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
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.
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.