Walking Speed Modulates Neck-Shoulder Strain During Smartphone Use with Backpack Load.

Area of Science:

• Biomechanics and Ergonomics
• Musculoskeletal Health
• Human-Computer Interaction

Background:

• Concurrent smartphone use and backpack carriage create ergonomic challenges for young adults.
• The influence of walking speed on this dual-task biomechanical strain is not well understood.

Purpose of the Study:

• To investigate how walking speed, backpack load, and gender affect postural alignment and neck-shoulder muscle activity during smartphone use.
• To quantify the biomechanical strain associated with carrying backpacks and using smartphones.

Main Methods:

• Thirty university students (15 males, 15 females) participated.
• Motion capture and surface electromyography (EMG) assessed posture and muscle activity.
• Participants completed 12 conditions: 3 backpack loads (0%, 5%, 10% body weight) and 4 locomotor states (standing, slow, normal, fast walking).

Main Results:

• Increased backpack load significantly worsened neck flexion and upper-trunk posture, while faster walking increased lumbar flexion and neck-shoulder muscle activity (CES, UTZ).
• Upper trapezius (UTZ) activation approached fatigue thresholds (15% MVC) with moderate loads and faster walking.
• Females exhibited more upright postures but higher muscle activity than males.

Conclusions:

• Walking speed is a critical factor modulating musculoskeletal strain during combined smartphone use and load carriage.
• Backpack loads exceeding 5% of body weight may elevate the risk of neck-shoulder strain.
• Reducing smartphone use during fast walking is recommended to prevent neck-shoulder fatigue and discomfort.