Parkinson disease (PD) is a neurodegenerative disorder which influences approximately 6.1 million people worldwide[1]. Parkinson's patients exhibit both motor and non-motor symptoms, including tremors, spasticity, balance issues, hypomimia, micrographia, dysarthria, and dystonia, which hinder daily tasks and increase reliance on assistive devices [2]. PD occurs due to reduction of dopamine producing neuron in basal ganglion of the cerebrum. Parkinson disease patient show increase motor deficit, balance instability, and cognitive decline at advance stage. Stooped posture, masked facial expression, forward flexion of lumbar spine, reduced arm swing, slightly flex knees and hip, shuffling and short stepped gait are the symptomatic appearance of a patient with PD[3].
Postural instability and gait disturbance are associated with PD which leads to falls and freezing of gait (FOG)[4]. In PD patient, FOG occurs multiple time in a day, which increase the chances of fall in PD patients. Fall-injuries reduce mobility, fear of fall, and increase dependence on external sources are all associated with FOG [5].
Slowness of movement (Bradykinesia) is the hallmark sign associated with Parkinson disease[6]. It has a significant role in the impairment and QOL of those with mild to moderate Parkinson disease. It is difficult for a patient of Parkinson’s disease to perform a motor task efficiently, they usually have problems with walking, writing, transferring from one place to another or turning around. Bradykinesia occurs due to impaired neurotransmitter function, bradyphrenia, rigidity and muscle stiffness, postural instability. Bradykinesia occurs due to gradual decrease in amplitude and velocity during movement reoccurrence[7]. Rigidity is one the essential motor symptom associated with PD. It affects various body parts by increasing muscle tone, stiffness and resistance to movement which make difficult to start a movement. It not only affects the limbs but also effect on facial muscles, neck and trunk[8]. PD Patients experienced cogwheel rigidity (a jerky resistance to movement) and lead-pipe rigidity (a constant resistance throughout the movement)[9]. Rigidity in PD makes it hard to initiate a movement, do fine motor tasks, balance and co-ordination and maintain a relaxed posture. It leads to functional limitations, gait disturbance, pain and discomfort, emotional impact, communication difficulty, and impact on posture and balance[10]. Tremors are also the hallmark sign of motor symptoms associated with PD. These include involuntary or shaking movement of hands and fingers and/or other body parts. In PD, there are three type of tremors occur: resting tremors, postural tremor and kinetic tremors[11]. They start asymmetrically, but progress to involve both sides. Simple activities such as writing, buttoning clothes, and eating are challenging to perform for PD patients. It also effect on coordination and lead the difficulties with balance and posture[12]. The most prevalent non-motor symptom that occur in PD patient is cognitive Impairment (CI). This problem encountered at advance stage of Parkinson’s[13]. At that time of PD diagnosis, almost 20–30% patients have mild CI [13]. CI varies patient to patient but it is definitely affect the patient’s memory, attention, decision-making power and visual-spatial abilities [14]. It is difficult for PD individual to perform a dual task due to CI. Dual task (DT) walking refers to a task in which an individual doing two tasks at the same time, such as walking while counting and remembering a list of word[15]. In PD patient it is difficult to perform a dual task because it causes high risk of fall. Fall risk in Parkinson’s patient is increase while doing dual task. Frequent falling effects on the psychological and physical condition of PD patients[4]. DT reduces the speed velocity and step length in PD patient, they are unable to execute two tasks concurrently[2].
Levodopa is the most productive treatment for the PD, although there are some side effects as nausea, vomiting, low blood pressure, dyskinesia, and psychiatric symptoms [16]. The side-effects of Levodopa can be managed by managing the dosage or adding additional medication. Dopamine agonist may initially control symptoms of many patients but at advance stage of Parkinson’s disease, levodopa and poly-therapy is again and again necessary[17]. Recently, a promising new therapeutic strategy for the rehabilitation of patients with hemiparesis and poor pace has been made possible by the use of electromechanical equipment like treadmill training. Treadmill training (TT) is a novel rehabilitation intervention that has shown promise in improving walking performance in individual with PD[18]. There is verification that the Treadmill training may improve the walking performance while doing secondary task[19]. In recent researches treadmill training are used to improve the speed of walking and gait pattern that helps in dynamic balance control and reduced the possibility of fall in patient with PD[20]. Speed dependent TT with partial weight support on PD patient help to restoring the gait pattern. Training on speed dependent treadmill, while performing cognitively challenging task such as counting backwards or naming things, helps the patient to improve walking speed while doing another task simultaneously[21]. It also improves the functional independence in Parkinson’s patients. One of the major goals of rehabilitation is to restore walking after Parkinson's disease. TT is important to increase the speed of walking and improve the DT in patients with PD. This research determined the effects of speed dependent treadmill training on dual task performance in patients with Parkinson’s disease. Mainly Parkinson’s patients have issue in DT performance. Therefore, according to result variation in speed may be used as a treatment option.