It's easy to get confused with all the terminology cyclists throw out. Just trying to tell athletes how to complete a workout I find myself using RPM, RPE, FTP, HR, AC, LT and others. In the hope of clarifying these terms, I wrote this guide on the Cadence blog in 2007 and I still recommend it for anyone that wants a quick definition of a term they hear and don't understand.
Although this list is fairly inclusive, in the interest of being concise I didn't elaborate much on any of the terms. One concept that needs some elaboration is the concept of threshold. You may have heard the following terms:
-Lactate Threshold (LT)
- Aerobic/Anaerobic Threshold Threshold (AT)
- Ventilatory Threshold (VT)
- Functional Threshold (FT)
Do they all mean the same thing or are they all different? Well, it's kind of both.
The first thing to understand is that cycling is that it is mostly an endurance sport. In short, this means that what you can do is less important than how long you can do it for. For example, Lelisa Desisa, winner of last year's Boston marathon, finished with a time of just over 2 hours and 10 minutes. This means that he averaged 4:58 mile splits. Now, even I could run half a mile at that pace. Heck, if I trained for it, I might even be able to a full mile under 5 minutes, but I can say with 100% certainty that no matter how much I train, I will NEVER be able to run 26.2 miles at sub 5 min-mile pace! Similarly, it is estimated that Tony Martin averaged over 450 watts for an hour and 5 minutes last year when he won the World Time Trial Championships. Again, most cyclists can hit 450 watts... for a few seconds. A strong amateur can probably do it for a few minutes. 450 watts for an hour is another story.
So if it's all (or at least mostly) about how long you can sustain an effort, the next question is "What stops you from being able to sustain that effort longer?" It is here that I think back to my Industrial Engineering classes (see Mom, I'm using that degree after all!). Traditionally, Industrial Engineers look at manufacturing processes and see if they can identify "limiters" or "bottlenecks" to the system that hold it back from operating faster and more efficiently. A simple example that everyone can relate to would be a Lemonade Stand. Let's say Jack and Jill have a popular lemonade stand and customers are lined up around the block. Jill is at her booth squeezing lemons, mixing the juice with sugar and water, pouring it into cups and selling it to the customers. Meanwhile, Jack is riding back and forth to and from the grocery store on his bike to buy lemons and sugar. If enough customers come along, Jill starts to use more lemons and sugar than Jack is bringing in, so she starts to dip into her lemon reserve. Luckily, these lemons are Meyer lemons, which are sweet so the lemonade doesn't need as much extra sugar. Still, they are more expensive than regular lemons and there's only so many of them. Once these reserves are exhausted, Jack and Jill's business is going to come to a screeching halt.
If we assume that there is an unlimited supply of water and cups, here are the potential limiters to the lemonade stand:
- Lemon supply (how fast Jack can get to and from the grocery store on his bike, how much money does he have and how much he can hold in his backpack)
- Sugar supply (same as above)
- Size of Meyer lemon reserve stockpile
- Jill's lemonade production ability (how fast she can squeeze the lemons, mix the ingredients and sell the lemonade to the customers)
You've probably figured this out buy now but in my analogy, Jill is like the legs and Jack is like the heart and lungs of the cyclist. In order to operate, the muscles need a constant influx of oxygen and energy (in the form of muscle glycogen). As intensity increases, there comes a point where the heart and lungs can't keep up. Luckily, the muscles can tap into their glycogen reserves and operate without oxygen (Anaerobically) for a while, but just like the Meyer lemons these reserves are limited and once depleted... game over.
Here are the potential limiters for the cyclist*:
- Glycogen supply (how fast the body can metabolize energy and get it to the muscles)
- Oxygen supply (how much oxygen the lungs can take in and get it to the muscles)
- Size of muscle Glycogen reserves
- Muscle fatigue, strength and efficiency
*note to all you ex. phys./kinesiology majors reading this- this is vastly oversimplified so when you're studying for your next test I'd suggest reading your textbook, not just copying this.
Whenever we talk about threshold, we're talking about a "tipping point" at which the effort is no longer sustainable. Just to clarify, threshold is not the point of failure, it is the point that failure becomes imminent unless the effort is reduced or halted in order to return to a state of equilibrium. Once we know where that point is, we can train more appropriately in order to a) be more efficient below this point and b) raise the level at which it occurs. Most coaches base training zones on percentages of threshold so they can use workouts to target specific systems, thereby raising output and efficiency. How they find that point varies widely.
Let's get back to those terms again...
- Ventilatory Threshold (VT): This relates to breathing and oxygen delivery. The assumption is that with a sustainable effort (below threshold) breathing will be stable and at an unsustainable effort (above threshold), breathing will not stabilize because the body is fighting a losing battle. You start to breath harder and harder even when the effort is consistent. If you don't slow down or stop, failure will occur. Think about climbing a short (3-5 minute) hill at a very hard but consistent pace. By the time you reach the top of the hill, your breathing rate and heart rate are probably a lot higher than at the bottom or even the middle of the hill. Contrast this with riding the hill at a more moderate pace. Even if you are going a bit harder on the hill, if your pace is sustainable, HR and breathing should go up a little but then stabilize. The trouble is, testing to find VT is somewhat of an inexact science. Most tests involve a progressive ramp up of effort. For example, the cyclist rides at 150 watts for 5 minutes, 175 watts for 5 minutes, 200 watts for 5 minutes and so on. Meanwhile, breathing rate and heart rate are recorded. At some stage, heart rate and breathing ride throughout the effort instead of stabilizing. Using a machine to monitor gas exchange helps identify VT more accurately but there is still quite a bit of error involved.
During a VO2 Max test, the rider breathes through a mask. Respiration rate, volume, % of CO2 and O2 are measured to determine efficiency, Ventilatory Threshold and maximal aerobic exertion capability.
-Lactate Threshold (LT): A misconception many athletes have is that lactate (aka lactic acid) is what causes the "burning" in your muscles and forces you to slow down. Simply put, that's not true. Lactic acid only occurs on very small concentrations in the blood (0.5-12 mmol/L), so we're not exactly getting into acid for blood territory here. The only reason we look at lactic acid at all is because it is relatively easy to test for. With a small drop of blood and a portable lactate analyzer it is possible to see blood lactate concentration quickly and easily. Lactic acid is a bi-product of anaerobic energy production, so higher concentrations indicate that the effort is more anaerobic. Getting back to the lemonade stand analogy, it would be like looking at the lemon peels that were discarded. If we saw a lot of Meyer lemon peels as opposed to regular lemon peels, it indicates that Jill has been dipping into her reserves. A lactate threshold test is also a progressive ramp up test. Here though, you take a drop of blood just before the end of each stage. At lower, sustainable intensities, blood lactate concentrations tend to run in the 0.5-3.0 range. As intensity increases to unsustainable levels, lactate levels start to go up exponentially. For most athletes, a lactate concentration of 4.0 mmol/L signifies a "breakpoint", which is what we call Lactate Threshold.
Measuring blood lactate concentration with a portable lactate analyzer
- Aerobic/Anaerobic Threshold (AT): Simply put, this is another name for Lactate Threshold. Some exercise physiologists object to these terms though because they imply that the transition from Aerobic to Anaerobic is like flipping a switch. In reality most levels of exertion are a combination of aerobic and anaerobic. The type of energy used is related to the different types of muscle fibers that are used in the effort. Those that have driven hybrid cars before have undoubtedly seen the little meter that shows you how much you are relying on the battery and how much you are relying on the engine. Unless you drive around at 20 mph all the time, you can't keep it at 100% battery; most of the time you are using a combination of the battery and engine. Of course, if you put the pedal to the floor you will notice your miles per gallon gage take a free fall. So the correct question is not "When does the effort go from aerobic to anaerobic?", it's "When is the effort no longer aerobically sustainable?". Below threshold, as long as you are taking in enough fuel and water, you should be able to maintain an effort indefinitely (muscle efficiencies aside). Above threshold you are fighting a losing battle and the further above threshold you are, the faster you reach the point of failure.
The Hybrid System Indicator gauge on a Toyota Prius. When the gauge is below the middle line, the car is running on battery power alone. When the gauge is over the line, the power comes from both battery and engine.
- Functional Threshold (FT): Functional threshold is an all-encompassing term. While VT focuses on oxygen and LT focuses on energy production, the premise of FT is that it doesn't matter what causes the bottleneck, only that there is a bottleneck. Functional Threshold is defined as the maximal effort you can sustain for 60 minutes. By looking at what you can actually do rather than examining physiological metrics, it doesn't matter what the limiter is. It's as if instead of calculating lemons in vs. lemons out or sugar in vs. sugar out we just told Jack & Jill to serve as many customers as possible in 60 minutes and measured that. The basic assumption is that 60 minutes is enough time that failure will occur if the effort is unsustainable.
There are 2 main problems with this method: 1. How do we know you that it's really a maximal effort? 60 minutes is a long time and for many athletes extremely high motivation is required for such an effort, especially if it's just for the sake of a test. But if the athlete hold's themself back because they are afraid of the pain or out of fear that they might blow up, it's not really a test of maximal exertion is it? 2. Not everyone has the muscular strength and efficiency to complete a 60 minute TT. Even many well trained elite cyclists aren't able to do it, even if motivation and pacing aren't issues. Most bike racers, unless they are 40K TT or long hill climb TT specialists, simply don't train for that type of effort and it would be a waste of their time to do so.
So is there an easier way to estimate FT? Yes, in fact there are a number of ways. 1. Most trained cyclists can complete a 20 minute time trial effort. We can assume that a cyclist can maintain 5% higher power and heart rate for a maximal 20 minute effort than a maximal 60 minute effort. A 20 minute effort isn't short, but it should be long enough. Now there is evidence that some cyclists will over-estimate their FT using this method. As a result, some coaches recommend a maximal 5 minute effort before the 20 minute effort, but in my opinion this is not necessary for most athletes. Another way to approximate FT would be to look at Normalized Power from a 1 hour maximal variably paced effort. This might be appropriate if you don't do any 40k time trials but you do a lot of really hard 1 hour criteriums or group rides where you are close to the point of failure. By looking at normalized power instead of average power, it is possible to take into account the highly variable nature of the effort.
Once threshold is established, it really comes in handy for doing your workouts better. Here is a chart I made up that shows percentages of FTP (Functional Threshold Power) in real numbers:
Percentages of FTP for various FTP levels. The right hand column, RPE, is a rating for perceived exertion from 0 to 20, with 0 being lying in bed at rest and 20 being sprinting as hard as you can with no regard for pacing.
Here is the same chart for various FT HR (Function Threshold Heart Rate) values. Heart rate is an imperfect measure of exertion in many ways (varies greatly from person to person, inherent delayed reaction to changes in effort, greatly affected by heat, hydration and fatigue) but it can still be very useful. Once you know your FTHR, it won't change much at all. For example, if you know your FTHR is 170, it will be 170 whether you are in great shape or horrible shape. One of the difficulties with training by power is that FTP can change quite quickly. Of course, the other big advantage to training with Heart Rate instead of Power is that you can buy a heart rate monitor for $20. A reliable power meter will probably cost you at least $800.
Percentages of FTHR and RPE for various FTHR levels.
Even if you don't train with power, it's important to think about what threshold feels like. Being able to pinpoint the changes to your body at each small step along the way towards threshold, at threshold, over threshold, way over threshold and as far over threshold as you can get without it being a sprint will help you train better and race better. As the philosopher Plato once said, "The first and best victory is to conquer self". The first step towards conquering yourself is knowing yourself.
Colin Sandberg is the owner and head coach of Backbone Performance, LLC. He is a Cat. 1 road racer, a USA Cycling Level II coach and a UCI Director Sportif. He is also head coach at Young Medalists High Performance and race director for Team Young Medalists. If you have questions or comments, feel free to use the comments section or email us. Thanks for reading!
Post-Publication Addendum:
After publishing this I received a note from Andy Coggan (who is literally the authority on training & racing with power meters) on my Facebook Page correcting my imprecise definitions of Functional Threshold and Lactate Threshold. Specifically, this is what he said:
"I highly commend you for attempting to bring some clarity to an often-confusing area (esp. since some seem intent on intentionally muddying the waters). If I might make a couple of suggestions in furtherance of that goal: 1) FTP is not and never has been, defined as the power that you can maintain for *exactly* 60 min (or even exactly 40 km, for that matter). 2) While some occasionally refer to an exercise intensity corresponding to a fixed blood lactate concentration of 4 mmol/L as "anaerobic threshold", it is more commonly known/recognized as OBAL (for onset of blood lactate accumulation...which really represent the onset of *continual* blood lactate accumulation, at least on average)."
Let me address these 2 things:
1. RE: Functional Threshold Power. The true definition of Functional Threshold Power, per "Training and Racing with a Power Meter" (which Andy co-wrote with Hunter Allen) is "The highest power that a rider can maintain in a quasi-steady state without fatiguing for approximately one hour". "Quasi steady state" means that the effort is relatively consistent. For example, if I have an FTP of 300 watts and I start off my 60 minute TT at 400 watts the first 3 minutes, chances are my final average for the hour will be far less than 300 watts. Poor pacing aside, if I decide to go harder on the uphills and recover on the downhills of a hilly TT course, I might end up with a faster time but a lower average power. The "quasi" only means that no effort on the bike is truly steady state, there are always at least some minor power fluctuations. "Without fatiguing" means that if a rider goes above their threshold, they will fatigue much more quickly. "Approximately one hour" means that there's nothing magical about exactly 60 minutes, it's just a time period that we generally agree is sufficient in determining if the effort is sustainable or not. Does it matter if you use a 55 or 65 minute effort instead? Not really. For more on this, check out this article that Andy wrote in 2008.
2. RE: OBLA. The point Andy makes here is that to call the point that a rider reaches 4.0 mmol/L of lactic acid (AKA OBLA or onset of blood lactate accumulation) in a progressive ramp up test "Anaerobic Threshold", which I said was the same thing as "Lactic Threshold" is somewhat inaccurate. First of all, it is not universally agreed upon that 4.0 is the right number. Many exercise physiologists prefer to look at the graph (power vs. lactate concentration) and identify the point at which the curve changes from a linear rise to an exponential rise. In my experience, this is quite difficult and imprecise. If you have 5 different people picking this point, it's very possible that you might get 5 different answers. The advantage of 4.0 is that it will be picked the same way every time. The reason lactate testing has been so widely used for so long is because there is a very good correlation between OBLA and endurance performance ability. That said, "good correlation" doesn't mean that it works for everyone. When I used to administer a lot of lactate threshold tests, I would often see riders that did a lot of high intensity/short duration training (I.e. hill reps, hard group rides, sprints) but very little moderate intensity/longer duration training (i.e. endurance & tempo rides, 10-20 minute threshold intervals). With many of these athletes, LT/OBLA results would usually predict a much lower threshold wattage than a 95% of a 20 minute TT effort or by looking at Normalized Power for a really hard hour long effort.
Thanks again Andy for your suggestions. Feel free to comment any time you like!