Delayed Onset Muscle Soreness

 

Why are you so sore after an increased intensity workout? Muscle Science: Part 2! (Missed Part 1: How Muscles Work)?

 

Image Source: Clarkson PM, Nosaka K, Braun B. Muscle function after exercise-induced muscle damage and rapid adaptation. Med Sci Sports Exerc. 1992 May;24(5):512–520

 

Delayed Onset Muscle Soreness is a condition of muscle pain, soreness or stiffness felt 12-72 hours after exercise. It is prevalent at the beginning of a new an exercise program, after a change in sports activities, or after a dramatic increase in the duration or intensity of exercise.

 

What causes Delayed Onset Muscle Soreness? There are 6 theories*:

 

1.Lactic Acid

This is often percieved as the cause, but it is unlikely. Lactic Acid levels return to normal within 1 hour of exercise, and do not rise within 72 hours. Lactic Acid is therefore more likely rellated to immediate, acute pain.

 

2.Muscle Spasm

Increased levels of resting muscle activity have been observed after exercise. Why?

• Muscle contraction causes a compression of local blood vessels + accumulation of pain
• Creates a cycle of pain/increased muscle spasm in response to pain, followed by compression of blood vessesl

Studies have been inconclusive as to the effect on Delayed Onset Muscle Soreness.

 

3.Connective Tissue Damage

Connective Tissue (collagen) forms sheaths around bundles of muscle fibres. The presence of certain amino acids (Hydroxyproline and Hydroxylysine) have been found in urine following exercise. These amino acids can indicate collagen degradation by overuse or strain damage. However, they are present in both collagen synthesis (building) and degradation, so the mechanism is unclear.

 

4.Calcium Accumulation

Calcium accumulates in injured muscles following sarcomere (muscle functional unit) damage. This affects cellular respiration, and ATP (energy) production slows.

 

5. Muscle Damage

Creatine Kinase (CK) is an indicator of muscle membrane permeability, as it is usually only found within skeletal and cardiac muscle. The disruption of the sarcomere enables diffusion of CK into interstitial fluid.

 

Sarcomere (muscle functional unit) with and without exercise.

Image Source: Paulsen G, et al : Subcellular movement and expression of HSP27, {alpha}B-crystallin, and HSP70 after two bouts of eccentric exercise in humans. J Appl Physiol 2009, 107:570-582.

 

There is a significant time difference between peak CK plasma levels, and soreness, so muscle damage is only a partial explanation.

 

6.Inflammation Theory

Inflammatory cell infiltration is evident following repetitive eccentric muscle action. The breakdown of muscle fibres results in accumulation of proteins, attracting monocytes and neutrophils. This influx of protein-rich fluid causes osmotic pressure to be exerted, and pain is felt.

 

 

It’s not likely that just one theory can explain Delayed Onset Muscle Soreness: it’s likely a combination of two or more.

 

Rest assured: All of this protein influx/osmotic pressure/sarcomere blurring related pain is temporary! Your body is good at healing itself, and becoming stronger. However, there are things you can do to speed up the process!

 

Up next in the Muscle Science series: recovering from Delayed Onset Muscle Soreness. What you can do, and what won’t help (the results may surprise you!)

*Six Theories of Delayed Onset Muscle Soreness Source: Cheung K, Hume PA, Maxwell L: Delayed onset muscle soreness: treatment strategies and performance factors. Sports Medicine 2003, 33:145-164.

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