Welcome to our discussion of internal sensors and their use in sports analytics. Of course, our last topic focused on external sensors which were able to measure things like speed, distance, acceleration, and body position. And in fact, measures like speed and acceleration can be considered measures of absolute intensity as these can be applied to anyone. These are often used in large population health studies to talk about exercise intensity as low or moderate or vigorous, based on accelerometer readings. Next up, we'll discuss devices with sensors that evaluate internal measures. These are the devices that are the most exciting to me as they provide a glimpse into what is happening physiologically to the wearer. This moves from simply how fast is one moving an external measure to how much effort is being invested into the activity. For example, with a heart rate measurement. Therefore, as we move to talking about internal sensors and internal measurements, we'll begin to focus on relative intensity. So when it comes to internal devices, these are measuring quantities within the body, for example, heart rate or pulse oximetry. That little piece that you have fit on your finger. If you're in a hospital, that's collecting information about heart rate and oxygenation of the blood. Yeah, but we're going to talk also about skeletal muscle oxygenation and breathing rate. And of course, breathing rate is one of the easiest things that we can use as a measure of relative intensity. For example, if two people were running down the road together with identical velocity and acceleratory measurements, it would be their breathing rate that would give us a quick and dirty measure of the relative intensity of the exercise for each person. For this topic will dig in to look at some different wearables that can help quantify the relative intensity of training. What is relative intensity? It's the amount of effort needed to perform exercise relative to the overall capacity of that individual athlete. So this helps to individualize training sessions rather than focus on absolute workloads such as running velocity. Smart watches are currently ubiquitous in the United States. Everywhere you look, it seems you see a Fitbit or an Apple watch. However, a few brands that you may not know are Biostrap and Whoop. The Whoop device we will discuss very soon. These smart watches have different capacities depending on the sensors they contain. As we discussed in our introductory lesson, some examples of internal measures that these devices report on include heart rate via PPG or photoplay tomography. Or ECG in some of the newest devices where one can actually use a connection from their finger to the device to connect the electrical circuit across the heart and receive electrocardiogram measures. But these devices also will record things like stress levels. And typically are incorporating three different metrics responsiveness, exertion balance, and sleep patterns. But what are the actual sensors that these devices are using in order to provide us these different metrics? Well, some of the sensors are provided here. The electrodermal activity, for example, has been incorporated into many devices of late. It's a measure of skin conductance, which is related to one's arousal or stress state. Other measures include responsiveness, which is a metric calculated from the combination of heart rate data and electrodermal activity. The exertion balance, which is a metric generated by considering an individual's amount of physical activity and inactivity. And sleep patterns, which is an analysis of your sleep quantity and quality. But which of these defined variables here are actually using internal measures. It is likely device-dependent. For example, if a device says they are measuring one's physical activity, it could be based on heart rate or accelerometory or both. In the case of the Whoop device, whoop is monitoring primarily heart rate. And it's incorporating measures of the resting heart rate, the breathing rate, the heart rate variability. And each of these is incorporated into their stress level metric, known as strain. Very classic Internal measures include resting heart rate. Which was around when I was a 15-year old interested in training and recovery. Resting heart rate was recommended for athletes to be measuring each morning upon awakening in order to determine whether one's body was properly recovered. So this idea is definitely not new. And yet, resting heart rate is incorporated into many measures these days. The breathing rate, which is the number of breaths taken over a period of time typically given in minutes. But also important, of course, is breathing depth, which is rarely measured. And finally, heart rate variability, which is a measure of how much variability there is in the time between each individual heartbeat. Which is typically recorded in milliseconds. I would call all these true internal measures, along with heart rate. And are being used as the basis of many metrics that companies have put together to try and capture training stress or recovery scores. In our next lesson, will dig in a bit to one of the oldest internal measures, that of heart rate, to see if it is worth paying attention to or not.
