Physiology of disability
When thinking about the human body, the spinal cord can be thought of as the control tower of all movements. Without proper spinal cord function, movements can be limited, impaired, or nonexistent. A Spinal Cord Injury (SCI) occurs when a portion or all of the spinal cord or nerve endings of the spinal cord are damaged. The impact of the impairment is dependent on a number of factors including location of damage along the spinal cord, degree of damage done to the spinal cord, and specific nerves that were damaged along the spinal cord.
Most human movements would not be possible without the spinal cord. The brain and the spinal cord are considered part of the Central Nervous System (CNS) and work together to receive sensory information from the Peripheral Nervous System (PNS). The PNS is comprised of nerves that run off of the spinal cord between each vertebrae that receive specific sensory information through muscle spindles within the muscle, the golgi-tendon organs which receives input regarding tension from the body’s tendons, and dermatomes which are nerve endings that receive input regarding pressure from the body’s skin. These components of the PNS work together to relay sensory information to the CNS. With this sensory information from the PNS, the CNS is able to sort the sensory information into purposeful impulses which are relayed down the spinal cord to the PNS. When the PNS receives this impulse form the CNS, muscular contraction (tightening or shortening of the muscle) occurs.
To create a muscular contraction within a motor unit (muscle fibers belonging to a singular motor neuron) the CNS and PNS are needed. The CNS sends an electrical impulse to the PNS, the PNS then transitions the electrical impulse to an action potential (AP). An action potential is the chemical signal that runs through the muscle fiber of the motor unit where the electrical activity changes within a muscle causing contraction. Without the impulse successfully passing between the CNS and PNS, muscular contraction would not occur. This is called the All-Or-None principle in which a muscle fiber contracts at full strength, or does not contract at all. When damage is done along the spinal cord, the PNS is unable to receive information from the CNS and therefore muscular contraction at and below the level of injury is unlikely to occur. However, the location of injury and severity of injury determine how well the PNS and CNS communicate.
Location and severity are two critical factors when assessing an individual with a spinal cord injury and their functional ability levels. The location of the injury determines where the break in CNS and PNS communication will occur along their spinal cord. The signal from the CNS is unable to continue to travel down the CNS at the point of injury. Therefore the PNS will receive no impulse from the CNS. Without this input from the CNS, the PNS is unable to create muscular contraction. In complete spinal cord injuries 90% or more is damaged at the site of injury. If less than 90% of the spinal cord is damaged it is considered to be an incomplete spinal cord injury. Generally speaking, if an individual obtained an upper level spinal cord injury (Cervical, and upper Thoracic region), then all muscle fibers from that point of injury and below are damaged. When injuries occur to the spinal cord below the level of T2 then the individual is considered to be a paraplegic (having full arm function). When the injury to the spinal cord is at or above T2 then the individual is classified as a quadriplegic (decreased function ability of arms, trunk, and legs).
Some key locations of spinal cord injuries include the following:
● C1-C4 location: may require a ventilator, have paralysis of arms, hands, legs, and trunk
● C5 location: individual has control of shoulders and biceps, but not hand or wrist
● C6 level: wrist control but no hand function, wrist extension is easier than wrist flexion
● C7 & T1 location : may have some control of hands, no thermoregulation homeostasis (inability to regulate body temperature)loss of bladder and bowel control
● T-2 location: full function of arms and hands, with mild trunk control
● T2-T5 location: have use of Quadratus Lumborum (can be used to aid in hip flexion)
● T6-T12 location: more use of back extensors and abdominal control, good balance in unsupported stated position, and may have ability to stand with adaptive equipment
● C1-T12 locations: loss of bladder and bowel control
● L1-L5 location: impairment in hip and knee flexion and extension, very limited impairment in trunk control
● S1-S5 location: less impairment in hip and knee flexion and extension, can typically stand with adaptive equipment, little to no impairment in trunk stability
Physiology of intervention
The location of spinal cord injury directly impacts if a muscle fiber is able to contract. To create preferred movements, multiple muscles have to work together (coordinated flexion and elongation). For any specific movement, the body will use muscles as agonists, which contract to complete a majority of the desired movement. The antagonist muscles elongate in opposition to the agonist muscle during a
desired movement. If the coordination of the agonist and antagonist muscles does not occur, the desired movement will not be completed or will be completed poorly. The synergist muscles help to stabilize and assist the agonist during a desired movement. With proper spinal cord function, the agonist and synergists muscles contract while the antagonist muscles elongate to create the desired movements. It is crucial to work the synergistic muscles in individuals with SCI to increase their stabilizing strength.
In addition to working on muscular strength and muscular endurance stabilizing strength is important to incorporate in exercise prescriptions (ExRx) of a person with a SCI. This is due largely to the fact that these individuals have a decreased ability level within their stabilizing muscles, therefore it is important to attempt to work as many stabilizing exercises into their prescription as possible. People with SCI are often in wheelchairs that provide them with stabilization through the back, arms, and foot plates of their wheelchair. Some activities of daily living (ADLs) can be completed from this position however, others require that an individual has more degrees of freedom to complete the ADL. For example, reaching forward to open a drawer to get out a utensil requires additional stabilizing strength. A person who has worked on their stabilizer muscles in an exercise setting will be more successful in completing these ADLs outside of the exercise setting. To incorporate stabilizer muscles into the exercises of a person with a SCI they can complete exercises from a mat table that does not provide them with the known stability of their wheelchair, thus causing their stabilizing muscles to engage and work harder during exercises (even if these exercises are not stabilizer focused). Engagement of the stabilizer muscles can also be achieved through body weight exercises and the use of adaptive equipment. Purposefully targeting core stabilizers can be achieved through crawling movement patterns. When crawling, one must use stabilization strength in order to transfer weight onto one side of the body while attempting to recruit additional muscles to flex at the hip allowing forward movement on the no weight bearing leg. When one hip moves forward, the body must regain balance with a change in the center of gravity; actions completed by core stabilizing muscles. In addition to the benefits of core stabilization that occurs during exercise, the individual is working to prevent further loss of bone density and creating purposeful compensatory mechanisms.
Physiology of our program
A worthwhile exercise program for this population group applies principles and concepts of exercise to individuals with SCIs in a safe, effective, and meaningful way. Through modification and adaptation to exercises one can challenge an individual with a SCI consequently improving their quality of life.
A successful way to challenge the body and modify an exercise is to change the leverage angle (LA) at which the exercise is performed. This will change the difficulty or ease at which the exercise is completed. By changing the LA, the agonist is able to remain the targeted muscle due to the fact that a decreased force is needed to complete the desired movement. For example, changing the LA of a pushup for an individual with a mid to lower level SCI they will be able to complete the exercise with proper form and full range of motion (ROM). Once an individual can complete several pushups at a specific LA, it is appropriate to decrease the LA of the pushup. The lower the LA, the greater force required to complete the pushup. The goal of changing LA is to continue to challenge an individual in a safe and effective manner, working towards the completion of a push up with proper form and full ROM at the lowest LA achievable for the individual’s location of injury.
A specific principle needed when working with an individual with a spinal cord injury is the use of the stretch-shortening cycle. The stretch-shortening cycle (SSC) occurs when a muscle is stretched / elongated, the receptors in the attached tendons send a reflex to the attached muscle to contract, in order to prevent injury. SSC is used in all ballistic movements. The body of someone with a SCI still possesses reflexes, making the use of incorporating exercises that utilize the SSC critical in their ExRx. Applying the SSC to an individual's ExRx can be achieved through exercises that force muscles to stretch/elongate in order to promote muscular contraction. A successful application of this principle is through bounce squats. *Please note that these need to be conducted in a safe manner for the individual with a SCI, meaning a variety of modifications may be necessary (ie. harness, resistance bands, personal lifts, hand support, etc.).* When completing a bounce squat, the quadriceps muscles are elongated/ stretched. Due to this stretching, receptors in the Patella Tendon send a reflex to the quadricep muscle causing contraction. Progression in this exercise is achieved by decreasing the resistance (unloading force) support needed. When working with an individual with a SCI, it is necessary to decrease the amount of assistance during a weight bearing exercise, rather than increasing the output required to complete the exercise. This is largely due to the fact that the CNS and PNS are still not communicating, instead we are focusing on the use of reflexes present in the body to complete the desired movement.
Compensatory mechanisms can be a beneficial concept to understand the application of when writing an ExRx for someone with a SCI. This concept states that the body will overachieve in one area to compensate for failures in another. For example, the Quadratus Lumborum is typically used as a back extensor muscle, however someone with a SCI is able to use it to aid in hip flexion. The ability to engage in assisted ‘hip flexion’ can be utilized in crawling or walking with assistive devices.
The intersection of all of these concepts is through walking with the support of assistive devices. For example, an individual with SCI would be able to stand from their chair (SSC), then utilize their triceps to decrease the weight through their lower body (changing LA), then incorporate stabilizing strength to stand in the assistive device, then must incorporate other supporting muscles such as the Quadratus Lumborum to use during hip flexion, and once progress is made, the amount of support from an assistive device can be decreased.
When incorporating all of this information, great client success can be achieved with a lot of hard work, determination, and skilled exercise physiologists to create and modify the ExRx. One individual with a lower level SCI that has been following an ExRx that hits all of the components of this article has been able to dramatically improve his quality of life. When starting this ExRx, this individual did not have the ability to walk. Through applying the concept of changing LA he increased his tricep strength. This tricep strength was achieved through completing pushups on his knees with his hands on a 12 inch plyometric box. Then progressed to being able to stand and complete push ups with his hand on a 36 inch plyometric box. After the physiological adaptations occurred and the LA of the box was decreased accordingly, the individual was able to successfully complete over 20 pushups with full range of motion with his feet on the ground and hands also on the ground. Through the focus of proper pushup form and progression, the individual with a SCI was working to improve his stabilization strength as well. By way of improved tricep and stabilizer strength he was able to stand upright inside of an assistive walking device (walker). He recruited other muscles in order to flex at the hip but also increased his quad strength through SSC by completing bounce squats consistently. Due to all of the hard work and physical adaptations, this same individual is now walking over 30 feet with no assistive devices other than an ankle brace.
Written by ATP's Jess Johnson & Matt Costa