The Reliability of Electromyographic Normalization Methods for Cycling Analyses.

Electromyography (EMG) is normalized in relation to a reference maximum voluntary contraction (MVC) value. Different normalization techniques are available but the most reliable method for cycling movements is unknown. This study investigated the reliability of different normalization techniques for cycling analyses. Twenty-five male cyclists (age 24.13 ± 2.79 years, body height 176.22 ± 4.87 cm and body mass 67.23 ± 4.19 kg, BMI = 21.70 ± 2.60 kg·m-1) performed different normalization procedures on two occasions, within the same testing session. The rectus femoris, biceps femoris, gastrocnemius and tibialis anterior muscles were examined. Participants performed isometric normalizations (IMVC) using an isokinetic dynamometer. Five minutes of submaximal cycling (180 W) were also undertaken, allowing the mean (DMA) and peak (PDA) activation from each muscle to serve as reference values. Finally, a 10 s cycling sprint (MxDA) trial was undertaken and the highest activation from each muscle was used as the reference value. Differences between reference EMG amplitude, as a function of normalization technique and time, were examined using repeated measures ANOVAs. The test-retest reliability of each technique was also examined using linear regression, intraclass correlations and Cronbach's alpha. The results showed that EMG amplitude differed significantly between normalization techniques for all muscles, with the IMVC and MxDA methods demonstrating the highest amplitudes. The highest levels of reliability were observed for the PDA technique for all muscles; therefore, our results support the utilization of this method for cycling analyses.

The test-retest reliability of knee joint center location techniques.

The principal source of measurement error in three-dimensional analyses is the definition of the joint center about which segmental rotations occur. The hip joint has received considerable attention in three-dimensional modeling analyses yet the reliability of the different techniques for the definition of the knee joint center has yet to be established. This study investigated the reliability of five different knee joint center estimation techniques: femoral epicondyle, femoral condyle, tibial ridge, plugin- gait, and functional. Twelve male participants walked at 1.25 m·s-1 and three-dimensional kinetics/kinematics of the knee and ankle were collected. The knee joint center was defined twice using each technique (test-and-retest) and the joint kinetic/kinematic data were applied to both. Wilcoxon rank tests and intraclass correlation coefficients (ICCs) were used to compare test and retest angular parameters and kinematic waveforms. The results show significant differences in coronal and transverse planes angulation using the tibial ridge, plug-in-gait, and functional methods. The strongest test-retest ICCs were observed for the femoral epicondyle and femoral condyle configurations. The findings from the current investigation advocate that the femoral epicondyle and femoral condyle techniques for the estimation of the knee joint center are currently the most reliable techniques.

The influence of 3D kinematic and electromyographical parameters on cycling economy.

PURPOSE: Economy is considered to be a key factor for the determination of performance in endurance events such as cycling. There have been no investigations which have related cycling economy to simultaneous measurements of 3D kinematics and muscular activation. This study examined selected biomechanical and neuromuscular parameters which have the strongest association with cycling economy. METHODS: Twenty-five trained cyclists (31.27 ± 3.19 years) completed steady state cycling time trials at a workload of 180 W. Simultaneous measurements of 3D kinematics and electromyographical parameters were obtained. Continuous measurements of expired gases were used to provide a measure of cycling economy. RESULTS: A multiple regression analysis showed that key parameters of peak knee extension velocity and mean activity of the rectus femoris muscles were significant predictors of VO2 during steady state cycling (P < 0.01). CONCLUSION: This study has documented the key biomechanical parameters pertinent to cycling economy. As economy has been shown to influence aerobic performance, future work should focus on optimising these parameters to improve cycling economy.