Different Neuromuscular Control Strategies In Dominant And Non-dominant Handwriting

PURPOSE: Writing with the non-dominant hand or without visibility can impact text legibility. This study investigates muscle activation and handwriting features under various sensory conditions, to uncover neuromuscular control strategies in handwriting. METHODS: Twelve right-handed graduate students (6 M, 6 F, 27.2 ± 2.4 yrs old) completed 4 handwriting tasks using dominant and non-dominant hands, with eyes open or closed. They wrote each of the 5 isolated letters and 3 words with a single stroke, repeating each randomly 8 times. Writing metrics, including time, length, speed, and pen pressure, were recorded using a graphic tablet. Electromyographic signals from 12 muscles across both arms, including abductor pollicis brevis (APB), first dorsal interosseous (FDI), extensor carpi radialis (ECR), flexor carpi ulnaris (FCU), anterior deltoid muscle (ADM), and upper trapezius (UT), were measured using surface electromyography (Fig. 1). The root mean square (RMS) was used to quantify the muscle activity. RESULTS: Fig. 1 below shows the non-dominant hand increased time and length (t = 7.866, p < 0.0001; t = 10.691, p < 0.0001, respectively), while reducing pen pressure (t = -4.417, p = 0.0001). The closed eyes reduced time (t = -3.640, p = 0.0009), while enhancing length and speed (t = 4.250, p = 0.0002; t = 3.978, p < 0.0004, respectively). The RMS amplitude decreased for FDI, ECR, and FCU muscles on the non-dominant side (t = -2.977, p = 0.0054; t = -2.503, p = 0.0174; t = -4.783, p < 0.0001, respectively), while it increased for ADM (t = 5.954, p < 0.0001). No significant interaction effects were found in any of the indicators (all, p > 0.05). CONCLUSIONS: Visual and hand-use independently influence various features in handwriting. Different muscle activation strategies exist between bilateral hands, with increased activation of proximal limb muscles when using the non-dominant hand, which may serve as a compensatory mechanism to maintain the clarity and accuracy of handwriting.