Time trial performance and body size

[Sports Science Editor]

Lab tests are a common tool for predicting fitness levels. Conducting them on a regular basis allows athletes to monitor their progress throughout the year and provides vital data / feedback.

In addition to monitoring progress, lab tests can be used to predict race performance. If a group of athletes each complete a time trial on the same turbo, theoretically the one who averages the highest power output should be the fastest cyclist in a time trial. Jobson et al (2007)* questioned whether this was actually the case and set out to determine if lab based tests were an accurate predictor of race performance on the road.

A total of 23 cyclists each completed a 25 mile time trial in the laboratory (on a kingcycle) and a 25 mile time trial on a recognised RTTC course. Body measurements of each rider were also recorded.

Results
The first thing of note was that all participants rode slower on the road than they did on the kingcycle, despite an accurate calibration procedure before starting the lab test. More significantly, the larger the participant, the greater the difference between lab and road performance (larger riders slowed more on the road).

The tests indicated that body mass was the main determinant of difference between lab and road performances. Body weight has long been recognised as a key indicator of road performance and the “power to weight ratio” is often used as an indicator of performance. To calculate your own “power to weight ratio”, complete a RAMP test on a turbo which gives power output and divide the end score (maximal aerobic power output) by body weight (kg) to calculate watts per kg. Note that there are many different RMP test protocols and many different turbo trainers with power output displayed. The test and the turbo will determine results to a large extent and the same test and turbo must e used for future tests t ensure validity of results.

If we use “power to weight ratio” to explain the differences encountered between the lab and road performances, the explanation would broadly be - “the large riders scored higher power outputs on the kingcycle, but when they rode outdoors, they couldn’t carry all that weight uphill, so the lighter riders performed relatively better”. That would be a fair explanation had the road test not taken place on a flat RTTC 25 mile course - surely on the flat weight isn’t an issue, right?

Jordon et al concluded that weight was not the issue, but that body surface was the key factor. The calculation for BSA (body surface) is height (cm) x eight (kg) /3600with the answer given as m3. Body size is therefore relevant for both flat and hilly courses – on hilly courses gravity plays an important role and on flat courses smaller riders cut a smaller hole though the air due to less “frontal resistance”. It is important to identify that “body weight” affects uphill performance whilst “body surface area” (body size) affects performance on flat courses. In addition to calculating your power to weight ration (w/kg), the power to surface area ration (w/ m3) should also be considered.

Conclusions
Don’t presume that big and powerful riders will always outperform smaller riders on flat courses. Frontal resistance has a large effect upon performance and smaller riders benefit as a consequence. As you are likely to be going faster on flat courses, frontal resistance becomes even more of an issue. If you are a big rider, change your position to generate as little frontal resistance as possible. Ride in front of a mirroe or video yourself from the front to get the best “shape”, consider an aero helmet and wear a tight fitting skin suit. Small is fast.


* Do laboratory based tests give an accurate indication of potential race performances, taken from - Jobson et al (2007) The ecological validity of laboratory cycling; doesbody size explain the difference between laboratory and field based cycling performance. Journal of Sports Sciences 25 (1): 3-9


About the author of this training article
Marc Laithwaite, is Sports Science & Coaching Director, at The Endurance Coach. Mark has a Bsc (Hons) sports science and is working towards his Phd sports science. He is a member of the British Association of Sports and Exercise Scientists (BASES), a British Cycling Federation Blood Analyst, BTF Level 3 Coach & Coach Educator, UKA Level 3 Coach and ABCC Level 3 Coach.

The Endurance coach, provides sports science and coaching support services for endurance athletes. Their services include VO2 max testing, lactate profiling and metabolic assessment for endurance athletes of all standards in their own sports testing lab. The Endurance Coach also runs a range of training camps throughout the year and offers physiotherapy and rehabilitation services. For more information or if you are looking for world leading coaches to assist you, e-mail The Endurance Coach.

© The Endurance Coach

[Neil Buckley]

Thats a very interesting article, true point guess smaller you are with the correct techiuqe less to get yourself around!!!