Monday, November 12, 2007

Power Demands of Cyclocross Racing: Part 2

It was another exciting round of cyclocross racing in New Jersey at Beacon and Highland Park this past weekend; both were UCI races and part of the Mid-Atlantic Cross Series. Davide Frattini and Georgia Gould won both days with the right combination of form and fitness. Georgia impressed us all by winning the Men's B race on Saturday and placing well again on Sunday (starting at the back of the field both days) before riding away from all her competitors in the women's races both days.

Last week I posted power numbers for some of the riders that rode with PowerTap wheels in the Spring Mountain race. Just to refresh, a few things immediately stand out about these files:

1. Very non steady-state efforts
2. Relatively low power; far less than what the riders would be capable of producing for a steady-state effort of the same duration.
3. Low cadence. Average cadences were 67-80 rpm.

So what makes cyclocross so hard? It certainly isn't the high average power, or even normalized power. Is it the low cadence? Is it the running? How important is technical ability? Does better technique mean that a rider will not have to put out as much power to go the same speed? And finally, what qualities make a good cross racer?

When you look at power files from any cyclocross race, there are 3 "modes" that a racer will be in almost all the time:

1. Sub-Maximal. This is the point that is just short of a sprint, about a 9.5 out of 10 on the intensity scale. In non-technical sections with good traction and no obstacles, riders can really lay down the power. These efforts can range anywhere from 2-3 seconds up to about 30 seconds on courses with long open sections. In the course of a 60 minute race a rider may have to make up to 200 of these efforts. Though the length of the efforts is highly course dependant, they are rarely over 30 seconds. Since Normalized Power is calculated using a 30 second rolling average, that number will not truly reflect the difficulty of the race like it will in criteriums and road races that include regular 30 second+ hard efforts.

2. Coasting. No power is applied to the pedals. This could occur going down a hill, into a turn or into the barriers. These efforts typically range from 1-5 seconds.

3. Braking. Although braking and coasting will both register as zero power, I will make the distinction here because braking is actually the application of additional opposing force. Remember my definition of Speed = [Power - opposing force]. On a flat road, about 85% of the opposing force is from aerodynamic drag with the other 15% from gravity, rolling resistance and drivetrain resistance. When a rider goes uphill, more of the resistance is from gravity and as they slow down the amount of aerodyamic drag increases. Off road, aerodynamic resistance is minimal because of the slower speeds, but rolling resistance is much more significant. Braking force is rarely considered in road racing because the brakes are used so infrequently, but it is highly significant off road. So maybe before you go on that crash diet and try to lose 10 lbs, you should ask yourself if you could brake a little less, or perhaps not quite as hard.

4. Soft Pedaling. These are the sections that are too technical for a rider to go full throttle, but they can still pedal through. These usually occur around tight turns or off-camber sections of the course. These efforts are usually 3-10 seconds in duration. Power output is typically in the recovery or endurance zones.

What is conspicuously missing here are the long steady state efforts that would occur often in road racing and even in mountain biking.

If we examine in detail the file of a technically proficient rider, you will see that they spend less time coasting and more time pedaling. A good technical rider is still soft-pedaling when others are coasting. This means that they will come much closer to actually producing the power they are capable of (as we saw with Kyle last week).

The other factor is that the better technical rider makes less severe decellerations. Less severe decelleration means that the reacceleration is also less severe. Think of it this way: every time you lose speed through an obstacle you have to get back up to speed after you clear the obstacle. If you don't lose as much speed, you don't have to apply as much power or apply power for as long to get back up to speed. This energy savings adds up. Though some of us have more matches to burn than others, no one has an unlimited number of matches. Every re-acceleration takes energy and causes muscular fatigue, so a rider that is constantly slamming on his brakes and then sprinting back up to speed is at a distinct disadvantage and most likely won't have much left at the end of the race to sprint, attack or chase.

As evidence of this, we can examine a couple close races at Spring Mountain. In the B race, Woody and Johann were 2nd and 3rd, respectively, and finished only 5 seconds apart. Woody, as the better technical rider, spent 8 minutes and 27 seconds (~19%) at sub-maximal power levels (>5.5 watts/kg) whereas Johann spent 9 minutes and 11 seconds (~20%) in that zone. In the elite race, we can examine John (4th place) and Colin (5th place) who finished 1 minute apart. John spent 13 minutes and 10 seconds (21%) at sub-maximal power levels compared to Colin's 15 minutes and 24 seconds (25%).

So, what does it take to be a good cross racer?

1. The ability to make repeated sub-maximal efforts with little recovery.

2. Good technical skills: more time pedaling, less time coasting, less time braking and less severe braking. This of course, should all be done while keeping it upright :)

3. Good muscular strength. This is necessary because of the low cadence/high torque nature of the sport.

Of course, there are other factors as well, such as being able to start a race with a 15-30 second all out sprint, transitioning on and off the bike well, being able to run with the bike, and of course, a lot of mental toughness. Next week I will talk about how we can create workouts and race strategies that will best capture the unique demands of cross racing and help racers minimize their weaknesses and maximize their strengths.

This weekend Trenton will host the biggest weekend of cross racing on the East Coast, so I hope to see you all out there with your cowbells!

Wednesday, November 7, 2007

Another Multi-sport Season Draws to a Close - Now what?

by Mikael Hanson , Director of Performance for Cadence Cycling and Multisport Centers - NYC

If you are anything like me, the arrival of fall elicits mixed emotions. Sure, the turning of the leaves signals the much-anticipated start of the football season and the approach of another World Series, but it also means the days are rapidly growing shorter and the that slight edge in the morning air can only mean Winter is knocking on the door - signaling the end of another racing season. Regardless how you're season ended up (good, bad, or just plain ugly), one thing everyone needs is good old fashion rest.

A few years back, Inside Triathlon magazine ran an interview with multi-sport legend Ken Glah where he outlined his five steps to racing longevity. While we all may not have racing resumes as impressive as Kens' that does not mean we can not benefit from his years of wisdom for extending our own racing careers (my own has lasted over 25 years and I see no signs of stopping anytime soon!)

1. Enjoy your training - This is the only reason to be involved in our sport, so find the aspects of training you like the most and focus on those.
2. Enjoy the races - Which may come from the sheer thrill of competition, but also doing races in different destinations is a great way to include family and friends.
3. Be realistic - If you are in the sport for many years, it is important to adjust your goals from year to year, making sure they are attainable (as unreachable goals will only disappoint and decrease your enjoyment).
4. Don't just train - While the three main disciplines will dominate your time, engaging in other activities will keep you going for the long term (such as regular massages, weight training, yoga, pilates, and stretching).
5. Take time off - Yes, training and racing are addictive, but it is critical to include recovery time in your schedule as well as planned time off during the year. You will never last in this sport if you don't have a rich personal life outside of triathlon.

So, with nearly six months before the start of next season, how should we approach the long days of winter? The first step many of us fail to take is the brief, albeit necessary off-season break. Depending on your own level of obsession with training, this break should be a period of one to three weeks where one does not worry about hill repeats, weekly running mileage, or exotic Brick workouts. Leave the triathlon toys at home and take some time to enjoy your family and friends. Go to a football game, take a drive in the country, go for a hike in the hills (yes, some form of mild exercise is okay). Reward yourself for a successful season. Personally I like to start my end of the season break minutes after finishing the Thanksgiving Day Turkey Trot in Philadelphia, as images of steaming apple pie and mountains of turkey always seem to make me run a bit faster than normal.

During your break, it is important to take a hard look at your recent season and ask yourself several questions (and yes, honesty counts)! What worked in your training? What didn't work? Where were your strengths? Your weaknesses? And finally, what are your goals for the upcoming season? Only after you have accurately answered these questions, can you begin to address the next season.

Once your mini-break is over, it is time to EASE back into training, with an emphasis on the word EASE. With so many months before your first event, there is no need to rush into your training. However, one must realize the importance of building a solid foundation in the early season (January to March). Take a page from Lance Armstrong's training, as he has often said that the Tour de France is won in December and not July. Use the off-season to focus on your weaker sports. For me, a duathlete at heart who has converted to triathlons, that would mean leaving the bike alone for a few extra weeks while I focus on including a few extra sessions in the pool. This is also a great time to try your hand at a little cross-training outside of the regular multi-sport disciplines. Cross-country skiing, roller blading, and hiking are all great endurance building activities, while yoga and pilates can help with your core strength and flexibility – all things we begin to lose as we get older.

Riding Indoors
While many will ride almost year-round (multi-rider centers like Cadence certainly help here), come January the bulk of us need to consider re-introducing ourselves to the two-wheeled machine gathering dust in the corner. However as the weather deteriorates and darkness reigns, I find that many athletes actually dread climbing on their trainer, stating that riding indoors is about as exciting as watching paint dry. Perhaps these people suffer from a lack of imagination, as I for one relish the opportunity to ride indoors. Where else can one combine watching TV with a workout?

There are several things one can do to make riding indoors more enjoyable. First of all, your environment is a huge factor in how comfortable you are while riding indoors. For me, the closed confines of a NYC apartment can lead to some stuffy riding conditions. The first thing one should invest in (after a good indoor trainer for your bike) is a fan. Even on the coldest winter days, I crack the window a touch and aim the fan directly in my face, thus keeping the overheating to a minimum. Make sure you have a towel draped over the handlebars and for those of you with hardwood floors place another one on the ground below your bike, as you will sweat (trust me on this one!) The next item on the list is entertainment. Listening to music is always an option, but this only helps out one of our senses. I need more stimulation when riding at home. Why not ride while watching your favorite football or basketball team play? Or better yet, how about watching Lance win one of his Tour de France titles on tape? My favorite source of riding entertainment is a good old James Bond flick.

Now what to do while riding. Sure, watching Brett Favre or James Bond will help pass the time, but you still have to think about your workout. Try adding some spice to your indoor ride, while keeping in mind we are still in the off-season. One thing to focus on in the off-season is your technique. High cadence drills will help improve one’s mechanics by making your pedaling smoother and more efficient. Another drill to work on is one-legged drills. Pedaling with one leg helps develop that circular pedaling motion by incorporating more muscles into one’s pedal stoke, thus spreading out the workload smoothing out the dead spots (which will ultimately reduce muscle fatigue and help increase endurance, strength and power). After your warm-up and drills time for the core portion of the ride. In the off-season intensity takes a back seat to re-establishing a foundation and building back strength. If you are watching TV while riding, try an over-gear interval or hill climb whenever your football team has the ball, throw in a 30 second standing effort for every touchdown or turnover, or do a large-gear seated climb for the duration of every car chase. Just use your imagination and I ensure you will see the time fly by, and you'll get a great work out on top of it.

Running Indoors
Even in our northern climate, there are many who successfully run outdoors year-round, thus never need to face the boredom often associated with the treadmill. Coming from a cycling background, I will be the first to admit that the thought of running on the treadmill used to send a chill up my spine. Let's be real, on a scale from one to ten, the boredom factor is quite high for a treadmill run, especially when compared to the alternatives. But if you think about it, what separates the treadmill from say swimming laps at the pool or riding your bike indoors? Both offer little in the way of engaging scenery, so then, why do we all approach running on the treadmill with such trepidation?

Instead of climbing on the treadmill with the aim of slogging out 30 minutes before succumbing to boredom, plan your workout in advance, making sure you have all of the necessary tools to assist you. As overheating is always a concern indoors, make sure you are equipped with a towel and water bottle. Then there is the entertainment aspect of the workout. Unlike riding a bike trainer, where your bike is in a fixed position, a treadmill does require a certain amount of attention to maintain your place on that moving black carpet. While following a TV show on the treadmill may prove disorienting, listening to music can be your savior. Now that you are properly equipped, what do we do for a workout? With the ability to manipulate not only your speed, but also your incline, the workout possibilities are literally endless. Always try to keep a modest incline on the treadmill (say 1%) to better simulate actual outdoor running conditions, which we all know include wind and rarely a perfectly flat road.

Here is one treadmill workout I enjoy doing: This workout is a modified ladder with changes in both speed and incline. After a 1-mile warm-up, pick a modest base speed to run at (say 7mph for example). At your base speed, run 1/4 mi at 2% incline, then 1/4 mi at a 3% grade, then 1/4 mi at 4%. After those 3 quarters, drop the incline back to 1% and inch the speed (say 0.1 or 0.2 mph) and repeat the progression. See how long you can do this for!

Nutritional Thoughts
The off-season typically means lower training volumes for most of us, as we slowly rebuild our fitness levels as the season approaches. Fewer four hour plus bikes rides, means less of a need for that Krispy Kreme doughnut in the fuel tank. While I am a self-proclaimed doughnut junkie in the summer months (something I share with pro triathlete Hunter Kemper - who actually served Krispy Kremes at his wedding), one must exhibit some self-restraint in the dead of winter. Some weight gain over the holidays is expected and normal, however we don't want to over do it. A rule of thumb is to try an avoid weight gains of ten percent or more on your frame (15lbs on a 150lb frame), as those extra pounds will come back to haunt you if they are still hanging around come June. By no means does this mean we should starve ourselves during the holidays, just pay close attention to the soda and alcohol intake, leave the extra dinner rolls for the in-laws, try avoid eating after 8pm, perhaps consume a tad less pasta for dinner, and the one that kills me - less Krispy Kreme breakfasts!

Remember, while the majority of us are not professional athletes, we all share a small obsession for our chosen sport and the lifestyle that accompanies it, so rest and train smart so you can enjoy a lifetime of racing success!

See you next season!

Monday, November 5, 2007

Power Demands of Cyclocross Racing: Part 1

For the past couple weekends, coach Mike Kuhn and I have had the pleasure of going to some cyclocross races at Lehigh Valley, Fogelsville, Fair Hill and then yesterday at Spring Mountain. Cadence has partnered with CycleOps for these events and CycleOps has generously provided 10 Fluid trainers for riders to warm up on as well as 2 wireless PowerTap demo wheels for riders to use. We have encouraged riders to ride and race on these wheels. Many have never used a power meter before and are curious about what to expect. Others would like to test the durability of the PowerTap wheel in some of the harshest conditions imaginable. Personally, I look at it as a great opportunity to collect data. Though power meters are very common on the road, you don't see too many in cross races so naturally there isn't much out there in the way of literature on training and racing with a power meter for cyclocross racing. Here are some basic stats on some of the riders that rode Sunday's race at Spring Mountain:

Woody: 2nd place in Men's B race
Weight: 175 lbs
Background: Cat. 3 road racer, former messenger
Duration: 44:48
Avg. Power: 271
Avg. Speed: 12.1 mph
Avg. Cadence: 80 rpm
Normalized Power: 297 watts

Johann: 3rd place in Men's B race.
Weight: 200 lbs
Background: Cat. 2 road racer
Duration: 44:53
Avg. Power: 286 watts
Avg. HR: 186 bpm
Avg. Speed: 12.0 mph
Avg. Cadence: 79 rpm
Normalized Power: 316 watts

Chris: 7th place in Men's B race
Weight: 180 lbs
Background: Cat. 4 road racer, Ex-BMXer
Duration: 45:59
Avg. Power: 253 watts
Avg. HR: 180 bpm
Avg. Speed: 11.7 mph
Avg. Cadence: 70 rpm
Normalized Power: 275 watts

Kyle: 3rd place in Men's A race
Weight: 134 lbs
Background: Pro Mountain Biker
Duration: 34:36 (the data recorded is for the beginning of the race... Kyle had a mechanical and had to take a bike change)
Avg. Power: 234 watts
Avg. HR: 182 bpm
Avg. Speed: 12.7 mph
Avg. Cadence: 76 rpm
Normalized Power: 260 watts

John: 4th place in Men's A race
Weight: 160 lbs
Background: Cat. 1 Road Racer
Duration: 1:05:56
Avg. Power: 227 watts
Avg. HR: 175 bpm
Avg. Speed: 12.2 mph
Avg. Cadence: 74 rpm
Normalized Power: 250 watts

Colin: 5th place in Men's A race
Weight: 170 lbs
Background: Cat. 1 road racer
Duration: 1:06:59
Avg. Power: 245 watts
Avg. HR: 187 bpm
Avg. Speed: 12.1 mph
Avg. Cadence: 67 rpm
Normalized Power: 269 watts

Erik: 10th place in Men's A race (also raced in B race)
Weight: 185 lbs
Background: Cat. 4/espoir road racer/track racer
Duration: 1:02:54
Avg. Power: 203 watts
Avg. HR: 187 bpm
Avg. Speed: 10.1 mph
Avg. Cadence: 76 rpm
Normalized Power: 240 watts

For a definition of these terms, look at my last entry on this blog. The first thing that stands out to me about these files is how low the power is. Every one of these riders is capable of producing more power than they did here but the technical sections make it difficult to use that power. A good technical rider will spend more of the time pedaling and less time coasting. Kyle is certainly the most technically proficient of these riders and he is able to come much closer to actually producing the power he is capable of producing. However, it is important to remember that most riders will fade in the later laps of the race so with only 35 minutes of data, Kyle's numbers are most likely a bit high.

The other thing that stands out about these files, at least compared to a road race or criterium is how low the cadence is. This is primarily because a lot of time is spent coasting, usually just before obstacles or technical sections. However, cadence will be lower even when pedaling during cyclocross because a bigger gear will generally make it less likely that the rider will lose traction.

More to come later on how we can use these files to better identify riders' strengths and weaknesses and design individualized workouts and training plans that can help maximize their potential.

Mike and I plan on being at a lot of cross races in the upcoming weeks, so if you are there feel free to stop by, warm up on the CycleOps trainer and demo one of the wheels. Here's the schedule:

November 10th: Beacon Cyclocross, Bridgton, NJ
November 11th: Highland Park Cyclocross, Highland Park, NJ
November 17th: Mercer Cup Cyclocross #1 (USGP #3), Trenton, NJ
November 18th: Mercer Cup Cyclocross #2 (USGP #4), Trenton, NJ
November 25th: MABRA Championships, Taneytown, MD (tentative)
December 1st: Carlisle Cross Classic (MAC #5), Carlisle, PA
December 2nd: Capitol Cross Classic (MAC #6), Reston, VA

See you there!

Friday, November 2, 2007

Power Terms

I've had requests from some athletes to provide a list of some of our commonly used terms with particular regard to power, so here goes...

Speed = a measure of the velocity of the bike, measured in mph or kph. Speed is not a good measure of exertion or intensity while cycling because it is greatly affected by opposing forces such as wind, grade, road surface, drafting, gravity (body & bike weight), aerodynamic profile and friction (drivetrain efficiency) as well as power. It is important to remember though, that races are won by the fastest rider, not the rider with the most power. Speed = Power - Opposing Forces (aerodynamic, gravity, rolling resistance) so in the end a rider must optimize this equation by increasing power and decreasing opposing forces as much as possible to produce maximum speed.

Cadence = a measure of the velocity of the cranks, measured in rpm. Under constant conditions, if rpm increases, power increases. "Normal" rpm for most riders on a flat road is 85-100 rpm. Lower rpms (less than 85 rpm) will place more of the stress on muscular strength, and thereby cause more muscular fatigue and higher rpms (greater than 100) will place more of the stress on aerobic capacity (and cause less muscular fatigue) but the rider will be less efficient since the "dead spot" in the pedal stroke will occur more often. Depending on the efficiency of the rider, higher rpms may cause higher oxygen utilization, heart rate and glycogen usage. Every rider will have their own optimal rpm where they can produce the most power for a given period of time. It should be noted, though that this ideal rpm for the rider will change based on the type and length of event.

Torque = a measure of the angular force applied to the pedals, measured in inch pounds or foot pounds. Under constant conditions, if torque increases (the rider uses a harder gear), power increases. Riders with better muscular strength should be able to produce and sustain more torque with less muscular fatigue.

Power = a measure of the work over time done by the rider to push the bike forward, measured in watts. Power = Torque x RPM. Power will increase (under constant conditions) if torque or rpm is increased.

Power/Weight Ratio = a measure of power over a given period of time relative to the body weight of the athlete. Power to weight ratio at functional threshold (see below for definition) or Lactate threshold is most commonly used. It is speculated that to win the Tour de France a rider must have an FT power to weight ratio of around 7.0 watts/kg (in the case of Lance Armstrong, this came out to approximately 500 watts at threshold at a weight of 160 pounds!). Power to weight ratio is important because it requires more power for a heavier rider to travel the same velocity than for a lighter rider. However, it is important to remember that gravitational resistance is just one of many opposing forces while riding and only a small percentage of the opposing force on a flat road.

Heart Rate (HR) = A measure of the frequency of an athlete's heart beats, measured in beats per minute (bpm). As exertion increases, heart rate will increase. However, there is a delay in the response of heart rate (as exertion increases, heart rate will take some time to raise and as exertion decreases heart rate will take some time to drop). Therefore, heart rate is not a good measure of exertion in shorter efforts. Additionally, heart rate is greatly affected by heat, hydration and fatigue. There is also a great difference in heart rate values from athlete to athlete, even with the same level of relative exertion.

Work = average power x time, measured in kJ. Work done will increase if power increases or if time increases, so work is a measure of intensity and duration. A given route (under constant conditions) should require a given amount of work that will remain constant regardless of speed. In other words, if the speed is low the power will be lower and the duration will be higher. If the speed is high the power will be higher and the duration will be lower. Either way, the work done will remain the same. Work should not to be confused with energy burned by the rider, measured in kCal, which depends on rider efficiency and is better estimated using heart rate and/or oxygen consumption.

Work = average power x time, measured in kJ. Work done will increase if power increases or if time increases, so work is a measure of intensity and duration. A given route (under constant conditions) should require a given amount of work that will remain constant regardless of speed. In other words, if the speed is low the power will be lower and the duration will be higher. If the speed is high the power will be higher and the duration will be lower. Either way, the work done will remain the same. Work should not to be confused with energy burned by the rider, measured in kCal, which depends on rider efficiency and is better estimated using heart rate and/or oxygen consumption.

Normalized Power (NP) = calculated power over a given duration that better takes into account non-steady state efforts. Average power will decrease if there are significant recovery periods during warmup, cooldown or in between efforts but the stress of the ride does not necessarily decrease (think of driving a car… you can average under the speed limit but it doesn’t mean you won't get a ticket). Therefore, average power is not a good measure of exertion for non steady state efforts such as races, hilly rides and many group rides. Normalized power should reflect the actual intensity of the effort. It is calculated by taking a 30 second rolling average of the power values, taking these values to the 4th power, averaging these values and taking the 4th route of this number. Therefore, when the power spikes very high, these spikes will be given exponential weighting. For example, a criterium may produce an average power of only 160 watts (due to the regular periods of coasting) but the same race might yield a normalized power of 280 watts (due to the many accelerations). Though normalized power is a very good measure of true exertion, because NP works on a 30 second rolling average, rides with power spikes of less than 30 seconds may not be weighted as highly as expected and likewise other rides that contain maximal efforts of 30-60 seconds may be weighted more highly than expected.

Functional Threshold (FT) = the maximum power a rider can produce for a period of 60 minutes. This can be estimated by completing a 60 minute time trial, a 60 minute "race-type effort" with a high normalized power (commonly a difficult criterium or fast group ride), by taking 95% of the power produced in a 20 minute time trial, 90% of the power produced in an 8 minute time trial or by completing a lactate threshold test in the lab.

Intensity Factor (IF) = the normalized power for a ride with respect to the functional threshold of the rider = NP/FT. Therefore an effort at 100% of threshold should equal an IF of 1.0. If the rider has an IF of over 1.05 for over an hour, their functional threshold may have increased since the last test (or their power meter needs to be calibrated)

Training Stress Score (TSS) = a measure of the intensity and duration of the ride. Intensity is measured in IF and duration is measured in minutes. If the ride is harder the IF will be higher and therefore the TSS will be higher. If the duration of the ride is increased, the TSS will increase as well. As a rule of thumb, most people should be able to recover from a workout with a TSS of 150 or less in 1 day 150-300 in 2 days, 300-450 in 3 days and a workout with a TSS of over 450 should require more than 3 days recovery. However, actual recovery rates will be affected greatly by fitness level and fatigue as well as recovery habits (nutrition, sleep, massage, etc.). It is also important to remember that if a rider’s FT changes it will affect the IF for the ride, which will in turn affect the TSS for the ride. For example, if a rider increases his FT, the same workout done at the same wattage will produce a lower IF and a lower TSS.

Acute Training Load (ATL) = a measure of short term exercise fatigue level using TSS values from workouts. This is usually calculated using a 5 or 7 day time constant. A rider's ATL will increase incrementally if the TSS value for the day is greater than their ATL and decrease incrementally if the TSS value for the day is less than their current ATL. The greater difference between the rider's TSS and their ATL, the more the ATL will change.

Chronic Training Load (CTL) = a measure of overall fitness level using TSS values from workouts. This is usually calculated using a 30 or 42 day time constant. A rider's CTL will increase incrementally if the TSS value for the day is greater than their current CTL and decrease incrementally if the TSS value for the day is less than their current CTL. The greater difference between the rider's TSS and their CTL, the more the CTL will change. This implies that the higher the level of fitness, the more it takes to keep raising the fitness.

Training Stress Balance (TSB) = CTL - ATL. When an athlete peaks for an event, they should have a high TSB (a high level of fitness and a low level of fatigue). If an athlete takes a break at the end of the season and then resumes training after a break, their fitness (CTL) will most likely be low but their fatigue (ATL) should be low. When the athlete first resumes training, their ATL will go up quickly, and their CTL will remain low at first (meaning that their fatigue is high and fitness is low). After a long and intense training period, CTL will most likely be high, but ATL will be high as well so the athlete will be unable to fully utilize his high level of fitness until he takes a rest period and allows the ATL to decrease. In general, athletes should avoid TSBs of less than -40 for risk of injury, illness and/or overtraining. TSB should be at least above 0 for B races and over 20 for A races. If CTL is high, a period of high ATL will not produce as low of a TSB than if the CTL were lower. This implies that if fitness is high the same amount of training may not cause as much fatigue.

* Normalized Power, Intensity Factor, Training Stress Score, Acute Training Load, Chronic Training Load and Training Stress Balance are terms created by Andy Coggan and Hunter Allen as ways to objectively model the stress of training and the body's short and long term responses to this stress. To read more about these terms, you should read their book, "Training and Racing with a Power Meter". Though these models hold up very well when compared to other objective and subjective models, it is important to remember that the human body also operates with a certain degree of unpredictability. In other words, we are not robots.