The Science Behind Muscle Soreness

muscle pain

The Science Behind Muscle Soreness

Can thousands of elite athletes and trainers be wrong when they spend thousands of dollars to employee massage therapists and take them across the country on bike races, or provide precious space in the medical tents at the Olympics, or allow the female massage therapist an unprecedented seat on the bench in the San Diego Padre’s dugout? Massage does work. However, as technology and science advance, the theories about why it works are evolving.

The search for the cause of muscle soreness and fatigue began more than a century ago. In the late 19th century, fermentation chemists realized that juice left to ferment without adequate oxygen resulted in acid products. In the early 20th century, when physiologists stimulated isolated frog muscles to contract until exhaustion, they found that the tissues had accumulated high amounts of lactic acid. Since then, the idea that lactic acid accumulation causes muscle fatigue has persisted.

More recently, the lactic acid paradigm has shifted. Lactic acid is understood to be more than just a waste product of exercise. Muscles make lactic acid to fuel cells not only in the muscle that produced the lactate, but also as an energy source that can be sent off to adjacent muscle cells for fuel. Lactic acid has also been found to fuel fibers in the heart and cells in the brain. The liver prefers to use lactic acid to make glucose for the blood when exercise is prolonged. The production of lactic acid is stimulated, in part, by circulating adrenalin; the combination of adrenalin and lactic acid helps protect against the electrolyte imbalance across muscle membranes brought on by the loss of potassium.

Lactic acid is not simply the end result of an oxygen-deprived muscle, accumulating and resulting in muscle fatigue and soreness. Rather, it is an important intermediary in numerous metabolic processes and pathways within and between cells. It is a central player in cellular, regional, and whole body metabolism. Lactic acid is a key contributor of energy, supporting nearly every metabolic function in the body.

Now that we understand that lactic acid is not waste to be flushed out of the muscles, what is the cause of muscle soreness and fatigue and what role does massage have in relieving those post-exercise symptoms?

We know:

  • training helps people burn lactic acid more efficiently by growing the mitochondria in muscle cells
  • intense exercise, particularly interval training, generates big lactate loads, and the body adapts by building up mitochondria to clear lactic acid quickly
  • delayed onset muscle soreness (DOMS) is the pain or discomfort often felt 24-72 hours after eccentric contraction exercise or exertion accompanied by unaccustomed training levels–once thought to be caused by lactic acid buildup but now attributed to inflammation and micro-tears in the muscle fibers, fascia, and nociceptors
  • massage reduces soreness and swelling in athletes post-exercise, and significantly reduces pain in people experiencing DOMS by as much as 25-50 percent

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