BIOMECHANICAL RESPONSE TO LADDER SLIPPING EVENTS: EFFECTS OF HAND PLACEMENT ON RESPONSE AND RECOVERY 1 Alyssa J. Paul, M.S., 1 Marissa Lovell, 1 Naira Campbell-Kyureghyan, Ph.D. and 1 Kurt Beschorner, Ph.D. 1 University of Wisconsin Milwaukee, Milwaukee, WI, USA email: paulaj@uwm.edu INTRODUCTION Falls are one of the most frequent work-related events causing fatal injury [1]. In 2011, the use of ladders resulted in 116 fatal injuries [2]. Additionally, non-fatal injuries involving ladders resulted in the most time away from work (a key measure of injury severity) at 14 days [2]. Studies have investigated the role of hand placement and grip strength during unperturbed ladder climbing [3, 4], as well as ladder design and orientation [5]. Few studies have considered ladder climbing as a whole body process or examined the body’s response to a slip while climbing a ladder. This study characterizes the event sequencing of unexpected slips from a ladder and investigates muscle response to a slip. Furthermore, this study aims to identify differences in the response time to a ladder slip when using a rail grasping climbing strategy compared with a rung grasping strategy. METHODS IRB approval and informed consent were obtained from thirty-two subjects (10 females) aged 18 to 65. Inclusion criteria required regularly climbing a ladder. Exclusion criteria included: weight over 250 pounds, pregnancy and musculoskeletal, neurological or balance disorders. All subjects were fitted with shoes, athletic clothing and a harness. Forty-six reflective markers and 12 EMGs were placed on the subjects. Bilateral muscles included the vastus laterales, medial hamstrings, anterior deltoids, biceps, triceps, and forearm wrist flexors. A custom, vertically oriented ladder was equipped with a spinning fourth rung, which could be set in a position to freely spin or be secured. Marker position and EMG data were captured at 100 Hz and 1000 Hz respectively, via a Motion Analysis Corporation System (Santa Rosa, CA). Subjects were randomly assigned to two different climbing strategies with their hands placed on the rung (RG) or rail (RL). A climbing trial consisted of one ascent and one descent of the ladder. For each climbing strategy, the subject performed 5 to 6 unperturbed trials, with the slip rung locked in place and then one trial with the slip rung allowed to freely spin to induce a slip or fall. In-between trials the subjects performed a fatigue walk outside of the lab so they were unaware of status of the spinning rung. A belaying system (including: belayer, spotter, harness and impact mat) was used to ensure safety of all participants. Slips were defined as when the foot completely slipped off the slip rung during a perturbed trial. Slips and falls were analyzed with respect to their unperturbed baseline trials. Events during climbing such as foot contact and foot off were identified by tracking the vertical position of markers attached to the foot during climbing. A second order, high pass Butterworth filter, with 10 Hz cutoff frequency, was applied to the electromyography (EMG) data. After filtering, root mean squared (RMS) signal smoothing was performed with a time constant of 30 ms. The resulting RMS signals for each trial were then normalized to maximum activity from baseline climbing. For each climbing strategy, the normalized RMS signals of the unperturbed trials were averaged together to provide mean and standard deviation baseline muscle activity. Muscle response onset was identified when the slip EMG activity exceeded 1 standard deviation of baseline climbing activity for a minimum of 50ms. An ANOVA was performed to determine the effect of hand placement on the onset of muscle activity after slip initiation.