Auditory Rhythmic Stimulation for Gait Training
- 1 Introduction
- 2 Clinical application
- 3 Suggestions
- 4 Resources
- 5 References
Gait training in the rehabilitation of different movement disorders has had multiple treatment approaches, one of the most current and with greater evidence of effectiveness for its facilitating effect for functional walking is auditory rhythmic signaling, acoustic rhythmic cueing or auditory rhythmic stimulation. In which acoustic rhythms produced by metronomes or previously selected music, signal the cadence during walking so that the patient synchronizes their footsteps with the rhythm or stimulus heard.
Achieving this synchronization results in instantaneous and prolonged effects that are transferred to various characteristics or parameters of the gait:
- Increases step length, cadence, and symmetry
- Improves the functional walking ability manifested by increasing gait speed and therefore produces faster walking and longer strides.
Mechanism of action
To achieve gait, inputs are required from various levels of the motor control system: cerebral cortex, brainstem, cerebellum, and central nervous system.  In addition, the ability to modify the gait with the acoustic rhythms depends on how well the gait is linked to the rhythm and the effectiveness of the acoustic rhythms to modify the gait depends on the speed of the metronome.
Mechanism of action in the motor control system
It has been shown that the highest auditory rhythmic signaling, i.e. A constant auditory stimulus at a frequency of 110% of the normal cadence of the patient, increases the accuracy of the central motor impulse and therefore the impulse force of the nerve over which the command is issued. Consequently, the regulation of the skeletal muscles by the central nervous system can reinforce the coordination between agonizing-antagonist muscles. 
The rhythmic auditory signals activate the motor neuronal spinal nuclei through the reticulospinal pathway, this makes it possible to train the coordination of axial and proximal movements by motor commands. In addition, some studies suggest that increased excitability on this pathway decreases muscle reaction time to improve walking speed.
The effect that the acoustic rhythm has as a feedback stimulus in gait is achieved by increasing the excitation in the subcortical nuclei that adjust the balance with the bilateral movement of the trunk and proximal muscles, which makes possible the reactive motor coordination is driven by the stimulus feedback.
The way in which gait adjusts to the acoustic stimulus is called auditory-motor coordination. Knowing the ability of auditory-motor coordination of a patient allows the physical therapist to modify the metronome to achieve the most optimal coupling between gait and rhythm and therefore obtain better results in the modification of gait parameters through acoustic rhythmic stimulation.
Studies have shown that if the rhythm of the metronome is slower than the rate that the patient can maintain, patients anticipate the rhythm with their footsteps. This is explained by the dynamics of the coupled oscillators that describe that the derivation phase, which means the period of time it takes to match the footstep to the stimulus, will be longer for the metronome speeds slower than the patient's preferred rate.
While the variability in relative time, i.e. The time it takes the patient to synchronize their footsteps with the rhythm, will be shorter if the frequency of the metronome is closer to the patient's preferred rate. The decrease in this period of time reflects a better auditory-motor coordination 1 Therefore, the farther the frequency of the metronome from the patient's cadence is, the patient will require more steps to synchronize his footsteps with the beat
The auditory-motor coordination is better if the stimulus frequency is close to the patient's preferred rate, therefore the efficiency of the acoustic rhythms in symmetry, fluidity, and gait adaptability will also be greater.
The frequency of the metronome.
Generally, 3 different stimulus frequencies are used for auditory cueing 90%, 100% and 110% of the patient's cadence. However, in one study it was found that using 110% of the patient's cadence is the best frequency as an auditory rhythmic signal to improve the stride length, cadence and gait speed due to the aforementioned mechanism, that this signal frequency achieves on the motor control system.
- Cerebrovascular accident
- Cerebral palsy
- Huntington's disease
The 2 populations most benefited by the effects achieved by signaling or auditory rhythmic stimulation as a method of gait rehabilitation are patients with Parkinson's and cerebral vascular events because they increase their speed, stride length, and cadence.
In addition, there are studies that demonstrate its effectiveness also in adult patients with Cerebral Palsy and is currently receiving more attention on its effects of improvement in gait ability in older adults and prevention of falls. So its effectiveness could be applied to any population with movement disorders, which have disturbances in gait pace.
|Characteristics of the gait in different populations|
|Healthy Adult||1 -1.2m/s speed; 1.1 - 1.4m. stride length; 102 - 114 in cadence|
|Older Adult||Unstable, disorderly rhythm, speed and length of stride decreased and risk of major fall|
|Patient with Parkinson disease||Abnormal posture, abnormal gait pattern with stride length and decreased speed and disorder in rhythm|
|Patient with Cerebral Vascular Accident||Speed, length of stride, cadence, phase of support in only one leg decreased and the phase of double support is greater in duration.. Temporary asymmetry.
(The parameters of the gait after an EVC are approximately half of the normal values
Evidence of effectiveness
The lack of selective movements and coordination due to spasticity and muscle weakness in patients with cerebral palsy is the greatest disability.
The treatment in patients with cerebral palsy is mainly based on the neurodevelopmental approach, which, by facilitating sensorimotor components (muscle tone and reflexes) and by inhibiting abnormal movement patterns, improves functional movement, especially in the gross motor skills, postural control and stability; However, Bobath noted that these achievements do not transfer to the activities of daily life; Due to this fact, auditory rhythmic stimulation, because of its mechanism of auditory-motor synchronization over the reticulospinal tract, is one of the new methods in gait training.
When making comparisons between neurodevelopment treatment and auditory rhythmic stimulation, positive results were obtained in the temporal parameters of the gait and some of the kinematic parameters in the patients treated with auditory rhythmic stimulation.
|Temporary patterns:||Kinematic patterns:|
|Cadence, speed, stride length, step length increased significantly after 3 weeks of gait training in patients with rhythmic auditory stimulation.||Pelvis: Excessive anterior tilt significantly decreased in patients with rhythmic auditory stimulation, this has as a positive consequence, a significant improvement in the pattern of the general pathological gait characterized by spasticity in the hip flexors|
|Stride time, step time and support phase decreased significantly after 3 weeks of gait training in patients with rhythmic auditory stimulation.||Hip: decreased excessive flexion and worse movement in adduction, abduction, internal rotation and external rotation with rhythmic auditory stimulation during walking. Therefore, to improve the parameters of internal rotation movement and extension, it is suggested to use the neurodevelopmental method, which obtained significant improvements for these two planes because it stabilizes pelvis and hip by acting on muscle tone and postural alignment besides improving the dissociation of pelvic members|
|Some parts of the gait cycle were moderately normalized as in the support and swing phase after 3 weeks of gait training in patients with rhythmic auditory stimulation.|
In reference to the temporal patterns, the auditory rhythmic stimulation approach improved the measurements or parameters of a functional walk.
Auditory rhythmic stimulation improves functional gait in patients with spastic cerebral palsy manifested by increased speed, while the neurodevelopmental approach improves stability during walking manifested by increased stride time.
Cerebral Vascular Accident (CVA)
Training with cadence signaling improves gait parameters by increasing its speed 0.23 m / s, stride length 0.21 m, 19 steps/minute in cadence, gait symmetry 13-15% 
The improvement in the speed of walking is important because there are studies that show that the probability of presenting severe disability in patients with subacute EVC decreases if its speed in the gait increases to at least 0.16m / s. In addition, there is evidence that the speed improvement at 0.13m / s is already considered a clinically significant achievement.
The speed increase of the gait is accompanied by the improvement in stride length, which suggests that adding signaling to the cadence is not detrimental to the quality of the movement. This is important because some health professionals believe that by increasing the speed of the signaling rhythm, they will increase the pace and speed of the gait but sacrifice the stride length.
Huntington's disease (HD)
Although few studies have assessed the impact of auditory rhythmic stimulation on affected gait or hand function in HD, this neurodegenerative disorder, characterized by instability and uncontrollable jerky movements, also impacts the basal ganglia, arguably of interest in the context of rhythm. Large-scale meta-analyses are not possible here, but previous findings indicate that whereas gait velocity can reportedly be adapted to RAS, this is the case for period and not phase entrainment, and only for metronomes and not music. More recently, HD patients were also found unable to synchronize their gait to a metronome, and a recent review deemed there was insufficient evidence for the usefulness of auditory rhythmic stimulation in HD . Considering upper-limb function, HD patients were able to turn a crank in phase bilaterally, but not 180° out of phase. Interestingly, auditory rhythmic stimulation did not help, dissociating HD from Parkinson's patients, whose task performance did benefit from metronome cueing.
Although training of locomotor timing skills, identified as part of the disorder, has been suggested to improve movement in HD , the use of auditory stimulation does not appear to modulate movement directly. The executive function deficit that is typical for HD  may be related to sensorimotor synchronization capabilities and specifically phase entrainment, suggesting more subconscious cognitive involvement in synchronizing to specific accents and predicting temporal structure, differentiating the basal ganglia dysfunction of HD from Parkinson's in terms of synchronization abilities.
The main movement problems associated with Parkinson's are tremor, rigidity, bradykinesia and postural instability, leading to problems with gait and balance. The use of auditory rhythmic stabiliazation for movement (generally gait) is most developed for this population, as the positive effects of rhythmic cueing are relatively well established. A comprehensive review of these findings was recently provided, including a meta-analysis of RCTs on the efficacy of music-based movement therapy for Parkinson's shows that walking interventions yield better carry-over results to gait measures than dancing intervention.
About half of Parkinson's patients develop a symptom called freezing, or motor blocks, which is a common cause of falls, occurring less often in patients with tremor as their main symptom. A study looking at the effect of auditory cues on motor learning in Parkinson's patients  found that Parkinson's patients with freezing symptoms (unlike controls and Parkinson's patients without freezing) showed no indication of training-induced plasticity (measured as cortico-motor excitability with MEPs) after self-paced hand movement training, whereas after cued movement training, MEP changes did occur, similar to the other two groups. This suggests that patients who experience freezing benefit crucially from auditory cues in this paradigm, whereas non-freezers also learn without cues. Thus, the usefulness of cues may be moderated by specific symptoms, at least for upper-limb movement. The finding that Parkinson's patients generally do not report any great reduction of symptoms while listening to music  may also relate to a need for specificity of the cue and the patient subgroup.
It is important to identify the characteristics or parameters of the gait such as symmetry, adaptability, fluidity, speed, cadence, stride length, etc. to evaluate the recovery of motor function and guide the retraining treatment of the gait, paying special attention to the symmetry and cadence as intervention objectives.
Speed is commonly used as an index to assess gait ability. However, if the physical therapist wants to obtain better results in the use of auditory rhythmic stimulation it is necessary to consider the auditory-motor coordination of the patient, since this will allow him to make optimal modifications to the patterns of walking through the adjustments in the metronome that are more effective for the coupling between gait and rhythm.
If the frequency of the stimulus approaches the preferred rate, the patient will take approximately 4 steps to adjust their pace to the rhythm. The faster or slower the frequency with respect to the patient's cadence, he/she will need a greater number of steps. Therefore, a good way to start is to use stimulus frequencies similar or close to the preferred cadence.
- The patient walks barefoot 10 m 3 times at his preferred speed or 7 min
- The cadence is calculated (steps/minute)
- The rhythm of the metronome adjusts to the patient's cadence
- The auditory rhythmic stimulus is applied, and the patient is asked to synchronize his footsteps with the rhythm
- Once the synchronization is achieved, the necessary adjustments in the metronome frequency can be made. The evidence suggests greater effectiveness at 110% of the patient's cadence
If the rhythm has a constant frequency, this signal will promote temporary symmetry when walking 
If the frequency of the rhythm increases, the cadence and therefore the speed, increase
- 2 metronomes can be used to sign the pace of 2 steps per stride: according to evidence  the gait can be modulated more effectively when both footsteps are signaled using a different tone for each heel shock stimulus (440 Hz left foot ) (1000 Hz right), this generates greater stability in auditory-motor coordination
- 30 minutes of training is suggested for 4 weeks, 4 times a week.
- The cadence signaling in gait training is an easy, inexpensive and easy to apply intervention, in addition to not requiring permanent and thorough supervision by the PT for patient safety.
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