Fatigue Curves

by Alan Couzens, MS (Sports Science)

As long course athletes, we have some unique fitness requirements when it comes to race day performance -- requirements that may or may not be accurately expressed by the plethora of short duration fitness tests that fill the popular training literature: Functional Threshold Tests (that we abridge because the full 60 minutes hurts too much J), CP5s, VO2max tests, VDOTS, Lactate Threshold tests, etc, etc. While these tests are a good indicator of how fast an athlete is, they don’t deal very well with the other element of the ironman performance equation -- endurance. Put another way, how long can the athlete hold a given speed/percentage of his or her max fitness?

Gordo wrote an article about this key limiter some time ago in his piece on training in the fourth dimension. He concluded that, “If you are experiencing significant fade (power or pace) then you are endurance limited (regardless of what your FT performance indicates).” This article will be about how to go about quantifying just "how limited" you are when it comes to endurance for your respective event. In my previous series on "what it takes" I concluded that finishing an ironman requires pretty modest fitness but very good endurance. Similarly, winning an ironman requires very good fitness coupled with superior endurance. So let’s delve into this a little more, what constitutes good, bad or superior endurance?

Coaches such as Joe Friel and George Dallam have looked at this problem of quantifying endurance in some depth. Dallam’s concept of the athletic fatigue curve is a useful way of expressing the relative endurance strengths and weaknesses of two athletes who may have the same short term numbers. Simply, a fatigue curve looks at the rate of pace/power degradation over increased duration in a given athlete. A couple examples from two athletes that I currently work with are shown below (click to enlarge):

Power (in watts) is expressed on the y-axis. Duration (in hours) is expressed on the x-axis. Athlete 1 is a middle of the pack age-grouper (IM best of 12:23) with better than average results over sprint and short course races. Athlete 2 is an established long course athlete -- a Kona qualifier with an ironman best of 10:03.

As you can see, in addition to exhibiting significantly different long course results, these two athletes also exhibit different fatigue curves, with Athlete 1 leading the way through to ~20 mins and Athlete 2 taking over at that point and widening the gap as the duration increases. If we were to compare these two athletes at FTP (one hour duration), very little difference is shown (about 7 watts; 283 versus 290W). However, if we look further down the curve, the difference at six hours increases to about 50 watts! Same aerobic power but significantly different aerobic capacity.

You’ll see the formula for the best fit equation in the top right hand corner of the diagram. Athlete 1 exhibits a fatigue index of -0.151, while athlete 2 exhibits an index of -0.109. An easier way to express these differences may be in the form of percent fade. Athlete 1 loses 10% power as the duration doubles. Athlete 2 only loses 7%. Despite very similar FTPs, this difference in fade has marked implications on each athletes respective Ironman race performance!

So, what’s a good level of fade?

For a long course athlete, the answer would be as little as possible. However, this may not be the case for athletes who race over a shorter duration, where a fine balance of aerobic and anaerobic capacity is required. Here are some typical numbers for different athletes/events:

Obviously, these numbers speak to the level of aerobic basework required for different events. Even a 1500m runner requires substantial fatigue resistance to complement their speed/anaerobic capacity in order to be successful. Likewise, an elite sprinter requires more than pure 100% sprint training. A certain work capacity is a pre-requisite before the specific training hits full speed.

To put these numbers into better "iron-perspective," in order to hold AeT intensity (approximately 60% VO2max) over the course of a 10 hour ironman requires a fatigue rate of better than 8%. Until the prospective ironman athlete has reached this level, there is little cause for specific preparation designed to raise the VO2max or FTP. For most athletes there is much greater upside in minimizing the swing at the end of the curve. Put another way, from our first example, Athlete 1 would need either a (massive) 75W increase in VO2 watts (~1L/min!) or a (measly) 3% shift  in the fatigue curve to create the same 10 hour power as Athlete 2.

Okay, so maybe ‘"measly" is a bit of an over-statement but the salient point is that while for many already well trained athletes, an increase of 75 watts may be a pipe dream, an improvement of 3% in the fatigue curve over multiple years of basework is bordering on expected. Coyle, et al. (1988, 1991), showed differences in one hour TT performance and LT relative to max power output indicative of a 6% change in the fatigue curve (improving from 10% to 4%) when comparing new cyclists (2.7 years) with those cyclists with a 10 year training history. On the other hand, the difference in VO2 power between the two groups was only in the range of 25W!

Hopefully this article has helped to answer the question of what "type" of fitness you most need. By looking at individual fatigue curves in the context of the athlete’s ability and event, we can readily determine potential weak spots that may help to guide the upcoming phase of training. With very few exceptions, most long course athletes have significant upside to building more base.

Train smart

Heart Rate Profiles Tue/Wed Nights Races

Raced a TT on Tuesday night coming 3rd so quite pleased.  Wed night was a lap XC race at Nevis Range.  Pretty hardcore with really steep freeride on the downs and quite a kick in the up's.  Quite a difference when you look at the HR profiles.  Tramlining on the TT showing form, and big peaks and troughs in the typical XC  profile. The XC's are testing in this respect, but as I have dropped down to 67 kg from 70kg I am tearing up hill and feeling really strong. Not sure where I came as came home quick due to midgies, but I have a feeling I did ok.  Next XC is in July venue TBC.  I have an inkling that we could work out a track at lower Glencoe Mountain by using the West Highland Way out East then up to the old track and back to the chairlift for a lap race so will need to investigate. Endurance road ride tomorrow then need to think about the next big event.  Maybe the "Chain Reaction" Sportive followed next day by the 100 mile MTB at Selkirk.

Fitness-Constrained vs Fuel-Constrained

by Alan Couzens, MS (Sports Science)

You know you’re fuel constrained when….

• You take a bottle of Gatorade with you for your trip to the mail box
• You "hit the wall" in a 50 meter swim race
• Your top tube starts looking like a Vegas buffet…

If any of the above resonate with you just a little bit you might be an athlete who is more "fuel-constrained" than "fitness-constrained." You will often hear the coaches tossing around these terms so I felt it prudent to do up a little article explaining what we mean by this in a little more depth.

An average-sized athlete will have 2000-3000 kcal of stored glycogen within their muscles and liver. Once they use up this energy store, the body must operate almost solely from the combustion of fat, which it can do but at a very slow rate. One could think of it as the difference between throwing a piece of pine wood on the fire versus a piece of coal.

Furthermore, the brain depends solely on glucose as its fuel supply, so when the body starts running short on glycogen/glucose, folks can start acting a little cuckoo -- disoriented, poorly coordinated, slurred speech, etc. We’ve all seen pictures of this on the Kona finish line. If glycogen starts getting low, most of us will ease up before we get to this point of meltdown and will give in to the experience of low energy/motivation that accompanies low blood glucose.

Because of this fact, sometimes it’s hard to determine just what the cause of slowing down late in a longer race is. Many athletes will just feel like they don’t "have it" during the run and will attribute this to a lack of general fitness or the need to HTFU. In reality, the interaction between physiology and psychology is complex and a bit of self-talk and a positive mantra won’t cut it over the long term when blood sugar starts to fall.

And so, we’re left with a situation in which the athlete must meter out his glycogen stores over the race duration in order to arrive at the finish line at the appropriate pace and, more importantly, on his own two feet. Going back to our hypothetical average athlete toeing the line with 2000 kcal worth of glycogen in the tank, the question becomes, how long will I last? At the typical high efforts associated with a sprint- or olympic-distance triathlon, an average-sized athlete may find himself putting out 250-280W or 900-1008 kj/hr. Assuming normal economy numbers, this is equivalent to 830-930 kcal/hr. In other words, if most of this energy comes from glycogen (as it does at very high intensities) he’ll be done in a little over two hours. Thus, for competitive age group athletes, races up to an olympic-distance tri can be considered a fitness-constrained rather than a fuel-constrained event, as the athlete is somewhat likely to cross the line with a little gas in the tank.

So, if the athlete isn’t running out of fuel, what causes him to slow down? The fitness variable that prevents the athlete from going faster in this case is the accumulation of lactate. In other words, athletes who are not limited by their fuel stores are constrained by how high their maximal lactate steady state or "threshold" is. While having reasonable metabolic fitness is important to olympic-distance racing (and to athletes' general tolerance to training load), it is athletes' threshold numbers that separate the sheep from the goats.

Stepping up a distance to the half ironman, things get a little more variable. At similarly high power outputs of approximately 830kcal/hr at 250W for four or more hours, it takes a pretty special athlete to not be metabolically limited. In the longer races, athletes can expect to get 240kcal/hr from "on course carbohydrate," but this still leaves them about 500kcal/hr short. Unless they’re going under four hours (for a total endogenous output of 2000kcal) fat oxidation is likely to come into play. Much less so for a small, fast athlete, but for a larger, more powerful athlete it can become a key limiter to racing fast in a half ironman.

Finally, stepping up to a full ironman, just about everyone -- even the elites -- is fuel constrained. Even if we use the same output -- 250W/830kcal/hr for an elite ironman race, the writing is on the wall when it comes to running out of carbs. If an elite ironman wants to meter 2000kcal of reserves over eight hours, even with an "on course" carb contribution of 240kcal/hr, this still means that he can only dip into the reserves for 2000/8 = 250kcal/hr. This leaves the athlete about 240kcal/hr short meaning he must generate greater than 4kcal/min from fat. Now, this is assuming a pretty small athlete in a Boardman like position to be going anything close to eight hours on 250W. You can imagine the situation for bigger athletes!

I ran some numbers on the sort of output that Lance Armstrong would be forced to put out in order to be competitive in Kona for a recent Inside Triathlon piece written by the G-man. As a bigger athlete, with an obvious bike strength, I hypothesized that Lance would be putting out over 1000kcal/hr on the bike. Even as a bigger athlete, likely starting with glycogen stores closer to 3000kcal (about 360/hr) and with on course carb contribution of 240-280kcal/hr, this still leaves him being forced to generate 400+kcal/hr or about 7kcal/min from fat. While not impossible, these numbers are freakish in a different way to his freakish threshold power of 6.7W/kg. While Lance can generate almost 50% more relative power at threshold than the bulk of elite ironman athletes, this type of fitness is not specific to ironman racing. Lance would be moving from an event that is fitness-constrained to an event which is fuel-constrained.

When it comes to "key limiters" in ironman racing, understanding what category you fall into -- fitness-constrained versus fuel-constrained will go a long way towards directing you towards the most effective training for your personal limiters.

Train Smart

Mamore Lodge Hill TT

Mamore Lodge: Hill Climb Challenge - Road Bike  

Gearing:  Chainset 50/34 on an 11-26 Cassette

Distance: 1 mile - Time 10 min - VAM 3,428 ft/hr

Loch Eil 25 Time Trial

Last nights TT was in very good with almost perfect conditions. My excuses for not for not doing too well being that I trained hard on monday thinking that I wouldn't make the TT as I wasn't sure if one of my older kids would be off work to look after Rebekah.  Despite being tired I did ok and I am pleased with my HR/Speed profile which ran in parallel.  The little extra up to my normal TT heart rate of 95% would have given me under the hour for 25.  Maybe next time.  Need to sort my watch as the distance ERTRO is out.

When It All Goes Wrong

Nice sequence of pictures from the 4 X finals at the UCI World Cup Nevis Range last weekend, when Sarsha Huntington crashed badly. Paul Roe off the mark fast to the scene. Apparently she can't walk due to holes in her legs from the brake levers, and many cuts and bruises but, nothing that won't heal in time. It's worth a click on the images for a large size to see how lucky she was!

Rare Goat Seen at Glencoe Ski Centre

A late mid summer skier has spotted the rare "Dahu" mountain Goat at White Corries.  Probably the first sighting outside the French alps of this unique animal.

The top of the "Spring Run" June 6th 2010

Below is a clip showing just how unusual this goat is!