Gas exchange measurements.
Cardiorespiratory pulmonary data were continuously monitored and measured every 10 s using a mass spectrometer breath-by-breath automated system (MGA-1100, Marquette, NY): minute ventilation (V̇E), oxygen uptake (V̇O2), carbon dioxide production (V̇CO2), respiratory equivalents for O2 (V̇E/V̇O2) and CO2 (V̇E/V̇CO2), respiratory quotient (R), breathing frequency (f), and tidal volume (VT). Heart rate (HR) was measured every 15 s using a telemetry system (Polar Racer, Polar Electro, Kempele, Finland).
The results are expressed as means ± SEM. After the verification of a normal distribution (Gaussian graphical distribution), cardiorespiratory data such as V̇O2, V̇E, V̇E/V̇O2, V̇E/V̇CO2, R, VT, f, and HR were compared using a two - way analysis of variance (ANOVA) with repeated measures (time, chainring). Statistical significance was accepted at the P < 0.05 level.
None of the cardiorespiratory variables (V̇O2, V̇E, V̇E/V̇O2, V̇E/V̇CO2, R, f, VT, HR) showed significant differences between chainring trials in terms of average values or kinematics (Figs. 3–5).
The performance was significantly greater using the eccentric chainring (64.25 ± 1.05 vs 69.08 ± 1.38 s, P < 0.004, with the eccentric and the round design, respectively).
The most important finding of the present study was that the eccentric chainring significantly improved performance during an all-out 1-km cycle test without any change in metabolic variables.
To ensure precision and reliability in the measurement of physiological responses, each athlete used his own bicycle for both cycling tests. The order of use of circular and eccentric chainrings was randomized. Testing was scheduled to avoid conflicts with both race schedules and periods of intense training. Adaptation to the eccentric chainring design presented one potential obstacle to the validity of this study. None of the athletes had ridden using the eccentric design before the study. To familiarize them with the velocity pattern offered by this particular design, each test began with a 20-min warm-up ride using the scheduled chainring, a protocol that has been shown to be effective in learning a new motor task (24).
Studies that have tested the theoretical benefits of noncircular chainrings have used either a maximal and exhaustive test (V̇O2max test) or a rectangular, long-duration test. Both tests have indicated that noncircular chainrings are no more efficient than standard chainrings (4,9,12,14). The authors of these studies had hypothesized that the noncircular chainrings would increase cycling efficiency by decreasing the internal work, which was defined as the sum of absolute changes in total mechanical energy—thus the work to move the limbs (23,25). In unpublished studies, our group investigated the effect of an eccentric chainring during similar tests (V̇O2max test and long-duration rectangular test) with both eccentric chainring users and nonusers. The eccentric users had been training with the eccentric chainring for at least 1 month. The results showed greater oxygen uptake—thus lower efficiency—for the eccentric chainring users in every test, even for long-term users. We hypothesized that the eccentric chainring induced changes in the biomechanical patterns, which increased the metabolic cost and thus masked the expected mechanical advantages. Indeed, the revolution described by the pedal is a perfect circle with a fictitious center 25 mm ahead of the center of the crank arm. However, if considered from the point of the applied forces (the center of the crank), the pedal describes an elliptical circle that changes at the moment the cyclist applies maximal vertical force during the downstroke and upstroke. This thus changes the usual pattern of force application. It has been well documented that changes in optimal biomechanical pattern increase the energy cost of motion (2, 18), most likely in relation with the recruitment of different muscle fibers.
We therefore hypothesized that the theoretical advantage of the eccentric chainring would be best observed during short and intense cycling exercise where the aim is not to minimize oxygen consumption but to cycle as fast as possible. The test chosen was the all-out 1-km sprint because it is a classic indoor cycling event and is both brief and intense. The significant improvement in test performance showed that the mechanical advantage (increasing crank arm length during the downstroke and decreasing length during the upstroke) was greater than the supposed muscular disadvantage (change in biomechanical pattern), at least for short distances performed in laboratory. This may be explained by the higher torque during the downstroke resulting from the greater crank length during this cycling phase. Indeed, as stated earlier, Coyle et al. (3) demonstrated that the difference between “elite national class” and “good state class” cyclists is the combination of higher power output and higher peak torque about the center of the crank. They proposed that this last is caused by the application of higher vertical forces to the crank arm during the cycling downstroke.
Each cyclist used his own bicycle rather than the laboratory cycle-ergometer to more closely simulate road conditions. However, this condition did not offer the same inertia and freedom of movement as real road or velodrome conditions, and it thus may have influenced the crank torque pattern (19). Moreover, we did not measure the change in the cycling position induced by the eccentric chainring. Instead, each cyclist verbally informed us on leaving that he had been comfortable riding but that his cycling position had changed a little using this design. Changes in cycling position are known to induce changes in aerodynamic resistance (1). Air drag increases with the square of the speed such that, at bicycling speeds of 60 km·h-1, wind resistance is responsible for more than 90% of the total energy cost (15, 20). We therefore need to be cautious in suggesting that this eccentric chainring could enhance performance during indoor and outdoor velodrome tests. Differences have also been demonstrated between preferred and optimal positioning during cycle ergometry (10). Because the cycling position was freely chosen in our study, we may assume that the subjects used less than optimal positions during both tests.
Our subjects were road and off-road cyclists and triathletes, representing a partial selection of the different sports populations that might benefit from use of the eccentric chainring. Because none of them were indoor cycling specialists, however, we did not study the population that would seem to benefit most from this design. Because of its variable crank arm length, the eccentric chainring seems to be particularly adapted for velodrome cycling events, whatever the gradient of the track.
The findings of the present study demonstrate that the eccentric chainring significantly improved the cycling performance during an all-out 1-km test. However, further studies with indoor cycling specialists using tests on a velodrome would be helpful to define the maximal possibilities of such a chainring.
Address for technical explanation concerning the “Pro race” eccentric chainring: Mr. Eric Valat, 20, Rue Paul Verlaine, 34790, Grabbels, France; E-mail: email@example.com, contact@pro-racenet, http://www.pro-race.net.
Address for correspondence: Olivier Hue, Laboratoire ACTE, UFR-STAPS Antilles-Guyane, Université Antilles-Guyane, Campus de Fouillole, 97159 Pointe à Pitre; E-mail: HueO@wanadoo.fr.
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Keywords:© 2001 Lippincott Williams & Wilkins, Inc.
PHYSIOLOGY; HEART RATE; SPRINT EXERCISE; BIOMECHANICS