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The aim of this study was to test the validity and the reliability of the G-Cog which is a new BMX powermeter allowing for the measurements of the acceleration on X-Y-Z axis (250 Hz) at the BMX rear wheel. These measurements allow computing lateral, angular, linear acceleration, angular, linear velocity and the distance. Mechanical measurements at submaximal intensities in standardized laboratory conditions and during maximal exercises in the field conditions were performed to analyse the reliability of the G-Cog accelerometers. The performances were evaluated in comparison with an industrial accelerometer and with 2 powermeters, the SRM and PowerTap. Our results in laboratory conditions show that the G-Cog measurements have low value of variation coefficient (CV=2.35%). These results suggest that the G-cog accelerometers measurements are reproducible. The ratio limits of agreement of the rear hub angular velocity differences between the SRM and the G-Cog were 1.010 × ÷ 1.024 (95%CI=0.986-1.034) and between PowerTap and G-Cog were 0.993 × ÷ 1.019 (95%CI=0.974-1.012). In conclusion, our results suggest that the G-Cog angular velocity measurements are valid and reliable compared with SRM and PowerTap and could be used to analyse the kinematics during BMX actual conditions., (© Georg Thieme Verlag KG Stuttgart · New York.)

The aim of this study was to test the validity and reliability of the G-Cog which is a new BMX power meter allowing for the measurements of the power output (250 Hz) at the BMX rear wheel during actual cycling and laboratory conditions. Sprints in road cycling (6-8 s) from static start and incremental tests in the laboratory (100-400 W) have been performed to analyse the validity and reliability of the power output values by comparison with 2 devices: The PowerTap and the SRM which are considered as the gold standard. The most important finding of this study is that the G-Cog power output data were not valid and reliable during sprint and standardised laboratory tests compared with the SRM and the PowerTap devices. During the sprint and the laboratory tests the ratio limits of agreement of the power output differences between the SRM and G-Cog were 1.884×÷1.970 (95% CI = .956-3.711) and 12.126×÷16.281 (95% CI = 0.745-197.430), respectively. In conclusion, the G-Cog must be used with caution regarding the power output measurements. Nevertheless, the G-Cog could be used for the first time to analyse the determinants of the BMX performance from the pedalling profile., (© Georg Thieme Verlag KG Stuttgart · New York.)

The purpose of this study was to test the validity and reliability of a new method to estimate the projected frontal area of the body during cycling. To illustrate the use of this method in another cycling speciality (i.e. mountain bike), the NM data were coupled with a powermeter measurement to determine the projected frontal area and the coefficient of drag in actual conditions. Nine male cyclists had their frontal area determined from digital photographic images in a laboratory while seated on their bicycles in two positions:Upright Position (UP) and Traditional Aerodynamic Position (TAP). For each position, the projected frontal area for the body of the cyclist as well as the cyclist and his bicycle were measured using a new method with computer aided-design software, the method of weighing photographs and the digitizing method. The results showed that no significant difference existed between the new method and the method of weighing photographs in the measurement of the frontal area of the body of cyclists in UP (p=0.43) and TAP (p=0.14), or between the new method and the digitizing method in measurement of the frontal area for the cyclist and his bicycle in UP (p=0.12) and TAP (p=0.31). The coefficients of variation of the new method and the method of weighing photographs were 0.1% and 1.26%, respectively. In conclusion, the new method was valid and reliable in estimating the frontal area compared with the method of weighing photographs and the digitizing method.

The SRM power measuring crank system is nowadays a popular device for cycling power output (PO) measurements in the field and in laboratories. The PowerTap (CycleOps, Madison, USA) is a more recent and less well-known device that allows mobile PO measurements of cycling via the rear wheel hub. The aim of this study is to test the validity and reliability of the PowerTap by comparing it with the most accurate (i.e. the scientific model) of the SRM system. The validity of the PowerTap is tested during i) sub-maximal incremental intensities (ranging from 100 to 420 W) on a treadmill with different pedalling cadences (45 to 120 rpm) and cycling positions (standing and seated) on different grades, ii) a continuous sub-maximal intensity lasting 30 min, iii) a maximal intensity (8-s sprint), and iiii) real road cycling. The reliability is assessed by repeating ten times the sub-maximal incremental and continuous tests. The results show a good validity of the PowerTap during sub-maximal intensities between 100 and 450 W (mean PO difference -1.2 +/- 1.3 %) when it is compared to the scientific SRM model, but less validity for the maximal PO during sprint exercise, where the validity appears to depend on the gear ratio. The reliability of the PowerTap during the sub-maximal intensities is similar to the scientific SRM model (the coefficient of variation is respectively 0.9 to 2.9 % and 0.7 to 2.1 % for PowerTap and SRM). The PowerTap must be considered as a suitable device for PO measurements during sub-maximal real road cycling and in sub-maximal laboratory tests.

The purpose of this study was to determine the validity and the reliability of a stationary electromagnetically-braked cycle ergometer (Axiom PowerTrain) against the SRM power measuring crankset. Nineteen male competitive cyclists completed four tests on their bicycle equipped with a 20-strain gauges SRM crankset: a maximal aerobic power (MAP) test and three 10-min time trials (TTs) with three different simulated slopes (0, 3, and 6 %). The Axiom ergometer overestimated (p <0.05) the SRM power output during the last stage of the MAP test and during TTs, by 5 % and 12 %, respectively. Power output (PO) of the Axiom ergometer drifted significantly (p <0.05) with the time during TT. These findings indicate that the Axiom ergometer does not provide a valid measure of PO compared with SRM. However, the small coefficient of variation (2.2 %) during the MAP test indicates that the Axiom provides a reliable PO and that it can be used e.g. for relative PO comparisons with competitive cyclists during a race season.

The aim of this study was to investigate the metabolic and physiological responses to a laboratory-based simulated 30-min individual time-trial (ITT 30 ) in cycling at a self-selected intensity. Twelve experienced triathletes (n = 4 women) performed a progressive incremental exercise test on a cycle ergometer to determine .VO2max (52 +/- 5 ml x min -1 x kg -1), maximum power output (300 +/- 12 W), and the second ventilatory threshold. Then, the subjects completed an ITT30 at self-selected work intensity on a stationary ergometer equipped with the SRM Training System. In all subjects, during the ITT30, heart rate and minute ventilation increased (p < 0.05) progressively whereas oxygen consumption and power output remained unchanged. Triathletes rode at consistent pacing corresponding to their highest steady state of blood lactate concentration that increased by no more than 1.0 mmol x l -1 during the final 20-min of ITT30. The self-selected intensity of triathletes during ITT30 represented 88 +/- 5 % (mean +/- SD) of .VO2max and was not significantly different to the energy demand corresponding to the second ventilatory threshold (84 +/- 5 % of .VO2max). Our data suggest that ITT 30 at a self-selected intensity is a good predictor of individual endurance capacity and may be used to estimate racing pace for training purposes. This performance test for the identification of the exercise intensity that demarcate "steady state" is less troublesome than some of the traditional methods, limiting testing to a single session.