Category Archives: Hot Weather

Training with power, HR, and RPE.

Recently, I’ve been spending a good bit of my time reading and thinking about foundational training, how to optimize endurance training, and things related. There are various reasons for this recent interest, but among them is the relevance to most people’s training at this time of year… usually, the off-season is a time for moderate to heavy endurance training (relative to our fitness/competitive goals). In any case, what follows are some of my recent thoughts on the subject.

Boiled down, without any commentary:

Use power and HR to set upper and lower limits for most of your endurance workouts, but generally focus more on HR.

Use power to set most guidelines for higher intensity efforts and workouts, but pay some attention to HR and RPE.

Use both RPE and power for efforts and workouts above aerobic capacity/VO2 max intensities.

Should I use power, HR, or RPE to gauge my endurance workouts or training pace? What do each of those metrics have to offer me in evaluating my training?

Well, that’s tough. Power is the only way to actually measure work being done on a bike and the rate of work being done. Or, if you’re running, your pace is clearly the measure of how quickly you’re covering a given distance. In some sense, this is all that matters. Heart rate will tell us how challenging our workout is for our aerobic systems, which is clearly key. If we’re trying to enhance endurance, then we’re ultimately trying to enhance how much we can get out of each unit of aerobic effort. In some sense, we’re trying to squeeze the most out of each heartbeat. Then again, perceived exertion (rate of perceived exertion = RPE) increasingly appears to be the bottom line for measuring fatigue and effort relative to our current fitness or potential. If you’re fresh or tired, fed or fasted, hot or cold, etc. etc. your sensations of perceived exertion is directly tied to your ability to keep exercising. More and more scientists these days would go so far as to say that the feeling of fatigue is fatigue.

So what now? Power will tell me how much work I’m doing, but nothing about how hard that is for me at my current fitness level, nor will it tell me whether I’m getting fitter in any direct fashion. HR will tell me only how hard I’m working relative to my current aerobic fitness level, with some feedback from things like heat, dietary status, fatigue, etc. but won’t tell me anything about how that level is progressing or how I compare now to last month or last year. RPE will tell me the end result of my body’s internal integration of all of the factors that affect fatigue, including HR, but will include other things like dietary status, motivation, mental fatigue, etc. into those biological equations, and again, won’t tell me anything about actual work being done and fitness level without outside feedback.

After spending some time thinking about these ideas, reading what other people have to say, and recalling my experiences in my own training, I think it’s really ideal to pay attention to all three and use each of the three metrics to create guidelines or constraints for your training, and to use the relation of the three metrics to each other to gauge your progress. Namely, consider doing the following:

HR – Since HR is the best direct gauge of aerobic effort relative to your current fitness level, I would probably say that if you’re only going to pay attention to one thing during endurance oriented workouts, then I would say you should pay attention to HR. Create a HR range that you’ll strive for the duration of your endurance workouts, high enough that it’s actually a workout, but low enough that you can keep it in that range almost the whole time you’re out, with the exception of warm-up, possible harder efforts, and a cool-down.

Power (or running pace) – Create a range, again, so that the workout requires a lot of work, but easy enough that you can keep it going. Aim for a high-aerobic power output if you’re cycling, below your tempo pace but high enough that it’s going to tire you out over the 3, 4, or 5 hours that you’re out on your bike. Likewise for running, except that we can use pace very effectively as a substitute for power, usually going a little slower than your marathon race pace.

RPE – With both HR and power guidelines in place, pay attention to how easy or hard things feel. If it’s easy from start to finish, increase the HR and power you’re shooting for by a small margin, but if it’s difficult or impossible to finish your goal workouts in those HR and power  ranges, then reduce  your goal power and HR until you find a sweet spot that’s achievable but challenging.

With these ideas in mind, I’ve found that some of my best endurance training on the bike occurs when I aim to keep my HR in the 120-130 bpm range, power in the 250-300w range, and my effort steady but not hard. For me, it’s very difficult to have an average HR above 125-130 for a ride of any duration, but if I can keep my HR mostly in the 120s with occasional spikes above that on hills where I ride tempo/threshold type efforts, then I can complete a very productive endurance ride and not slow significantly at the end. If I ride much under that, then I know it wasn’t much of a workout or the workout was geared towards other goals, in which case my HR may or may not have been relevant. If I try to keep my HR above 130 for long periods of time, then unless I’m highly caffeinated, I know from experience that I can’t keep that average up for more than a few hours on a steady endurance ride, so there’s no point in blowing my effort in the first half of a 5 hour ride when it would be more productive to keep it steady most of the time. Likewise with power. Cruising around in the low 200w range is very easy for me, whereas keeping my power above 300w is quite challenging for the duration of a long ride, but sometimes do-able for up to 4 hours or so. In either case, though, if I’m doing a ride at a very low power or HR, I’ll know from the feel of it that I’m really not challenging my body’s endurance fitness much at all. Likewise, if I try to go out and hammer for 4-5 hours straight on my bike, but crumble as soon as I get to the top of the last hill at 4:30 into my ride, then I know that I’ve overshot and significantly increased the stress on my body while minimally increasing the fitness boost I might get from that ride. Especially when you’re trying to slowly but surely build your endurance, it’s better to have workouts that are moderately challenging. You should do workouts that take focus to complete, but don’t leave you in a hormonal or metabolic dump after the fact.

Along similar lines, I think that if you have a long progression of workouts that you want to use to gauge your aerobic fitness, I would be very curious to look at the ratio of power to average HR over those months or years of training. This is not something that I’ve yet done in any significant fashion yet, but I was planning to start experimenting with and looking into this. I would wager that one of the best indicators of aerobic fitness would be that for rides of a similar structure and conducted with similar RPE, would be to see your power/HR ratio go up. Namely, you can do more watts at a given HR or a fixed wattage at a lower HR. Ultimately, I would expect this to be maybe the best measure of aerobic fitness, or even just by definition what aerobic fitness means to us in real world measurements.

Should I use power, HR, or RPE for my threshold or interval workouts?

For higher intensity workouts, power or pace will matter much more than HR and RPE, because we’re specifically trying to increase the rate at which we can do work and go faster. Threshold or higher intensity efforts will be most effectively measured by power; HR and RPE will vary much more with respect to these efforts and won’t be a reliable indicator that we’re doing the kinds of efforts or the kind of intensity that we’re really aiming for. Unlike endurance workouts, power will often act to provide motivation and a lower limit of performance for a lot of higher intensity efforts.

Basically, if you’re trying to work on your threshold, you should have an intensity range equal to or just below your 30-45m peak power that you use to conduct your workout/efforts. Or if you’re doing aerobic capacity/VO2 max efforts, aim to be 10-25% above your threshold power. In both cases, ignore your HR unless you see it getting so high that you know it will become a limiting factor. For example, if you’re doing a threshold climbing effort in the heat of summer, a high HR will almost certainly indicate that even though the power you’re doing is well within your capabilities, probably at the HR required to deliver oxygen to your muscles and blood to your skin you won’t be able to maintain the effort for the goal length of the effort in question. Often, for anaerobic capacity efforts, I would say that you should have a good idea from past experience what power you should be capable of for various durations, but for these high-intensity efforts, the power you’re actually able to do for a given effort during a given workout will vary, so I would encourage you to pay about equal attention to power and RPE (i.e. how hard you’re pushing), and defer to RPE if there’s some decoupling of the two metrics relative to the norm. That is, both shoot for a goal power and aim for an effort level that you know will be appropriately challenging for the type of effort you’re doing and its timing in your training, both within the workout and within your training season.

As an example, let’s say that John has a 40 minute PR on a climb near him when he did a hill-climb there last year. During that effort, he averaged 300w and had good pacing so that his power was fairly consistently between 280 and 330 the whole time without a drop off towards the end (i.e. he had about a 300w average for any given quarter of the effort). If John’s doing a threshold workout, he should probably make an effort to average 280-300w for his 15 or 20 or 30m threshold efforts. If his HR is 5-10 beats high because it’s a hot day, then he should consider lowering his power so that his HR falls at or just below his highest average TT/hill-climb HR. If John’s doing mid-season 5x3m VO2 efforts with 10-12m recovery one day, then he should aim for probably 340-360w average for those efforts. Because the efforts are too short to have overheating and elevated HR be a serious issue, as long as he keeps track of drinking enough if it’s hot, then John can go crazy trying to keep his power at a challenging, but achievable level without paying much or any attention to his HR. Or, when John dials in his maximal 30s efforts by doing, say, 8x30s max effort with 3m recovery, he probably knows ahead of time what power he’ll see for each of those efforts, but depending on whether he had a tough workout a day or two beforehand, whether he’s doing these efforts uphill or on flat ground, whether he’s doing them 1h into his 2h ride, or 4h into his 5h ride, the power may well vary notably. But should he shoot for a power that he can’t actually do unless he’s totally fresh or be content with a power that’s well below what he’s capable of because his fitness is coming along and he’s well recovered from last weekend’s racing? Not by a long shot. If he’s doing maximal 30s efforts to improve his high-end power and tolerance to the stress of those efforts (neurological, chemical, and cardiovascular), then he should just go as hard as he can for those efforts, regardless of the power or HR numbers he sees on his computer. In all likelihood, since he’s done similar efforts recently in training and in races, he could probably guess within a very small margin of error ahead of time what power and HR numbers he’ll see, but again, they aren’t necessarily what matter. The stress to his body relative to what his body is capable of at the moment is what matters, so if anything RPE or perceived effort are really what matter for this workout.

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How can I deal with exercise in the heat?

Right now it’s the height of the warmest time of the year for us living in the Northern Hemisphere, and a lot of us are having to find ways of training and competing successfully in temperatures that range far higher than what we get most of the rest of the year. For those of us that live in coastal regions, like myself in the San Francisco Bay Area, most of the year, we may only see temperatures in the 50s and 60s fahrenheit (or the 10s c). This time of year, it may be up to 100 or more (over 35 c) when I ride over the hills for most of my rides. I’m sure it’s much the same for most of us. So what are we supposed to do about it? How do we cope with the heat? (I’ll try to keep it brief, but I’ll also just throw down some bullet points at the end to try to leave you with some basic take home points… so if you’re short on time, just skip to the bottom.)

Well, first off, I would want to point a few things out that should make us a little pleased that we get to work out in the heat. For one thing, when you engage in endurance training in the heat, your body makes adaptations that help you perform better across all temperature conditions, both cool and hot. That’s an area of research in which some people are showing interest, because it’s quite notable how much performance can increase after exercising in the heat. The most obvious change that occurs is that your blood volume increases as you retain more water, and you have an increased pool from which to draw for sweating and heat dissipation.

Another thing worth pointing out that is very important is that while you want to stay relatively hydrated when working out in the heat, you don’t want to overconsume water. If you get dehydrated, then you may slow down and see your performance suffer, but that isn’t cause for you to drink tons of water. Rather, drinking too much water can and will dilute your body’s electrolyte balance and can lead to hyponatremia, which is a more common cause of heat-related health issues, mainly related to poor nerve function and resulting heart problems. Also, somewhat ironically, getting slightly to moderately dehydrated in training is actually going to be more effective at helping you adapt to the heat than consuming tons of fluids and electrolytes, because doing so mitigates the actual fluid/electrolyte stresses of heat training.

Be aware that it is relatively rare for you to actually overheat in the heat. Most of what goes on with your reduced performance or a lowering of your tolerance of a certain pace or workload is a preemptive reduction of effort and increase in perceived exertion managed by your brain to keep you from overheating in the first place. Under all circumstances, keeping your body from overheating is a priority for your brain, but in the heat, you’re consciously and unconsciously aware that such an event may happen sooner, so you slow down more quickly or reach a state of failure sooner precisely because you’re avoiding a point where your body is in real danger. That’s not to say, that you can’t or won’t ever actually overheat and run the risk of real harm, but in general, for most people in most circumstances, you’ll quit or slow down before that happens. The biggest risk is probably when you have a driven, motivated athlete with a high pain tolerance and limited prior heat adaptation; then we may have more cause for concern.

Whether you’re exercising in the heat or in cooler conditions, you are almost necessarily going to lose weight during a training session of any substantial length. When your body stores glycogen in your muscles, it also stores 3-4 times the same mass of water, so if you burn through 500g of stored glycogen, you’re going to be taking 2000g of weight out of your muscles. (500g of stored glycogen is about the maximum usually quoted for a fully carbohydrate loaded endurance athlete.) So, even if you were able to fully maintain the same water and electrolyte balance over the course of running a marathon or doing a tough 5 hour bike ride, you’ll almost inevitably lose about 2kg (5lbs) of body weight. So, don’t panic if you come home from your ride and see the scales showing a loss of 1kg or more (2-3lbs or more). Rather, if you come home and you aren’t lighter, that probably means that you were consuming more fluids than is necessary or ideal, and you’ve diluted your body’s electrolytes, so you probably need to take in a little extra salt. You definitely should not be drinking enough fluids to avoid any and all weight loss during a training session. If you do, you’re increasing your risk of hyponatremia. You should drink as much as you are thirsty, and make sure that you’re taking in electrolytes along with your fluids, but expect to lose a little water and carbohydrate weight during any training session lasting more than about an hour or two, running or biking respectively.

In any case, the biggest thing that can be done to increase your performance in the heat is to just get used to it by training in the heat. When you train in the heat, you will not be able to maintain the same power output or pace for as long as you would be able in cooler conditions, so you should just be aware of that and accept the fact that you will be slightly slower and usually feel more fatigued in the later portions of your workout sessions. Still, because the changes in water retention are probably the most significant adaptation you get to the heat, the most helpful training you can do in the heat is endurance training (i.e. longer and less intense rather than shorter and more intense). Doing longer sessions in the heat will lead you to lose more fluids and will cause a greater stress on your body’s heat management and water retention mechanisms, and for that reason should yield the most gains in performance once your body adapts. Again, this is most helpful when you train long enough to get at least a little dehydrated. You should always be drinking and taking in electrolytes, but over the course of a longer training session, some level of dehydration is probably inevitable.

For shorter training sessions, there is much less time to lose fluids and and therefore have more limited ability to sweat and cope with the heat, so you can often do fairly intense short rides even in the heat, but longer ones can’t be done with the same intensity as they can when it’s cool. One nice thing about the heat is that your warm-up time will be reduced for the obvious reason that it’s warmer outside and it will take less time for your blood vessels to dilate and your working muscles to get up to their optimal operating temperature. So, don’t be concerned about being unable to get in the intensity you want on the days that you plan harder workouts, because you can usually get it in early or late in the day, or by just condensing the time taken for the workout so that you don’t get too hot or dehydrated.

Aside from the actual internal changes that your body makes to cope with the heat from training, there are things that you can do with your body to help it cope better. When you train in the heat, your body produces anti-diuretic hormone (or “vassopressin,” depending on where you’re from), and your body doesn’t give up as much water. Another way to force your body to retain water is to increase your sodium consumption. So, it’s important for endurance athletes to consume more sodium in the heat, to help them absorb and retain more water and to replace the salt that is inevitably lost through sweating… One of the worst things you can do is to be on a low-sodium diet in the heat and to simply increase your water consumption, because it reduces your body’s ability to retain water and increases your risk of hyponatremia, both of which are performance limiting and potentially risky to your health. So, that being said, after working out in the heat, be sure to drink an electrolyte drink mix, eat salty snacks, or even consider a product like Pedialyte to keep your body’s electorlytes topped off.

Lastly, a lot can be done while you’re exercising to keep cool. First off, make sure that you have appropriate apparel. Namely, wear lighter weight, more breathable fabrics and less layers. Consider pouring water on your head and body. The cooling effect of cold water on your head, neck and upper back and chest is profoundly relieving and can reduce your perceived exertion and prolong the time you can sustain a hard effort. Even if you don’t have cool water on hand, even warm water has a profound cooling effect, because as soon as it’s on your skin and it starts to evaporate, heat will be drawn from your body as the evaporating water molecules take thermal energy with them… this is the reason that sweating works. As sweat or other fluids evaporate off your skin, they take heat with them and cool you off. And, along similar lines, consider putting ice in your jersey. Ice-socks are usually made of short stretches of panty-hose material filled with ice and then tied-off. These can easily be handed up to competing athletes and tucked under their jersey behind the neck and will help the athlete stay cooler longer.

So, what’s the take home, and what do I do? Something like the following:

– try to train in the heat, so that you can adapt to it

– pre-hydrate and stay hydrated with fluids and electrolytes when you need to perform well

– don’t be afraid to get a little dehydrated when you’re training, because it’s inevitable with longer sessions and it will help you adapt (still be sure to drink and take electrolytes, just don’t overdo it)

– never just drink a ton of water, you won’t retain it well and you’ll dilute your body’s electrolytes, which can be risky

– stuff ice in your clothes, pour water on your head, and stay cool while reducing your body’s need to sweat

– take in extra sodium before competition, so that you’ll retain more water and perform better

– take in extra sodium after competition and training so that you replace lost electrolytes, retain water better, and keep your body in healthy balance