Treating Sore Muscles and Tendons

W. Steven Pray, PhD, DPh


US Pharmacist. 2006;31(5) 

Muscle/tendon soreness affects virtually everyone, regardless if the patient is a serious athlete or engages in exercise on an intermittent, recreational basis. The widespread nature of muscle soreness is due partly to the various activities that produce it. Muscle soreness is a response to sports, exercise, work, travel, or daily activities.

Exercise that leads to muscle soreness and pain causes increases in muscle enzymes in the bloodstream, inflammation, and structural damage.[1] These coexist with a decrease in the patient's range of motion and strength in the affected area(s).

Exercise is thought to induce microtears in the muscle, leading to muscular soreness and fatigue.[1] Significant research on muscle soreness has focused on eccentric muscle contractions. During this type of muscular movement, muscles lengthen, which causes the microtears characteristic of exercise-induced muscle damage.[2] This occurs because of simple physics: If a stretched muscle is subjected to a given load, the abnormally lengthened fibers undergo increased tension, compared to the same muscle in the unstretched state, and the same number of muscle fibers must endure an increased load-to-fiber ratio.[2] This also explains why muscle motions that are isometric, shortening, or concentric do not induce fatigue as readily.

Some exercises are more damaging to muscle than others. For instance, downhill running, hiking, descending stairs, and lowering weights are all eccentric in nature, causing a greater incidence of muscle soreness.[1,2] By contrast, cycling does not involve eccentric motions and is less prone to lead to muscle soreness.

Muscle soreness occurs at the highest level about 24 to 48 hours after injurious exercise, reaching a peak within 48 to 72 hours, and disappearing five to seven days after the exercise.[2] Inflammation also increases, to reach its peak a few days after the exercise. Interestingly, the first bout of exercise is most likely to produce soreness. If the patient engages in the same exercise a second time, the phenomenon of adaptation ensures less muscle soreness and a more rapid recovery of full strength.[2] Adaptation can provide protection for as long as six months.

Pharmacists can recommend radically differing modalities to treat muscle soreness, including external and internal analgesics, as well as application of heating devices and constant low-level heat therapy via therapeutic heat wraps.

External Analgesics. Most external analgesics (e.g., benzocaine, pramoxine, hydrocortisone) are not indicated for muscle soreness. Those that have this indication are known as counterirritants. While they have been used for decades, their efficacy is limited for many reasons.

Counterirritants are placed into four distinct categories, depending on the action they have when applied topically.[3] The first category includes capsaicin and capsicum--two ingredients seldom incorporated into muscle soreness products. Rather, these ingredients are primary components of "pepper" creams, such as Zostrix and Capzasin, which are mainly used for postherpetic neuralgia.

Methyl nicotinate is an example from another category of external analgesics: those that directly dilate superficial vessels. This ingredient is rarely included in the formulas of external analgesic combinations. As a vasodilator, it has the remote possibility of causing fainting if it is applied over large sections of the body.

A third group of external analgesics produces cooling upon initial application; yet, with continued friction or rubbing, the cooling changes to warmth. This group includes camphor and menthol.

A final group produces redness, irritation, and warmth upon initial application, with the warmth intensifying if the patient continues to apply friction to the site of application. The most common muscle soreness ingredient from this group is methyl salicylate. Topical application can lead to systemic absorption; thus, the patient should be given traditional salicylate use precautions and drug interaction warnings.[4,5]

A major limitation to counterirritant use is their superficial action. If the patient's muscles are sore, an ideal therapy would penetrate to the muscle to provide relief. However, during the FDA OTC Review, the panel exploring the utility of counterirritants reject­ed claims that counterirritants penetrate skin to enter muscles or joints.[3] Their action is compared to scratching an itch, as they help mask the underlying discomfort. External analgesics should not be used in patients younger than 2 years, nor should they be used for more than seven days. Use in conjunction with a heating pad, hot water bottle, heat lamp, or heated gel pack can cause severe burns and is not recommended. Most counter­ irritants, especially methyl salicylate and camphor, have an odor that many patients find highly objectionable. Counterirritants have also been implicated in contact dermatitis, dermal absorption of active ingredients, toxicity/death upon accidental or intentional ingestion, and fetal problems in pregnant patients.[6,7,8,9,10,11]

External Products of Unknown Efficacy. Despite a lack of evidence, emu oil continues to be touted as a remedy for sore muscles and is linked with several other unproven claims. Some marketers of the "blue" ointments and creams (e.g., Blue Stuff) add menthol or other proven counterirritants. Any perceived benefit would probably be no greater than that expected from the counterirritant alone. Similarly, trolamine (also known as triethanolamine salicylate, as found in Aspercreme, Sportscreme, Mobisyl, and Myoflex) has been promoted for years for relief of muscle soreness. However, external analgesic documents provided by the FDA on its Web site shows that trolamine has not been proved safe or effective for this use.[12]

Internal Analgesics. Internal analgesics (e.g., Aleve, Advil, Motrin IB, Orudis KT, Tylenol) can relieve muscular aches and pains and are safe if all label directions are followed. The pharmacist can urge patients to adhere to the age limitations indicated on the containers of these products, although companies publish dosing charts for certain products (e.g., Tylenol) which purport to indicate safe doses for pain in newborns and children under age 2. These dosage charts are of questionable legality, as the doses are not FDA approved to be shown on the product labels.

Internal Products of Unknown Efficacy. Glucosamine/chondroitin and S-adenosylmethionine (SAMe) are also widely promoted for muscle problems, but without sufficient supporting evidence. As dietary supplements, they evade the FDA requirements for research to prove safety and efficacy through the 1994 Dietary Supplement Health and Education Act. Oral homeopathic arnica 30x was investigated for muscle soreness and was found to be ineffective.[13] The pharmacist should be careful in recommending these products.

Cryotherapy vs. Thermotherapy. Regarding acute injuries, traditional treatment has five components, referred to as PRICE: protection, rest, ice, compression, and elevation. Cold therapy (cryotherapy) is valuable in limiting the extent of injury and reducing the time needed in rehabilitation. Yet, after 24 to 72 hours, cryotherapy is of little efficacy; thermotherapy may be instituted. Cryotherapy also has little efficacy for nonacute muscle problems, such as muscle soreness and repetitive use syndromes. In these cases, thermotherapy can provide relief.

Pharmacists have been able to recommend such thermotherapy devices as hot water bottles, microwavable gel packs, exothermic crystalline cascade liquids (e.g., Zap Pac), and heating pads. Each has disadvantages. None of them allow the wearer to engage in work or sports, since they cannot be secured to the body. Heating pads require continual access to electricity, which restricts patient mobility, even around the house. None can achieve and maintain a constant heat level. Hot water bottles must be refilled, while gel packs must be rewarmed. Crystalline cascade products require reboiling and subsequent cooling before they can be reused. Heating pads utilize a thermostat that does not allow them to maintain a constant heat level. Heating pads can also cause burns, even on the low-power setting.[14,15,16,17,18]

The advent of therapeutic heat wraps (e.g., ThermaCare) has revolutionized thermotherapy.[19] They reduce pain and disability in patients with acute and subacute low back pain.[20] After the package is opened, an innovative set of discs containing iron begins to oxidize, producing a low-level heat of 104ºF. This low-level heat is far safer than that obtained with heating pads. It also maintains the heat at a constant temperature over the eight-hour wearing time, which no other nonprescription modality can currently achieve. The devices can also be worn during work or recreational activities, so that the patient has an uninterrupted session of therapy. Finally, after the eight-hour wearing time, the patient experiences sustained relief for a full 24 hours. Patients can sleep with therapeutic heat wrap devices in place, a practice that the Consumer Product Safety Commission and FDA cautioned against at any time with heating pads because of the substantial risk of burns.[17,18,21] Pregnant patients and those with diabetes, rheumatoid arthritis, poor circulation, or heart disease (e.g., hypertension) should consult a physician before using therapeutic heat wraps. Patients ages 55 and older should wear heat wraps over a thin layer of clothing to reduce the risk of a burn.

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