Proximal forearm extensor muscle strain is reduced when driving nails using a shock-controlled hammer Kimberly A. Buchanan a , Maria Maza a , Carlos E. Pérez-Vázquez a , Thomas Y. Yen a,b , Richard Kijowski c , Fang Liu c , Robert G. Radwin a,b, ⁎ a Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, WI, USA b Department of Industrial and Systems Engineering, University of Wisconsin-Madison, Madison, WI, USA c Department of Radiology, University of Wisconsin-Madison, Madison, WI, USA abstract article info Article history: Received 28 February 2016 Accepted 6 August 2016 Background: Repetitive hammer use has been associated with strain and musculoskeletal injuries. This study in- vestigated if using a shock-control hammer reduces forearm muscle strain by observing adverse physiological re- sponses (i.e. inflammation and localized edema) after use. Methods: Three matched framing hammers were studied, including a wood-handle, steel-handle, and shock- control hammer. Fifty volunteers wererandomly assigned to use one of these hammers at a fatiguing pace of one strike every second, to seat 20 nails in a wood beam. Magnetic resonance imaging was used to scan the fore- arm muscles for inflammation before the task, immediately after hammering, and one to two days after. Electro- myogram signals were measured to estimate grip exertions and localized muscle fatigue. High-speed video was used to calculate the energy of nail strikes. Findings: While estimated grip force was similar across the three hammers, the shock-control hammer had 40% greater kinetic energy upon impact and markedly less proximal extensor muscle edema than the wood-handle and steel-handle hammers, immediately after use (p b .05). Interpretation: Less edema observed for the shock-control hammer suggests that isolating handle shock can mit- igate strain in proximal forearm extensor muscles. © 2016 Elsevier Ltd. All rights reserved. Keywords: Ergonomics Lateral epicondylitis Magnetic resonance imaging Muscle edema Work related musculoskeletal disorders 1. Introduction Upper arm musculoskeletal disorders, such as lateral elbow tendinopathy, lateral epicondylitis, or “tennis elbow” are associated with strenuous tasks and manual work (Descatha et al., 2015), and were the subject of several recent prospective epidemiological studies (Fan et al., 2014; Herquelot et al., 2013; Descatha et al., 2013). Proximal elbow musculoskeletal injuries have been related to hammering (Geoffroy et al., 1994; Stasinopoulos and Johnson, 2006) and were ob- served in metal workers that hammered 8.4 h daily (Gangopadhyay et al., 2007). Previous study of hammers from a biomechanical standpoint (Drillis et al., 1963) demonstrated that striking efficiency depended on the loca- tion of the hammer center of gravity and its radius of gyration. The prin- ciple of ‘bend the tool and not the wrist’ was tested and found that using a bent hammer handle marginally reduced ulnar deviation, muscle fatigue, and subjective discomfort (Schoenmarklin and Marras, 1989a, 1989b). Karwowski et al. (2003) observed that weight and grip softness did not affect the number of nails hammered straight, while subjects identified handle design, weight, and hammer mass distribution as crit- ical factors affecting their performance. Côté et al. (2005) found that re- petitive hammering while fatigued affected motions of the wrist and elbow, suggesting adaptive strategies for sustaining productive work may increase the risk of injury to the neck and shoulders. There is considerable indirect evidence that the shock loading in the hands from hammers could plausibly affect the risk of injury (Blackwell and Cole, 1994). Radwin et al. (1989) demonstrated that impulsive loading from power hand tools at different intensities affected forearm muscle responses. Delayed-onset muscle soreness and edema are often experienced following intense eccentric exercise (Shellock et al., 1991; Foley et al., 1999). The mechanism of edema is not well under- stood, but is associated with increased permeability of the blood vessels in response to inflammation following muscle damage, and is a poten- tial precursor to the development of musculoskeletal injury. Signs of edema may be indicative of strain affecting involved anatomical regions. Although hammering has been previously studied, no research has rigorously investigated use of shock-control hammer handles. Henning et al. (1992) considered forces generated by the impact between the ten- nis racket and ball and vibration transferred to the arm, to investigate how racket characteristics transmitted vibration to the forearm in tennis elbow. Clinical Biomechanics 38 (2016) 22–28 ⁎ Corresponding author at: Department of Biomedical Engineering, University of Wisconsin-Madison, 1550 Engineering Drive, Madison, WI 52706, USA. E-mail address: radwin@engr.wisc.edu (R.G. Radwin). http://dx.doi.org/10.1016/j.clinbiomech.2016.08.004 0268-0033/© 2016 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Clinical Biomechanics journal homepage: www.elsevier.com/locate/clinbiomech