This observational cross-sectional study examined associations among second-to-fourth digit ratio, handgrip strength, problematic smartphone-use symptoms, problematic Internet-use symptoms, and self-reported smartphone usage time in university students from different regional backgrounds. The analytic sample included 173 students aged 17-26 years from Turkish, Middle Asian, African, and Asian regional backgrounds. Participants completed validated self-report scales for smartphone-use and Internet-use symptoms, and underwent anthropometric, hand morphology, and handgrip strength measurements. The study did not involve randomization, treatment assignment, intervention, or follow-up.

This exploratory observational cross-sectional study evaluated whether bilateral second-to-fourth digit ratio and handgrip strength were associated with smartphone-addiction symptom scores, Internet-addiction symptom scores, and self-reported smartphone usage time among university students from different regional backgrounds. The final analytic sample consisted of 173 participants aged 17-26 years, including Turkish, Middle Asian, African, and Asian students. Regional-background comparisons and sex-specific associations were analyzed using descriptive statistics, group comparisons, correlation analyses, and sensitivity analyses adjusted for age and body mass index. The study was observational only and did not include any intervention, random allocation, treatment exposure, clinical procedure, or prospective follow-up.

Inclusion Criteria:

• University students aged 17-26 years.
• Classifiable sex and regional-background information.
• Ability to understand the study procedures.
• Written informed consent provided.
• For participants younger than the legal age of majority, additional parent or legal guardian consent obtained according to institutional requirements.

Exclusion Criteria:

• Previous finger operation.
• Finger prosthesis.
• Median, radial, or ulnar nerve deformity.
• Carpal tunnel syndrome.
• Developmental or mental disorder preventing participation or valid assessment.

University students aged 17-26 years from Turkish, Middle Asian, African, and Asian regional backgrounds studying at Bandırma Onyedi Eylül University.

Individual participant data will not be publicly shared because the dataset contains participant-level behavioral and anthropometric information. Data may be available from the corresponding author upon reasonable request and subject to ethical and institutional approval.