In Japan, compensable occupational diseases are officially listed in Appended table 1 and 2 of Ordinance for Enforcement of the Labour Standards Act. The category No. 3 (diseases caused by work with extreme physical tension) includes a subcategory of (d): musculoskeletal disorders of the back of the head, neck, shoulder girdle, upper arm, forearm, or fingers due to work which require repeated input into a computer or other operation involving excessive tension on the upper limbs. Local labour standard bureau is in charge of judging the work-relatedness. The detailed criterion was first published as a notice from the Labour Standard Bureau, Ministry of Labour on Feb 5, 1975, as ‘Judgment criterion for work-relatedness of upper extremity disorders from keypunching work’ (Notification No. 59, 1975) and revised on Feb 3, 1997, as ‘Judgment criterion for work-relatedness of diseases from upper extremity work’ (Notification No. 65, 1997). Target diseases of the criterion include humeral epicondylitis, cubital tunnel syndrome, supinator syndrome, wrist tendonitis, carpal tunnel syndrome and cervico-omo-brachial syndrome (COBS; nonspecific symptoms of neck, shoulder and upper extremity). Three indispensable conditions of the required exposure for determining work-relatedness are:

• long (≥6 months in general) and heavy workload to the upper extremity,

• excessive (≥10% increase, ≥20% increase/day for 10 days/months or ≥20% increase/hour for ≥1/3 hours/day) workload for 3 months preceding symptoms and

• reasonable time course.

The criterion requires careful and comprehensive judgment of the work-relatedness of individual cases referring to the working environment, heteronomous and restrictive nature of the work, their age, physical strength, life style at home, etc. It recommends avoiding diagnosing as COBS; however, it still allows use of COBS when the specified diagnoses are difficult. According to the workers’ compensation statistics in 2016, there were 153 cases of upper extremity diseases out of 7361 cases of occupational diseases in total with 4 or more lost work-days.