When to Take a Rest Day

Like many cyclists, I have big plans.  Today, however, I am taking a day off instead of my planned workout.  I usually plan my workouts about a month in advance and almost always plan more than I can actually handle.  I would probably drive a coach absolutely nuts because I rarely end up doing the exact ride I planned the month before, although I find the planning helpful to keep my workouts oriented to my long term goals.

Why don’t I do the ride as planned?  There are quite a few reasons ranging from weather, group rides or training races, family schedule, babysitting availability, and the topic of this post: fatigue.  I need to be well rested enough to stress my body thoroughly on hard days, and I also need to keep my overall fatigue in check so I don’t end up needing a large chunk of time off (a few days or even a week) to be ready to ride hard again.  Knowing when I need a rest day is very important.

First I’ll go into some basic physiologic background.  If you’re familiar with maximum heart rate, threshold heart rate and threshold power, you can skip this section.


Max Heart Rate: You may have heard the 220 minus your age formula to calculate maximum heart rate.  Unfortunately the formula is pretty much worthless to anyone training for endurance sports using a heart rate monitor, as it can vary by 20 bpm.  If you don’t have a season of race data to look over, a 100% effort over 5-8 minutes after a thorough warm up should get you pretty close.  As you gain fitness over the course of a season, expect Max HR to decrease a few BPM.  My Max HR is 179.

Lactate Threshold: Most of the time, our body uses glucose and oxygen to produce energy.  When oxygen isn’t available, glucose can be used without oxygen, leaving lacic acid as a byproduct.  Even as you sit in your chair, some of your muscle cells don’t receive enough oxygen and utilize anaerobic metabolism, producing lactic acid which is quickly cleared.  As your workload increases during exercise, the amount of anaerobic metabolism increases.  The body has a ‘tipping point’ where more lactic acid is produced than can be eliminated, and lactic acid starts to build up in the bloodstream.  The lactic acid buildup is closely associated with muscle fatigue/failure and the ‘tipping point’ is called “Lactate Threshold”.

Lactate Threshold Heart Rate & Power:  This is the heart rate at which a particular person reaches their lactate threshold.  My threshold heart rate has been essentially unchanged since I first measured it in 2000.  My threshold heart rate is 164 bpm.  Power at Lactate Threshold is one of the best predictors of cycling performance, and is also quite sensitive to training.  My power at threshold is 330 watts.

Details of this week

As I have mentioned recently, I’ve felt that overall I’m not recovering like I’d hope this season between workouts.  Therefore I was pleasantly surprised when I was able to produce season-high 4-minute power on Monday after two days off, despite a grueling 3.5 hour ride with 9,000 feet of climbing on Friday.  My Max HR on Monday was 175, and any time I can hit Friel Zone 5c (174+) I know I am reasonably fresh.

I rode a basic endurance ride on Tuesday.  I was hoping to burn some calories and keep my aerobic engine burning without adding undue fatigue for my training race Wednesday, and a long, hard ride Thursday.  I rode two hours steady in Zone 2, and although my heart rate / power ratio seemed normal, my RPE (Rating of Perceived Exertion) was a little higher than expected.

Wednesday’s training crit came next.  The race went OK and I got a good workout in, but my legs didn’t quite have the ‘snap’ I needed when the speeds really increased.  At one point I was off the front alone and it felt like I was riding in quicksand.  Once I got home and downloaded my data I could see I was much more fatigued than I had hoped.

A Tale of Two Races

Training Crit 4/25: Avg HR 158, Avg Power 299w, Normalized Power 330w, Max HR: 173

Above is my power file from last week’s training race.  Normalized Power is calculated to approximate the physiologic stress more accurately than average power when power output is highly variable.  Normalized power is exactly my threshold at 330w.  Both my average and Max HR are slightly lower than I would expect in an ideal ‘race ready’ state.

Training Crit 5/2: Avg HR 151, Avg Power 297w, Normalized Power 326w, Max HR: 165

Here we can see the markers of fatigue quite clearly.  The power output (both Normalized and average) are nearly identical between races, but heart rate is much lower.  In fact, considering normalized power was roughly my threshold power and it was a 55 minute race where I contested the sprint, I would expect to see average and maximum heart rates almost 15 bpm higher for each with ideal recovery!


I could slog through a long ride today.  I wouldn’t be able to go hard enough to stress my body’s anaerobic systems very much, and I would accumulate additional fatigue.  The following two days I’ll be resting at work, but I would likely still be overly fatigued for Sunday’s Deer Trail Road Race.  By taking today off, I’ll hopefully be able to race strong at Deer Trail and be able to get quality training the rest of next week as well.

Remember, all of my power files are available to browse using the “Complete Training Archive” link on the right.  Make sure to check “show workouts” and select the date range you’re looking for.  I also have a related post from last year here: Gauging Recovery from Heart Rate and Power.

About Russell

I have been racing bicycles for a decade. This blog will chronicle my efforts as a Category 1 road racer lining up with the pros.
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11 Responses to When to Take a Rest Day

  1. says:

    Man! You feeling fatigued is equivalent to my feeling pretty good. I guess still have my work cut out for me.

    • says:

      Keep in mind that my power wasn’t much lower yesterday, although I was still showing signs of fatigue. So I may not have been racing much slower than normal, but was missing that extra something that can produce a good result on race day.

      Keep at it and you’ll get there.

  2. Brian P says:

    As simple as it sounds, I’m a little confused by maximum heart rate. Is this the simply the highest heart rate you have seen over the course of a year, or is it a more “typical” max heart rate you get in a sprint? I’ll see 182 once or twice a year, but more typically about 180. A nuance, but I’m curious.

    • says:

      A good question. I’ll see 179 a couple times a season but will see 175-176 as my peak heart rate during many races.

  3. Brian P says:

    As an aside, I see I made a comment in the blog post you referenced from last year. I’ve been reading your blog for a while, and you simply have the most interesting and informative blog I’ve read about training for racing. Better, even, than any of the big name gurus. Keep up the good work!!

    I just broke down and bought a second hand power tap wheel, so I’m going to go back and revisit some of you posts about training with power. I’m sure there are some great nuggets I missed.

    Finally, I read something the other day about Tabata intervals. Seems wacky, but was curious if you had thoughts or experiences. I have found that managing fatigue when substituting intensity for duration can be challenging.

    From wikipedia:
    Tabata method:
    A popular regimen based on a 1996 study uses 20 seconds of ultra-intense exercise (at an intensity of about 170% of VO2max) followed by 10 seconds of rest, repeated continuously for 4 minutes (8 cycles). Tabata called this the IE1 protocol. In the original study, athletes using this method trained 4 times per week, plus another day of steady-state training, and obtained gains similar to a group of athletes who did steady state (70% VO2max) training 5 times per week. The steady state group had a higher VO2max at the end (from 52 to 57 ml/kg/min), but the Tabata group had started lower and gained more overall (from 48 to 55 ml/kg/min). Also, only the Tabata group had gained anaerobic capacity benefits.

    • says:

      Thanks for the kind words. From the ever increasing blog views and comments like yours, I can tell that I’m doing something right.

      As for Tabata style intervals, I do them occasionally during cyclocross season. I’ve found the intervals closely match race-like efforts, which makes them ideally suited for training. They’re similar to accelerating out of repeated corners in a criterium, rolling turns in a small group, and attacking when everyone is at their limit.

      However, I find intervals with such rigid structure and short timeframes (20 seconds on, 10 off, etc) difficult to perform on the road, which I why I utilize them during cyclocross season when I need an intense workout indoors during bad weather. During road season I would much rather get a similar anaerobic workout in a training race. In a training race (or a real race) I can get the anaerobic intervals in addition to cornering, technique, and most importantly practice reading a race.

      • Brian P says:

        I’m impressed that you can do those full sprints on the rollers! I would so fall off the bike and crack my head. I was doing some high intensity training on the cycle ops trainer, and worried about what kind of stress I was putting on the bike after I broke the steel skewer.

  4. says:

    How long did it take you to get your ftp up to 330? What did you start at and how much of an increase do you get per season?

  5. Andrew says:

    It seems like there are a lot of really good pro’s who are relatively pretty young. That evan guy, phinney, guy in ToC last year who almost won (Van Der something. lol), plus some top guys at the tour of gila this year. I know nutrition and power meters are important, but it’s like you either have the talent or you don’t. Nutrition can help a 35 year old guy get faster, but not to beat phinney or evan. To race in Europe at a top level, I’m pretty sure you know before you are 22. There will always be one exception, but that’s also true when playing the powerball. Somebody will win, but you need to be realistic. My point is , Don’t buy Dura-Ace, you will do fine with Ultegra. Don’t buy a 10k bike, you will be fine with a 2.5k bike. Don’t buy a 3k power meter, you will be fine with a HR. Don’t buy $300 pedals, you will be fine with $100 pedals….etc..

    • says:

      I agree that top level, world class aspirations are unlikely for those over a certain age, but I think many people are capable of performance at a high level regardless of exceptional natural ability.

      While I am happy to have top-level equipment on the road, I had to earn it and didn’t have anything fancy before I was a Cat 2. In the time-trial I’ve been using old/substandard equipment and performing at quite a high level. There are diminishing returns as equipment skyrockets in price. A $700 road bike from craigslist would race nearly as well as a new one at $7000, but many of us also appreciate the bicycle itself and consider them to be part of our enjoyment of the sport.

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