Power Variation Strategies in Cycling Time Trials

Louis Grisez

Overview Abstract Introducing Cycling Creation of a Mathematical Model Initial Conditions Calibration Results

Abstract The ultimate goal of cycling time trials

Need for a pacing strategy Energy Depletion

Mean work rate and various pacing strategies.

This research is a verification of the steady state approximation used in "Power variation strategies for cycling time trials: A differential equation model" by author, Graeme P.Boswell Seeks to improve the optimal pacing strategy found previously

using a steady-state approximation.

Energy based differential equation

Model will be used in theoretical courses with varying conditions and cyclists of different masses.

An Introduction to Cycling Competitive event rode in the fastest way possible National, world, and Olympic championship events Races are a primarily measurement of athletic ability

over a period of time. Only known tactic: Suggested method: uniform work output rate

Assumption: constant conditions of power output as well as resistive forces

Refined method: Altered power output Models altering course conditions such as road gradient

This is done as an improved method compared to the steady state approximation in reducing the time needed to complete the course.

Previous studies (Gordon, 2005; Swain 1997) have shown the validity of variable power output approximations.

The Steady State Accelerations are assumed to be instantaneous (Swain 1997).

Considered being in steady state

Showed that the refined method had a time saving effect as high as 8.3 percent compared to the constant work rate. This actually increased with the growing incline of the track.

Problem concerning these assumptions instantaneous acceleration: do not directly apply to road cycling This problem was later improved by Atkinson's improved calibration

model. Kinetic energy and speed were observed at one second intervals.

Jumps in velocity were approximated as continuous acceleration. changes in velocity between the transitions were ignored

The variable pacing strategy used by both Swain and Atkinson increased the mean power beyond the constant power approximation by as high as 10 percent due to the ascending time being greater than the descending time. As a burden, this pacing strategy may be overestimated.

Mathematical Model Cyclist must apply power to the drive

chain.

The combined speed of the bicycle is a function of the difference between P and Δ P is applied power Δ is power of resistive forces

Three Resistive forces Gravity Rolling Wind

Mathematical Model Rate of change of kinetic energy

Mathematical Model Assuming there are no changes in the

rider's velocity due to varying grades, surfaces, wind strength and applied power, the previous equation becomes

This is the steady state

Initial Conditions Initial data points, given by G. Boswell to be:

x(0)=0 v(0)=0

Initial data points used v(0)=1 Small enough to be negligible in terms of final output. This is also the first instance in which procedure

differed from that of previous work done by G. Boswell.

Assuming there are no changes in the rider's velocity due to varying grades, surfaces, wind strength and applied power, equation $(5)$ can be written as

Calibration Constants need to be defined Assumption:

Rider does not refer to tuck position

Cyclists were pulled behind vehicles Eliminates the variability of power output

and small changes in velocity

Human Athletic Performance

Human Athletic Performance

Oxygen limitation Events last 2-3 hours

Average oxygen intake of 3.7 (Swain,1997)

Human biomechanical performance 25% efficient

Courses 10 [km] flat

5 [km] uphill followed by 5 [km] downhill

Alternating 1 [km] sections

Alternating 0.5 [km] sections

Variable gradients of: 5, 10, 15% Variable power of: 5, 10, 15%

Pacing Strategies Research separates from G. Boswell Initial:

Increase of power as a percent Decrease using

Final: Increase of power as a percent Decrease of power as same percent

Solution Methods Use of MATLAB 2012

Numerical Solver ode45

Set of 4 integrated for loops

Results of Change in KE

Compared to data found by G. Boswell 2% error Less time for cyclist to complete course

Results of Change in KE

Results of Change in KE

Results of Change in KE

Progress on Steady State Use of ode solver to model the original

steady state approximation

Function is to create comparable data to variable pacing strategy

Results show a very high error MATLAB solver error

Possible benefits Time saving could be potentially over

10%

Conclusion Cycling as a whole Relevance of a pacing strategy Results Future Improvements

Hickethier, D. (2013). Personal interview

Di Prampero, P.E., Cortelli, G. Mognomi, P., & Saibene, F. (1979). Equation of motion of a cyclist. Journal of Applied Physiology, 47, 201-206.

Gordon, S (2005). Optimizing distribution of power during a cycling time trial. Sports Engineering, 8, 81-90.

Graeme P. Boswell (2012): Power variation strategies for cycling time trials: A differential equation model, Journal of Sports Sciences, 30:7, 651-659.

Martin, J. C., Gardner, A. S., Barras, M., & Martin, D. T. (2006) Modelling sprint cycling using field-derived parameters and forward integration. Medicine and Science in Sports and Exercise, 3, 592-597.