Coordination and timing of spine and hip joints during full body reaching tasks

Abstract

Coupling of spine and hip joints during full body reaching tasks was investigated in 16 participants (8 male and 8 female) who performed reaching tasks at comfortable and fast-paced movement speeds to three targets located in a para-sagittal plane. The participants paused at target contact for 500ms and then returned to an upright posture. Three-dimensional joint motions of the spine and hip were recorded using an electromagnetic tracking device. We found an effect of movement phase (i.e., reach and return) on the onset timing of the spine and hip joints. For most target locations and movement speeds, spine motion onset preceded hip motion onset during the reaching phase of the movement task. In the reach phase, when averaged across all movement conditions, spine joint motion preceded hip joint motion by an average of 48.9ms. In contrast, in the return phase, hip joint motion preceded spine joint motion by an average of 63.0ms. Additionally, when participants were instructed to use either a knee flexion or knee extension strategy to perform the reaching tasks there was no effect of movement strategy on timing of the spine and hip. There was also no effect of target height on the spine-hip ratio, but as movement speed increased, the spine/hip ratio decreased for all target locations due primarily to an increase in hip joint excursion. The findings indicate clear differences in onset timing of the spine and hip joints during reaching tasks that necessitate some forward bending of the trunk and that onset timing is reversed for the return to an upright posture.

Figure 1

A diagrammatic representation of how target locations were normalized to each subject’s anthropomorphic characteristics. Target locations were determined for each subject based on their hip height, trunk length, and arm length. The high target was located such that the subject could, in theory, reach the target by flexing the hips 40° with shoulder flexed to 90° and the elbow extended. N.B. Target locations were determined mathematically and subjects were not actually placed in the positions illustrated.

Figure 2

A) The time series data from the spine and hip joint of a typical subject performing a movement trial to the low target. B) The time series angular velocity data derived from the data in A. The differences in onset timing of the spine and hip are obvious from visual inspection of joint velocity data.

Figure 3

The mean spine hip joint latencies normalized to movement time are plotted for both phases of the movement trials to each target location. A) Joint onset latencies, and B) Peak velocity latencies. The data were averaged across gender and movement speed and the error bars represent standard error of the mean. Negative values indicate that spine motion preceded hip motion and positive values indicate that hip motion preceded spine motion.

Figure 4

The mean spine hip ratio (± SEM) for each quartile of movement for both phases of the movement task is plotted. The spine hip ratios for each quartile were averaged over target height, movement speed and gender. For the movement towards the target, the spine motion is greater than hip motion for the first two quartiles of motion. The opposite is true for the return to upright posture.

Figure 5

The effect of target location and movement speed on A) spine hip ratio, B) spine joint excursion, and C) hip joint excursion is depicted. The data were averaged across gender and standard error bars plotted.

Figure 6

The mean spine hip ratio (± SEM) for each quartile of movement for the forward bend test is plotted.