Investigation of Anticipatory Postural Adjustments during One-Leg Stance Using Inertial Sensors: Evidence from Subjects with Parkinsonism

Abstract

The One-Leg Stance (OLS) test is a widely adopted tool for the clinical assessment of balance in the elderly and in subjects with neurological disorders. It was previously showed that the ability to control anticipatory postural adjustments (APAs) prior to lifting one leg is significantly impaired by idiopathic Parkinson's disease (iPD). However, it is not known how APAs are affected by other types of parkinsonism, such as frontal gait disorders (FGD). In this study, an instrumented OLS test based on wearable inertial sensors is proposed to investigate both the initial anticipatory phase and the subsequent unipedal balance. The sensitivity and the validity of the test have been evaluated. Twenty-five subjects with iPD presenting freezing of gait (FOG), 33 with iPD without FOG, 13 with FGD, and 32 healthy elderly controls were recruited. All subjects wore three inertial sensors positioned on the posterior trunk (L4-L5), and on the left and right frontal face of the tibias. Participants were asked to lift a foot and stand on a single leg as long as possible with eyes open, as proposed by the mini-BESTest. Temporal parameters and trunk acceleration were extracted from sensors and compared among groups. The results showed that, regarding the anticipatory phase, the peak of mediolateral trunk acceleration was significantly reduced compared to healthy controls (p < 0.05) in subjects with iPD with and without FOG, but not in FGD group (p = 0.151). Regarding the balance phase duration, a significant shortening was found in the three parkinsonian groups compared to controls (p < 0.001). Moreover, balance was significantly longer (p < 0.001) in iPD subjects without FOG compared to subjects with FGD and iPD subjects presenting FOG. Strong correlations between balance duration extracted by sensors and clinical mini-BESTest scores were found (ρ > 0.74), demonstrating the method's validity. Our findings support the validity of the proposed method for assessing the OLS test and its sensitivity in distinguishing among the tested groups. The instrumented test discriminated between healthy controls and people with parkinsonism and among the three groups with parkinsonism. The objective characterization of the initial anticipatory phase represents an interesting improvement compared to most clinical OLS tests.

Keywords: Parkinson’s disease; anticipatory postural adjustments; balance control; frontal gait disorders; single-leg stance; unipedal balance; wearable sensors.

Figures

Figure 1

Wearable sensors placement.

Figure 2

Algorithms for the analysis of the dynamic phase. (A) Flowchart describing the procedure for the detection of the beginning of the rising movement of the lifted limb (Tlift). (B) Procedure for the identification of the anticipatory postural adjustment onset (Tonset) and the mediolateral (ML)-peak acceleration (Tpeak).

Figure 3

Algorithms for the analysis of the static balance phase. (A) Flowchart describing the procedure for the detection of the beginning of the unipedal balance (Tstart). (B) Procedure for the identification of the end of the unipedal balance (Tstop).

Figure 4

Instrumental parameters extracted from wearable sensors during One-Leg Stance on the most affected side for healthy controls (HC), idiopathic Parkinson’s disease without freezing of gait (iPD-noFOG), idiopathic Parkinson’s disease with freezing of gait (iPD-FOG), and frontal gait disorders (FGD) groups. (A) Time-to-peak, (B) peak-to-balance, (C) balance duration, (D) peak of mediolateral trunk acceleration [mediolateral (ML)-peak]. Circles and whiskers represent, respectively, mean and SE adjusted for age through analysis of covariance procedure. *p < 0.05, **p < 0.01, ***p < 0.001 (Bonferroni–Holm post hoc comparison).

Figure 5

Correlation between the balance duration on the most affected leg measured through the wearable sensors and the mini-BESTest task score (top), Anticipatory Subscore (center), and total score (bottom). Spearman’s rank correlation coefficient (ρ) and the correspondent p-values are reported.

Figure 6

Comparison between balance duration measured through wearable sensors and task duration measured by stopwatch during the execution of the One-Leg Stance test on the most affected side. On the left, linear correlation between the two variables. Pearson’s correlation coefficient (r) and the correspondent p-value are reported. On the right, Bland–Altman plot. The central dotted lines represent the mean difference between the two measures, while the upper and lower lines represent the limits of agreement.