Early Postural Instability in Parkinson’s Disease: A Biomechanical Analysis of the Pull Test

Table 2

Clinical and demographic details of healthy subjects and PD patients and their subgroups, descriptive data from the study variables, force to reach the backward limit of stability, posturographic variables, and muscular latencies.

Variable	HS	PD	HS vs. PD value	PD H–Y I-II	HS vs. PD I-II value	PD H–Y III	PD I-II vs. PD III value
Number of subjects	64	32		22		10
Age (y)	45 [22–81]	72 [45–86]	<0.001	69.5 [45–82]	<0.001	73 [69–86]	0.023
Women	38 (59%)	15 (47%)	0.246	9 (41%)	0.189	6 (60%)	0.316
Weight (kg)	68.4 (12.7)	71.0 (12.8)	0.240	72.0 (13.2)	0.183	68.9 (12.1)	0.529
Height (cm)	167.5 (11.3)	166.1 (8.7)	0.926	168.2 (6.9)	0.455	161.4 (10.8)	0.097
BMI (kg/m²)	24.6 (4.0)	25.7 (3.7)	0.108	25.3 (3.1)	0.138	26.6 (4.8)	1.0
Motor UPDRS	No	16.4 (8.0)	—	12.4 (3.9)	—	25.2 (7.7)	<0.001
Disease duration (y)	No	6.4 (4.2)	—	5.3 (4.0)	—	8.7 (4.0)	0.017
Motor fluctuations	No	9 (28.1%)	—	4 (18.2%)	—	5 (50%)	0.064
Fallers	No	9 (28.1%)	—	2 (9.1%)	—	7 (70%)	<0.001
FBLoS (N)	98.1 (48.9)	60.2 (37.7)	<0.001	70.5 (39.8)	0.004	37.7 (18.9)	0.023
Posturographic variables
X avg (cm)	0.7 [0.3–1.3]	0.9 [0.5–2.0]	0.001	0.9 [0.5–1.8]	0.020	1.9 [1.2–2.4]	0.029
X right (cm)	1.3 [0.9–1.8]	1.4 [1.0–2.2]	0.048	1.4 [1.0–2.1]	0.048	1.3 [0.9–3.7]	0.924
X left (cm)	1.2 [0.9–1.8]	1.3 [1.0–1.9]	0.261	1.3 [1.0–1.9]	0.307	1.3 [0.9–3.1]	0.825
X SD (cm)	0.5 [0.4–0.8]	0.6 [0.5–0.8]	0.045	0.6 [0.5–0.8]	0.073	0.6 [0.4–1.2]	0.674
Y avg (cm)	6.9 [5.4–9.0]	3.8 [2.2–5.5]	<0.001	3.8 [3.0–5.4]	<0.001	1.8 [0.6–7.6]	0.068
Y ant (cm)	3.2 [2.5–4.0]	3.2 [2.1–4.7]	0.692	3.3 [2.2–4.8]	0.411	3.0 [1.6–3.5]	0.216
Y post (cm)	3.3 [2.7–4.1]	3.9 [3.1–5.2]	<0.001	3.9 [3.1–5.3]	<0.001	4.0 [2.8–5.3]	0.894
Y SD (cm)	1.9 [1.5–2.4]	2.2 [1.5–2.9]	0.015	2.3 [1.5–3.0]	0.016	2.1 [1.6–2.4]	0.493
Vx right (cm/s)	13.3 [8.1–21.5]	14.3 [8.5–23.4]	0.677	14.3 [8.4–23.3]	0.767	12.9 [8.3–56.2]	0.735
Vx left (cm/s)	20.1 [13.1–33.0]	21.6 [13.5–33.7]	0.684	21.6 [13.6–34.0]	0.639	21.6 [11.5–29.7]	0.691
Vy ant (cm/s)	13.6 [8.3–22.2]	15.1 [9.2–23.3]	0.289	14.9 [9.3–22.4]	0.464	19.7 [7.8–39.4]	0.295
Vy post (cm/s)	40.3 [28.7–56.1]	40.7 [25.0–61.1]	0.775	43.2 [26.0–61.3]	0.445	29.4 [23.5–48.2]	0.238
V avg (cm/s)	3.2 [2.5–3.9]	3.2 [2.7–4.4]	0.137	3.2 [2.7–4.4]	0.147	3.3 [2.8–4.2]	1.000
Rectangular area (cm²)	17.6 [10.9–26.1]	20.4 [12.6–35.3]	0.018	20.6 [13.5–35.0]	0.015	15.2 [9.7–53.8]	0.791
Circular area (cm²)	8.3 [5.5–12.4]	8.4 [5.8–14.9]	0.179	8.7 [5.8–14.8]	0.218	7.7 [5.3–28.3]	0.871
Area95 (cm²)	17.3 [10.7–27.6]	20.9 [13.1–34.8]	0.034	20.9 [13.4–33.9]	0.034	17.5 [11.3–49.0]	0.918
Major95 (cm)	4.7 [3.9–5.9]	5.6 [3.9–7.2]	0.014	5.7 [3.8–7.3]	0.015	5.2 [4.0–6.1]	0.470
Minor95 (cm)	1.2 [0.9–1.6]	1.3 [0.9–1.7]	0.196	1.3 [0.9–1.7]	0.221	1.1 [0.8–2.8]	0.930
Path length (cm)	31.6 [24.6–39.3]	32.2 [26.8–44.0]	0.133	32.1 [26.8–44.2]	0.143	32.5 [27.5–42.1]	1.000
Muscular latencies (msec)
First pull:
Tibialis anterior	85.9 (19.0)	99.8 (23.6)	0.013	100.5 (27.4)	0.026	98.2 (13.2)	0.819
Gastrocnemius lateralis	93.9 (24.3)	103.7 (28.4)	0.206	105.4 (33.5)	0.210	99.6 (8.8)	0.513
Vastus lateralis	98.9 (16.9)	102.0 (23.8)	0.652	103.9 (27.3)	0.549	97.3 (11.8)	0.454
Biceps femoris	101.1 (15.5)	105.3 (23.1)	0.609	109.0 (25.3)	0.390	95.0 (12.9)	0.189
Rectus abdominis	90.7 (31.7)	135.5 (36.3)	0.061	132.3 (38.2)	0.055	140.2 (10.1)	0.412
Paravertebral muscles	120.6 (43.8)	136.1 (23.8)	0.499	125.8 (14.1)	0.814	150.0 (30.0)	0.207
Subsequent pulls:
Tibialis anterior	80.3 (19.1)	98.3 (24.6)	<0.001	98.7 (24.9)	<0.001	95.5 (24.0)	0.701
Gastrocnemius lateralis	88.8 (22.5)	107.9 (26.7)	<0.001	107.8 (26.9)	<0.001	108.9 (27.0)	0.910
Vastus lateralis	95.9 (22.5)	109.3 (31.5)	0.004	110.9 (32.3)	0.002	95.0 (20.0)	0.208
Biceps femoris	108.7 (26.1)	126.6 (31.9)	<0.001	127.8 (33.1)	<0.001	114.0 (6.2)	0.014
Rectus abdominis	102.8 (28.3)	128.2 (30.7)	<0.001	127.3 (30.5)	<0.001	165.0 (32.1)	0.230
Paravertebral muscles	138.3 (45.1)	149.9 (55.1)	0.196	150.3 (55.9)	0.190	143.3 (49.2)	0.834

Data are presented as means (SD) and medians [IQR] for continuous variables. Age is presented with median [minimum-maximum]. Qualitative variables are expressed as frequencies. P values were obtained using the Mann–Whitney U test for nonnormal continuous variables, the Student's t-test for normal continuous variables, and the chi-square test for categorical variables. HS: healthy subjects; PD: Parkinson’s disease patients; y: years; kg: kilograms; cm: centimeters; msec: milliseconds; UPDRS: Unified Parkinson's Disease Rating Scale; FBLoS: force to reach the backward limit of stability; N: Newton.