Asymmetries in both physiology and anatomy at different levels of the central nervous system, which controls the upper extremities, are well-established. These asymmetries, related to handedness, are evident in the motor cortex and corticospinal tract. Moreover, variances have been identified in peripheral nervous pathways, including elevated sensory detection thresholds and increased conduction velocities in the motor nerve of the dominant arm.

Apart from disparities in the nervous system, differences also arise in the muscles. Prolonged preferential utilization of muscles on the dominant side of the body may lead to alterations in muscle fiber composition, characterized by a higher predominance of slow-twitch type I fibers.

Modern technology plays a key role in daily human life. This involves keeping pace with rapid changes in the field of communication technology. In this context, smartphones have become an essential part of life, not only in matters related to communication, but also as essential social accessories. As a result of this social involvement in communication technology, young children have become avid smartphones users. Holding a phone in hand needs support from fingers, flexion of hand and wrist, so holding the phone in same position for long periods can cause huge amount of stress on the structures present in the hand. This stress can cause injuries and damages in longer periods.

To address this objective, we will examine muscle synergies on the dominant sides in right-handed and left-handed participants while performing upper limb motor tasks. To accomplish this, we will conduct the following: Comparative analysis of motor and sensory nerve conduction velocities (radial, median, and ulnar) in right-handed and left-handed individuals during smartphone use. Comparison of hand muscle activation between right-handed and left-handed individuals during smartphone use.

Handedness is a well-recognized behavioral phenomenon characterized by a preference for using one hand over the other. This study investigates the impact of handedness on electromyographic (EMG) activity of hand muscles and nerve conduction velocity during smartphone use.

This interventional parallel study included 70 participants (35 left-handed, 35 right-handed) aged 12 - 14 years inclusion criteria: normal BMI (16.5-24 kg/m²) no regular athletic activity, Participants shared the same socioeconomic level used the same smartphone model (6.7-inch touchscreen).

Exclusion criteria included:

peripheral nerve injury upper extremity movement limitations history of upper extremity fractures or deformities, neurological disorders such as peripheral neuropathy due to type I diabetes mellitus.

EMG activity and nerve conduction velocities (radial, median, and ulnar nerves) will be measured before and during smartphone use. Muscle activation will be assessed for the abductor pollicis longus (APL), extensor carpi radialis (ECR), flexor carpi ulnaris (FCU), and first dorsal interosseous muscles. Statistical analysis will be conducted to identify significant differences between left-handed and right-handed participants.

Inclusion Criteria:

• normal BMI (16.5-24 kg/m²)
• no regular athletic activity, participated.
• Participants shared the same socioeconomic level
• used the same smartphone model (6.7-inch touchscreen)

Exclusion Criteria:

• peripheral nerve injury
• upper extremity movement limitations
• history of upper extremity fractures or deformities,
• neurological disorders such as peripheral neuropathy due to type I diabetes mellitus.

Seventy adolescents (35 left-handed, 35 right-handed) aged 12 to 14 years, with normal BMI (16.5-24 kg/m²) and no regular athletic activity, participated. Participants shared the same socioeconomic level and used the same smartphone model (6.7-inch touchscreen).