 heart rate variability a useful metric to measure recovery. This is what we'll be discussing today by taking a look at the science. I'll be going into what exactly HRV is and how it's useful for us and talking specifically about the whoop strap which has quickly become one of the most popular ways for cyclists and other athletes to measure HRV. I've been testing the whoop strap for a couple months now and at the end of the video I'll give you my own personal experience using it and whether or not I think it's worth it. Welcome back to another video. If you're a fairly serious cyclist you've probably heard of the whoop strap or perhaps you're already using one. For those of you who haven't and are asking yourselves what the heck a whoop is basically it's a wristworn device that measures your heart rate variability among other metrics related to recovery. It's by no means the only device that does this but it is currently one of the most popular. I'll be discussing training with HRV in general and then training specifically with whoop. Before we get into that though it's important to know what we're talking about when we talk about HRV. Heart rate variability or HRV is the variation over time of the period between consecutive heart beats. That's right your heart actually doesn't beat in perfectly timed intervals. There are fractions of a second difference in the time between each beat. Measuring this gives us insight into the status of our autonomic nervous system which can tell us a lot about how well recovered we are. A shift in the autonomic nervous system to the sympathetic drive commonly known as the fight or flight response over the parasympathetic drive can be an indication of fatigue. When this occurs you'll often see less variability in the time between heart beats which is thought to mean that you're fatigued although not always but we'll get into that in a minute. Heart rate variability is one of the metrics that whoop uses to determine your recovery score along with changes in resting heart rate and your sleep duration. Whoop also measures other things like your sleep quality and your exercise strain etc which I will be touching on but this video is going to focus mainly on HRV. The reason this is such a big deal and it has been gaining a lot of attention from cyclists and other endurance athletes is because it could potentially be giving us insight into an extremely important aspect of training that we haven't really had access to. Proper training is a fine line between too much and not enough. You want to stress your body enough that it makes adaptations but not so much that you can't recover and end up overtraining. The most common way to make sure you aren't overtraining is just seeing how you feel. If you feel good then you ride hard and if you don't then you rest. While you should by no means ignore how you feel relying solely on it can be problematic especially judging by the vast number of endurance athletes that live in a constant state of overtraining. You know they say there's no such thing as overtraining just under recovery but I'd actually argue that there's no such thing as overtraining just under consumption of hypergain, beast mode, mass gain, or raw addition. There are training metrics like ATL and TSB aimed at determining your fatigue levels but these don't take into account anything that's actually going on in your body. This is where HRV comes in and if it works it could revolutionize training. Just like when cyclists started to use power meters they could finally measure their output on the bike this could allow us to finally quantify recovery and although often overlooked recovery is a huge component of the performance equation. Let's not get too far ahead of ourselves though. First things first is HRV a good method for gauging recovery. This study on the relation between heart rate variability and training load had runners perform three weeks of hard training followed by a recovery week. They found that HRV decreased throughout the three hard weeks and then came back up during the rest week. They stated that when recorded during the night heart rate variability appeared to be a better tool than resting heart rate to evaluate accumulated physical fatigue as it magnified the induced changes in autonomic nervous system activity. It is fairly common for athletes to monitor the resting heart rate to get an idea of how fatigued they are but it appears that HRV may be a better indicator of this and further studies on HRV and athletes come to similar conclusions. Like for example this study done on swimmers which had a three week intensive training period and a two week tapering period. Again HRV increases during the training period and decreases during the resting period. They found that the decrease in A&S activity during the intensive training is correlated with a loss in performance and the rebound in A&S activity during the tapering tracks with a gain in performance. Interestingly the speed of the rebound during the tapering period was quite different between swimmers. So HRV is looking like a promising tool to measure fatigue although to be fair there are studies that suggest otherwise. For example this study on night HRV and overtraining had subjects increase their training load by 100% in four weeks and they found that HRV during sleep does not seem to be a valid marker of overtraining. This systematic review and meta-analysis stated that studies leading to reductions in performance suggested that overreaching had little effect on resting HRV. This disagreement may be the result of methodological issues that should be investigated further namely the effect of utilizing isolated values compared with weekly rolling average values and also the impact of posture and recording time of day. The method in which you record and looking at trends over a week versus a single day may be key when looking at HRV. For example this study on evaluating training adaptations with heart rate measures found that the averaging of resting heart rate and HRV values over a one week period appears to be a superior method for evaluating positive adaptations to training compared with addressing its values on a single isolated day. While your day to day HRV can go up and down in response to a hard training day or a recovery day or other factors in your life that have nothing to do with training if you want to get a good idea of whether or not you're overtraining you're going to have to zoom out and look at your HRV over the course of a week and whoop does this for you but does this mean that looking at day to day HRV is useless? Well maybe but perhaps if you happen to have a low HRV on a particular day that might mean that you shouldn't go out and do high-intensity intervals that day on the contrary if you happen to have a high HRV on a particular day maybe that means you should get after it. Fortunately this idea of using HRV to determine your training prescription has been tested. This study on endurance training guided by daily heart rate variability divided subjects into two groups one that prescribed training based off of HRV and one that followed a preset training plan but they found was that maximal running velocity improved more in the HRV group and this was achieved with fewer high-intensity sessions in the HRV group than the control. Essentially using HRV told participants to take it easy more often and that actually produced better results. Now there are two problems that I have with this study though the subjects were moderately fit males not endurance athletes and they had the control group do four high-intensity sessions a week while research suggests that closer to two or three is optimal. Luckily though another study was done that addressed these concerns. This study on training prescription with HRV used actual endurance runners in the study and had the group that followed the preset plan do two or three high-intensity sessions per week and again they found greater improvement in 3000 meter running performance in the group that based training off of HRV and again this was done using fewer hit sessions. This goes along the lines of what I've said in so many videos when it comes to high-intensity training less is more. The group with the preset plan averaged 2.2 hit sessions per week while the HRV group averaged just 1.7 sessions per week with a lot more variation in the number of sessions between individuals. We would expect this as some individuals can recover faster than others and HRV seems to be a good way of determining this at least from these studies. If you're a regular viewer of my videos you've heard me talk about how important it is to be well rested for your interval sessions. Using HRV may be a way of ensuring that you're doing your intervals in a recovered state meaning that you do the intervals with higher quality leading to greater fitness gains. So far we've been working under the assumption that a higher HRV is always better however this may not always be the case. This review on heart rate variability in elite endurance athletes stated that HRV can remain depressed in the lead-up to competition during a taper despite achievement of an optimal performance like in this study on world class rowers who still went on to win medals at the world championships despite a reduced HRV. The reduction in HRV prior to competition possibly reflects the HRV response to consecutive days of high-intensity training with a reduction in training volume in the case of a taper. It could also be HRV saturation at low heart rate levels. If this should tell you anything it's this. It's probably not a good idea to look at your HRV before a race. If it's lower than you'd like this could probably get in your head and make you perform worse when in fact it wasn't really that big a factor. You know this is actually starting to sound like a pretty useful device. I can use my terrible recovery score as another excuse for why I got dropped. You can change the date of your intervals if you aren't fully recovered but you can't change the date of your race. I would instead wait until after the race to look at your HRV and then relate that to how you felt during the race. The review goes on to explain how HRV response can be different in highly trained individuals. In these athletes the HRV response to training is variable with studies showing no change in fitness despite an increase in HRV and other studies showing decreases in HRV despite increases in fitness. As such a common misconception is that there is a direct linear relationship between HRV and the parasympathetic influence on heart rate. In reality however the relationship is quadratic. Things get more complicated when measuring HRV in well-trained athletes and it's not as simple as low is bad and high is good. And HRV responses are highly individual and require longitudinal monitoring and seven-day rolling averages to get meaningful data. Essentially the more well-trained you are the trickier it becomes to use HRV to monitor recovery. This doesn't mean that it can't be used but perhaps it should be taken with a grain of salt or perhaps the data would be more useful than zooming out and taking a look at weekly trends rather than individual days. With that I want to relate this to my own experience using loop for the past couple months. I will say studies like the one where they put subjects into an HRV group and a preset training group got me excited. I can see easily designing training around this principle using loop. It would be as simple as green means it's a high intensity day, yellow means it's an endurance day, and red means take the day off. Based off of my experience however I don't know that this would actually work in practice. There have been days where I've been in the green but clearly wasn't fully recovered. One day in particular comes to mind where I was near the end of a hard training block but I woke up and I was in the green even though my legs felt like trash. I was surprised but thought hey why not try to eke out one more day before the rest day. I got on the bike and struggled to maintain zone two for two hours. In reality I needed rest. I've also seen my HRV not improve much during a recovery week much like in the study on the world class rowers. That being said there definitely are times where the recovery score makes sense where I've been in the red after a hard day or in the green after a recovery day. There could be a couple of reasons for this. One is that being well trained may make using HRV more problematic. The other is that just as the research suggests it may be more beneficial to look at the week as a whole rather than individual days which loop allows you to do. If your weekly average HRV keeps going down or perhaps you had many days in the red during the week perhaps that should sound some alarm bells. What we keep coming back to here is the age old advice of listen to your body. HRV is a tool and it can help guide your training decisions but it shouldn't be the end all be all. If you wake up and whoop says that you're in the green but you feel like you got hit by a truck then maybe it's not a good idea to go out and do high intensity intervals. If however you're on the fence about how you feel maybe you really want to get in a hard session but you think you might be more sore than you should be and you check whoop and see that you are fully recovered that might be a sign that you're good to go. This is how I've been viewing the recovery score. It doesn't determine my training prescription for the day but rather acts as confirmation as to whether or not I should go hard or take it easy based on how I feel. One thing that whoop can help you with is habit tracking. Whoop is a sleep tracker which can encourage you to get more sleep which is the biggest thing that you can do for your recovery. This study on the effect of wearables on sleep actually tested whoop and found that it improved sleep quality even though the total daily sleep remained unchanged. They also found that it was able to measure sleep and heart rate with low bias and precision errors. Whoop seems to be a very accurate sleep tracker and even without the recovery score this could help some people recover faster by showing them how much sleep they actually get and encouraging them to change their habits. HRV is also affected by factors other than exercise. One obvious example is drinking alcohol which has been shown to reduce HRV. Most people who use whoop can tell you that a night of drinking can have a big effect on the recovery score the next day. This is another example of how using whoop may lead to better recovery habits. Now let's talk about the strain tracker that whoop has. Whoop gives you a strain score for the day that goes up to 21. Why 21? I have no idea. I guess whoop just doesn't like nice round numbers. I could see your average active individual getting some use out of this feature but for serious cyclists who already use a power meter and a heart rate monitor this feature is pretty useless. The real analysis of how stressful a ride was on your body should be done after the ride on training peaks mainly by looking at metrics like TSS. For me almost every time I ride if it's not a recovery ride I get a strain score of 20 plus and remember that 21 is supposed to be the maximum. Most of these are just long endurance rides and I wouldn't classify them as a 20 on a 21 point scale. Call me crazy but I would think that having a strain score close to the maximum that you could possibly get five days a week would be close to impossible. Um is that a challenge? Here hold my beer. I thought that over time whoop would learn how much strain I usually put on my body on a day-to-day basis and adjust but this hasn't been the case even after a couple months of using it. So is whoop or other HRV monitors for that matter a technology that's going to revolutionize training like the power meter did? Uh no I don't see that happening but that doesn't mean that it's useless far from it actually. Being able to monitor recovery is valuable even if you should take that recovery score with a grain of salt. It doesn't replace listening to your body but instead can act as confirmation that yes you should go hard today or no you should take today off. And on top of that I think there's potential for it to improve your recovery habits like getting enough sleep reducing the amount of alcohol you consume etc. And then of course there's the price tag. While the band itself isn't that expensive you'll have to pay a monthly membership that ranges from $30 to $18 per month depending on what package you get. Is it worth it? My answer for other expensive training tools like a power meter for example is 100% yes. For this product however I'm a little bit more hesitant. Let's say 60% yes. Let me get this straight this product tells me that I shouldn't go hard all the time that I'm drinking too much and I have to pay a monthly subscription for it. Yeah that's 100% no. Thanks for watching. If you enjoyed this video be sure to give it a like, subscribe for weekly science-based cycling videos just like this one and share this video with your cycling friends. I'll see you in the next one.