european college of sport science

Saturday, June 27th, 2009
Kohler G & Boutellier U (2005) Eur J Appl Physiol 94: 188-195
Lucia A et al. (2001) Med Sci Sports Exerc 33: 1361-1366
Nesi X et al. (2004) Can J Appl Physiol 29: 146-156
Zehr EP (2005) Exerc Sport Sci Rev 33: 54-60
THE PULL UP ACTION IN CYCLING: IMPLICATIONS FOR PERFORMANCE AND TRAINABILITY
MORNIEUX, G.
UNIVERSITY OF FREIBURG
Introduction: The pull up action in cycling refers to the ability to apply an effective pedal force (i.e. tangential to the crank displacement
and in the same direction than its rotation) during the upstroke phase. However, it is questionable to which extent this action would be
beneficial for the performance. Takaishi et al. (1998) have reported lower oxygen uptake for elite than for recreational riders. They argued
that lower oxygen uptake was associated with a greater pull up action. Hence, training this pull up action might be relevant. It has been
showed that a feedback training (instantaneous representation of the pedal forces profiles while riding) would allow modifying the pedalling
pattern (Sanderson and Cavanagh, 1990). Therefore the aim of this study was to determine i) to which extent the pull up action might
be beneficial for performance in cycling and ii) how it could be trained.
Methods: Elite and recreational cyclists were measured on a SRM ergometer, instrumented with 2D pedal forces transducers (Powertec).
Oxygen uptake and electromyography for different relevant muscles were recorded. Subjects rode either with single pedal, clipless, or
clipless and the pedal force feedback. This feedback allowed subjects controlling their pull up action. Finally subjects participated to a
training study with this feedback (2x a week/6 weeks).
Results: Results have showed no significant difference for all aforementioned parameters for both cyclist groups when cycling with clipless
vs. without. However, using feedback enhanced significantly the effective pedal force during the upstroke while increasing also the
oxygen uptake. With feedback, tibialis anterior, rectus femoris and biceps femoris activity increased significantly. Furthermore, timing
parameters (on/off) for these muscles changed. After 6 weeks feedback training, subjects altered significantly their pedalling pattern.
Indeed, pedal forces were higher during the upstroke and therefore lower during downstroke, whatever the power output tested (i.e. 100,
200 and 300Watts). The control group, which trained without feedback, did not show such changes.
Discussion: Clipless did not allow any pull up action during sub-maximal cycling. However, pedalling with feedback helped to achieve
this pull up action and changed therefore the pedalling pattern. Unfortunately, this increase in pedalling effectiveness also impaired
oxygen uptake, as reported by Korff et al. (2007). As a consequence, even if the pull up action seems to have benefits for pedalling mechanics,
performance might rather be impaired, at least as long as subjects are not used to this action.
After a pull up action training, subjects had learned how to pull up on the pedal. Therefore it is possible to change the pedalling pattern
and to enhance the pull up action.
References
Korff T et al. (2007). Med Sci Sports Exerc, 39, 991-5
Sanderson DJ, Cavanagh PR (1990). Can J Spt Sci, 15, 38-42
Takaishi T et al. (1998). Med Sci Sports Exerc, 30, 442-9
10:15 - 11:45
Invited symposia
IS-BM06 Biomechanics in Alpine Skiing
MEASURING TECHNOLOGY AND PHYSICS IN ALPINE SKI RACING
SUPEJ, M.
SWEDISH WINTER SPORTS RESEARCH CENTER, OSTERSUND, SWEDEN AND FACULTY OF SPORT, UNIVERSITY OF LJUBLJANA, LJUBLJANA,
SLOVENIA
Evaluating performance in top level ski racing is crucial for improvement of the athletes. This is the area, which is normally covered by
physics and/or technology. To use physics and technology to the highest extend, it is important to understand the scheme of approaching
the problem. If one scale of the world is investigated, then one scale bellow should be understood. For example, when we would like
to evaluate skier’s velocity (kinematics), we should understand the acting forces (dynamics), which are the reason for the movement. This
is “one scale bellow”. To continue, the skier is affected by gravity, ground reaction force including the friction, air drag etc. To understand
whether these are strong or weak, another “scale bellow” should be investigated, e.g. for air drag the fluid dynamics, for friction the turn
and gliding principles, material and snow properties. The further we investigate, closer to the atomic or subatomic scale we come.
As an example of this approach in physics and technology, the consequence of carving entering WC races will be discussed. The
changes occurred in the turning principles, i.e. carving instead of skidding, therefore basic physical parameter values several “scales
bellow” were altered. Therefore, it was inevitable that the whole structure up to the racing technique was needed to be adopted. Basics
steps of the mechanical modelling of the “new” single motion technique (Supej et al., 2002), its evaluation by computer simulation, forces
measurements and performance measurements comparing to the “old” double motion technique will be presented.
The details in performance are important, even when the racing technique is known. There physical principles of mechanical energy can
be used, more specifically: diff(e-mech) (Supej, 2008), which represents “one scale bellow” the velocity and time that are normally used to
classify the racers. The latest technology, i.e. high end GNSS RTK system, can be used to measure and calculate diff(e-mech). But GNSS
devices survey only the antenna position and not the skier’s CG. The CG can be approximated by improved methodology of measurement
and mechanical modelling (Supej et al., 2008).
There are also many other examples in alpine skiing, where physics and technology are working hand in hand. Beside that, most of the
sensors work on physical principles. To conclude, physics and technology are deeply related.
OSLO/NORWAY, JUNE 24-27, 2009 519