Skip to main content
. Author manuscript; available in PMC: 2010 Feb 19.
Published in final edited form as: J Biomech. 2006 Jul 28;40(6):1318–1325. doi: 10.1016/j.jbiomech.2006.05.016

Table 2.

Mean ± SD kinematics of anteroposterior stability as a function of age group, slip outcome, the presence or absence of a protective stepping response, and as related to the odds of falling.

Variable Young Older Odds Ratio
Recover
(n = 31)		 Fall:Step
(n = 11)		 Recover
(n = 8)		 Fall:Step
(n = 18)		 Fall:No-Step
(n = 10)		 For
Falling a
At Slip Onset:
 XCOM (%ft len) 0.5 ± 7.4 −6.5 ± 7.7 d 2.7 ± 8.6 6.9 ± 9.0 10.1 ± 10.4 0.81
 dXCOM/dt (m/s g⋅bh) 0.10 ± 0.01 0.09 ± 0.02 0.09 ± 0.01 0.09 ± 0.01 0.09 ± 0.02 1.56
 Stability (%) 8.9 ± 4.1 4.5 ± 4.7 d 9.4 ± 4.7 11.6 ± 4.5 13.0 ± 5.0 0.92
At Mid-Slip:b
 XCOM (%ft len) −10.6 ± 10.5 −19.0 ± 5.5 −15.3 ± 9.1 −11.8 ± 12.9 −9.0 ± 8.7 1.20
 dXCOM/dt (m/s g⋅bh) −0.11 ± 0.08 −0.12 ± 0.05 −0.20 ± 0.07 f −0.18 ± 0.06 f −0.16 ± 0.06 1.45
 Stability (%) −14.6 ± 9.7 −20.1 ± 6.1 −25.3 ± 8.3 e −21.4 ± 7.8 e −18.9 ± 0.06 1.49
At 1st Step Initiation: c
 XCOM (%ft len) −15.8 ± 16.7 −26.3 ± 16.2 −22.4 ± 25.2 −16.0 ± 25.9 – 1.23
 dXCOM/dt (m/s g⋅bh) −0.06 ± 0.10 −0.07 ± 0.07 −0.14 ± 0.09 e −0.10 ± 0.10 e – 1.11
 Stability (%) −13.2 ± 13.7 −19.3 ± 10.0 −23.2 ± 12.7 −16.8 ± 13.8 – 1.27
At 1st Step Touchdown:
 XCOM (%ft len) 39.0 ± 23.8 6.5 ± 31.5 i 20.7 ± 21.1 f −15.3 ± 27.8 f,i – 6.67 j
 dXCOM/dt (m/s g⋅bh) −0.01 ± 0.06 −0.01 ± 0.03 −0.05 ± 0.04 −0.02 ± 0.05 – 0.93
 Stability (%) 7.5 ± 8.6 −0.8 ± 9.3 h −0.6 ± 5.5 f −4.7 ± 5.2 f,h – 4.55 j

XCOM = center of mass (COM) anteriorly-directed position relative to heel of posterior foot in ground contact; dXCOM/dt = COM forward velocity relative to support surface of posterior foot in ground contact; Stability = distance of COM state from model-predicted boundary for backward balance loss (<0 indicates unstable); g = 9.81 m/s2; ft len = foot length; bh = body height.

a

Factor by which the odds of falling change for a decrease of 1 SD in the variable across all subjects.

b

Excludes 9 Young Recover, 4 Young Fall:Step, and 1 Older Recover subject who stepped before the posterior foot reached the slip midpoint.

c

Step initiation could not be identified in 1 Young Recover, 1 Young Fall:Step, and 3 Older Fall:Step subjects.

d

p < .05 vs. Young Recover and Older Fall:Step (interaction of age group and slip outcome).

e

p < .05

f

p < .01 vs. Young (main effect of age group).

h

p < .01

i

p < .001 vs. Recover (main effect of slip outcome).

j

p < .001 for Odds Ratio ≠ 1.