Chapter 4: Skeletal Muscle-Relaxant Drugs

It is not uncommon for an athlete to experience muscle strains, trauma, or mild chronic irritation as a result of athletic participation. Sometimes traumatic injury or irritation to muscle tissue has an associated unwanted muscle spasm that can inhibit the progress or participation of an athlete. Trauma-caused muscle spasm typically results in an increase in afferent pain impulses from the traumatized area, which in turn causes an increase in efferent messages from the CNS to the muscle and a resultant chronic tension. Often the athletic trainer uses thermal modalities or other manual techniques to overcome the associated muscle tension. Because the physician, under certain conditions, may treat these symptoms by prescribing a skeletal muscle relaxant, the athletic trainer needs to have a basic understanding of these types of drugs.

Skeletal muscle relaxants can be helpful in managing the symptoms of moderate muscle spasms caused by muscle contusions, strains, and other traumatic muscle injuries. However, it is important to note that there is an ongoing debate in the medical community regarding the effectiveness, or, more correctly, the appropriateness of the use of skeletal muscle relaxants. Some physicians contend that muscle relaxants can be beneficial for short-term muscle spasm, but tend to be overused for patients with chronic pain.⁶ Many physicians also point out that, in spite of overwhelming evidence that skeletal muscle spasm is nonexistent; they are continually deluged with seductive incentives to prescribe expensive muscle relaxants.⁵ The writer of a letter to the editor of the Journal of the Canadian Medical Association stated, "There is no proof that pain symptoms or decreased range of motion result directly from abnormality or spasm of muscles."¹⁰ These diverse ideas indicate a division in the medical field regarding the use of muscle relaxants in a general sense. Because some team physicians prescribe muscle relaxants to certain athletes, it is important that the athletic trainer be aware of the positive and negative aspects of these drugs. The intent of this chapter is to provide a brief overview of these drugs for the athletic trainer's general awareness of this drug class.

The athletic trainer should understand the difference between muscle spasm and muscle spasticity. The athletic trainer will be exposed more often to muscle spasm because this condition is more commonly a result of irritation or trauma to healthy muscle tissue. Muscle spasm resulting from athletic injury trauma results in a loss of range of motion and increased pain in the general area of the tissue damage. Spasticity is a generalized rigidity of the musculature. A brief explanation of spasticity will be helpful to the athletic trainer's overall understanding of the two muscular problems.

Muscle spasticity is caused by a central nervous system (CNS) dysfunction more commonly known as an upper motor neuron lesion. Spasticity is a muscle stretch reflex that is exaggerated in the individual's limb or limbs. Rapid lengthening of the affected muscle results in a contraction of the stretched muscle. Spasticity is technically not a disease process but a result of motor interruption, typically in the upper motor complex of the CNS.¹⁴ Spasticity is more commonly associated with cerebral palsy, paraplegia, or quadriplegia, and is considered a more permanent disorder. The physician's approach to treating spasticity will be much different than the approach to treating muscle spasms.

During a muscle spasm, involuntary tension is developed in the muscle, and the athlete is unable to completely relax the muscle. As mentioned, this muscle spasm will be affected by the pain impulses from the muscle to the CNS. With an increase in the amount of pain impulses traveling from the muscle, there is a concomitant increase in tension in the muscle. This is commonly referred to as the pains-pasm-pain cycle of the injury process. Chronic muscle spasm can result in muscle atrophy in the specific muscle or muscle group.

If the athlete experiences muscle spasm and associated pain that do not allow him or her to get enough rest as is necessary for healing, the physician may prescribe a muscle relaxant. Typically, this will be a centrally acting drug, meaning that the drug works on the CNS somewhere in or along the afferent or efferent pathways of the muscle.

A disorder that is known to be associated with muscle spasms is "malignant hyperthermia" (MH), which has been diagnosed in some athletes and also in individuals who have recently been under anesthesia.² In the general population, this disorder is linked to a genetic predisposition that causes the carrier to be more sensitive to the gases used in anesthesia. This increased sensitivity to anesthesia gases causes the person suffering from MH to experience tachycardia, tachypnea, generalized muscular contractures (rigidity), cyanosis, skin mottling, possibly fever, and sometimes hyperthermia. In rare instances, death is possible. Athletes suffering from this disorder are the focus of this explanation.

Malignant hyperthermia is a disorder usually associated with athletes who exercise in hot and humid environments. It results in an excessive breakdown of muscle tissue. When an athlete experiences a reduction in water intake, this can have a negative impact on cellular function or cellular damage. When muscle cells are damaged by a lack of water intake, an imbalance arises in the calcium homeostasis of the cell. This calcium imbalance can lead to muscle necrosis and possibly rhabdomyolysis. The administration of dantrolene in the early stages of MH, in combination with cooling and hyperventilation, can reverse the destructive process.⁸ However, often a diagnosis of MH is not made before the athlete begins to experience the effects of this muscle cell breakdown.^1,4

Athletes who exercise for long periods of time in hot and humid environments need to drink plenty of water and rest periodically. If an athlete exercising in a stressful environment begins to suffer from hyperthermia, CNS difficulties (dizziness, confusion, lapses of consciousness), or other common heat–stress-related symptoms, he or she should stop exercising and have his or her recovery monitored carefully.

The transition from exertional heat stroke to MH is not common, but can occur in individuals with the genetic trait. You will want to monitor the athlete for increased symptoms of tachycardia, tachypnea, cyanosis, skin mottling, and fever when monitoring heat-related stresses. Exertional heat stroke has been associated with MH, and therefore the athletic trainer should be cognizant of this disorder because it could occur during almost any of the sports seasons. When you suspect that an athlete has experienced a significant heat stress situation, it is important to continue to monitor the weight, CNS, and kidney functions of the athlete. Timely and appropriate treatment of this problem will help the athlete and reduce the problems that the athletic trainer and team physician must deal with later.

Spasms

The exact mechanism of action of skeletal muscle relaxants is not well known at this time. The use of centrally acting muscle-relaxant drugs is not a frequent first-line treatment in the athletic population. It should also be noted that the specific purpose of muscle relaxants to decrease muscle spasm continues to be questioned as a therapeutic intervention.³ The use of these drugs may result in a mild general sedative effect, producing an overall relaxation of the entire body.^7,13 This sedative effect results in a reduction of CNS impulses, which reduces the overall activity of the individual muscle. In short, it is not clear that centrally acting muscle-relaxant drugs directly affect the muscles. It is suggested that these drugs create a sedative effect, which allows the athlete to relax, rest, and allow the muscle to repair itself, thus reducing the amount of muscle spasm the athlete experiences.

The centrally acting muscle relaxants are usually combined with an analgesic like aspirin or acetaminophen to assist with associated pain. Physicians use different types of analgesics based on onset of action, duration, and possible adverse effects for the individual.

As can be seen by reviewing Table 4–1, the drugs prescribed for skeletal muscle spasms display a variety of pharmacodynamics parameters, including onset and duration of action. These factors should be taken into consideration because these drug agents may affect the ability of the athlete to practice or compete. Skeletal muscle relaxants do have a depressing effect on the CNS and therefore can produce sluggishness or even cause the athlete to sleep. Most of the drugs prescribed have an onset of action between 30 and 60 minutes. Knowledge of this will help you explain to the athlete when he or she should take the medication to minimize any associated lethargy. The duration of action varies among these drugs, and this is another important point for the athlete to be cognizant of when trying to participate in rehabilitation programs or attend practices. Drugs with a shorter duration of action will allow participation in rehabilitation and practices. Obviously, drugs with a longer duration of action (12–24 hours) will prevent the athlete from participation in many team activities.

Spasticity

Some muscle-relaxant drugs are considered direct acting. These drugs are most commonly used for treatment of spasticity because their efforts are directed to the individual cells. The use of these drugs is common in individuals who have experienced some type of CNS lesion from an accident at birth (cerebral lesion) or some type of spinal cord accident that results in spasticity. If the athletic trainer is working with disabled athletes, he or she may want to learn more about the use of direct-acting skeletal muscle relaxants in this population.

The muscle relaxants have adverse effects that the athletic trainer should be aware of when talking with the athlete taking these drugs. The main adverse effect is drowsiness.¹³ The instructions on the prescription container will indicate that the athlete should not drive a motor vehicle or perform other activities requiring a high level of motor functioning or reaction capabilities. The athlete may also experience lack of muscle coordination, dizziness, headache, or nausea when taking these medications. These drugs are known to become addictive, and the athlete can develop a tolerance to them. Additionally, the muscle-relaxant drugs can have an additive effect with alcohol that creates an increased sedative effect, sometimes resulting in death.^7,11 When skeletal muscle relaxants are taken in combination with antihistamines, other CNS depressants, or monoamine oxidase inhibitors, there is an additive effect creating increased CNS depression (Box 4–1).

Muscle relaxants can be abused by some athletes, can be obtained illegally, and have a potential for dependence.¹³ The athletic trainer should encourage the athlete to discontinue the use of these drugs as soon as he or she is able to function without them. Additionally, skeletal muscle relaxants are among the most commonly reported drugs of abuse by health-care professionals.⁹ In addition to monitoring your athletes' use of these drugs, you may want to watch for signs of abuse among your fellow athletic trainers and the other health-care professionals you work with on a daily basis. Take the appropriate steps to assist those in need if they are abusing skeletal muscle relaxants or any other drugs.

1. What is the difference between muscle spasm and spasticity?

   1. Spasm is usually a result of muscle trauma.

   2. Spasm is usually a result of a CNS lesion.

   3. Spasticity is usually a result of intense activity

   4. Spasticity is usually a result of prolonged muscle contraction.

2. The use of prescription muscle relaxant drugs in combination with which of the following will reduce muscle spasm?

   1. Thermal modalities

   2. Regular practice and activity

   3. Correct sitting posture

   4. Psychological counseling

3. Prescription muscle relaxants have what effect when combined with alcohol?

   1. Additive

   2. Excitatory

   3. No effect

   4. Stabilizing

4. The main adverse effect of muscle relaxants mentioned in this chapter is:

   1. General sedation.

   2. General excitation.

   3. Loss of memory.

   4. Lack of motivation.

5. When is the best time to schedule an athlete who takes muscle relaxants to come in for adjunct therapy?

   1. During the end portion of the drug's duration of action

   2. During the middle portion of the drug's duration of action

   3. During the most relaxed time for the athlete

   4. During the athlete's regular practice session