Increased Fall Risk is Associated with Elevated Ankle Co-contraction in Older Adults

Ryan Appell, Michael McKay, Hannah Nawaz, Joanna Roth, Robert Sigler, Jacqueline Third, Mark Walker, Erika Nelson-Wong

Background

•Increased co-contraction in older adults (Hortobogyi et al. 2009; Chu et al. 2009; Cenciarini et al. 2009; Benjuya et al. 2004)

• Increased co-contraction associated with history of falls (Ho and Bendrups 2002)

•Co-contraction is not predictive of postural sway (Reynolds 2010)

•Does co-contraction during static balance tasks predict fall risk?

Purpose

•To determine if co-contraction of the anterior and posterior ankle musculature during static balance challenges is associated with fall risk, as determined by the Four Square Step Test (FSST) in older adults.

European Journal of Applied Physiology, 2011, Submitted in review.

Inclusion Criteria

•Recruited from independent living facilities and surrounding community

•Age > 55 years•Absence of cardiovascular and pulmonary

co-morbidities•Independence with community mobility

with or without assistive device

Methods

• Participant Characteristics▫ 8 male, 15 female▫ Age: 73.0 ± 6.4 years

• Electromyography (EMG)▫ Anterior Tibialis▫ Lateral Gastrocnemius

Methods – Static Balance

Romberg (ROM) Sharpened Romberg (SROM)

Single Leg Standing (SLS)

Methods – Four Square Step Test

Dite et al (2002)At risk to fall > 12 secNot at risk to fall < 12 sec

Methods – EMG Analysis

•Co-contraction quantified by co-contraction index (CCI)

•High CCI = Top 50th percentile•Low CCI = Bottom 50th percentile

Lewek et al (2004)

Methods – Statistical Treatment

•Chi-square▫High/Low CCI and at-risk/not-at-risk to fall

•Sn, Sp, + LR, - LR, OR•Pearson product moment correlation

▫Actual CCI score vs. actual FSST time •One-way ANOVA

▫CCI score by fall risk category •p < 0.05

Results

n = 8

n = 15

14.22 s

8.87 s

No group differences between average ages

p < 0.001

Results

•High/Low CCI associated (p < 0.05) with fall risk except ROM eyes closed

•FSST times correlated with CCI values for SROM eyes open (r = 0.42) and eyes closed (r = 0.57) and SLS (r = 0.54)

Balance Challenge Condition

Sn (95% CI)

Sp (95% CI)

+LR(95% CI)

-LR(95% CI)

OR(95% CI)

Romberg, Eyes Open

0.88 (0.53, 0.98)

0.75 (0.47, 0.91)

3.5 (1.3, 9.7)

0.17 (0.03, 1.1)

21.0 (1.78, 248.1)

Romberg, Eyes Closed

0.62 (0.31, 0.86)

0.50 (0.25, 0.75)

1.25 (0.57, 2.7)

0.75 (0.26, 2.2)

1.67 (0.27, 10.3)

Sharpened Romberg, Eyes Open

0.86 (0.49, 0.97)

0.67 (0.39, 0.86)

2.57 (1.09, 6.05)

0.21 (0.03, 1.37)

12.0 (1.05, 136.8)

Sharpened Romberg,

Eyes Closed

0.88 (0.53, 0.98)

0.64 (0.35, 0.85)

2.41 (1.06, 5.50)

0.20 (0.03, 0.30)

12.3 (1.08, 139.0)

Single Leg Standing

0.88 (0.53, 0.98)

0.67 (0.39, 0.86)

2.62 (1.13, 6.09)

0.19 (0.03, 1.23)

14.0 (1.25, 156.6)

Balance Challenge Condition

Sn (95% CI)

Sp (95% CI)

+LR(95% CI)

-LR(95% CI)

OR(95% CI)

Romberg, Eyes Open

0.88 (0.53, 0.98)

0.75 (0.47, 0.91)

3.5 (1.3, 9.7)

0.17 (0.03, 1.1)

21.0 (1.78, 248.1)

Romberg, Eyes Closed

0.62 (0.31, 0.86)

0.50 (0.25, 0.75)

1.25 (0.57, 2.7)

0.75 (0.26, 2.2)

1.67 (0.27, 10.3)

Sharpened Romberg, Eyes Open

0.86 (0.49, 0.97)

0.67 (0.39, 0.86)

2.57 (1.09, 6.05)

0.21 (0.03, 1.37)

12.0 (1.05, 136.8)

Sharpened Romberg,

Eyes Closed

0.88 (0.53, 0.98)

0.64 (0.35, 0.85)

2.41 (1.06, 5.50)

0.20 (0.03, 0.30)

12.3 (1.08, 139.0)

Single Leg Standing

0.88 (0.53, 0.98)

0.67 (0.39, 0.86)

2.62 (1.13, 6.09)

0.19 (0.03, 1.23)

14.0 (1.25, 156.6)

Results

* p < 0.05

Conclusions

•Co-contraction is positively correlated with fall-risk as determined by the FSST

•Participants with high CCI scores on ROM were 21 times more likely to be in at-risk to fall group

•Participants who had higher fall-risk demonstrated clearly different muscle activation patterns than participants not at-risk to fall

Clinical Implications

•Co-contraction may be an important predictor in determining patients who are at risk for falls

•Provides insight into commonly used static balance tests and translation to dynamic balance performance

• Intervention efforts may need to focus on a dissociation of co-contraction about the ankle

Future Work

•Specific intervention studies that target co-contraction

•Subjects with various balance disorders, diagnoses

•Determination of specific cut-off scores for determination of fall risk via co-contraction measures

Thank You!

Special Thanks to: ▫ Residents of Highland and

Argyle Senior Centers▫ Dr. Wendy Anamaet▫ Dr. Amy Hammerich▫ Dr. Larisa Hoffman▫ Dr. Marcia Smith▫ Dr. Barb Tschoepe▫ Mr. Ira Gorman▫ Regis University DPT Class of

2011Regis University Sponsored Projects Academic Research Council (SPARC)