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CYCLING PERFORMANCE TIPS

Latest update:5/29/2023

Heart Rate Monitors

CONTENTS

The Heart Rate Monitor (HRM) is touted by many cyclists and trainers as the most significant training advance in the last ten years. Although many coaches refuse to work with an athlete without the physiologic training information it provides, HRMs have their detractors. And that small backlash is slowly growing. An alternative to a HRM, not quite as technical and rigid, uses perceived effort as a measure of your level of exertion.

BASIC CARDIOVASCULAR PHYSIOLOGY

First, let's review the basic physiology of the circulatory system asking ourselves the question "What does the heart rate really indicate?" The components of the cardiovascular system are:

the heart (the pump)
the arteries (a distribution system)
the capillaries (the exchange system where gases, nutrients, and other chemical compounds move to and from surrounding tissue
the veins (which are the return circuit)

With every heart beat (contraction of the heart pump), a certain amount of blood (stroke volume) is pushed through the system. The contraction frequency of the heart is the heart rate (HR). The amount of blood moved to the cells of the body every minute is the product of the heart rate and stroke volume (HR x strove volume).

With physical activity (exercise) more oxygen is required by the muscle cells, and the circulatory system responds by increasing the heart rate (and the cardiac output). With aerobic training, the actual amount of blood pumped per heart beat (stroke volume) increases and the efficiency of the exchange process at the capillary level improves. The result is a lower heart rate for any level of physical activity in the trained versus the untrained individual. Thus aerobic training benefits include:

a lower resting heart rate
a lower heart rate for a specific level of exertion
an increased exercise capacity at an individual's maximum heart rate.

The training effect results when the heart muscle is "stressed" by an increase in cardiac output (just as muscles in the arms and legs respond to the stress of lifting free weights). As the cardiac output is directly proportional to the heart rate, a heart rate monitor (HRM) can be used to structure and monitor an aerobic training program. (For additional background see Basic Exercise Physiology - the cardiac system.)

TERMINOLOGY

Here are some definitions you'll encounter in the literature on heart rate monitors:

bpm = beats per minute
Max HR (MHR) = maximum heart rate (expressed in beats per minute)
target heart rate = the training heart rate (usually a range of values)
anaerobic threshold (AT)* (synonymous with lactate threshold). Lactate production occurs with muscle cell activity and increases as activity becomes more vigorous. Lactic acid is metabolized by the muscle cells, but at some point they cannot eliminate (or oxidize) the lactate as fast as it is being produced and the blood lactate level begins to increase. In trained athletes, this threshold for lactate buildup occurs at a higher activity level or percentage of the athlete's MHR or aerobic capacity. For all practical purposes, the AT is the highest heart rate you can maintain for a race or hard ride lasting up to an hour. As the AT increases with aerobic conditioning, it is considered one of the standard measurements to track training. The AT is usually reached at 80-90% of your maximum heart rate, but in elite riders rises to 90-93% of their maximum heart rate.(See also Basic Exercise Physiology - measures of cardiovascular fitness.)
lactate threshold (LT). See anaerobic threshold.

* Determining your actual Anaerobic Threshold (synonyms are lactate threshold, AT, LT, Concini test). Accurate laboratory determination of your anaerobic threshold requires frequent blood draws while pedaling an ergometer at steadily increasing workloads. But for training purposes, the following approach is an alternative. Using a single gear, start cycling at 35 kph. Slowly increase speed on a flat course by 1km/hr every 300 meters (1/5 mile). Chart heart rate vs speed. Anaerobic Threshold is the "breakpoint" where heart rate levels off relative to speed.

Let's assume you have decided to use a heart rate monitor in your training program. The first step is calculating your MHR or maximum heart rate.

CALCULATING YOUR MAXIMUM HEART RATE (MHR)

Interest in the Maximum Heart Rate is based on the fact that it is a readily available surrogate for VO2max, the gold standard for assessing maximum exercise capacity and designing training programs.

I'm sure that at some point you have heard the mantra "MHR is 220 minus your age in years". However this is just a rough figure and much less accurate than a real life, on bike, determination. I ran across the following website which not only goes into detail about the various studies supporting MHR determination, but also provides a calculator that will serve you better than the 220 - age in years. After reviewing the various studies, they suggest the following calculation (quoted directly from the website).

To determine your maximum heart rate you could use the following, which combines the Miller formula with the research from Londeree and Moeschberger.

Use the Miller formula of MHR = 217 - (0.85 x age) to calculate MHR
Subtract 3 beats for elite athletes under 30
Add 2 beats for 50 year old elite athletes
Add 4 beats for 55+ year old elite athletes
Use this MHR value for running training
Subtract 3 beats for rowing training
Subtract 5 beats for bicycle training

Just as we all vary in height and body habitus, everyone has their own personal maximum heart rate that is genetically "hardwired". Our maximum heart rate generally decreases one bpm (beat per minute) per year we age. Although the MHR of a teenager might be on average 220 beats per minute, for an individual this can vary +/- 11 beats per minute from that average (209-231 bpm). The same variation holds true as we age. Thus a 40 year old who would be expected to have a MHR of around 180 (220-40) could vary from 169 to 191 as his or her own personal MHR.

Can you slow the inevitable age related decrease in MHR? Although it has traditionally been taught that an individuals MHR is genetically hard wired (within a certain range) and your personal MHR will decrease with age, a recent study suggests that we may be able to blunt the aging effect by maintaining our cardiovascular fitness with regular exercise. You can read Dr.Mirkin's take on this study. Bottom line: "Use it or lose it" once again appears to apply.

Maximum heart rates are "sport specific" i.e. they vary from one sport to another. Thus you cannot use your maximum heart rate from running to plan a cycling training program without risking overtraining. Cardiac hemodynamics and maximal sympathetic drive are influenced to some degree by 1) body position during exercise and to a significant degree by 2) muscle mass involvement. If an activity is restricted to upper-body muscle mass, peak heart rates will generally be considerably lower than in whole body activities (more muscle mass involved). For example, a triathlete with a max heart rate during running of 180, may only hit 176 on the bike, and 171 during swimming. To keep our terminology clear, it would be best if we call the running heart rate the "Maximal Heart Rate" and the highest heart rates observed in cycling and swimming, "Peak Heart rates for each event. Knowing your peak heart rate for each discipline helps you to more accurately structure the intensity of your training.

Identifying your peak heart rate will help you identify your aerobic threshold for a particular sport. Trying to increase, or train, at your peak heart rate may lead to injury and over training. Finding your peak heart rate for each sport you are training for will help you set up your target zone heart rates (see next section) making your training more efficient.

The only limit to the length of time one can ride at 100% of their MHR is personal discomfort. This level of activity does not "strain" the heart muscle or have other harmful effects on the heart itself. Although this level of activity might be considered in a competitive race or event for a short sprint, maximizing the benefits of a training program is the result of a mixture of recovery and hard days.

It is much more productive (in improving your cycling performance) to focus on how long you can hold your aerobic threshold rather than tiring yourself trying to improve your peak (maximum) heart rate. Your aerobic threshold (or lactate threshold) is about 12 beats below your maximum (84-90% of your MHR). Training at your aerobic threshold is useful because this is the pace you race at and can be sustained for 30 minutes or longer depending on your fitness. As the time you can hold 100% MHR is considerably shorter than the time you can ride at 84-90% MHR, the art of racing is finding the right mix to get you to the finish line first.

If you are interested in finding your personal peak (maximum) heart rate for cycling, the following on bike approach will give you that number. If you are overweight or have a family history of heart disease I'd suggest that you talk to your family physician or consult a cardiologist first.

Actual MHR - Warm up thoroughly (15 minutes on the flats). On a long, steady hill (doesn't have to be steep) increase effort every minute for at least 5 minutes until you can't go any faster (sitting, not standing). Then sprint for 15 seconds (it is OK to stand at this point). Stop, get off the bike (this is for safety reasons - not mandatory) and immediately check your heart rate, which should now be at its maximum. Count the number of beats for a full 30 seconds - then double that number (the doubled number should be your peak heart rate for bicycling in beats per minute. Similar results can be obtained on a stationary trainer.

HEART RATE TRAINING ZONES

There are 5 training "zones" or heart rate ranges. These are arbitrary divisions and can differ from article to article or coach to coach. They are based on the fact that there is an increase in heart rate (and cardiac output) as the oxygen consumption of the exercising muscle increases, and the concept that there are benefits of applying variable stress to develop exercise tolerance in heart and skeletal muscle.

Metabolically, as exercise intensity increases and one moves up from one training zone to the next, there is a shift in the energy source for the skeletal muscle cells from fat to carbohydrates - below 70% MHR, fat is utilized preferentially. As MHR is approached, there is another shift towards anaerobic (without oxygen) metabolism which adds an increase in lactic acid production to the equation.

The Heart Rate Intensity Zones are generally divided as follows:

Zone 1 65% of MHR (recovery rides)
Zone 2 65-72% of MHR (endurance events)
Zone 3 73-80% of MHR (high level aerobic activity)
Zone 4 84-90% of MHR (lactate threshold(LT,AT); time trialing)
Zone 5 91-100% of MHR (sprints and anaerobic training)

If you always train at low heart rates, you will develop endurance with no top end speed. Conversely if you train hard most of the time, you'll never recover completely and chronic fatigue will poison your performance. The solution is to mix hard training with easy pedaling in the proper proportions.

I'd suggest that the optimal approach is to train below 80% of maximum heart rate (zones 1 to 3) on your easy days to build your aerobic base and is at a low enough stress level to facilitate muscle recovery. And then, when you have a good training base, push training to include several days a week above 85% MHR to improve your high level performance. But avoid training in the no man's land or mediocre middle at 80-85% of MHR where it's too difficult to maintain the pace for the long rides needed to build endurance, but not hard enough to significantly improve your overall aerobic performance and increase your lactate threshold.

Training programs should be individualized, but once a good base is developed early in the season within Zones 1 and 2, most programs conform to the following general "rules".

TRAINING TIPS USING A HEART RATE MONITOR

Tips for a training week: (see also mileage tips and training options)

one long recovery ride at zone 1 or 2
one long day (to be at event distance + 10 to 20%) at the MHR you have planned for the event. If it is an endurance event, that might be 70% MHR, and if a time trialing event, 85 - 90% MHR.
- For example: If you are aiming towards a 20 mile race, take 10 - 20% of the event distance, add it to the event distance which then gives you 22 to 24 miles at 70% MHR for an endurance event and a target HR of 85 - 90% MHR for a time trial event.
three high intensity days in zone 4
one or two interval workout days (which will be counted as one of the three high intensity zone 4 days. These interval days could be structured as follows:
- warm up at zone 1 heart rate
- 20 min at zone 3
- 5 min at zone 4
- 7 intervals - hit 90% MHR, then recover until you are back to 60 - 65% MHR
- 5 min at zone 4
- 20 min atone 3
- warm down at zone 1
the sixth and seventh days of the week can be rest days off the bike or (very) slow recovery rides at a zone 1 or 2 level of exertion to stretch out your muscles.

VALIDITY OF MAXIMUM HEART RATE FOR TRAINING

I was asked about my preference for calculating MHR> I use perceived exertion for my training rides so have never worried about my maximum heart rate (MHR). I find a HRM distracting - just one more number to follow.

The other issue is reliability. In a recent review MHR was overestimated by eight (61.5%) and underestimated by five (38.5%) MHR formulas.

For any specific MHR prediction, the result was more likely to be an underestimation than over (thus true MHR was more likely to be higher than predicted).
MHR formula tend to overestimate the maximum heart rate for younger exercisers and underestimate the maximum rate for older ones.
With regular training and high cardiopulmonary fitness, MHR decrease less with age than peers. So the MHR of a regular rider would more likely be higher than predicted for age.

Add up all these potential errors and it seems to me that perceived exertion is just as "scientific" as following HR numbers.

TRAINING WITH HEART RATE VERSUS PERCEIVED EXERTION

The emperor may have no clothes. Anyone who has ever trained for aerobic and sprint sports has heard about heart rate training zones. They imply a scientific precision that may in fact be no more than marketing (by trainers, physicians, and the heart rate monitor industry.) It may be similar to the story of the 10,000 step craze. Where diD that number come from? A controlled study? A review of the health of populations? No, it came from the advertising department of the pedometer manufacturer who needed to develop a market for their product.

In fact, the controversy begins with the simple (you would assume) idea of a standardized maximum heart rate.

Training requires applying physiologic stress, and to apply appropriate stress (enough to improve, but not enough to increase the risk of injury) you need a metric. But what is the best metric? The idea of a scientific number (heart rate and heart rate zones) was appealing. But anyone who has compared perceived exertion and heart rate zones has found that they often diverge. That is probably because heart rate at any specified level of exertion can be influence by many factors - room/air temperature, clothing, training status, anxiety, level of exercise recovery, and caffeine use, to name just a few.

Perceived exertion makes a bit more sense as a metric. As an embodiment of the "central governor" it reflects heart rate, levels of lactic acid, the levels of various hormones, our emotional state, glycogen reserves, and where we are in our recovery from a prior ride. A much more robust gauge, and why, to quote: "...many trainers and exercisers prefer the RPE scale."

Training requires identification of a target for improvement. What are our targets?

The musculoskeletal system - strengthen the muscles, ligaments, shoulder muscles, and skin on the butt to endure long hours on the bike.
The cardiovascular system - improve the heart's stroke volume and increase the number of capillaries in the muscles to improve oxygen delivery.
The removal of byproducts of metabolism - lactic acid and other acidic products of metabolism.

You hear a lot about improving the efficiency of fat as a fuel, but I contend that comes along for the ride - a freebie as an integral part of improving our LT. And I am not a believer that eating a carbohydrate deficient diet improves that any further.

So we really we have just have 3 training zones which are easily identified using a perceived exertion metric:

Moderate- the recovery ride. Usually in the range of 50 - 60% MHR (or %VO2max). The rate at which we do most of our very long rides to "build up endurance".
Strenuous - rides at our LT for 30 minutes to several hours. These improve the total work we can do over a set period of time and translate into improved times for longer rides. And as the LT increases as we ride, the %MHR as a metric is a moving target.
Sprints - all out intervals at our MHR (VO2max) for 30 second which encourages CV improvement with vascularization of the muscle. I don't think a HR monitor or zones provides me, personally,more helpful information than just using PE, once I have dialed in my own awareness to how hard I am working. Several quotes say it as well as I can:

First: "After only a few training sessions you will be accustomed to the RPE feeling and will no longer need to know your HR. By using only RPE you are not limited to knowing your HR and can modify your training intensity based on how you feel. This becomes increasingly important when exercising outside in hot and humid environments and when you are exercising for long periods of time. Once you know what a 14 - 17 on the RPE scale feels like, you can exercise anywhere, on any piece of equipment, and be confident you are in your optimal training zone."

And

Second: "Dr. Fritz Hagerman, an exercise physiologist at Ohio University, said he had learned from more than three decades of studying world class rowers that the whole idea of a formula to predict an individual's maximum heart rate was ludicrous.

Now let's look at a few of the pros and cons on the use of a HRM.

CARDIAC DRIFT

Cardiac drift is the term used to define the gradual increase in heart rate that occurs during prolonged exercise bouts being performed at a constant intensity. The heart rate increases and stroke volume decreases with cardiac output remaining unchanged.

What is behind this physiologic change? Part is the response to dehydration. Maintain hydration and the amount of drift (increase in HR) can be decreased by about 50%. This implies the primary cause is a decrease in stroke volume with a secondary increase in heart rate as compensation to maintain a stable cardiac output.

Other factors behind drift might be an increase in core temperature and cellular level metabolic changes.

It's important to understand that this increase in heart rate is not a sign of underlying heart disease or over training. And for those using a heart rate monitor for training to realize that training to a specific heart rate (or zone) will lead to a gradual decrease in wattages achieved as exercise time passes. This is why using perceived exertion or a watt meter is a more precise tool for a structured training regimen.

PROS AND CONS

The ADVANTAGES of a HRM include its use:

as a motivational tool - like a coach ; brings objectivity to a training program.
to teach beginners to read their bodies and avoid anaerobic overtraining.
to aid in doling out energy during time trialing or climbing, saving some for the final effort.
to analyze race efforts and design a personalized training program.
to spot overtraining (heart rate 10% higher than normal on awakening for several consecutive days).

The DISADVANTAGES of a HRM are:

its inconsistency - at the same heart rate you're not always putting out the same effort day to day.
cardiac drift
the lack of scientific support - there is no evidence training with a HRM improve competitive performance.
too much data, esp with elaborate HRMs, with little agreement on how to use this information to improve training or performance.
the lag time in heart rate response to a change in exertion - 15 to 30 sec lag with 2 to 3 min to stabilize at the new level of exertion.
its incompatibility with group training.
it distracts from dangerous road hazards.

A Reader's Question:

Q. I am a 69 year old male cyclist, ride 3/4 times each week, and ride 180/200 miles over the week. covering up to 180/200 averaging 16 mph over undulating terrain. Steep short hills I can kick over however long steep or long climbs I get into the red! My worry is that my heart rate which averages around 142 bpm on these rides top out at 180.

Obviously this is well over the recommended 220 - 69 = 151! I have no real problems with the high rate but it does concern me if this is causing too much stress on my heart. I recover after the efforts fairly quickly. As yesterday I kept with the group over a 10k steady climb but heart rate was at 176. Over the top it took 2/3 minutes to get back down to my usual rate of 130/140 bpm. Continuing to complete a 112k ride over 4 hours and 8 min? Your comments and advice would be appreciated.

I do not think you can over stress your heart without some warning from your body that you are reaching your limits - either chest pain or shortness of breath to a degree that you would have to slow down.
The use of 220 minus your age for maximum heart rate is not reliable. This commentary on MHR is well researched and is, I think, a definitive commentary on Maximum Heart Rate. To quote from their conclusions: "...the most accurate general equation is ... HR max = 205.8 - (0.685 x age)." With a standard deviation of 6.4 bpm. (For those of you not used to statistics and standard deviation, SD is calculated in a way that 99.7% of a population lie within the mean + or - 3 standard deviations.) So 99.7% of 69 year olds could have a MHR as high as:
- (205.8 - (0.685 x 69) + (3 x 6.4) =
- (205.8 - 47) + 19.2 =
- 159 + 19 = 178
and still be within "the normal" range. Basically you are at the upper limits of the wide normal range. This wide variation means each individual needs to measure their personal MHR and calculate their own personal training zones from it. That being said, there is still enough variability from day to day that even that personal approach to using MHR is much less precise than using a power meter (watts of output) to structure training zones.
The rapid return towards normal of your MHR is a another example of how MHR can be used in training. From Dr. Mirkin.com "...A healthy person's heart rate drops about 20 beats in one minute after all- out exercise, while fit athletes' heart rates can drop more than 50 beats in one minute." So it sounds as if you are well within that 20 bpm limit as the HR fell while still riding with the group (rather than stopping.)

USING A HRM TO AVOID OVERTRAINING

A heart monitor can provide you with clues as to whether you are risking an overtraining situation - and thus should take an extra day of rest. Do a warm up that takes you to the foot of a familiar hill. Climb at your usual pace while keeping one eye on your HRM. One of four things will happen:

Heart rate is higher than normal and legs feel tired
Heart rate is normal and legs feel tired
Heart rate is higher than normal and legs feel good
Heart rate is normal and legs feel good

In the first situation, your recovery from previous rides isn't close to what it should be. Head on home and take the day off. Pushing on will only put you in a deeper hole. In the second and third scenarios, your recovery is incomplete, but not to the extent of #1. You can continue riding, but only if you can keep distance and intensity moderate. Scenario number four indicates you are right on schedule with your training.

Your resting heart rate (RHR) is another indicator of your degree of training (and monitor for moving into an over trained state). As you train, your resting heart rate should fall as a result of the increased efficiency of the circulatory system. The heart will increase the volume of blood pumped per beat, and the peripheral muscle cells will become more effective at extracting oxygen from the blood passing through their capillary networks. The RHR for an untrained individual is 60 to 80 beats per minute. With training, it is not uncommon to see the RHR fall into the high 40s or low 50s. And as mentioned above, regular monitoring of your resting heart rate in the mornings (before getting up and beginning your daily activities) can be used as a monitor for overtraining (heart rate on awakening and before getting out of bed 10% higher than your personal normal for several consecutive days).

SLOW HEART RATE

A slow heart rate is considered a sign of good health. As one conditions, the heart will beat more slowly for any specific level of activity - including at rest. That is why the resting heart rate is a good measure of cardiovascular conditioning. The two exceptions are hypothermia, where a slow heart rate is a reason for alarm, and the other is a heart rhythm disorder. The latter can indicate heart disease, generally comes on quite suddenly, and is occasionally associated with an irregularity of the pulse.

AN OPPOSING OPINION

But there are differences of opinion on the usefulness of a heart rate monitor for training and competing. So keep an open mind and don't consider the HRM as the only real key to success. The following is from an Aussie coach, Graham Fowler:

"I have observed a number of different %max heart rates during time trials. My nephew once rode a junior nationals ITT at 100%MHR. He didn't win it needless to say however didn't crack either. Obviously he was very fit or his MHR was inaccurate. I advise riders to ride just above (1 to 5 beats per min) what they consider threshold. This is around 92%max hr. This mark needs to be derived in training. I am aware of race day anxiety causing the heart rate to elevate somewhat so the hr is not such a good measure with an anxious rider. I am more inclined in the future the train with heart rate to establish a perceived effort (pe), and then remove the heart rate meter during racing and ride on pe alone. "

THE BOTTOM LINE

The following question may help to illustrate a few points.

Q. I am 48 years old and a new MTB biker. I am working to keep/improve my shape in a controlled way, so I am using a HR monitor on my MTB bike. Until now I used Max HR of 180, just because quite often I reached this figure. Last time after accelerating my HR for 15 minutes, on a mountain steep trail I reached (for more than a minute) a HR of 182 -185 (in total it was 3 minutes of 8.7% trail with avg. speed of 8 km/h, avg. HR of 178 and max of 185) and I could continue without a problem with the trail.

My questions are:

Should I consider my Max HR as 185? or what should it be?
As it is quite far from my theoretical Max HR, what does it mean: Am I in good shape? Not in good shape? Means nothing (just genetic)?

A. Here are a few thoughts-

Maximum heart rate is very individual and all the rules to "calculate" MHR are just approximations to get you into the ballpark for you. Your maximum heart rate is what you have actually measured for yourself (185 for you).
Maximum heart rate has nothing to do with what shape you are in. And yes, it is probably related more to your inherited physiology (genetics) - assuming you are healthy - than anything else.
Use your maximum heart rate (and %'s thereof - training zones) as general training guidelines, not absolutes. Which means a difference of MHR of 180 versus 185, really is not that big a deal. This is not engineering (which is precise and reproducible day to day), but a biologic system which can vary from day to day. That's why perceived effort - which takes into account day to day variation in your biology - as a training tool makes more sense to me.

Q. I am going to be training for the Paris Brest Paris in 2011 and would like to know how I can use heart rate or perceived exertion information to improve my training. The pace of brevets is only an average of 9.5 mph in order to get under the time cut off. Do you think need a HRM? M.M.

A. PBP is the ultimate endurance event. So cardiovascular training is not going to be the challenge as much as your musculoskeletal conditioning. You will probably be riding at 50 - 60 % VO2max most of the time and thus are burning a fair amount of fat calories as opposed to sprint type events. So no need to worry about intervals, and in fact as you are going to want to train at most somewhere around 70 - 75% VO2 max., I would go for "perceived exertion" that is "how you feel" as the best barometer. A HRM might drive you to do more than is necessary - and lead to burn out if you are only focused on training to the numbers.

5 MYTHS ABOUT MAXIMUM HEART RATE (AND THE USE OF HRMs)

For decades, the holy grail of training tools for the amateur athlete lacking access to a sophisticated lab was the heart rate monitor (HRM). Although maximum heart rate (MHR) was touted as THE way to monitor your recovery, lactate threshold, as well as design your heart-rate training zones, the numbers are not as precise we might hope. A number of variables (level of fitness, the ambient temperature i.e how hot it is, the status of recovery from prior rides, how much stress you're under that day i.e performance anxiety) all modify your heart rate for any level of activity.

The referenced article from bicycling.com points out 5 common myths that highlight the weakness of a HRM as a training tool.

"If You Go Over Your Max HR, Your Heart Explodes". If you have normal coronary arteries and none of the unusual congenital heart abnormalities which can cause rhythm problems in athletes, the body monitors itself quite effectively to prevent irreversible damage from excessive exertion. Although one can maintain a supra-maximal effort for a few minutes before your "central governor" takes over and limits further exertion at that level, there is no permanent damage from going too hard for too long. The reason one limits time at MHR (or a percentage of MHR) is to gain maximum training benefit (longer is not better) as well as to avoid the real risk of burnout from overtraining.
"Your Max HR Is the Same For Everyone Your Age". Maximum heart rate varies from individual to individual and is genetically determined for each of us. It cannot be increased by more training. And a higher MHR does not determine the upper limit of aerobic performance. There are many variables that define maximum performance including the amount of blood pumped per heart beat (stroke volume), pulmonary efficiency (oxygenating the blood in the lungs), removal of oxygen at the capillary/cell membrane interface by the exercising muscle. And to a great degree it is how long one can maintain their MHR (which can be increased with training) that defines award wining performance.
"Heart Rate Is A Measurement Of How Hard You're Working". Your heart rate increases with the amount of work being done by your muscles, but lags behind the actual level of work at any given moment. That lag is one reason a HRM is not a great tool to track maximum effort. A power meter (watts produced by muscle activity) or perceived exertion are better tools to define your level of exertion (and stress being put on the muscles) than are tracking the numbers or your heart rate training zones. This is not to say HR numbers are of no use, but they are much less precise than adding a few extra watts measured on a power meter as part of a training interval program.
"If I'm Not Working at My Max Heart Rate, I'm Not Working Hard Enough". Your maximum heart rate is not the number you should train to every day. It reflects maximum, or at least close to maximum, effort. And if you worked at this level everyday you would quickly burnout with an overtraining syndrome of some sort. Your training should be a balance of maximum effort (intervals) 2 - 3 times a week interspersed with recovery rides and endurance rides of longer distances at a more moderate pace. These less intense training days can be paced using heart rate zones (a % of MHR).
"As Long as You're Working Under Your Max, You Don't Have to Worry About a Cardiac Incident". If you have a history of heart disease or risk factors (high blood pressure, family history, or diabetes are a few examples) exercising below a certain work thresholds do not protect you from a heart attack. Heart attacks happen at all levels of exertion and if you are worried, you should have a stress treadmill before undertaking any exercise regimen.

So there you are. A few myths about heart monitors and MHR specifically. And remember, you don't need a gizmo to measure exertion (power meter, heart rate monitor) to give structure to your training program. Perceived exertion is easy and just as effective.