Measurement of muscle passive stiffness in vibration-exposed groundskeepers.

OBJECTIVE: Currently, there is no standardized method to quantify musculoskeletal health of hand-arm vibration syndrome (HAVS). This study evaluated passive stiffness (PS) of the abductor pollicis brevis (APB) muscle among groundskeepers and examined the potential relationship of the PS with lifetime hand-arm vibration (HAV) exposure of the workers. METHODS: PS of APB muscle was measured using a myotonometer among 17 groundskeepers and 10 office workers for 3 days. Study participants’ HAV exposure, demographic information, social history, and health-related information were pulled from our previous studies conducted in parallel with the present study. Linear mixed models were employed to estimate the association between lifetime HAV exposure dose and PS. RESULTS: The average PS for right and left hands was 509.7 N/m (range 402.2–752.9 N/m) and 501.7 N/m (range 380.4–660.7 N/m), respectively, in the exposure group and 422.0 N/m (range 365.0–517.2 N/m) and 430.3 N/m (range 359.2–591.9 N/m), respectively, in the reference group. A significant positive association between lifetime HAV exposure and PS was observed in the multivariable linear mixed model after adjusting for age, body mass index, and race/ethnicity (right hand: β = 6.972 and p-value = 0.0128; left hand: β = 9.039 and p-value = 0.0108). CONCLUSIONS: A significant association between lifetime HAV exposure and PS was found, supporting PS measurement using myotonometry as a promising health indicator for muscular disorders induced by HAV.