POST EXERCISE MUSCLE SORENESS
Hough gave the first detailed description of delayed-onset muscle soreness (DOMS) in 1902. DOMS is a widely recognized entity and is experienced by nearly everyone during his/her lifetime.
It is defined as the sensation of discomfort or pain in the skeletal muscles following physical activity, usually eccentric, to which an individual is not accustomed.
PATHOPHYSIOLOGY
MUSCLE PAIN MECHANISM
The sensation of pain in skeletal muscle is transmitted by myelinated group III (A-delta fiber) and unmyelinated group IV (C-fiber) afferent fibers. Group III and IV sensory neurons terminate in free nerve endings.
The free nerve endings are distributed primarily in the muscle connective tissue between fibers (especially in the regions of arterioles and capillaries) and at the musculotendinous junctions. The larger myelinated group III fibers are believed to transmit sharp, localized pain. The group IV fibers carry dull, diffuse pain.
The sensation of DOMS is carried primarily by group IV afferent fibers. The free nerve endings of group IV afferent fibers in muscles are polymodal and respond to a variety of stimuli, including chemical, mechanical, and thermal.
Chemical substances that elicit action potentials in muscle group IV fibers in order of effectiveness are bradykinin, 5-hydroxytryptamine (serotonin), histamine, and potassium.
ETIOLOGY AND PATHOPHYSIOLOGY
DOMS results from overuse of the muscle. Any activity in which the muscle produces higher forces than usual or in which it produces forces over a longer time period than usual can cause DOMS.
According to Tiidus and Ianuzzo, the degree of muscle soreness is related to the intensity of the muscle contractions and to the duration of the exercise. The intensity seems to be more important in the
determination than is the duration.
Five hypotheses are used to explain the pathophysiology of DOMS.
v Structural damage from high tension
o This hypothesis originally was proposed by Hough and is the most scientifically accepted theory. The delayed pain is related directly to the development of peak forces and to the rate of force development in rhythmic contractions. DOMS is not related to the state of fatigue of the muscle.
o The rhythmic and tetanic contractions that cause the greatest acute fatigue and discomfort in the muscles during exercise results in the least delayed pain following the exertion.
o The structural damage is evident in muscles that are not trained for the particular exercise.
v Metabolic waste product accumulation
o One of the most popular concepts in the lay exercise community is that delayed soreness is a result of lactic acid accumulation in the muscles.
o The degeneration and regeneration of muscle fibers observed after 2-3 hours of ischemia are similar temporally and quantitatively to the forces resulting from exercise-induced injury.
o An apparent relationship exists between exercise intensity and the extent of soreness. Much evidence against the metabolic hypothesis also may be noted. The most convincing evidence is that the muscle contractions that cause the greatest degree of soreness require relatively low energy expenditure.
o Exercise involving eccentric contractions requires lower oxygen consumption and produces less lactate than does exercise with concentric contractions at the same power output.
o Energy use per unit area of active muscle appears to be less in eccentric exercise than in equivalent concentric exercise.
o Schwane and colleagues tested the metabolic hypothesis. Their results indicated that downhill running requires significantly lower oxygen uptake (VO2) and produces less lactic acid than does level running but that it nonetheless results in greater DOMS.
v Increased temperature
o Type III and IV nerve endings are sensitive to temperatures of 38-48°C.
o Elevated temperature could conceivably damage the structural element in the muscle, resulting in necrosis of muscle fibers and breakdown of connective tissues. Eccentric muscle exercise may generate higher local temperatures than do concentric contractions. Rhabdomyolysis (extreme of DOMS) is more prevalent in untrained subjects during exercise in the heat.
v Spastic contracture
o Studies by Travell and co-investigators in 1942 and a later series of experiments by Cobb and colleagues demonstrated elevated electromyographic activity in sore muscles. Altered nerve control and vasoconstriction lead to decreased blood flow and ischemia, which in turn initiate a pain-spasm-pain cycle. The magnitude of pain depends on the number of motor units involved.
o Other investigators have been unable to detect increased electrical activity in sore muscles.
v Myofibrillar remodeling
o The literature suggests that myofibrillar and cytoskeletal alterations are the hallmarks of DOMS and that they reflect adaptive remodeling of the myofibrils.
o There are 4 main types of changes:
§ Amorphous widened Z-disks
§ Amorphous sarcomeres
§ Double Z-disks
§ Supernumerary sarcomeres
SEX
Stupka and colleagues showed that muscle damage following unaccustomed eccentric exercise is similar in males and females; however, the inflammatory response is attenuated in women.
MacIntyre and coauthors found that the patterns of DOMS and torque differed between males and females after eccentric exercise.
In a study by Dannecker and colleagues, no sex differences were detected, except that higher affective ratios were reported by men than by women.
AGE
DOMS generally is not reported in children. Adults of all ages can experience DOMS.
CLINICAL
HISTORY
A history of heavy, unaccustomed exercise, particularly involving eccentric muscle contractions (eg, downhill exercise) is reported.
The patient complains of pain, soreness, swelling, and a stiff or tender muscle spasm.
The muscles are sensitive, especially upon palpation or movement.
Decreased range of motion and reduced strength is noted (especially 24-48 hours postexercise).
The patient has a sense of reduced mobility or flexibility.
DOMS begins 8-24 hours after exercise and peaks 24-72 hours postexercise; it then subsides over the next 5-7 days
Acute onset muscle soreness begins during exercise and continues for approximately 4-6 hours after exercise.
PHYSICAL
The tenderness often is described as localized in the distal portion of the muscle, in the region of the musculotendinous junction. According to one study, tenderness in this region could be due to the fact that muscle pain receptors are most concentrated in the region of the tendon and connective tissue in the muscle. The fibers' angles to the long axis of the muscle are greatest in the region of the musculotendinous junction, increasing the susceptibility of the fibers to mechanical trauma.
In severe DOMS, the pain is generalized throughout most of the muscle belly.
Swelling of the muscle belly can occur.
Muscle tenderness is present.
Decreased muscle strength and flexibility also are noted.
CAUSES
Heavy, unaccustomed exercises contribute to the development of DOMS.
Exercise involving eccentric muscle contractions results in greater disruption or injury to the muscle tissues than does concentric exercise. Thus, any form of exercise with eccentric muscle contractions causes more DOMS than does exercise with concentric muscle contractions. Ample evidence from histologic studies, electron microscopic examination, and serum enzymes of muscular origin supports this notion.
To produce a given muscle force, fewer motor units are activated in an eccentric contraction than in a concentric contraction. In eccentric contractions, the force is distributed over a smaller cross-sectional area of muscle. The increased tension per unit of area could cause mechanical disruption of structural elements in the muscle fibers themselves or in the connective tissue that is in series with the contractile elements; however, it has not been proven that injury to muscle cells or to connective tissue is the causative factor in DOMS.
Comparative features of pain during or immediately following exercise, delayed onset muscle soreness, and muscle cramps associated with exercise.
DIAGNOSIS
LABORATORY STUDIES
Serum creatinine kinase level usually is elevated, but it is nonspecific.
IMAGING STUDIES
In a study by Dierking and colleagues, diagnostic ultrasonography, when used in the diagnosis of DOMS, was not sensitive enough to detect changes in a cross-sectional muscle area.
Magnetic resonance imaging (MRI) can detect muscle edema in DOMS but is not indicated clinically for the diagnosis. In a prospective evaluation of DOMS, abnormalities found in MRI persisted up to 3 weeks longer than did symptoms.
HISTOLOGIC FINDINGS
Immediately after exercise, free erythrocytes and mitochondria may be observed in the extracellular spaces.
Increase in the numbers of circulating neutrophils and interleukin-1 occurs within 24 hours after exercise. A prolonged increase in ultrastructural damage and muscle protein degradation occurs, as well as a depletion of muscle glycogen stores.
Friden and colleagues observed Z-line streaming within eccentrically exercised muscle fibers that occasionally led to total disruption of the Z-band area; this resulted in disorganization of surrounding myofilaments.
From 1-3 days postexercise, the period of time when DOMS is most intense, phagocytes are present in the muscle fibers, and injury to the muscle usually is more apparent.
TREATMENT
PHYSICAL THERAPY
Although it provides only temporary relief, exercise of the sore muscle probably is the best way to reduce DOMS. Muscular soreness diminishes acutely with exercise.
With the cessation of exercise, however, the soreness returns, and this cycle continues until the muscle becomes conditioned sufficiently through training.
Why exercise decreases DOMS is not clear, although several possibilities exist, including the following:
Breakup of adhesions from the injured, sore muscles takes place during exercise.
Increased blood flow or temperature in the muscle helps to decrease the accumulation of noxious waste products.
Endorphin release by neurons in the central nervous system increases during exercise.
Increased afferent input is noted from large, low-threshold sensory units in the muscles (muscle group-Ia, Ib, and II fibers [gate control theory]).
Subjects direct attention to the activity and away from the pain.
The training effect appears to be highly specific, not only for the particular muscles involved in the exercise, but also for the type of contractions performed. For example, Schwane and Armstrong found that in rats, the muscle damage that occurs during downhill running is prevented by downhill or level training but not by uphill training.
Ice-water immersion and ice massage are frequently used, particularly among high-level athletes, to minimize the symptoms of DOMS.
OTHER TREATMENT
Ø A study by Barlas and colleagues indicated that acupuncture generally is not effective in the treatment of DOMS ; however, an unblinded study by Lin and Yang suggested that acupuncture is effective against DOMS.
Ø Mekjavic and co-investigators concluded that hyperbaric oxygen therapy does not affect recovery from delayed onset muscle soreness.
Ø Zhang and colleagues noted that a double layer of Farabloc, an electromagnetic shield, wrapped around the thigh has been shown to reduce DOMS.
Ø In a study by Craig and coauthors, combined low-intensity laser therapy was not shown to be effective against DOMS. However, a study by Douris and colleagues that used 8 J/cm2 of phototherapy did show a beneficial effect.
Ø In one small (6 subjects in each group), randomized, double-blind, placebo-controlled study by Hasson and coauthors, individuals treated with pulsed ultrasonographic therapy (PUS) showed significantly reduced soreness. However, in a larger (12 patients in each group) randomized, double-blind, placebo-controlled study by Craig and co-investigators, no significant benefit from PUS was demonstrated. In a study by Ciccone and coauthors, there was some suggestion that ultrasonography may enhance DOMS and that phonophoresis with salicylate may have therapeutic benefits.
Ø Tourville and colleagues showed that sensory-level, high-volt, pulsed electrical current was not effective in reducing the measured variables associated with DOMS.
Ø Transcutaneous electrical nerve stimulation (TENS), in an uncontrolled study by Denegar and Perrin, showed some benefit in relieving the soreness associated with DOMS ; however, in a randomized, placebo-controlled study by Craig and colleagues, the use of TENS did not show any significant benefit.
Ø In a small study by Hasson and coauthors, dexamethasone iontophoresis immediately after exercise was shown to decrease muscle soreness perception in DOMS.
MEDICATION
In many controlled studies, general analgesics and nonsteroidal anti-inflammatory medications have not been consistently effective against postexercise muscle soreness.
In a randomized, placebo-controlled study, Cannavino and colleagues showed that transdermal 10% ketoprofen cream was effective in alleviating self-reported DOMS in isolated quadriceps muscles of patients following repetitive muscle contraction, particularly after 48 hours. This relief was
apparently secondary to the effects of the medication, because no other medications or pain relief measures were used in the study.
Oral ascorbic acid (vitamin C) and other antioxidants also have been investigated as possible medications for DOMS, with mixed results. A study by Connolly and coauthors suggested that a vitamin-C supplementation protocol of 1000 mg taken 3 times a day for 8 days is ineffective in protecting against selected markers for DOMS.
The homeopathic medicine Arnica 30x was studied in a randomized, double-blind, placebo-controlled study and was found to be ineffective in treating DOMS.
Bajaj and colleagues showed that the prophylactic intake of tolperisone hydrochloride provides no relief of postexercise muscle soreness but that it does result in a reduction in isometric force.
In a randomized, placebo-controlled study, Connolly and co-investigators showed that tart cherry juice can decrease some of the symptoms of exercise-induced muscle damage. Most notably,
strength loss averaged over the 4 days after eccentric exercise was 22% with the placebo but only 4% with the cherry juice.