Introduction

Numerous factors cause Lower Back Pain (LBP), one of the most common of which is erroneous object lifting. Indeed, one of the most significant factors that cause LBP among handling workers is poor lifting technique. Therefore, healthcare providers always recommend a proper lifting technique in which the hands are positioned close to the body while lifting objects to avoid spinal injuries. The everyday task that most pertinently influences spine and hip kinematics is lifting objects from the ground, which is a systematic and regular activity especially for persons occupied in physical labour [1]. Commonly, employers provide training sessions for their staff engaged in handling duties to prevent LBP [2]. This training mainly educates them on the proper way to lift objects, as this can place a considerable load on the spine and is regularly mentioned as provoking LBP [3]. Indeed, human spinal Range of Motion (ROM) information is key to developing clinicians’ awareness of spinal disorders [4]. Accurate knowledge of physiological movement of the lumbar spine and hip regions and the behaviour of each regional movement during an object-lifting task is important. Spine and hip motion play an essential role in daily functional activities, such as self-caring or performing occupational duties. The interest of researchers and therapists in movement behaviour has grown, revealing the extent of injuries suffered and also bringing about improvements in movement behaviour. Measuring the regional breakdown of spinal motion in the sagittal plane and describing the relative motion of different regions of the spine can provide useful clinical information, which can be used in clinical procedures for spinal assessment [5]. A considerable amount of literature has been focused on measuring the lumbar spine comparative to hip movement, while performing a number of daily duties [1,6-8]. However, the majority of these studies have treated the lumbar spine as a single region. Over the last ten years, a number of studies have adopted multi-regional lumbar spine models across clinical populations [9,10] and healthy subjects [4,5,11-14], identifying differences in regional contribution. Clinical studies have previously confirmed differences in this ratio between those with and without back pain [1,8], whilst alterations in this ratio affect the bending and compressive stresses on the lumbar spine [15,16]. Subsequently, another study investigated how the upper and lower lumbar regions contributed to spinal movement relative to hip motion, when performing everyday tasks [5]. Unfortunately, study [5] focused on the lumbar spine while the other spinal regions were overlooked in terms of movement over time relative to hip kinematic behaviours. The study of a multi-regional lumbar spine model versus hip motion over time during object lifting has not yet been undertaken. Data arising from such a study would significantly assist in achieving a better understanding of lumbar spine kinematics, especially when supplemented by multiregional velocities [17], as the relative movement behaviour of the hip and its interaction with the lumbar spine is considered important [18,19]. Therefore, this study aimed to examine if modelling the cephalocaudal regions into four separate regions would give a different kinematic pattern of spinal motion with respect to hip motion. This is the first study to adopt this approach to the kinematic analysis of multi-spinal regions against the hip region during an object-lifting task.

Materials and Methods

Participants

Thirty-two male participants (mean age =28.2 ± 4.2 years; weight =74.4 ± 11 kg; height =1.70 ± 0.04 meters) agreed to participate in this study. The Scientific Research Ethical Committee at Najran University approved this study (Ethic no. 442-37-5101 at 22- 01-1442), and its participants were recruited via social media applications which were used to advertise to staff, undergraduate students, and the community surrounding Najran University. In addition, the researcher also issued invitations orally, meaning our cohort was a convenience-based sample. This study faced difficulty in recruiting both genders, particularly females; therefore, all participants in this study were male. Moreover, among those who initially agreed to participate, some of them denied to complete the experimental process when they asked to get their shirts off in order to attach sensors into their bodies. All participants were selected based on specific criteria. Each participant was provided with a sheet containing the study information, indicating their rights, confirming the confidentiality of information, outlining potential risks, and explaining what to do in the event of something going wrong. Each participant had consented to participate. Finally, participants provided written informed consent before participating in this study.

Instrumentation

A six tri-axial accelerometer sensors system was applied on a number of points on each participant’s body. This system was explained in a previously published study [4] and had shown excellent reliability relating to spinal motion analysis with an intraclass correlation coefficient between 0.88 and 0.99 and a standard error of measurement between 0.4° and 5.2°. Moreover, the tri-axial accelerometer sensors system has been used to measure spinal regions and hip kinematics in a number of other studies [4,5,11].

Procedures

All of the experiments were conducted in the research laboratory of the physiotherapy clinics in the College of Applied Medical Sciences, Najran University. Participants were asked to wear light clothes when it came to measuring their height and weight and to then sit on a chair without a backrest. A medical swab was used to disinfect the places where the sensor needed to be attached. Sensors were affixed using double-sided adhesive tape at six different locations: the forehead, the first and twelfth thoracic vertebra, the third lumbar vertebra, the first sacral vertebra (Figure 1), and the lateral aspect of the mid-thigh. The sensors measured the movement and velocities of the headneck, thoracic, upper and lower lumbar regions associated with hip during the task of lifting an object off the ground (a 5 kg dumbbell (1 pc)) and returning to an upright position. Such an approach was also used by Alqhtani et al. [11] to measure spinal regions over time relatively