Pedal cycle
In cycling, the pedaling cycle is the sequence of movements (the pedaling movement ) in the course of a turn of the crank. It is therefore the smallest unit of movement that is constantly repeated in the same form when cycling .
Basics
The pedal cycle extends over a full rotation around the bottom bracket axle and is usually carried out continuously with a large number of repetitions. When the foot is placed on the pedal, a connection is created between the crank and the lower extremity . A distinction must be kicking in a sitting position and Trettechniken, in which the driver rises from the saddle and rides "standing" as the so-called saddle . When using so-called "safety pedal" which usually as a hook pedal or clipless pedal to be referred to, the shoe is rigidly coupled to the pedals so that forces can be exerted in all directions on the pedal and the pedal crank.
Because of the uniformity in the repetition of movements, the pedaling cycle is well suited for detailed investigations, for example in biomechanics . The aim of the investigations is usually to make the service provision more economical , i.e. to increase the efficiency of the pedaling movement. The objects of investigation are the performance provided, as well as the moments and forces that occur. A focus on the forces led to a model that is known under the name "Runder Tritt". A shortcoming of this ideal is that it does not reflect the performance that is ultimately important in cycling . An explanation of how the muscle power is transferred to the drive cannot be derived from this.
Phases
The phases of the pedaling cycle are the subject of extensive studies of the pedaling movement of a cyclist . The focus is on the curve of torque over time and its typical course in the four main sectors of the pedaling cycle.
For better understanding, the demarcation of the phases is based on the dial of a clock.
Printing phase
When the rider is standing or not too far behind the bottom bracket and pedaling clockwise , the greatest force is applied in the pressure phase, which ranges from "half past two" (45 °) to "half past four" (135 °). The further the rider sits behind or, in the case of some recumbent bikes, ultimately even under the bottom bracket, the more this area shifts counterclockwise. The torque remains at a high level over the entire printing phase .
Pulling phase (sliding phase)
The pulling phase for a racing bike is roughly between “half past four” (135 °) and “half past eight” (225 °). In the pulling phase, the foot “glides” backwards with comparatively little effort - hence the alternative term “sliding phase”. The foot passes through the bottom dead center .
Since pedals are in cycling generally used by firm fixation (formerly "hooks and straps," today Klickpedale ) allow tangential force developed in each phase of the Tretzyklus, it is basically possible also during the pull phase, to generate a high torque.
In fact, the lowest forces are usually developed in the pulling phase. Biomechanics cannot offer an explanation for this up to now.
Lifting phase
This phase is sometimes misunderstood as the "pull phase". In the model between "half past seven" (225 °) and "half past ten " (315 °), the lifting phase is the weakest phase in terms of the force effect . With respect to the force application already relevant here forces must be applied to lift the leg (12 to 15 kg). A negative torque usually occurs here, i. H. the upward moving leg is lifted upwards by the force of the other, downward moving leg. Even with top amateurs and professionals, there is hardly any positive torque here. Only with maximum effort - high acceleration, sprint - (or when driving in a temporarily too high gear) and is really pulled on the pedals in this phase .
Thrust phase
This phase lies between "half past ten" (315 °) and "half past one" (45 °). Good stylists on the bike are able to exert noticeably high forces on the pedal during the push phase and initiate the push phase in a smooth transition. This partially compensates for the weakness of the pulling phase (in which the other leg is in each case), even if in this phase both legs together are not able to exert a torque that would be comparable to the torque in addition of the pushing and lifting phase .
optimization
"The round step" is a term from the training theory of cycling. The goal is to make the pedaling movement as smooth as possible. Apart from the legs themselves, the body should be as calm as possible, since rocking and rocking in the middle and upper part of the body leads to a loss of energy. For efficient locomotion, it is recommended to ride with a higher cadence , which inexperienced riders usually cannot achieve without getting into an uncomfortable and exhausting rocking movement.
Traditionally, the round step is trained by driving with very small gear ratios, i.e. with a high cadence . In winter training in particular, bicycles without gear shifting and with a fixed gear are used, which force you to pedal quickly.
The emphasis on the round step has also led to misunderstandings that are gradually being uncovered (see references and literature).
Empirical studies show that all racing cyclists, including the world's best rail and road riders, are far from generating a constant torque over the entire pedaling cycle . While the very low (mostly slightly negative) torque in the lifting phase is compensated for by the very high use of force in the pressure phase of the other leg, comparatively little power is provided in the push phase and pull phase . Optimizations of the pedaling cycle aim to improve the use of force in these phases and to harmonize the transitions between the phases.
A technical possibility to smooth the physiologically caused, uneven torque curve is seen, among other things, in the use of elliptical chainrings. Best known are the chainrings made by Shimano, known as " Biopace " . Its effect is controversial. Evaluations of experiences with this type of chainrings come to ambiguous results.
In accordance with the training principle of opposites , the pedaling cycle is not only trained by driving with small gear ratios, but also by driving with very high gears and correspondingly low cadence.
literature
- Wolfgang Petzke: Muscle performance and efficiency when cycling. Performance of joint movements - explanation of the "round step". In: competitive sport. No. 3, 2006, ISSN 0341-7387 , pp. 47-54, online (PDF; 1.34 MB) .
- Florian Hoppel: Round step in cycling - comparison of the pedaling economy with different pedal systems using EMG. GRIN Verlag, Munich 2008, ISBN 978-3-640-18079-0 .