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Analyzing Power Meter Accuracy: Time vs Weight and Watts

See the workout graphs at bottom.

One (1) pound costs time of about 6 seconds on this ascent for a Total Riding Weight (TRW) of 200 pounds at 20:00 (1200 seconds), since 1 pound is 1/200 and thus 1/200 of 1200 is 6 seconds. We can discount this a little for friction, but hard data shows this to be a reasonable figure.

The 2nd and 3rd ascents are significantly slower than they ought to be, if the SRM power meter is accurate: the drop in riding weight and the increase in watts should deliver significantly lower times than actually measured. This implies that either the scale is inaccurate (provably accurate and precise both, over years!) or the SRM wattage is wrong.

In a nutshell:

  • If total riding weight (TRW) drops by 2.3% (4.6 pounds as here), then the time should drop by about the same percentage for the same wattage (there are frictional forces , but these are all but identical for the negligible speed difference between ascents).
  • If power (watts) increases by 6% (e.g., 316 vs 298 watts), then ascent time should drop by about the ratio of the two (298/316), assuming the same weight (the wattage numbers are 3.3% and 6.0% higher for the 2nd and 3rd ascents vs the first ascent).

The numbers don’t work: the combination of lower TRW and higher watts should have dropped the time significantly more (the time should have been 30 seconds faster on ascent #3).

The scale claims a weight loss of (200.0 to 194.9 pounds over a 2-hour workout. That’s a loss of 5.1 pounds = 2.5 pounds per hour, or about 1.16 liters of fluid lost per hour (1L = 2.2 pounds). That figure is inline with years of experience.

Therefore, the SRM power measurement is substantially off, well out of range of the claimed 1% accuracy. Actual wattage must have been nearly identical for all three ascents, since the theoretical times for the same weight match actual times. In other words, there was no change in weight (impossible) or the SRM power figures were too high for the 2nd and 3rd ascents.

Calculation of ascent time variation from actual + weight + watts

Mouse over to see ascents #1, #2, #2. These are “negative intervals” meaning that each successive effort is at a lower time.

 

Old La Honda ascents

Starting the Anaerobic Climbing Training: 3 Ascents of Old La Honda (negative intervals)

With three double centuries showing a strong aerobic base, I deemed the time ripe to begin anaerobic and power training on Old La Honda.

These ascents were intended to be just at or above lactate threshold, a goal the quadriceps confirmed grumpily.

My max HR is 172, so 150 bpm (first ascent) is 86% of max, and 155 bpm (3rd ascent) is 90% of max HR. But as I get in peak shape, HR does not like to go above 92% of max unless it’s quite hot, or the effort is extreme.

Weight vs watts vs time analysis follows.

Mouse over to see ascents #1, #2, #2. These are “negative intervals” meaning that each successive effort is at a lower time.

Old La Honda ascents

Calibrating for Distance and Speed Accuracy (Tire Circumference), 700 X 22C vs 700 X 25C

Experience proves that GPS is absolutely useless in the vast majority of my riding situations, with errors up to 20% when mountain biking under tree cover (twists and turns and switchbacks, dropped signal, canyons, etc). Even on a road bike I often ride under tree cover and there are tight turns.

GPS satellite errors are often low, but sometimes surprisingly variable. Of course, GPS has one big advantage: errors are not cumulative over a long ride. But the accuracy over distance is not very good in many cases. For wide open roads and straight lines, it is fine.

GPS total error over distance might also be affected by grade; it’s unclear that GPS ever logs road distance properly when riding on, say, an 8% or 18% grade (e.g., “as the crow flies” vs cyclist glued to undulating/climbing road). That would presumably depend on the GPS unit. But no GPS can properly measure up-and-down short-length dips in the course; the accuracy and precision are just not there.

How to measure

When I road-bike, I calibrate my SRM PC7 accurately (it reads out to 0.001 mile using a wheel sensor).

Ideally, one would have a known distance on flat ground: a 400m track or strip of pavement marked exactly for distance; ride the distance, then adjust the calibration so that it reads exactly right. I don’t have that facility anywhere nearby.

I lay down a long tape measure, then carefully roll the bike so that at least four revolutions are made of the wheel to increase accuracy. I’m on the bike so as to incur typical tire squish. I take the distance, divide by four (revolutions) and plug this number into the SRM.

The numbers will depend on body weight, inflation pressure, type of tire and its size. Thus getting your own number can yield a more accurate speed and distance than some generic assumed number.

Settings for the SRM Power Control 7 head unit

22C vs 25C circumference

Here’s what I found for myself for the front wheel (my sensor is on it).

These are pressures that I typically ride and total riding weight was ~200 pounds (~178 pound rider fully clothed, lights on bike, saddlebag, etc):

 Veloflex Record 700 X 22C @ 120 psi: 2014 mm

Veloflex Roubaix 700 X 25C @ 110 psi: 2123 mm

The difference is 0.9%. That doesn’t sound like much, but it equates to a 1.76 mile error for a 200 mile double century, which dovetails with what I’ve observed when riding a Veloflex Roubaix with the PC7 being calibrated for the Record.

Note that if you were assessing, say, an aero wheel or aero riding position, that 0.9% difference translates to 0.27 miles per hour at 30 mph. Which is of no particular interest in general, but very significant if you’re goal is to assess gear for winning, say, a time trial. Put another way, 0.9% of 30 minutes is 16 seconds—huge in a race like that.

Three Double Centuries, a Week Apart

A double century is a great way to establish and prove out a deep aerobic base for any hard race like the Everest Challenge. I completed these three double centuries on March 7 and March 14 and March 21, 2015—three Saturdays, a week apart.

I chose to do 3 in a row with the explicit intent of reducing body fat and laying in a deep aerobic capability for more intense training for the rest of the year. The effort was a success on both counts.

See also To Draft or Not to Draft: What Does it Accomplish?

  • All of my double century efforts are solo time trials, meaning I do ZERO drafting (though I might pull others). This is much harder than expending 2/3 to 1/2 the effort in a pack. Even two riders sharing the load give each other a considerable break.
  • Actual mileage can vary from what is shown in the graph. Not having calibrated for 25C tires (vs my usual 22C), my SRM PC7 seems to have been off (low) by a percent or so.
  • All three events ridden with Veloflex Roubaix tubulars tires and a Lightweight Standard rear wheel and Lightweight Autobahn VR front wheel.

Southern Inyo Double Century, March 7 2015

This double century starts from Lone Pine, CA. This was my first double for 2015.

The far reach on the ride was to the border of Death Valley National Park. Here I had to wait briefly for a required sign-in, but I also had to take a 'dump' really badly and no restrooms, so I then had to stop again for relief about 5 minutes later. Somehow this shut me down and broke my mojo; up until then I had been feeling terrific. After that I felt marginal, and later, downright crappy. :;

Later at the high point of the course (mile ~133) I ate a sugar cookie, thus breaking the “never eat untested food” rule. I paid for it dearly with a terrible gut ache for miles 150-200 or so (after the descent).

Something went very wrong in general with fueling and hydration; I lost all appetite and sense of thirst at about mile 140, or rather I had no desire to eat or drink anything of any kind. Even Hammer gel I could scarcely gag down. It was literally having to force myself to eat and drink, but the gut ache made it a very unattractive proposition. The power decline is obvious by mile 150 but actually started earlier around mile 100 (just after the 'dump'). Physiologically I had goofed somehow: clear and excessive urine (overhydration) for the first 6 hours of the event was a constant nuisance. I did take Endurolytes so it wasn’t lack of electrolytes.

Together with painful big toes (new shoes and orthotics, 3 weeks with them prior), the last 50 miles were physically very unpleasant. I had to grin and bear it the best I could and I had to stop and just stand for 5 minutes at about mile 180, which helped. I felt like I wanted to throw up once I finished and it took about 90 minutes before I could eat. But after that, everything went back to normal.

At mile ~120, my rear tire flatted with two ~1/3mm diameter X 20mm long stainless steel wires embedded in the rear tire, just after I had missed a turn and ridden too far the wrong way. Once I got back on course, the good luck was the location—about 1/4 mile from my car (the route crosses back on itself). So I rode back to my car and swapped the rear wheel. Later, Stan’s No Tubes completely sealed the pinholes and I used this same wheel/tire for the next two double centuries as well. Stan’s NoTubes is great for such pinholes, and the tires can still take full pressure with no chance of blowing out the sealant (larger holes get you home with Stan’s, but tend to blow out the sealant sooner or later, re-flatting).

Kilojoules: 7697

Power and heart rate with elevation profile for Southern Inyo Double Century

Joshua Tree Double Century, March 7 2015

Due to a faultily memorized map lacking a “Y” turn (lacking in my mind), I took the wrong turn and did 12 extra miles and about 1400 vertical feet more than the standard course. So it was well beyond a double century.

There was no support within the park, so I rode unsupported for over 80 miles, which left me dehydrated and hot. Scarfing a liter of cold water upon reaching the interstate highway just out of the park, I partially revived, but It seemed to kill my performance for the rest of the day (120 miles or so to go after that!). Temperatures ranged from 39°F at the higher elevations at sunrise within the park to 90°F or so on the post-park outer areas. It’s never really possible to rehydrate properly while riding once too far gone, so this screwed the day. I was very, very glad to be done.

Still, I recovered faster from this one than the Southern Inyo (above). Just 48 hours later, I had a nice strong ride, albeit the muscles still need a full 4 days to be back at 90%, and probably 6 days to be truly back at 100%.

Course: About 68 miles is through Joshua Tree National Park, which are enjoyable miles with good pavement. The rest of the course ranges from boring to “the road never ends” slow climbs to some really unpleasant junk miles along the interstate highway, including dodging bits of tires, rocks, screws, bolts and having to wait ~5 minutes for a semi trailer truck with billowing brake smoke. By a miracle I did not flat on this section or this day.

Kilojoules: 7870

Power and heart rate with elevation profile for Joshua Tree Double Century

Solvang Spring Double Century, March 7 2015

Aside from a few badly timed stoplights, nothing untoward. No flats (first time in 3 efforts!), which was sheer luck since never in any event have I seen so many people with so many flat tires. The junk-miles portions of the course are littered with glass on some sections, with constant vigilance required. Dangerous drivers near Pismo Beach in heavy traffic cut me off three times; extreme caution is needed. I heard similar stories from other riders.

I was able to maintain good power the entire ride and even finish stronger than ever. I attribute this to a 245 calorie/hour intake of Hammer Nutrition HEED, Hammer Perpetuem solids, GU gels, and some junk candy (black licorice, two mini candy bars, 5 sticks of red vines, one small pack gummies). For me at least, gels and HEED just don’t do it fully (these are almost entirely maltodextrin); the liver should not remain idle; it has a job to do, so scarfing some sucrose and fructose at mile 80 on up at it keeps it active, converting about 60 calories/hour of those sugars into glucose—very significant in context of overall fueling intake of 245 calories/hour (which is about the limit of what the stomach can process during such an event, assuming good hydration).

This was a solo time trial (ZERO drafting though I sometimes “pull” others). Nearly all riders with faster times were pacelining (one fast group that went by had 7 or 8 riders, making it a hugely easier effort 80% of the time for all the riders). Thus their times are not comparable; a different event in the reality of actual performance (a great deal of resting/coasting!). And some riders consistently blow through stop signs and lights (*that* is outright cheating, and illegal too). I do not wish to “win” by someone else’s wind-blocking exertions, and certainly not by cheating. In a RACE, yes I *will* draft (within my racing category), since that is part of the race strategy and cannot be set aside in a race.

Solvang Spring Double 2015 results. Total clock time for me includes some bad luck with stop lights and stop signs (traffic), and some route verification.

Kilojoules: 7517

Power and heart rate with elevation profile for Solvang Spring Double Century

The High Quality Camera for Cycling

See The Camera for Cycling over on my photography site.

FOR SALE: Look 595 Ultra size large
ZIPP 404 tubular rear wheel with DuraAce cassette and mounted new tire

FOR SALE: ZIPP 404 tubular rear wheel

Cleaning out the garage, and I ride my Lightweight wheels these days.

Low miles. A steal at $450 with new tire and DuraAce cassette.

Contact me to inquire.

FOR SALE: Look 595 Ultra size large
ZIPP 404 tubular rear wheel with DuraAce cassette and mounted new tire

FOR SALE: LOOK 595 Ultra frameset

The LOOK 595 Ultra is a fantastic bike— see my review of the LOOK 595 Ultra including build details and image gallery.

This is the 'Ultra' which is more stiff than the regular version, but actually a more comfortable ride due to the carbon used for the frame—highly recommended versus monocoque “dead wood” carbon frames.

The 595 Ultra was a spare bike, and I find that I just always ride my Moots Vamoots RSL. In fact this bike is all but brand-new. It has a minor scratch on the frame (as it did when I bought). Of course, never crashed or abused in any way.

The bike has about 1500 miles on it. Seriously— I keep detailed records for every ride and that’s what it adds up to.

  • Size large (see chart below).
  • Includes ZIPP 404 rear tubular wheel with DuraAce cassette (no front wheel).
  • Includes DuraAce brakes front and rear.
  • Includes brand-new Shimano DuraAce 53 X 39 crank (10 speed).
  • Wired for 10-speed DuraAce Di2 electronic shifting (external). This can be stripped if you wish to run mechanical, but you'd need mechanical shifters.
  • Includes Shimano Vibe Pro handlebar and with nice fresh double bar wrap installed with stem as shown).
  • Serious local buyers welcome to come see the bike.

As described above: $1200 (bargain price considering all the extra on it).
Frame only: $900
With front and rear Di2 derailleurs, battery and charger: $1700

See the build notes for build details, though it now has the Shimano Vibe Pro handlebar on it.

This is a superb ride in superb condition. Low mileage (lightly used spare bike), never crashed, never abused.

Contact me to inquire. Asking $3300.

FOR SALE: Look 595 Ultra size large
FOR SALE: Look 595 Ultra size large
FOR SALE: Look 595 Ultra size large, size chart
FOR SALE: Look 595 Ultra size large, size chart

As I had built it below(NOT for sale this way).

FOR SALE: Look 595 Ultra size large, size charge
FOR SALE: Look 595 Ultra size large

Fresh Food is Best: Additives to Keep Food Fresh May Disrupt the Gut Biome

Science new reports in Additives that keep foods fresh may sour in the gut; These compounds can disrupt intestinal bacteria, cause inflammation, mouse study suggests:

Food additives may keep snacks fresh and tasty looking, but they can wreak havoc on the gut. These additives disrupt the intestine’s protection from bacteria and boost inflammation in mice, scientists report online February 25 in Nature.

The new research “underscores the fact that a lot of things we eat … may not be as safe as we think they are,” says Eugene Chang, a gastroenterologist at the University of Chicago.

Additives called emulsifiers help many foods, including ice cream, salad dressing, pasta sauce, bread and cookies, stay fresh on supermarket shelves. To see whether the additives play a role in inflammatory conditions, researchers fed emulsifiers to mice for 12 weeks.

The mice put on weight and made proteins that signal inflammation. More inflammation-causing microbes also showed up in the bacterial communities in the mice’s guts.

...

The jury is out on this one. But why eat processed food with preservatives when so many fresh foods are available?

Details in Dietary emulsifiers impact the mouse gut microbiota promoting colitis and metabolic syndrome.

... in mice, relatively low concentrations of two commonly used emulsifiers, namely carboxymethylcellulose and polysorbate-80, induced low-grade inflammation and obesity/metabolic syndrome in wild-type hosts and promoted robust colitis in mice predisposed to this disorder.

Emulsifier-induced metabolic syndrome was associated with microbiota encroachment, altered species composition and increased pro-inflammatory potential. These results suggest that the broad use of emulsifying agents might be contributing to an increased societal incidence of obesity/metabolic syndrome and other chronic inflammatory diseases

Anti-Oxidants Might be Counterproductive for Athletes

Science new reports in For athletes, antioxidant pills may not help performance; Some supplements can blunt the positive effects of exercise training:

...the American College of Sports Medicine estimates that around half of elite athletes take vitamins in hopes of keeping their bodies fit and boosting endurance.

... It’s that American mentality,” says Jay Williams, a professor in the department of human nutrition, foods and exercise at Virginia Tech in Blacksburg. “If some is good, more is better.”

Except when it might be worse. In a scientific reboot, many newer, more rigorous studies are contradicting decades of previous thinking, finding little support for — if not outright harm from — antioxidant supplements for athletes. Although antioxidants obtained from food appear to do a body good, the colossal doses in supplements may disrupt a cell’s built-in system for coping with oxidative stress. And it appears that muscles under exertion may need a certain level of oxidative beating to adapt and strengthen over time. If the recent research holds up, it means one of the very things athletes commonly do to help their bodies could not only waste money but may even undermine the benefit from those hours of dedication.

Be sure to read the entire article. At best, the research suggest little harm; at worst it suggests a substantial negative.

A healthy diet surely needs little supplementation. Special cases for special reasons always exist, but it makes little sense that carefully chosen foods are somehow inadequate, especially since the body is adaptable an frugal when necessary.

Aggressive Start to 2015: Two March Double Centuries Planned, Maybe 3

I’m planning an aggressive training year, because I wish to beat my best effort in the 2012 Everest Challenge. And because the peripheral neuropathy still comes and goes, and it has degraded my ability to work at the computer. So getting on the bike makes it go away within 45 minutes, and it stays better for some days. But the P.N. still has my toes weirded out and a little uncomfortable.

Lean and strong for peak condition means 9 months of training for EC. Body weight is trending to 174-175 pounds (lost ~5 pounds of fat in ~2 months), and aerobic condition is already at very high levels (see graph below).

A couple of double centuries should bump up condition to 2012 levels by April. Hopefully 2015 won’t deliver bad luck as did 2013 (surgery) and 2014 (gut problem all year).

So I’ve signed up for the Southern Inyo Double Century on March 7, followed by the Solvang Spring Double on March 22. Possibly if the timing works and the conditions are favorable, I’ll insert the Joshua Tree Double Century on March 14. Then in April there is the grueling Devil Mountain Double, followed by Alta Alpine 8-Pass Challenge in June.

Preparing For a Double Century (Dry Run / Pre-Test)

Extensive endurance workout at 70-75% of max heart rate (fully aerobic), recovery ride

Fitness Pre-test for a Double Century

I did this 6-hour ride in late February, having signed up for an early March double century with a similar amount of climbing, but twice the distance.

I also wanted a good “shock to the body” by doing this ride to force a bump up in fitness. The distance and power levels and feel of the legs post-ride suggest a likely 5-day recovery period which should result in a bump up in fitness. Past experience suggests that to get to the “next level” of fitness requires periodic shocks odf this kind. Double centuries are good for that, which is why I have two scheduled for March.

Preparing For a Double Century (Dry Run / Pre-Test)

Extensive endurance workout at 70-75% of max heart rate (fully aerobic), recovery ride

How to lose ~1 Pound of Body Fat in a Single Day

I discuss how a great deal of fat can be “burned” off in a single day.

Lose a Pound of Fat in ONE Day: Century Fat Burner

See also Fat Loss vs Weight Loss and Muscle Loss.

Extensive endurance workout at 70-75% of max heart rate (fully aerobic), recovery ride

Extensive Endurance Workouts: Three Examples

I discuss three endurance workouts that I performed within the past 5 days, showing how I train for the Everest Challenge and for double centuries and similar.

Extensive and Intensive Endurance Workouts, 3 Examples

Extensive endurance workout at 70-75% of max heart rate (fully aerobic), recovery ride

Custom Orthotic Foot bed for Cyclists at 3DBikeFit: Fixing the Power Transfer Kinetic Chain

For the first time in forever, my the big metatarsal (big toe joint) in my right foot now plants my foot firmly as it ought to be, just like the left foot.

This foot placement issue has dogged as long as I can remember (forever I think), but a custom orthotic by 3DBikeFit.com has finally made my right foot placement symmetric with my left, fixing the weakness in the kinetic chain.

Read more...

Kevin Bailey of 3DBikeFit.com making a custom orthotic (shaping phase)

Training and Fitness: Why and How to Track Morning Resting Heart Rate (MRHR)

I should have been tracking this at the start of training season, but hadn’t. So I’ve just started again. So far, there are only three data points shown below, the first being the day after two very hard training days (4 hour ride and 3 hour ride on two weekend days). So the 44 figure is on another moderate day (2 hours); the 42 bpm follows an easier day, and the 41 bpm figure follows a 1/2 of baseline workout (600 kilojoules).

It's only a few beats drop, but the resting heart rate can be seen to decline a bit over the course of the week as recovery progresses from the hard ride on 16 Feb, in spite of a 6 day rolling average workout energy of 1952 kilojoules per day (1866 kilocalories/day).

3248, 2296, 1391, 667, 2541, 1573 = 1952/1866 kilojoules/kilocalories / day
(first figure 6 days old, last figure newest)

The workouts following the hardest and longest 32348 kj workout (on a Saturday) were designed as disciplined extensive endurance workouts so as to stress only the aerobic system, not muscle strength. The strategy clearly was effective.

Fully rested (taking 2 days off), I expect something around 38 (to be confirmed, but I have observed figures as low as 32 in the past).

Morning resting heart rate (bpm), start of data gathering (5 days/mornings)

Tracking Morning Resting Heart Rate (MRHR)

Tracking MRHR gives clues as to recovery or illness and other factors:

  • MRHR will be relatively high the day after a hard workout (5 to 10 beats, depending on a variety of factors).
  • MRHR will be up by 5 to 25 beats in the case of illness. Skip training if illness seems apparent; it’s a red flag.
  • MRHR can do odd things if overtrained; any significant variation from typical is cause for some thought at least. Recording heart rate overnight against a “known well rested” baseline adds a lot more insight than just a morning check.
  • Hydration and stress and medications can affect MRHR.
  • MRHR drops steadily as fitness increases, thus it is an excellent long-term tracker of fitness gains (provided one allows for full recovery).
  • MRHR is generally lower with age, at least for fit people (maximum heart rate drops by about 1 beat per year, but minimum heart rate also declines a bit).
  • Heart rate is a personal measure; don’t bother comparing your own heart rate to someone else’s; there is no real “normal”, only a very wide range of physiological normals. Do not confuse statistics of populations with your own personal physiology. This is why tracking your own normal is important.

How I measure MRHR

  1. Before rising in the morning, strap on heart rate band*.
  2. Lie flat on back, relax completely, record a multi-minute interval at rest.

Any movement (even raising an arm) can push HR up a few beats, so be consistent in position and lie still. Take the *average* (mean) heart rate over the lowest 2-minute interval. If the device does not record, observe the heart rate on the device; use the consistently lowest reading (not necessarily the lowest number).

* Counting heart beats by sensing one’s own pulse introduces error by a few beats because some muscle activation is generally required to to do (at complete rest on one’s back, even a little muscle activation can introduce 10% error, e.g., 4 beats on top of 40). But as long as done consistently each day, this is fine for the purpose of trends (but the true MRHR may be a few beats lower).

Shown below is a 3+ minute recording at rest averaging 41 beats (bpm).

Morning resting heart rate (bpm) recorded for nearly 4 minutes
Get Up To 64GB of Memory!
Get Up To 64GB of Memory!

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