Hello, and welcome back. In our first lesson, we introduce the different types of sensors, and devices. This time we'll be discussing in greater detail the external devices. Classic measures for this include GPS, and accelerometry, which are incorporated into most wearable technology that are available these days. These devices can provide a lot of detailed information. Let's look into how they are used. What do these external devices actually measure? GPS will determine how far, and the velocity of movement. This is especially relevant for runners that are going in a straight line with an intention of getting from point A to point B. Accelerometers will pick up all movements that cause the device to move, this will include movements that do not result in any distance moved as measured by GPS. We'll later compare accelerometry loads with GPS data, for example, distance and velocity. However, it's evident that the two measures are not evaluating the same endpoints. Acceleration can detect activity without ever moving forward or back or right or left while GPS would likely evaluate motion in the vertical plane, has no distance or velocity. Regarding external devices, these can measure impact, which would be the amount of stress a user experiences from a certain movement resulting from some form of acceleration, for example, landing from a jump, accelerating in a specific direction, or making a sudden move, for example, a cut in basketball. Some wearable tech devices are designed to specifically detect and measure particular acceleration patterns, for example, the volleyball dataset that we examined last time is designed to use accelerometry to identify, record, and then characterize all of the jumps that are performed by the wear. In addition to counting jumps, it also predicts the vertical height attained, and the landing impact. It's important to appreciate that the Vert is only able to detect force above 2Gs. We've used this device before for examining running and when one is running at a slow pace, may not even detect the running motion. The landing impact metric from Vert tells you whether your recent jumps have been good or high impact. The company reports that the landing impact metric is determined by the predicted vertical jump height, the landing force, and the landing form. As we discussed previously, this information can be used by coaches, and players to keep a log of the daily efforts, and training volume. The Zephyr BH3 is a small device that is capable of collecting very detailed information for long periods. Different than the Vert, the BH3 is collecting the raw accelerometry data rather than providing specific information regarding jumps and jump heights and landing impacts. This has its pros and cons. If you're wanting to see everything, then a device like this is capturing all the information, and recording it for later download. Although not the focus of this lesson, the device is also capable of measuring heart rate, and breathing rate. The BH3 collects the accelerometry data at one Kilohertz or 1,000 Hertz, which means 1,000 points per second. It also can measure posture with a gyroscope, and it can measure peak acceleration, activity, which is combination of the accelerometry data, as well as impact. The Catapult device also contains triaxial accelerometry, and it uses an algorithm to calculate a player load from the acceleration data. This player load can be used to evaluate the training effort on a daily basis and is used to try, and optimize the training effort across the season in order to avoid under or overtraining as well as overuse injuries. This is important in order to avoid under or overtraining as well as overuse injuries. The measure that we will evaluate in the Python is the acute to chronic workload ratio or ACWR. Incidentally, the Catapult device can use GPS for measuring velocity, and distance when outdoors or alternatively, it can use LPS or local positioning system for quantifying movement in specially equipped indoor facilities. The Catapult player algorithm is shown here, and it outlines that the player load is really a function of the sum of the accelerations across the three directional planes. This calculation is sometimes called the instantaneous player load, describing the sum of the accelerations from one measure to the next. However, the more commonly used measure is the accumulated player load that we see here. This is the sum of all the instantaneous measures across a time period of interests, which might include one playing football or one entire game, or an entire week of practice. One possible use of this measure is to provide a carefully determine limit to the amount of practice effort to be given, for example, when a player is returning from injury or on the day prior to a big competition, a coach or a trainer could use the player load in order to limit the amount of training that the athlete is performing. That's all for this lesson. In our next lesson, we'll jump into some of these measures to take a closer look at their use for measuring effort in games, and practices.
