The information hiding between the two sides
Most movement assessments produce a single summary: a gait speed, a balance score, a repetition count. Those numbers are useful, but they average across the whole body and can mask where the real story lives. Often the more telling signal is the difference between the left side and the right—how evenly weight is loaded, how symmetric stride length is, whether one limb consistently does less of the work.
Why asymmetry matters clinically
After an injury, surgery, or a neurological event, the body adapts by favoring the stronger or less painful side. That compensation can keep a patient functional in the short term while quietly slowing recovery, overloading the dominant limb, or raising fall risk. A healthy-looking global score can hide a substantial side-to-side gap. In a study of 54 independently walking stroke survivors, more than half showed statistically significant temporal asymmetry, and that asymmetry was associated with slower walking and with poorer motor recovery of the affected leg and foot (Patterson et al., 2008). Watching how a gap like that narrows over time can be a more informative read on progress than the headline number alone.
Why it's hard to see by eye
Subtle asymmetry is genuinely difficult to observe. A limp at the extremes is obvious; a modest difference in stance time or stride length is not, even when it is clinically meaningful. Visual estimation also varies between clinicians and between visits: when physical therapists rated the same videotaped gait, agreement on spatiotemporal features like step length and stance time was only slight to moderate (Eastlack et al., 1991). A real change and a change in who's watching become hard to tell apart.
Consistency is what makes the comparison trustworthy
Asymmetry is only meaningful as a comparison—left against right, and this visit against the last. That requires capturing both sides the same way every time and expressing the difference with a consistent formula — symmetry research itself has lacked a standard, which is why Patterson and colleagues (2010) recommended the symmetry ratio of step length, swing time, and stance time for standardization — using a method whose accuracy against laboratory motion capture is documented. Objective, standardized measurement turns side-to-side differences into a trend a clinician can track, supporting the decision of when to progress load, adjust a plan of care, or flag a compensation pattern early. Read alongside clinical judgment, it's not a substitute for it—it's a sharper view of what's changing and where.
References
- Patterson KK, Parafianowicz I, Danells CJ, et al. Gait asymmetry in community-ambulating stroke survivors. Archives of Physical Medicine and Rehabilitation. 2008;89(2):304-310. doi:10.1016/j.apmr.2007.08.142
- Patterson KK, Gage WH, Brooks D, Black SE, McIlroy WE. Evaluation of gait symmetry after stroke: a comparison of current methods and recommendations for standardization. Gait & Posture. 2010;31(2):241-246. doi:10.1016/j.gaitpost.2009.10.014
- Eastlack ME, Arvidson J, Snyder-Mackler L, Danoff JV, McGarvey CL. Interrater reliability of videotaped observational gait-analysis assessments. Physical Therapy. 1991;71(6):465-472. doi:10.1093/ptj/71.6.465