Observations On Threshold
Sunday, February 19, 2012 at 01:22PM 
Ben Parsons givin' er at Jackson - photo: Mark GockeIntervals. The very thought of the word makes my pulse rise. From my first exposure to them as a 14 year old swimmer to my weekly date with them now, intervals inspire varying degrees of pain and satisfaction while preparing me to perform at my best. If you want to go fast in an endurance event, there is no substitute for regular exposure to high intensity training. While I maintain that the bulk of one's training should consist of relatively low intensity effort for reasons best covered by Mark Twight here, twice-weekly bouts of threshold or higher work prepares us for competitive effort. Zone 2 training may lay the aerobic foundation but zone 4 and 5 efforts are what bring out our best performances.
There's more than one way to skin this intensity cat. Athletes and coaches alike spend lots of time thinking of ways to structure these efforts and get the work done. Many athletes obsess about rest/work schemes. After all these years, I'm not sure that little differences matter all that much.
More rest, higher work intensity, less rest, more pain, long, short, pyramids, etc. They all stress our physiology in ways that bring about adaptation which allows us to go faster. On the other hand, I have come to believe that longer intervals (20-40 minutes) are valuable in sports that require lengthy threshold efforts (skimo and MTB). Other than that, break them up as you like. Vary the mix from week to week and try to stay entertained. But the pain will be there and it must be faced head on, regardless of the structure.
As a target event approaches (1-3 weeks out), paring down the work interval and increasing the rest will keep your efforts sharp and fatigue at a minimum. The right mix and volume likely varies from athlete to athlete. Cookie cutter recommendations offer a place to start but probably stray from each individual's ideal. Trial and error are the way.
Earlier this winter, as I prepared for the National Skimo Championships in Jackson, I made some observations about interval structure and my response to them that I want to share here. It raises some questions to which I don't really have an answer but thought that putting it out there may yield some insight from readers (MFT? WW? You out there?).
Nothing earth shattering here but simply some thoughts about the appearance of two HR graphs from two different threshold-type sessions. Both workouts took place on the same stretch of terrain on Snow King ski hill in town. Basically, the "loads" were similar. Ski gear was the same. Heart rate is measured using a Suunto T6 wrist computer and downloaded to Movescount. My speed is unknown as I did not track overall time over the distance. But my HR response is nearly identical. For what it's worth, the efforts "felt" the same. I know, a nearly worthless statement but... whatever.
The first involves a steady state effort at threshold. As you can see, my HR ramps up predictably and is maintained relatively constant through the duration of the bout. 
A second effort reveals the same response. A couple of sharp spikes in HR are the result of brief supraventricular arrhythmias, probably stemming from catacholamine release during the hard interval. As long as these are brief and not symptomatic, there is nothing for me to worry about.
The second graph is the result of a similar length effort but done as a series of 30 seconds hard, 30 seconds easy efforts. Initial HR response rises more slowly but then is maintained throughout the bout. Small dips in HR are seen giving the graph the sawtooth appearance.
At a glance, the trends of the graphs are nearly identical.
So, with two essentially identical HR responses to two exercise bouts, can I assume that their impact on my physiology is the same? I honestly don't know. I will say that the effort during the 30/30 is of higher quality. However, I use a different movement pattern to drive HR up during the short work interval. This certainly has a different motor patterning impact on technique. This style of "running" is similar to what we do for the first 30-40 seconds of a race but not something sustainable after that.
One could ask if it's worth "practicing" this type of pattern since it's not the one I will use for the majority of the race. I don't know. The movement pattern is one used at the start of events and I have broken into it during flat sections of climbs or charging into transitions. It has merit. But, really, I use it in the 30/30s due to its higher metabolic demand. Plus, it's kinda fun.
The other part of this equation is the "power output" of the different stride patterns. If we had power meters like cyclists do I think my wattage would be higher with the running style stride. This certainly creates a different physiologic demand, even at a short duration, than the more sustainable stride pattern. How this impacts overall conditioning is unknown to me.
For now, varying these motor patterns on the way to creating metabolic stress simply feels right to me. It also breaks up the monotony of training. Both of these are worthy psychological factors that probably have a positive impact on my overall preparation. Hard to really know for sure. Other opinions welcome. - Brian
intervals, skimo, suunto, threshold in Skimo Training
Reader Comments (10)
Regarding the arrhythmias, are you sure they are ventricular? I would think more likely short bursts of SVT.
You're absolutely right. My mistake. These little ectopic hits are almost always supraventricular. Seems to me I've seen PACs, as well, before exercise bouts.
Thanks for keeping me straight.
Lactate.
Completing a steady state interval for 15min would indicate that you were never going over threshold. If you had measured, odds are you were 4mmol lactate or under the whole time. If you are doing the 30/30s right you should be going over threshold then recovering over and over again. Say hitting 6mmol after the work half and dropping back to 3 in the recovery half. You are basically spiking your lactate every time, thus forcing your body to clear more total lactic acid. Heart rate doesn't respond instantaneously, so the graphs look like you are doing a lot more similar workouts than you really are. Longer work and rest periods would make the differences on the heart rate graphs more apparent, but would become a different training stimulus.
I guess a good analogy would be lifting weights. If you were to do three sets of five reps with 100kg you would have lifted a total of 1500kg. If you did one set of thirty reps with 50kg you would also have lifted a total of 1500kg. So the total workload would be similar at first glance, but in reality the training effect would be far different.
Tyler,
Good analogy and one not lost on me. I guess my question, then, and still is, whether exposure to 6 mmol of lactate has merit for a skimo racer. There are many who believe that too much of this stuff "damages" the aerobic machinery and this has been born out by many athletes in several sports during periods of coaching style variations. When intervals became popular in distance running, American performance on the world stage dropped into the toilet. Moving back to volume and a more selective use of intensity has created a resurgence of American runners at the elite level. Fascinating.
My hunch is that the above threshold "teasing" that goes on is useful in careful dosings but I don't know how much. I do know I love the way they feel. There is a crispness in movement that is possible with frequent rest bouts that you just don't get at steady state.
Thanks for your input.
Well, that's where the rubber really hits the road, isn't it? We know that racing is painful and that it is so because we toy with our LT throughout a moderate-length (2-4 hours) endurance event. So we conclude - appropriately - that if we can bump up our LT while simultaneously training our body to oxidize substrate more efficiently, we'll increase our capacity to go harder for longer. And, since man is a pattern-seeking machine, we then conclude that more harder training is the key. The implied equation might look something like this: P = C(V*S/R), where P: pace, C: constant, V: volume, S: stress (intensity) and R: recovery. The question being... what is the constant? At some point, as Brian points out, the equation ends up with a negative value for P, at least on a trending basis if you are plotting the values for P. Not that this answers Brian's question, of course, but it is a frame for my next point.
It is NOT about lacate accumulation. Therefore, intervals that appear to increase the "lactate buffering" capacity of the body may not actually accomplish what we think they accomplish. I'm not a PhD in this subject, but I'll try to summarize:
The development of acidosis during intense exercise has traditionally been explained by the increased production of lactic acid, causing the release of a proton and the formation of the acid salt sodium lactate. On the basis of this explanation, if the rate of lactate production is high enough, the cellular proton buffering capacity can be exceeded, resulting in a decrease in cellular pH. These biochemical events have been termed lactic acidosis. The lactic acidosis of exercise has been a classic explanation of the biochemistry of acidosis for more than 80 years. This belief has led to the interpretation that lactate production causes acidosis and, in turn, that increased lactate production is one of the several causes of muscle fatigue during intense exercise.A review of recent literature, however, presents clear evidence that there is NO biochemical support for lactate production causing acidosis. Lactate production retards, not causes, acidosis. Similarly, there is a wealth of research evidence to show that acidosis is caused by reactions other than lactate production. Without getting over my skis here, it is only when the exercise intensity increases beyond steady state (sub LT) that there is a need for greater reliance on ATP regeneration from glycolysis and the phosphagen system. The ATP that is supplied from these nonmitochondrial sources and is eventually used to fuel muscle contraction increases proton release and causes the acidosis of intense exercise. Lactate production increases under these cellular conditions to prevent pyruvate accumulation and supply the NAD+ needed for phase 2 of glycolysis. Thus increased lactate production coincides with cellular acidosis and remains a good indirect marker for cell metabolic conditions that induce metabolic acidosis. If muscle did not produce lactate, acidosis and muscle fatigue would occur more quickly and exercise performance would be severely impaired.
So, with all of this in mind, I'd suggest that the benefit of the 30/30 intervals is that you train the body to more efficiently produce and metabolize lactate... and that these intervals introduce an enormous metabolic stress load which, over time, can measurably undermine the very energy delivery systems an athlete is attempting to train.
This is why it is so damn hard to remain "race fit" or to maintain a peak, for more than a 3-6 weeks (depending on one's overall training volume and programming). An athlete must do supra-LT intervals to trigger the adaptations necessary for peak output, but those same intervals eventually corrode the energy delivery systems which permit peak output.
So, yes, I'd say that these kinds of intervals are absolutely critical for race "sharpness" for all the reasons Brian outlines in his post. But they must also be treated with an enormous amount of respect. Which is nearly impossible for most competitive athletes because the short-term results from intervals like these is so damn seductive: they make you fast, so you want to do them all the time, and presume that if you just keep doing them, you'll get even faster.
Nope. There is no free lunch, and trees don't grow to the sky.
Great post, man. Flame away.
Nothing to add, just wanted to say, great post and great comments.
a skimo blogger hurrah. Gradually working my way through these blogs as i recuperate from foot surgery hopefully in time to get fit for next winters season. Particularly liked this rant as often debate with myself as to which type of interval session to do when and as am 45 but still getting faster I know i need to be more clever and sciency. I think if your racing requires short bursts but not much overall in the grand scheme of things then thats what ought to be reflected in your training. So yes do some short intervals to replicate starts and even finishes but not much of the overall volume unless like me this is where you really suck in which case best to do a bit more of it.
Quick question are your HR zones for skimo the same as those for biking and running?
a skimo blogger hurrah. Gradually working my way through these blogs as i recuperate from foot surgery hopefully in time to get fit for next winters season. Particularly liked this rant as often debate with myself as to which type of interval session to do when and as am 45 but still getting faster I know i need to be more clever and sciency. I think if your racing requires short bursts but not much overall in the grand scheme of things then thats what ought to be reflected in your training. So yes do some short intervals to replicate starts and even finishes but not much of the overall volume unless like me this is where you really suck in which case best to do a bit more of it.
Very thoughtful and useful analysis and comments -- will try to build into my training program