COORDINATION AND TIMING OF SPINE AND HIP MOTION DURING FULL BODY REACHING TASKS Gary E. Gibson, and James S. Thomas Ph.D, P.T. School of Physical Therapy, Ohio University, Athens, OH Introduction Coupling of the spine and hip joint, or spine-hip ratio, has been described as an important aspect of clinical examination of the spine for years. It has been proposed that as an individual flexes or extends the trunk, the spine joints and hip joints work in unison, though not necessarily contributing the same amounts of motion, to achieve the necessary movement (Cailliet, 1981). Accordingly, there have been numerous studies that have investigated this relationship not only with forward flexion (Porter et al. 1997, Paquet et al. 1994, Esola et al. 1996, Lariviere et al. 2000, Lee et al. 2002, Wong et al. 2004, McClure et al. 1997), but also with weighted and unweighted extension tasks from a flexed position (McClure et al. 1997, Granata et al. 2000, Nelson et al. 1995). A limitation of these previous studies was that the movements performed were constrained to either a simple forward bend test (FBT) or a weighted lifting task. The FBT requires the individual to attempt to touch their toes while keeping the knees straight. While this motion has been used clinically to asses lumbar and spine motion, it is not a very functional task for most people. With regard to the weighted lifting tasks, these were also quite constrained, requiring the subjects to lift only with the trunk while keeping the knees extended. In contrast to the FBT, functional unconstrained movements such as reaching for a car door can be completed in an infinite number of configurations of the trunk and limb segments due to the large number of joints involved in these tasks. Thomas et al (1998) used full body reaching tasks to study spine-hip coordination with less movement constraints. However, that investigation was limited to only one movement speed and only examined the change in spine and hip motions from the initial movement to target contact. There were no analyses of the movement back to an upright posture or the potential timing differences of the spine and hip joints. The purpose of this study was to investigate the timing and latencies of the spine and hip joints and the resulting coordination between them during unconstrained reaching tasks. We also sought to identify the effects of varying movement speeds and target heights on the movement patterns used to accomplish these tasks. Methods The time-series changes in orientation of the forearm, humerus, trunk, pelvis, thigh, and shank were measured in 16 subjects (8 males and 8 females) performing whole-body reaching tasks. In this paradigm the targets were located around a clock face such that the subject could, in theory, reach them by flexing the hips 40º, 60º, and 80º with the shoulder flexed 90º and the elbow extended. The target locations were chosen to create a task that progressively challenges the subject with larger excursions of the trunk. The segment orientation angles were measured in a counterclockwise direction as seen from the subjects right side, starting with horizontal equal to zero degrees. Subjects reached for the targets at two speeds (self-selected and fast-paced) and were given no instructions on the limb segment geometry to use while performing these reaching tasks. Joint motion onsets, angular velocities, angular displacements, and spine/hip ratios were determined using custom algorithms created in Matlab™. Data Analysis Separate paired t-tests were performed to determine timing differences in the onset of spine and hip joint motions for each target height and movement speed. These analyses were done for both the movement towards the target and for the return movement from target contact to an upright posture. Mixed-model ANOVAs were performed to determine effects of movement speed, gender, and target height on the motions of the spine and hip. Results, cont. Raw joint angle data and joint velocity data are illustrated in Figure 1. There is a reversal in onset timing when comparing movement toward the target with return movement to an upright posture. This is illustrated by the differences in peak velocities plotted in Figure 1B. The mean latencies for all trials are shown in Figure 3A-F. Negative values indicate spine motion preceding hip motion and positive values indicate hip motion preceding spine motion. In reaching trials to the 60º target, spine onset preceded hip onset by an average of 109 ms for comfortable-paced movements (t=8.73, p<.05) and by 53 ms for fast-paced movements (t=4.14, p<.05). In contrast, during the return movement from target contact to upright posture, hip onset preceded spine onset by an average of 85 ms for fast-paced movements (t=30.7, p<.05). (Fig. 3, C & D) In reaching trials to the 80º target, spine onset preceded hip onset by an average of 131ms for comfortable-paced movements (t=8.58, p<.05) and 68 ms for the fast-paced movements (t=5.48, p<.05). In return movements from the 80º target, hip onset preceded spine onset by an average of 75 ms for comfortable-paced movements (t=3.83, p<.05) and by 93 ms for the fast-paced movements (t=3.28, p<.05). (Fig. 3, E & F) The effects of onset timing of the spine and hip motions on the lumbar-pelvic rhythm are illustrated in Figure 2 which shows spine and hip angles plotted against each other for an individual trial of a single subject. The differences in onset timing are clearly demonstrated by the reversal of the curvature of the plots. The slope of the curve changes at roughly the same spine (15° ) and hip (8° ) angle for both portions of the task, but the change occurs at the beginning of the forward bend while occurring at the end of the return. On average, there was an increase in spine excursion (F=5.617, p<.05) and a subsequent decrease in hip excursion (F=46.115, p<.05) for fast movements compared to comfortable pace movements. There was a significant movement speed by target height interaction in spine movement (F=7.363, p<.05) as is evidenced by differences for 60º and 80º targets, but not for the 40º target (Figure 4). Conclusions These findings suggest a difference in the timing of spine and hip motions used in whole body reaching tasks and that the spine hip ratio is speed dependent. Both of these findings may hold clinical significance when examining movement patterns of individuals with back pain. This research was supported by The National Institutes of Health Grant R01-HD to J.S. Thomas Figure 3. Mean motion latencies, both forward bend and return to upright for A) 40 degrees at a Comfortable pace, B) 40 degrees at a Fast pace, C) 60 degrees at a Comfortable pace, D) 60 degrees at a Fast pace, E) 80 degrees at a Comfortable pace, and F) 80 degrees at a Fast pace. Figure 1. A) Plot of joint angle data from a typical trial. B) Plot of velocity data from the same trial. In movement toward the target, peak velocity of the spine (1) preceded peak velocity of the hip (2). In movement returning to an upright posture, peak velocity of the hip (3) preceded peak velocity of the spine (4). Figure 2. (A) Spine angle plotted against hip angle for the forward bend portion and (B) return portion of a typical reaching trial. These data were from the same trial as Figure 1. Figure 4. A) Mean change in spine joint angle for self-selected and fast-paced trials. B) Mean change in hip joint angle for self-selected and fast-paced trials.