You've finally decided to conduct a field test and teach your students about threshold-based training. Your first field test went great, you've been training for awhile with the new numbers. And you're about to do your first re-test. Now what? How do you interpret the results? How do you answer your students' questions? What if their heart rates don't increased? Does that mean they haven't improved fitness? This article will be quite long so I will answer this in two sections. Part 1 will suggest how to interpret subsequent HR field tests. Part 2 will look at the results of power field tests.

ICA member Sharon recently emailed me with some questions about retesting. Sharon owns a small studio with 9 bikes and has done threshold testing on everyone. They are approaching the first time they will retest, after training with their heart rate zones for three months. Sharon asks:

What is it that I will be looking for? Does the number change or can they just do more at that same number? So confused, please help. 

I am assuming that Sharon did a field test to estimate lactate threshold heart rate (LTHR), and not a threshold functional power test (FTP). However, I am going to answer this question for both scenarios because the answer is slightly different for each one. Today's answer is on heart rate and what you can interpret from subsequent retests. Later I will address how to interpret subsequent testing when using power.

LT Heart Rate

First I want to reiterate a point. A 20-minute or two 8-minute field tests are reasonably reliable means to estimate lactate threshold heart rate (LTHR). I always make sure I remind my students that we are estimating LT, we are not actually measuring it. Lactate Threshold implies that you have measured the lactate itself. This is done with a device that measures actual blood lactate while you are performing a graded exercise test. Metabolic tests are supposedly measuring anaerobic threshold, though some physiologists do not like the term anaerobic threshold because there is no "thing" called an "anaerobic", so how can it have a threshold? Anaerobic is a state, not a "thing" (See? It's even hard to describe!) Ventilatory threshold (VT) is closely associated with LT, though it is a separate physiologic occurrence.

Field tests have been found by exercise physiologists and coaches to correlate very well with the effort level at LTHR. But, there is a definite learning curve when taking field tests. The very first time a rider participates in a field test, there is often trepidation. Questions and doubt pop into their heads, like "will it hurt?" "what if I can't make it the whole way?" "I'm not good enough." "I'm not fit enough."

Once they've experienced their first test, they know what to expect. These tests are never "easy", but some of the fear dissipates. Often after the first test, they realize that they could have gone a little harder.

It's also important to remember the potential variability with heart rate. Heres a reminder of some of the things that may or may not affect one's heart rate on any given field test day:

• dehydration
• heat/humidity
• lack of sleep
• acute or chronic fatigue
• stress, both acute (as in fear, or worry about the test) or chronic (due to a whole host of possible causes from personal to exercise related)
• overtraining (can depress or increase HR)
  
• medications
• caffeine
• and more...
  

We try to minimize some of these things by keeping as many conditions the same from test to test, but we (us, as instructors, as well as our students) don't always have control over some of these things. These things may affect one's first test, or the second test or anytime we take a test, so it follows that one is not always 100% sure of how one might have done in the absence of that variable.

Retesting

In my 12-week periodized programs, I usually schedule three field tests, one at the beginning, one half-way through and one at the end. One of the reasons for that middle test is to minimize the learning curve. Any increase in HR between the first and second tests is not likely to indicate with any kind of certainty that it was due to fitness improvement. It may be, but it also may be entirely due to knowing what to expect and having the mental ability to push longer and harder. That in itself is a benefit, but in the absence of power meters, we really don't have any idea whether they actually improved this metabolic marker or not. What if they were stressed, dehydrated, or fearful the first time around and then just got it better the second time?

When you do your first re-test, before you even start the test, it's important to let your students know what to expect with the results. I always tell them early on that they may not see an improvement in their field tested LTHR estimate, but that does not mean they haven't gained fitness. Here is my typical announcement just before the second field test:

Welcome to our second field test. Do you remember how you felt last time we did this? Some of you might have been a little fearful or worried, but you all survived, didn't you? It wasn't easy, not in the least, but it also probably wasn't as scary as you might have thought. You all did great! We were able to come up with a meaningful set of numbers for you to train by. For some of you we had to tweak those numbers a little bit in the weeks that followed as we validated your test.

Most of the hard work in this 12-week periodized program is in the second half of the program. The past 5-6 weeks have been spent more in Zones 2 and 3, with a few forays into Zone 4. Those workouts have been designed to cause adaptations that improve aerobic development, muscular endurance, leg speed and force development in those leg muscles. The workouts so far have not been designed to raise your threshold. So if we were able to test your power output chances are you wouldn't see a huge increase in your power at threshold (unless you were really starting from a place of low fitness). Now if your first field test 6 weeks ago was an accurate assessment of how hard you could push yourself for 20-minutes and you weren't fatigued or stressed or hesitant, then likely, you won't see much of an improvement in those heart rate numbers today. On the other hand, if you do see an improvement today, it might be simply because you have more confidence in yourself and don't hold back out of fear. And that's a good thing. It will give us more accurate numbers with which to train for the rest of this program.

Please remember, in the absence of a quantifiable measurement like power, we really do not know for sure. Heart rate is too affected by other variables. However, what I can tell you is that these next 6 weeks of this program, we will be doing workouts that are designed to improve your threshold. They will be much harder than the past 6 weeks, and they are extremely effective. I still must warn you, that you may not see a HR improvement when we do our final re-test 6 weeks from now. But that doesn't mean you will not have improved - the amount of power that you can put out at that same heart rate might improve significantly - but we don't have power meters to measure it. You will feel it though - it will be anecdotal. You will feel that sense of "wow, I can go longer, and harder than I could before".

Yes, that's a long speech, but they need to hear it!

So when I do the third field test, I remind them of what I said about not really knowing with 100% certainty whether any increase will be due to an actual improvement in LT. Now that they have gotten over the learning curve and fear, and now that we have been training harder and harder, with longer and longer efforts at (or above) threshold, there is a chance that some of them might see a difference. This is especially true of the ones who were less fit to start - they had a longer way to go with their fitness. Be aware that your long time stronger cyclists may not see a difference in LTHR; it is those riders that would benefit more from the power meters, because it may very well show that their LTHR hasn't increased, but their power at threshold has.

Here is a an example of my speech a few days before my third field test:

If you do not see an improvement in your LTHR today, do not be upset with yourself. You know in your heart if you've been committed and working the program properly. You can feel it in your heart when you know you are stronger, more fit - those hard hard workouts don't suck quite as bad as they used to! Suffering is an inevitable part of cycling, and even the best and most fit athletes in the world still suffer. But as you get more fit, you can go just a little longer, a little harder before that sufferfest begins! You can test yourself on a climb outside - if you can ride up it faster than you could before while staying at or below your threshold, then you have improved your power at threshold. 

There IS a chance, however, that some of you might see an increase in your estimated LTHR. Will we be able to say "hey Mary! You HAVE raised your lactate threshold!"? Maybe yes, maybe no. Again, without power we cannot be 100% sure. BUT....if you make sure you are rested, and hydrated, and prepared for that final field test, if we try to keep as many things constant from test to test, then yes, at some point we can say, "Hey, Mary, you consistently test at a LTHR that is 6 heart beats higher than you used to. We know you have trained consistently and wisely and progressively. So, I think we can safely assume that you have bought yourself about 5 or 6 more heart beats before your body makes that switch to predominantly anaerobic metabolism. And THAT is a very good thing"!

So, as you can see, you still cannot promise them that an increase in their HR is due to an increase in LT without the quantifiable proof of power. However, that being said, I trust increases in LTHR after the third test more than I do after the second test simply from the learning curve standpoint. In this way, the second test serves as a way to re-establish a more realistic baseline.

For those who do not see an improvement in the third test, and who seem upset about it, make sure to praise them, empower them, and remind them how much they have worked. Assure them that if they know that they have done the work correctly, then their power at threshold will undoubtedly have improved.

For those who do show an increase in their HR, and you know they have tested at least twice or more prior to that, and you know they have been consistent, and especially if they were starting from a place of low fitness (yes, a lot of qualifiers, I know), then it IS possible that their LT has improved. Improvement can range from 3-8% (a few beats are not statistically significant, remember, it is an average, so there is a margin of error). The higher the improvement, the lower the fitness at which they were likely starting. A more seasoned cyclist, as explained above, is less likely to see a size-able increase in LTHR.

I'll use myself as an example. I've been doing 20-minute field tests like these for a long time. I usually range from 157 - 161. Early in the season I'm closer to 157, and when I am more fit and after a solid training program, I am usually closer to 161. With this history and pattern, I can safely assume that I've increased my LTHR from the 157 to the 161 (~3%). Could I take it higher? Probably not much. The highest number I've ever seen on my HR monitor (about 5 years ago, and I thought I was going to die) is 176, so 161 is approximately 92% of that. There is a physiological limit to how high one can raise LTHR, but with even more focused training (from quitting my jobs and taking up cycling as a career!) I could most definitely significantly increase my power output at that particular threshold heart rate.

Does that make sense?

Let me get back to Sharon's question and her scenario with her group. They have been training for three months and they are about to do their first retest. She doesn't have the benefit of that middle test, which serves as a tool to redetermine a baseline and minimize the effects of the learning curve. On the other hand, they have probably been working harder in these recent weeks, doing workouts designed to improve threshold, such as longer threshold intervals. Therefore, it is possible that their training program would have indeed increased their LT, or at least their power at LT. All of the logic that I've explained above still applies, so be sure to explain to them what an increase in their LTHR may or may not mean.

And then next time you do this program, Sharon (and everyone else) make sure to include three tests (beginning, middle and end) to minimize the effects of that learning curve.

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