Thursday, August 19

More science waffle: Blood Lactate

Blood Lactate
Lactate production especially when expressed as a function of power output is the single most important physiological determinant of cycling performance as lactate production is an individual response (McLellan &Jacobs, 1989; Stegman & Kinderman, 1982). Both lactate threshold (1mmol rise in blood lactate above baseline) and onset of blood lactate accumulation (when blood lactate reaches 4mmol) have been shown to be valid predictors of cycling economy in a range of events (Faria et al., 2005). A relationship has been shown to exist between average power output during a 90 minute time trial and the lactate threshold, as calculated by the D-max method (Bentley, 2001). This study also showed a correlation between the average power during a 90 minute time trial and peak aerobic power output. This relationship between the lactate threshold and maximal aerobic power output over longer durations leads us to believe that both peak and sub-maximal measures of blood lactate are possible predictors of cycling performance.

These lactate thresholds becomes ever more important during individual time trials where athletes are working at or just above the lactate threshold (Mujika & Padilla, 2001). In ultra endurance races extended efforts (55-60% of VO2max) are performed at or above the lactate threshold by solo riders (Laursen, 1999). The ability to predict performance over extended durations at this intensity can be of great benefit to a cyclist. The lactate threshold is the level at which a cyclist is able too hold a given intensity for ‘a very long time’ before they start to feel the effects of fatigue. A solo cyclist will aim to remain at this level for as much as possible allowing them to exercise predominantly aerobically utilising both carbohydrate and fat stores to produce ATP. In effect is the steady state that most of a road racing is performed (Muijka & Padilla, 2001). Unlike road racing this effort must be maintained for much longer periods. The greater the percentage of heart rate max or VO2max that the lactate threshold occurs at the more economical a cyclist is said to be. By having a lactate threshold that occurs later a cyclist will be able to produce more mechanical power with less of a metabolic cost. An understanding of the lactate threshold response can allow a cap to be placed on the intensity that they may cycle at in order to complete these events solo while lowering the chance of unnecessary fatigue or glycogen depletion over the duration of the event.

During high intensity ultra endurance the riders are able to recover between bouts of cycling. This results in cyclists racing at or above OBLA (Laursen P., 1999). OBLA is the level at which a cyclist has started to work nearly entirely anaerobically. They are not able to supply enough oxygen to return to aerobic glycolysis and are now producing lactate at a much higher rate. This anaerobic threshold is the level above which a cyclist can only maintain a maximal effort for very short periods of time. A cyclist can only maintain this effort for very short periods of time. If they are able to raise the point at which OBLA occurs it stands to reason that they would be able to prolong the effects of fatigue and hold this intensity for longer. With a cyclist understanding the intensity they are capable of sustaining for these relatively short durations, and its impact on recovery, it is possible to work near maximally to gain the greatest possible result. Unlike solo cyclists a boundary can be placed at a much higher intensity (75-85% VO2max) and result in much higher power outputs and speeds.

For cycling describing the lactate threshold as a heart-rate can lead to problems. As heart rate is a response to an input, a hill or sprint, it lags behind. Consequently measuring the changes in power output at these different blood lactate responses may lead to a much better determinant of cycling performance (Muijka & Padilla, 2001). By giving a cyclist a measure of their lactate threshold expressed in Watts an athlete can pace efforts by this measure. Depending on the demands of an event or session they can attempt to stay as close or far away from their lactate threshold so as to maximise performance.

Tuesday, August 17

Split of ideas

I've decided to split my day to day ramblings from my training focused on IM Lanzarote.

Normal stuff will stay here where you are.

Other stuff here

Other site will be more of a progress report and ripping apart my own power files and running stats. This will remain the stream of conciousness that it is.

Thursday, August 12

Science Nerding

Maybe of help to anyone thinking about a power system. Quick chunk nabbed from my Lit Review I'm working on:

The SRM (Schoberer Rad Messtechnik, Welldorf, Germany) crankset was one of the first portable power measuring tools available to the cycling community as a large, albeit at a high price. The SRM system calculates power output from the torque and angular velocity generated at the bottom bracket of the bicycle (E. Farria et al, 2005). This is achieved through a system of strain gauges located between the cranks and the chainrings which measures the deformation between the two. This is proportional to the torque being generated during each pedal rotation. Several studies have validated the crankset and its test to test repeatability (A. Gardner et al., 2004; W. Bertucci et al., 2005; S. Duc et al., 2007;A Juekendrup et al, 2003) and it has been shown to be a valid system in both laboratory and field conditions. Variations of the crankset now exist for both scientific measurement (accuracy +/- 0.5%, weight 827g), Professional (accuracy +/- 2.5%, weight 560g), and amateur (accuracy +/- 5%, weight 640).

The PowerTap (Saris Cycling Group, Madison, U.S.A) is a power measuring device which is located within the rear hub of the bicycle. It calculates power in a similar manner to the SRM system with 4 strain gauges located within the rear hub. The advantage being that it measures the power that is transferred to the rear hub; this takes into account any power loss through the drivetrain of the bicycle. This gives an accurate measure of the power being applied to propel the cyclist. Like the SRM the Powertap has been validated and shown to be a reliable and repeatable source of power measurement (Gardner et al., 2004; Bertucci et al., 2005; Duc et al., 2007). However the price of the PowerTap is over €1,000 cheaper than the base model SRM, has a reported accuracy of 2.5%, and weighs 579g at the most basic model making it a more appealing option for amateur cyclists who want consistent power measurement.

The Ergomo Pro (SG Sensortechnik GmbH & Co, KG, Mörfeldn-Walldorf, Germany) is a system that is located in the bottom bracket of the cyclist bicycle. It measures power generated through a photo-interrupter system which measures the torque generated in the bottom bracket (Coggan, 2006; Duc et al., 2007). This system does not use a strain gauge system like the SRM and PowerTap and is free from any temperature related problems (Duc et al., 2007). However, the sensors that measure the torque generated are only located in the left hand side of the bottom bracket. In order to generate a total score for the torque the figures gained are simply doubled and then recorded by the system (Duc et al., 2007; Coggan, 2006). Although the Ergomo Pro has a purported accuracy of +/- 1% this calculation system inherently introduces a large measure of error as cyclists rarely generate the exact same force through both legs (Burke, 1996; Daly, 1976). This has been shown in studies comparing the Ergomo Pro to both the SRM and PowerTap systems (Duc et al., 2007). The next generation Ergomo Pro, due for release in autumn 2010, further reduces the weight below 344g, while aiming to increase the accuracy through new algorithms and design. Unlike the SRM and PowerTap the Ergomo suffers from no temperature related issues and is not affected by electronic or radio interference.

Friday, August 6

First Cross Ride

Got out on the first cross ride of the season last week. IT felt good. Slow to mount, slow to corner hard, but it will come with time. Feeling fit, if a little fat.

Work is working for a change. The brain has started to fire again, and coffee in no longer results in nothing out. Few late nights this week in the lab but by choice rather than guilt.

Late night tonight, going to reward myself with an early morning cross ride tomorrow, then maybe a curry!

Wednesday, August 4

Cyclocross Preparation

This the season to get skinny, and muddy, and wrecked.

Tonight the CX bike will be re constructed. During the summer Uncle John is a mild mannered bike that has seen me to the top of some of the highest Cols in the French Alps, spent numerous hours preparing me for the triathlon season, and has suffered the indignity of being locked beside lower class bike in college.

Come August Uncle John gets and ictch. He needs to feel the grit in his chain, the mud under his tires, and needs to go sideways in corners rather than straight through. Gears get stripped from 50.39 to a single 42 on the front. Rear ratios change. Tires are shed for some grip and the tubs need to get attention.

Tonight the cross bits come out of the attic. The clinchers go on for some training. Tire marks on the 2009 nationals course is the plan. Hopefully i can remember how to corner and remount.