Single, Wearable Motion Sensor Detects Trunk Instability, Poor Walking Symmetry in Study

A single, wearable motion sensor placed on the lower back successfully detected poor trunk stability and walking symmetry in adults with Prader-Willi syndrome (PWS), a study showed.

These findings suggest that this technology may provide a simple, low-cost, and ecologic way to collect and analyze data on PWS patients’ walking abilities, the researchers said.

The study, “Changes in symmetry during gait in adults with Prader-Willi syndrome,” was published in the journal Computer Methods in Biomechanics and Biomedical Engineering.

People with PWS show poor balance and have walking difficulties, which are generally associated with excessive weight and physical features such as small feet, short stature, scoliosis (a sideways curvature of the spine), and low muscle tone.

Most studies on patients’ walking abilities have been performed in specialized laboratory settings using motion capture systems that record and digitize people’s movements in three dimensions.

Such systems provide accurate data on a large set of walking parameters. But they are expensive and require complex and time-consuming procedures.

Low-cost systems using small wireless motion sensors recently have been used — successfully — to analyze walking patterns in healthy individuals and in those with conditions associated with motor impairment. These conditions include obesity, Parkinson’s disease, multiple sclerosis, and Down syndrome.

Unlike lab-based systems, such equipment has the advantage of analyzing movement in situations similar to those encountered in daily life.

While they allow the assessment of conventional spatio-temporal parameters — including walking speed, step or stride length, and stride frequency — they also can evaluate less conventional metrics, such as the harmonic ratio, which measures step-to-step symmetry based on trunk movement. Of note, the trunk is a person’s body apart from the head and limbs.

Notably, only one previous study reported the use of wearable motion sensors — four devices placed on the breastbone (sternum), pelvis, and at the level of each ankle — to evaluate the walking patterns of PWS patients. The study included 11 children with PWS, with a median age of 5.3 years.

The data showed that the PWS children had reduced stride length, increased stride frequency, and reduced walking symmetry, compared with healthy children.

Now, researchers in Italy evaluated whether a single validated motion sensor placed on the lower back could provide relevant information to better characterize the walking difficulties of adults with PWS.

In particular, they focused on the potential of using the harmonic ratio, alone or in combination with standard spatio-temporal parameters, to differentiate the walking symmetry of PWS patients and healthy people. The study compared 20 adults with PWS and 20 age- and sex-matched unaffected individuals.

The PWS patients — 11 women and nine men — had a mean age of 35.6 years and were followed at the Istituto Auxologico Italiano, in Italy.

After the placement of the single device and a brief familiarization period, all participants were requested to walk along a straight line in a 20-meter (65-foot) hallway at a self-selected speed and in the most natural manner. Each participant performed the task four times, with a mean (average) of 19 strides in each attempt.

The results showed that, compared with controls, the individuals with PWS walked with a slightly higher stride frequency and shorter stride length; however, these differences were not statistically significant. In turn, the PWS patients showed significantly lower harmonic ratio values, indicating poorer trunk stability and walking symmetry, than participants without the disease.

These findings, which were consistent with those previously reported using multiple motion sensors, highlight the potential of this single sensor to successfully analyze walking patterns in people with PWS.

The data also showed that trunk movements and the harmonic ratio “provide novel information on gait in people with PWS that could not be extracted from spatio-temporal parameters only,” the researchers wrote.

In addition, using this sensor allows the evaluation of patients both in indoor and outdoor environments, and does not require individuals to undress for the device placement, which can have a psychological impact.

These results may be important from a clinical and rehabilitative point of view as they provide a promising and practical alternative to standard walking analysis systems with a “very simple, low-cost and ecological methodology,” the team wrote.

Further studies will help validate the usefulness of this wearable sensor, particularly ones that include larger groups of PWS patients and compare them with obese people, instead of the non-obese controls who participated in this study.

“This study warrants continued research to refine the best characterization of walking strategy in PWS by applying innovative procedures … in an environment with fewer restrictions than the laboratory of analysis of movement,” the researchers concluded.