An Analysis of Lower Limb Coordination Variability in Unilateral Tasks in Healthy Adults: A Possible Prognostic Tool

Abstract

Interlimb coordination variability analysis can shed light into the dynamics of higher order coordination and motor control. However, it is not clear how the interlimb coordination of people with no known injuries change in similar activities with increasing difficulty. This study aimed to ascertain if the interlimb coordination variability range and patterns of healthy participants change in different unilateral functional tasks with increasing complexity and whether leg dominance affects the interlimb coordination variability. In this cross-sectional study fourteen younger participants with no known injuries completed three repeated unilateral sit-to-stands (UniSTS), step-ups (SUs), and continuous-hops (Hops). Using four inertial sensors mounted on the lower legs and thighs, angular rotation of thighs and shanks were recorded. Using Hilbert transform, the phase angle of each segment and then the continuous relative phase (CRP) of the two segments were measured. The CRP is indicative of the interlimb coordination. Finally, the linear and the nonlinear shank-thigh coordination variability of each participant in each task was calculated. The results show that the linear shank-thigh coordination variability was significantly smaller in the SUs compared to both UniSTS and Hops in both legs. There were no significant differences found between the latter two tests in their linear coordination variability. However, Hops were found to have significantly larger nonlinear shank-thigh coordination variability compared to the SUs and the UniSTS. This can be due to larger vertical and horizontal forces required for the task and can reveal inadequate motor control during the movement. The combination of nonlinear and linear interlimb coordination variability can provide more insight into human movement as they measure different aspects of coordination variability. It was also seen that leg dominance does not affect the lower limb coordination variability in participants with no known injuries. The results should be tested in participants recovering from lower limb injuries.

Keywords: continuous hops; interlimb coordination; interlimb coordination variability; unilateral functional tasks; unilateral sit to stand.

FIGURE 1

The standardization procedures for (A) UniSTS, (B) SUs, and (C) Hops in starting and ending position, with a sagittal plane view and frontal plane view. Two inertial sensors were attached to the shanks and two to the thighs of the participants.

FIGURE 2

Schematic overview of the calculation of the shank-thigh coordination measures. (A) i) The angular rotation of the right thigh and lower leg in the sagittal plane in one repetition of the SUs. (A) ii) The right shank-thigh continuous relative phase (CRP) over the full cycle of one repetition of the SUs. (A) iii) The mean of the CRP over the functional cycle is calculated and averaged for each repetition in each functional task for each participant and is referred to as the MRP. (B–C) The process was repeated for the second and the third repetitions. The standard deviation of the MRP over the three repetitions in every task is referred to as the linear coordination variability (sdMRP).

FIGURE 3

(A) Shank-thigh CRP in three repetitions of the UniSTS. (B) Shank-thigh CRP in three repetitions of the Hops. (C) Shank-thigh CRP in three repetitions of the SUs. The nonlinear coordination variability is measured by the SampEn applied to the overall shank-thigh CRP in all repetitions. The higher SampEn is indicative of larger interlimb coordination variability and irregularity.

FIGURE 4

(A) The bar plot of the linear right and left shank-thigh coordination variability results measured by the sdMRP of the participants in UniSTS, SUs, and Hops. (B) The bar plot of the non-linear right and left shank-thigh coordination variability results measured by the SampEn CRP of the participants in UniSTS, SUs, and Hops. The significant differences (p < 0.05, r > 0.5) are shown by * for UniSTS vs. SUs, ^# for Hops vs. SUs, and ⁺ for UniSTS vs. Hops.