Kinetics is all about the relationship between motion, forces and torques. Measuring these allow us to measure the outcome of movement patterns that result from the interplay of joint rotations influenced by muscle contractions. To understand the output of motion, such as the produced forces, we use advanced techniques like force platforms and dynamometers.
One of the most used technologies in Kinetics is the force platform. These devices measure ground reaction forces and provide us with profound insights into human movement. Some of the parameters that can be measured include velocity, power, displacement, and temporal parameters. Moreover, they can often map out left-right asymmetry, especially when working with bilateral systems.
Force platforms are widely used in sports, particularly for conducting jump tests. These tests are highly reliable and repeatable. Because force platforms require minimal setup time, they are very suitable for testing large groups of athletes quickly and efficiently.
However, there is an important catch. Many force platforms consist of hundreds, if not thousands of sensors that calculate the pressure someone exerts on the plate. This means they calculate the sum of all applied forces, not just the vertical force. In other words, they measure not only the vertical force but also the sum of vertical, lateral, and horizontal forces. Although the vertical force is often the most critical in various movements, even those that may appear horizontal at first glance, this leads to a significant drawback: the collected data is less precise and useful than desired.
In essence, these force platforms measure “pressure” rather than actual force, while the direction of force can be crucial, even in vertical movements like jumps. If accuracy and versatility are essential, it should be considered to invest in a multi-axis (and more expensive) force platform capable of conducting measurements in multiple directions.
Another drawback of relying solely on force measurements is that they provide information about how much force is being produced but not about how it is generated. In other words, if you run 100 meters in 11 seconds, you know what you’ve achieved but not how you accomplished it. Moreover, who’s to say that this was the correct method, allowing you to do it countless times in the future? It’s also possible that in the next attempt, you might get injured due to improper force production.
David Winter emphasized the importance of understanding inertia effects. Especially in patients with conditions such as cerebral palsy, he observed that body movement and control can be different. He noted that these inertia effects could alter the joint moment sign and, therefore, advocated for a more comprehensive biomechanical model that not only considered maximum load but also how the body motorically controls and adapts movements. A commonly chosen solution is, therefore, to combine force measurements with kinematic data obtained using motion capture systems. Read more about this topic in our blog about
 Whittaker, E.T. 1988. A Treatise on the Analytical Dynamics of Partical and Rigid Bodies. Cambridge: Press Syndicate of the University of Cambridge.
 Rowe, P.J. 2019. Time to deliver on the legacy of pioneers such as Professor John P. Paul (1927-2013). Medical Engineering & Physics, 72, 66-69.