Heat Consequences of Aero Road Helmets

By: Zack Allison, Senior Consultant

While sitting on the couch between races at Gateway Cup, the Think Finance p/b Trek Stores Cycling Team and two Source Endurance coaches jumped into  a discussion on aero road helmets. The weather for this particular race weekend in Saint Louis was an average of around 100F at each of the races. The major question was if the aerodynamic benefit of aero helmets outweighs the power loss from overheating on a hot day.  We decided to try and find studies on the subject of whether aero helmets cause power loss due to overheating. We knew it would be a task to find applicable studies on overheating from a specific type of helmet but we did our best.

Good Aero Position

Bad Aero Position

First we looked at the aerodynamic benefit of aero helmets. The study Benchmark of Aerodynamic Cycling Helmets Using a Refined Wind Tunnel Test Protocol for Helmet Drag Research by Stephanie Sidelko of MIT , compared 10 different aero helmets to a standard road helmet on aerodynamic efficiency. Using different angles of yaw, or different directions of wind, they set out to determine just how aerodynamic these helmets were. At the MIT Wright Brother Wind Tunnel, scientists measured the drag of these 10 aero helmets at 30mph. Another variable added to the study, increasing its relevance, is different angles of how helmets sit on a rider’s head. We all have seen an aero helmet on a rider; a good helmet position has the tip of the helmet touching or very close to the rider’s back and a bad position has the rider’s helmet pointing straight up in the air. The scientists took this into account by moving the helmet on the mannequin’s head to mimic these positions and also comparing these values to the normal road helmet.

The fact that some riders put their heads down and many riders have bad aero helmet positions is a big reason why aero helmets are losing their tails. Many of the newest designs in aero helmets have a chopped tail or no tail at all. Road aero helmets are, in many cases, more aerodynamic than an aero helmet with a bad fit.

The results of the study showed that every aero helmet, in position 1 and 2 on the rider’s head as represented in bar graph form in “figure 6 below”  was more aero dynamic than a standard road helmet. At position 3 on the rider’s head, which is basically with the tail of the helmet pointed straight up, most aero helmets were still faster than a standard road helmet but by less of a margin. It is difficult to transfer these drag numbers into wattages as every rider has different wattage numbers at threshold and different positions. An aero helmet is up to 8% reduction in drag at 30mph so for a rider with a threshold of 425 watts, this comes out to around 30 watts of power under these specific conditions according to this study. Each helmet tested in this study had different drag characteristics based on its shape indicating that, as the aero helmet position changes, there is more drag associated with aero helmets with larger tails. The take home point, however, is that in the correct position, an aero helmet is much more efficient than a standard road helmet.    

"Figure 6"

Now that we know aero helmets are faster than standard road helmets we can try to find out if these helmets are creating an amount of extra heat that is hindering our performance.  For that we have to find a new study. Looking for information on heat dissipation of standard road helmets vs. aero road helmets we found the study AERODYNAMIC EFFICIENCY AND THERMAL COMFORT OF BICYCLE HELMETS to be the most relevant.  “Firoz Alam, Simon Watkins, Aliakbar Akbarzadeh and Aleksandar Subic” This study had nearly the same protocol as the aerodynamic study mentioned above except that this study was conducted in a wind tunnel, used various road helmets and put a heating element on the mannequin’s head. The heating element was heated to 140 degrees Fahrenheit and then, while the wind in the tunnel was blowing at controlled speeds, the sensors on the heating element would read temperatures

telling us which helmet had the best ventilation. This study also compared aerodynamic factors of the helmets it tested using different pitches of air. The pitches of air take into account the 2 things: 1. different helmet positions on the rider’s head, as we have seen in the previous study and 2. the relevance of vent placement on the helmet itself, which we will see later is key in keeping a rider cool with an aero helmet.

The results of this study on how heat is dissipated in different levels of road helmets showed that the more aerodynamic the helmet, the less heat was dissipated. In other words ventilation comes at the price of heat dissipation. The helmets that were most aero in the study were actually multi-use helmets that looked very close to the Air Attack by Giro. One of the helmets with vents un-taped is seen on the right. The vents were taped in the study.

 The results of the study showed that the helmets with the worst aerodynamic performance were the most ventilated and looked close to modern helmets of today’s professional peloton. We don’t know the temperature of the wind tunnel air and the 140 degrees of heat that they started with in the helmet is not really close to temperatures in your helmet while on the starting line of a hot Midwest Criterium but we can use it to see just how much heat we are retaining in our aero road helmets compared to our super light, highly ventilated helmets. The most ventilated helmet at a 0 yaw and 0 degree pitch angle of air, or a straight head wind, went from 140 degrees to 75 degrees. This is a 65 degree difference. The most aero helmet with vents taped is significantly more aero than the most ventilated helmet. The temperature inside this helmet dropped from 140 to 124, only a 16 degree drop in temperature in the wind tunnel.

This tells us that the vents work on helmets to cool your head and that there IS in fact a very real danger of overheating from use of an aero road helmet in hot races. There are other factors in the study that we have to take into account before we try to “estimate” at temperature at which an aero road helmet starts to hinder performance.

   What was interesting is that, using different pitches of air and focusing air on specific vents, the study could tell us what types of vents worked on the helmets they tested and what vents did very little in dissipating heat. You can have a helmet with huge vents that does not dissipate heat very well and you can have a helmet with very small, aero, strategically placed vents that dissipate heat very efficiently. The vents on the Air attack and Specialized Evade aero road helmets, as seen here, seem to be small but could be more effective than some larger vents. It’s important to remember that the temperatures used in the latter study are not skin temperature measurements;  the experiment used a heating element and measured drops in heat to see which of the tested helmets had the best ventilation. Also the vents on the most aero helmet in the study were taped.  I’ve never seen anyone tape the vents on a Giro Air Attack but that could drastically change the ventilation and aerodynamic numbers.

Specialized Evade, notice innovative vents and placement

Another major point of the study AERODYNAMIC EFFICIENCY AND THERMAL COMFORT OF BICYCLE HELMETS is that placements of vents are crucial to how they work. The study used different pitches and angles of air to see effects on temperature. Some helmets performed better at different pitches of air, showing us that vents work in different ways. If a vent works best to dissipate heat at 90 degrees of pitch, or straight down, then it’s likely not very useful as you will never really get that air flow unless you are riding with your head all the way down (not recommended). Some helmets have vents that work best at a level air flow. If an aero helmet can utilize smaller vents to reduce drag by making those vents in ideal places and sizes for ventilation then it will be a superior helmet.

These studies work on a fundamental level for us. We Can compare the findings in these studies to helmets currently on the market, how aero dynamic they are, and how well they dissipate heat. The actual temperature changes would be per individual and per helmet and would vary depending on air density, humidity, wind speed, and direction, color of the helmet, and acclimatization of the rider. Fundamentally what we can take away from this research is that aero road helmets are significantly more aerodynamic than standard road helmets. They WILL save you watts. Aero helmets are also significantly warmer than heavily ventilated road helmets. If your event is already dependent on keeping cool then a performance enhancement made by wearing an aero road helmet will have heat consequences. The Source Endurance team gave a rough estimation of 75-90F degrees for when we would trade an aero road helmet for a more ventilated one. Again this would depend on speed of the event and a dozen other factors on race day.  In most situations, where your event is not blistering hot, an aero road helmet will be more efficient. 

Offseason Training, Don't Waste Your Base (2 of 2)

By: John Hobbs, MEd. Senior Consultant

  Once it was observed that many of the benefits seen with longer and easier training sessions were also seen with shorter and harder workouts, the next step was to identify which changes do and do not occur among the two training modalities.  By analyzing training adaptations at different intensities in individuals of various fitness, multiple changes occur at the cellular and enzymatic level when any of the variables are altered.  So while aerobic gains of types do occur at very high intensities that also occur at lower intensities, as various enzymes and cells are pushed in different ways at the various workloads, the changes are not the same across the board.  Changes in fiber type of muscles, enzyme activity, expression of various proteins and a whole slew of activities are dependent on intensity, volume, and fitness of the individual.     As a result, hopping on the trainer and cranking out maximal efforts does not provide the same benefits as lower intensity efforts of longer duration.  Additionally, the negative health and training ramifications as well as stagnation that occur with long periods of intense training make the combination of early and late season intensity impractical and counterproductive to an athlete's form.

Which periodization model is best for you?

            The individual athlete is a key in the assessment of the changes.  A fit athlete may only see some of the changes observed in an individual of lower fitness level, and even then, the gains may be smaller.  Additionally the benefits seen by two individuals of similar performance levels may not be the same due to the fact that the one athlete has already exploited the changes in previous training (ie enzyme x increase significantly in one athlete but not the other).

What about this model? 

Does this one work? 

So many models!

At this point is seems that we've just talked ourselves in a corner by arguing the typical base training paradigm is not a good way to go in the off season and  neither are short hard rides.  In the end, the training has to fit the needs of the rider.  By moderately increasing exercise intensity to the tempo and steady state type work, we can compensate for the lack of volume that average athletes have.  This allows for an overload to take place, but still allowing for adaptations to occur that may not be seen at higher intensities.  The question still stands of how to address the demands of a 3+ hour race.  The overload provided during a standard training week with three to four hour ride in the typical base training zone on the weekend does not provide most athletes with sufficient overload of various physiological systems to provide a training benefit.  But by including intervals during the week, the overall training stress is increased which can, in-turn lead to stimulation of various adaptations.  And while it may seem like we are contradicting ourselves, training volume can increase even as intensity increases with training.  While following the periodization format exactly as the theory dictates would not allow for this, it can be done in proper increments as dictated by the overall stress of the current training.  This is where the coach and physiologist is able to bridge the gap between science and practical implication of training.  As coaches we realize that long rides are not available all weekends to every athlete. As physiologists, we have the expertise to adjust the training to allow for workouts to address the needs of longer events.  Athletes may see the duration of their long rides increase in periods of relatively high training intensity.  The increases may be small and not occur every week, but it allows for appropriate training for specific events.

It is possible none of these work for YOU.

Often times, SE consultants don't stick to any of these models. 

This one? Often times SE must generate a custom model.  

            As touched on earlier, the main variable in designing an off-season training plan is the athlete.  A blanket statement that high intensity workouts do not belong in the off-season would be inappropriate at the least.  These workouts may, in fact, be beneficial to a population of athletes under proper circumstances.

            While various physiological principals were covered and stances taken based on data, it is noted that no studies or peer-reviewed literature was cited, as is contrary to typical articles.  The frustration felt by those hoping to reference sources, critique the statements made, and those who are just fellow science geeks is understood.  Rather than explain a scientific principal, the goal of this article is to illustrate the madness behind the coaches’ methods and provide background information on the structure of training during this period.

Offseason Training, Don't Waste Your Base (1 of 2)

By: John Hobbs, MEd. Senior Consultant            

The off-season doesn't exist to many racers on structured training plans.  It’s a period to race cyclo-cross and/or recover for a short bit before prepping for the next season’s races.  This period can also be tremendously beneficial in gaining fitness.  However, the elements are against most racers with cold weather, snow and ice, and jobs and families to get back to.  Couple this with flawed anecdotal training, and valuable saddle time is wasted.

Staying fit in the off-season with CX is becoming more popular

            As stated in previous articles, and likely your coach, a primary goal of this period is to ensure athletes are recovered.  This means from injuries, training, as well as psychologically.  In the same way this early training can help build an athlete, it can also contribute to failure if these recovery demands are not met.

            The term “base training” is usually applied to this early season work.  Professional cyclists usually throw this around as the emphasis of early saddle time. The concept often encompasses long rides of low intensity.  But, there are several faults with this thought process, especially when applied to amateur athletes with regular jobs and life demands.

            Principals of training include intensity, frequency, and duration of training.  This combination must  involve some form of overload  in order to see adaptations leading to improvement.  In the stereotypical base training, the athlete achieves this overload through a high amount of volume with low intensity.  This can be effective if the athlete is able to train sufficiently.  But the reality is that most athletes are not able to make the commitment to this quantity of saddle time and end up riding slow and short rather than the slow and long that is required to provide sufficient volume.  And as an athlete, the maximum must be gained for the time available for training.  So, an overload must be provided by altering some other aspect of training—intensity.

Most athletes make a daily transformation from  suits...

            

At first glance, several legitimate question arise regarding this principal.  These regard specificity of training to the competitive events and the periodization format that drives structured training.   Under the periodization structure, training starts with a higher volume and lower intensity and adjusts with more intensity and lower volume as competition nears.  Additionally, most cycling races involve hours of saddle time come race day.  So, it would seem natural that a block of high volume, low intensity training would fit the bill.  But, the amount of time required to provide an overload is not practical for most individuals.  The value of longer rides and adaptations that can occur with high mileage  can not be negated, especially when you’re looking at a three or four hour race.  As a result, these adaptations need to be sought in a more practical means.

From suits to kits on a daily basis. 

            Its been documented in several studies that many of the adaptations that occur at low-intensity exercises occur more rapidly at higher intensities with less training time.  With this in mind, athletes could justify swinging to the other side of the spectrum and do hard, short workouts.  And, that’s exactly what some do in the winter driving home VO2 max type workouts on the indoor trainer.  But, this approach isn’t necessarily effective either.  While increased intensity can provide an overload in less time, all training adaptations are not the same.  With the present emphasis on HIIT (high intensity interval training), this concept is lost when gross generalizations on performance are made similar to a political candidate saying “Americans will have lower taxes.”     

Sports’ secret weapon: sleep. By: Michael J. Breus, PhD

The search for performance enhancement leads some athletes to turn some pretty dark corners. It’s a shame, and not just because doping is dangerous, unethical, and frequently illegal. It’s also a shame because athletes at all levels of play have access to a powerful tool to improve their performance, one that won’t break any laws or put anyone’s health at risk.   

What’s this wonder drug? Sleep.  

There’s been a welcome up tick in the attention paid by the media and athletic professionals to the benefits of sleep for competitive athletes, and to the research that shows just how sleep can improve physical performance in sport. This season, the NY Jets brought sleep specialists into the locker room, signaling their intention to use sleep as part of their training strategy. At the other end of the spectrum, I was disappointed toread that Manchester United is addressing its players sleep issues by issuing sleeping pills. This strategy—and the coach’s seemingly cavalier attitude toward medicating players for sleep—is not what I recommend when I suggest that athletes and coaches pay more attention to
sleep.  

In recent years, Stanford University’s Center for Sleep Sciences and Medicine has been at the leading edge of examining the sleep-sport performance connection. Researchers there have conducted studies with several groups of Stanford student-athletes, examining the effects of extended sleep on athletic performance. Here’s a sampling of their results, which show improvements across a variety of sports:

Swimming: Five members of the Stanford men’s and women’s swimming teams increased their sleep goal to 10 hours per night for a period of 6-7 weeks. This led to improvements in speed, reaction time, turn times and kick strokes. Swimmers shaved an average of .51 seconds off a 15-meter sprint, they left the blocks .15 seconds faster, shaved .10 seconds off their average turn time, and added an average of 5 kicks to their stroke frequency. Out of the water, swimmers reported reductions in their levels of daytime sleepiness, improvements to their mood, more energy and less fatigue.

Tennis: Researchers asked five members of the women’s tennis team to increase their sleep goal to 10 hours per night for 5-6 weeks. Players improved their sprint times, dropping from an average of 19.12 to 17.56 seconds. They also increased their serve accuracy, going from an average of 12.6 valid serves to 15.61.

Football: Seven players on the Stanford football team spent 7-8 weeks attempting to sleep for 10 hours per night. Their extended sleep resulted in improvements to their 20-yard shuttle—average time decreased to 4.61 seconds from 4.71—and to their 40-yard dash, which dropped to an average of 4.89 from 4.99 seconds. (Both the shuttle and the dash are among the drills conducted at the NFL Scouting Combine.) Players also reported improvements to their daytime energy levels and mood, and reduced daytime fatigue.  

Basketball: For 5-7 weeks, 11 members of the university’s basketball team extended their nightly sleep to 10 hours. As a result, shooting accuracy among the players improved significantly: Free throw shooting improved 9%, and three point shooting 9.2%.

Sensing a pattern? Extending sleep times translated into significant improvements to critical game-day skills. Worth noting: not all athletes across these studies actually slept for 10 hours per night, but attempting to sleep for 10 hours per night got them additional sleep compared to their regular routine. According to researchers, many of these athletes came to their sleep-sport studies already sleep deprived.

And that gets to the flipside of the advantages that additional sleep can give to athletes. Sleep deficiency can inhibit performance. Research shows lack of sleep can also affect the longevity of players’ careers. Two recent studies investigated the relationship between sleep and career duration and stability among NFL players and MLB players. The NFL study looked at 55 players from across the league. Those who reported higher levels of daytime sleepiness were less likely to remain with the team that drafted them than those players who reported lower levels of daytime tiredness. And MLB players who reported higher levels of daytime tiredness had attrition rates far higher than league averages.

There’s also evidence that sleep can increase the risk of injury among athletes. In this study of teenage student-athletes, those who slept at least eight hours per night were 68 percent less likely to injure themselves playing sports than those who slept less than eight hours nightly. Researchers examined the sleep patterns and sports-related injuries of 112 male and female athletes from grades 7-12. They discovered that sleep and age were the most significant factors in assessing injury risk. (In addition to being more injury-prone when short on sleep, students were also more likely to injure themselves as they moved to higher grade levels.)

So what’s behind the performance boost from sleep?  

The cognitive benefits of sleep translate onto the field. Memory, learning, reaction time and focus: sleep is critical to the brain’s ability to perform these mental tasks efficiently and well. The brain uses sleep toconsolidate memory into longer-term knowledge, clearing the area of the brain used for short-term memory in preparation to absorb new information. During sleep, the brain also works to prioritize the information it thinks will be important in the future. Sleep deprivation has well-studied negative effects on reaction times—and even a single night of sleep deprivation can slow quick  response times.

Sleep promotes muscle recovery. Sleep is a critical time for cell regeneration and repair in the body. During non-REM stages of sleep, cell division and regeneration actually becomes more active than during waking hours. Insufficient sleep, on the other hand, hinders muscle recovery.

Sleep is a stress reducer. Sleep and stress have a tangled relationship—and both are dangerous to healthy immune function when we don’t get enough (sleep), or have too much (stress). Stress can interfere with sleep—this study ranked worry as the most common cause of sleeplessness among adults 34-79. But lack of sleep can also affect mood, and make us more susceptible to stress and anxiety.

Is sleep the next big thing in sports? I’d say it’s more than earned its shot in the big show. 

Sweet Dreams,

Michael J. Breus, PhD 

Crank length, What’s Your Size?

Zack Allison, BS
Source Endurance, Senior Coach

What length is your road crank? If you are less than 5 feet tall you are likely running 165mm cranks. If your height is 5’5” – 6 feet you are likely spinning 172.5mm cranks. Over 6 feet and the length “standards start to vary.” 175mm? 180? Custom length specially made? What actually makes these the right lengths for peak power and efficiency?

Just for fun I took a look at some of the “greats” of cycling and what lengths they ran during the hour record.  Some of these could be bogus but it’s interesting to think about before we go into the science of crank lengths.

Here is a chart of hour record holders over the years. Notice the crank lengths.

Indurain ran 190mm cranks. Huge for a track but there aren’t really any needs to accelerate fast. I couldn’t find any information on the rationale of such an outlier of crank length for his record. Boardman ran 170’s and is not a small man stretching to 6 feet 2 inches tall. The track hour record is relevant to this discussion as there are people of all different sizes holding the record for periods of time all running different length cranks not correlating to their height. Now that it seems like history has told us that crank length has very little if any correlation let’s dig deeper.

*We've been advised that Indurain actually ran 180mm cranks made by Campy, who have never made 190mm cranks.  Thanks for the correction Kris. 

Scientifically, “what is best and why” is a loaded question. When looking at crank length vs. power you take into account leverage. There are three forms of simple levers with a bicycle crank, and a wheel barrow being second class levers.  Check out this class two lever diagram to the right.

If you consider your crank/bottom bracket system as a second class lever, the length of the crank arm is the effort arm. The fulcrum is at the bottom bracket on the crank arm and the effort force of you pushing or pulling on the pedals is at the other end of the crank arm. Since this is a simple second class lever, the longer the effort arm, or crank arm, the larger the mechanical advantage, or more leverage. In the above picture the effort arm is from the line labeled effort to the fulcrum. The longer the effort arm is the easier it is to move the load, yet the further you have to move it.

MA= Fb/Fa= a/b

The law above is the “law of the lever.”  It shows that if the distance a from the fulcrum to where the input force is applied is greater than the distance b (from fulcrum to where the output force is applied), then the lever amplifies the input force. In our case the input force can be considered the power you apply to the pedals. If you simplify this and apply it to a bike, the longer your crank, the more your force is “amplified” to the cassette and forward movement. Just like if you are trying to take your bottom bracket out after 8 years. Its stuck, your normal 150mm bottom bracket tool isn’t working to you use a “cheater bar” to make the tool longer, increasing the effort arm, increasing the force, yet you are exerting the same force you had on the tool before the cheater bar.

Lets apply this to crank length on a larger scale. Let’s say you have 300mm cranks. This is overly long but for the sake of argument the same principles will apply for 160mm vs 175mm cranks. You have now extended your effort arm by almost 100% if you started with 170mm cranks. You could feasibly, on a climb for example, stick it in your big ring and power up 20% grades with half the force that you were applying with your 170mm cranks. Mathematically this works out in the equation above.

So why do we not all run 180mm cranks? There’s more to your pedal stroke than just force. There is the distance your foot has to travel and the force length curve of your muscles. Every muscle has the same force length curve. It looks like this. If you double your crank length, you also double the distance and speed your feet has to move to turn the crank, and your muscles experience a further stretch and contraction than with shorter cranks.

What this is showing is that as your muscle stretches its amount of force changes. Each single muscle fiber can produce a certain amount of force. The amount of force it can produce never changes; to produce more force your body recruits more fibers. As you see in the diagram your muscle, at its most lengthened position can produce no force. Your muscle at its most shortened position can produce no force. Think about if you are stretching your quadriceps while standing with your hand and you try to straighten your leg. You can give some force, but it’s not nearly as much force as your quad can produce when it’s only slightly bent. Same as if you are in a low squat, it is much harder to begin the lift, than to finish it out.

We can apply this to the crank length argument. If you run a crank length that is too long you will be brining your muscles though a range of motion that is not optimal for the muscle force length curve. As you are at the top of your pedal stroke with a crank that is too long you will be shortening your hamstrings, and stretching your quads so much that they are well out of their optimal length to produce force.

When deciding on crank length, if you are not willing to accept, “you get what comes on the bike” you have to consider all of these variables and how you fit on the bike. Too long of a crank and you are not efficient in your muscle contractions or the distance your foot has to travel each pedal stroke. Too short of a crank length and the amount of force you have to exert on the pedals out weights the smaller range of motion.

This is where we get into how to pick your specific crank length. There are a few variables. 1. Crank application. Are you climbing, sprinting, cross riding, all of the above? 2. How long are your femurs?

Track bikes will not have the same crank length as mountain bikes as the force’s produced are vastly different each different discipline. In track riding you have one gear, you need to be able to accelerate that gear but also spin the gear very fast to maintain top speeds. In mountain you need more torque to power over obstinacies and up steep climbs. You will run a longer crank, usually up 1 standard size for mountain than for road and usually two sized from track to mountain crank lengths. If you need more torque and force like in mountain you need a longer effort arm in your lever, a longer crank arm. You would not be able to spin this longer crank arm on the track. Road you need both qualities so you run the in-between based on your femur size.

Much of crank length choice is “standardized” to bike size. If you are running a 52-58 you are likely on 172.5mm Anything more and you are on 175’s anything less than a 54 and you are on 170’s. A better measurement of what your crank length should be is based on Femur length. Femur length will dictate most of which crank length will keep you in your force length curve during your entire pedal stoke. In most cases your height/ stand over height will dictate how long your femurs are, and therefore you are receiving the right size cranks on your bike automatically. Before you settle for this technique measure your femur length and decide for yourself. If you have a longer femur length for a 5 foot 2inch person you may want to move up to 172.5mm cranks over the 170s that came on your 50centimeter frame.

In the study “Influence of crank length on cycle ergometry performance of well-trained female cross-country mountain bike athletes” Trained female mountain bikers were tested at different intensities for efficiency of pedal stroke based on different crank lengths. The results fall in line with what we have discussed. Crank lengths do change the properties of power output and should be specialized for each discipline but in any one discipline for example road, there is not an advantage to running long cranks or short cranks rather cranks that optimize efficiency for your femur length will be the best.  Stay tuned as I discuss how to incorporate femur length into crank arm length choice.

                

Pedaling Efficiency at Low vs High intensity

By: Zack Allison, BS. 

Source Endurance Senior Coach

Many things go into a pedal stroke. Consider that the daily commuter just pushes down on his flat pedals, making one dimension of force. As this commuter pedals harder to make the red light, his RPMs increase and he starts to bounce on the saddle and inefficiently gain speed to make the light. On the other hand, as the elite-level racer picks up the pace to follow an attack from the field, he shifts up and smoothly increases power at close to the same cadence and,  ideally, the same trained efficient pedal stroke. 

Last week I sat in on a little experiment with Category 1 racer Whitney Schultz. We had Whitney ride the Computrainer and used its extensive programming capabilities to break down her pedal stroke in all directions - left and right and up and down. We originally thought that Whitney’s stroke was imbalanced; it looked like she was favoring her right leg. When she was on the Computrainer it showed that she was never favoring one leg over 2%. This is good but we need to do more experiments. She may be recruiting other muscles to make up the difference that a back injury created. With more fatigue she may start to favor one leg - we’ll see.  

        

This is Whitney Schultz on the Computrainer. The screen shows her left leg contributing 49% , while her right does 51% of the workload, all at 200 watts.  The blue bars show her down-stroke and the purple/red/yellow bars show the up- and back-strokes. Whitney, being an accomplished racer, would not see these bars move very much between her current 200 watts and a hill at 350 watts. This pedal consistency shows efficiency. If your stroke changes at higher watts, you are recruiting muscles not normally used in a pedal stroke and you will fatigue faster.

Based on the principle of muscle recruitment, your body recruits motor units at different efforts. One “motor unit” is one muscle fiber and its motor neuron that activates that muscle. If you are pedaling at 100 watts, your body will recruit as few slow twitch fibers as necessary to do that action. As you pick up the pace to 200 watts, your body will recruit just the number of motor units necessary to complete this activity. If you take this principle all the way up to a 1300 watt maximal sprint, your body has recruited all of the fast and slow twitch muscles it has to perform this max effort. This principle will affect your stroke.  

There are physically more motor units on the anterior (front) side of your upper leg that, including your gluteus muscles, perform “knee extension” or pushing down on the pedals.  The diagram below shows for a full pedal stroke where muscles are engaged and resting. As you can see, your gluteus and quadriceps muscles are big muscle groups and have a larger range of force. This means you can have a smooth pedal stroke but your stroke will not produce even forces all the way around. 

In any normal stroke the goal is to make a circle and have a smooth and efficient stroke. This has many issues. Your quadriceps are stronger than your hamstrings. If you expect your hamstrings to be as powerful as your quadriceps, you will have an uneven stroke when your hamstrings cramp and fatigue. The good thing is that your cranks are attached to each other so your force on the pedals doesn’t have to make uneven speeds in your stroke.

The goal of your pedal stroke is to be consistent. Your quadriceps will be doing more work but they have a larger muscle area, therefore more strength and there is no avoiding that. What you, as a cyclist, should work on is keeping your pedal stroke consistent at every power interval. You will change your stroke based on if you are climbing or descending but increasing watts on a consistent grade should have as little change as possible on your form.

This video shows Eric Marcotte of Elbowz Racing pedaling at 300W

Eric again at 500W.

Notice Eric's stroke is the same in each video. At 500 watts, Eric is well above his lactate threshold (LT) and is recruiting pretty much all of his muscle fibers and has his core engaged more but his basic pedal stroke is the same, even though he is recruiting 85-95% of his motor units as discussed above . This is what any racer should strive for. Despite his high effort, his pedal stroke remains efficient. As he fatigues he may start to have certain motor units’ fatigue. As his hamstrings fatigue he may start to recruit his back muscles to compensate changing his stroke. This is why a strong core is crucial and why lesser trained cyclists have more back fatigue on long rides.

Returning to the example of the commuter on flat pedals, his form changes from efficient to inefficient when he doubles his power to make the light. When you double your power from 200 to 400 watts your pedal stroke should be the same. If it is different, you are becoming inefficient at higher watts, which is the last thing you need. If this seems impossible you may need to check your fit and crank length. Otherwise get out there and do your workouts but be aware of your pedal stroke and the source of some inefficiencies. 

Ischemic Preconditioning

   John Hobbs, MS         

One interesting aspect of studying exercise physiology is the ability to incorporate a multi-discipline approach to developing new ideas.  The major underlying theme is the body being placed under a form of stress and monitoring the response.  The crossover between exercise science and medical research is well founded as it’s not uncommon to see researchers in Exercise Physiology performing studies regarding heart disease, modalities to simulate bleeding, sub-cellular changes to tissue, to a further variety of topics.    With these relationships in mind, an anesthesiologist brought up the topic of a surgical technique called ischemic preconditioning.    Essentially, the blood flow to a limb is temporarily occluded and then allowed to re-purfuse for a short duration.  Several cycles of this treatment serves to protect the heart during surgery. The concept is intriguing due to its mechanism and questions regarding implementation with the limited research on athletes currently available.

            Specificity is an attribute that is highly stressed to athletes.  If you want to run faster, you have to actually run fast and any other training has to closely mimic the demands placed by running.  The medical background of ischemic preconditioning is similar.  It is well documented that by stressing the heart, various proteins are produced to serve as protective mechanisms, such as heat shock proteins.  The stress required is small and relatively long lasting with single bouts of exercise producing benefits lasting weeks.  The cascade of events leading to this protective mechanism is involved with a variety of variables including gender based hormone production and age.   The end result is increased protection against what is called ischemic-reperfusion injury—essentially the heart cells being starved of oxygen, becoming damaged, and then rupturing once oxygen is re-introduced. 

            The method used preoperatively seems to negate the concept of specificity.  In a pre-operative hospital setting, a protocol occluding a patient’s arm with a blood pressure cuff can be applied resulting in better outcomes in procedures involving the heart.  What is novel about the procedure is that the stress applied to a remote site provides benefits to a distant location.  While systemic messengers in the body are nothing new with basic hormones being taught in high school biology, the signaling with this protocol does not follow the same  principals.  It could be equated to doing bicep curls to increase your 40K time trial.

            Limited research is available on the topic regarding athletic performance.  Two recent publications by Jean-St-Michel et al. (2011) and Groot et al. (2010) evaluate the application of the concept to exercise performance.  While the tendency is to find all the holes in the research and conclusions and question validity, the limited work available on this topic would favor time spent delving deeper in to the mechanisms and  implementation of the practice.

            Both Jean-St-Michel et al. and Patricia et al. implemented  ischemic preconditioning prior immediately prior to exercise testing.  The former utilized the arm as the treatment site in swimmers with the latter performing the treatment on the legs of cyclists.  Both showed benefits due to the treatment.

            In evaluating the swimmers, the researchers found a benefit to maximal intensity exercise illustrated by 100 meter swim times.  The authors noted, the benefit seen was relatively small, being less than a second, but competitively significant as top level events over that distance.  An increase in the stroke count was also noted in the treatment data.  This could be significant as swimming speed relies on the relationship of the distance covered per stroke and the speed of the stroke (Jean-St-Michel et al. 2011).  A question emerges if the alteration of stroke count is a physiological response allowing for a faster stroke rate with decreased fatigue, or an alteration in form due to the preconditioning.  Regardless, the end result in an increase is swim performance.

            The cycling group showed improvement in VO2 max and in the maximal power output achieved during the testing.  The researchers attributed this to improved endothelial function, essentially the diameter of the blood vessels, for a partial cause of the improvement (Groot et al. 2010).  It must be noted that this theory contradicts data and commonly taught limiters to VO2max in athletes.  But, that is the nature of science with constant remodeling and invalidating of theories.  Additionally, the research methods may not have been conducive to the highest level of validity.  The end result of the study, however is the same—increased performance.  Further work will provide reinforcement or dismissal of the theory regarding the mechanism.

            When evaluating the studies presented, an important note is the fact that the benefits were seen only in maximal exercise efforts.  While this could provide a benefit to events specializing in a maximal effort only, such as a 100 meter swim, the benefits have yet to be evaluated across endurance activities.  Based on the various differences in limiters of performance, the protocol may or may not be effective.  Additionally, duration and intensity of exercise prior to the maximal exercise testing has not been evaluated.   This is to say that a cyclist attacking two miles from the finish may have the benefit “washed out” by the previous sixty miles of racing.

            One interesting note is the fact that both of the studies regard exercise as a possible ischemic event whose stress contributes to fatigue.  So, in a more practical application than bringing a blood pressure cuff to competition maybe to utilize high intensity bouts of exercise as the means to illicit ischemic preconditioning.  While neither of the articles directly associates this concept with their findings, this could add to data supporting high intensity intervals in to a warm-up prior to a race.

            A final note on the research procedure is the fact that the ischemic event was utilized in a limb directly implemented in the exercise.  The cycling study utilized both legs which allowed to demonstrate the existence of a benefit, but not isolate it to the legs.  The work by Jean-St-Michel et al. attempted to focus in on the possible cause of the benefits.  By using one arm, they hoped to demonstrate a positive effect at a site other than the occluded arm.  This closely mirrors the ischemic precondition previously presented as being used in surgical procedures.  The researchers went a step further by using the blood from the swimmers before and after conditioning in rat hearts undergoing ischemia.  The results showed that the blood drawn after the ischemic conditioning served to protect the rat heart. 

            These data serve as starting points for evaluating the use of a possible supplement to training.  Athletes must use caution however, before incorporating these practices in to training as extrapolating benefits of medical practices to the athletic arena routinely occurs with no other significant benefit shown other than separating athletes from their dollar.  As with any novel theory or application, further study is required.  While these initial studies show possible promise further work may reveal a cumulative effect that could allow for training with a blood pressure cuff while you lounge on the couch or the fact that a quick bout of push-ups during staging at a race could provide a small benefit.

References

Jean-St-Michel, E., et al. (2011).  Remote Preconditioning Improves Maximal Performance in Highly Trained Athletes.  Medicine and Science in Sports and Exercise, 43(7) 1280-1286.

Groot, P., Thijssen, D., Sanchez,M., Ellenkamp, R., Hopman, M. (2010).  Ischemic preconditioning improves maximal performance in humans. European Journal of Applied Physiology, 108(1) 140-146.