[The strain on the rider's arms in straight-ahead motorcycle operation].

The causes of vibration hazards to motorcycle mail deliverers have been considered to be due to the vibrations from the motorcycle, strain on the rider's hands and arms, cold conditions, and duration of the operation and others, and the rider's muscle tone in handling the motorcycle rises as the stability of the motorcycle decreases. In this report, the steering angle and banking of the motorcycle, vibration on the handgrips and EMG on the rider's arms and shoulders were measured during motorcycle operation with weights placed on the front and rear carriers. The relationship between the stability of the motorcycle, vibration on the handgrips and strain on the rider's arms and shoulders measured by EMG are also discussed. The following results were obtained. 1. When weights were placed on the front and rear carriers, the motorcycle became unstable especially at low vehicle speed, and handling became difficult. 2. The acceleration levels of the vibrations on the left handgrip exceeded the 4-8 exposure guideline of ISO when the vehicle speed was 50 km/h with weights. 3. When the weights were placed on the front or rear carrier, the vibration levels on the left grip were generally larger than those without weights. 4. The differences in vibration acceleration levels or vibration levels by weights could not be determined. 5. The EMGs of the musculus extensor digitorum (arms) and musculus trapezius (shoulders) increases with increase of vehicle speed. 6. There were no obvious differences in the EMG on the rider's arm and shoulders under straight-ahead operation by weight loading combinations.(ABSTRACT TRUNCATED AT 250 WORDS)