OVERVIEW OF SPINAL CORD INJURY
The spinal cord is the highway that transports impulses, both sensory and motor, between the brain and the peripheral nerves. Damage to the spinal cord that interferes with nerve transmissions can prevent (or seriously weaken) contraction in the muscle that is innervated by these nerves.
It is estimated that approximately 11,000 new cases of spinal cord injury (SCI) occur annually with about 47% resulting in tetraplegia and 52% resulting in paraplegia (1,2). Tetraplegia (formerly know as quadriplegia) refers to partial or complete paralysis of all 4 extremities and the trunk, including respiratory muscles, and is caused by lesions of the cervical section of the spinal cord. Partial or complete paralysis of entire or part of the trunk and both lower extremities is termed paraplegia and is caused by lesions of the thoracic or lumbar spinal cord or sacral roots (8). More than half of the SCIs occur in individuals between 16 and 30 years of age, and more than 80% of SCI are experienced by men. Recent estimates indicate that between 250,000 and 400,000 people are presently living with SCI or spinal dysfunction (1,2,8). Adaptive and accessible physical fitness programs are needed to address this large and predominantly sedentary population of people, not only to improve their health but also to accommodate the increasing interest in sports participation and recreational activities for individuals with physical disabilities.
Most SCIs are the result of a traumatic event that severs the spinal cord or causes swelling and rupturing of the myelin sheath that covers the nerve fibers (3). Nerves innervated at and below the point of SCI will not function properly, resulting in impaired sensation and motor control. SCIs are categorized first according to where the injury occurs (3). For example, a lesion at the first thoracic level is classified as T1, and an injury at the first lumbar level is classified as L1. SCIs are categorized second as either a complete or an incomplete cord lesion. A complete cord lesion prevents movement in the muscles innervated below the injury level (paralysis), whereas an incomplete cord lesion permits some degree of muscle function (paresis). This is why individuals with injury at the same point on the spinal column may have different neuromuscular abilities. SCIs are categorized third according to the areas of the body that are affected by the nerve damage. For example, injury at or below T1 affects the body below the level of the upper abdominals, and the individual is said to have paraplegia. Injury above T1 affects the arms, trunk, and legs and is referred to as tetraplegia. The Table presents classifications for SCI according to lesion level, and the muscle groups that respond to exercise training.
Management of SCI involves a team of medical professionals, including neurosurgeons, orthopedic surgeons, urologists, physiatrists, physical therapists, and nurses. Medications may be administered to treat spasticity (spasmolytics), prevent blood clots (antithrombics), and address urinary tract infections (antibiotics).
SCI adversely affects physical activity responses, especially the reduced capacity to engage in large-muscle endurance exercise, apart from electrical stimulation modalities. Major limiting factors are the inability to stimulate the autonomic nervous and cardiovascular systems to adequately support levels for more intense aerobic activity and higher metabolic responses (4). Of course, reduced physical activity leads to a variety of debilitating conditions, including bone loss; muscle atrophy (skeletal and myocardial); reduced lean weight, body water content, and blood volume; and increased fat/fat percentage (4). Perhaps, the primary concern for people with SCI is autonomic dysreflexia, an extreme response to mass activation of the autonomic nervous system resulting in a rapid blood pressure elevation (e.g., 300/200 mm Hg) (4).
BENEFITS OF RESISTANCE AND AEROBIC TRAINING FOR PERSONS WITH SPINAL CORD INJURY
Although strenuous aerobic activity is not well tolerated because of orthostatic (postural low blood pressure) and exercise hypotension, as well as potential thermoregulatory problems, persons with SCI can attain beneficial physiological adaptations through appropriate training. Figoni et al. (4) reported improvements of 10-20% in peak power output and peak oxygen consumption. Other desirable outcomes for persons with SCI who do regular strength and endurance exercise include greater active muscle mass, greater muscle strength, more efficient manual wheelchair propulsion, and more functional independence (4). Compared with their nonexercising peers, physically active individuals with SCI may experience up to 23% more capacity for maximum cardiac output and up to 22% more capacity for maximum stroke volume (7). A study in which all the participants had paraplegia showed positive physiological responses to 12 weeks of circuit resistance training (6). On average, the 10 male participants in this study increased their peak oxygen consumption by 30%, time to fatigue by 31%, peak power output by 16%, and overall upper-body strength by 21%.
Active individuals with paraplegia can attain high levels of upper-body fitness, including muscular strength, muscular endurance, and aerobic capacity. Because of the lower levels of neuromuscular and autonomic function, persons with tetraplegia typically achieve less than half the upper-body physical abilities of those with paraplegia.
In addition to enhanced feelings of well-being, exercise provides important health benefits and risk factor reduction for SCI participants. Appropriate exercise increases muscular and cardiovascular function, improves muscle balance and posture, and reduces the risk of health problems associated with physical inactivity.
With respect to physical function, persons with SCI require up to 25% of heart rate reserve to perform activities of daily living and up to 50% of heart rate reserve to manually propel their wheelchairs up inclines (4). Clearly, higher levels of personal fitness enhance the ability to perform these physical functions and to participate in more challenging recreational and athletic activities such as wheelchair sports.
The mechanisms for increasing strength/endurance in the trained muscle are the same for persons with and without SCI and are based on the principles of progressive resistance exercise. However, improvements in aerobic capacity are largely because of greater muscle strength and increased oxygen diffusion into trained muscle tissue. Currently, research does not indicate that persons with SCI can significantly increase their peak cardiovascular responses of heart rate, stroke volume, and cardiac output (4).
The fitness goals for SCI exercisers are similar to other people, namely, increased functional capacity, improved health risk factors, and enhanced self-image (7). The training objectives should include all the major fitness factors including muscle strength/endurance, aerobic capacity, joint flexibility, and coordination for high-skill functional/recreation tasks (5). More specifically, SCI exercisers place highest priority on aerobic fitness and muscle strength/endurance, followed by blood pressure maintenance and general health (5).
Wheelchair propulsion is provided by the muscles of the upper body and arms, which can render the shoulders, elbows, and wrists susceptible to overuse injuries, tendon inflammation, and joint degeneration (5). Surveys of wheelchair athletes have indicated that almost 60% of the reported injuries are to the shoulders and elbows, and more than 20% of the wheelchair athletes have experienced carpal tunnel syndrome (7). Care must be taken to train the responsive muscle groups in a balanced manner, with emphasis on strengthening the weaker muscles and stretching the stronger/tighter muscles.
Perhaps, no group of people has a greater need for regular resistance and endurance exercise than those with SCI. The restricted physical activity and seated posture make appropriately designed exercise a most important component of their lifestyle. In addition to muscular and cardiovascular limitations, persons with SCI may experience additional problems with skin, bones, bladder, bowels, illness, hypotension, hypertension, and thermoregulation (4). Appropriately designed exercise programs must address these health issues with training adaptations that facilitate safe and effective activity sessions. The One on One Column presents the training principles, protocols, programs, and procedures recommended for people with SCI, with specific exercises for improving muscular and cardiovascular fitness.
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. O'Sullivan SB, Schmitz, TJ, eds. Philadelphia, PA: F.A. Davis Company, 1994. pp. 533-535.