Measuring & Mastering the Many Faces of Force
Athlete Training and Health is proud to partner with TruStrength Tech to announce the launch of their one-of-a-kind performance and rehabilitation device, the TruStrength Tech Max.
Mark Pryer, Senior Applied Performance Coach at Athlete Training at Health
John Cronin, Chief Science Officer at Athlete Training at Health; Professor in Strength and Conditioning at AUT University
In sports medicine and sports performance, force is the defining mechanical variable that is of interest to both sets of practitioners. Typically sports medicine professionals aim to restore force capability, while those interested in sports performance want to increase force capability. What is force? How do you measure it? Why is it important to measure? All of these valid questions are ones that practitioners in these respective fields seek to answer daily for the betterment of their clients and athletes.
Force is defined as any action (active force) that tends to maintain or alter the motion of a body, otherwise known as a reaction or reactive force (1). Everything you physically undertake is initiated by some sort of force production, from brushing your teeth or sitting down, to the most explosive athletic activities. Hence, practitioners are interested in ensuring patrons have the prerequisite force capability or strength for daily living activities, resistance to injury, success on the sports field and beyond.
So, what does force look like? It has many faces. Did you know that you are a force? Your body mass may equal 150 pounds; however, when it is multiplied by gravitational acceleration (9.8 m/s2) your body mass becomes a body weight (~700 Newtons), which is a load force or an external force that keeps you stuck to earth. To become airborne, you need to produce internal forces within the muscles and tendons of your body that exceed the 700 N of body weight or downward force. Those who produce greater internal forces relative to their body weight (external force) typically jump higher and move faster.
What are some of the other faces of force? You can have pulling or tensile forces like those seen in a tug-of-war. The opposite of pulling forces are pushing or compressive forces, as seen in pushing a car. Some other forces are vertical, horizontal/anterior-posterior, and mediolateral. And so on!
Multitudinous types of forces are responsible for human movement. To restore or improve the many faces of force, you must have the ability to measure this quality. Just as there are abounding types of force, there are just as many different force measures. To name a few important measures, look at peak/maximum force, mean/average force, explosive force/rate of force development, and isometric/static force or dynamic force.
Proliferate technologies have been invented to measure and monitor force: from simple hand-held dynamometers (HHD) to gold standard force plates and isokinetic dynamometers (see Figures). HHD are commonly used in medical settings to assess force outputs for injured joints. HHDs can be held in one hand and used to measure the force applied to the pad by the client. This is useful, however, there are limitations in that HHD typically measures only maximum or peak force, usually collects at low sampling rates, and cannot measure strength qualities such as rate of force development. Typically these peak force measurements are not reliable given the handheld nature of the device (2).
At the other end of the spectrum are gold-standard measurement devices such as force plates and isokinetic dynamometers, which can reliably measure a myriad of variables. However, these devices are limited by their expense, utility, and portability. For example, isokinetic dynamometers are costly, not portable, and require time with the technology to collect and produce reliable data (i.e., usually technicians collect data). Force plates have become more accessible given new leasing arrangements; however, they are still cumbersome to transport, expensive, are better designed for measuring lower body force qualities, and the learning curve for usage and interpretation of the results can be steep for some practitioners.
Does a compromise exist? Yes, in the form of load cell technology first conceptualized in 1843 by Charles Wheatstone. Scientists and practitioners have innovated this technology to make it easy to use, highly portable, reliable, accessible (cost point), and of extreme utility. With that in mind, we’d like to introduce you to the newest and perhaps best application of this technology, the TruStrength Tech Max (TST Max).
The TruStrength Tech Max is a load cell in the traditional sense, with an expanded capability due to proprietary technology that allows the end user to gather a more robust sense of the forces applied to the device. The TST Max is highly portable and highly customizable, with various attachments that can be used in almost any application by practically anyone straight out of the box. The device is completely wireless and connects via Bluetooth to your chosen tablet, allowing you to collect data in real time. Considering utility, the TST Max can measure and monitor:
- Tensile, compressive, and shear forces
- Vertical, horizontal (anterior-posterior), and mediolateral forces
- Static and dynamic forces (e.g. force feedback on elastic resistance)
- Peak and mean force
- Rate of force development
- Impulse (force x time)
The device can provide real-time movement analysis programs for hip abduction and adduction, shoulder rotation, isometric mid-thigh pull, and other user-defined exercises.
In a sports medicine setting, measuring and monitoring force is essential. For clients and athletes that are returning from injury, tissue loading is often conservative and under-dosed during the acute stage of rehab. This is often due to the limitations of certain technologies, such as the HHD discussed previously, but also due to the difficulty in consistently measuring force in daily rehabilitative activities and preferring to rely on qualitative measures instead. While this has worked for generations of practitioners, there has been a “call to arms” in the industry for a more quantitative values-based approach to care, especially in the interest of justifying reimbursement in the wake of changing healthcare policies.
The TST Max’ multiple attachment points provide versatility and add a variety of new dimensions to existing testing and training methods. One novel way of implementing this into existing practice is quantifying the use of rubber-based resistance. Rubber bands (therabands) are used daily across therapy practices worldwide; however, any prescription of resistance with this tool is problematic given its elastic band properties, the variation amongst bands and manufacturers, the age of the band, and associated loss of elasticity. These limitations can be circumvented by using the TSSG to calibrate your rubber bands via force-distance curves regularly and also provide real-time feedback on the elastic resistance provided. To utilize the TSSG in this manner, a band is attached to one end of the device, which is attached to either a rack or another immovable object. Once operational, the tablet will show real-time readouts of the force being applied via the band. This allows the practitioner to prescribe exercise interventions that will progressively overload the injured client in a safe, quantified manner. This, in turn, should optimize client outcomes and return to activity.
For coaches who are looking to maximize performance, the TST Max can be integrated into daily practice for testing, training, and monitoring. At ATH, the Max has become an integral part of our assessment protocols for our youth, collegiate, and professional athletes; adult population; and for those recovering from an injury – particularly with our measure of general overall strength, the isometric mid-thigh pull. The measurement of strength performance allows the practitioner to understand the athlete’s long-term progress better and customize training based on the identified weaknesses. Importantly, the isometric mid-thigh pull has been shown to correlate with measures of sprinting and jumping, with higher-performing athletes typically scoring better on each (3). But that’s a limited perspective of the device’s capabilities. The device's unique design allows for the ultimate customization for coaches looking to integrate testing into their existing programs. As compared to force plate technology, the Max can be used for testing and training each body part in multiple planes of motion, with relative ease, just by changing the configuration of the device, i.e., changing out the ends of the device. Its utility and portability make TSSG an ideal tool for any practitioner wanting to take their diagnostics and exercise prescription to the next level.
Finally, the device has been used in research to uncover some finer points surrounding ballistic events, such as throwing a baseball. Trey Job, Senior Director of Sports Science and Coach Development with ATH, referenced in Job et al. (4) used the Max to detect differences in shoulder strength across multiple positions of internal rotation. This was done by testing rotational strength while seated and supine. The results of this study can inform training and rehabilitation practices for coaches and clinicians worldwide by allowing them to pick a testing and training position that most closely matches the desired adaptation.
Force is a natural phenomenon that occurs with regularity in the world around us in many forms; being able to master its measurement opens limitless doors to what the human physiologically can achieve. For clinicians and coaches worldwide, technology has evolved to allow for the measurement and gradation of force inputs in new, reliable, and easier ways. The new TST Max allows for testing and monitoring to be performed at multiple angles and the utilization of an infinite amount of variations to be added to the practitioner's repertoire.
With liberation from the limitations of historic force measurement devices, what do you believe is the next territory for our increasingly unencumbered physical capabilities?
Encyclopædia Britannica, inc. (n.d.). Force. Encyclopædia Britannica. Retrieved March 22, 2023, from https://www.britannica.com/science/force-physics
Grootswagers, P., Vaes, A. M., Hangelbroek, R., Tieland, M., van Loon, L. J., & de Groot, L. C. (2022). Relative validity and reliability of isometric lower extremity strength assessment in older adults by using a handheld dynamometer. Sports Health: A Multidisciplinary Approach, 14(6), 899–905. https://doi.org/10.1177/19417381211063847
Giles, G., Lutton, G., & Martin, J. (2022, December 15). Scoping Review of the Isometric Mid-Thigh Pull Performance Relationship to Dynamic Sport Performance Assessments. Journal of Functional Morphology and Kinesiology, 7(4), 114. https://doi.org/10.3390/jfmk7040114
Job, T. D., Neville, J., Cahill, M. J., Bourgeois, F. A., Crotin, R. L., & Cronin, J. B. (2021, December 23). Training Methods to Increase Throwing Velocity in Baseball Athletes: A Brief Review. Strength & Conditioning Journal, 44(4), 1–9. https://doi.org/10.1519/ssc.0000000000000694