Come ti sei trovato con le corone ovali?
Benefici? impressioni?
Ogni nuova, se così si può definire, trovata può essere interessante, soprattuto se realmente rispecchia ciò che è riportato dal venditore.....
Ho trovato alcuni studi che riguardano "non -circular chainrings", non si parla in modo specifico delle rotor, ma credo che la cosa si possa tranquillamente generalizzare....
1: Eur J Appl Physiol. 2004 Jan;91(1):100-4. Epub 2003 Sep 4.
Links
Physiological responses during cycling with noncircular "Harmonic" and circular chainrings.
Ratel S,
Duché P,
Hautier CA,
Williams CA,
Bedu M.
Laboratoire Interuniversitaire de Biologie des Activités Physiques et Sportives, UFR de Médecine-Université d'Auvergne, Clermont-Ferrand, France.
sratel@wanadoo.fr
The aim of the present study was to compare physiological data obtained during cycling using a noncircular "Harmonic" chainring versus a standard circular chainring over a range of speeds and slopes in endurance-trained cyclists. Thirteen male subnational cyclists (16-45 years) performed two maximal graded exercises on their own bicycle: one with a circular chainring, the other with a Harmonic chainring with the same gearwheel (52 teeth). The two chainrings were randomly assigned to avoid learning effects. The tests were carried out on a simulator. Speeds and/or slopes were increased every 2 min 30 s until exhaustion of the subject. Ventilation, oxygen uptake, carbon dioxide output, respiratory exchange ratio, and heart rate were continuously measured during the tests. Blood lactate concentration was measured during the last 30 s of each level. No significant difference was observed in any of the submaximal parameters measured during the tests ( P>0.05). Similarly, maximal values were not statistically different ( P>0.05). In conclusion, although the design of the Harmonic chainring was based on optimization analysis, comparison of the physiological response in this study did not translate into an advantage of the Harmonic over circular chainring during submaximal and maximal pedaling in trained cyclists.
PMID: 12955523 [PubMed - indexed for MEDLINE]
1: Med Sci Sports Exerc. 1992 Oct;24(10):1114-22.
Links
Physiological response to cycling with both circular and noncircular chainrings.
Hull ML,
Williams M,
Williams K,
Kautz S.
Department of Mechanical Engineering, University of California, Davis 95616.
The purpose of this study was to compare physiological variables of endurance-trained cyclists riding with four different chainring designs: round,
Shimano Biopace, and two engineered ellipse designs. The ellipse designated Eng10 had the crank arm oriented 10 degrees forward of the major (i.e. longer) axis. Eighty degrees further forward, along the minor axis, was the crank arm orientation for the second ellipse, Eng90. With the major to minor axis ratio of 22.9 cm/16.8 cm (1.36), both ellipses imposed a crank angular velocity variation of 27% relative to the highest velocity assuming constant chain velocity. Best described as a skewed ellipse (i.e., major and minor axes not perpendicular), the Biopace had a major to minor axis ratio of 1.09 thus giving a crank angular velocity variation of 8%. Eleven male cyclists rode at a high (80% of maximum VO2) and a low (60% of maximum VO2) workrate using each chainring. The study was conducted over four consecutive days with the presentation order of the chainrings randomized. Open circuit spirometry was used to collect continuous respiratory data. Heart rate, blood lactate, and cadence values also were measured. None of the physiological variables including rates of oxygen consumption showed significant differences among the chainrings. Thus, the gross efficiency of cycling was not improved by any of the noncircular chainrings. For cycling events where efficiency is a determinant of performance, the noncircular chainrings do not offer any advantage over round chainrings.
PMID: 1435158 [PubMed - indexed for MEDLINE]
1: Int J Sports Med. 1992 Apr;13(3):264-9.
Links
Efficiency of trained cyclists using circular and noncircular chainrings.
Cullen LK,
Andrew K,
Lair KR,
Widger MJ,
Timson BF.
Department of Physical Education, Eastern Illinois University, Charleston 61920.
The purpose of this study was to determine oxygen consumption (VO2), heart rate (HR) response, and rating of perceived exertion (RPE) of trained cyclists using noncircular and circular chainrings over a range of gears and pedal cadences. The subjects included 7 male cyclists (6 USCF licensed riders, 1 national qualifying triathlete). Each subject rode his own bicycle mounted on a wind-trainer at gears of 5.92 and 7.33 meters with noncircular and circular chainrings at pedal cadences of 50, 70, and 90 rpm. VO2, HR, RPE, and respiratory exchange ratio (RER) measurements were made during each of the 12 rides. Mean percent VO2max for each condition ranged from 28.7 +/- 2.1% with the 5.92 meter gear at 50 rpm to 83.4 +/- 4.3% using the 7.33 meter gear at 90 rpm. The results indicate no significant difference in any of the parameters measured between the two chainrings for any of the experimental conditions. The data indicate that the noncircular chainrings used in this study were not more efficient than the standard circular chainring for trained cyclists.
PMID: 1601563 [PubMed - indexed for MEDLINE]
Non sto ad analizzare ogni singolo studio..... tutti riportano che non ci sono variazioni significative rispetto alle corone circolari.
Mi sarebbe piaciuto trovare differenze significative, anche perchè le forme sono molto carine ed accattivanti.... però conviene risparmiare i soldi per altri oggettini più utili.
Anche perchè sui siti dei produttori si trovano casualmente risultati stratosferici con la loro corona... ma se fosse relamente così non pensate che tutti le utilizzerebbero già da tempo ?
Andrea