The Ugly Truth About Training Zones

Exercise physiology textbooks generally devote several chapters to the three energy systems that power muscle contractions and how the three systems interact to support various intensities and durations of exercise. They tell us that adenosine tri-phosphate or ATP is the carrier that finally delivers energy for muscle contractions no matter what the source of that energy may be. Then they describe how the anaerobic alactic or phosphagen system supports intense efforts up to 30 seconds by releasing energy that is already stored in the muscle as ATP or as creatine phosphate, which can quickly recharge ATP.

After 15-30 seconds when ATP and CP are depleted, the anaerobic glycolysis or lactate-producing system becomes dominant. This system splits glucose (sugar that can come from the blood or be stored in muscle cells as glycogen) into pyruvate, producing a small amount of ATP in the process. During hard efforts, pyruvate is converted to lactate which diffuses out of muscle cells and into the blood stream. This glycolytic system supports hard efforts up to a few minutes, but cannot produce ATP as fast as a muscle can use it, so the maximum power produced by a muscle decreases as the anaerobic lactic system takes over from the phosphagen system.

As the hard effort continues beyond a few minutes, aerobic metabolism kicks in. Pyruvate or lactate is oxidized to carbon dioxide and water, and more ATP is produced. Aerobic metabolism releases much more energy than does glycolysis for each molecule of glucose consumed, but the rate of ATP production by aerobic metabolism is much less than that by glycolysis and pace must drop yet again. Aerobic metabolism can produce a steady output until fuel is exhausted, which can take many hours, depending on training and fueling.

Understanding the three energy systems helps us to understand why hard efforts feel the way they do. Most riders can sprint all out for about 15-20 seconds. At that point preformed ATP and CP in the muscles are becoming depleted, anaerobic lactic metabolism is ramping up, and power drops a bit. A 15-20 second effort can be done as a sprint. If the effort will last more than 20 second and up to four minutes or so, it can be done with a gaspingly “anaerobic” effort, but a bit slower than a sprint. If it will take much more than four minutes, it will be powered by the aerobic energy system and will again be slower than the shorter effort, no matter how much the rider wills him- or herself to maintain speed. (I put “anaerobic” in quotes because that word is so often misused. It actually means “without consuming oxygen”. If you think “anaerobic” efforts are made without consuming oxygen, try holding your breath next time you go flat out for several minutes.)

Specificity of Effort

The three sources of muscle power really are three different systems. They rely on separate collections of substances and structures inside and around muscle cells. The strength of each system can separately change with training. The specific enzymes that make up the phosphagen, glycolytic and aerobic energy systems increase in the days after training that challenges a particular system, and decrease again when those systems haven’t recently been challenged.

Because muscle cells use specific enzymes to accomplish the tasks involved in the different energy pathways, physiologists can literally take a small sample of muscle and, by analyzing its enzyme content, determine the training state of an individual. An athlete with a high level of anaerobic glycolysis enzymes but low levels of aerobic enzymes will be good in the kilometer or pursuit for instance, but not good for longer time trials or road races. (Lest you be tempted, no, you can’t benefit by eating ATP or muscle enzymes. They have to be present inside each separate muscle cell and have to be produced there to be usable).

Since different specific enzymes are used by the three different energy systems and are produced after training that challenges the particular system that uses them, improving ability in one specific system requires training that challenges that system. Long rides at a steady pace will boost sprinting ability a tiny bit, but really developing a sprint requires making short, hard efforts that maximally challenge the phosphagen system. Sprinting all out will do a little to develop the ability to go gut bustingly hard for the final lap of a crit, but the only way to really optimize that ability is to make flat-out efforts of several minutes duration to challenge the glycolytic system. The only way to build aerobic endurance beyond a low level is to ride aerobically for extended times. Riding at a “hard aerobic” pace may be minimally more effective than a lower pace for developing aerobic power, but if the power creeps up just a little more, challenging the anaerobic lactic system, then fatigue comes quickly and the aerobic challenge does not last long enough to cause much aerobic development.

Zone training works because different intensities of exercise challenge and develop the different energy systems. If a rider trains in specific power or heart rate zones calculated to stimulate aerobic-, glycolytic- or phosphagen-system development, he or she can be confident of developing particular abilities needed for riding long races; hanging on during attacks and setting up for the finish; and sprinting, respectively. Appropriately balancing rest and stimulation to the three systems in ways that change with the time of year can bring the rider to racing form in time for his or her key races.

Calculating Zones

There are many methods of setting up heart rate and power zones. Here’s the one Wenzel Coaching uses for setting up heart rate zones:

  • Rest Zone: Below 60% of maximum heart rate
  • Recovery Zone: 59-70% of maximum heart rate
  • Endurance Zone: 69-80% of maximum heart rate (but keep this zone at last five beats below LT so the top of the zone may be below 80% of max if the LT is low)
  • Moderate Zone: 92-96% of LT
  • Hard Zone: 98-102% of LT
  • All Out: Heart rate varies

And for for setting up power zones from a measured FTP:

  • Recovery Zone: Up to 55% of FTP
  • Endurance Zone: 56-75% of FTP
  • Moderate Zone: 76-92% of FTP
  • Hard Zone: 93-105% of LT
  • VO2-max Zone: 106-120% of FTP

There are several other systems of setting up zones that are just as good. So long as zones are developed from individual heart rate or power numbers, how the endpoints are set doesn’t matter nearly as much as what is done between them. Any zones based on assuming that maximum heart rate is a function of age are garbage, right on the average but wrong in most cases.

Here’s a way to set up zones if you don’t have a heart rate monitor or power meter.

  • Recovery Zone: Feels trivial, can’t really feel pedals pushing back on feet
  • Endurance Zone: Pushing on pedals but still having enough breath to sing
  • Moderate Zone: Can chat but not sing
  • Hard Zone: Can talk in short sentences
  • All out: Breathing hard, can only force out a few words before… needing… a breath

The Dirty Secret About Zones

Zones are totally artificial. The phosphagen, glycolytic and aerobic energy systems are all running all the time. A particular exercise may rely on one more than another, but every exercise uses all three systems to some extent. Every muscle contraction no matter how mild or forceful is powered by ATP. That ATP is always produced, either in advance or in the moment, mostly by splitting glucose or oxidizing fat. Glycolysis and aerobic metabolism are going on all the time. At lower intensities aerobic metabolism keeps up with glycolysis, burning up pyruvate as fast as it is produced. At higher intensity, glycolysis outspeeds aerobic metabolism and lactate accumulates even thought the aerobic system is going full tilt. All three systems are working any time one exercises. The aerobic system doesn’t shut down when a rider reaches “anaerobic” intensity.

The endpoints of training zones are really arbitrary. Systems that use different numbers or percentages can work equally well. Zone endpoints aren’t firm metabolic boundaries but points in transition zones where one energy system’s contribution is increasing while another’s is decreasing.

When riders first start zone training they often find it difficult to obey a zone. They find themselves going a little too hard or not quite hard enough and have to adjust repeatedly. My newer clients often want to know how they did. Did they get enough time in zone? Is five minutes at five beats above zone okay? What if it was ten beats? I tell them that five beats above would be better than ten. Zero would be better than five. Two minutes over would be better than five and no time over would be better than two minutes. Through almost two decades of coaching I have seen that riders who stay in their zones make more progress and race better than those who don’t, but why does it matter? If zone endpoints are arbitrary, why does going a few beats or watts above zone for a few minutes now and then have a negative impact on performance?

The Values of Zone Training

Staying in training zones matters for at least four reasons. First, the easy one: It works: In general a rider who is new to zone training and really commits to it will find that within six to eight weeks they can ride the same average pace for a long ride staying in the Endurance Zone as they could riding hard before they started zone training. They also finish each ride feeling much fresher, recover more quickly, and can do those rides day after day where the same distance and the same average speed used to leave them exhausted for days. A few weeks later, their average speeds on long rides are higher than they’ve ever been and their buddies start to wonder what’s going on. A few months later, unless they are really goofing up nutrition or recovery, they are sustaining paces that hurt riders who are doing a similar volumes of less-organized training.

Physiology and the work-rest balance: If a rider is in the zone the plan or coach has specified, he or she is developing the energy system that the coach or plan-maker had in mind. A little below the zone, he or she is still challenging the right system, but not quite as much and development slows. A little above the zone and the rider can’t sustain quite the same volume of training he or she could with a bit more discipline. If the rider has the ability to recover from far more riding than he or she has time to do, no big deal, but if recovery is a limiter, as it usually is, then staying in the right zone leads to the best possible use of the greatest possible fraction of the available time. If the rider actually stays in the suggested zone, then he or she can also learn from the results of the training. If there was a bit of fatigue, or a bit of left over energy, the training can be adjusted.

Discipline: The rider who surges uses up matches and tires sooner than the one who rides a steadier power output. The rider who can stay in a zone on a training ride can hold a steady pace in a TT or off the front of a race or when chasing. Keeping the effort steady and without spikes is key to performance and a skill that is learned during zone training.

Self-awareness: Most successful athletes have a well-developed sense of training intensity and of their own state of fatigue or readiness for harder training. Training in zones helps athletes learn the feel of different levels of effort. More important, it helps a rider to identify fatigue quickly. If it becomes difficult to maintain a heart rate or power that was easier to hit early in the ride or on another day, fatigue is present. Until one has enough self-awareness to back off before fatigue gets out-of-hand, carefully staying in a zone for a prescribed amount of time helps in avoiding overtraining by avoiding spikes of higher intensity that bring rapid fatigue. It is almost impossible to become a top elite rider without moving past needing a monitor to tell one how hard to ride, but for the vast majority, there is plenty of room to safely improve with the help of a plan built around training zones.

There is danger to zone training too. Riders must remember to focus on the accumulation of high quality training hours, not hours “in zone”. It’s easy to get the two confused. Trying to stay in the Endurance Zone for four hours despite feeling tired after only two is an error. If this becomes a daily occurrence, the rider will end up overtrained. Smarter riders remember that the zone is a tool for identifying the correct feel and bags the ride when the feel changes, even if that means getting fewer hours. For the rider who lacks self-awareness, an objective coach is invaluable. The coach who can recognize fatigue can help a rider adjust training zones or durations to get better results by avoiding excessive fatigue, wasted training hours and extended recovery.

Are Zones for You?

The ugly truth about training zones is that they are arbitrary, unnecessary, and overhyped. Many top riders don’t use them. If you are already a world-beating elite cyclist, please keep doing whatever you’ve been doing for training. If you’ve not been training with heart rate or power zones and your performance is less than you’d like it to be though, consider getting a good book on training or signing up with a coach who can teach you zone training methods. The results of committing to training zones are often nearly miraculous.

Scott Saifer, M.S. and the coaches of Wenzel Coaching use training zones and regular conversations with their clients to constantly adjust training so as to efficiently reach athletic goals. We are currently accepting clients with all levels of experience from beginners through aspiring elite and elite. To inquire about working with Scott or one of the 45 other Wenzel Coaches, please call 503-233-4346 or visit us on the web at

This article first appeared in ROAD Magazine in September of 2011.

2 comments on “The Ugly Truth About Training Zones
  1. Adam Beevers says:

    Great article. I have been trying to find out why each zone helps specific aspects of training.

    However, what I didn’t understand is that you mention that training in a zone not matching the intended effect won’t help, e.g. high intensity zone doesn’t help endurance. My question is why are we taught to to do shorter high intensity reps to boost our endurance capabilities (more when you’re short on time)

    It would be great if you could get back to me on this.

    Many thanks

    Adam Beevers

    • Scott Saifer, M.S. says:

      Hi Adam,
      This is actually a huge question with lots of subtleties in the answer. Let’s start with the big picture: An athlete who has more time to train has an advantage, even if the busier athlete is willing to work harder. If working harder actually gave a dependably bigger fitness boost, the less busy athlete would train harder, right? There is another factor we are not yet considering: Recovery.
      There are three variables to consider: Available time, benefit per minute at any given intensity, and time required to recover per minute of any given intensity. The short workout to exhaustion takes more time to recover from than the longer workout that gives the same benefit. The problem with the “if you are busy just go harder” philosophy is that the required recovery time increases more rapidly with intensity than does the fitness benefit. It’s not that somewhat higher intensity doesn’t challenge the same physiological energy system as somewhat lower intensity, but that you can’t do enough time at a higher intensity day after day to catch up with another rider who can do more time at a lower intensity.
      If your schedule dictates that you have one short day each week, do your hard intervals that day, but if you have to do short workouts every day, don’t do hard intervals every day.
      Now some details… Higher intensity can substitute for longer rides, but only if the higher intensity still challenges the same physiological system. Sprinting doesn’t improve aerobic capacity other than in people who are minimally aerobically trained because it doesn’t rely on aerobic metabolism. VO2-max level efforts do boost aerobic capacity, but are so fatiguing and require so much recovery that they have to be used very judiciously. When you have a short time in which to train, you still want to finish the day as tired or not tired as you would on a day when you have more time to train. If the coach ordered up a 3 hour zone-2 endurance ride and you only have an hour, you might do well to warm up and then do a nice 40-minute block of zone-3, if you are fit enough to recover from that by the next day. If not, you’d be better off staying in zone 2 because consistency of training is more important than total work done.