The be between 30°-150° of the anterior crank

The development of non-circular chainrings (NCCs) for commercial use began in the late 1970’s and their use by professional cyclists came later on in the 1980’s. Various models have been developed over the years since, including the Shimano Biopace ring, Rotor’s Q-ring range and the Osymetric brand used by Tour de France winners Bradley Wiggins and Chris Froome.

Traditional circular chainrings (CCs) are designed so that when the crank arms are vertical (0° and 180°) force exertion is minimal and when the crank arms are horizontal (90°) force exertion is maximal (Ericson & Nisell, 1988). The angular velocity of the crank remains constant throughout a revolution when using a CC (Broker, 2003; Horvais et al., 2007).

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Within their research Ericson and Nisell (1988) suggested that the effective force applied to the pedals whilst using a CC was not constant but sinusoidal. As a result of this study Cullen et al., (1992) deduced that it would theoretically be possible to alter the total power output of a cyclist’s pedal stroke by optimally selecting a chainring shape to match the biomechanical and physiological demands of the moving leg. This suggestion led to the development of NCC’s with a small radius at top and bottom dead centre (TDC, BDC) and a larger radius during the downstroke and upstroke (Horvais et al., 2007) of the pedaling motion. This maximizes time spent in the power phase and decreases time at TDC and BDC (Hintzy et al., 2015; Horvais et al., 2007; Neptune and Herzog, 2000). The power phase is suggested to be between 30°-150° of the anterior crank arm (Zameziati et al., 2006). Cullen et al (1992) state that the largest contributing factor of an NCC is that the changing angular velocity experienced in each revolution of the pedals will enable a rider to stay closer to their maximum power output for a larger portion of the pedal stroke. Kautz and Neptune (1994) have suggested that the internal work required to pedal is relative to the external workload of the resistance of the crank. NCC’s reduce the external work required via the decrease in velocity during the power phase due to the increased radius of the chainring. This allows the muscles to generate greater power for longer as per the force-velocity relationship; more actin-myosin cross bridges are formed. It has been theorised that this would allow for reduced energy consumption due to the maintenance of the kinetic energy of the leg, which in turn may allow for a greater power output, increased muscular efficiency and reduced O2 consumption (Rankin & Neptune, 2008; Abbiss., 2005). However, Ratel et al (2003) concluded that the use of a NCC does not result in less O2 uptake during submaximal and maximal cycling, therefore it is suggested that link between the physiological demand and the reduced external work of the downstroke is insignificant.

 

The development of the Shimano Biopace chainring, following Ericsen and Nisell’s (1988) research, created excitement within the world of cycling and sports scientists quickly began testing the components influence on performance and physiological variables. Okajima (1983) concluded that the Biopace chainring improved cycling efficiency Coyle et al (1991) suggested that efficiency in cycling could be related to the absolute rate of oxygen consumption at lactate threshold. by reducing leg joint torques and muscle EMG relative to those of a circular chainring at a given power output.

 

Further research refutes these findings; Hull et al (1992) focused on the comparison of the Shimano Biopace NCC with a standard CC. It was found amongst the eleven, male, trained endurance cyclists, that the type of ring used had no significant effect on physiological efficiency or performance with no significant difference in blood lactate, heart rate or oxygen consumption. The results from Hull et al’s study are supported by Cullen et al’s (1992) assessment of seven experienced male cyclists and their performance using NCC’s and CC’s. The data recorded within Cullen et al’s (1992) study didn’t indicate any significant difference in physiological efficiency or performance when using using a NCC. Contrary to the studies mentioned above; Hansen et al’s (2009) research comparing the Shimano Biopace to a CC showed significantly lower blood lactate during a 10-minute bout at 180W whilst using the Biopace chainring.

 

There has been a large amount of uncertainty for some time in both the world of cycling and sports science as to whether swapping a CC for a NCC alternative has any benefit. Following the release of Shimano’s Biopace chainring, researchers have begun to conduct more testing into the use of NCC’s.

Rankin and Neptune (2008) calculated the optimal shape of a chainring to maximize power through the pedal stroke and it was predicted that the proposed elliptical chainring could significantly improve crank power by 3%. The final design from Rankin and Neptune (2008) was very similar to the Osymetric chainring that has been suggested for use in the proposed study and was found to improve average power by 2.9% at 60, 90 and 120rpm. This increase in power was attributed to increased muscular work from the gluteus maximus, vastus muscles, soleus and gastrocnemius; most likely as a result of the force-velocity relationship previously mentioned.

Various physiologists and sports scientists have carried out research into the use of NCC’s during sprint scenarios but have yet to find conclusive evidence. O’Hara et al (2012) examined the effects of chainring type on 1km time trial performance. Having conducted sub-maximal testing and a 1km time trial using CC’s, the participants were required to train on Rotor Q NCC’s over a six-week intervention period. It could be questioned as to whether this intervention period was required as Neptune and Herzog (2000) have indicated that the muscle coordination adaptation to the NCC’s can occur within the first 10–20 crank cycles. The results of the study showed significantly greater average speed and power and a significantly reduced time for the 1km time trial and reduced oxygen consumption and heart rate during the submaximal testing in the intervention period. Hue et al (2001) found no significant difference in physiological variables during a 1km time trial but participants recorded significantly faster times over the stated distance using the NCC. This leads to the suggestion of whether the improvement in performance was related to the psychology of using a NCC.

In a later study, Hue et al (2007) assessed the efficacy of NCC’s versus CC’s over a 1km outdoor track time trial. Whilst high in ecological validity, the findings of the study lacked significance and no difference was seen in performance or in the recorded physiological variables.

 

 

Over longer time trial distances and in laboratory based incremental tests, research has found similar results:

Peiffer and Abbiss (2010) assessed the influence of NCC’s in comparison with CC’s during a 10km time trial performed by competent male cyclists. There was found to be no difference in mean power output or the rate of perceived exertion (measured at 3, 6 and 8.5km) by the athletes. Interestingly, on average HR was greater when using the NCC as opposed to the CC. The results of the study suggest NCC’s do not provide a performance benefit during a 10km time trial. Ratel et al’s (2004) study into the physiological response to using NCC’s also found no significant difference between chainrings. In both sub maximal and maximal testing which included a range of speeds and gradients the physiological response to using the NCC did not translate into it being advantageous over CC’s within the study.

 

Rodriguez –Marroyo et al (2009) adopted a different approach to testing. The effect of NCC’s during both aerobic and anaerobic procedures were assessed: Fifteen professional road cyclists performed both incremental and sub-maximal aerobic tests and the Wingate anaerobic test. It was found within the anaerobic test that both peak and average power outputs were significantly greater whilst using the NCC. No difference was found in the aerobic conditions. Similar results were found by Martin et al. (2002) which show increases in maximal single-leg cycling power when using a NCC, which supported the previous results obtained by Hue et al. (2001), showing an improvement in an all-out 1-km laboratory test.

 

Research has been conducted within different cycling disciplines that also proved to be inconclusive: In a study looking at BMX sprint performance of both elite and novice riders, Mateo-March et al (2014) identified that use of the Rotor Q-ring significantly improved initial acceleration out of the start gates of elite riders but all other results were trivial. Jeukendrup and Martin (2012) suggest that novice riders are in fact more likely to benefit from equipment alterations than elite athletes, contrary to Mateo-March et al’s (2014) findings. These conflicting results both suggest that improvement is reliant on ability level and with relation to the use of NCC’s could highlight a possible avenue of future research.

In a recent study on non-cyclists, Hintzy and Horvais (2015) determined that the use of an Osymetric chainring resulted in a higher maximal aerobic power during an incremental maximal test. Hintzy and Horvais (2015) explain the result by suggesting that the use of the Osymetric ring enabled the participants to save energy throughout the stages of the test allowing for exhaustion at a higher increment than when using the CC’s. This would lead us to believe that a link, albeit tenuous, does exist between bicycle drivetrain modifications and physiological responses.