Use of the Teager-Kaiser Energy operator for muscle activity detection in children

Abstract

The purpose of this study was to demonstrate the usefulness of the Teager-Kaiser Energy (TKE) operator to assess surface electromyographic (sEMG) activity from the hip and trunk muscles during pediatric gait in children with and without cerebral palsy (CP). Muscle activity was recorded from the trapezius, erector spinae, rectus abdominus, external oblique, gluteus maximus and medius, rectus femoris, and semitendinosus bilaterally in ten children with typical development (TD) and five children with CP ages 44.4 +/- 18.6 months. Duration of muscle activity was calculated as a percentage of the gait cycle, and compared to two common onset detection methods, a standard deviation (SD) amplitude threshold method, and the visual inspection from two raters (R1, R2). Relative and absolute agreement was determined using intraclass correlation coefficients (ICCs) and Bland-Altman plots. Of the two automated methods, the TKE method demonstrated better agreement with visual inspection (0.45-0.89) than the SD (0.11-0.76) method. The Bland-Altman plots indicated a smaller bias and 95% confidence interval for the TKE method in comparison to the raters (TKE to R1: -5, 113%; TKE to R2: 4, 95%; SD to R1: -24, 170%; SD to R2: -15, 151%). The use of the TKE operator may better detect sEMG activity in children than the standard amplitude method.

FIGURE 1

Representative data for the gluteus medius for one child with typical development (TD) and one with cerebral palsy (CP); (a) Raw EMG traces of the static baseline trial; (b) Raw signals during walking used by raters for visual assessment. Thick solid and dashed lines parallel to x-axis represent muscle activation as determined by R1 and R2, respectively. Percent activation was determined to be 44 and 41% by R1 and R2, respectively, for the child with TD and 72 and 63% for the child with CP; (c) SD amplitude curve. The dashed lines indicate the threshold level determined from comparison to the baseline EMG. All activity above the threshold was considered “on,” which resulted in 0% activation for both children; (d) TKE curves. The dashed lines indicate the threshold level determined from comparison to the baseline EMG. All activity above the threshold was considered “on,” which resulted in 43.5% activation for the child with TD and 61.2% for the child with CP.

FIGURE 1

Representative data for the gluteus medius for one child with typical development (TD) and one with cerebral palsy (CP); (a) Raw EMG traces of the static baseline trial; (b) Raw signals during walking used by raters for visual assessment. Thick solid and dashed lines parallel to x-axis represent muscle activation as determined by R1 and R2, respectively. Percent activation was determined to be 44 and 41% by R1 and R2, respectively, for the child with TD and 72 and 63% for the child with CP; (c) SD amplitude curve. The dashed lines indicate the threshold level determined from comparison to the baseline EMG. All activity above the threshold was considered “on,” which resulted in 0% activation for both children; (d) TKE curves. The dashed lines indicate the threshold level determined from comparison to the baseline EMG. All activity above the threshold was considered “on,” which resulted in 43.5% activation for the child with TD and 61.2% for the child with CP.

FIGURE 2

Representative data for the rectus abdominus for one child with typical development (TD) and one with cerebral palsy (CP); (a) Raw EMG traces of the static baseline trial; (b) Raw signals during walking used by raters for visual assessment. Thick solid and dashed lines parallel to x-axis represent muscle activation as determined by R1 and R2, respectively. Thick dashed line parallel to x-axis represents muscle activation as determined by R2, 0% for the child with TD and 59% of the gait cycle for the child with CP. R1 did not determine that the muscle was activated during any period of the gait cycle for either child; (c) SD amplitude curve. The dashed lines indicate the threshold level determined from comparison to the baseline EMG. All activity above the threshold was considered “on,” which resulted in 100% activation for both children; (d) TKE curves. The dashed lines indicate the threshold level determined from comparison to the baseline EMG. All activity above the threshold was considered “on,” which resulted in 0% activation for the child with TD and 39% for the child with CP.

FIGURE 2

Representative data for the rectus abdominus for one child with typical development (TD) and one with cerebral palsy (CP); (a) Raw EMG traces of the static baseline trial; (b) Raw signals during walking used by raters for visual assessment. Thick solid and dashed lines parallel to x-axis represent muscle activation as determined by R1 and R2, respectively. Thick dashed line parallel to x-axis represents muscle activation as determined by R2, 0% for the child with TD and 59% of the gait cycle for the child with CP. R1 did not determine that the muscle was activated during any period of the gait cycle for either child; (c) SD amplitude curve. The dashed lines indicate the threshold level determined from comparison to the baseline EMG. All activity above the threshold was considered “on,” which resulted in 100% activation for both children; (d) TKE curves. The dashed lines indicate the threshold level determined from comparison to the baseline EMG. All activity above the threshold was considered “on,” which resulted in 0% activation for the child with TD and 39% for the child with CP.

FIGURE 3

Bland-Altman plots for the TKE and SD methods, which examine the agreement between the methods and the two raters (R1 and R2) with respect to overall muscle activity The y-axis represents the subtraction of method from the rater, whereas the x-axis represents the average of the two. The 95% limits of agreement are represented as grey lines, and mean bias is represented as a solid black line.