Summary
Background: The barbell squat is a popularly used lower limb rehabilitation exercise. It is also
an integral exercise in injury risk screening protocols. To date athlete/patient technique
has been assessed using expensive laboratory equipment or subjective clinical judgement;
both of which are not without shortcomings. Inertial measurement units (IMUs) may
offer a low cost solution for the objective evaluation of athlete/patient technique.
However, it is not yet known if global classification techniques are effective in
identifying naturally occurring, minor deviations in barbell squat technique.
Objectives: The aims of this study were to: (a) determine if in combination or in isolation,
IMUs positioned on the lumbar spine, thigh and shank are capable of distinguishing
between acceptable and aberrant barbell squat technique; (b) determine the capabilities
of an IMU system at identifying specific natural deviations from acceptable barbell
squat technique; and (c) compare a personalised (N=1) classifier to a global classifier
in identifying the above.
Methods: Fifty-five healthy volunteers (37 males, 18 females, age = 24.21 +/- 5.25 years,
height = 1.75 +/- 0.1 m, body mass = 75.09 +/- 13.56 kg) participated in the study.
All participants performed a barbell squat 3-repeti- tion maximum max strength test.
IMUs were positioned on participants’ lumbar spine, both shanks and both thighs; these
were utilized to record tri-axial accelerometer, gyroscope and magnetometer data during
all repetitions of the barbell squat exercise. Technique was assessed and labelled
by a Chartered Physiotherapist using an evaluation framework. Features were extracted
from the labelled IMU data. These features were used to train and evaluate both global
and personalised random forests classifiers.
Results: Global classification techniques produced poor accuracy (AC), sensitivity (SE) and
specificity (SP) scores in binary classification even with a 5 IMU set-up in both
binary (AC: 64%, SE: 70%, SP: 28%) and multi- class classification (AC: 59%, SE: 24%,
SP: 84%). However, utilising personalised classification techniques even with a single
IMU positioned on the left thigh produced good binary classification scores (AC: 81%,
SE: 81%, SP: 84%) and moderate-to-good multi- class scores (AC: 69%, SE: 70%, SP:
89%).
Conclusions: There are a number of challenges in developing global classification exercise technique
evaluation systems for rehabilitation exercises such as the barbell squat. Building
large, balanced data sets to train such systems is difficult and time intensive. Minor,
naturally occurring deviations may not be detected utilising global classification
approaches. Personalised classification approaches allow for higher accuracy and greater
system efficiency for end-users in detecting naturally occurring barbell squat technique
deviations. Applying this approach also allows for a single-IMU set up to achieve
similar accuracy to a multi-IMU setup, which reduces total system cost and maximises
system usability.
Keywords
Exercise therapy - biomedical technology - lower extremity - physical therapy speciality
- inertial measurement units
