Wingate performance and surface EMG frequency variables are not affected by caffeine ingestion
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Notice bibliographique
Résumé
The ergogenic effect of caffeine and its mechanism of action on short-term, high-intensity exercise are controversial. One proposed mechanism is caffeine's stimulatory effect on the central nervous system and thus, motor-unit excitation. The latter is non-invasively determined from surface electromyographic signal (EMG) frequency measures. The purpose of this study was to determine if power output and surface EMG frequency variables during high-intensity cycling were altered following caffeine ingestion. Eighteen recreationally active college males (mean +/- SD age, 21.5 +/- 1.8 y; height, 181.8 +/- 0.5 cm; body mass, 84.7 +/- 11.4 kg) performed the Wingate test (WG) after ingestion of gelatin capsules containing either placebo (PL; dextrose) or caffeine (CAFF; 5 mg/kg body mass). The trials were separated by 1 week and subjects were asked to withdraw from all caffeine-containing products for 48 h before each trial. From the resulting power-time records, peak power (PP; highest power output in 5 s), minimum power (MP; lowest power output in 5 s), and the percent decline in power (Pd) were calculated. Surface EMG records of the right vastus lateralis (VL) and the gastrocnemius (GA) muscles corresponding to the PP and MP periods were collected and used to determine the integrated electromyogram (IEMG), the mean (MNPF), and the median (MDPF) of the signal's power spectrum. A 2-way repeated measures analysis of variance (ANOVA) (treatment x time) was conducted to determine the effect of caffeine on these variables across levels of time. Caffeine ingestion had no effect on PP (PL, 1049 +/- 192 W; CAFF, 1098 +/- 198 W), MP (PL, 762 +/- 104 W; CAFF, 802 +/- 124 W), or the Pd (PL, 47% +/- 8.9%; CAFF, 48.2% +/- 7.3%) compared with the placebo. For both muscles, MNPF and MDPF diminished significantly (p < 0.001) across time and to a similar degree in both the CAFF and PL trials. Regardless of muscle, CAFF had no effect on the percent change in IEMG from the first 5 s to the last 5 s. For both treatments, the GA displayed a significantly (p < 0.05) greater pre vs. post percent decline in the EMG signal amplitude compared with the VL. These results indicate that caffeine does not impact power output during a 30 s high-intensity cycling bout. Furthermore, these data suggest that caffeine does not impact the neuromuscular drive as indicated by the similar IEMG scores between treatments. Similarly, caffeine does not seem to impact the frequency content of the surface EMG signal and thus the nature of recruited motor units before and after the expression of fatigue. The lack of decline in the IEMG in the VL despite the decline in power output over the course of the WG suggests a peripheral as opposed to a neural mechanism of fatigue in this muscle. The significant difference in the pre vs. post percent decline in the GA IEMG score further supports this notion. The pre vs. post decline in the IEMG noted in the GA may suggest a fatigue-triggered change in pedaling mechanics that may promote dominance of knee extensors with less reliance on plantar flexors.
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Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découle