Why we invested in IMU motion capture technology

By John Cockcroft, PhD – Neuromechanics Unit Manager, Stellenbosch University (Stellenbosch, South Africa)

At Stellenbosch University we have developed a state of the art equipment array in our Neuromechanics Laboratory. We use it for more fundamental research in healthcare, engineering and sports as well as for delivering analytical services to companies, clinicians and coaches.

As sensor systems become more mobile, we are also empowered to move out of the lab. Below is a picture of one of our outdoor research projects using a Vicon motion capture system. Following the trend of portability, optical motion capture systems have developed to the point where we can collect data outdoors.

This has worked for us for some projects, but we often face challenges with this kind of setup.

  • Time constraints – set-up and tear down are time intensive and often the environments we are measuring in need to be used by other groups throughout the day.

  • Space constraints – traditional testing spaces are often tiny and cluttered making deployment impractical.

  • Usability – this type of equipment is quite bulky and therefore not easily transported or deployed remotely on a regular basis.

  • Laptop – to move out of the lab, data acquisition software needs to be able to be run on a laptop.

This is why we invested in IMU motion capture technology.

We have added mobile technologies to our laboratory arsenal. In particular, the addition of the MyoMotion inertial measurement unit (IMU) system has allowed us to record 3D motion data without the challenges of using a full optical system. An IMU is a small wearable sensor module (containing gyroscopes, accelerometers and magnetometers) that can accurately measure its angular position in space hundreds of times a second without needing any external infrastructure. By placing IMUs on different segments of the body, the skeletal posture of a person can be reconstructed. This can be used to animate an avatar or to analyze data such as joint angles. More advanced IMU systems also provide temporal-spatial information such as ground contact timing and distance covered overground, and enable synchronization with other measurement devices.

 

Better ecological validity.

We can now measure physical behavior in the natural environment. For example, we can analyze the sit-to-stand performance of a stroke patient during rehabilitation exercises at home or in the clinic. This is much less invasive and time-consuming for the patient than travelling to a laboratory and going through a marker placement routine for analysis using an optical motion capture system. Our IMU system is also easier to set up and use than an optical system so we are able to train young researchers to collect this kind of data quite easily. With IMU and pressure mapping data that we collect with our portable lab system, we can quantify levels of impairment during sit-to-stand more accurately and objectively than with only visual inspection. We are able to quickly measure metrics such as trunk stability and load bearing asymmetry, and even give real-time feedback, which can help the clinician to provide the best service to the patient.

Better access to populations.

Recruitment to the lab is logistically difficult, but with field testing you can often collect data more time- and cost-efficiently. Recently we’ve been traveling to rural schools to perform functional movement testing on young children with fetal alcohol syndrome disorder. We typically arrive in the morning about 30 minutes before the first class and set up a testing space in an empty room. Learners are then able to quickly leave their classroom for a single lesson, usually in pairs, and walk down the corridor to be tested. We use a variety of functional tests to assess gross and fine motor control, including single-leg hopping, single leg standing and pegboard tests. IMU data is collected synchronously with pressure platform data and two video streams. We usually collect data for the entire morning and on a good day we can complete about 8 participant protocols. With this kind of field testing approach, we are able to test many more children per day with minimal disruption to their schedule and ours. Similarly, bringing the lab to the participants is also beneficial when working with professional sports teams.

New experimental possibilities.

We want to ask questions and conduct experiments that are not possible in our laboratory. With our IMU system, we can assess the running technique of an elite sprinter on the athletics track during training and provide immediate feedback. For example, some coaches that we work with are interested in a sprinter’s postural profile during sprint starts and how the coordination patterns between different body segments evolve during the transition to an upright position. We use a portable lab system that perfectly synchronizes high-speed video streams with the IMU data, which means we are able to easily overlay postural information from the IMUs on top of ground contact timing data in one software package.

Wearable technology is advancing rapidly and will soon become a crucial component of any laboratory’s equipment arsenal. Research facilities will continue using optical motion capture systems and other lab-based equipment, but increasingly they are looking to take advantage of mobile sensing solutions – especially for research studies in the more applied sciences. Services in the fields of healthcare and sports science are also evolving towards an evidence-based approach, and practitioners are searching for ways to perform advanced analytics in the natural setting more quickly and easily.

All in all, we really need to get high-end technology out of the lab and into our daily lives. The good news is, it is beginning to happen.