1. The biomarker of interest: the “healthy” 1/f pattern in walking.
Can the presence of a 1/f structure in stride-to-stride variability enable us to withstand falls?
1Jenny A. Kent, 1Andreas Skiadopoulos, 1Jordan F Wickstrom and 1,2Nicholas Stergiou
1 University of Nebraska Omaha, Omaha, NE, USA 2 University of Nebraska Medical Center, Omaha, NE, USA
INTRODUCTION
RESULTS AND DISCUSSION
Falls threaten independence, and severely compromise quality of life.
Nationally, for the one third of older adults that fall each year, 20-30% of incidents result in moderate-to-severe injuries1, greatly increasing the risk of being placed in a nursing home, a fear of falling, activity limitation, reduced mobility and decreased physical fitness2. 
There is great need for a quantifiable and objective measure that can detect individuals at risk of falls to allow for timely intervention.
The biomarker of interest: the “healthy” 1/f pattern in walking.  
During healthy walking a 1/f frequency spectrum can be seen in the stride-to- stride intervals between successive steps. Faster-than-average steps tend to follow faster-than-average steps and slower steps tend to follow slower steps (Figure 1). 
The presence of this pattern is thought to be linked to our ability to adapt to a continually changing environment3. 
This 1/f pattern degrades to varying extents with aging and pathology. Patterns become either more random and disordered (“the Drunken Sailor”) or, at the other extreme, more periodic and overly-constrained (robot-like) (Figure 1) 4.
No significant differences in walking speed were identified across groups (p=0.717).
There were no significant differences in either the deviation or the recovery time across conditions (p>0.05; Figure 3, Figure 4).
It is possible that this lack of significance is due to the small sample sizes of the groups.
Alternatively, the ‘artificially degraded’ gait of healthy adults from metronome synchronization may not sufficiently reflect an unadaptable pathological system, despite superficial similarities in stride-to-stride interval patterns.
Figure 3: Maximum trunk deviation following perturbation.
Smaller values indicate less disruption.
All differences non-significant (p=0.119).
Purpose : Determine whether the presence of the 1/f hallmark in walking patterns is related to an increased ability to withstand perturbations.
Hypothesis : The extent to which this healthy variability biomarker is present in stride-to-stride patterns will correlate with the severity of the response to, and recovery time following, a perturbation to walking. 
Figure 4: Rate of recovery of trunk motion following perturbation.
Higher exponent values indicate a faster rate of recovery.
All differences non-significant (p=0.288).
CONCLUSIONS
These preliminary results suggest that the temporal pattern of walking, when artificially degraded, in itself does not affect recovery following an induced trip.
The study is limited by a small sample size and the use of young healthy adults.
A similar experimental design using individuals who naturally exhibit the 1/f hallmark to varying extents may be warranted.
Figure 1: Healthy and pathological walking characterized by stride patterns
METHODS
21 healthy young adults (age 19-35yrs; Table 1) walked on a dual-belt treadmill at preferred speed for 25 min to establish baseline stepping characteristics.
They then walked for 45 min in one of four auditory metronome conditions – no metronome, or periodic, 1/f, or white-patterned metronome (Figure 2).
If in a metronome group, participants were asked to synchronize their stepping with the auditory metronome.
In the second trial, after 25 min, one belt of the treadmill was stopped for 500ms, delivering a brief perturbation, after which the participant continued walking.
Whole body motion capture data were acquired at 100 Hz for all trials.
Trip severity and time to recovery were quantified based on the movement of the trunk during and after the perturbation respectively.
Figure 2: Auditory metronomes corresponding to different stride patterns
REFERENCES
1. Sterling DA, et al. (2001) Journal of Trauma and Acute Care Surgery, 50(1),
2. Zijlstra GAR, et al. (2007) Age and ageing, 36(3),
3. Stergiou N, et al. (2006) Journal of Neurologic Physical Therapy, 30(3),
4. Hausdorff JM, et al. (1996) Journal of Applied Physiology, 80(5),
Table 1: Cohort, by metronome group
 Group
Gender
Height (m)
Mass (kg)
None (n=4)
2M, 2F
1.71 (0.13)
67.7 (14.5)
Periodic (n=6)
4M, 2F
1.77 (0.12)
70.6 (9.1)
Pink (n=5)
3M, 2F
1.77 (0.04)
75.0 (5.8)
White (n=6)
69.2 (10.5)
ACKNOWLEDGEMENTS
This work was supported by the Center for Research in Human Movement Variability of the University of Nebraska at Omaha, NIH (P20GM109090), and NIH (1R15HD086828).