Thursday, August 23, 2007
Wednesday, August 22, 2007
Rolling resistance shall be defined as the resistance to steady forward motion due to frictional losses between the surface of the wheel and the surface on which it rolls.
Rolling resistance coefficients range from 0.002 to 0.010 while rolling on smooth surface
Next to aerodynamics, rolling resistance is the next biggest contributor to forward motion on level road cycling
There is less energy loss with a 700c wheel vs. 650c wheel due to less tire deformation as it rolls over a smooth surface
Reducing tire size from 27 inches to 16 inches increases rolling resistance by 40%
Skinnier tires (<19mm)>19mm) at similar tire pressures
A solid tire would have the lowest rolling resistance of any air filled tire on a perfectly smooth surface
Thinner tire fabrics made with higher threads per inch (TPI) bend and deform easier than thicker ones.
Thinner tires have less material to deform and thus less energy is lost as the tire rolls.
Thicker inner tubes create higher rolling resistance.
The greater the TPI, the less rubber needed and the better the rolling resistance.
Generally speaking, the best tire pressure for the least amount of rolling resistance on a typical road surface is around 100-120 PSI.
Different rubber compositions have different resistances. In general, replacing carbon black with silica-silane reduces rolling resistance, but also increases tire wear.
No, you think about it...
Which riders tires will last longer, a sprinter or a time-trialist?
Which tire wears the fastest, the front or the rear?
Monday, August 13, 2007
Thursday, August 2, 2007
If you are an endurance cyclist you have probably experienced fatigue. Although some fatigue is ok, and even desirable, severe fatigue can be very detrimental to your fitness and your goals. As an athlete or coach you must be able to differentiate between fatigue that will yield performance enhancements and that which will hamper growth and recovery.
An athlete who is unable to produce the same performance they did just a week ago is fatigued. Put simply, fatigue is the inability to perform at a level that was once possible in recent history (excluding illness or injury).
Athletes can perceive fatigue differently. Some athletes avoid fatigue at all cost while others never slow down. If training becomes excessive enough and poor recovery habits are taken persistent fatigue can follow which will ultimately interfere with performance.
One of the difficult aspects of training and coaching is determining how much training and stress will fatigue an individual athlete and if how this fatigue will impact their training prescription.
Power meters and heart rate monitoring have made the diagnosis of fatigue and the ability to track the amount of training stress easier and more accurate. Frequent fitness testing with a power meter or field test allows cyclists to document the effects of training on particular aspects of performance. For an athlete, a range of performance and perceptions may follow a rigorous training block;
1. The athlete feels good and performance is improved
2. The athlete feels good but performance is poor
3. The athlete feels tired and performance is poor
4. The athlete feels tired but performance is excellent
Depending on the training and recovery prior to the test, all responses are possible and all results indicate something different. With the use of power meters, every cycling effort can be compared to a personal best clearly indicating when a cyclist is tired and when they are fresh. Patterns between training and performance will emerge providing insight into managing fatigue.
There are four main classifications of fatigue and they are described below.
There is little denying the perception of fatigue but oftentimes once you get going you are feeling great and beating the locals feeling full of energy. Experienced athletes know that it usually takes exercise to evaluate whether fatigue is severe enough or not to cancel a training session. Perceptual fatigue can be very persuasive so don't give up without trying. You may be capable of much more than you imagined. If you have finished a sufficient warm-up and you are struggling to reach and hold the given power levels then it is advisable to listen to what your body is saying and take a break!
SHORT-TERM PRODUCTIVE FATIGUE
Every daily training session results in short-term fatigue. As you become tired, heart rate and the perception of effort increases for a given workload or power output. Fatigue may increase to the point that a desired workload is not achievable. However, after a good meal and sleep most athletes will be ready for more abuse the next day. If the training bout is severe enough, two to three days may be required to regain previous form. This is considered short-term fatigue and is productive because the performance outcome is positive, increasing your performance, after sufficient recovery.
LONG-TERM PRODUCTIVE FATIGUE
What happens when you train hard for six days in a row? As you would expect, you are probably tired. Many times a fatigued cyclist can find it difficult to cope with a hard training session for up to a week after this effort. There are often complaints about heavy legs and heart rate suppression during hard efforts. The training which leads to this sustained fatigue is termed 'overreaching'. Fortunately for those suffering from this type of fatigue, performance rebounds to desirable levels following 7-12 days of quality recovery. However, many athletes mismanage this fatigue and start training or competing well before they are fully recovered. Ironically, it is the athlete that feels the best that is most at risk for this type of fatigue. Athletes experiencing great form feel like superman, neglecting the proper nutrition and recovery habits needed. But eventually the fatigue will accumulate. Often the most severe fatigue comes following a week or two of incredible form. Be very careful when power production reaches an all-time high. With appropriate management - particularly the inclusion of recovery days in your training program - it's possible to maintain top form for weeks, if not months.
LONG-TERM NON-PRODUCTIVE FATIGUE
This type of fatigue is commonly known as overtraining. Many athletes are extremely motivated, very fit, and also living a very stressful lifestyle. These situations often cause a loss in fitness before fatigue dissipates. Thus, despite rigorous training and following weeks of recovery, performance never rebounds. Lifestyle stress, poor nutrition and disturbed sleep all contribute to the extremely heavy fatigue experienced by athletes.
Despite numerous attempts by sport scientists, there is no one physiological marker that can be used to identify the magnitude of fatigue or that when it has reached some critical level. Although resting heart rate can be a useful indicator of training stress there is little solid scientific data to support using this marker as a guide to training.
It's important not to confuse overtraining with non-specific training. It is possible that a lack of specific training for a certain event is responsible for the poor performance. Lots of cycling on the flat is unlikely to promote a rider's climbing capacity. So when evaluating your performance also think about the amount of specific training you've been doing for your event. Again, if a cyclist is using a power meter and recording training sessions it becomes fairly easy to retrospectively examine the time spent at a power output and cadence that is sport specific. Unfortunately, an athlete with persistent fatigue may need to stop training and focus on a good diet and adequate rest.
When it comes to cycling and endurance sports, fatigue is almost always present and can develop in many different forms. Most types are easy to deal with and fairly short lived. However, the perception of fatigue is not always associated with performance. Athletes should try out their legs and start a training session before making the conclusion that they are too tired to train. General or short-term fatigue is characterized by an increased perception of effort for a given power output, but the ability to produce power is generally maintained. More severe or long-term fatigue is associated with a decrease in performance and possibly a suppressed heart rate and elevated perception of effort for a given power output. Although excessive training can lead to persistent fatigue, this condition is very rare. When endurance athletes are unusually tired for a long time there are usually other environmental variables contributing to it.
Fortunately, power meters can now be used to track training volume and quantify whether performance is really compromised. This type of feedback combined with frequent performance testing can be used by cyclists to better understand the effects of fatiguing bouts of training and racing.