Don: Cycling Tech

Perfect Response: An Effective VO2 Interval Session

posted Mar 25, 2014, 8:18 AM by Donald Vescio   [ updated Mar 25, 2014, 8:48 AM by Elaine Vescio ]

Today, Elaine completed an interval session that was comprised of four VO2 efforts, followed by one strength-endurance effort.  VO2 efforts are short, intense efforts that expend a significant amount of anaerobic power.  Both power (expressed in watts) and heart rate are at levels above threshold.  By definition, anaerobic efforts don't last long and emphasize energy pathways very different from what are used in aerobic intervals, which take place below threshold.   Think of VO2 intervals as well-paced, extended sprints that last no longer than three minutes.

 

Below is Elaine's HR and power data from the morning's session:

 



(click for larger view)

 


Note that Elaine maintained consistent power for each of her VO2 efforts (intervals 1-4), which was approximately twenty-five watts above her normal threshold.  (When you are as physically small as Elaine, twenty-five watts is huge.)  What's interesting is how her heart rate responded to each of the VO2 efforts.  For the first interval, her heart rate was below threshold; for the second and third, her heart rate was just below and just above threshold, respectively.  For the fourth interval, her heart rate was clearly above threshold. 

 

Also note how her heart rate slopes upward during the course of each interval.  Heart rate response lags behind effort, and if Elaine tried to ping her heart rate near threshold in the first minute of her three minute effort, she would have started too hard and would not have been able to complete the full duration of the interval.  The upward sloping heart rate curve is indicative of a properly paced VO2 effort.  If the effort was done at a lower specified intensity, heart rate still would slope upward, but the curve would be much shallower.

 

Each VO2 interval was three minutes in length, and recovery (~60% of FTP) was five minutes.  Given that her heart rate gradually escalated for each effort might suggest that recovery could have been lengthened by another minute.  But because her power curves were consistent across all four intervals, the upward heart rate drift most likely can be attributed to a build of heat. (I've always have said that Elaine is hot!)  Short version, I would not have changed any of the parameters associated with Elaine's VO2 intervals.

 

After the fourth VO2 effort, Elaine ended her session with an eight minute high resistance (100% FTP), low cadence (70-75 RPM effort).  Note how there is minimal variation in power, as she's riding at a lower intensity (at FTP, not above); also note how her heart rate curve is shallower and peaks lower than those for her VO2 efforts.  Again, this is a perfectly paced effort.

 

Looking at the data above, this was a successful session.  Elaine worked on top-end power, as well as low-end strength.  She gained the most benefit from VO2s 2-4, and her strength-endurance interval.  Her first interval was important, but mostly as preparation for the following efforts.  

Power Meters: Direct Force, Opposing Force, and Virtual

posted Mar 21, 2014, 2:44 PM by Donald Vescio   [ updated Mar 23, 2014, 1:13 PM by Elaine Vescio ]

We are in a golden age of options for cyclists interested in assessing performance and structuring workouts through the use of power.  Not too long ago, power-guided training and racing was the province of a few: always very expensive and often difficult to use, power meters primarily benefited those who were willing to take the time to understand the quirks of their devices and able to ensure that they were properly configured and calibrated to improve their accuracy.  Today, power meters are much simpler to use, they have gone down in cost, and they tend to be very reliable tools for even novice and intermediate cyclists.  Power is an important metric for cyclists to track, as it provides insight into how much work was done on the bike and, when viewed over time, how fitness and performances are impacted by training.  

While the cost of power meters has dropped significantly in the past three years, it still can be a barrier for many riders.  New devices from Stages and PowerTap can be had for less than $800 (plus the cost of a computer/head unit); the average price point seems to have settled around $1,600, which is the cost of a decent new TT bike, or a very good-to-excellent used TT bike.  And if a rider has multiple bikes, then the cost of ownership for training with direct force power meters goes up, either through the real cost of additional units or mounting hardware, or through time and labor associated with swapping power devices from one bike to the next.  Not every rider will want to spend money for a dedicated power meter, but there are options available for those interested in receiving some of the benefits of training with power, without the high cost.

There are three categories of power-based training tools available today: direct force power meters; opposing force power meters, and virtual power calculations.  It's important to understand the benefits and potential disadvantages of each system before making an investment in this area.

Direct force power meters represent "original" power measure technologies.  Normally based on strain gauges or similar concepts, direct force power meters measure how a part on the bicycle deforms under force.  This deformation can seen in how crank arms and pedal spindles bend, or how rear axles and bottom brackets twist when a rider presses down on the pedals.  Direct force power meters represent mature technologies that are highly precise and accurate.  While each manufacturer might implement their technology in a unique manner, all function in much the same way.  SRM, PowerTap, Quarq, and Stages are among the main competitors in this area.  In general, direct force meters are considered the gold standard in power meters.

SRM--the original power meter

Opposing force power meters take a different approach.  Rather than directly measuring the deformation of a specific part on the bicycle, they instead calculate opposing forces on the rider, such as the grade of the road, the rolling resistance of the tires, the speed of the rider, and the force of the wind.  While this approach is simple in concept--Newton describes it in the form of force = mass * acceleration--the difficulty is in the details.  In order to get an accurate and repeatable measures of power based on opposing forces, many complex calculations need to be completed very quickly, and the quality of the calculations depends on the accuracy of initial assumptions.  For example, for an opposing force power meter to work acceptably, the weight of the rider and bike must be factored in, as well as the aerodynamic drag of the rider's position (which can be problematic, as this value will change depending on the clothing a rider wears, equipment that is used, and position on the bike). 

Fortunately, processing power today is inexpensive and modeling is sophisticated, so opposing force power meters do represent a viable alternative to their direct force cousins.  For most riders, the biggest practical difference between direct force and opposing force power meters is granularity: direct force power meters are excellent at measuring short and variable duration of power, such as what occurs when sprinting, while opposing force power meters do better for longer, more sustained efforts.  In other words, when properly configured, opposing force power meters are remarkably consistent with direct force models.  iBike's Newton is state of the art in opposing force power meters, and its purchase cost and overall cost of ownership can be much lower than that of a direct force power meter.


iBike opposing force power meter


Virtual power meters take the general concepts associated with opposing force power meters and take them to a higher level of abstraction so that power is calculated based on mathematical assumptions.  Services like Strava, TrainerRoad, and Tour de Giro all provide power calculations based on your performance.  Virtual power meters tend to be most accurate when rider performance is steady and there are few environmental variations.  For instance, it's relatively easy to calculate power associated with a steady climb, as speeds will be low (smaller aerodynamic impact) and effort steady; for long rides on variable terrain and/or in changing winds, calculations become less precise and more advisory.  Factor in additional variables such as aerodynamics and rolling resistance, power calculations become more suggestive.  Virtual power is a great option for providing a rider with a very general, high-level sense of overall performance, but it is not accurate enough or replicable enough to rely on exclusively for structured training. 





Increasingly, serious riders are seeing the benefit of indoor structured training, and power calculation plays an important role in increasing the efficacy of a rider's sessions.  A standard trainer and power meter can be used for structure interval workouts and guided tempo and threshold sessions; the same equipment that is used to measure power outdoors is used for indoor training.  And if one does not have a direct force power meter, then all one needs to do to train with power indoors is to purchase an inexpensive Ant+ cadence and speed pickup to use in association with an indoor trainer.  Most manufacturers provide what's called a power curve associated with their popular trainer models.  A power curve is an estimation of the amount of power that needs to be generated to achieve a specific wheel speed as expressed in miles per hour.   Power curves will vary with specific trainer settings, as well as with other variables such as tire inflation, the amount of pressure the trainer's roller applied to the wheel, and even the temperature of the air in the room in which training takes place.



Power curve for Cyclops SuperMagneto Pro trainer


Online services such as TrainerRoad and Tour de Giro base their power assumptions on the power curves of specific trainers, but these values should be seen at best as approximations, as they neither are accurate or replicable.  This is not to say that TrainerRoad or Tour de Giro are not useful for indoor training--on the contrary, they offer the opportunity for highly structured workouts in a relatively consistent environment, provided that one understands that the data associated with the training sessions is descriptive and qualitative in nature.  The data is not accurate or replicable enough to establish a precise value for thresholds or other training zones.

Another option for training with power indoors is a device like a Computrainer, which calculates power directly and which can be calibrated to zero out the importance of the trainer's press-on force at the rear wheel.  What differentiates the Computrainer from riding a standard trainer with a direct force power meter or with virtual power is the ability to do ergometer-based efforts.  What an ergometer will do is force a rider to produce a specified amount of watts, regardless of a number of variables: if an ergometer is set for 300 watts, then the rider must produce 300 watts, no matter the gear being used, cadence selected, or speed of the wheel.  Think of ergometer workouts as training with power in reverse--rather than trying to hit specific power values, the rider is forced to perform at a certain level of intensity, no matter the motivation or focus.  Power meter/trainer intervals have greater scope for variability during individual efforts, as the rider has to focus consciously to maintain an even pace at an appropriate output.  In terms of return on exercise investment, it is difficult to beat ergometer-based interval sessions.





Computrainer--perhaps the best of the best in indoor power training


While all of this might sound complicated, the takeaways are relatively simple.
  • Direct force power meters have the highest cost of entrance, but they offer the greatest repeatability and accuracy for data collection and analysis.
  • Opposing force power meters have a lower cost of entrance and can yield consistent and accurate data for longer duration efforts, provided that some care is taken in setup and configuration.
  • Virtual power is a low-cost entry into training with power, though it neither is accurate or consistent.
Like many things in life, take time to think about how you will use your power data.  If you're looking for general trends and are not interested in using your power data for detailed performance testing or aerodynamic field testing, then virtual power may be worth a consideration.  If you are on a relatively tight budget and are willing to take care in setup and configuration, then an opposing force power meter might be a good match.  If you are seeking accuracy and precision to guide your training and assess your performance, then a direct force power meter or a more sophisticated indoor system like a Computrainer would be your best investment.

Cycling Data Explored (Part One)

posted Mar 18, 2014, 1:36 PM by Donald Vescio   [ updated Mar 18, 2014, 1:40 PM ]

With the advent of relatively affordable power meters and a range of indoor trainers that directly measure force, it is easy to collect a large amount of data associated with individual training sessions.  At first, this information can be daunting, but a general understanding of how this data might be viewed will go a long way toward demystifying the analysis of your performance.


The problem with training data, and especially when it includes power and heart rate (HR), is that the numbers appear precise, and we assume that the specificity of these numbers would be useful in understanding our workouts.  While there are times in which precise numbers are important (for instance, in establishing thresholds), identifying and analyzing trends offer greater utility.  Remember, a data point represents specific information at a specific period in time; what we want to track are patterns over time, which tell us how were are performing.


In the following example, a cyclist was asked to complete the following workout:


  • Two intervals at anaerobic threshold, nine minutes in duration, and at a self-selected cadence.


  • One strength interval below threshold, ten minutes in duration, and at a cadence of 70-75 RPM.  The intensity of this interval was to approach--but not exceed--threshold as measured by watts.



The cyclist reported that this was a strong session and uploaded his data file.  




On first view, this graphical representation of the workout looks very complicated.  But it really isn’t all that bad, especially if we peel away information that offers little value for analysis.  


Here’s the color code for the different graphs:

  • Green = altitude

  • Dark Blue = temperature

  • Light Blue = miles per hour

  • Red = heart rate

  • Yellow =  cadence

  • Purple =  power


As this session was performed indoors on a trainer, we don’t need to worry about altitude or temperature. Outside, these variables can have a big impact on performance, but indoors they can be removed.  Here’s a clearer cut of the data, with altitude and temperature hidden:




Okay--this looks a little more manageable.  Because this is an indoor trainer ride, we also don’t need to worry about wheel speed, which is removed from the following view:




What remains is data associated with cadence, heart rate, and power.  Rather than looking at specific numerical values at this time, I first look for any patterns or outlying features.    For example:


  • HR for the first two intervals is higher than the third, which implies specific responses to varying intensities

  • The first two intervals were performed at higher intensities than the third, as indicated by higher average HR and power values.

  • The variation in power for intervals one and three is less than the variation in the second interval; in other words, there are greater peaks and drops in the purple graph for the second interval than the other two efforts.

  • The greater variation in power in the second interval could be indicative of fatigue--the cyclist had more difficulty sustaining an average wattage than in the first effort, so his power output is marked by a series of surges (and drops for recovery).

  • At the end of the second interval, the cyclist tried to accelerate and boost his power, as indicated by the sharp purple and yellow spikes.  Also note that cadence for the second interval was slightly more irregular than for intervals one and interval three (the strength interval).


So far, then, the data tells me that the cyclist did a strong, consistent first interval at (or slightly above) AT, while he struggled a bit with the second.  Because the level of intensity was lower for the third interval (as intended), variances in watts and cadence narrowed back down.  What I know so far is that the cyclist did two strong intervals, but that the second interval was a little harder than the first.


While it’s fashionable for some cyclists to disregard HR data associated with their rides, it actually provides useful insight.  In very simple terms, power is an expression of the work being done on the bike, while HR describes how we respond to this work.  There are a good number of variables that help shape our HR responses, but when taken holistically, HR provides interesting insight.  


The following has all data removed from the display, except for heart rate:




Note the HR curves associated with each interval.  For the first interval, HR increases steadily for the effort.  For the second, HR is almost at the same level as the conclusion of the first, and it rapidly rises for the duration of the effort.  This rapid response (and particularly the sharp HR peak at the end of the second interval) suggests that the cyclist was only partially recovered from the first effort and that he struggled at the end to accelerate at the end of the interval to meet his target watts.  The HR curve for the third interval is both flatter and lower, which is expected for the lower intensity prescribed for this effort.  For the third interval, HR response is clear, but steady, and well below the levels of the first two; this was a perfect curve for the effort attempted.


I can confirm my observations by superimposing cadence curves (yellow) on HR (red):





In this view, the only items of note are that there was greater cadence variability in the second interval, as well as a slightly higher overall average cadence.  Variations in cadence  and overall RPMs impact HR: the greater the variations of cadence and the higher the RPMs, the greater the potential impact on HR.  Note how steady both HR and cadence is for the final, lower intensity, lower cadence effort.


Finally, I can look at HR and power superimposed on the same graph:





Again, no surprise in this view.  As the duration of the interval increases, HR also increases.  For intervals one and three, power is relatively consistent and has low variability.  Interval two is the one outlier in that there was greater variability in power (and remember from above, also in cadence) and a sharper increase in HR.    My summary, then, is:


  • This was a productive workout.  The cyclist paced two of three intervals consistently, and demonstrated some fatigue in interval two.  


  • Given that this was the final workout for a challenging cycle, some level of fatigue would be expected.  This is a good culmination of a series of productive sessions.


In all of the analysis above, note that there was no reference to specific data values and that we focused on trends and anomalies in the graphs.  If we stopped at this point, we would have a useable (and useful!) understanding of a workout that can be used for future planning and assessment purposes.


Now, the next step for me would be to look at specific data values to deepening my profile of the session.  This process also is straightforward, especially after a qualitative analysis of the same information.   But this is a topic for another article.


Data analysis need not be complicated or scary.  If you look for patterns in how the data is graphed, you’ll gain greater insight into your performance  Remember, keep in mind that you always want to look at the big picture first. Even if you don’t go into more detail in your analysis, you will learn more about yourself and how to assess your training and race sessions.


Crank Length and Power Production

posted Sep 2, 2013, 5:55 AM by Donald Vescio   [ updated Sep 3, 2013, 2:36 PM by Elaine Vescio ]

I have written two earlier articles on the importance of crank length and the variables that one might consider when selecting a crankset that will help optimize performance.  Until relatively recently, most cyclists would adopt a rough proportional scale when identifying appropriate crank lengths--tall riders used long cranks (normally between 175 - 180 millimeters in length), small riders used short cranks (normally between 165 - 170 millimeters), while those riders in-between used mid-length cranks (170 - 172.5 millimeters).  Some riders further refined this rule of thumb, going to slightly longer cranks if they were going to be doing events that skewed toward big gear, high force efforts, such as time trials.  More recently, researchers have begun examining crank length in the context of bike fit and physiological parameters.  I wrote about the relationship between crank length and hip angles in an earlier post and discussed the benefits of short cranks in terms of body position and power production; in another, I discussed how crank length also can be related to type one and type two muscle fiber recruitment. This entry will take a look at the relationship between crank length and overall pedaling efficiency, and how crank length can positively impact power production in ways that initially might be seen as counterintuitive.

Okay--to start, we need to think about how power is produced.  Power a measure of how much work we're doing on a ride--the higher the power (normally expressed in watts), the harder we're working.  Power is based on the factor of two variables:
 
 
Power =  force x angular velocity
 
More simply,
 
Power = how hard we press down on the pedals multiplied by how fast we turn the pedals in a circle (aka "RPM")
 
 
There are lots of way of generating power: you can push down very hard on the pedals at a relatively slow cadence, which privileges muscle strength over cardio fitness; or you can push down relatively lightly on the pedals, but turn them at a high cadence, which privileges cardio fitness over muscle strength.  You can read more about cadence and power production here.
 
The goal of performance cycling is to product as much power as possible with as little physiological cost as possible.  Riding exclusively at lower cadences can cause premature muscle fatigue, negatively impacting performance; riding at too high of a cadence can result in excessively high heart and respiratory rates, with lead to premature physiological fatigue.  The key is figuring out how to balance the variables of force and cadence in a way that's sustainable for the duration of the event.
 
One of the best ways to visualize the relationship between pedal speed and crank length is to image a weight attached to the end of a two foot cord.  The cord is spun in a circle at a constant rpm, say sixty revolutions per minute; if the weight is attached to a two foot cord, we can calculate the speed that the weight must travel to match the sixty rpm value.  Next, imagine that the same weight now is attached to a six foot cord and is then spun at the same rpm.  Because the cord is three times longer, the circle that the weight will travel has a radius that's also three times longer--in simpler terms, the longer the cord, the bigger the circle the weight will travel when spun 360 degrees.
 
Remember, though, in this example that while the length of the cords attached to the weight varies, the rpm of the spinning weight remains constant.  So, in order for the weight to move at the same rpm, the weight on the long cord has to travel much faster than the weight attached to the short cord.  Both weights have the same rpm, but each travels at a different speed to achieve this common value.
 
In terms of pedaling, we tend to focus almost exclusively on rpm, forgetting that pedal speed is another important factor in our calculations.  For a given rpm, the pedal must travel faster when using long cranks than short; to pedal at 90 rpm on my 175mm cranks, my foot has to travel much more quickly than it would if I were to use 165mm cranks.  Think of the pedal and crank relationship as we did the weight and cord, described above:
 
 
 
 
To achieve the same rpm, pedal A has to travel faster than pedal B.
 
 
In practice, this means that many riders experience an increase in cadence when they shift to shorter cranks.  The reason for this is that they have adapted to the higher foot speed associated with longer cranks to achieve a given rpm; until full adaptation occurs with shorter cranks, cadence will be higher.  Higher cadences also mean that less force needs to be applied to the pedals to achieve a given power value.  Less force means that muscle strength--which fails more quickly than cardio fitness--is retained for a longer period of time.
 
Putting all of this together really isn't that complicated.  Shorter cranks means that one can ride in an aggressively aero position without losing power; shorter cranks also are better suited to the recruitment of slow twitch muscle fibers, characteristic of most endurance athletes; and shorter cranks enable higher cadences, which can translate into increase power at lower muscular cost.
 
In the ideal world, one might consider training on long cranks and racing on short cranks as a way to maintain high pedal speed in competition.  Short cranks are a viable option for most riders, and research has demonstrated that very short cranks will not negatively impact power production.  Today, it is not uncommon to see elite athletes with crank lengths 165mm or shorter.  Short cranks are worth consideration by age group competitors as well.
 
 
 
 

Crank Length and Hip Angles: Increasing Power and Comfort

posted Sep 2, 2013, 4:54 AM by Donald Vescio

The single most important factor in achieving optimal aerodynamics on the bike is to focus on the position of your body.  The latest and greatest wheels, frames, and helmets contribute no more than 20% of a rider's total aerodynamic drag under the best of conditions; before investing your funds on equipment that may or may not work for you, consider your bike fit first.

In general, there are no secrets to establishing a solid aerodynamic position on the bike:  You want your head and shoulders low enough to reduce your front profile into the wind without significantly compromising your power and you want your hands and arms fairly close together.  That’s it--sounds simple, doesn't it?  The challenge is in how to meet these two objectives.

There are two physiological factors that impact on our aerodynamic positioning: our body size and morphology; our flexibility.  In order to get down into a low aerodynamic position and still be able to ride powerfully, one needs to have fairly good hip, lower back, and hamstring flexibility.  A critical component of this equation is the angle described by the top of a rider's thighs and his/her torso (this is called 'hip angle").  In the stick image below, the red arc indicates hip angle:

Figure 1

 

Now, the tighter one's hip angle, the more one feels constricted when riding in an aero position, and in extreme cases, a rider's thighs actually may hit the abdomen or chest while pedaling.  Additionally, tight hip angles can reduce the amount of power generated by a rider because it is more difficult to move the crank over the top of the top of the pedal stroke (tight hip angle=less leverage).   

Achieving an aero position on a road bike is difficult in that most road frames are designed to be ridden with the seat set back behind the cranks.  This design works very effectively when riding with traditional handlebars--it really hasn't changed in over one hundred years--but it doesn't work so well when aerobars are added to the equation.  Adding aerobars to a road bike significantly tightens the rider's hip angle:

While one can establish a remarkably aero position with aerobars on a road bike, the tradeoff most likely will be loss of power, lower back and hip pain, and potentially compromised bike handling. 

The reason why triathlon bikes have steep seat angles (i.e., the seat is positioned much more forward of the crank than on road bikes) is to enable a rider to get down into a low aerodynamic position without constricting the angle of the hip.  Try visualizing it like this: one can keep the hip angle the same when lowering the aerobars by moving the seat forward, which will rotate the entire body clockwise. Because the body itself is being rotated forward, the hip angle remains the same, while the arms drop lower:

 

Figure 2: Aero position on triathlon bike:
Arc=hip angle; rectangle =  seat; circle = crank

Figure 3: Aero position on a road bike:
Arc=hip angle; rectangle =  seat; circle = crank

In figures two and three, note the relatively positions of the seat and crank:  the more forward the seat, the lower the aero position can be, while preserving a relatively open hip angle.  The take away is relatively straightforward: in most instances, if one wants to use traditional aerobars and achieve a good aerodynamic position, then a triathlon frame with a forward seat position is a must.  Putting aerobars on a standard road bike will result in either a significantly impinged hip angle (not great for power or comfort) or aerobars placed so high as to negate any aerodynamic advantage that they might offer.

But suppose you already have a triathlon bike and want to get lower to be more aerodynamic, or suppose you already have a pretty good aero position but want to get a little more power.  The next variable to look at after seat position is crankarm length. 

There are many studies that indicated that crank length in itself does not measurably impact power output.  Traditionally, long crank arms have been used for time trials because they provide, the argument goes, more leverage than short crank arms; the more leverage one has, the bigger the gear one can push at a given cadence, which means more speed.  The problem with long crank arms is that they describe a much bigger circle that a rider's legs must travel for each revolution of the crank; making this circle bigger effectively tightens the hip angle, as the leg must travel higher in relationship to the torso to complete one pedal revolution.

If an open hip angle is advantageous to power production and comfort, and if one wants to maintain or achieve a lower aerobar position, then it would make sense to go with a shorter crank arm length, especially as short cranks have little to no impact on overall power production.  In other words, by moving from a long crank to a short crank, one can either open up the hip angle for one's current position, or realize some play to drop the aerobars for a more aggressive position.  But in order to go the same speed with shorter cranks, the rider will need to slightly increase his/her cadence to compensate for the loss of gain.

This is where a little math is needed, but it's not so bad and you're almost there.  Traditionally, riders have measured gear size by expressing it as a ratio (which is not too intuitive) or distance traveled per revolution of the crank (called "development").  For example, suppose that you're riding a bike with a 50 tooth chainring and a 25 tooth cassette cog; this combination can be expressed in a variety of ways:

  • Gearing: 50x25

  • Ratio: 2:1

  • Gear Development:  54 inches (chainring divided by cassette cog, multiplied by wheel size; for a 50x25 gearing combination, the bike will travel forward 54 inches for each revolution of the crank)

The problem with each of the expressions above is that they don't take into account the effect that crank arm length has on gearing. The concept of gain ratio factors in the circle described by the crank; while the math is fairly simple, the real take away is that long cranks have a greater impact on overall gearing than short cranks.  Here's an example based on my own riding:

I've been using 175mm cranks for lots of years for TTs; I prefer a large gear and a slower cadence (~75-80), which has tested well for me in terms of power and HR. I'm also 5'7" tall, which makes 175mm cranks long for me by most traditional standards. 

Okay--if I figure out the gain ratios for 175 and 170 cranks, I get the following approximate values for a top gear: 

  • 170-->radius ratio ~2; 2(56x11)=10.18 gain ratio
  • 175-->radius ratio ~1.95; 1.95(56x11)=9.92 gain ratio
  • Difference between the two gain ratios is ~2%

What this tells me is that while the numbers say that I'd need to spin slightly faster for the same gearing to be at the same speed if I went to shorter cranks, the difference would only be 2%--which isn't very much.  

But--by going with a shorter crank, I would reduce my hip angle, which means that I either can get lower in front for a more aero position (which I don't need to do), or I should be able maintain my current position, but push the same watts more efficiently. In other words, it looks like a shift to a shorter crank length for one my height might have more value than the benefits traditionally associated with using longer cranks for TTs.

What does all of this mean?

  • Body position is the single most important variable in establishing an aero position on the bike.

  • Tight hip angles can mean lower power output and greater physical discomfort.

  • Low front positions on the bike generally mean better aerodynamics.

  • Moving the seat forward (or adopting a triathlon-specific bike) enables the aerobars to be lowered while maintain an open hip angle.

  • Short cranks (say 165mm or less) can be advantageous in further opening up the hip angle.

  • Switching to shorter cranks means that there needs to be a slight increase in cadence to achieve the same speed for a given gear ratio.

Again, there are many variables that factor into a good, aerodynamic bike position and it is worth the time and expense to visit a professional fitter to help you get started.  One you have a solid baseline position, you'll be able to experiment with seat position and crankarm length to further optimize your performance.

Cadence

posted Jul 22, 2013, 9:25 AM by Donald Vescio

I'm frequently asked questions about cadence and whether there is an preferred cadence for racing.  Over the years, there has been a good amount of research into cadence, but interest in this topic really came to the fore during the Lance Armstrong years, when he dominated his rivals in the mountains with a much higher RPMs than we were accustomed to seeing.  A number of riders have tried to emulate Armstrong's high cadence, not fully understanding the relationship between cadence and performance.  And coupled with cycling's long traditions--always ride at 90 rpm or you'll hurt your knees--it might be time to review some the research associated with cadence and performance.

First, to provide some reassurance: your body is a remarkable machine, and the vast majority of riders automatically self-select their most natural preferred cadence, depending on the demands they they are placed on their bodies and the demands required by the course.  In general, most riders will self-select higher cadences for shorter events, and lower cadences for long events; also in general, most riders seem to adopt cadences in the range of 80 - 95 rpm, though there certainly are riders who perform optimally beyond either end of this range.  There is a good amount of research that suggests that artificially varying cadence independent of physiological or event considerations does not always yield performance improvements.    Simply saying something like, "I need to ride at a cadence of 95," doesn't take into account the many factors that determine how we perform during the course of an event.

Cadence describes the movement of the foot and lower leg around the center axis of the crank.  Power is the measure of how much work we're doing on a bike.  The higher the power, the more work that we're doing and (in most cases) the faster we ride.  Power is calculated by a simple formula: how hard we press down on the pedals (force), multiplied by how fast we spin the pedals around (cadence).  High cadences require less application of force than low cadences; a cadence of 70 rpm requires a greater amount of force applied to the pedals than a cadence of 100 rpm.  Low cadences depend much more on strength than high cadences; high cadences  depend much more on overall cardiovascular fitness than low cadences.  Short form is this: if your legs feel tired and heavy, shift to a smaller gear and increase your cadence; if your breathing and heart rate seems overly tasked, shift to a bigger gear and decrease your cadence.  And above all else, trust your bodies--some people naturally perform more effectively at lower cadence, while others at higher rpms.  

Now for some nuances.  In events in which there are lots of accelerations (such as a road race, criterium, or segment of a triathlon/TT course with lots of turns), it often is advantageous to ride at a slightly higher cadence than your normal, as a smaller gear would require less force to increase speed than a big gear (think: you're in a car at a stop light; it's easier to accelerate in first gear than in fourth).  A slightly higher cadence in a ride with lots of accelerations will carry a higher toll on your heart and respiratory rates, but a much lower cost in terms of strength, and your legs should feel stronger near the end of the race.  If you know that your ride will end with a series of long, difficult climbs, consider starting the race at a slightly higher cadence, saving you leg strength for later.  If it is hot on race day and you're feeling tired and having a difficult time raising your heart and respiratory rates, consider using a slightly bigger gear and lower cadence to accommodate the environmental and physiological stresses on your body.  If you're going down a long hill, when it's difficult to generate watts, consider using a big gear and low cadence, this time with light pressure on your pedals, to enable you to recover both your legs and your heart rate.  If you're approaching a long climb, shift to a smaller gear early on its slopes, as this may help you save some strength for later in the climb.  At the top of a climb, accelerate to speed in a small gear, using the same strategy that you'd use in a course with lots of transitions.

Here's the short version.  It's useful to occasionally train yourself to ride at very high and low cadences to expand the range of your effective cadence.  (You'll have more opportunities to determine your efforts--rather than have the course dictate your efforts--on the course if you have an effective cadence range of 20 rpms than you would with a range of 10 rpms).  Pay attention to the cues offered by your body and adjust cadence to meet the needs of your legs and your heart rate/breathing.  Don't slavishly emulate the cadences of your favorite athletes, as their physiological and biomechanical requirements likely will be different than your own.

Back to Armstrong,  If you carefully watch Armstrong's performances during his Tour de France runs, you'll note that Armstrong's cadence wasn't all that different than that of his rivals.  It only was when he attacked on the major climbs did you see a significant increase in cadence.  Armstrong did this--and was able to do this--to leverage his tremendous cardiovascular capacity, while saving his legs for later in the climbs.  His rivals did not have the same reserves as Armstrong, so their emulation of his cadence on the climbs as met with mixed success.


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Quantifying Training Sessions

posted Jun 25, 2013, 7:02 AM by Donald Vescio


©Vmps/Don Vescio 2013


Structuring training sessions used to be easy.  A coach would specify either a distance (ride 25 miles) or time (ride for 120 minutes)  for a cyclist’s workout, and the rider would report back whether the session was completed as planned.  More advanced coaches might combine the metrics of time and distance as a way to specify intensity: “Ride 25 miles in one hour,” or “Ride 30 miles in two hours, small gear.”  Specifying distance or time certainly was much better than less scientific forms of coaching, like, “ride hard for awhile, and then do some hills.”  Specifying time and distance introduced some measurable parameters into the cyclist’s training program, though they were not perfect (one can ride a hard hilly 25 miles, or an easy, flat 25 miles, for instance).  Combining time and distance metrics helped coaches and athletes determine the relative intensities associated with specific training sessions.


Today, coaches and athletes can adopt a much more sophisticated approach to how workouts are scheduled and how these sessions can be assessed consistently and accurately.  With the affordability of a wide range of training tools, such as heart rate monitors, power meters, and GPS devices, it never has been easier to capture performance data.  With all of this availability of data, the issue becomes one of determining which data is of greatest value when describing a training session’s intent, or in assessing the efficacy of a training session after the fact.


There are two schools of thought regarding data use for planning and assessing workouts.  The first relies on a fixed metric, such as power or heart rate; more sophisticated versions of fixed metrics are normalized power, intensity factor, and (for running) Vdot values.   Fixed metrics are based on an understanding that specific performance values must be met in order to achieve success in a workout or competition, and if these values are not reached, then the athlete will not reach his or her goals.  For instance, to ride a 25 mile time trial in one hour, the athlete must be able to maintain a 25 mph average pace; in more detail, this rider may need to average 380 watts and maintain a heart rate between 155 - 162 to ride the 25 miles in one hour.  In this model, training sessions would be based on meeting specific performance minimums, regardless of how the athlete might feel at a given training session. The thought behind this method of training is that by hitting specific values, an athlete will be better prepared to me the target goals of competition.


The only problem with this method is that frequently coaches and athletes don’t factor in the more qualitative variables that impact training and race performance, such as fatigue, motivation, injury, or physical exhaustion.  For example, later this week I am scheduled to do four VO2 efforts (these are very hard three minute intervals); for each interval, my target wattage will be 410 watts.   If I'm rested, I can complete this session and not struggle too much; if I'm tired, at the end of a cycle, etc., then I might not be able to complete the repetitions.  While the performance measure--watts, pace, etc.--are pretty fixed, my physiological response to the efforts is not.  This is where Recorded Perceived Exertion (RPE) comes in.


When I schedule a session for my clients, I'll specify three values: heart rate zone(s), watts (pace or Vdot can be used for running and swimming), and RPE.  All of them cross-reference each other.  A session might read something like:


3VO2 efforts, 400 watts, HR Z5, RPE 8-9.  


Here's where the interesting part comes in.  I need to make sure that my client understands that the progression of values, from most to least important, run like this:


  1. RPE  = our physiological and psychological response to the work being done

  2. Watts (or Vdot, etc.) = amount work being done during the activity

  3. Heart Rate = how our bodies are responding the work demands being placed on it


If RPE is too high for the specified effort, then we cut back on repetitions and/or duration.  If RPE is too easy for the specified workout, then we'd consider adding additional intensity for subsequent workouts.  HR is used as a general gauge for recovery (if HR is too low or too high for session, then recovery might be in order).


Now, there is a huge amount of research that indicates that for event pacing, RPE should take priority over specific metric like pace, watts, etc.  If I am not recovered, motivated, etc., then telling me that I need to ride at 300 watts for my HIM won't help me--it only will cause me to blow up early in the event.  Similarly, telling me to ride at 300 watts when I'm recovered and peaked might encourage me to ride easier than I could have.  


It's important to have specific performance metrics that can be used to establish baseline performance, and I think that's what things like Vdot, normalized power, and intensity factor come in.  That said, all of these values need to be contextualized in terms of the impact that the effort has on the athlete, as exclusive use of the quantifiable metrics can yield premature exhaustion and over-training.


As for athlete's who overestimate their suffering quotient, use the HR/power data to normalize their response:


"Elaine, what the hell are you talking about?  A RPE of 9, and a zone two heart rate, and you were mostly riding down hill?  Are you sure that the session was as hard as you thought?"  


Think of all of this data as having the most value when considered over time.  Always use multiple metrics when specifying workouts, and regularly cross reference and correlate quantifiable data with recorded perceived exertion.  Over time, athletes will find that RPE will become their most powerful pacing and on-the-spot assessment tool in their preparation kits.




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RPE Chart
Rate of Perceived Exertion
©Vmps/Don Vescio 2013



Level

Effort

10

Maximal:  Almost impossible to continue; completely out of breath; unable to talk

8-9

Extremely Strong: Very difficult to maintain exercise intensity; can barely breath and speak a single word

6-7

Very Strong: On the verge of becoming uncomfortable; short of breath; can speak a sentence

5

Strong: Heavy breathing; conversation punctuated by gasps

3-4

Moderate: Moderately heavy breathing; can hold short conversation

2

Light: Can exercise for hours; relatively easy to breath, can hold a conversation

1

Very Light: Basic movement and activity



Intervals: Example of Using Data to Assess Pacing

posted Jun 11, 2013, 7:30 AM by Donald Vescio   [ updated Jun 11, 2013, 7:32 AM ]

This is the time of the season when it’s important to incorporate intervals into one’s training plan to build the cycling strength and speed necessary for successful competition.  The basic concept behind intervals is simple—ride at an intensity much higher than you’d race, and you’ll race faster at lower intensities. 

The keys to successful interval sessions are duration and pacing.  Keep the interval durations relatively short, and try to pace the intervals as evenly as possible.  In a good interval session, the last few intervals should feel much more difficult than the first few, due to accumulated fatigue.  Another way to look at interval pacing is that opening intervals should seem a bit easier than the intervals that conclude a session.

I’ll cover a lot more about interval length, duration, and intensity in another article.  For now, let’s take a look at the data captured from an athlete’s interval session (click image for full size view):

There are three lines on this graph: yellow =  cadence; red = heart rate; pink = watts.  By looking at these lines, one can get a good sense of the pacing of the athlete’s interval session.  Looking at the watts (pink) line, the athlete’s wattage was both higher and more variable for the final two efforts than they were for the first three; also note how the heart rate line trends up more steeply and reaches a higher point for the final two intervals as well.  The average watts for the final two intervals was 310; the average watts for the first three was ~290.

The take away from this graph is that the athlete could have ridden his first three intervals at a slightly higher intensity, say ~300 watts, which would be sustainable across all five efforts.   For this specific session, a little more intensity at the start of the workout probably would have resulted in less variation across the full set of efforts.

Tracking your data is important not only when you’re riding—it’s even more useful after your ride, when it can be used to determine how well you met your session’s goals.

Four Cycling Tips

posted Jan 22, 2013, 8:10 AM by Donald Vescio   [ updated Nov 21, 2013, 11:10 AM ]

Adjust Cadence and Gearing for Recovery
Power is the measure of the amount of work that you’re doing on a bicycle.  Power is determined
by how hard you push down on your pedals (force) and how fast you turn them in a circle (RPM).  Force draws heavily on leg strength; sustaining a fast cadence requires good cardiovascular fitness.  In a race, if your legs feel tired, shift to a smaller gear and increase your cadence, which will require less leg strength for a given effort.  If your heart and respiratory rates are high, shift to a bigger and decrease your cadence, which offloads some stress to your legs.



Aerodynamics Matter
When riding, most of your energy is used to overcome wind resistance.  Aerodynamics are important, whether you are a fast or slow rider.  The three most effective aerodynamic purchases one can make, in descending order of importance, are: aerobars (and a good bike fit to go with them); aero helmet (generally,
fewer vents means a faster design); aero front wheel (think in terms of 50 - 60mm rim depth).  Additional aero purchases will yield additional incremental benefits.  And for slower riders, the percentages gained by aerodynamic savings are greater than for fast riders, as slower riders are on the course for a longer period of time.  Aero matters for all riders.



Train Indoors--Even in the Summer
A number of professional triathletes do the bulk of their training indoors, and you should consider doing so, too.  Indoor cycling eliminates many of the variables that can disrupt your training when riding outside, such as traffic, terrain, weather, and other distractions.  Indoors, it’s far easier to control your performance variables, such as cadence, power, perceived exertion, and heart rate; as a plus, riding indoors also eliminates soft pedaling and coasting during your session, thus maximizing the productivity of your training time.  So consider doing some of your rides indoors, even in the summer--you’ll find that it will increase the effectiveness of almost any training program.



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Use an Alarm
While I  capture a wide range of performance data (power, cadence, altitude gain, etc.) every time that I ride my bike, mostly it’s used for post-session analysis.  When I race, I keep things as simple as possible to minimize distractions, preferring to set my pace by perceived exertion (which is later correlated with the data from the ride).  What I do, though, to ensure that I don’t ride too hard in a long event is to set my computer to send an alarm when my cadence drops below a certain level (which means I’m pushing too big of a gear), or if my heart rate exceeds a maximum level for the event (which means my level of exertion may be too high for the event).  The alarm settings help ensure that I don’t work too hard in a long event, which may negatively impact my pacing.

Air Dams and Frame Design

posted Aug 22, 2012, 6:29 AM by Donald Vescio   [ updated Aug 22, 2012, 11:15 AM ]

Based on Cervelo's remarkable success with their P series bikes, most top-level time trial and triathlon frame design emphasize tight clearances so that wheels and other components can draft frame members, with the goal of presenting as continuous of an aspect possible into the airflow, so that its disruption is minimal.  (You can click on the images below for more detailed views.)



Note the close proximity of the rear wheel to the seat tube in the photo above.

Not withstanding the success of this school of frame design on the road and triathlon circuits, there is a competing philosophy that attempts to factor in the impact that a forward rotating wheel has on overall aerodynamics. 





As the thought goes, when a wheel rapidly spins forward, it also is creating forward rotation of air; when a wheel if fitted tightly to a frame, the frame's tight clearance creates a dam that blocks this secondary airflow, thereby creating unwanted drag.  The company Look is a proponent of this philosophy.  In the photo below, note the clearance between the rear wheel and the frame's seat tube:



In the 2012 Olympics, see how Great Britain's track bikes were designed with ample clearances around the crowns of their forks:




Recently, I've begun testing this design philosophy (greater wheel clearances mean less drag) on a Kestrel Talon, which has long proven to be a top aero performer in static wind tunnel tests.  My goal is to establish how effective the Talon's rear wheel design is in comparison to the industry standard Cervelo P3C.  So far, the preliminary results are interesting.




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