bike75.gif (2872 bytes)


  Last updated: 10/30/2019


High Intensity Training

Interval training is based on the observation that when physical stress is applied to biologic systems, it leads to physical and metabolic changes that adapt to the stress being applied. And this adaptation occurs with any type of physical activity. Interval training consists of repeated sets of intense physical activity (the stress) followed by periods of recovery. The relaxation interval allows the body to recover and prepare for the next period of stress. Using this intermittent stress/recovery approach, interval training allows longer total training time (for that day's exercise) at one's peak level of performance (the stress). One study (in runners) found that continuous, maximal performance could be sustained for only 0.8 miles (to exhaustion) while a similar level of peak exertion could be maintained for a total of over 4 miles when the training session consisted of shorter intervals. But the down side of using intervals as a training tool is that training program drop out rates double when intervals are used. (see also High Intensity Training.)

A recent study once again demonstrated the efficiency of using intervals to provide a training boost. The study looked at two exercise routines - 10 minutes including 3 intervals versus 45 minutes of a steady moderate workout. There was a 3rd control group with no exercise program. The two routines:

Their conclusion "Twelve weeks of brief intense interval exercise improved indices of cardiometabolic health to the same extent as traditional endurance training in sedentary men, despite a five-fold lower (1/5) the exercise volume and time commitment." So if you have limited time, intervals give you more training benefit for the time you have available. And as we will see, if you add interval training to a standard endurance training program, the group using intervals will get pull ahead of the LSD (long slow distance) group in their level of fitness as measured by VO2max.

Intervals are more effective when:

It is intensity of intervals, not frequency or duration, that is the key to a successful interval training program. A study of a 10 week interval training program found the following in a group of cyclists (all groups started off the study with a with a base of 40 minutes of intervals 6 times a week):

The VO2max of the first two groups held constant, while that of the third decreased. The conclusion: intensity is more important than either the duration of the intervals or the frequency per week in maximizing the performance benefit of an interval program.

However, there are also ramifications of decreasing total exercise volumes (that is the total number of hours on the bike per week) which can result in a decrease in endurance (defined as time to exhaustion riding at 75% VO2max). Thus it is the combination of intensity of exercise (best achieved with intervals) and total time on the bike (or volume) of exercise (from the long slow distance rides) that determines a cyclist's overall performance in an event or on a longer ride.

There is also evidence that your level of training impacts the benefit you will get from interval training. In 2015, Place et al showed that the basic cell changes which are intermediaries in muscle cell adaptation to interval stress were minimized in the highly trained athlete.

What if you are feeling fatigued on your interval day - or just don't have the time for the complete set of intervals planned for the day? We know from weight-training studies that the first set or two provides the stimulus for most of the improvement gained during multi-set workouts. If you do five sets of bench presses, for instance, much of the benefit occurs during the first set. The second set stimulates most of the remaining improvement possible from the session. The final three sets do relatively little. It is likely that the same applies to interval training. Thus the first set of intervals (or two) most likely provide the bulk if the benefit and the remaining intervals are subject to the law of diminishing returns. Thus with just two repeats you will most likely gain a large percentage of the possible benefits. So if you are feeling tired on your interval day, take a break and come back fresh, ready to give 100% the interval day. IF you avoid listening to your body, you will increase the odds of either burnout and the inevitable decrease in energy that comes with overtraining.

There are potential risks beyond burnout. The data is pretty clear. You can over exercise your cardiovascular system - to the detriment of your physical health. But how much is too much? Unfortunately we, the baby boomers, are at the leading edge of the curve of a new group of ultra athletes - and only time will sort out the answer. Until then each of us will have to answer that for ourselves.

A modification of interval training (fartlek training) uses alternate periods of slow and fast riding to improve aerobic capacity. It is basically a "mini-interval" as described below and is not as precise as interval training. It allows the flexibility based on the perception of how the rider feels at the time. Its advantages are:

And as there is overwhelming evidence that intervals are the secret to improving your performance, this approach makes the most sense. It implies that you should do intervals as often as it feels right. You will have your focused interval days dedicated to intervals, and then on other days (even long slow days) will add short lower intensity burst to stimulate the muscles. But it requires you to be flexible and not do intervals when you are feeling tired.

High Intensity Training (HIT) is an interval program for athletes already at a high level of training. In many ways it is the "icing on the cake" which gives the elite athlete that final edge for their event.

And finally, HIIT is a great strategy to maintain your CV fitness while on vacation, or during those long dark days of winter when you can't get out on the road. "...HIIT requires an all out effort for 30 to 60 seconds followed by a minute of recovery. Repeat five sets - three times a week. can maintain your aerobic fitness with just 3 ten minute sessions a week."


When you train to your maximum (pushing your aerobic limits), adaptive changes occur in both the cardiovascular system as well as within the muscle and muscle cells themselves which allow you to push even further into your anaerobic zone the next time out. These include:

What is the basic physiology? For those interested, in 2015 Place et al moved us a step closer to understanding the stimulus to mitochondrial change in the cell. What I found most interesting was that antioxidants appear to blunt this stimulus and highly trained athletes appear to derive less relative benefit from their interval training. For them, intervals are more important to maintain training benefits rather than a path to continued additional improvement over time.

This study suggested that resistance exercise (weight training) also produces mitochondrial changes similar to those seen with training using cycling intervals. Thus resistance training makes sense as a supplement to (and should be part of) a more traditional aerobic interval training program.

You can monitor the level of anaerobic stress to your muscle cells by tracking "the burn" which occurs with anaerobic metabolism. Originally the burn was felt to be from the build up of lactic acid , but studies in subjects who, because of a genetic defect, do not produce lactic acid demonstrated the same discomfort with anaerobic exercise as normal riders. So rather than lactic acid, the culprit is most likely another acidic intermediary metabolic byproduct or other cellular changes in the muscle fiber itself.


For your focused interval training, short exercise intervals are 15 to 90 seconds in length and almost always anaerobic in intensity (perceived exertion of 10). Longer intervals are from 2 to 5 minutes duration and due to gradual lactic acid build up are at a slightly lower intensity. Your goal should be a total of 10 to 20 minutes of hard pedaling during the active intervals (don't count warm up, recovery, or cool down). If you are just beginning an interval training program, you might consider starting with 5 minutes of peak effort per riding session

To get the maximum benefit from interval training, it is important to allow adequate recovery time between intervals, although it is not necessary that your heart rate return entirely to normal before the next interval. If you are using a heart rate monitor, wait for your heart rate to drop to 60 or 65% of your maximum heart rate. If you are using perceived exertion (i.e. how you feel), wait until your breathing has returned to it's normal depth and rate.

The relaxation or recovery phase for each interval should be active rest (easy spinning) a duration that varies with the duration of your intervals. As you have not built up significant metabolic byproducts with a short interval, the recovery period will be shorter than with longer intervals and their oxygen debt to be paid and metabolic byproducts which need to be cleared from the muscle.

And don't forget a 20 to 30 minute warm up and a 15 minute cool down at the beginning and end of your session. I like this approach used by Dr. Mirkin:

Here's another suggestion from the webzine: Dial up some telephone pole sprints. When we're training alone, sprinting against imaginary opponents can be deadly dull. Next time you feel like some speed work, use telephone poles as sprint markers. After warming up, start by sprinting from one pole to the next and then spinning easily for 4 poles. Repeat 3-5 times. To vary the drill and increase the effective length of your sprint, go all out for 2 poles, spin easily for the next 4, and repeat 3 times. Of course, all telephone poles aren't the same distance apart. Use the varying spacing to simulate race conditions. After all, you never know how long you'll need to sprint. Go hard to the next pole, no matter how far it is, then spin for a minute or two to recover. Follow this with another sprint between poles. It's perfect for developing the ability to rev up in an instant and then hold your speed for the required distance.

HOW HARD (intensity) for HOW LONG (duration) and HOW OFTEN (frequency)?

We know that intervals improve endurance performance as the muscles and cardiovascular system respond to the stresses of aerobic (as well as resistance) exercise. But how much stress i.e. how long should you push an interval to maximize the benefit but minimize the risk of injury or overtraining?

There are three components to an interval training program.

  1. Intensity
  2. Duration
  3. Frequency
I am going to paraphrase directly from a Dr. Mirkin blog:

"Short intervals last less than 30 seconds each, while long intervals are can last more than two minutes each. The most efficient, time-saving and health-benefiting way to interval train is to use short intervals (Scan J Med & Sci in Sports.)

You can do many more short intervals than long intervals because they do not cause as much muscle damage and do not lead to a build up of significant amounts of lactic acid in less than 30 seconds. Long intervals cause more muscle damage and such high levels of lactic acid that you can do very few of them in a single workout. They also take longer to recover between workouts, that is before you can do your next interval workout.

Recreational athletes can train purely with short intervals, but competitive athletes need long as well as short intervals. The longer intervals train them to "ride through" the lactic acid build up that occurs in intervals over 30 seconds in length.

The faster you ride your intervals, the greater your gain in the ability to take in and use oxygen (VO2max), and the faster you will ride or run. The length of time you can hold an interval pace depends on the intensity of the interval. The more intense your interval pace, the shorter the time you can maintain it. It appears that even competitive athletes can maintain maximum exertion intervals for only 30 seconds before they gradually slow.

This study nicely demonstrates that short intervals improved one-hour race times the most. The study compared 30-second all-out, 5-minute all-out, and 40--min all-out bouts of cycling. In 10 weeks of twice-a-week, effort-matched trials, they found that short interval training was more effective than long intervals in improving mean power output and VO2max (the maximal amount of oxygen you can take in and use per minute and the best laboratory measure of how fast a cyclist can ride or a runner can run over a distance.

And the intensity and duration of your intervals will impact the third aspect of an interval training program, the frequency (times per week) of your interval training days. The longer your intervals, the more minor muscle damage and the more necessary an easier riding day before your next interval session.

By frequency, I am referring to the number and timing of dedicated interval training days per week. I could not find much data on interval frequency in the scientific literature, but from all I've read, Dr. Mirkin's article on interval training makes the most sense to me. Dr. Mirkin is a big proponent of incorporating some training stress into every riding day (even on a slow easy day). But he also is not an advocate of riding every, advocating day listening to your body and getting off the bike if your legs are telling you that it is not a day to ride. So when he talks about intervals, you have to pay close attention to be sure you understand which type of interval he is addressing. He could be talking about:

How do you roll this into your training week? I would agree with Dr. Mirkin, "A sound endurance program should include or two workouts with many short intervals, and probably at least one workout that includes a few long intervals each week." The dedicated short interval days would include 6 or 8 - 30 second intervals. The long interval day would be 2 or 3 - 2 minute intervals. And the remainder of the riding days that week would have "mini-intervals" embedded on a random basis.

And if you're not confused enough at this point, here is a summary of other approaches to interval training.


What is the ideal balance in training intensity? All studies point to intervals as the best path to improvement but how much of your time on the bike should be intervals, and how much lower intensities?

I found this well written article which nicely covers the subject of training intensity balance. And for those interested, the abstract of the original scientific paper. Although these are papers on running, the CV training benefits should be quite similar for cycling (and swimming).

So we know (real science, not personal stories) that if you short change your recovery (riding at lower training intensities) you not only fail to gain any benefit from the extra work you are putting in, but are actually sacrificing your performance.

So 20% of your training TIME at a moderate to high intensity, a perceived effort of 6 - 10 or > 77% MHR. And 80% of your training time at a PE of 4 or less.

Now that you have the numbers, the challenge will be to keep those "slow and easy rides slow and easy. My guess is you will have to work to keep that HR down.


I've often wondered if HIT would improve my endurance riding. Intuitively I suspected it would. What is the science?

In the first article (abstract, full article) approximately 15 min of intense exercise over 2 wk (a pretty short time) DOUBLED endurance capacity (exercise at ~ 80% VO2max) in active individuals.

The second study (abstract, full article) was done in well trained competitive cyclists instead of recreationally active adults. Endurance performance in a 40 km time trial improved after interval training (a minute off of a 57 minute result). The improvement appeared to be from the muscles increased ability to buffer the acidic products of metabolism rather than any change in the riders' VO2max.

Finally, a third study, a review, supported the improvement in endurance performance without a change in VO2max. The authors indicated an increased "tolerance" for fatigue, perhaps from an increase in the efficiency of the muscles (using less energy per unit of distance).

So there is solid evidence that intervals not only increase your VO2max for short sprint performance, but also your endurance performance (rides done at ~ 80% VO2max.)


I am going to digress a bit on Dr. Mirkin's philosophy of daily metabolic stress to enhance performance - what he calls "no junk miles". Junk miles are a focus on total miles, ridden at any speed, as compared to a focus on how hard you are riding that day. It is, of course, a balance of 1) adequate miles to be comfortable on the bike for long rides as well as 2) intervals of some sort every day you ride.

How did we arrive at what had been gospel - twice a week intervals? Why not do intervals more frequently? The medical literature is interesting in how standards develop. A study is done, in this case looking at interval training twice a week. Subsequent investigators use the same frequency for their studies. And without further investigation twice a week becomes the defacto "optimum". The demands of a balanced training program reinforce this frequency. You need a long day at some point during the week to get use to longer times on the saddle, an occasional day of restful spinning to minimize the risk of overtraining and burnout, maybe a ride during the week with friends, a day or two off the bike with bad weather or to take care of family or work responsibilities, and soon an ideal training week has room for just 2 (or perhaps 3) focused interval days.

But this personal observation from Dr. Mirkin suggests that you should incorporate periods of increased exertion (intervals really) into every ride. He came to this conclusion based on personal observations that the more traditional approach was not working for him and his tandem partner. In his words: "....every time that you exercise intensely, you damage your muscles. You know this has happened when your muscles feel tight, heavy or sore on the next day. To deal with this soreness, we followed a program of racing as fast as we could three times a week (Tuesdays, Thursdays and Saturdays). On the other four days we would recover by riding 20 to 30 miles slowly, at about 10 to 11 miles per hour. But something was wrong with this program because we were gradually losing our ability to ride as fast as we had in a previous year. We were doing too many junk miles on our four recovery days each week."

He decided that fewer rest days were actually better for them, and that when he eliminated the rest days (at least a regimented number per week) he actually had less overall muscle pain. He also speculated that every ride should include some stress to provide the stimulus to maintain or improve his speed. And finally, he felt that the only reason to do extra easy miles was to acclimate the riders' butts and shoulders to prolonged time in the saddle. Basically that "....Slow riding or running does not increase your ability to take in and use oxygen and it does not make your muscles stronger."

So they changed their training - not more rest, but more intervals "...riding a short distance fast enough to make you very short of breath. Then you slow down until you recover your breath, and keep on alternating short fast bursts with slow recoveries until your legs start to feel stiff and heavy. Then you stop the workout for that day." Intervals were worked into every riding day. Maybe 50 - 100 pedal strokes (which at a normal cadence is about a minute). And this number was based on how the legs felt. Not an arbitrary number to be mindlessly achieved. "On some interval days, we would do 50 pedal-stroke repeats, resting between each long enough to get our breath back. Other days we would do 100 or 150 pedal stroke repeats. We never plan to do a fixed number of intervals. Instead we would stop the intervals as soon as our legs started to feel heavy or stiff, or when our legs did not recover and continued to feel tired a minute after finishing a fast interval."

So instead of a mandatory one or two rest days every week, they rested based on how they felt. "...then as you continue to ride, your leg muscles usually start to feel better and you can ride fast after you have warmed up. However, if your legs do not feel fresh after you have warmed up for more than 15 minutes, you should just take the day off. So some weeks this might lead to more days off the bike, and other weeks riding everyday might happen."

With this approach it was the duration and intensity of intervals that would change from day to day. Not the traditional 2 days of focused interval riding with intervals that might be longer in duration. And the total riding time might end up being less than the average "preplanned" ride. Even on what would traditionally be a long slow distance ride, intervals (hills could be substituted) were done. Not as a focused period of time within the ride, but randomly throughout the ride (a fartlick or mini-interval). And finally, even on a rest day of easy spinning there would be mild changes in tempo throughout the ride.

But this required one to listen to their legs. Along with adding the physiologic stress of interval training to every ride was the concept of backing off, or stopping completely, if the legs were tired after the warm up. Not an 'I must ride' approach to training. My guess is that a lot of us take this approach already, varying our tempo. How is Dr. Mirkin's approach different?

My impression is that cyclists are a pretty focused group. This suggests we need to change that focus from the weekly schedule of riding days of different types and instead look at each day as it comes, rest if tired, push a bit every time we are on the bike, and still keep a day or two of focused interval training.


I was asked: "How 'healthy' is the high intensity cycling that I've been doing (at over 50's)? By high intensity I mean continuous effort at 85-90% HRMax with touches of 100% HRMax. And then a few days later I ran across this article in the NYT that stated, assuming no family or personal history of heart disease, there was "... no evidence .there is a level of exercise that is dangerous or too much for a normal, healthy person." Although this is generally true, there is sound evidence that there is indeed an upper limit for cardiac healthy exercise. The curve of benefits versus exercise volume doesn't just plateau, it probably starts to drop off as the extremes are reached . A few examples:

So what is the answer to the reader's question? First, there is no solid data on the upper limit of beneficial exercise (where more is really less health wise). And my comments assume you have no family or personal history of cardiac disease or sudden death.

There are two potential health risks from high intensity cycling - Musculoskeletal (or overuse) injuries and cardiovascular. The musculoskeletal injuries are known to all of us who exercise and participate in aerobic sports. Overuse leads to injury. And the cure is to listen to your body, and if it hurts when you are using it, decrease your activity level. The cardiovascular risks appear to be from repeated stress at the ultraendurance event level. (Pushing through the pain, as it were.) Although acute stress might cause some modest cardiac muscle injury (and leakage of muscle enzymes into the blood where they can be measured) this heals within a few days, and only with repeated injury/healing/injury does scarring appear to be a risk.

There is no evidence that short term, high level exertion such as 30 to 60 second intervals is harmful and also no sound evidence that intervals longer than this add benefit to cardiovascular fitness. The answer and My Bottom Line? Pushing your limits (within reason) is not harmful to your health. But cardiovascular risk appears as you move to the ultra event level.


If you have a heart rate monitor, you can key intervals to your maximum heart rate. Ride your intervals at 80 to 90% of your maximum heart rate and spin easily until your heart rate drops to 60 to 65% of maximum.


Here is an excerpt from that suggests a way you might use rolling hills as an alternative to intervals. As these are not always found spaced appropriately, they might be considered as "fartleks".

Find a road where little hills come one after another. Attacking these humps can be a peak experience -- like riding a roller coaster. You fly up one side, blast down the other and use your momentum to conquer the next rise.

But if you use improper technique, you can get bogged down. Instead of grinning, you're grinding. You churn up, coast down to catch your breath, then bang against the next wall.

Rhythm is everything. Here's how to keep yours on successive climbs: --As you ride into a hill that takes just seconds to climb, shift one gear lower (next larger cog) than you might normally use. Stay seated and spin fast for about two thirds of the climb.

--If you're riding with others, they'll probably be standing, pedaling slower than you and maybe pulling a little ahead. Don't worry about getting dropped. Keep spinning. You're saving your legs.

-- In the final third of the hill, click to a bigger gear (next smaller cog), stand and apply the pressure. Your legs will still have snap, thanks to spinning to this point. When you hit it right, you'll know where the phrase "dancing up the hill" comes from.

You'll roll right by your laboring companions. Even better, your momentum will carry you over, down and well into the next rise. Then do it again.


These training techniques simulate what happens in road racing. They're great workouts and guaranteed monotony-busters as well. Warm up and settle into a single pace line moving at a moderate speed. Then try one of the following:


You can decrease your time on long endurance rides with a little interval training. You might try these two tricks on your next long ride.


When you are on a long ride -- for you -- a slow, meandering pace can make you feel sluggish or even bored. Before that happens, give your legs (and your bottom side) a little lift. Throw in a short "pickup" every few minutes. Pickups are like sprints but not as hard.

Watch for opportunities. Get out of the saddle and accelerate away from stop signs, over short hills, out of turns or past the lair of a troublesome mutt. Don't script these pickups. Instead, do them when the terrain or situation asks for it. To do a pickup, choose a cog 2-3 teeth smaller (higher gear) than you'd normally use for the situation. So, if you'd usually roll over a rise in a 53x21-tooth, use the 53x19. Don't sprint all-out. That's not the purpose. Instead, simply stand and wind up the gear for 10-12 seconds. Effort should be about 80% of a flat-out sprint. You shouldn't be panting after you sit down. A few deep breaths should get you back to the ride's baseline effort. You'll be amazed at how much better you feel on longer rides when you relieve saddle pressure and treat your legs to these brisk efforts.


I'm a firm believer that training programs based on a clear understanding of human physiology will provide better results. Although trial and error will ultimately achieve the same ends, the data from scientific articles should get you there faster while occasionally providing unexpected surprises that might put you a step ahead of the competition.

The traditional teaching has been that the stress of aerobic training leads to adaptive changes in the muscle cell that improve performance. This article suggests that the physiology behind training improvements is slightly more complex than previously suspected.

Mitochondria are the powerhouses of our muscle cells. They contain the enzymes that convert glycogen and fats into the ATP needed to power muscle contraction. With aerobic training, we know the mitochondria increase in both size and number increasing the amount of ATP that can be produced per minute (assuming there is sufficient fuel (carbohydrates) and oxygen delivered to the exercising cell.)

We also knew that regular aerobic training changes the types and numbers of bacteria in our colon (the microbiome) I never understood why exercise might have this effect. Was it the fact that athletes see diet as part of a training program and eat healthier with more fiber and vegetables (which we also know changes the composition of the microbiome)?

The bacteria of the microbiome metabolize unabsorbed food material from our diet (generally fiber), in turn manufacture short chain fatty acids (which are absorbed and provide a modest amount of additional energy for our cells) as well as producing various small molecules that can affect energy metabolism.

This article puts forth a good argument that our mitochondria in some way affect colon bacterial composition which in return produces molecules that will positively influence mitochondrial metabolism and growth. A positive feedback loop which magnifies the benefits of aerobic training.

So what, you might ask., is the point? There are no clear training take-aways......yet. But if we can isolate the bacterial products that stimulate mitochondrial growth, we may have a cue as to how we might magnify the benefits of aerobic training. And as we know our diet can directly affect the microbiome, perhaps we will find helpful or harmful diets that should be included/avoided to maximize a training benefit.

So no recommendations yet. Just a nice example demonstrating how complex physiology can be, and illustrate how a clear understanding could give us clues to provide a competitive edge.


Do you ride a fast 50 miler or century but want to improve you time trialing or short distance performance?. Then use intervals. If you ride 50 miles (or 100) then you have the endurance base. Now you need to add speed work.

Add intervals of 3 minute duration - repeat 5 times - to your program (ridden at a pace a bit faster than your speed in a time trial and a lot more intense than your century pace). Then spin easy for 3 minutes between each effort. Twice a week. And never back to back days. For variety, longer intervals are also effective - perhaps 10 to 20 minutes at your time trial intensity with two or three repeats.

The following question from a reader suggest that riding with weight is another alternative (just like riding into the wind) to add intensity to your training, simulating an increased load and thus generating a training response. I've had similar comments from other readers.

Q.I was wondering whether you know something about the following: I am riding about 150 pretty fast miles a week, usually with a 12-15 pound backpack (because it is my commute and I carry a laptop and clothes etc.). Sometimes I ride without the backpack and noticed that I am considerably faster. While this is of course not surprising I was wondering whether 'riding with weights' could actually be a useful training technique -- I couldn't find any information about this. - MS

A. Mike, as I mentioned above, added weight (speed remaining the same) is a way to add a stress to your muscles and CV system, which will adapt, and then you will be able to perform more effectively when unburdened. It is the same reason one would weight train as part of a program, or train on a clunker and then get out a titanium frame for that important ride. Dick

Questions on content or suggestions to improve this page are appreciated.

Cycling Performance Tips
Home | Table of Contents | Local Services/Information