Inertial Measurement Units for Clinical Movement Analysis: Reliability and Concurrent Validity

Abstract

The aim of this study was to investigate the reliability and concurrent validity of a commercially available Xsens MVN BIOMECH inertial-sensor-based motion capture system during clinically relevant functional activities. A clinician with no prior experience of motion capture technologies and an experienced clinical movement scientist each assessed 26 healthy participants within each of two sessions using a camera-based motion capture system and the MVN BIOMECH system. Participants performed overground walking, squatting, and jumping. Sessions were separated by 4 ± 3 days. Reliability was evaluated using intraclass correlation coefficient and standard error of measurement, and validity was evaluated using the coefficient of multiple correlation and the linear fit method. Day-to-day reliability was generally fair-to-excellent in all three planes for hip, knee, and ankle joint angles in all three tasks. Within-day (between-rater) reliability was fair-to-excellent in all three planes during walking and squatting, and poor-to-high during jumping. Validity was excellent in the sagittal plane for hip, knee, and ankle joint angles in all three tasks and acceptable in frontal and transverse planes in squat and jump activity across joints. Our results suggest that the MVN BIOMECH system can be used by a clinician to quantify lower-limb joint angles in clinically relevant movements.

Keywords: biomechanics; functional activity; gait; inertial measurement units; kinematics; motion analysis; reliability; repeatability.

Figure A1

Within-session intraclass correlation coefficient of VICON data collected in session 1. Intraclass correlation coefficient is shown for the minimum angle (min; top row), maximum angle (max; second row), range of motion (ROM; third row) and angle at heel strike (@HS; bottom row) for the hip (left-most column), knee (centre column) and ankle (right-most column) joints in the sagittal (Sag), frontal (Frnt) and transverse (Tran) planes of movement. The three data points in each plane correspond to the walk (left-most point; circle), squat (centre point; square) and jump (right-most point; diamond) tasks. Grey shading indicates values considered to indicate excellent reliability.

Figure A2

Within-session standard error of measurement of VICON data collected in session 1. Standard error of measurement is shown for the minimum angle (min; top row), maximum angle (max; second row), range of motion (ROM; third row) and angle at heel strike (@HS; bottom row) for the hip (left-most column), knee (centre column) and ankle (right-most column) joints in the sagittal (Sag), frontal (Frnt) and transverse (Tran) planes of movement. The three data points in each plane correspond to the walk (left-most point; circle), squat (centre point; square) and jump (right-most point; diamond) tasks. Grey shading indicates values considered to indicate excellent reliability.

Figure 1

Between-session (within-rater) intraclass correlation coefficient of MVN data collected by rater 1 (musculoskeletal physiotherapist) in sessions 1 and 2. Intraclass correlation coefficient is shown for the minimum angle (min; top row), maximum angle (max; second row), range of motion (ROM; third row) and angle at heel strike (@HS; bottom row) for the hip (left-most column), knee (centre column) and ankle (right-most column) joints in the sagittal (Sag), frontal (Frnt) and transverse (Tran) planes of movement. The three data points in each plane correspond to the walk (left-most point; circle), squat (centre point; square) and jump (right-most point; diamond) tasks. Grey shading indicates values considered to indicate excellent reliability.

Figure 2

Between-session (within-rater) standard error of measurement of MVN data collected by rater 1 (musculoskeletal physiotherapist) in sessions 1 and 2. Standard error of measurement is shown for the minimum angle (min; top row), maximum angle (max; second row), range of motion (ROM; third row) and angle at heel strike (@HS; bottom row) for the hip (left-most column), knee (centre column) and ankle (right-most column) joints in the sagittal (Sag), frontal (Frnt) and transverse (Tran) planes of movement. The three data points in each plane correspond to the walk (left-most point; circle), squat (centre point; square) and jump (right-most point; diamond) tasks. Grey shading indicates values considered to indicate excellent reliability.

Figure 3

Between-rater intraclass correlation coefficient of MVN data collected by rater 1 (musculoskeletal physiotherapist) and rater 2 (clinical movement scientist) in session 1. Intraclass correlation coefficient is shown for the minimum angle (min; top row), maximum angle (max; second row), range of motion (ROM; third row) and angle at heel strike (@HS; bottom row) for the hip (left-most column), knee (centre column) and ankle (right-most column) joints in the sagittal (Sag), frontal (Frnt) and transverse (Tran) planes of movement. The three data points in each plane correspond to the walk (left-most point; circle), squat (centre point; square) and jump (right-most point; diamond) tasks. Grey shading indicates values considered to indicate excellent reliability.

Figure 4

Between-rater standard error of measurement of MVN data collected by rater 1 (musculoskeletal physiotherapist) and rater 2 (clinical movement scientist) in session 1. Standard error of measurement is shown for the minimum angle (min; top row), maximum angle (max; second row), range of motion (ROM; third row) and angle at heel strike (@HS; bottom row) for the hip (left-most column), knee (centre column) and ankle (right-most column) joints in the sagittal (Sag), frontal (Frnt) and transverse (Tran) planes of movement. The three data points in each plane correspond to the walk (left-most point; circle), squat (centre point; square) and jump (right-most point; diamond) tasks. Grey shading indicates values considered to indicate excellent reliability.

Figure 5

Sagittal plane joint angles throughout the movement cycle for each participant. Time series of hip (top row), knee (middle row) and ankle (bottom row) joint angles obtained from VICON (black) and MVN BIOMECH (red) systems for each participant during walk (left), squat (centre), and jump (right). Y-axis represents joint angles in degrees and X-axis represent the movement cycle in percentage.

Figure 6

Frontal plane joint angles throughout the movement cycle for each participant. Time series of hip (top row), knee (middle row) and ankle (bottom row) joint angles obtained from VICON (black) and MVN BIOMECH (red) systems for each participant during walk (left), squat (centre), and jump (right). Y-axis represents joint angles in degrees and X-axis represent the movement cycle in percentage. Y-axis scale is the same as in Figure 5 to allow comparison.

Figure 7

Transverse plane joint angles throughout the movement cycle for each participant. Time series of hip (top row), knee (middle row) and ankle (bottom row) joint angles obtained from VICON (black) and MVN BIOMECH (red) systems for each participant during walk (left), squat (centre), and jump (right). Y-axis represents joint angles in degrees and X-axis represent the movement cycle in percentage. Y-axis scale is the same as in Figure 5 and Figure 6 to allow comparison.

Figure 8

Difference between MVN BIOMECH and VICON data at discrete, clinically relevant events. The difference in minimum angle (Δmin; top row), maximum angle (Δmax; second row), range of motion (ΔROM; third row) and angle at heel strike (Δ@HS; bottom row) between the MVN BIOMECH and VICON systems for the hip (left), knee (centre) and ankle (right) joints in the sagittal (Sag), frontal (Frnt) and transverse (Tran) planes of movement. The three data points in each plane correspond to the walk (left-most point; circle), squat (centre point; square) and jump (right-most point; diamond) tasks. Positive values indicate that MVN BIOMECH angle was larger than VICON angle. Error bars indicate 95% confidence interval of the difference.

Figure 8

Difference between MVN BIOMECH and VICON data at discrete, clinically relevant events. The difference in minimum angle (Δmin; top row), maximum angle (Δmax; second row), range of motion (ΔROM; third row) and angle at heel strike (Δ@HS; bottom row) between the MVN BIOMECH and VICON systems for the hip (left), knee (centre) and ankle (right) joints in the sagittal (Sag), frontal (Frnt) and transverse (Tran) planes of movement. The three data points in each plane correspond to the walk (left-most point; circle), squat (centre point; square) and jump (right-most point; diamond) tasks. Positive values indicate that MVN BIOMECH angle was larger than VICON angle. Error bars indicate 95% confidence interval of the difference.

Figure 9

The coefficient of multiple correlation (CMC) between MVN BIOMECH and VICON data before (CMC₁; top row) and after (CMC₂; bottom row) offset removal for the hip (left), knee (centre) and ankle (right) joints in the sagittal (Sag), frontal (Frnt) and transverse (Tran) planes of movement. CMC is reported only for joints and planes where all values are real numbers [39]. Where there are three data points in each plane they correspond to the walk (left-most point; circle), squat (centre point; square) and jump (right-most point; diamond) tasks. Where there is only one data point it corresponds to the walk task. Error bars indicate 95% confidence intervals.

Figure 10

The outcome parameters of linear fit method comparing MVN BIOMECH and VICON data. Outcome parameters are α1 (scaling factor; top row), α0 (scalar addition; middle row) and R² (strength of the linear relation between the two signals; bottom row) for the hip (left), knee (centre) and ankle (right) joints in the sagittal (Sag), frontal (Frnt) and transverse (Tran) planes of movement. The three data points in each plane correspond to the walk (left-most point; circle), squat (centre point; square) and jump (right-most point; diamond) tasks. Error bars indicate 95% confidence intervals.