68 International Journal of Science and Engineering Investigations vol. 2, issue 16, May 2013 ISSN: 2251-8843 Metabolic Response to Repetitive Lifting Tasks: Predetermined vs. Self-Selected Pace Trish G. Sevene 1 , Mark DeBeliso 2 , Chad Harris 3 , Joseph M. Berning 4 , Mike Climstein 5 , Kent J. Adams 6 1,6 California State University Monterey Bay, Seaside, California, US 2 Southern Utah University, Cedar City, Utah, US 3 LaGrange College, LaGrange, Georgia, US 4 New Mexico State University, Las Cruces, New Mexico, US 5 Bond University, Faculty of Health Science and Medicine, Gold Coast, Queensland, Australia ( 1 tsevene@csumb.edu, 6 kadams@csumb.edu) Abstract- Understanding the metabolic demands of repetitive lifting tasks with different pacing strategies may help increase productivity and prevent injuries. The purpose of this study was to determine the metabolic response of repetitive lifting tasks performed with different loads and different pacing strategies. Metabolic parameters were recorded as eight male participants (age = 24 ± 6 yr, height = 173 ± 9 cm, weight = 83 ± 23 kg) participated in predetermined pace (PP) and self- selected pace (SP) weight transfer tasks. The tasks required participants to transfer two 11.4, 15.9, and 20.5 kg weight plates individually back and forth a distance of 195.6 cm horizontally and 115.6 cm vertically (lift from 40.6 cm to 156.2 cm high). Task PP required participants to transfer the 6 weight plates each minute for 10 min (i.e., 60 total transfers); task SP required participants to make the 60 transfers in 10 min or less at a self-selected pace. Statistical analyses were made using both steady state and complete task metabolic data. Results were as follows: significant (p = 0.000) differences were observed in VO 2 based on pacing strategy (PP or SP) during the transfer of 11.4 kg (PP = 13.0 ± 2.3 vs. SP = 17.8 ± 3.7 ml . kg -1 . min -1 ), 15.9 kg (PP = 14.5 ± 2.9 vs. SP = 19.3 ± 4.9 ml . kg -1 . min -1 ), and 20.5 kg weights (PP = 17.5 ± 4.2 vs. SP = 21.7 ± 5.3 ml . kg -1 . min -1 ); mean VO 2 and HR were significantly (p = 0.000) higher during SP (19.6 ± 4.9 ml . kg -1 . min -1 , 123 ± 13 bpm) than during PP (15.0 ± 3.7 ml . kg -1 . min -1 , 109 ± 12 bpm); mean time (min) to completion was significantly faster during SP: 11.4 kg (6.5 ± 1.0), 15.9 kg (6.9 ± 1.0), and 20.5 kg (7.6 ± 1.0); regardless of pacing strategy, oxygen cost (VO 2 ) was significantly higher (p < 0.05) as weight transferred increased; and time to complete the SP transfer task increased as weight increased; also, there was no significant difference (p < 0.05) in total (i.e., sum of the three work bouts) energy expenditure between SP (169.0 ± 20.0 kcal) and PP (173.0 ± 17.7 kcal). In conclusion: 1) when self-selecting pace, mean VO 2 and HR were significantly higher than during predetermined pace at all workloads; 2) metabolic costs increased with increasing workload; 3) task completion was always quicker when pace was self-selected, but total energy expenditure was similar. Keywords- work; weight transfer; pacing. I. INTRODUCTION Repetitive movement of weighted objects is the foundation of many occupations [1, 2] and injuries in the workplace are commonly associated with these lifting tasks. Work-related musculoskeletal disorders (MSDs) represent a major portion of work-related injuries and have significant economic and social costs [3, 4, 5]. Often, the same task involves a variety of lifting strategies (e.g., pacing) to ease fatigue and boredom and adapt to various constraints such as a spacing (clearance), reach, etc. [2, 5, 6]. Recognizing that MSDs occur in a complex system with many factors [6, 7, 8], it is important to isolate and analyze physiological work stress in a variety of conditions [5]. Basic research can then be applied to better analyze various tasks within work systems. Work pacing strategies are an important part of production design. Understanding the metabolic demands of repetitive lifting tasks with different pacing strategies may help prevent injury and increase productivity. Research on pacing strategy has primarily focused on athletic competition, with an emphasis on endurance exercise [9-15]. Overall, what regulates pacing strategy remains unclear [9-15]. It has been suggested however, that strategies encompass both feedback from internal receptors (e.g., perceived exertion, muscular effort, body temperature) and external factors (e.g., work task remaining, task control, past experiences with similar tasks) [9-15]. A review of the literature revealed no studies that assessed the physiological stress of repetitive lifting tasks with different pacing strategies. However, it is reasonable to hypothesize that the same factors control the regulation of pacing during these strenuous lifting tasks as in exercise. Physiological work stress is typically assessed as a function of metabolic response to a given work task focusing on variables such as oxygen consumption, caloric cost, and heart rate [16]. Energy expenditure or caloric cost (kcal/min)