The association between low back pain and spine movement control suggests that it is important to reliably quantify movement behavior. One method to characterize spine movement behavior is to measure the local dynamic stability (LDS) of spine movement during a repetitive flexion task in which a participant is asked to touch multiple targets repetitively. Within the literature, it has been well established that an individual's focus of attention (FOA) can modulate their neuromuscular control and affect task performance. The goal of this project was to examine the unknown effect of FOA on LDS measurements and timing error during a repetitive spine flexion task that is commonly used to assess movement control. Fourteen healthy adults (7 male) were instructed to touch two targets (shoulder height and knee height) to the beat of a metronome (4 s/cycle) for 35 consecutive cycles. They completed this task under internal (focus on trunk movement) and external (focus on targets) FOA conditions. Motion capture data of the trunk and sacrum were collected at 120 Hz. The lumbar spine angle was defined as the orientation of the trunk relative to the pelvis. The local divergence exponent (λmax) was calculated from the sum of squares of the 3-dimensional spine angle. Timing error was calculated as the time difference between target touches and metronome beats. Changing an individual's FOA had no effect on λmax calculations or timing error. Although clear task instructions are important, it is not essential to control for FOA during this movement assessment protocol.
Keywords: Constrained action hypothesis; Local divergence exponents; Lyapunov analysis; Motor control; Movement.
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