Effects on the crank torque profile when changing pedalling cadence in level ground and uphill road cycling
Introduction
The last years, the winners of the 3-week stage races (i.e. Giro d’Italia, Tour de France, Vuelta a Espana) were usually riders who excelled in the hilly climbing sections of the races. Moreover, many elite cyclists claim difficulties using a specific gear ratio in the first hilly stage. This could possibly be due to changes in pedalling biomechanics (cycling position, pedalling cadence, crank torque profile), between level ground and uphill road cycling. Most of the investigations conducted on pedalling biomechanics in cycling were focused on laboratory conditions. The lack of research on uphill road cycling is partly due to the difficulty in obtaining data during road cycling. In the laboratory, the uphill cycling studies have used classical ergometers (Patterson and Pearson, 1983; Kautz et al., 1991; Swain and Wilcox, 1992; Caldwell et al., 1998; Li and Caldwell, 1998; Padilla et al., 1999) or treadmills (Heil, 1998; Hansen et al (2002a), Hansen et al (2002b). Caldwell et al. (1998) have studied the crank torque profile of level ground and uphill cycling in seated position on a Velodyne ergometer (at 82 and 65 rpm, respectively). They were not able to show if a change in road slope (0–8%) had an influence on crank torque profile because the two conditions studied did not have the same pedalling cadence. Hansen et al (2002a), Hansen et al (2002b) have studied level ground and uphill cycling on a treadmill by changing the slope and crank inertial load (kg m2). The crank inertial load varied with the gear ratio and the mass (kg) of the cyclist (Martin et al., 1997; Fregly et al., 2000; Hansen et al (2002a), Hansen et al (2002b)). When cyclists ride in the field, they need to change their gear ratio according to the slope, thus affecting the pedalling cadence. Thus, during uphill cycling the crank inertial load is lower than in level ground conditions. Hansen et al (2002a), Hansen et al (2002b) have shown that the crank torque profile was modified by varying the crank inertial load. They showed that during cycling with a high crank inertial load value, peak crank torque was significantly higher (+5%) compared with a low crank inertial load value. However, compared with the field, the simulation of the cyclist's crank inertial load is not similar in the laboratory due to the inertia of the ergometer flywheel. With a non-modified classical ergometer (like Monark ergometer) it is also difficult to simulate the habitual body position of the cyclist.
The crank torque represents the kinetics of the propulsive torque (N m) within the crank cycle. These kinetics are a determinant of cycling performance (Coyle et al., 1991), since it represents an important variable of the power output (power output (rad s−1)). The torque is determined by the product of the effective force (Fe) (applied perpendicularly to the crank arm) and the length of the crank arm (m)(). Thus, Fe represents the propulsive force in cycling. From a mechanical point of view, the ideal situation when riding a bicycle is to exclusively generate a constant Fe (Patterson and Moreno, 1990). However, such a situation is not possible during pedalling. Indeed, the crank cycle is sub-divided into four 90° power output sectors (Faria, 1992). Considering that the 0°crank angle corresponds to the vertical position of the left crank arm (pedal in high position), sectors 1 (between a 315° and 45°) and 3 (between 135° and 225°) are associated with the top (DPtop, see nomenclature) and the bottom (DPbot) dead point of the crank cycle, respectively. When the pedal is in these two sectors, the crank torque is minimal. Sector 2 (between 45° and 135°) corresponds to the push-down phase, and sector 4 (between 225° and 315°) to the pull-up phase. When the pedal is moving downward, a greater force is generated (push-down phase) compared with the phase where the pedal is moving upward (pull-up phase). The optimisation of the crank cycle in cycling can contribute to improvements of performance (Coyle et al., 1991).
To the best of our knowledge, the characteristics of the crank torque during level ground and uphill road cycling are not clear and have not been studied.
The first aim of this study was to analyse the crank torque profiles in level ground and uphill road cycling in the seated position at the same pedalling cadence (80 rpm) and power output. The second aim was to analyse the effect of changing pedalling cadence on the crank torque profiles at the same power output during level ground and uphill road cycling. The torque was measured with the SRM training system device. The first hypothesis of this study was that uphill and level cycling at the same pedalling cadence and power output would elicite different crank inertial loads, which would result in changes in crank torque profiles, especially on DPtop, DPbot and on peak torque (Tpeak). We hypothesised that the crank torque value at DPtop, DPbot and on Tpeak would decrease on uphill road cycling when the crank inertial load value would be low.
The second hypothesis was that a change of pedalling cadence on level ground and uphill road cycling would elicite an alteration of torque values especially in the power sector (sector 2). Possibly, the torque values would be differently altered when the pedalling cadence changes in level ground compared to uphill road cycling.
Section snippets
Subjects
Seven male competitive cyclists (age 25.5±4.9 years, height: , body mass: , maximal aerobic power (MAP): ), in their preparative training period of the race season, participated in the study. Each subject was informed of all details of the testing and signed an informed consent.
Instrumentation
Each subject rode on a classical race bicycle (10.2 kg) equipped with “clipless” pedals during the field tests. Before beginning the test, the cyclist adjusted the bicycle to his habitual
Effect on the crank torque profile of the cycling conditions (level ground vs. uphill cycling)
For L80 () tended (p<0.06) to be lower compared with U80 (+26%)(Fig. 2). The other measured variables were no significantly different between L80 and U80.
Effect on the crank torque profile of varying pedalling cadence (60–100 rpm) on the same terrain (level ground or uphill)
Our results indicate that on the same terrain torque applied to the crank arm increased in the power output sector when the pedalling cadence decreased. During L80 and were higher compared with the L100 (+19% and +14% respectively)(Fig. 3). The Tpeak and Tdelta during U60 were significantly (p<0.01) higher (close
Discussion
The hypotheses of this study were that a change (1) in terrain (i.e. level ground vs. uphill cycling) and (2) in pedalling cadence (60–100 rpm) would elicit different crank torque profiles. The first important finding of this study is that during U80 the crank torque profile was only slightly modified compared with L80. We have shown that between these two conditions, there was only a tendency for a difference (p<0.06) in . The second important finding is that the crank torque profile
Acknowledgements
We thank Pierre Monpied of the Statistics department of the National Research Agronomique Institute of Nancy (France) for assistance in statistical analysis. We also thank Vincent Villerius and Catherine Capitan (France) for technical help.
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