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Comparing the lactate and EMG thresholds of recreational cyclists during incremental pedaling exercise

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Abstract:

The purpose of this study was to determine the validity of using the electromyography (EMG) signal as a noninvasive method of estimating the lactate threshold (LT) power output in recreational cyclists. Using an electromagnetic bicycle ergometer and constant pedaling cadence of 80 rpm, 24 recreational cyclists performed an incremental exercise protocol that consisted of stepwise increases in power output of 25 W every 3 min until exhaustion. The EMG signal was recorded from the right vastus lateralis (VL) and right rectus femoris (RF) throughout the test. Blood samples were taken from the fingertip every 3 min. The LT was determined by examining the relation between the lactate concentration and the power output using a log-log transformation model. The root mean square (RMS) value from the EMG signal was calculated for every 1-second non-superimposing window. Sets of pairs of straight regression lines were plotted and the corresponding determination coefficients (R2) were calculated. The intersection point of the pair of lines with the highest R2 product was chosen to represent the EMG threshold (EMGT). The results showed that the correlation coefficients (r) between EMGT and LT were significant (p < 0.01) and high for the VL (r = 0.826) and RF (r = 0.872). The RF and VL muscles showed similar behavior during the maximal incremental test and the EMGT and LT power output were equivalent for both muscles. The validity of using EMG to estimate the LT power output in recreational cyclists was confirmed.

La présente étude a eu pour but de valider l’emploi du signal EMG pour estimer de façon non effractive le seuil lactique (SL) chez les cyclistes de loisir. Vingt-quatre cyclistes sur cycloergomètre électromagnétique ont suivi un protocole d’exercice consistant en des augmentations progressives de puissance de 25 W toutes les 3 min jusqu’à épuisement, à une cadence constante de 80 rpm. On a enregistré le signal EMG sur le muscle vaste externe droit (VE) et le muscle droit antérieur de la cuisse (FD) pendant toute la durée du test. On a prélevé des échantillons sanguins au bout des doigts toutes les 3 min. On a déterminé le SL en examinant la relation bilogarithmique entre la concentration de lactate et la puissance. On a calculé la valeur efficace du signal EMG pour des segments d’une seconde ne se chevauchant pas. On a tracé les paires de droites de régression et calculé les coefficients de détermination (R2) correspondants. On a choisi le point d’intersection des deux droites avec le produit R2 le plus élevé pour représenter le seuil EMG (SEMG). Les résultats ont montré que les coefficients de corrélation (r) entre le SEMG et le SL étaient significatifs (p < 0,1) et élevés pour les muscles VE (r = 0,826) et FD (r = 0,872). Les deux muscles ont montré un comportement similaire durant le test progressif maximal, ainsi qu’une puissance au SEMG et au SL équivalente. On a confirmé l’utilité de l’EMG pour estimer le SL chez les cyclistes de loisir.

Document Type: Research Article

Publication date: 2008-05-01

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  • Published since 1929, this monthly journal reports current research in all aspects of physiology, nutrition, pharmacology, and toxicology, contributed by recognized experts and scientists. It publishes symposium reviews and award lectures and occasionally dedicates entire issues or portions of issues to subjects of special interest to its international readership.
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