Joint posture and temporal determinants of handwriting speed and legibility in an Indian cohort

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Aim The study aimed to analyze the biodemographic, temporal, and joint postural determinants of handwriting speed and legibility, and to explore their potential relevance to forensic handwriting research. Methods A cross-sectional study was conducted among 209 medical students (mean age 21.4 ± 1.5 years; 64% female) at a tertiary teaching hospital in India. Participants copied a standardized text under uniform conditions. High-resolution photographs captured wrist, thumb, and index finger joint angles during writing. Writing speed, fluency, and legibility were quantified using validated metrics. Correlation and multivariable regression analyses identified independent predictors of handwriting performance. Results Mean writing speed was 127.4 ± 22.1 letters per minute, and mechanical fluency was 120.4 ± 22 words per five minutes. Writing speed correlated significantly with the second proximal interphalangeal (PIP) joint angle, whereas legibility correlated with the thumb interphalangeal (IP) joint angle. After adjusting for confounders, the PIP joint angle remained an independent predictor of writing speed (β = 0.32, 95% CI: 0.14–0.51, p < 0.001), and the thumb IP angle predicted legibility (β = 0.27, 95% CI: 0.10–0.45, p < 0.001). Medium of instruction and academic performance were also significant predictors of writing speed (p < 0.001). Conclusion Handwriting performance is governed by joint mechanics and biodemographic variables influencing speed and legibility. These findings provide baseline postural data for Indian writers and may offer preliminary biomechanical reference observations relevant to future forensic handwriting research. However, further validation using authentic forensic handwriting samples is required before practical forensic applicability can be established.