Influence of Jackhammer Weight on Grip Pressure, Muscle Activity, and Hand–Arm Vibration of the Operator

Abstract

OCCUPATIONAL APPLICATIONS The conventional (41 kg) jackhammer is most commonly used in construction, and it is widely believed that a lighter jackhammer would be less effective or unable to perform certain tasks. We compared the performance of two hammers (conventional and 35% lighter) at breaking a 15 cm reinforced concrete slab, and found that some trade-offs exist between the two. Benefits of using a 35% lighter tool were mainly in reduction of muscle activity, shorter lifts, and some reduction in grip pressure. However, the lighter tool resulted in an elevated vibration dose, mainly due to an increase in task time though there were no major changes in vibration magnitude measured on the hand. Based on these results, a lightweight jackhammer may be suitable for breaking a concrete slab, and could provide a two-fold reduction in low-back injury risk due to lifting, as well as allow a population with a larger range of strength and stature to perform this task.TECHNICAL ABSTRACT Background: Construction and utility workers traditionally use 40 kg jackhammers to break pavement, and this task involves exposures to several injury risk factors. Lighter jackhammers are not commonly utilized, as it is commonly believed that they would not be able to perform the task. While some preliminary research by our team has determined that lightweight jackhammers can perform the wide range of tasks required for breaking pavement, the benefits/limitations of using a lightweight jackhammer have not been fully explored. Purpose: To perform a biomechanical evaluation of and quantify the difference between operating a conventional and a lightweight jackhammer during the lifting and operating phases. Methods: Twelve volunteer jackhammer operators were instructed to break a 0.9 m × 0.9 m section of 15 cm thick reinforced concrete along pre-painted diagonal lines. Two pneumatic jackhammers were used: a lightweight jackhammer (27 kg) and conventional jackhammer (41 kg). Throughout each task, upper-body muscle activity, task time, grip pressure, and vibration magnitude and frequency were measured. Results: Using the lightweight jackhammer resulted in a 58% increase in task time and consequently resulted in increasing the partial vibration dose value by 36%. Nevertheless, 40% less muscle activity was required to lift the lighter jackhammer and 25% less upper-body muscle activity was used during the operational phase. Surprisingly, an inverse relationship was found between grip pressure and hand–arm vibration for both jackhammer weights. Conclusions: A reduction in jackhammer weight offers some potential biomechanical benefits to the operator, specifically reducing the overall muscular effort during task performance and up to two-fold reduction in muscular demands due to lifting, as well as a reduction in grip pressure. Potential adverse effects of the lightweight jackhammer are an increased task time and duration-adjusted vibration dose.