Comparison of Muscle Activity in Exercise Bike and Elliptical Trainer in Individuals With Spinal Cord Injury

Spinal cord injury is caused by any mechanism of injury that attacks and impairs the integrity of the spinal cord, preventing it from performing its functions.

It is estimated that the incidence of spinal cord trauma in Brazil is greater than 10,000 new cases per year, 80% being men and 60% aged between 10 and 30 years, with trauma being the predominant cause.

Initial trauma causes injuries by mechanical force, which can cause damage by compression, laceration or section. Any damage to this structure triggers an inflammatory response with edema and, consequently, ischemia, gradually aggravating the injury process, compromising neuronal homeostasis.

The ASIA scale is globally standardized to assess the type of injury. With this scale it is possible to assess the sensory levels preserved through the corresponding dermatomes at each level, testing the superficial and deep sensitivity below the level of the lesion. Motor level is assessed by myotomes, grading the strength of each muscle corresponding to spinal levels.

Neurological disorders resulting from spinal cord injury compromise motor, sensory and autonomic functions, resulting in total or partial loss of voluntary muscle activity, sensitivity, functioning of the urinary, intestinal, respiratory, circulatory and reproductive systems. At the corresponding level, epicritic sensitivity is preserved as it courses in the ipsilateral posterior funiculus. There will also be loss of painful and thermal sensations due to disruption of the nerve fibers that cross the white commissure.

Muscle weakness is the most limiting impairment caused by neurological damage. There is a limitation of activity and several restrictions, which influence the quality of life. The deficit in muscle strength leads to limitations in performing a series of functional activities. The strength of major muscles or muscle groups contributes to functional capacity. Functional independence is positively associated with the peak torque performed by the muscles used to perform a given task.

Physiotherapy has an essential role in the acute and chronic care of these patients, acting as a guide, promoting a greater level of independence, and should aim at preventing deformities, modulating muscle tone, enhancing respiratory muscle function, using various techniques such as transfer training, postural changes, wheelchair handling, balance training, orthostatism and, within the patient's functional potential, restoration of gait and lower limb function, benefiting the performance of activities of daily living, and quality of life.

In spinal cord injury, the deficit of muscle activation compromises many functional actions such as the development of gait, but there are encouraging results with physical therapy techniques that are effective in improving the prognosis of locomotor movement.

Therefore, a set of factors influence gait, which results from an interaction and organization of the neural and mechanical systems, in addition to musculoskeletal dynamics, modulation of the upper nervous system and the afferent pathway, which is also controlled by the Central Pattern Generator through a programming based on a predetermined spinal circuit, capable of producing a rhythm associated with gait.

The Central Pattern Generator is a network of neurons that can produce a variety of movement activity, responsible for automating gait, which depends on feedback from proprioceptors and higher nerve interactions. This generator is responsible for rhythmic motor patterns, generated by inhibitory and excitatory processes of the lower limbs during movements. There is an excitatory and inhibitory relay between agonist and antagonist muscles alternating between limbs.

In these patients, this neuronal domain is compromised, making it difficult to modulate muscle activation. However, recent studies have suggested the existence of effective responses in locomotor training with partial body weight support, leading to an improvement in locomotor patterns.

Locomotor training with partial weight bearing for neurological patients has been studied and considered an important therapeutic mechanism in order to reduce the effects caused by changes in spinal cord injury, being able to fully explore the activation of the patient's potential inducing neural plasticity, providing motor related relearning to the specific task.

Locomotor exercises are based on standardized neural activity. Process by which the central nervous system develops its structure and function in human growth. Continuous repetition of movement can help create this neural pattern in the brain and spinal cord.

There are some devices used in the physiotherapy routine that work rhythmically, for locomotor training and activation of several muscles recruited in the performance of these motor tasks, including the elliptical and the bicycle.

The elliptical is a walking simulator and can also be used for this purpose, which is advantageous in this modality as it reduces the impact on joints, benefiting individuals with impaired balance, as the feet remain in continuous contact with the support surface.

The elliptical provides training with cyclic movement, alternating the lower limbs through a system of levers and sliding axles. When compared to walking on a treadmill, studies suggest that the elliptical reduces plantar pressure in the contact phase of the heel, in addition to reducing the impact of the foot with the contact surface, increasing muscle involvement and increasing the contact phase. individuals with balance deficits.

During the use of the elliptical, the trunk, hip and knee maintain a greater degree of flexion, indicating greater muscle activation of the glutes and vastus lateralis, compared to walking on the ground.

In addition to the elliptical, the static bicycle, used in routine motor rehabilitation, can also be a means of training and muscle recruitment. There is movement of the knees during pedaling, the extension being the most impactful, since knee flexion is passive, as there is no greater activation of the flexors.

The pedaling variation is composed of two phases, the ascending, when the pedals move from the bottom to the top, and the descent, where the pedal displacement occurs from the top to the bottom, with greater power.

Cycling exercise can be used for muscle activation and strengthening, also performed rhythmically and alternately between the pedals. In the descending phase, there is activation of the muscles: gluteus maximus, gluteus medius, vastus intermedius, vastus lateralis, vastus medialis, rectus femoris, gastrocnemius and soleus, with hip and knee extension. In the so-called ascending phase, the ilipsoas, hamstrings and tibialis anterior muscles are activated with consequent flexion of the hip and knee.

Electromyography is a representation of the motor control of the muscular system through the placement of electrodes in the motor units and capture of electrical activity. The electromyographic analysis is used not only to verify muscle activity, but also to determine the periods of coactivation of agonist and antagonist muscles, and can assess activity for function, contraction and learning.

The electromyography signal originates from the electrical activity of the endplate. Thus, the electromyographic signal is generated by the union of the activation potentials of the motor units that are recruited concomitantly, resulting in the interference tracing.

Electromyographic biofeedback is an electronic instrument that provides information (feedback) to an individual about a physiological function or response.