Caffeine-induced increase in voluntary activation and strength of the quadriceps muscle during isometric, concentric and eccentric contractions

Abstract

This study investigated effects of caffeine ingestion (8 mg/kg) on maximum voluntary torque (MVT) and voluntary activation of the quadriceps during isometric, concentric and eccentric contractions. Fourteen subjects ingested caffeine and placebo in a randomized, controlled, counterbalanced, double-blind crossover design. Neuromuscular tests were performed before and 1 h after oral caffeine and placebo intake. MVTs were measured and the interpolated twitch technique was applied during isometric, concentric and eccentric contractions to assess voluntary activation. Furthermore, normalized root mean square of the EMG signal was calculated and evoked spinal reflex responses (H-reflex evoked at rest and during weak isometric voluntary contraction) as well as twitch torques were analyzed. Caffeine increased MVT by 26.4 N m (95%CI: 9.3-43.5 N m, P = 0.004), 22.5 N m (95%CI: 3.1-42.0 N m, P = 0.025) and 22.5 N m (95%CI: 2.2-42.7 N m, P = 0.032) for isometric, concentric and eccentric contractions. Strength enhancements were associated with increases in voluntary activation. Explosive voluntary strength and voluntary activation at the onset of contraction were significantly increased following caffeine ingestion. Changes in spinal reflex responses and at the muscle level were not observed. Data suggest that caffeine ingestion induced an acute increase in voluntary activation that was responsible for the increased strength regardless of the contraction mode.

The influence of caffeine ingestion on strength and power performance in female team-sport players

“…The mechanism by which caffeine produces ergogenic effects for muscular strength and power activity is not well understood, although it is most likely to involve a supraspinally-driven increase in voluntary muscle activation [4, 13]. For endurance exercise, caffeine elicits performance benefits primarily via adenosine receptor antagonism [1].…”

“…When caffeine supplementation has shown a significant effect on leg muscle strength, this appears primarily in the knee extensors, as opposed to the knee flexors and smaller muscle groups [3]. While initial studies reported the enhancement of peak torque for isometric exercise only [11, 12], recent work has shown a caffeine-induced increase in knee extensor strength regardless of contraction mode [13]. The effect of caffeine intake on power output is unclear [2, 10].…”

Intersession reliability of the interpolated twitch technique applied during isometric, concentric, and eccentric actions of the human knee extensor muscles

“…following fatiguing exercise, muscle damage, and training . Moreover, the interpolated twitch technique was applied during dynamic actions of the quadriceps muscle . Since %VA was found to depend on the type of muscle action, the assessment of %VA during dynamic contractions might yield additional information about acute and chronic adaptations in neural drive.…”

“…6 Moreover, the interpolated twitch technique was applied during dynamic actions of the quadriceps muscle. [7][8][9][10][11] Since %VA was found to depend on the type of muscle action 12 , the assessment of %VA during dynamic contractions might yield additional information about acute and chronic adaptations in neural drive. Although it has been shown that %VA during isometric contractions can be reliably assessed using single and paired electrical stimuli 13,14 , little is known about the intersession reliability of the interpolated twitch technique applied during dynamic actions of the knee extensor muscles.…”

Caffeine Supplementation as an Ergogenic Aid for Muscular Strength and Endurance: A Recommendation for Coaches and Athletes

“…Alterations to pain perception following caffeine supplementation have also been reported [31] most likely due to enhanced secretion of β-endorphins [32]. More specifically to strength performance, possible mechanisms also include increased muscle activation [33], motor unit recruitment [34], and enhanced excitation contraction coupling [35].…”