Beginner's Guide: Cycling Training by Heart Rate
Training zones are important to structure your training and provide us with a means to monitor our intensity. Heart rate gives us some insight into the stress that our training is putting on our body, which makes it great for monitoring intensity. But heart rate is not infallible: it is affected by temperature, hydration, illness, fatigue, and other factors. It behaves differently at different effort levels, and it lags effort by quite a bit - it is not good for monitoring short intervals. Training by heart rate alone is not always ideal, but athletes can make tremendous progress with just their bike, a good heart rate chest strap, and good route selection.
When I write workouts for athletes, I take into account that athlete's experience, the development of their body "feel", and what metrics they have access to. For most competitive cyclists these days, that means writing a lot of workouts based on power. The ubiquity of Zwift training also necessitates power-based workouts for those athletes with the ability to train indoors. Whether you have a power meter or not, monitoring your heart rate - or at least recording it - on every ride that you do is important.
Maybe the best way to train your aerobic base, however, is by heart rate! Base endurance riding where you monitor your intensity based on a certain percentage of maximum heart rate is a fantastic way to establish and maintain your aerobic base. I often pace my long rides solely based on heart rate, and I sometimes put a heart rate cap on long rides to ensure that athletes stay aerobic and aren't incurring unnecessary fatigue.
To do so, you must know your maximum heart rate. I prefer to set lower aerobic zones based on maximum heart rate because it's a relatively easy number to determine and in trained athletes it won't change over the course of a season if measured properly the first time.
Some good rules of thumb for aerobic riding:
Zone 2 as previously described, exists between roughly 65% and 80% of maximum heart rate.
The calculation is simple: take maximum heart rate times 0.65, and again by 0.80, and those numbers give you your zone 2. (For me: 188bpm is my max on the bike, so the low end is .65*184 = 122bpm; the high end is 0.8*184 = 150bpm).
When I prescribe long zone 2 riding in the off-season and early base development, I will generally aim for 65-70% of max HR, and put a cap at 75% for athletes to try to stay below.
As you progress your base development, you can spend more and more time up around 75% of heart rate and then increase up towards 80% for periods of time in hopes of increasing the power that you can create aerobically at that relatively easy effort. But these rides are best done in moderation, and I don't recommend spending 4 hours every Saturday banging out effort at 80% of maximum heart rate: you'll get the same adaptations at the lower efforts without incurring nearly as much fatigue. Make no mistake, you can make tremendous gains simply by riding at those lower intensities for longer and longer duration.
But what about riding at harder efforts?
Heart rate starts to become less useful when you ride above your "anaerobic threshold". I'll spare the physiology lesson and complexities of all the different thresholds here... for our purposes, "Anaerobic threshold", "Functional Threshold Power", and other terms such as "Mean Lactate Steady State" and "Second Lactate Threshold" or "LT2" are in the same ballpark for many people. Crudely put, you know when you're above this threshold because this is where you start to feel The Burn! The higher the power, the quicker the burn starts to come on.
Your ability to sustain efforts above threshold declines rapidly. Most people can sustain efforts at or just below threshold for at least 35 minutes, and some very well-trained people can get out to 70 minutes or more. When you start to get just above threshold, most people will struggle to hold these efforts for more than a few minutes before they need to reduce intensity. You know it when you're there!
Here we are talking about Zone 4 and beyond as previously described.
In order to use heart rate to ride around threshold, it is useful to conduct a test to determine your Lactate Threshold Heart Rate or LTHR.
The test is relatively simple but very challenging to conduct correctly.
Testing for Lactate Threshold Heart Rate
I recommend doing this on a flat course with as little traffic and few stops as possible. Fiesta Island is great; the Strand is pretty good; your trainer can be good for this provided you have adequate cooling (get more fans!), as well. (It should go without saying - wear your heart rate monitor for this test!)
Warmup: At least 15 minutes of riding, steadily raising your effort to endurance and then tempo efforts (up to a 5 out of 10 RPE) lifting cadence near 100rpm to get the legs and cardiovascular system ready. After warmup, reduce intensity for a few minutes and spin your legs out.
Test: Ride a 30-minute time trial. Spend the first five minutes building into the effort you think you can sustain for 30 minutes. It is critical that you do not go out too hard on these types of tests - pacing is an important skill to learn. Ideally, you end the 30 minutes completely buried, knowing you couldn't go much longer, or at all. The effort should be steady, however, going easy for 25 minutes and smashing the last 5 doesn't help, nor does smashing the first 10 minutes, blowing up, and dialing your effort way back.
The effort itself should be uncomfortable, but sustainable. You should feel lactate accumulating - a slight burning sensation - but you can feel your body able to clear it enough to continue your effort. Breathing will be steady: hard but controllable and not ragged. When you're done, you're glad it's over and need to stop to recover.
Press the "Lap" function on your head unit when you start, and again at the 10 minute mark of your test.
Cooldown: Spin home, or ride very easy for 5-10 minutes until breathing is recovered and HR has come down into or below zone 2 HR described above.
Your LTHR is your average heart rate for the final 20 minutes of this test. Use your preferred analytical software (TrainingPeaks, Garmin Connect, Wahoo, TrainerRoad, or even Strava) to determine your average heart rate for this 20-minute "lap." Without the software, you can also take your HR at the start of the 20 minute interval, and add HR at the end of the interval, then divide by 2. (e.g.: 169bpm + 173bpm = 342bpm / 2 = 171bpm - BAM! LTHR).
Great! What do I do with that?
Once you know your LTHR, you can build time riding at or slightly below this value - threshold intervals. These will help you to build your sustainable power, which means you'll do less work to stay with the fast group, and have more left at the end when it counts! When using heart rate to guide these intervals, you generally want to keep them longer - 8 minutes or more, preferably 10 minutes out to 25 minutes or longer as your fitness grows.
A solid baseline HR-based threshold workout might look like this:
Warmup: 15 minutes building effort through zone 2 HR up to just below LTHR for 1 minute at the end, recover for 5 minutes prior to starting intervals.
Main set: 3 x 10 minutes at 1-3bpm below LTHR. Do not allow HR to exceed +1bpm above LTHR. Rest 3 minutes between intervals.
Cooldown: 5-10 minutes of easy spinning.
My LTHR resides around 168bpm, so this workout for me would be 3x10 minutes spent between 165-167bpm, not to exceed 169bpm.
Training Maximum Aerobic Power (MAP)
Another good use of heart rate is when conducting Maximum Aerobic Power intervals (in Zone 5). You'll commonly hear this work referred to as VO2max work, as well. These intervals are very intense, generally 3-8 minutes in duration, with rest intervals approximately equal to the length of the work interval.
A common starting point prescription from me for a trained athlete would be 3 x 6min all-out MAP intervals on 6 minutes rest. The goal of these intervals is to maximize your sustainable, repeatable power output for each interval, and to accumulate as much time above 90% of maximum heart rate as possible. (90% of max HR correlates closely to LTHR for some, but not all, athletes).
To execute intervals like this, I like to ride on a hill. In the first interval, I'll go as hard as I can sustain for the entire duration. My goal for the rest of the intervals that day is to get to the same part of the climb in the same amount of time. As you do more intervals, you will get tired, and you won't get to the same part of the climb, but this is a good way to judge your effort without a power meter. Get as close as you can to where you finished the first interval every time!
Not many people in the world should do more than 24 minutes of this type of work. If you're brand new to this type of work, I'd recommend 15 minutes as a starting point (e.g. 3 x 5 min), and plan for plenty of recovery after doing sets of these. A good outcome for these workouts is spending 12-18 minutes above 90% of maximum HR (this is not the same as interval time - your HR will need to come up at the start of each interval... for a set of 3x5 MAP intervals, you might only see 9 or 10 minutes above 90% max HR).
I like to train these "MAP" intervals roughly three months before my major races to raise my aerobic ceiling. Then I train threshold intervals to raise my threshold underneath it. As your key events approach, you can then touch up your time spent at these power levels in different ways - they are great race preparation.
There are many different ways to train, and levers to pull at various times., but I hope this provides some insight as to how to train when you only have access to heart rate. As always, I'm happy to answer questions or point you in the right direction. In particular, if you're interested in training MAP/VO2max intervals and have questions, or want to know about progressions for these and threshold intervals, reach out and I'll give you some tips and cautions to make sure they're an effective part of your training program, and not detracting from your other work.