Effects of caffeine on neuromuscular function

Abstract

This double-blind, repeated-measures study examined the effects of caffeine on neuromuscular function. Eleven male volunteers [22.3 +/- 2.4 (SD) yr] came to the laboratory for control, placebo, and caffeine (6 mg/kg dose) trials. Each trial consisted of 10 x 1-ms stimulation of the tibial nerve to elicit maximal H reflexes of the soleus, four attempts at a maximal voluntary contraction (MVC) of the right knee extensors, six brief submaximal contractions, and a 50% MVC held to fatigue. Isometric force and surface electromyographic signals were recorded continuously. The degree of maximal voluntary activation was assessed with the twitch-interpolation technique. Single-unit recordings were made with tungsten microelectrodes during the submaximal contractions. Voluntary activation at MVC increased by 3.50 +/- 1.01 (SE) % (P < 0. 01), but there was no change in H-reflex amplitude, suggesting that caffeine increases maximal voluntary activation at a supraspinal level. Neither the force-EMG relationship nor motor unit firing rates were altered by caffeine. Subjects were able to hold a 50% MVC for an average of 66.1 s in the absence of caffeine. Time to fatigue (T(lim)) increased by 25.80 +/- 16.06% after caffeine administration (P < 0.05). There was no significant change in T(lim) from pretest to posttest in the control or placebo trials. The increase in T(lim) was associated with an attenuated decline in twitch amplitude, which would suggest that the mechanism is, at least in part, peripheral.

Effect of a Pre-Exercise Energy Supplement on the Acute Hormonal Response to Resistance Exercise

“…No significant increases from PRE were seen in glucose concentrations for both S (5.30 6 0.40 mmolÁL 21 ) and P (5.50 6 1.12 mmolÁL 21 ). Lactate concentrations were significantly increased IP for both S (17.8 6 5.7 mmolÁL ), and remained increased from PRE throughout the 30-minute recovery period, but no significant group differences were observed.…”

Assessing Voluntary Muscle Activation with the Twitch Interpolation Technique

“…Incomplete activation of the ankle plantarflexors is commonly observed and voluntary activation levels of 90 to 99% have typically been reported [31,35,68] . In comparison with other muscles, relatively low levels of quadriceps femoris activation (85-95%) have frequently been observed [21,23,40,41,69,70,71,72,73,74,75] .…”

“…Three factors should be borne in mind when interpreting the available evidence. Firstly, in a number of the earlier studies voluntary activation of the elbow flexors [7,95] and quadriceps femoris muscles [8,96,97] appeared to be complete prior to training although subsequent experiments employing more sensitive techniques have shown that the same muscles are typically not fully activated [14,15,17,21,66,73] . Secondly, when activation deficits have been observed, dynamic resistance training was employed whilst the tests of voluntary activation were isometric [71,98] .…”

Carbohydrate and Caffeine Improves High-Intensity Running of Elite Rugby League Interchange Players During Simulated Match Play

“…Reductions in RPE are caused by caffeine restricting adenosine from binding to the adenosine receptors in the brain, thus blocking the inhibitory action of the adenosine on the central nervous system (12,31). Caffeine also increases motor unit recruitment and drive to the muscle that enhances muscular force production (25). A greater force production facilitated by caffeine ingestion might therefore have contributed to improved sprint performance in the CHO-C trial.…”

“…As an adenosine antagonist (11), caffeine moves freely across the blood-brain barrier, with the central nervous system (CNS) its primary target (12). Effects include reduced perceptions of effort and pain (9,27), increased central drive (25) and, to a lesser extent, increased muscle force and endurance (39).…”