The prevalence of myofascial pain ranges from 30 to 93% and can result in sensorimotor and autonomic deficits. In routine neuromuscular electrical stimulation, conventional electrode placement (CEP) and inverse electrode placement (IEP) are used to deliver electrical stimulation for pain modulation. However, Whether pain modulation can be achieved better from the intramuscular electrical stimulation (IMES) using the inverse electrode placement (IEP) or the conventional electrode placement (CEP) is still an open issue. Thus, current study's aim to compare the effects of IMES using IEP and CEP, and sham-IMES on pressure pain threshold (PPT), EMG activity, upper trapezius (UT) muscle length and pain severity in the UT muscle with myofascial trigger points (MTrPs) among young adults.

Myofascial trigger points (MTrPs) are defined as discrete areas of tenderness in taut bands of skeletal muscles that are painful. The upper trapezius (UT) muscle has been found to be often affected by MTrPs, which can result in altered sensory-motor function.

MTrPs may be related to pressure pain sensitivity and alterations in the upper trapezius muscle activity. A reduction in PPTs and increased electromyographic (EMG) activity of the UT muscle with MTrPs can be respectively interpreted as increased pain receptors sensitization and motor endplate activity.

In routine clinical practice, exercises, TrP injections, medications, and alternative therapies such as acupuncture dry needling (DN) are used to treat MTrPs. In recent years, some studies have reported that intramuscularly delivered electrical stimulation is a potential resource for the management of myofascial pain syndrome (MPS). Evidence from the literature suggests that IMES is effective in conditions such as adhesive capsulitis, MPS, and other non-traumatic musculoskeletal disorders.

In routine neuromuscular electrical stimulation, conventional electrode placement (CEP) is used, in which an active cathode pole is placed in the peripheral target tissue and a reference anode is placed over the spinal level for peripheral pain modulation. Inverse electrode placement (IEP) is a alternate electrode placement method in which a cathode pole is placed over the spinal level and an anode pole over the distal parts of the limbs. IEP model experiments on MPS and non-traumatic shoulder pain disorders achieved significant clinical outcomes for shoulder pain and associated functional disabilities.

Although IMES is effective in reducing the pain threshold and changing EMG activity, the difference between the effects of IMES based on IEP and CEP on PPT and EMG activity (%MVIC) remains unknown. In line with previous study findings, this study hypothesized that IMES using IEP would achieve significant changes in the PPT, EMG activity, muscle length, and pain severity of the UT muscle with TrPs compared with IMES using CEP and Sham-IMES

Inclusion Criteria:

• Clinical diagnosis of myofascial trigger points in the upper trapezius (UT) muscle.
• Pressure pain threshold range between 0.5 to 1.5 kg/cm2

Exclusion Criteria:

• Shoulder conditions such as adhesive capsulitis, impingement syndrome, etc.
• Individuals with cervical radiculopathy,
• Nutritional deficiencies,
• Metabolic disorders such as obesity, diabetes mellitus,
• Participation in strength training,
• Cardiac pacemakers,
• History of migraine, epilepsy, electrophobia, needle phobia, skin diseases.

Each random number concealed within the small opaque envelope, later all numbers concealed within the large opaque envelope. An independent researcher who was not part of the study generated 36 random (computer generated) numbers, and an office clerk was involved in the allotment of the specified interventions. The intervention provider, outcome assessors and statistician are blinded to interventions.