Acute muscle soreness (AMS) is the pain felt in

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of mus ...

s during and immediately, up to 24 hours, after strenuous

physical exercise Exercise is a body activity that enhances or maintains physical fitness and overall health and wellness. It is performed for various reasons, to aid growth and improve strength, develop muscles and the cardiovascular system, hone athletic s ...

. The pain appears within a minute of contracting the muscle and it will disappear within two or three minutes or up to several hours after relaxing it. The following causes have been proposed for acute muscle soreness: * Accumulation of chemical end products of exercise in muscle cells such as lactic acid and H⁺ *

Muscle fatigue Muscle fatigue is the decline in ability of muscles to generate force. It can be a result of vigorous exercise but abnormal fatigue may be caused by barriers to or interference with the different stages of muscle contraction. There are two main ca ...

(the muscle tires and cannot contract any more) There are no modern effective treatments for AMS.

Cause

Muscle soreness can stem from strain on the

sarcomere A sarcomere (Greek σάρξ ''sarx'' "flesh", μέρος ''meros'' "part") is the smallest functional unit of striated muscle tissue. It is the repeating unit between two Z-lines. Skeletal muscles are composed of tubular muscle cells (called mus ...

, the muscle's functional unit. Due to the mechanism of activation of the unit by the nerves, which accumulates

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...

that further degrades sarcomeres. This degradation initiates the body inflammatory response, and has to be supported by surrounding connective tissues. The

inflammatory cell White blood cells, also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from multi ...

s and

cytokine Cytokines are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are peptides and cannot cross the lipid bilayer of cells to enter the cytoplasm. Cytokines have been shown to be involved in au ...

s stimulates the pain receptors that causes the acute pain associated with AMS. Repair of the sarcomere and the surround connective tissue leads to delayed onset muscle soreness, which peaks between 24 and 72 hours after

exercise Exercise is a body activity that enhances or maintains physical fitness and overall health and wellness. It is performed for various reasons, to aid growth and improve strength, develop muscles and the cardiovascular system, hone athletic ...

. Another causes of AMS would be from cramps during or after workout, which has been theorized to have been caused by two pathways: *

Dehydration In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...

Electrolyte imbalance Electrolyte imbalance, or water-electrolyte imbalance, is an abnormality in the concentration of electrolytes in the body. Electrolytes play a vital role in maintaining homeostasis in the body. They help to regulate heart and neurological function, ...

Dehydration

Dehydration theory states that

extracellular fluid In cell biology, extracellular fluid (ECF) denotes all body fluid outside the cells of any multicellular organism. Total body water in healthy adults is about 60% (range 45 to 75%) of total body weight; women and the obese typically have a low ...

(ECF) compartment becomes contracted due to the excessive

sweat Perspiration, also known as sweating, is the production of fluids secreted by the sweat glands in the skin of mammals. Two types of sweat glands can be found in humans: eccrine glands and apocrine glands. The eccrine sweat glands are distrib ...

ing, causing the volume to decrease to the point until the muscles are contracted until the fluids can re-inhabit the

vacuum A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or " void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often ...

. Excessive sweating can also cause the electrolyte imbalance theory, which is sweating disturbs the body's balance of

electrolyte An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon ...

, which results in exciting

motor neuron A motor neuron (or motoneuron or efferent neuron) is a neuron whose cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly or indirect ...

s and spontaneous discharge. The feeling of soreness can also be attributed to the lack contraction from the muscle, which can lead to overexertion of the muscle. The decrease in contraction has been theorized to have been caused by the high level of concentrations of

proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...

created by

glycolysis Glycolysis is the metabolic pathway that converts glucose () into pyruvate (). The free energy released in this process is used to form the high-energy molecules adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide (NADH ...

. Excess in protons displaces

ions which is used within the fibers in activating the sarcomere, resulting in a reduced contractile force.

Electrolyte imbalance

When exercising,

lactic acid Lactic acid is an organic acid. It has a molecular formula . It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as well as nat ...

becomes lactate and H+ through glycolysis. With more lactic consumed during the process, there will be a higher H+ concentration, thus lowering the

blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the cir ...

’s

pH level In chemistry, pH (), historically denoting "potential of hydrogen" (or "power of hydrogen"), is a scale used to specify the acidity or basicity of an aqueous solution. Acidic solutions (solutions with higher concentrations of ions) are me ...

. This low pH level will affect the energy production process through the inhibition of phosphofructokinase. Phosphofructokinase is a key

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

in glycolytic process, which produces energy. With a pH of 6.4, there will be no glycolysis process existed, thus no energy will be produced. Higher concentration of H+ will also cause the loss of contractile force through the misplacement of calcium in

muscle fiber A muscle cell is also known as a myocyte when referring to either a cardiac muscle cell (cardiomyocyte), or a smooth muscle cell as these are both small cells. A skeletal muscle cell is long and threadlike with many nuclei and is called a muscl ...

, the misplacement of calcium in muscle fiber will disturb the formation of

actin Actin is a family of globular multi-functional proteins that form microfilaments in the cytoskeleton, and the thin filaments in muscle fibrils. It is found in essentially all eukaryotic cells, where it may be present at a concentration of ov ...

myosin Myosins () are a superfamily of motor proteins best known for their roles in muscle contraction and in a wide range of other motility processes in eukaryotes. They are ATP-dependent and responsible for actin-based motility. The first myosin (M ...

cross-bridge.

Treatments

There are conflicting research in terms of treatments of muscle soreness.

Stretching and muscle soreness

Stretching immediately before or after a workout does provide little help, but is not significant enough to be considered as a preventative measure.

References

{{Pain Exercise physiology Acute pain