The use of motion capture is growing in all areas of sport and entertainment, especially at the elite level. As the technology migrates from research into clinical and commercial training businesses, there are challenges in using the data to make informed choices.
In this guide, we look at the top options in motion capture and show the important differences in what the specific technologies can do and what they cannot. Motion capture is a very vague term, and this article articulates what exactly is true 3-D motion capture and what is not. Motion capture is evolving and increasing in use at all levels, and sports performance professionals must stay current on the best options and best practices available.
What Is 3-D Motion Capture?
Motion capture is a very loose term, and capturing motion can mean nearly anything now. However, it usually refers to a modified recording of total body motion in three dimensions. Now that IMU sensors have entered the market, an accelerometer with a gyro can seem like true motion capture, but there is a difference between measuring motion with a few sensors and capturing a body in action. Most readers will envision reflective markings on a body to digitize an athlete in three dimensions when the term motion capture is brought up, but it’s extremely important to know what makes up a true 3-D recording.There is a difference between measuring motion with a few sensors and capturing a body in action. Click To Tweet
A small sensor does have the ability to collect orientation data, but unless it collects all of the body, those systems should be seen as motion sensors, and some systems do create compete renderings of movement from recordings. The criteria for true 3-D motion capture is the following:
- Creates a complete and fully authentic acquisition of total body motion.
- Provides anatomical orientation of points of reference.
- Requires a direct recording of three dimensions of data.
- Able to collect ballistic activities with high frequency of measurement.
As you can see from this list, unless all of the requirements are met, it’s easy to confuse a single sensor recording of movement that’s raw and out of context as motion capture. IMUs used together can create motion capture data from calculations, but add another level of complexity to the challenge of measuring body motions. Markerless cameras, such as the Microsoft Kinect device, use an infrared laser and camera together to create depth in three dimensions, but those systems have limitations in sport.
How Does Motion Capture Work?
Motion capture is one part marking and tracking the body and one part converting that information into data that is useful for both research and applications in markets such as entertainment. The amount of detail and precision a user of motion capture needs determines how the data is collected, as each system has abilities and constraints with both accuracy and flexibility of the information. Some motion capture systems are designed for indoor use but have some outdoor functions that are effective and appropriate. Capturing full body motion requires a controlled environment for the system to have enough robustness to collect data properly.
Two clear options exist with motion capture: marker or optical systems and markerless solutions. Motion capture using video is possible, but most research-grade systems prefer using infrared cameras and reflective markers. Some less-precise systems are growing in popularity because they are inexpensive and solve easier problems, like treadmill analysis with running. These new, less-accurate systems are now taking over a narrow part of the motion capture market.
Wearable bodysuits, usually with IMU sensors, are becoming more popular because of their portability, but they are seen as more clinical options that demand less data granularity and precision. High-performance motion capture systems are so fine that they can see facial expressions and fingers move in great detail, such as a person playing the piano. Without oversimplifying the process, motion capture begins by recording motion from cameras and tagged body parts, or estimates motion by using more limited cameras and IMU sensors.
After the data is captured, additional filtering and calculations are performed to clean the data up and ensure that motion artifacts do not create false reporting. Reflective markers are placed on the body with specific guidelines to ensure the data is accurate and precise because muscle and skin can move at high velocity, creating a challenge with data quality. Anatomical landmarks are selected for their reliability and their value in connecting joint motion. IMU bodysuits and systems follow a similar approach with placements, but they have unique locations based on their equipment design rather than following a scientific best practice. Markerless systems require proper camera setup based on needs, as most systems look at motions that are stationary in positioning such as walking in place, squatting up and down, and doing other basic functions.
The final step is taking the data and converting it into reports or using a function that transforms it into animation or simulation. In addition to the data collected by the motion capture, companies create solutions that enable users to combine multiple data sets, such as force plates and EMG readings. Most of the development in the last few years has been on the software side of optical systems and the hardware side of markerless and IMU solutions. All types of solutions require a lot of data smoothing and cleaning, but more work is needed with IMUs in general versus optical options.
Different Options With Motion Capture Hardware
For the most part, motion capture hardware is designed for research or very progressive clinical needs. Video analysis is more common as a biofeedback option with coaches, but motion capture is growing due to the IMU market. The optical market, also known as the camera-based systems, tend to be more research appropriate, while the sensor market tends to be more clinical and sports performance oriented.
For example, Motus provides a single sensor option for throwing athletes, such as those that pitch (baseball), bowl (cricket), and pass (American football). While that system captures movements near the elbow, it is mainly a calculation because many assumptions are made when other data sets are not available, such as the trunk and legs. IMU systems tend to have less accuracy and precision, but the technology is improving and slowly closing the gap.Motion capture technology’s most obvious value is its automatic analysis of data for the user. Click To Tweet
We should not include conventional video—even with multiple cameras—as a motion capture option, for several reasons. The most obvious value of motion capture is that technology automatically analyzes the data instead of the software user having to do it manually. Some video systems automate video like motion capture, digitizing the series of cameras to calculate movement, but the issue with this technique is that lighting restrictions and other factors with visual data can limit high-precision requirements. Direct markers have a more reliable history of stable data, but due to the confines of competition, video is still viable because markers are not practical or appropriate.
Markers are commonly small ball-like attachments the size of a marble or reflective circles applied on athletes. Some systems use wrap-like attachments, like sweatbands and wristbands, and some systems provide suits fitted by trained users. Markerless camera options just use hardware to capture video, but they provide far less information and require the hardware to be extremely close to the user, such as a few feet away. Those systems currently can’t assess sporting actions that are very fast or have high displacement requirements.
Some systems provide synchronization hardware and other tools for advanced studies or specific needs, such as underwater filming and remote capturing. Most of the equipment beyond cameras and markers is designed to help trigger the start and stop of other sensors, like force plates, EMG, and in-shoe pressure. Some systems include virtual reality headsets or ways to connect to those devices, but most accessories are simple cabling and the like.
Understanding Motion Capture Software
Most software options for motion capture have two purposes: converting the motion data into an animation for either scientific replay or entertainment uses. Nearly all companies provide a replay option, and some of the software enables the viewer to choose perspectives and animation styles, such as line (stick figures), skeleton, or human figure. Advanced software can measure very precise movements in isolation or create reports based on analysis methodology best practices. Several options of software are hardware agnostic, meaning nearly any hardware can connect to the software.
The goal of the software for sports is to display motion that is free of the visual debris that video sometimes contains. Like video, motion capture helps as a way to connect other data sets that are less visual, such as EMG and force analysis. Researchers can see the relationships between movement and muscle recruitment, along with ground reaction forces if needed.The goal of motion capture software for sports is to display motion without visual debris. Click To Tweet
Sometimes the movements with motion capture are not actually measured, as users just want qualitative views to synchronize with quantified measures such as kinetic data from sensors. Manual analysis is sometimes performed with motion capture software, especially in research on cyclical movements. Endurance sports—those that are typically cyclical, such as running—usually average or statistically evaluate repetitive motions in order to gain insight into biomechanical faults or possible technique errors.
Software platforms can range from very expensive suites to streamlined 3-D players, but nearly all research software has enough overlap that differences are very minor. Some software platforms are only file manager options, as the expectation from hardware providers is that the platform market will allow for the analysis of analog data. Thus, they reduce their software development to focus just on hardware. Hardware-only and software-only options are rare, but a few small companies exist that only provide one or the other.
Best Uses of Motion Capture in Sport
Practitioners often use a motion capture solution to view the function of the body in all perspectives and extract joint angles. Those in the performance field, such as biomechanists, want the data to study how athletes move, while medical specialists want to see why athletes get hurt in the first place. The sports medicine field is interested in dysfunction prior, during, and after injury, and the performance space needs to learn what makes an athlete succeed regarding movement. There is a pattern of diminished performance and increased risk of injury when baseline data falls, and coaches and medical professionals sometimes use motion capture technology to handle important or complex injuries.
The most common motion capture use is gait analysis. While other movements are important in sport, nearly every land-based activity will include some sort of running motion, be it sprinting, jogging, or walking. Some clinics have spent an enormous amount of resources on reeducation programs for injured athletes, but most of the private facilities use motion capture analysis for brand or facility marketing, rather than true intervention-based solutions.
The workflow of motion capture is not a major burden, but it’s also not group-friendly, nor an instant feedback solution. Smaller applications, like single IMU sensor solutions, may leverage smart devices effectively for biofeedback; however, due to the incomplete picture, it’s not true motion capture and you should not confuse it with complete analysis.
Like video analysis, it is invaluable for athletes to have the opportunity to see themselves on screen in different speeds and perspectives. Most elite athletes in Olympic sports will eventually experience some form of motion capture, but plenty of athletes will only see it on TV.
Example Options in Motion Capture Technology
There are more than two dozen vendors of sport-specific motion capture systems, and plenty of other solutions are excellent and effective in adding value to teams, hospitals, and private facilities. We left several companies out of this review, including software solutions like C-Motion. This isn’t because they aren’t worth listing, but because access to every system (for review purposes) is nearly impossible.
Qualisys: One of the few companies outside the United States, Swedish-based Qualisys provides solutions for a myriad of needs beyond sport, such as animation and engineering. They focus on the virtual reality market and have solutions that help with underwater demands. One of the strengths of the company is the integration of its products with other systems (force plates) and software like MATLAB and LabVIEW. They are innovative, and quickly took advantage of the smartphone market by providing a 3-D player, as well as a trigger app for simple recording.
Vicon: This U.K. company is exceptionally strong in the optical camera-style system, but they recently took a risk by acquiring IMeasureU, a startup from New Zealand that provides a single IMU sensor option for athletes. Most of Vicon’s experience is in sports performance and clinical sciences, but they have success with entertainment as well. Like many companies in motion capture, they have traction in entertainment as well as engineering. Leading biomechanists and experts in movement science use Vicon as a way to quantify their work with athletes and patients.
Motion Analysis: One of the first companies to create a robust noise-free solution, Motion Analysis is from Santa Rosa, California, and got started in the early 1980s. Many of the pioneering studies on baseball started with Motion Analysis, and they have expanded to other markets like video games, animations, engineering, and even broadcasting. The company is well-known in sports due to their extensive development of cameras and software, and hundreds of research papers include their system as part of the materials section.
Xsens: A pioneer in wearable motion capture, Xsens is one of the leaders in the IMU-based option for movement analysis. Xsens is a Dutch company, but they have a strong presence in the U.S. as they are also located in Los Angeles. Their solutions range from sports to agriculture, as they are more than just a company looking to help with gait analysis and research. They are extremely connected to the engineering market, and have many applications outside biological sciences and sports performance. The strength of their system is that you can use it in real time, as well as in real-world settings such as manufacturing and outdoors.
OptiTrack: Another leader in motion capture, OptiTrack provides traditional optical solutions as well as the emerging markerless solutions. OptiTrack leads in animation, movement sciences, virtual reality, and robotics. They are an international company and provide their own proprietary software, as well as a software developer kit (SDK). They also offer additional plug-ins and tools to help synchronize force plates and other data sets. OptiTrack provides a validation study, showing it’s a viable solution for both research and the clinical market.
NDI: While not a sports performance motion capture option, NDI is a great example of how technology can maximize precision. Known as a medical solution, specifically surgery and hospital care, NDI provides both optical and electromagnetic tracking. However, NDI is not just for hospitals, as they provide military solutions and motion capture for body motion as well. NDI is a Canadian company, and has several patents and innovation awards. Finally, NDI is strong internationally, and has representation in Europe and Asia.
Phoenix Technologies, Inc.: This Canadian company is extremely strong in robotics and other technology markets, including space and industrial applications. The company focuses on portable cameras and wireless sensor solutions, and both can handle sport and clinical needs. One of the strengths of the product is its super-fast sampling rate and precision; features that explain why Phoenix has aerospace clients such as the International Space Station and NASA. While they have native software, they integrate with third-party options and can integrate with other platforms as well.
myoMOTION: Noraxon’s product, myoMOTION, has one of the most stunning visual displays of multiple data sets, and they are known for their EMG systems as well as their wearable IMU-based motion capture system. Noraxon is located in Arizona, and much of their past is linked to EMG. A few years ago, Noraxon made a strategic move to include more data integration with other sensors, such as force analysis and motion capture. Noraxon software creates reports and can be exported to third-party solutions for research as well as data mining.
All of these companies have enough differences that they require more comparisons and research beyond this guide. The most common request is training, meaning how to use not only the product, but motion capture in general. Most of the hands-on experience with Ph.D. programs or progressive graduate and undergraduate programs should be sufficient to effectively use the listed systems. Venturing outside of biomechanics poses a challenge for coaches, who may not have the kinesiology background to fully use motion capture, but some applications are not too demanding as plenty of college performance programs use motion capture effectively.
Motion Capture Is a True Investment
The cost of most motion capture systems is not cheap, and a full lab is over six figures, on average. Most vendors have a sales department that you can talk to, and some will demo the product if they are in your area. The best way to invest in motion capture is to first visit the top options at universities, as most research departments are open and using the system for noble purposes, not to create marketing buzz for their facility or clinic.
Conversely, at times it’s wise to look at commercial settings that do indeed provide privatized services, as those centers must be efficient and effective to stay in business. Motion capture is growing, and the solutions are getting better every year. Down the road, the future will be even more cutting-edge, but time will tell if markerless systems phase out conventional options.