Manual Material Handling (MMH) is defined as any activity that requires a person to exert a force to lift, lower, push, pull, carry, move, hold, or restrain a person or an object (Abadi et al., 2015).” Research over the past three to four decades has shown that manual material handling has a highly significant association with the development, precipitation, and prognosis of work-related musculoskeletal disorders (WRMSD) especially affecting the lower back region (Zurada, 2012). Evidence, as found by the National Institute of Occupational Safety and Health (NIOSH), states that “there is a relationship between lifting heavy weights and lower back pain (LBP)” (Stack, Ostrom, & Wilhelmsen,2016). According to an economic survey done in 2007-2008 in India, 98% of the employees in the country are employed in the informal sector, accounting for 53.9% of India’s gross domestic product. The informal sector involves frequent MMH tasks like lifting heavy objects, performing repetitive tasks, maintaining a fixed posture for a longer duration of time, overexertion, and non-neutral posture which have been found to be physical risk factors of LBP (Sarkar, Dev, Das, Chakrabarty, & Gangopadhyay, 2016).
During lifting, the extensor muscles of the posterior trunk generate large compression, tension, and shear forces that are transferred to the joints and connective tissues (tendons, ligaments, fascia, and discs) either directly or indirectly within the lower back. When these forces exceed the structural tolerance, it ensues injury at a microscopic or macroscopic level which results in the release of inflammatory cytokines leading to acute or chronic LBP (Neumann, 2017).
Fatigue being one of the major risk factors of low back pain and back injuries leads to compensatory muscle recruitment patterns which cause decrements in the ratio of lift-strength vs task requirements and changes in spinal load (Granata & Gottipati, 2008). Physical fatigue is described as decrements in muscular performance with continued effort accompanied by general sensations of tiredness or is alternatively defined as the inability to maintain the required power output to continue muscular work at a given intensity. It is classified 3 into two types central and peripheral. Peripheral fatigue occurs when the rate of energy delivery (ATP-PCr, anaerobic glycolysis, and oxidative metabolism) decreases, and metabolic by-products, such as lactate and H+ get accumulated, leading to failure of the muscle fiber’s contractile mechanism. Central fatigue occurs when there are alterations in the neural control of muscle contraction (Wilmore, Costill, & Kenney,2012)
With an intention to reduce the incidence of LBP, lifting aids have been developed, which are categorized as off-body and on-body lifting aids. When loads exceed human capability and require repetition, off-body lifting aids such as hoists and trolleys are often used whereas when the load is within human capability, an on-body lifting aid such as exoskeletons is used (Abdoli-Eramaki, Stevenson, Reid, & Bryant, 2007). Exoskeleton which is a wearable, external structure adds mechanical power to the human body thereby decreasing the direct load placed on the back hence preventing the risk of WRMSDs. It is typically classified as active (motorized) or passive (non-motorized). Active systems consist of single or multiple operating units to increase human competency, whereas passive systems use materials that possess the ability to store and release energy during movements to assist workers to perform physical movements. (Bosch, van Eck, Knitel, & de Looze, 2016; de Looze, Bosch, Krause, Stadler, & O’Sullivan, 2016).
On Body Personal Lift Assist Device (OBPLAD) is a non-motorized, passive device in which the elastic elements act as an external muscle power generator that gets compressed thereby storing energy during the descent phase of a lift. This stored energy is then released during the ascent phase of a lift. This device enables portions of forces and moments from the spinal column to be transferred to the shoulder, pelvic girdle, and knees (Lotz, Agnew, Godwin, & Stevenson, 2009). Theoretically, the device reduces the energy demand placed on the back musculature on lifting which has been seen in a series of laboratory experiments where dynamic lifting and static trunk bending were performed. (Bosch, van Eck, Knitel, & de Looze, 2016; de Looze, Bosch, Krause, Stadler, & O’Sullivan, 2016; Lotz, Agnew, Godwin, & Stevenson, 2009; Abdoli-E, Agnew, & Stevenson, 2006)
To the best of our knowledge majority of studies on the effect of OBPLAD on various physiological parameters and risk factors associated with lifting were done in laboratory settings, which is a simulation of actual work scenarios in a controlled environment. A need was identified to evaluate the effectiveness of these devices in real work environments involving actual material handlers. It was also found that there was a scarcity of retrievable data on the effectiveness of PLAD in Indian subjects.