A comparison of stability metrics based on inverted pendulum models for assessment of ramp walking

Nathaniel T. Pickle, Jason M. Wilken, Nicholas Fey, Anne K. Silverman

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


Maintaining balance on ramps is important for mobility. However, balance is commonly assessed using inverted pendulum-based metrics (e.g., margin of stability), which May not be appropriate for assessment of human walking on non-level surfaces. To investigate this, we analyzed stability on ramps using four different inverted pendulum models: extrapolated center of mass (XCOM), foot placement estimate (FPE), foot placement estimate neglecting angular momentum (FPE NoH ), and capture point (CAP). We analyzed experimental data from 10 able-bodied individuals walking on a ramp at 0, ±5, and ±10. Contrary to our hypothesis that the magnitude of differences between metrics would be greatest at ±10, we observed the greatest magnitude of differences between metrics at 0. In general, the stability metrics were bounded by FPE and CAP at each slope, consistent with prior studies of level walking. Our results also suggest that clinical providers and researchers should be aware that assessments that neglect angular momentum (e.g., margin of stability, XCOM) May underestimate stability in the sagittal-plane in comparison to analyses which incorporate angular momentum (e.g., FPE). Except for FPE NoH -CAP (r = 0.82), differences between metrics were only moderately correlated (|r|0.65) with violations of leg length assumptions in the underlying inverted pendulum models. The differences in FPE NoH relative to FPE and CAP were strongly correlated with body center of mass vertical velocity (max |r| = 0.92), suggesting that model representations of center of mass motion influence stability metrics. However, there was not a clear overall relationship between model inputs and differences in stability metrics. Future sensitivity analyses May provide additional insight into model characteristics that influence stability metrics.

Original languageEnglish (US)
Article numbere0206875
JournalPloS one
Issue number11
StatePublished - Nov 2018

ASJC Scopus subject areas

  • General Biochemistry, Genetics and Molecular Biology
  • General Agricultural and Biological Sciences
  • General


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