The influence of muscle relaxers on physiologic processes and exercise

Muscle relaxers are a class of drug that effectively decreases skeletal muscle function which in turn produces a tranquilizing effect. Botulinum toxin type-A (BoNT-A) is one type of muscle relaxer that could be commonly seen within a rehabilitation type setting. Research has shown that BoNT-A injections can produce positive outcomes when it comes to controlling spasticity and muscle tone. When considering the effects of exercise and BoNT-A, children who have cerebral palsy (CP) are a good target population to consider given the spasticity that often accompanies the disease. Research has shown that children who receive BoNT-A injections and strength training programs show both an increase in muscle volume as well as a rise in strength . The timing of the injections in relation to strength training did not seem to be a factor in strength improvement, and overall children with CP who received this injection had positive outcomes in their functional ability . This is clinically significant because therapists will be able to increase strength in areas that may be contracted with the assistance of BoNT-A injections.

Another Study looked at the effects of BoNT-A injections for treating spasticity in individuals who had suffered a stroke. As one could imagine, spasticity in the lower extremities can have detrimental effects on an individual’s ability to walk, and this can directly influence their ability to ambulate and gain back independence in life. Many individuals who have been affected by a stroke will have BoNT-A injections to reduce spasticity, but do not include therapeutic activities to either increase strength or function . The results of this study show that those who receive BoNT-A injections and a self-rehabilitation program improve their maximal gait speed, distance covered and max speed during 6MWT-modifeid (6 minute walk test), and time taken to go up or down a flight of stairs in comparison to those who only receive the injections . This research shows that a home stretching and strengthening program can help prevent muscle wasting, and can also improve gait patterns which will then increase an individual's ability to move around independently. 

Diazepam is just one of many muscle relaxers. Diazepam works by inhibiting the excitability of the central nervous system, or CNS. This happens when Diazepam binds to receptors at GABA synapses and boost the GABA inhibiting effects. This mechanism allows Diazepam to act as a muscle relaxer, and increases the GABA effect on alpha motor neuron activity in the spinal cord. One side effect of this drug is relaxation of the skeletal muscle, which will lead to sedation and less general motor activity. This can help someone who is recovering from a musculoskeletal injury. The sedation leads the patient to rest, which will lead to better healing during the initial time after the injury. Another side effect of this drug is not good. If a patient continues to use this drug, they can become addicted. Withdrawal symptoms can include seizures, anxiety, agitation, tachycardia, and sometimes death. This drug is best used for short-term relief for an injury.

Physiotherapists often use Diazepam and Baclofen to help patients. In patients without complications like stroke or a traumatic brain injury, these drugs can interfere with normal neuron changes that help improve motor activities. Lundbye-Jensen, J., Neilsen, J. B., Peterson, T. H., & Willerslev-Olsen, M. (2011) studied healthy patients learning a visuomotor skill. They taught the skill to 16 healthy subjects and used the primary motor cortex leg area in the brain to create responses in the anterior tibialis muscle. The authors found that Diazepam and Baclofen interrupt some of the neuroplastic changes that help patients improve their motor performance. Physiotherapists should use these medications with much caution, especially in healthy subjects. 

Botulism Toxin, after being purified from botulism, also works as a muscle relaxer. It attaches to presynaptic terminal membranes in the skeletomuscular junction. After binding, it destroys proteins that help to make acetylcholine. When it is injected into a specific muscle, the muscle is less exciteable, due to the smaller amount of acetylcholine. This allows the muscle to relax. It can also be used to help someone dress better, wash their hands, and other activites of daily living that use extension in the wrist, elbows, and fingers.

Like many other muscle relaxers, using botulinum can have adverse effects. Long term use inhibits the release of acetylcholine. A decrease in acetylcholine levels causes the muscle to relax, but a lack of acetylcholine paralyzes the muscle fibers. The paralysis in those muscle fibers can spread, and cause loss of function in the muscle.