INFLUENCE OF TOE CLIPS ON MECHANICAL CHARACTERISTICS OF SPRINT CYCLING

INTRODUCTION: Toe-clips are assumed to enhance the mechanical efficiency of pedaling. However, the effect of toe-clips on power production during the maximal sprint has not been extensively studied, especially when friction loaded cycle ergometers are used (Arsac et al., 1996, Capmal and Vandewalle, 1997). The aim of this study was to evaluate the effect of toe clips during maximal sprints performed on a friction loaded ergometer. METHODS: Force, velocity and power-production in cycling were studied during all-out sprints with (WI) and without (WO) toe-clips on a friction loaded ergometer. This friction loaded cycle ergometer (Monark 818E) was specifically equipped with both an optical encoder and a strain gauge in order to measure the instantaneous flywheel velocity and the friction force, respectively (Arsac et al., 1996). The power output at each pedal down stroke was computed as the product of velocity and total force (inertial force + friction force). Values of maximal force (F), maximal velocity (V), maximal power (P), optimal force at P (FP) and optimal velocity at P (VP) were determined. Twenty-four subjects volunteered for this study. They were specialists in cycling, whose age, height and body mass were 24 ± 5 years (mean ± SD), 178.3 ± 5.4 cm and 69 ± 7 kg respectively. Each subject performed four maximal sprints of 6-s duration with different (i) shoe-pedal interface (WI or WO) and (ii) friction force applied to the friction belt (0.5 or 1.1 N.kg-1 body mass). RESULTS: The mechanical data obtained in the WI and WO conditions are presented in table 1. F, V, P and FP were significantly higher in the WI than in the WO condition. These differences were observed at both 0.5 and 1.1 N.kg-1. VP was higher in the WI condition at 1.1 N.kg-1 only. See text for legend. DISCUSSION: Values of F, V and P were in agreement with the literature (Arsac et al., 1996, Capmal and Vandewalle, 1997). The significant enhancement observed on mechanical force and power production in the WI compared to the WO condition further support the hypothesis that toe clips could have a positive effect on the performance of sprint cycling. Higher force and power in WI are probably due to the fact that toe clips allow greater and longer activity of flexor and extensor lower limb muscles during a complete pedal revolution (Tate and Sherman, 1977). However, VP was not improved in the WI condition at 0.5 N.kg-1, suggesting that the toe clips effect is more efficient at high friction force and high power. REFERENCES: Arsac, L.M. et al. (1996). Eur. J. Appl. Physiol. 74, 100-106. Capmal, S. and Vandewalle, H. (997). Eur. J. Appl. Physiol. 76, 375-379. Tate, J. and Sherman, G. (1977). Bicycling 18, 57

GROUND REACTION FORCE COMPARISON BETWEEN BOTH FEET DURING GIANT SLALOM TURNS IN ALPINE SKIING

The purpose of this study was to measure the difference in normal force under both feet during alpine skiing giant slalom turns. Eleven experienced alpine skiers performed a giant slalom course at race intensity. All trials were recorded synchronously using a video camera and a plantar pressure measuring system. The mean force on the grouped two feet varied from 0.7 BW at the start of a turn to 1.5 BW during the steering phase of a turn performed in a steep slope condition. When skiing on FLAT slope condition, it reached only 1.3 BW. Results also showed that the outside foot receives significantly more pressure than the inside foot during the entire turn except the initiation phase. This last finding is not affected by slope steepness

Mechanical efficiency during hand–rim wheelchair propulsion: effects of base-line subtraction and power output

International audienc

Effects of a Non-Circular Chainring on Sprint Performance During a Cycle Ergometer Test

Non-circular chainrings have been reported to alter the crank angular velocity profile over a pedal revolution so that more time is spent in the effective power phase. The purpose of this study was to determine whether sprint cycling performance could be improved using a non-circular chainring (Osymetric: ellipticity 1.25 and crank lever mounted nearly perpendicular to the major axis), in comparison with a circular chainring. Twenty sprint cyclists performed an 8 s sprint on a cycle ergometer against a 0.5 N/kg-1 friction force in four crossing conditions (non-circular or circular chainring with or without clipless pedal). Instantaneous force, velocity and power were continuously measured during each sprint. Three main characteristic pedal downstrokes were selected: maximal force (in the beginning of the sprint), maximal power (towards the middle), and maximal velocity (at the end of the sprint). Both average and instantaneous force, velocity and power were calculated during the three selected pedal downstrokes. The important finding of this study was that the maximal power output was significantly higher (+ 4.3%, p < 0.05) when using the non-circular chainring independent from the shoe-pedal linkage condition. This improvement is mainly explained by a significantly higher instantaneous external force that occurs during the downstroke. Non-circular chainring can have potential benefits on sprint cycling performance

Effect of endurance training on different mechanical efficiency indices during submaximal cyclin in subjects unaccustomed to cycling

International audienceThe purpose of this study was to evaluate different efficiency indices, i.e., gross (GE: no baseline correction), net (NE: resting metabolism as baseline correction), and work (WE: unloaded exercise as baseline correction), to reveal the effect of endurance training on mechanical efficiency. Nine healthy sedentary women undertook an incremental test and submaximal cycling exercise, at an intensity corresponding to 50% of the pretraining peak oxygen uptake, before and after 6 weeks of endurance training (18 sessions of 45 min). The training effects on efficiency indices were tested by comparisons based on GE, NE, and WE as well as by the differences between the percentage changes of all indices (% GE, % NE, % WE). Endurance training resulted in significantly higher GE (+ 11.1%; p < 0.001) and NE (+ 9.1%; P < 0.01). Only minor significant improvement (+ 2.4%; p < 0.05) was observed with the WE index because the value used for baseline subtraction was significantly reduced by the training sessions, due perhaps to improvement in pedaling skill. As a consequence, % WE was significantly lower than % GE (p < 0.01) and % NE (p < 0.05), while % GE and % NE were not significantly different. We conclude that mechanical efficiency of cycling increases with training in women previously unfamiliar with cycling, and that the WE index is less sensitive to this training effect than GE and NE indices. Key words: gross efficiency, net efficiency, work efficiency, internal work, cycle ergomete

Influence of the base-line determination on work efficiency during submaximal cycling

Le type de correction utilisé pour la détermination de la ligne de base induit des modifications importantes dans les mesures du rendement musculaire sur ergocycl

Evolution de l'activité électromyographique au cours d'un test de pédalage de temps limite à 100 % de puissance maximale aérobie

Analyse de l'évolution de la fatigue neuromusculaire des muscles vastus lateralis et gastrocnemius medialis, et des mécanismes adaptatifs sous-jacents au processus de fatigue (mise en jeu de muscles synergistes) au cours d'un test temps limite de pédalage à 100 % de la PMA jusqu'à épuisemen