Welcome to the Threshold zone! Even if you don’t choose to train in the Z4 Threshold zone, it’s a place you’re no doubt familiar with, though maybe you are unfamiliar with its name. Here’s a hint: this is also known as the “shortness of breath” zone. Sound familiar? It’s the zone where you feel the burn in your legs as you quickly climb a set of stairs; where, when you reach the top, lean over, put your hands on your thighs and try to catch your breath, your mind slowly reminds you, “You’re really out of shape.”
The Threshold zone is so-called because, for most fit people, within this zone of 80-90% maximum heart rate is your threshold – your second lactate threshold and your high ventilatory threshold. Because these thresholds are so similar and so close together, for our purposes now, we are going to wrap them up and call this exercise intensity, heart rate number “threshold” (see Chapter 18 about the Threshold Training System). Above the threshold, oxygen debt starts to rapidly accumulate and lactates are spewing out. It can be a very uncomfortable place. But here’s the startling part about the threshold. In the unfit individual, it is common to see thresholds at around 60% of their maximum heart rate. And, in the extremely fit, it is common to see thresholds above 90% of their maximum heart rate. The chart on the next page gives you a view of the parts of Z4.
This is very important: if you are unfit and your threshold heart rate point is within your low zones, Z1-3, you can’t train in the Threshold zone. It’s simply too high a heart rate intensity. You need to stay below your threshold for all of your exercise. This is one of the primary reasons why exercise fails the healthy unfit: we’re asking them to train far above their thresholds.
Let’s say you are beginning an exercise program; you’re healthy, and you’re motivated to be successful. You are told to follow the arithmetic formula to calculate your exercise heart zones, so you use the 220 minus your age formula, which is on the wall charts at your athletic club. You start your program, jump into the 70%-85% heart rate range and can’t maintain that for more than 5-10 minutes, but you’re told that you are to stay there for at least 20 minutes, 4 days a week. At that intensity level, your chest is pounding, your breathing is faster than you could have imagined, and the pain is enormous. What do you do? If you are like most, you quit and then try and restart at some future time. The reason you failed is that you were told to train at a level that is above your threshold and cannot be sustained. It’s not your fault that you couldn’t do it. You were given the wrong information. Don’t be too hard on your trainers and coaches, though. In all likelihood, they didn’t know the correct information either. They were blinded by the accepted paradigms.
So, be warned that we are now leaving the comfort of the health and fitness areas of the wellness continuum. If you aren’t already fit or aren’t interested in training for performance’s sake, this might be where you choose to get off the bus. In other words, it’s okay to skip this chapter and the following one, which covers the Red Line zone, but do pick up the book again after these chapters, because there’s more to come for everyone. More on weight loss. More on performance. More.
HIGH INTENSITY, HIGH PERFORMANCE
Some fit folks hate this zone. There are others, though, who are threshold Z4 addicts, spending all of their training time hanging out here, producing endorphins and eating up lactic acid as if it were choco-late. We are concerned about the latter group (threshold junkies is their nickname) and encourage the former to try a few more sessions here because, if your goal is performance, you can get a lot of bang for your buck in the Threshold zone.
As we’ve just discussed, your threshold heart rate number changes with your conditioning. As you become more fit, your heart rate at this point is higher; as you become less fit, your heart rate at this point lowers. This is a moveable and trainable heart rate number – not a fixed one like maximum heart rate – threshold heart rate is dynamic.
If you are interested in high performance, one of your goals must be to raise your threshold as close as you possibly can to your maximum heart rate. In other words, your goal is to improve your maximum sustainable heart rate. It is the highest heart rate that you can sustain for a given distance without having your performance suffer. Racing at your maximum sustainable heart rate improves your performance in any athletic event. Researchers have discovered that maximum sustainable heart rate is one of the best predictor of your success. This high heart rate number is expressed as a percentage of your maximum number. For example, if I can run a 10K at my maximum sustainable heart rate of 175 bpm, for me that translates to 85% of my maximum heart rate.
The most obvious question is what kind of training is necessary to improve the threshold heart rate and maximum sustainable heart rate? For the answer, you would need to jump forward to Chapter 12 (“High Performance with Heart Zones Training”). For here, the brief answer is called the “At/About/ Around” Principle. That is, a large percentage of your “time in zone” needs to be at/about/around your threshold heart rate – up to 25%-50% of your training time if you are training to race competitively in the final training period.
Keep in mind, too, that your threshold heart rate number is specific to the activity in which you are engaged. If your threshold heart rate is 185 bpm running, it might well be 178 bpm cycling. It is postulated that these differences are related to the muscle mass used during the specific activities, as well as whether the activity is weight-bearing or not. Threshold heart rate is not only sport-specific, it is conditioned sport-specific. If you are currently fit running and unfit swimming, you can have a high threshold heart rate for running and a low threshold heart rate for swimming.
Triathletes are great examples of Threshold zone aficionados. We love to hammer as much as possible and to constantly test ourselves in all three sports: swimming, cycling, and running. When I first began doing triathlons in the early ‘80s, there was little to nothing written on cross-training or multi-sport programs. So, using the laboratory of the self and what little available research I could find, I decided to devise a self-test to determine my threshold. Each week I took this self test in one of the three disciplines, and, as the weeks went by, I watched my scores improve.
TWO NEW THRESHOLDS – LOW AND HIGH
The history of the term “threshold” dates back to 1923, when two exercise scientists, Doctors Hill and Lupton, first noticed that when skeletal muscles are subjected to increasing training loads their meta-bolic demands exceeded what the body could provide to them. It wasn’t until 1964, when the testing equipment became available to measure oxygen and carbon dioxide consumption and blood lactate changes, that the threshold first became measurable with lab tests. Physician scientist Karl Wasserman used the term “threshold” to define a particular training load where blood lactates first begin to rise above their resting levels. Since then, the meaning has evolved to refer to that effort when blood lactates concentration increases dramatically over their resting levels.
Of course the controversy over the true definition of threshold continues today among coaches but no longer among exercise researchers. The scientists have settled their arguments among them-selves. The majority now agree that there are many different ways to measure threshold using gas exchange, taking blood samples, using rating of perceived exertion, measuring shifts in breathing or ventilation to name a few. And, there is general agreement among scientists that there is not one, but two thresholds and that there are two major cor-responding physiological shifts: the low or first threshold and the high or second threshold. At each of these two thresholds there is a change, a shift in metabolic (think fuels) processes, a change in concentrations of lactate in the blood (lactate thresholds), an altering of total respiratory air inhaled compared with oxygen absorbed or carbon dioxide exhaled (ventilatory thresholds).
Generally speaking, the low threshold, also known as the first threshold or T1, is approximately but not precisely around 80% of one’s maximum heart rate. This is the point where blood lactate first begins to accumulate from the steady state, this is the effort when fat utilization begins to decrease, this is the intensity when there is a substan-tial increase in the absorption of oxygen compared to total inspired air. This is the low threshold heart rate number. This is the first threshold.
Move now to the high threshold, the second threshold. This is the exercise intensity at-about-or near 90% of maximum heart rate. This is the cross over point between aerobic and non-aerobic exercise. This is the intensity which is only sustainable for 20 to about 40 minutes for fit individuals. This is the point where blood lactate makes an exponential increase in concentration, this is the effort when fat utilization nearly turns off and pure glycogen is demanded, this is the intensity when there is a substantial increase in the expiration of carbon dioxide compared to total inspired air. This is T2 ,the high threshold heart rate number. This is the second threshold.
Both the low and the high thresholds are important exercise bio-markers. Both T1 and T2 have a role in training because they mark changes in the body’s response to exercise stress or higher intensity lev-els. For those just beginning exercise, avoid going above either threshold – it could be hazardous. For those training for performance, the second threshold is critical for raising your aerobic capacity, your max VO₂. The more oxygen you can efficiently process, the longer and the faster you can train and race. There are two ways to measure the first and second thresholds:
• Take a lab-quality test at a testing center, like the Heart Zones Testing Centers located throughout the USA.
• Take a field-test on your own or with a certified Heart Zones personal trainer or coach. Heart Zones has a packet of workout cards that include four different field tests for low threshold.
The first test provides more accurate results as well as more robust information. You learn more about threshold training in Chapter 18 so hand on, help is on the way. You can learn a ton from taking the lab test because it is the gold standard of endurance fitness testing. You find out your total caloric expenditure in each of the five zones, you find out the ratio of fat-to-carbohydrates that you burn; that is, if you are a better carbo or a better fat burner. You find out how fit you are comparatively – are you in the bottom 50% of your peer or age group or the top and if so where? The test costs about $160-$200 and can be done on a bike, treadmill, rower, or whatever your sport speciality.
Field tests for T1 and T2 are accurate but not precise. They are done with you and a heart rate monitor coupling heart rate data with re-spiratory response, rating of perceived exertion, and changes in your ability to speak comfortably. Field tests can be done on your own and are explained in detail by reading the free articles at www.heartzones.com/resources or by working with a coach or personal trainer who has been certified to conduct them, a Heart Zones CMS, Certified Metabolic Specialist. If you want to get the most out of your test results and the quality of the test, make sure that the lab or test center has experience with all levels of fitness enthusiasts and not just the competitive types.
More to come ..
Keep your eyes peeled as we continue to release excerpts throughout upcoming weeks. If you want to read the entire book, make sure to swing by our online store and grab a copy: The Heart Rate Monitor Guidebook.