Journal of Electromyography and Kinesiology
Volume 21, Issue 1 , Pages 13-17, February 2011

Effects of a noncircular chainring system on muscle activation during cycling

  • Frederico Dagnese

      Affiliations

    • Universidade Federal do Rio Grande do Sul, Exercise Research Laboratory, Porto Alere, RS, Brazil
    • ,
  • Felipe P. Carpes

      Affiliations

    • Universidade Federal do Pampa, Applied Neuromechanics Group, Uruguaiana, RS, Brazil
    • Corresponding Author InformationCorresponding author. Address: Universidade Federal do Pampa, Center for Health Sciences, BR 472km 592 – P.O. Box 118, CEP 97500-970, Uruguaiana, RS, Brazil. Tel.: +55 51 9661 2010; fax: +55 55 3413 1484.
    • ,
  • Elisandro de Assis Martins

      Affiliations

    • Universidade Federal de Santa Maria, Laboratory of Biomechanics, Santa Maria, RS, Brazil
    • ,
  • Darren Stefanyshyn

      Affiliations

    • University of Calgary, Human Performance Laboratory, Calgary, AB, Canada
    • ,
  • Carlos Bolli Mota

      Affiliations

    • Universidade Federal de Santa Maria, Laboratory of Biomechanics, Santa Maria, RS, Brazil

Received 17 October 2009; accepted 9 February 2010. published online 11 March 2010.

Article Outline

Abstract 

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 48h, one for each crank system. Each test started with a workload of 100W and was increased by 30W 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.

Keywords: Noncircular chainring, Muscle activity, Lower limb, Vastus lateralis, Mountain-bike, Equipment design

 

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1. Introduction 

Cyclists and coaches continuously pay attention to selection of equipment that can improve competitive cycling performance. Among the equipment designed to improve performance is the noncircular chainring systems. Most of these systems are proposed to optimize power output during the propulsion phase of pedaling (Kautz et al., 1991), due to greater recruitment of power producing muscles, such as the vastii group (Bini et al., 2008, Duc et al., 2005, Laplaud et al., 2006). Among the strategies to optimize the participation of these power producing muscles is the alteration of crank arm length (Lucia et al., 2004, Santalla et al., 2002), chainring geometry (Hull et al., 1992) and position of the chainring rotation axis (Martin et al., 2002). It is important to know that any equipment changes must be approved by the Union Cycliste Internationale (UCI) to be regularly used in official competitions.

Despite the interest in this new equipment, previous studies failed to show a significant influence of noncircular chainrings on submaximal cycling performance (Hull et al., 1992, Lucia et al., 2004, Rodriguez-Marroyo et al., 2009, Santalla et al., 2002). The reason for this result could be related to the fact that the functional cost of noncircular systems do not properly fit with muscle mechanics aspects such as the force–velocity relationship of skeletal muscle (Kautz and Hull, 1995). Shan (2008) reported changes in ankle kinematics such as range of motion (ROM) while pedaling with a noncircular crank system. ROM could modify the muscle length of the lower leg muscles (Sanderson and Amoroso, 2008), which could change the muscle activation patterns (Dingwell et al., 2008, Shan, 2008), the knee extension force (Li and Caldwell, 1998), and finally, influence the muscle force production by altering muscle mechanics characteristics (Herzog et al., 1990, Herzog et al., 1991).

To the best of our knowledge, the analysis of muscle activation during cycling with a commercial noncircular chainring system approved by UCI for regular use in competitive cycling has not been conducted yet. Quantitative analysis of the effectiveness of new designs is necessary since most of the proposed benefits are based only on empirical data (Rankin and Neptune, 2008). The aim of this study was to compare muscle activation and cycling performance during an incremental maximal cycling test while using a conventional crank system and a noncircular crank system approved by the UCI called Rotor Cranks®.

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2. Methods 

2.1. Subjects 

Seven mountain-bike trained cyclists participated in this study. They present mean±standard-deviation age of 25±4years, height of 1.78±0.09m, body mass of 74.5±10.0kg and similar preferred pedaling cadence. All of the subjects regularly participated in national level competitions during the last five years. Their weekly training volume covers approximately 300±50km. Only two subjects had never pedaled with the noncircular system tested. These subjects completed a familiarization trial in the week previous to data acquisition. All subjects were required to sign an informed consent form in accordance with the local committee of ethics in human research.

2.2. Experimental design 

The cyclists performed two incremental maximal cycling tests using an 18-speed bicycle (Scott Blackstone, Scott, United States) mounted on a stationary cycling simulator (Computrainer ProLab 3D, Racermate Inc., Seattle, WA, USA). The cycling simulator controlled the exercise workload and continuously recorded information of power output and cadence throughout the tests. Saddle and handlebar positions were individually adjusted by the athletes to optimize comfort according to their own bicycle adjustments, and then registered after the first evaluation to keep constant for the second evaluation. A rest period of 48h was permitted between the two tests. The crank arm length used was the same for all the subjects and all the subjects used clip less pedals (SPD 505L, Shimano Corp., Japan). For those cyclists who had never pedaled with the noncircular system, a familiarization trial was accomplished in the week previous to the data acquisition. This familiarization was performed for a period of fifteen minutes cycling at power output set between 100 and 200W with a freely chosen pedaling cadence.

2.3. Incremental maximal test 

Subjects performed the first incremental maximal with conventional or noncircular chainring system according to a randomized order. A rest period of 48h was included between the trials. For both systems, the test started after a warm-up period with a workload of 100W. The first stage started with workload of 100W which was increased 30W every minute until exhaustion (Bieuzen et al., 2007). Subjects cycled at their preferred pedaling cadence which was controlled by visual feedback to be consistent across the evaluation of both conventional and noncircular systems. Exhaustion was defined as the moment that the subject was no longer capable to maintain the preferred cadence. Maximal power output was defined as the power output of the last entire stage completed.

2.4. Noncircular and conventional cranks system 

Cyclists were evaluated while pedaling with a conventional crank system and a noncircular chainring crank set called Rotor Cranks® (Rotor Technologies, Spain). For the conventional crank system evaluation, the bicycle was equipped with a standard bottom bracket system (XT®, Shimano Corp., Japan). In the other test the bicycle was equipped with a Rotor Cranks® RS IV (Rotor Technologies, Spain). The Rotor Cranks® provides a relative angular movement between right and left cranks regulated by means of eccentric bearings working to shift forwards the right and left cranks throughout the crank revolution. The crank arms are not aligned throughout the whole crank revolution. These eccentric bearings work to avoid abrupt movements between the cranks permitting a smooth and progressive movement throughout the pedal revolution. The mechanical characteristics of this system were described elsewhere (Garcia-López et al., 2005, Lucia et al., 2004, Rodriguez-Marroyo et al., 2009, Santalla et al., 2002). For this investigation, Rotor Cranks® was placed in position 1, as previously assessed for road cyclists (Rodriguez-Marroyo et al., 2009).

2.5. Muscle activation assessment 

Electrical muscle activation was monitored by means of surface electromyography (EMG) from the right vastus lateralis (VL), rectus femoris (RF), biceps femoris (BF) and gastrocnemius medialis (GM). Pairs of Ag/AgCl electrodes (bipolar configuration) with a diameter of 22mm (Kendall Meditrace, Chicopee, Canada) were positioned over the skin after careful shaving and cleaning of the area with an abrasive cleaner and alcohol swabs to reduce skin impedance (De Luca, 1997). A reference electrode was placed over the skin of the acromion as a neutral site. The electrodes were placed over the belly of the muscles, parallel with the muscle fiber orientation (Hermens et al., 2000) and taped to the skin using micropore tape (3M Company, St Paul, MN, USA) to minimize artifact movement. Position of the electrodes were marked on the skin by using special pens in an attempt to position the electrodes in as repeatable a position as possible across the two trials. EMG signals were amplified and recorded at a sampling rate of 2000Hz with 14-bit resolution using the Lynx System (Lynx 1200, Lynx Technologies, Sao Paulo, BRA). The raw EMG signals were smoothed with a 4th order band-pass Butterworth digital filter at 10–500Hz. After full-wave rectification and off-set correction, the onset and offset of EMG activity were determined by the signals increase/decreases two standard-deviations above the baseline value recorded at rest between each EMG burst (Hodges and Bui, 1996).

EMG signals were acquired for the last 20s from each workload stage. Each pedaling revolution was detected by using an electrogoniometer fixed on the right cyclist’s knee and synchronized with the EMG system. The root-mean-square (RMS) value was calculated considering a window size of 40ms (Neptune et al., 1997) and used as an indirect indicator of the magnitude of muscle activation (Moritani et al., 1986). For each muscle, RMS was computed as the ensemble of 15 pedal revolutions. The RMS found at the first workload stage was considered for RMS normalization (Hug et al., 2004b). Data processing was accomplished using Origin 6.0 (Originlab Corp., Northampton, MA, USA).

2.6. Statistical procedures 

After visual inspection, mean and standard-deviation (SD) were calculated for all subjects’ data. Data distribution normalcy and sphericity were respectively verified by Shapiro–Wilk and Mauckly’s tests. The equality of variances was tested using Levene’s test. Cadence, power output, maximal heart rate and test duration were compared between the groups using a t-test. RMS was compared between crank systems using an ANOVA for repeated measures including two factors, crank system and workload (2×9), with Bonferroni correction for multiple comparisons. Where significant interactions were found, post hoc comparisons would consider use of t-tests. Significance level was set at 0.05 for all data analysis using SPPS 13.0 (SPSS Inc., Chicago IL, USA).

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3. Results 

There were no statistically significant differences between conventional and noncircular systems considering the pedaling cadence (106±5rpm for conventional and 106±4rpm for noncircular; P=0.655), maximal power output (366±36W and 357±34W for conventional and noncircular systems, respectively; P=0.317), maximal heart rate (185±19bpm and 183±12bpm for conventional and noncircular systems, respectively; P=0.60) and test duration (14.18±1.23min and 14.20±1.66min for conventional and noncircular systems, respectively; P=0.866). Since the workload stages of 400W and 430W were not completed by all the cyclists (two completed 400W and one completed 430W), the statistical EMG analysis considered the range from 100–370W, which was fully completed by all the athletes. The normalized EMG during the incremental test for each crank system and muscle is depicted in Fig. 1.

RMS increased significantly throughout the incremental test for the muscles VL, RF and BF (P<0.05). RMS from the GM did not increase significantly as the workload increased (P=0.224). Statistical comparisons of RMS using the ANOVA model did not reveal any statistically significant difference between the crank systems (Table 1), as well as no significant interaction between crank systems and workload.

Table 1. Statistical outcomes from the ANOVA considering factor “crank system” for comparison between conventional and noncircular systems throughout the incremental maximal cycling test.
MusclesFP
Vastus lateralis0.8460.393
Rectus femoris0.0190.894
Biceps femoris3.1520.126
Gastrocnemius medialis6.3650.515

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4. Discussion 

The aim of this study was to compare muscle activation and cycling performance during an incremental maximal cycling test while using a conventional crank system and a noncircular crank system approved by the UCI called Rotor Cranks®. Our main finding was that there was no significant effect of the noncircular chainring system evaluated on the magnitude of muscle activation during incremental maximal cycling when compared to a conventional system.

The noncircular chainring system did not affect the magnitude of muscle activation during an incremental maximal cycling test. Despite a previous study showing changes in ankle kinematics during cycling with a noncircular chainring system (Shan, 2008), the pedaling skill developed by training appears to support the same magnitude of muscle activation in trained cyclists (Chapman et al., 2009). A plausible reason for this finding is that neuromuscular adaptation to an altered mechanical pedaling task requires a short period of time, which can be less than one minute (MacIntosh et al., 2000).

The insignificant effect on muscle activation could be expected when considering that noncircular chainring systems failed to produce a greater power output than conventional systems (Lucia et al., 2004, Rodriguez-Marroyo et al., 2009, Santalla et al., 2002), As reported elsewhere (Kautz and Hull, 1995) equipment design frequently does not satisfy the expectations related to the muscle mechanical parameters; therefore, the relationship between mechanical and physiological performance is frequently unbalanced. The effects of workload on muscle activation, i.e. increase of muscle activation as workload increases, is well documented in the literature (for a review, see Hug and Dorel (2009)). The different magnitudes of increase in RMS as workload increases between the muscles are related to their functional roles. The small changes in muscle activation of the GM during an incremental maximal test has already been reported (Jorge and Hull, 1986) and supports its role in transferring energy across the ankle joint during cycling (Hug and Dorel, 2009). Mono-articular muscles such as the VL are considered power producers (Gregoire et al., 1984, Van Ingen Schenau et al., 1992) with a robust pattern of activation in trained cyclists (Hug et al., 2004a) whereas bi-articular muscles (for instance, RF, BF and GM) are mainly related to force transfer from the legs to the pedals (Gregoire et al., 1984, Van Ingen Schenau et al., 1992), presenting higher variability between subjects (Hug et al., 2004a). The no significant decrease in biceps femoris activation we observed in the last stage could be related to fatigue effects on the performance of this muscle. However, the decrease was similar between the two crank systems and could not be related to any advantage of one or the other of the crank systems assessed. Taken together, our results and the previous published literature concerning the noncircular chainring system tested present evidence to its lack of significance on biomechanical aspects of maximal cycling performance.

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5. Conclusion 

The noncircular chainring system assessed did not affect the magnitude of muscle activation during an incremental maximal test in trained cyclists. Our results suggest a similar muscular effort level regardless of cycling with conventional or noncircular chainring systems.

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Conflict of interest statement 

None declared.

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Acknowledgements 

This research was partially supported by the University of Calgary and CNPq.

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biography

Frederico Dagnese is a Master’s Student in Human Movement Sciences at Universidade Federal do Rio Grande do Sul. His research interests include cycling biomechanics and cyclists’ health. The research focuses on implication of sports equipment such as saddle and crank arms on pedaling performance.

biography

Felipe P. Carpes is an Associate Professor at the Center for Health Sciences in the Universidade Federal do Pampa. His research interests include the neuromechanics of lower extremity. The research focuses on developing a basic understanding of the neuromechanics of rhythmic movement during standing, walking and cycling and applying this information to training and rehabilitation.

biography

Elisandro de Assis Martins received his degree of Licenciate in Physical Education from Universidade Federal de Santa Maria. His research interest include cycling biomechanics and cyclists’ health.

biography

Darren Stefanyshyn is an Associate Professor at the Human Performance Laboratory in the University of Calgary. His research interests include sport biomechanics andthe engineering of sport equipment. The research focuses on developing a basic understanding of the mechanics of human movement during various athletic activities and applying this information to appropriate equipment selection for maximal performance.

biography

Carlos Bolli Mota is an Associate Professor at Center for Physical Education and Sports in the Universidade Federal de Santa Maria. His research interests include sport biomechanics and locomotion.

PII: S1050-6411(10)00029-5

doi:10.1016/j.jelekin.2010.02.005

Journal of Electromyography and Kinesiology
Volume 21, Issue 1 , Pages 13-17, February 2011

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