and type of use they experience. However, when the amount of use or level of stress on a muscle is too great, the fibers that make up the muscle are damaged. When this happens, the cells that make up muscle fibers degenerate and are replaced by new muscle cells. This process is known as the degeneration-regeneration cycle.

Following physical damage to muscle cells in training, degeneration begins with what is known as the inflammatory process. During this stage, various enzymes and immune cells known as macrophages serve as scavengers that gobble up the cellular debris left behind from muscle trauma and consequent muscle-cell death.

During the degeneration-regeneration cycle, almost all cellular structures are affected, representing a so-called dismantling period. This process begins within hours of the initial insult to the muscles trained.

The next step in the degeneration-regeneration cycle may be the most important. This is known as the proliferative phase. During this phase, skeletal muscle satellite cells begin to appear along the periphery of damaged muscle fibers. These satellite cells represent a muscle population of stem cells that will eventually differentiate into new muscle tissue.

What makes these cells unique is that their proliferation is brought about specifically by muscle trauma. As muscle satellite cells continue to proliferate and align themselves along the outer margins of the damaged muscle fibers, regeneration moves forward and new muscle-fiber proteins are synthesized.

This process continues until the damaged muscle fibers are completely regenerated.
The benefits of this complex process are numerous. When looking at muscle-cell regrowth in sedentary muscles, the muscle fibers seem to regenerate in a random orientation and remain relatively immature.

However, if the muscle fibers are cyclically exposed to various loads of stress and tension, they become well aligned, take up greater amounts of amino acids and synthesize more proteins. Other physiological benefits to training include an increase in intracellular mitochondria (the powerhouses of the cell), the number of capillaries, total blood flow and total oxygen-consumption capacity, leading to a profound rise in muscle metabolic activity. These increases yield a more well-developed and fatigue-resistant muscle.

While all forms of training are of great benefit, running offers a specific benefit due to the nature of muscle contractions it entails. The lengthening of an activated muscle is known as eccentric contraction. This type of muscle contraction is heavily relied upon during running and results in very high muscle force, tissue injury and consequent muscle soreness. Some or all of these factors provide a powerful strengthening stimulus to the muscle fibers that are broken down during running.

Making the Most of Your Training

Although muscle breakdown is needed in order to improve overall muscle fitness, it is important to remember that too much muscle trauma can have a negative effect, especially early in your training program. Below are a few steps to help you minimize harmful muscle damage and maximize muscle regeneration and recovery.

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