A novel method for measuring asymmetry in kinematic and kinetic variables: The normalized symmetry index

Abstract

Gait and movement asymmetries are important variables for assessing locomotor mechanics in humans and other animals and as a predictor of risk of injury and success of clinical interventions. The four indices used most often to assess symmetry are not well designed for different variable types and perform poorly when presented with cases of high asymmetry or when variables are of low magnitude and are easily influenced by small variation in the signal. The purpose of the present study was to test the performance of these indices on previously unpublished data on ACL-R patients and to propose a new index to resolve some of these limitations. The performance of four currently used indices and a new index-the Normalized Symmetry Index (NSI), which is scaled to the range of variables being tested across multiple trials-were compared using force and angular data on participants who had undergone anterior cruciate ligament reconstruction and healthy controls. The NSI performed well compared to all other indices with all variables and had the additional benefit of returning values that range from 0% (full symmetry) to ±100% (full asymmetry). Therefore, the NSI can serve as a universal index for assessing asymmetry in humans, nonhuman animal models, and in a clinical context for assessing risk for injury and clinical outcomes.

Quantitative body symmetry assessment during neurological examination

“…Therefore, such results are impossible and cannot be interpreted accurately. This is also noted by other researchers [42].…”

“…Healthy individuals have a considerably greater movement asymmetry compared to MS according to our obtained kinematic symmetry indices. It might be associated with a fact of higher joint variability in CO [42,45], that has been found over a short period of movement.…”

“…They can be as follows: Ratio Index (RI), which uses the ratio of the values for the two limbs [37]; Symmetry Index (SI) calculated from an average of the absolute values for both limbs [38]; Symmetry Index (S.I.) calculated from an average of the absolute maximal and minimal values for both limbs [39]; Gait Asymmetry (GA) index is a logarithmic transform of the RI [40], Symmetry Angle (SA) is a factor calculated for the angle of the vector plotted from the right and left values of discrete gait parameters in relation to the OX axis [41]; or Normalized Symmetry Index (NSI), which can be used easily in any setting and can serve as a universal index for assessing symmetry in a clinical context [42].…”

Quantifying Asymmetry in Gait: The Weighted Universal Symmetry Index to Evaluate 3D Ground Reaction Forces

“…The commonly used RI and SI (Patterson et al, 2010;Błazkiewicz et al, 2014;Viteckova et al, 2018) did not fulfill the proposed symmetry axioms and were not considered as acceptable methods within this work. The utility of these methods has been debated: some state these methods do not present a clear advantage to discriminate abilities (Queen et al, 2020), others conclude that the method selection depends crucially on the variables of investigation (Patterson et al, 2010;Błazkiewicz et al, 2014). Within this work, both the RI and SI could not be used for asymmetry analyses, as they require signals that do not cross the zero axis.…”

“…Due to the ease of data collection, GRF have been commonly used to assess gait asymmetry in unilaterally injured patients (McCrory et al, 2001;Aqil et al, 2016;Wiik et al, 2017). A number of available methods such as the Symmetry Index (SI) (Robinson et al, 1987), Ratio Index (RI) (Ganguli et al, 1974), the Symmetry Angle (SA) (Zifchock et al, 2008) or the recently introduced Normalized Symmetry Index (Queen et al, 2020) use collected GRF data to determine gait asymmetry. Yet major technical limitations in these methods have been described, such as artificial inflation (Herzog et al, 1989;Błazkiewicz et al, 2014), which excludes comparisons of irregular signals that are common in pathological gait.…”