Physiological responses during cycling with oval chainrings (Q-ring) and circular chainrings.

Author:Cordova, Alfredo
Position:Research article - Report
 
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Introduction

It is well established that cycling performance can be enhanced by optimizing biomechanical factors related to the aerodynamics of cyclist posture, such as frontal area, seat height, and seat tube angle (Gregor, 2000). In addition to the aerodynamics aspects, the specific chainring design adopted could also influence the pedalling mechanical performance (Cullen et al., 1992; Hull et al., 1992). The importance of the ring shape for cycling performance is explained by several factors. First, the forces applied to the pedal during a crank cycle are not constant; rather, they are produced in a nearly sinusoidal manner with minimal torque being produced at the top and bottom points of the crank cycle (Gregor, 2000; Hull et al., 1992). Second, the specific shape of the chainring determines the way the force is exerted throughout the pedal-crank revolution, which in turn 'configures' the biomechanical patterns of cyclists (Coyle et al., 1991; Sanderson et al., 2000; Hue et al., 2001). In addition, the chainring design determines how 'smooth' the pedal action is (especially the 'pull-up'), which can have an impact on the metabolic cost of motion (Lucia et al., 2001).

In the last decades, several designs of non-circular rings have been proposed (Cullen et al., 1992; Hull et al., 1992). The main feature of these devices is that they accelerate the upstroke and the downstroke. For example, Cullen et al. (1992) and Hull et al. (1992) described an elliptical chainring with the peak pedal angular velocity occurring when the angle of the cranks was at 66[degrees] and 246[degrees] from the upper dead spot. In addition, Hull and colleagues (1992) introduced an elliptical shape whose maximum speed was obtained when crank angles were 100[degrees] and 280[degrees] from the upper dead spot. In both designs, the crank arms were parallel to the longest axis of the ring. Despite the theoretical benefits of these designs, they did not result in improvement in the physiological variables as compared to the standard circular chainring. Subsequent to these pioneering attempts, other designs of noncircular rings were devised, such as the "O.Symetric Harmonic" (Barani et al., 1994; Hintzy et al., 2000; Hue et al., 2001). Remarkably, with this new equipment, Hue et al. (2001) showed that, during an "all-out" 1-km laboratory test, cycling performance was significantly improved (64.25 [+ or -] 1.05 s vs. 69.08 [+ or -] 1.38 s with the eccentric and the round designs, respectively), although the-cardiorespiratory variables were not influenced.

An alternative method of increasing power output was provided by the Rotor system (Santalla et al., 2002). This system makes each crank independent from the other such that they are no longer fixed at 180[degrees] (Henderson et al., 1977; Santalla et al., 2002). This configuration allows the angle between the cranks to vary so that the dead points (where torque production is minimal) are practically eliminated. Using this configuration, Santalla et al. (2002) demonstrated that, at exercise intensities between 60 and 90% V[O.sub.2max], delta efficiency was significantly higher with the eccentric than with the round design (24.4 [+ or -] 1.9% vs. 21.1 [+ or -] 1.1%, respectively). The Rotor Crank has since been shown to have no effect on time trial performance (Jobson et al., 2009).

Rotor Componentes Tecnologicos, S.L., has developed a new type of oval ring: "Variable Gear Rings (Q-rings)". The Q-ring design mimics the pedalling biomechanics of Rotor Cranks during the pedal downstroke, i.e., when cyclists generate their greatest power (Henderson et al., 1977; Santalla et al., 2002). This means that when the pedal is descending, the Q-ring progressively modulates the immediate gear, according to the leg's immediate capacity. Thus, Q-rings increase the diameter at the same time as the cyclist increases the force applied to the pedal during the downstroke (Figure 1). The theoretical advantages of the Q-ring design are that it: (1) eliminates the dead spots (Santalla et al., 2002; Lucia et al., 2004), (2) increases the crank arm length during the downstroke (Hue et al., 2001; Zamparo et al., 2002), and (3) slows the downstroke and accelerates the upstroke (Hull et al., 1992; Martin et al., 2002).

It was the purpose of this study to compare the physiological responses and performance of elite cyclists riding with two different chainring designs, oval Q-rings and conventional rings (C-rings), during an incremental exercise test and subsequent short sprints.

Methods

Participants

Fourteen male cyclists (senior license holders who have been competing in lower categories for several years) participated in this study. Participant characteristics are presented in Table 1. The evaluation protocol was designed according to the Helsinki Conference for research on human beings and according to the ethical standards in sports and exercise science research (Harriss and Atkinson, 2009). All cyclists were informed of the purpose of the study and the possible risks before they provided written consent.

From the start of the season (beginning of November) to the initiation of the tests (fourth week of February), participants cycled 5215 [+ or -] 178 km in training. Cyclists underwent an electrocardiographic evaluation and a blood test (biochemical and haematological parameters) screening prior to participation. None of the participants had previous experience in using Q-rings (Figure 1). Two weeks previous to the experiments, participants had the opportunity to test the Q-ring in order to become familiarized with this configuration. During these two weeks, participants followed the same programmed training consisting of approximately 400 km per week. The training protocol during a week comprised: two days of resistance training (RT, approximately 180 km each day), two days of interval training (IT, normally submaximal series of 5 min), and two days of "light" training (LT, approximately 60 km each day). These sessions were interspersed during the week: LT, IT, RT, LT, RT, IT, LT, etc.

Experimental procedure

Each participant was evaluated on two separate sessions: one with the C-ring, the other with the Q-ring. Sessions were randomly assigned and they were separated by 48 h. The participants were tested at approximately the same time of day (0900), and under similar environmental conditions (average temperature, 22[degrees]C; relative humidity, 65-70%), to minimize the influence of biological variability.

Laboratory tests were performed with a Computrainer (RacerMate--FloScan Instrument Co, USA). The advantage of this cyclotrainer is that it allows each participant to use the most suitable Q-ring regulation setting by means of the "spinscan", a tool that provides information about each individual's pedalling style. Moreover, each participant could use his own bicycle for the test. For all tests, the same rear wheel was used at the same inflation pressure (8 atm), and for each bicycle, a Q-ring or Cring was used...

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