Do Force Platforms, Pressure Sensors And Smart Insoles Do The Same Thing?

Force platforms, pressure sensors and smart insoles are all devices that a person can step on and get some insight related to their weight or the pressure they are exerting on those devices with each step. Other than that, they are quite different and can have very different applications. This post is just an attempt to break that down. Feel free to jump to the different sections that are of interest:

[Force PlatformsPressure SensorsSmart InsolesSummaryMore on Smart Insoles]

Force platforms

A Force Platform (FP) is an equipment that you would typically find in a lab – an engineering lab, a biomechanics lab, gait analysis lab, ergonomics lab.. you get the idea. They are great for measuring forces applied directly onto its surface. So when a force platform is placed on the ground, you could step on it to find out how much force you are exerting on the platform. For those platforms that measure multiple axes, you could also slide an object across the platform to measure resistance forces between the surfaces. In sports engineering, FPs enable studies in walking/running gait, jumping (and landing), friction measurements in water polo balls or shoes or gloves, the coefficient of restitution of balls, aerodynamic drag (when placed in a wind tunnel), and more.

IMG_1075

An example of a Kistler Force Platform (blue) set up in a wind tunnel

For anyone keen to explore what else is done with force platforms in sports engineering, feel free to do a quick search on these journals: Sports Engineering JournalSports Technology Journal or Journal of Sports Engineering & Technology.

Inside Force Platforms

The majority of Force Platforms in the market are set up with multiple Strain gauges or Piezoelectric sensors/elements that deform proportionally to the applied load. There is also the not so common Hall Effect sensing Force Platform which doesn’t require an external signal amplifier/conditioner like the strain gauges and piezoelectric sensors do. They are typically quite expensive and their prices vary with the number of sensors, size, construction, and additional data acquisition (or signal amplifier) systems.

For those who can’t afford the expensive systems and is adventurous enough to try and build something, a sports physics researcher from the University of Sydney wrote a paper providing details of a cheaper home made force plate. Essentially he used Piezos that were manufactured for sonar applications and they cost $25 each. A quick search on Instructables also showed one DIY instruction on making a strain gage force plate. For the slightly less adventurous, there is also the option of the Wii Balance Board as a cheap force plate alternative. There have been some validations of the gaming platform as a standing balance assessment tool, a golf swing analysis tool, and for use in other medical applications. The only downsides of the Wii Balance Board are the user weight limitation and that a custom software is required to access and read the data.

Pressure sensors

There are three main differences between Pressure sensors and Force platforms. Pressure sensors are typically flexible and can be placed on flat or curved surfaces, unlike Force platforms that have to be mounted rigidly. The other difference is pressure sensors do not measure force vectors. Thirdly (or a slight extension of the second), Pressure sensors only quantify pressure that is perpendicular to it (single axis) so it cannot determine shear forces or friction between two surfaces. Due to their flexibility, pressure sensors have been used to determine comfort and fit in aircraft seats for Paralympians, analyse medical mattresses, measure the pressure of grip during a golf swing, pressure distribution on bicycle handlebars, and more.

fsr402

Single force sensitive resistor (FSR) from interlink electronics

Pressure sensors are mostly made out of either resistive sensors or capacitive sensors. The main differences between them are the sensing material used and their electrodes. They can be constructed as single sensing nodes or they can also be constructed in a row-column array fashion. The advantage of the array or matrix construction (over single nodes) is that it requires fewer connections. In an array, the intersection between each row and column is a sensing node. So a 3 by 3 array creates 9 sensing nodes while only needing 6 connections.  On the other hand, 9 single sensing nodes will need 9+1 connections where the +1 is the common ground. The difference becomes much bigger as the number of sensing nodes increases (For example 100 sensing nodes can be achieved using a 10 by 10 array that needs 20 connections or 100 single sensing nodes that need 101 connections).

Single Sensor Nodes Vs Arrays 2

A simple illustration of Single sensing node Vs Sensor Matrix/Array

However, the matrix construction is not without its challenges. The matrix sensor circuit is prone to parasitic crosstalk (capacitive or resistive). This means when pressure is applied on one node or multiple nodes, the electrical readings for other (unactivated) nodes might be affected. This is also known as “ghosting”. Unless some correction is applied, the measurements/readings become inaccurate and potentially useless. Also, the bigger the matrix, the more complex the correction. But if accurate absolute readings are not required, then it’s fine.

A related side story

I have been following the development of this smart yoga mat that was successfully crowdfunded on Indiegogo back in Dec 2014. Fast forward to 2017, they are still struggling to deliver the product. Looking through their updates, we can see they had to deal with sensor accuracy (possibly the crosstalk or ghosting issue); and on top that, some other issues they had include sensor durability, mat materials suitability, and accuracy of their tracking algorithms (which they are using some form of AI). Having prototyped a smart exercise mat around the same time they started, I can fully understand the challenges and why it is taking that long. Then again I am not sure it is worth all that effort. Personally, I think that simply relying on a pressure sensing mat to monitor and give (technique) feedback on yoga poses (or any exercises) has its limitations. Adding camera tracking (possibly utilising the camera on the tablet) might help. That saying, it is not stopping others from developing similar products as seen in this video.

Smart Insoles

Smart Insoles or Instrumented Insoles are essentially pressure sensors made in the shape of a shoe sole. The sensors are usually made in a similar fashion described earlier. Most of the Smart Insoles are also built with IMUs so that it adds a bit more context to the pressure data such as whether the wearers are standing, walking, running or jumping. The greatest advantage of Smart Insoles is they allow feet pressure mapping and measurement on-the-go. Things like continual gait analysis and activity monitoring, and it even has medical application likes foot ulcer prevention and falls prevention.

contnt_img

Source: Footlogger.com

There are a couple of shoemakers that designed their shoes with the Smart Insole embedded within the shoe like the Altra IQ for running and the Iofit for tracking golf swing stance. The good thing about them is they have designed everything to fit properly into a shoe, made for a specific function. So users don’t run the risk of their Smart Insole not fitting properly into their shoes and collecting inaccurate measurements. On the other hand, users are restricted with specific shoes for pressure monitoring or activity analysis.  But at the end of the day, the pros and cons are really dependent on the individual.

Brief Summary

Going back to the question: “Do Force Platforms, Pressure Sensors and Smart Insoles do the same thing?”; there are some things that they are all capable of performing (e.g. gait analysis), but they all do it in a different way.  Also, there are certain measurements or monitoring that are unique for each sensor. Here’s a simple table that sums it up:

Sensors Measures shear force Measures Pressure Doesn’t require rigid mounting Portable Tracks Motion
Force Plates X X ✔/X
Pressure Sensors X ✔/X X
Smart Insoles X


More about Smart Insoles

Personally, I feel that Smart Insoles is a great idea, with many useful applications in sports and health. Over the last few years, there has been an increase in research and development in this area with many patents generated in the process; and companies around the world have come up with commercial products around the concept of Smart Insoles. It is definitely still in its early stages and I am not sure if it has even reached Early Adopters yet. Sadly, one company that I followed (Kinematix) has already closed shop due to a lack of funding. Perhaps it is ahead of its time like the adidas intelligent running shoe with intelligent active cushioning. Nevertheless, I believe the potential (of Smart Insoles) is there and I think targeting specific niches/problems will probably have a better outcome than designing for a generic application.

If you have an idea or project needing a smart insole or custom pressure sensor, feel free to contact us or leave a comment. We might be able to help you with it or at least point you in the right direction. As always, thanks for reading!

This post also appears on sportstechnologyblog.com: link.


Other related articles:

Advertisements

Tracking & Managing Anxiety in Athletes

The 2016 Rio Olympic games as with the previous games was a great platform for many tech companies to showcase their latest developments. There are radar and camera technologies that capture motion/biomechanics of an athlete on the field and in the pool. There are wearable devices that (also) track motion plus monitor physiological parameters 24/7. They aim to positively alter athlete behaviour and optimise performance. There are also sports apparel and equipment that were designed and developed (after much R&D) to enhance athlete performance. But we will leave that for another time.

Wearables for tracking performance

Going back to wearables and tracking systems; they often look at (somewhat) straightforward parameters – joint positions, speed (or velocity), height, acceleration, impact, angles, rotation rate, heart rate, heart rate variability, sleep and other physiological stuff. Sometimes coaches and athletes only need to look at a single parameter while other times they may need to examine a combination of variables and find correlations or visualise them over time to identify trends. Some companies go further by processing the above data and coming up with (trademarked) indexes such as Player-Load (Catapult), Windows of Trainability (Omegawave) and Recovery Score (Whoop). What they are trying to achieve is break down all the data that is being collected and deliver one metric that simplifies things and make it easy for coaches and athletes to measure performance (and recovery) .

In major games like the Olympics, where athletes trained years to prepare and qualify for that one event and possibly one moment, there can be a lot of anxiety and pressure to perform. Even if all the physical preparation has been done right, the results could still boil down to how well those emotions are managed; the difference could be between a podium finish or not performing as well as expected. So are there wearable technologies that monitor an athlete’s emotions and maybe warn the athlete of dangerous anxiety levels that can lead to choking or panic?

Wearables for tracking anxiety

Turns out there are a number of wearables in the market that do that. Here are three different types:

  1. Head-worn wearables that measure EEG signals (or brain activity) like the Emotive Insight and Muse. Although the Muse is designed as an aid for meditation and relaxation, it is basically monitoring four EEG channels to see how excited or relaxed a person’s brain is. The Emotive Insight has five EEG channels and looks at the user’s cognitive performance in areas such as Engagement, Focus, Interest, Relaxation, Stress, and Excitement. Emotive also has a higher spec neuroheadset that can look at fourteen EEG channels and goes into much more depth of what’s going on in a person’s mind and how he/she is feeling.

    emotiv_epoc_600

    Emotiv Epoc+: 14 channel wireless EEG system

  2. Wrist-worn devices that measure electrodermal activity (or EDA), blood volume pulse, skin temperature and motion; like the Feel and Empatica E4 wristbands. Based on research, measurements of EDA strongly reflect sympathetic activation which is linked to stress levels and excitement. Measuring heart rate variability through the blood volume pulse sensor also reflects sympathetic and parasympathetic activation. Skin temperature is another reliable measure of stress levels as shown in this research. Finally, motion tracking with inertial measurement units (or IMUs) helps identify the user’s activity and tries to place a connection between anxiety levels and what the user might be doing at that time.

     

     

    Screen Shot 2016-08-30 at 10.19.16 AM

    The Empatica E4 and Feel: 4 sensors packed on a wrist device

     

     

  3. Clipped-on devices that measure breathing frequency like the Spire. The Spire is built with force sensors; when it is secured onto the user’s waistband or bra, it detects the expansion/contraction of the user’s torso and diaphragm during breathing, thus deriving the breathing rate. Then algorithms are used to determine from the breathing waveforms whether the user is calm, tensed or focused.

 

Screen Shot 2016-08-30 at 12.30.42 PM

Spire: Breathing frequency tracker

 

Most of these devices also provide an accompanying app to monitor anxiety levels, and they prompt users to meditate or do breathing exercises. On a side note, a breathing exercise for lung patients was adapted for training athletes’ breathing technique and also focuses on dealing with anxiety. Athletes could also listen to brain.fm music that either helps them relax or stay focused. In a way, managing stress levels on a day-to-day basis can be beneficial for athletes because stress levels can increase the likelihood of an athlete falling sick or getting injured, and it also affects recovery.

Emotion Profiling for Performance

On the other hand, when it comes to performing well during competitions/races, some athletes actually perform better with some amount of anxiety. In fact, different athletes in different sports may perform better at varying levels of anxiety. In other words, some athletes perform well at high levels of arousal while others may perform better at lower levels of anxiety. It’s all about finding a sweet spot. As mentioned in this article, one widely used tool by coaches/athletes to identify that sweet spot or optimal performance zone is the individual zones of optimal functioning (IZOF) model. This is a qualitative analysis approach that involves the athlete recounting the emotional experiences related to successful and/or poor performances. All the emotions are then labelled and rated as described here, and this creates an individualised emotion profile showing which emotions are helpful for performance and which ones are unhelpful. Of course, this would only work if athletes have competed for a number of times previously and came out with different outcomes (winning or losing or setting new personal bests).

Performance-arousal-IZOF_2

Individualised emotion profiling (source: sportlyzer)

Ultimately we could utilise all the different wearables (and tools) mentioned above and somehow piece all that data together to shed some light on the inner workings of each individual athlete. Then the data could be used to “pivot” them in the optimal direction. But at the end of the day, its really down to the athletes themselves pushing hard every day and fighting battles with their body, mind and soul to get to where they would be. So let’s just salute the Olympic athletes for what they do and what they have achieved. And while we await the start of the Paralympics, I leave you with this video below by Under Armour and Michael Phelps. Thanks for reading!