Using Wearable Sensors In Combat Sports

Combat Sports

Combat sports or fighting sports as described in wikipedia is a competitive contact sport that usually involves one-on-one combat; and typically, a contestant wins by scoring more points than the opponent or by disabling the opponent. They can be broadly categorised as armed (fighting with a weapon, e.g. fencing or kendo) or unarmed. Unarmed combat sports can then be further broken down into three main types: striking, grappling and a mix of both.

Wearable Sensors In Combat Sports

The democratisation of wearable sensors in sports, in particularly, inertial sensors or IMUs, means that researchers and sports practitioners in combat sports had (and still have) the opportunity to use wearable sensors to measure and monitor performance or injuries. There has been quite a number of research done in this area and has been increasing since 2005 as found by this systematic review: Inertial Sensors for Performance Analysis in Combat Sports: A Systematic Review. As this (paper) is pretty comprehensive (at least from an applied research point of view), we will try to pick out some key interesting findings from this paper and also have a look at some wearable sensor products that are in the market.

The Research Part

Quick overview of the paper

The research paper is called a Systematic Review because the authors have searched (in a systematic way) through all the previously published research related to the topic (inertial sensors + combat sports). They then summarised all the key findings, and established what else is missing in this area (if any) and what kind of research work could be done going forward. So if there’s anyone interested in combat sports research using wearable sensors, (reading) this would be a good place to start.

Types of Combat Sports

The authors have sifted through 352 papers down to 36 papers/research that are relevant – meaning these 36 have all used inertial sensors (accelerometers or gyroscopes) in their combat sports research. Out of the 36, the top 3 combat sports that were investigated were 1) Boxing, 2) Karate and 3) Tae Kwon Do. The others included Boxtag, Mixed Martial Arts (MMA), Jujitsu, Brazilian Jujitsu (BJJ), Kickboxing, Kung Fu, Fencing, Muay Thai and different combinations of the above. This could also reflect the popularity of the sports in a broader sense.

Where were the sensors placed or worn?

There were four main areas where inertial sensors were worn on the athletes: Forearm/Wrist, Hip, Upper back and Leg/Ankle. Also, four of the research studies used full body motion sensors (e.g. Xsens and Shadow Motion). But the most commonly worn location was the Forearm/Wrist, which is a logical placement location to analyse metrics such as punch/strike acceleration and velocity.

Apart from being strapped onto the athletes, Sensors were most commonly placed on or embedded in the equipment. Some of those equipment included punching bag, head guard, mouth guard, vest, strike shield and protective hand wear.

Which Performance Features did they look at?

The most investigated performance feature was Strike quality. Strike quality includes measures such as Strike Acceleration, Velocity, Force and sometimes Accuracy. It was noted that being able to measure and monitor that metric during an athlete’s training would be really useful for coaches. It was also suggested that it would be more effective to place sensors on the athlete rather than on the equipment. For example having sensors in a punching bag could measure impact/force of an athlete’s punch. But when fatigue sets in and the athlete’s punch misses the bag, the effort wouldn’t be tracked. Whereas sensors on the athlete allows tracking of every effort and decline of effort which could reflect fatigue.

Second on the list was Head Impact which is considering the safety of athletes. In this case, it is more effective to have the sensors on the equipment (i.e. instrumented mouthguards or head guards). For detecting impacts, it only counts when a punch, strike or kick impacted those equipment. One interesting finding was that lots of TaeKwonDo kicks (to the head) could lead to concussion and turning/spinning kicks recorded an average of about 130g!

Some other key points/suggestions from the research

• Focus on what (Performance parameter) needs to be measured then decide on the placement of sensors based on that.
• Sensor hardware consideration: Typical accelerometers and gyroscopes only measure up to 16g and 2000°/s. Higher spec’ed sensors are required for measuring impacts and movements with higher rotational speeds (eg spinning kicks).
• Automatic scoring could be helpful to curb concussion and promote safety in combat sports.
• Automatic strike classification combined with automatic scoring would have lots of potential.
• There are still some challenges when it comes to implementing wearable sensors in a competition setting.

So with that in mind, let’s have a look at some of the wearable sensor products for combat sports.

Commercial products

FightCamp (Hykso hardware)

FightCamp is a subscription service for home boxing training. Their minimum starting package comes with two punch trackers (Hykso) and hand wraps. They also recommend that users have a punch bag and boxing gloves to have the full experience. From their promo video, how it works resembles other home fitness products/services like Mirror or Peloton. One main differentiating feature is the punch trackers that measures metrics such as punch count/volume, punch rate and output.

From the looks of it, it is mainly a fitness tracking tool and doesn’t look at boxing performance although the hardware was designed to also measure average punch velocity and recognise different punches.

StrikeTec

StrikeTec is similar to Hykso in that it is also a punching specific tracker. It comes with two sensors that are meant to be strapped on each wrist. When turned on and connected to the app, they track in real-time, metrics including punching speed, power, endurance, accuracy and they also identify punch type. But unlike FightCamp or Hykso that only operates on iOS, StrikeTec’s app only runs on Android at the moment.

Everlast + PIQ

Another boxing sensor system comes from a collaboration between Everlast and PIQ. PIQ Sports Intelligence developed the PIQ Robot (trademarked) – a smart sensor that can be customised for measuring performance in different sports. Everlast + PIQ is a boxing specific solution. Dubbed the PIQ Robot Blue, it is capable of doing punch recognition and tracking punch speed, punch count, intensity and retraction time. It is also able to measure impact of each punch which suggests it has a higher spec’ed accelerometer.

Kick.ai

After looking at three punching specific sensors, we come to one that measures kicks. Kick.ai developed a pair of martial arts sensors that are meant to be worn with ankle bands covering the achilles tendons. The current app is designed to suit martial arts like TaeKwonDo, Hapkido and Karate. It tracks metrics such as number of kicks (including splitting up left and right kicks), maximum and average kick velocities. It also has a timing feature that tracks reaction time. One thing they did was to try and filter out “false positives” or accidentally counting a movement as a kick. So it only counts kicks when the kick made an impact (i.e. hit a kick pad) which is pretty logical.

Similarities in research and what’s in the market

From the above, we can see there are some similarities in research and what is available commercially:

1. Boxing is really popular and lots of people are working in that space (3 out of the 4 sensor products are for boxing)
2. Measuring strike quality and placing sensors on the wrists is most common
3. Strike classification or determining strike type is really difficult to acheive (simply with two sensors) – researchers who did it used a lot more sensors or other sensing technology.
4. There isn’t any or much work done in grappling combat sports and it could be that it is highly complex to measure grappling performance and difficult to place sensors on athletes when there are so much contact involved in grappling.

Final Thoughts

Other sensing technologies

Besides wearable sensors or inertial sensors, there are other technologies that are applied in combat sports for measuring performance or detecting impacts. Various optical and camera tracking technologies have been mentioned in the above research including the use of optical MoCap systems and the Kinect sensor.

Pressure sensors have also been used to instrument a kendo sword’s grip to measure grip pressure during normal stance and attacking motions. One of the applications of this was to assist beginners in developing correct hand placements in kendo. The same researchers also developed a smart kote glove using the same pressure sensors with the aim of automating scoring during competition.

Other opportunities to explore

Load monitoring/injury prevention:- we mentioned above that there are a number of research about monitoring impacts particularly on the head. Those are of course critical. On the other hand, injuries can also happen due to overtraining. Being able to monitor or track fatigue could be used as a warning for combat sports athletes or coaches to slow down before injuries sets in and completely stops the athlete from training.

Competitions:- the Professional Fighters League recently launched the Smart Cage that tracks performance metrics of fighters during a fight. Those metrics include speed of strikes, power ratings and heart rate data. It’s unsure whether there are any wearable sensors worn on the fighters or if they rely on camera systems or it could be a combination. Whether its for automated scoring for performance tracking or even for fan engagement, this is a good start and I reckon more competitions should adopt such technologies.

And that’s our overview on this topic. If you have used the sensors mentioned above and/or would like to share your thoughts, feel free to leave a comment below. Once again, thanks for reading!