Delayed postural control during self-generated perturbations in the frail older adults

Figures & data

Table 1 Characteristics of patients in the frail group

Subject	Gender	Age	Height (cm)	Weight (kg)	TUG (s)	Gait speed (m/s)	Falls history	MMSE	Chronic diseases	Number of drugs
1	M	74	171	68	28	0.39	0	25	High blood pressure, dyslipemia, hypothyroidism, vesical instability	6
2	F	72	157	61	30	0.35	2	24	Arrhythmia, hypothyroidism, gastroesophageal reflux	6
3	M	78	176	78	16	0.65	1	28	High blood pressure, anxiety, vitamin deficiency	4
4	M	81	174	74	12	0.63	0	24	Aortic valve stenosis, prostate cancer, dyslipemia, type II diabetes, high blood pressure, gastroesophageal reflux	6
5	F	80	157	54	24	0.6	2	24	Depression, high blood pressure	4
6	M	77	169	58	18	0.61	0	26	Vitamin deficiency, gastroesophageal reflux	4
7	F	75	160	52	25	0.48	3	28	Arrhythmia, high blood pressure, chronic obstructive pulmonary disease, hip prosthesis, hypothyroidism, renal insufficiency	6
8	F	73	167	61	15	0.66	2	26	Arrhythmia, cataract, depression, thyroidectomy	4
9	M	77	176	88	21	0.58	0	26	Arrhythmia, tachycardia, hypothyroidism, hip prosthesis	5
10	M	78	176	83	23	0.37	3	27	Colon cancer, high blood pressure, osteoporosis, arrhythmia	5

Abbreviations: TUG, timed up-and-go; MMSE, Mini-Mental State Examination.

Figure 1 Representation of the subject position. (A) Position before the go-signal (initial position). (B) Position at the end of the hand movement.

Figure 2 Typical data for two representative subjects (left, control group; and right, frail group) for three trials in the choice reaction time condition. Upper panel: CoP displacement in the medio-lateral axis (X) and antero-posterior axis (Y). Middle panel: CoP velocity profiles. Lower panel: hand velocity profiles. Horizontal axis represents time; acquisition duration is divided into four phases: baseline (−600 ms to −150 ms); APA phase (−150 ms to t₀); IP (t₀ to 100 ms); and FP (between the hand deceleration beginning to the hand movement offset).

Abbreviations: APA, anticipatory postural adjustment; CoP, center of pressure; FP, final phase; IP, initial phase.

Table 2 Hand and CoP kinematics in the control group and the frail group for the SRT and the CRT conditions

Parameters	SRT		P-value	CRT		P-value
	Frail group	Control group	Group effect	Frail group	Control group	Group effect	Group × condition interaction
Hand RT (s)	0.326 ± 0.071	0.329 ± 0.077	0.931	0.382 ± 0.092	0.431 ± 0.045	0.162	0.305
Hand MT (s)	0.701 ± 0.125	0.423 ± 0.063	<0.001	0.707 ± 0.104	0.436 ± 0.057	<0.001	0.746
Hand PV (m · s^−1)	3.513 ± 0.984	4.689 ± 0.768	0.008	3.189 ± 0.583	4.6 ± 0.873	<0.001	0.305
TPVHand (s)	0.266 ± 0.068	0.163 ± 0.018	<0.001	0.262 ± 0.043	0.175 ± 0.017	<0.001	0.845
CoP MV (m · s^−1)	0.133 ± 0.073	0.209 ± 0.055	0.021	0.114 ± 0.072	0.2 ± 0.086	0.009	0.588
TMVCoP (s)	0.342 ± 0.157	0.151 ± 0.093	0.004	0.499 ± 0.201	0.149 ± 0.064	<0.001	0.008

Abbreviations: CoP, center of pressure; CRT, choice reaction time; MT, movement time; MV, maximal velocity; PV, peak velocity; RT, reaction time; SRT, simple reaction time; TMV_CoP, CoP time to maximal velocity; TPV_Hand, hand time to peak velocity.

Figure 3 NTPV_Hand and NTMV_CoP with respect to hand movement time, in the two groups and for the SRT and the CRT conditions.

Notes: Standard deviations are represented by vertical bars. Asterisks show a statistical significance of P < 0.05.
Abbreviations: APA, anticipatory postural adjustment; CoP, center of pressure; CRT, choice reaction time; NTMV_CoP, CoP normalized time to maximal velocity; NTPV_Hand, hand normalized time to peak velocity; SRT, simple reaction time.

Figure 4 CoP mean velocity during the baseline absolute values (left panel). CoP mean velocity during the APA, initial and final intervals, normalized values (right panel) in the CG and the FG.

Note: Standard deviations are represented by vertical bars. Asterisks show a statistical significance of P < 0.05.
Abbreviations: APA, anticipatory postural adjustment; CG, control group; CoP, center of pressure; CRT, choice reaction time; FG, frail group; NTMV_CoP, CoP normalized time to maximal velocity; NTMV_Hand, hand normalized time to maximal velocity.

Figure 5 Relationship between timed up-and-go scores and CoP time to maximal velocity in the control group (gray square) and the frail group (black triangle).

Abbreviation: CoP, center of pressure.