Noncircular Chainrings Research Articles

Noncircular Chainrings Do Not Influence Physiological Responses During Submaximal Cycling.

To determine the separate contributions of pedal speed and chainring shape/eccentricity to the metabolic cost of producing power and evaluate joint-specific kinematics and kinetics during submaximal cycling across 3 chainring eccentricities (CON = 1.0; LOW = 1.13; HIGH = 1.24). Eight cyclists performed submaximal cycling at power outputs eliciting 30%, 60%, and 90% of their individual lactate threshold at pedaling rates of 80rpm under each chainring condition (CON80rpm; LOW80rpm; HIGH80rpm) and at pedaling rates for the CON chainring chosen to match pedal speeds of the noncircular chainrings (CON78rpm to LOW80rpm; CON75rpm to HIGH80rpm). Physiological measures, metabolic cost, and gross efficiency were determined by indirect calorimetry. Pedal and joint-specific powers were determined using pedal forces and limb kinematics. Physiological and metabolic measures were not influenced by eccentricity and pedal speed (all Ps > .05). Angular velocities produced during knee and hip extension were lower with the HIGH80rpm condition compared with the CON80rpm condition (all Ps < .05), while angular velocity produced during ankle plantar flexion remained unchanged. Despite the noncircular chainrings imposing their eccentricity on joint angular kinematics, they did not reduce metabolic cost or increase gross efficiency. Our results suggest that noncircular chainrings neither improve nor compromise submaximal cycling performance in trained cyclists.

Noncircular Chainrings Do Not Influence Maximum Cycling Power.

Noncircular chainrings could increase cycling power by prolonging the powerful leg extension/flexion phases, and curtailing the low-power transition phases. We compared maximal cycling power-pedaling rate relationships, and joint-specific kinematics and powers across 3 chainring eccentricities (CON = 1.0; LOWecc = 1.13; HIGHecc = 1.24). Part I: Thirteen cyclists performed maximal inertial-load cycling under 3 chainring conditions. Maximum cycling power and optimal pedaling rate were determined. Part II: Ten cyclists performed maximal isokinetic cycling (120rpm) under the same 3 chainring conditions. Pedal and joint-specific powers were determined using pedal forces and limb kinematics. Neither maximal cycling power nor optimal pedaling rate differed across chainring conditions (all p > .05). Peak ankle angular velocity for HIGHecc was less than CON (p < .05), while knee and hip angular velocities were unaffected. Self-selected ankle joint-center trajectory was more eccentric than HIGHecc with an opposite orientation that increased velocity during extension/flexion and reduced velocity during transitions. Joint-specific powers did not differ across chainring conditions, with a small increase in power absorbed during ankle dorsiflexion with HIGHecc. Multiple degrees of freedom in the leg, crank, and pedal system allowed cyclists to manipulate ankle angular velocity to maintain their preferred knee and hip actions, suggesting maximizing extension/flexion and minimizing transition phases may be counterproductive for maximal power.

Positioning of Elliptical Chainrings During Wingate Testing; A Repeated Measures Case Study

Introduction: Manufacturers of non-circular bicycle chainrings claim that use of their products can increase power output during exercise. These chainrings are generally defined as the ellipse shaped by a large diameter (major axis) and small diameter (minor axis). By adjusting the major axis-to-crankarm angle, one is effectively changing the relationship between the greatest torque arm (major axis) and position of the crankarm when the leg is extending, taking advantage of the great force production capabilities of the leg at that point. A number of industry-sponsored “white papers” claiming increased performance have been released (Osymetric, n.d.; Barani et al, 1993). These results are trumpeted, promising great improvement for minimal work. Peer-reviewed literature is less than convinced; Bini et al (2012) found no chainring that provided consistent improvement in VO2 or HR. This result agrees with previous research on chainring shape and physiological response (Kautz and Hull, 1995; Leong, 2014; Hue et al, 2007; Ratel et al, 1998). Some studies posit that elliptical chainrings may provide mechanical benefits to a rider. Bini mentions a Spanish-language article which found subjects using elliptical chainrings for Wingate testing had 8% increases in average power and 9% increases in peak power output. O’Hara (2012) found that after submaximal riding, riders performed a 1-km time trial 1.6s faster than those using circular chainrings, at a higher speed (+.7kph) and power output (+26W). Similarly, Cordova et al (2014) found that elliptical chainrings produced 2.5-6.5% increases in power during short (20s) sprints after an incremental test. This study aims to build on previous literature while incorporating a novel finding from the field of computer science. A thesis by Malfait (2010) examined the relationship between the major axis of the chainring, and the crankarm: His findings showed most manufacturer setups were 7.5 – 66.5° out of phase. This finding, in conjunction with O’Hara and Cordova, lead us to believe that elliptical chainrings may be set up in an “optimal” fashion, compared to manufacturer recommended installation, which will provide greater mechanical advantage during Wingate testing than what has been previously shown.  Methods: One subject (male, 60.5kg, 175cm, BMI = 19.8) participated in this case study. He completed 15, 30-second Wingate tests against 7.5% of his body weight (4.54kg). All tests were performed on an electromagnetically braked cycle ergometer (Velotron Pro; Racermate, Seattle, WA).  Wingate order was randomized and each chainring condition (Circular “C”, Rotor Q-Ring “R”, Osymetric Rings “O”, Rotor Optimal “RO”, Osymetric Optimal “OO”) was repeated three times. Normal position for R was according to manufacturer-recommended setup at the bolt hole marked “···”. RO was achieved by rotating the chainring clockwise 3 bolt holes (~31°; Malfait recommendation, 33°). O is preset by the chainring having only 5 bolt holes. An adapter ring was manufactured to move the major axis to the desired position. For the sake of symmetry and structural integrity, holes were evenly spaced, so OO is a 36° clockwise rotation instead of Malfait’s recommended 39°. Peak power, mean power, and fatigue index (watts/s) were collected.  Results: Data was analyzed using a 1-way repeated measures ANOVA using Peak Power, Mean Power, and Fatigue Index as the independent variables. Mean power during the Wingate test was not significantly different between chainring conditions, F (4,14)=1.89, p=.2. Peak power trended towards significance, F (4,14)=3.82, p=.0505. Fatigue index was significant, F (4,14)=12.04, p=.0018. Post-hoc testing using Tukey’s HSD showed that fatigue index using the O chainring condition was significantly higher than C (p<.01), RO (p<.01), and OO (p<.01). The R chainring condition produced significantly higher fatigue index than C (p<.05) and OO (p<.05).  Conclusions: Although manufacturers have an interest in selling their products, peer-review research is hesitant to support their claims. Our current subject showed no major differences in performance, even using an exercise type thought to maximize the benefits of elliptical chainrings (sprinting). It is interesting to note that while it has not yet reached significance, the peak power of O condition is a good deal higher than any other. This may be the cause of significance in the fatigue index (where O was higher than C, RO, and OO). The increase in peak power, especially with a drop in minimum power at the end of the test, may have been enough to cause significance. We cannot yet say that O (or any chainring) is significantly better than any other chainring, especially given the non-significance of mean power output differences between conditions and the current case study design. These conclusions should be interpreted in the context of n=1. Data collection is ongoing in other subjects, and may affect significance of results presented here.

Submaximal Cycling Power Using Noncircular Chainrings

During cycling, muscular power is produced during both leg extension and flexion, with minimal power production occurring during the transitions. Prolonged extension and flexion phases and reduced transition phases could increase cycling power by allowing muscles to generate power for a greater portion of the cycle. Noncircular (NC) chainrings could prolong the powerful leg extension phase by varying crank angular velocity (ω) within the pedal cycle. Mixed findings from previous comparisons of circular (C) and NC chainrings may be related to different approaches in quantifying cycling power. One approach common to power meters is to calculate power as the product of average ω and torque (T) for the pedal cycle. This assumption might overestimate power with NC chainrings. PURPOSE: To determine the extent to which the assumption of constant ω overestimates power values during submaximal cycling. METHODS: Eight healthy participants (age=35±8 yr, mass=75±7 kg, height=1.8±0.1 m) performed 5-min steady state cycling on an isokinetic cycle ergometer using a NC chainring. Following a 5-min warm-up, participants cycled at 90% of lactate threshold power (219±51 W) at 80 rpm and repeated the protocol with a C chainring after a 5-min rest. Participants were visually blinded to chainring conditions. Pedal forces were measured with a force sensing pedal and pedal and crank position were measured with optical encoders. T and ω were measured at 240Hz. Power was calculated as: Method 1: P1=[(ΣNn-1 Tn)/N]x[(ΣNn-1 ωn)/N] and Method 2: P2=[ΣNn-1 (Tn x ωn)]/N. A paired t-test was used to compare differences in power calculations between chainring conditions. RESULTS: Calculated power (P1: 110±22 W; P2: 110±22 W) did not differ for C chainring condition. P1 (117±21 W) was 4±1% higher than P2 (112±21 W) for NC chainring condition (p<0.01). CONCLUSIONS: Method 1 overestimated power with a NC chainring as it did not account for the generally sinusoidal ω produced by the NC chainring, where the largest instantaneous T values occurred when instantaneous ω values were below the average. These results suggest that the assumption of constant ω may overestimate power when using NC chainrings and may explain reports of increased cycling power.

Non-circular chainring improves aerobic cycling performance in non-cyclists

Non-circular chainrings alter the crank velocity profile over a pedalling cycle. The aim of this study was to investigate the effect of this altered crank velocity profile on the aerobic performance compared to a circular chainring (CC). Ten male non-cyclists performed two incremental maximal tests at 80 rpm on a cycle ergometer: one with a circular (Shimano) and the other with a non-circular chainring Osymetric® (Somovedi), at least 50 h apart. Each test started with a workload of 100 W lasting 3 min. During the first 12 min, the workload was increased by 30 W every 3 min. Thereafter, the workload was increased by 30 W every 2 min until exhaustion. The power output, the intra-cycle crank angular velocity and the physiological parameters were monitored continuously, averaged over the last 30 s of each increment and at exhaustion, and compared for the two chainrings. Results showed a higher maximal aerobic power attained with the non-circular chainring (362.6 ± 37.9 vs. 338.8 ± 32.6 W, p < .001; moderate effect), which could be explained by a significantly lower energy expenditure during the first increment at 100 W. It could be hypothesised that the use of the non-circular chainring allowed saving a small part of energy expenditure throughout the test, allowing the exhaustion of the subject at a higher increment for a similar maximal energy expenditure, in comparison with a CC. Although this improvement is obtained only for non-cyclists, it allowed highlighting the link between cycling equipment modifying the pedalling motion and physiological responses.

Noncircular Chainrings Do Not Improve Maximum Cycling Power and Joint-Specific Power during Maximal Cycling

Net cycling power is mainly produced during leg extension and flexion actions with minimal power produced during the transition between extension and flexion. A possible strategy to maximize cycling power is to increase the time spent in extension and flexion, while decreasing the time spent in transition. Noncircular (NC) chainrings can be oriented to prolong the powerful leg extension phase by varying crank angular velocity (ω) within the pedal cycle. However, the degree to which instantaneous crank ω influence muscle and joint actions depends on the degrees of freedom (DOF) in the leg/crank/pedal system. Previous investigations on cycling power using NC chainrings have produced mixed findings. These mixed findings may be due to cyclists exploiting redundant DOF in the leg/crank/pedal system to manipulate joint ω independent of crank ω. PURPOSE: To evaluate the effects of NC chainrings on joint-specific kinematics and power production during maximal cycling. METHODS: Ten healthy trained cyclists (age=34±8yr, mass=72±9kg, height=1.8 ±0.1m) performed maximal cycling trials of 3 s at randomly assigned pedaling rates (60, 90, and 120 rpm), and chainring eccentricities (ratio of major-to-minor axis) of 1.0 (Cir), 1.13 (Rotor), and 1.24 (Osym), respectively. Participants were visually blinded to chainrings. Joint-specific powers were averaged over complete pedal revolutions and extension-flexion phases. Joint-specific kinematics were analyzed for the portion of the pedal cycle where NC chainrings imposed 80% of their eccentricities (ECC80) on crank ω. RESULTS: Joint-specific powers were unaffected by chainring eccentricity. Ankle extension ω was significantly reduced (-13±12% and -37±13% at 90 and 120 rpm, respectively; all p<0.05) with the Osym chainring, whereas knee and hip extension ω were unaffected. Crank ω, ankle, knee, and hip extension ω within ECC80 increased with increasing pedaling rates (all p<0.01). CONCLUSION: NC chainrings did not improve maximum cycling power or alter joint-specific power during maximal cycling. Knee and hip ω remained unaffected with only ankle ω affected by chainring eccentricity. These results suggest that the effects of the NC chainrings on crank ω were eliminated by the cyclists’ ankling action and thus did not alter the major power producing actions of the hip and knee.

Non-Circular Chainrings Do Not Improve Maximum Cycling Power or Change Optimal Pedaling Rate

Non-Circular Chainrings Do Not Improve Maximum Cycling Power or Change Optimal Pedaling Rate

Effect of chainring ovality on joint power during cycling at different workloads and cadences

Non-circular chainrings theoretically enhance cycling performance by increasing effective chainring diameter and varying crank velocity, but research has failed to consistently reproduce the benefits in cycling trials. The aim of this study was (1) to investigate the effect of different chainring shapes on sagittal knee joint moment and sagittal lower limb joint powers and (2) to investigate whether alterations are affected by cadence and workload. Fourteen elite cyclists cycled in six conditions (70, 90 and 110 rpm, each at 180 and 300 W), for 2 min each, using three chainrings of different ovalities (1.0–1.215). Kinematic data and pedal forces were collected. For most conditions, only the chainring with the highest ovality (1.215) was characterised by smaller sagittal knee joint moments, smaller relative sagittal knee joint power contribution and larger relative sagittal hip joint power contribution, which suggests a change from maximising efficiency to maximising power production. Effect sizes increased with higher cadences, but not with higher workload. This study has application for athletes, clinicians and sports equipment industry as a non-circular chainring can change joint-specific power generation and decrease knee joint moment, but certain ovality seems to be necessary to provoke this effect.

Sistemas de pedivela não-circulares e interfaces pedal-pedivela no ciclismo: uma revisão da literatura.

DOI: http://dx.doi.org/10.5007/1980-0037.2012v14n4p470 Noncircular chainrings and novel pedal to crank interfaces have been designed to optimize variables related to cycling performance (e.g. peak crank torque and efficiency), with conflicting results in terms of performance. Therefore, the aim of the present article was to review the theoretical background of noncircular chainrings and novel pedal to crank interfaces and their effects on biomechanical, physiological and performance variables. Reducing internal work, crank peak torque, and time spent at the top and bottom dead centres (12 o’clock and 6 o’clock positions, respectively) were among the various targets of noncircular chainrings and novel pedal to crank interface design. Changes in joint kinematics without effects on muscle activation were observed when cyclists were assessed using noncircular chainrings and novel pedal to crank interfaces. Conflicting results for economy/efficiency explain the unclear effects of noncircular chainrings on cycling performance and the positive effects of some novel pedal to crank interfaces on cycling economy/efficiency.

Effects of a noncircular chainring system on muscle activation during cycling

Previous studies evaluated cycling with noncircular chainrings and suggested that changes in muscle activation would occur in response to altered pedaling mechanics throughout the crank arm revolution. However, no previous study addressed this question. The aim of this study was to compare the magnitude of muscular activity between a conventional and a noncircular crank system during an incremental maximal cycling test. Seven mountain-bike trained cyclists completed two incremental maximal tests, separated by 48 h, one for each crank system. Each test started with a workload of 100 W and was increased by 30 W every minute until exhaustion. Power output, pedaling cadence and heart rate were monitored and compared between the crank systems using paired t-tests. Surface EMG was recorded from the right rectus femoris, vastus medialis, biceps femoris and gastrocnemius medialis. EMG was compared using a general linear model considering as factors the crank system and workload with post hoc analysis at α = 0.05. RMS presented effect of workload, but no effect of crank system was found for the muscles analyzed. The present results do not support effects of the noncircular crank system on variables of performance and muscle activation during incremental cycling in trained mountain bike cyclists.

NON-CIRCULAR CHAIN RING ALLOWS A REDUCTION OF JOINT LOADING IN CYCLING

Non-circular (NC) chain rings were primarily designed to improve the mechanical effectiveness of cycling. Their use can be investigated for application in rehabilitation: they could provide a solution to design an effective exercise reducing joint loading. The aim of this study was to analyze the differences in kinematics, energy consumption, and joint moments between circular and NC chain rings, then to identify a profile that can reduce joint loads, maintaining equal mechanical and metabolic works. Five young participants performed two tests on a cycloergometer; one with a circular chain ring and the other with an NC one. The test consisted in 15 min of cycling; during which they were asked to cycle at three different speeds and at two different powers. Stereophotogrammetric and metabolic data were acquired. Statistical analysis was applied on metabolic data. Joint angular velocities were obtained from kinematic data. A two-dimensional (2D) model of cycling was designed to estimate joint moments with both chain rings. A different ring profile was suggested to further reduce joint flexion peak moment. NC chain ring allows a reduction of flexion joint moments with respect to the circular one without significant difference in metabolic and kinematic data. The new profile proposed further decreases maximum knee flexion moment maintaining equal mechanical work.

A theoretical analysis of an optimal chainring shape to maximize crank power during isokinetic pedaling

Previous studies have sought to improve cycling performance by altering various aspects of the pedaling motion using novel crank–pedal mechanisms and non-circular chainrings. However, most designs have been based on empirical data and very few have provided significant improvements in cycling performance. The purpose of this study was to use a theoretical framework that included a detailed musculoskeletal model driven by individual muscle actuators, forward dynamic simulations and design optimization to determine if cycling performance (i.e., maximal power output) could be improved by optimizing the chainring shape to maximize average crank power during isokinetic pedaling conditions. The optimization identified a consistent non-circular chainring shape at pedaling rates of 60, 90 and 120 rpm with an average eccentricity of 1.29 that increased crank power by an average of 2.9% compared to a conventional circular chainring. The increase in average crank power was the result of the optimal chainrings slowing down the crank velocity during the downstroke (power phase) to allow muscles to generate power longer and produce more external work. The data also showed that chainrings with higher eccentricity increased negative muscle work following the power phase due to muscle activation–deactivation dynamics. Thus, the chainring shape that maximized average crank power balanced these competing demands by providing enough eccentricity to increase the external work generated by muscles during the power phase while minimizing negative work during the subsequent recovery phase.

Physiological response to cycling with both circular and noncircular chainrings

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.