Technology in Sport Part 5: Quantification (Kinetics)

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It’s been a while since I last wrote an entry in this blog series but I wanted to wrap it up with a final blog on ways that we can quantify kinetic variables. Kinetics refers to the forces that cause motion. As coaches, we primarily coach kinematics (the description of the motion without regard to the forces that cause it) with the implicit goal of affecting the kinetics (forces) of the task. With that said, it would obviously be of great value if we could somehow monitor, record, and track kinetic variables as a means of guiding training and testing physical readiness. Fortunately there are a couple ways to do this. As is the case on some of the technologies mentioned in previous installments in this series, some of the things mentioned here will likely not be available or practical to many coaches. Nonetheless, it’s good to know what is out there if for no other reason than it gives you familiarity with the sport science research that is being done using these methods. Here’s a brief list of some methods to monitor the kinetics of movement:

  • Inverse Dynamics: This is a method for computing forces and joint moments based on the kinematics of a performer and their inertial properties. The method of calculation is beyond the scope of this blog but the nice thing is that many higher level motion capture and analysis tools can do it for you. Inverse dynamics can compute the internal joint moments and forces using some special assumptions which can in turn be used to examine the relative contribution of various muscles or muscle groups. Inverse dynamics is frequently used with the following point on this list, muscle modeling.
  • Muscle Modeling: This is somewhat of an extension of inverse dynamics but muscle modeling involves an attempt to computer model the actions of the muscles knowing what is going on with the kinematics. While knowing this information might seem fairly unnecessary if you know the textbook definitions of what muscles cause what actions, the reality is much different and muscle modeling can provide some very interesting information. Muscles are the actuators of the body and the interplay between different muscles at different lengths, speeds and actions can be very different than what one might ordinarily expect. Determining the activation that produces a desired movement requires an extremely complex control algorithm, but when done well it can reveal some very interesting information about the specific actions of individual muscles. Here’s an example of a study on this site that used complex muscle modeling to examine the actions of the individual muscles in the hamstring muscle group to better understand the etiology of hamstring injuries.
  • Pressure Sensitive Insoles: These are insoles that are placed the shoe and linked to a data capture device either wirelessly or wired and can measure the pressure that the foot places on the insole of the shoe during any support or impact based activities. These insoles are actually quite thin and cheap and can be good for monitoring asymmetries in gait, predicting and preventing injuries, and determining appropriate footwear. I used these to study the foot pressures of peripheral neuropathy patients and found them quite easy to use. But unfortunately, because of the way the insoles must be made, the pads can only be used for a limited period of time and with greater impacts very few foot strikes would produce good data.
  • Force Plates: We already looked at force plates to some extent in one of the earlier installments in this series but we didn’t look at their use as much for truly examining kinetics. Using a force plate, one could determine the X, Y, Z force contributions of a given technique. I have had the opportunity to use these both with very good sprinters (both on a treadmill and a track) and with elite throwers (with the plates embedded in a throwing circle). In both cases, the data revealed some interesting tidbits of information. As an application of this science, one could use force plates to examine the effects of technical (kinematic) changes on the actual force and power production of the athlete. This would be particularly interesting to do with sprinting, where there remains much debate over whether technical training is necessary and if so, which techniques produce the most optimal force curves and performance.
  • Tendo Units: These measurement tools are quite popular in the sport of power lifting and are gaining popularity in college and NFL football strength programs. These devices can be used to determine force and power output in a wide range of activities. Although they are primarily used for examining uni-planar weight lifting activities, one nice thing about them is that you can also get resultant measures of acceleration and power in any and all dimensions.
  • Home Brew Calculations: Although not worthy of rigorous scientific standards, one could use some basic physics equations to get a general estimate of the global kinetics of a system. This would either require a high speed camera or for the athlete to do multiple reps (in which case you’d be getting average power or work). You’d also need some means of timing the movement accurately (see here for some ideas on that). For example, if one were doing snatches and you knew (or could fairly accurately predict) the vertical displacement of the bar from its starting position to the position at the point of the catch and could time the movement from initiation through the catch, you could figure out the work and power output performed on the bar. By factoring in the athlete’s body weight you could even get a loose estimate for total power output that might be useful for intra-athlete comparisons over time. To get a better idea of how to do these calculations you can read this article.

So that’s it. I’ve finally wrapped up this look at using technology in coaching. If you have any other ideas please feel free to share.

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