The Influence of Caffeine on Voluntary Muscle Activation

Effects of dietary nitrate, caffeine, and their combination on 20-km cycling time trial performance

The aim of this study was to examine the acute supplementation effects of dietary nitrate, caffeine, and their combination on 20-km cycling time trial performance. Using a randomized, counterbalanced, double-blind Latin-square design, 14 competitive female cyclists (age: 31 ± 7 years; height: 1.69 ± 0.07 m; body mass: 61.6 ± 6.0 kg) completed four 20-km time trials on a racing bicycle fitted to a turbo trainer. Approximately 2.5 hours before each trial, subjects consumed a 70-ml dose of concentrated beetroot juice containing either 0.45 g of dietary nitrate or with the nitrate content removed (placebo). One hour before each trial, subjects consumed a capsule containing either 5 mg·kg of caffeine or maltodextrin (placebo). There was a significant effect of supplementation on power output (p = 0.001), with post hoc tests revealing higher power outputs in caffeine (205 ± 21 W) vs. nitrate (194 ± 22 W) and placebo (194 ± 25 W) trials only. Caffeine-induced improvements in power output corresponded with significantly higher measures of heart rate (caffeine: 166 ± 12 b·min vs. placebo: 159 ± 15 b·min; p = 0.02), blood lactate (caffeine: 6.54 ± 2.40 mmol·L vs. placebo: 4.50 ± 2.11 mmol·L; p < 0.001), and respiratory exchange ratio (caffeine: 0.95 ± 0.04 vs. placebo: 0.91 ± 0.05; p = 0.03). There were no effects (p ≥ 0.05) of supplementation on cycling cadence, rating of perceived exertion, (Equation is included in full-text article.), or integrated electromyographic activity. The results of this study support the well-established beneficial effects of caffeine supplementation on endurance performance. In contrast, acute supplementation with dietary nitrate seems to have no effect on endurance performance and adds nothing to the benefits afforded by caffeine supplementation.

Half-time strategies to enhance second-half performance in team-sports players: a review and recommendations

A number of intermittent team sports require that two consecutive periods of play (lasting for ~30-45 min) are separated by a 10-20 min half-time break. The half-time practices employed by team-sports players generally include returning to the changing rooms, temporarily relaxing from the cognitive and physical demands of the first half, rehydration and re-fuelling strategies, addressing injury or equipment concerns, and receiving tactical instruction and coach feedback. However, the typically passive nature of these actions has been associated with physiological changes that impair performance during the second half. Both physical and cognitive performances have been found to decline in the initial stages of subsequent exercise that follows half-time. An increased risk of injury has also been observed during this period. Therefore, half-time provides sports scientists and strength and conditioning coaches with an opportunity to optimise second-half performance. An overview of strategies thought to benefit team-sports athletes is presented; specifically, the efficacy of heat maintenance strategies (including passive and active methods), post-activation potentiation, hormonal priming, and modified hydro-nutritional practices are discussed. A theoretical model of applying these strategies in a manner that compliments current practice is also offered.

Caffeine Affects Time to Exhaustion and Substrate Oxidation during Cycling at Maximal Lactate Steady State

This study analyzed the effects of caffeine intake on whole-body substrate metabolism and exercise tolerance during cycling by using a more individualized intensity for merging the subjects into homogeneous metabolic responses (the workload associated with the maximal lactate steady state—MLSS). MLSS was firstly determined in eight active males (25 ± 4 years, 176 ± 7 cm, 77 ± 11 kg) using from two to four constant-load tests of 30 min. On two following occasions, participants performed a test until exhaustion at the MLSS workload 1 h after taking either 6 mg/kg of body mass of caffeine or placebo (dextrose), in a randomized, double-blinded manner. Respiratory exchange ratio was calculated from gas exchange measurements. There was an improvement of 22.7% in time to exhaustion at MLSS workload following caffeine ingestion (95% confidence limits of ±10.3%, p = 0.002), which was accompanied by decrease in respiratory exchange ratio (p = 0.001). These results reinforce findings indicating that sparing of the endogenous carbohydrate stores could be one of the several physiological effects of caffeine during submaximal performance around 1 h.

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

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 efficacy of acute nutritional interventions on soccer skill performance

BACKGROUND

The use of nutritional ergogenic aids in team sports such as soccer is now commonplace. Aligned with the primary aim of soccer, which is to score more goals than the opposition within the allotted time, the quality of performance of technical actions (i.e., skills) executed during soccer-specific exercise is likely to determine success. However, when seeking to maintain soccer skill performance, information about the efficacy of nutritional interventions is lacking and factors which might modulate the efficacy of such strategies are unclear.

OBJECTIVE

This review aimed (i) to systematically evaluate the current research that examines the efficacy of nutritional interventions on soccer skills, and (ii) to provide a qualitative commentary on factors that have the potential to modulate the efficacy of such strategies.

DATA SOURCES

Relevant databases (PubMed and SPORTDiscus) were searched up to and including 1 July, 2013 for studies that investigated the efficacy of acute nutritional interventions on soccer skill performances.

STUDY SELECTION

Overall, 279 records were retrieved. Articles were sequentially excluded from the review based on specific criteria, being: (A) articles that did not report outcomes directly relating to skilled performances in soccer, (B) articles that examined the influence of interventions that were not nutritional in origin and/or were nutritional in origin but provided >3 hours before skill testing commenced, (C) articles that were review papers, and (D) post-acceptance withdrawal of articles methods from database.

STUDY APPRAISAL AND SYNTHESIS METHODS

Articles were independently assessed for the quality of the methods employed based upon the Physiotherapy Evidence Database (PEDro) scale. Records achieving a minimum PEDro score of 5 out of 10 were included in this review. Qualitative appraisal of 13 articles was performed after the application of exclusion criteria and quality assurance processes. The majority (n = 8) of articles examined the influence of carbohydrates on technical performance whereas fewer studies investigated the influence of caffeine ingestion (n = 2) and fluid provision (n = 3).

RESULTS

Findings were reported for a total of 171 participants and all but one of the included articles used cross-over study designs. Most participants (94 %) were male, highly trained (reported maximal aerobic capacity range 50-59 ml·kg(-1)·min(-1)) and exercised in temperate environments (reported temperature range 13-25 °C). Six of the eight studies reported that carbohydrates, consumed in the form of a 6-8 % solution of glucose, sucrose or maltodextrin at rates of 30-60 g·h(-1), enhanced at least one aspect of skilled performance over the duration of exercise (75-90 min). Although some evidence exists to support the consumption of caffeine (6 mg·kg(-1) body mass [BM]) and prescribed fluid to preserve skills performed during soccer-specific exercise, findings from the small number of included studies were inconsistent.

LIMITATIONS

The outcome measures and methods used to quantify skilled performance were not consistent across studies; consequently, it was not possible to perform meta-analyses to produce pooled effect sizes in this review.

CONCLUSIONS

The findings from this systematic review suggest that nutritional interventions, which provide carbohydrate, caffeine and fluid, have potential to preserve skills performed under conditions that induce soccer-specific fatigue. The weight of current evidence supports the consumption of carbohydrate, but is less conclusive with respect to caffeine and fluid provision. It is likely that the efficacy of a nutritional intervention will be modulated by factors including the dose consumed, the mode of administration, individual responsiveness to the intervention and interactions with other physiological changes occurring during soccer-specific exercise. Consequently, these factors should be considered when using carbohydrates, caffeine and fluid provision to maintain skilled performances in soccer. Future research should seek to optimise the nutritional strategies employed to maintain technical performance throughout match-play.

Cortical substrates of the effects of caffeine and time-on-task on perception of effort

Caffeine intake results in a decrease in perception of effort, but the cortical substrates of this perceptual effect of caffeine are unknown. The aim of this randomized counterbalanced double-blind crossover study was to investigate the effect of caffeine on the motor-related cortical potential (MRCP) and its relationship with rating of perceived effort (RPE). We also investigated whether MRCP is associated with the increase in RPE occurring over time during submaximal exercise. Twelve healthy female volunteers performed 100 intermittent isometric knee extensions at 61 ± 5% of their maximal torque 1.5 h after either caffeine (6 mg/kg) or placebo ingestion, while RPE, vastus lateralis electromyogram (EMG), and MRCP were recorded. RPE and MRCP amplitude at the vertex during the first contraction epoch (0–1 s) were significantly lower after caffeine ingestion compared with placebo ( P < 0.05) and were significantly higher during the second half of the submaximal intermittent isometric knee-extension protocol compared with the first half ( P < 0.05). No significant effects of caffeine and time-on-task were found for EMG amplitude and submaximal force output variables. The covariation between MRCP and RPE across both caffeine and time-on-task ( r10 = −0.335, P < 0.05) provides evidence in favor of the theory that perception of effort arises from neurocognitive processing of corollary discharges from premotor and motor areas of the cortex. Caffeine seems to reduce perception of effort through a reduction in the activity of cortical premotor and motor areas necessary to produce a submaximal force, and time-on-task has the opposite effect.

Effects of caffeine and carbohydrate mouth rinses on repeated sprint performance

Our purpose was to examine the effectiveness of carbohydrate and caffeine mouth rinses in enhancing repeated sprint ability. Previously, studies have shown that a carbohydrate mouth rinse (without ingestion) has beneficial effects on endurance performance that are related to changes in brain activity. Caffeine ingestion has also demonstrated positive effects on sprint performance. However, the effects of carbohydrate or caffeine mouth rinses on intermittent sprints have not been examined previously. Twelve males performed 5 × 6-s sprints interspersed with 24 s of active recovery on a cycle ergometer. Twenty-five milliliters of either a noncaloric placebo, a 6% glucose, or a 1.2% caffeine solution was rinsed in the mouth for 5 s prior to each sprint in a double-blinded and balanced cross-over design. Postexercise maximal heart rate and perceived exertion were recorded, along with power measures. A second experiment compared a combined caffeine-carbohydrate rinse with carbohydrate only. Compared with the placebo mouth rinse, carbohydrate substantially increased peak power in sprint 1 (22.1 ± 19.5 W; Cohen's effect size (ES), 0.81), and both caffeine (26.9 ± 26.9 W; ES, 0.71) and carbohydrate (39.1 ± 25.8 W; ES, 1.08) improved mean power in sprint 1. Experiment 2 demonstrated that a combination of caffeine and carbohydrate improved sprint 1 power production compared with carbohydrate alone (36.0 ± 37.3 W; ES, 0.81). We conclude that carbohydrate and (or) caffeine mouth rinses may rapidly enhance power production, which could have benefits for specific short sprint exercise performance. The ability of a mouth-rinse intervention to rapidly improve maximal exercise performance in the absence of fatigue suggests a central mechanism.

Effects of morning caffeine' ingestion on mood States, simple reaction time, and short-term maximal performance on elite judoists

PURPOSE

The purpose of the present study was to evaluate the ergogenic effect of caffeine ingestion on mood state, simple reaction time, and muscle power during the Wingate test recorded in the morning on elite Judoists.

METHODS

TWELVE ELITE JUDOISTS (AGE: 21.08 ± 1.16 years, body mass: 83.75 ± 20.2 kg, height: 1.76 ±6.57 m) participated in this study. Mood states, simple reaction time, and muscle power during the Wingate test were measured during two test sessions at 07:00 h and after placebo or caffeine ingestion (i.e. 5 mg/kg). Plasma concentrations of caffeine were measured before (T0) and 1-h after caffeine' ingestion (T1) and after the Wingate test (T3).

RESULTS

Our results revealed an increase of the anxiety and the vigor (P<0.01), a reduction of the simple reaction time (P<0.001) and an improvement of the peak and mean powers during the Wingate test. However, the fatigue index during this test was unaffected by the caffeine ingestion. In addition, plasma concentration of caffeine was significantly higher at T1 in comparison with T0.

CONCLUSIONS

In conclusion, the results of this study suggest that morning caffeine ingestion has ergogenic properties with the potential to benefit performance, increase anxiety and vigor, and decrease the simple reaction time.

The effects of low-dose caffeine on perceived pain during a grip to exhaustion task

This double-blind, placebo-controlled, within-subject experiment examined the effects of low-dose caffeine on pain reported during an exhaustive grip task. The grip task consisted of holding a metal block attached to standard Olympic weight plates with the arm at the side until the participants could no longer maintain their grip. Apparently healthy recreationally trained college-aged adults (men, n = 5; women, n = 5) were given either a piece of Stay Alert™ gum that delivered 85% of the effective dose of 100 mg of caffeine in 5 minutes or an identical placebo gum that contained no caffeine. Subsequently, pain perception and ratings of perceived exertion were recorded during an exhaustive grip task every 15 seconds and the overall time to exhaustion. No significant difference was found in time to exhaustion between treatments. A significant main effect of treatment for reported pain (p < 0.001, Φ = 0.377) was observed. Thus, in a population of recreationally trained college-aged adults, low-dose caffeine may attenuate the individual's perception of pain during a grip to exhaustion task.

Time to move beyond a brainless exercise physiology: the evidence for complex regulation of human exercise performance

In 1923, Nobel Laureate A.V. Hill proposed that maximal exercise performance is limited by the development of anaerobiosis in the exercising skeletal muscles. Variants of this theory have dominated teaching in the exercise sciences ever since, but 90 years later there is little biological evidence to support Hill’s belief, and much that disproves it. The cardinal weakness of the Hill model is that it allows no role for the brain in the regulation of exercise performance. As a result, it is unable to explain at least 6 common phenomena, including (i) differential pacing strategies for different exercise durations; (ii) the end spurt; (iii) the presence of fatigue even though homeostasis is maintained; (iv) fewer than 100% of the muscle fibers have been recruited in the exercising limbs; (v) the evidence that a range of interventions that act exclusively on the brain can modify exercise performance; and (vi) the finding that the rating of perceived exertion is a function of the relative exercise duration rather than the exercise intensity. Here I argue that the central governor model (CGM) is better able to explain these phenomena. In the CGM, exercise is seen as a behaviour that is regulated by complex systems in the central nervous system specifically to ensure that exercise terminates before there is a catastrophic biological failure. The complexity of this regulation cannot be appreciated if the body is studied as a collection of disconnected components, as is the usual approach in the modern exercise sciences.

Energy drinks: a review of use and safety for athletes

Energy drinks have increased in popularity in adolescents and young adults; however, concerns have been raised regarding the ingredients in energy drinks and their potential negative effects on health. Caffeine, the most physiologically active ingredient in energy drinks, is generally considered safe by the US Food and Drug Administration (FDA), although adverse effects can occur at varying amounts. Guarana, which contains caffeine in addition to small amounts of theobromine, theophylline, and tannins, is also recognized as safe by the FDA, although it may lead to caffeine toxicity when combined with caffeine. The amount of ginseng in energy drinks is typically far below the amount used as a dietary supplement, and is generally considered safe. Taurine, an intracellular amino acid, has been reported to have positive inotropic effects; however, this claim is not supported by research. Most energy drinks also contain sugar in an amount that exceeds the maximum recommended daily amount. Young athletes are increasingly using energy drinks because of the ergogenic effects of caffeine and the other ingredients found in these beverages. Energy drinks combined with alcohol are also gaining popularity in young adults, which poses significant concerns about health risks. Other health concerns related to consumption of energy drinks include case reports of seizures and cardiac arrest following energy drink consumption and dental enamel erosion resulting from the acidity of energy drinks.

Improved time to exhaustion following ingestion of the energy drink Amino Impact

BACKGROUND

The purpose of this study was to examine the effect of a commercially available energy drink on time to exhaustion during treadmill exercise. In addition, subjective measures of energy, focus, and fatigue were examined

METHODS

Fifteen subjects (9 men and 6 women; 20.9 +/- 1.0 y; 172.1 +/- 9.1 cm; 71.0 +/- 9.4 kg; 16.9 +/- 9.7% body fat) underwent two testing sessions administered in a randomized, double-blind fashion. Subjects reported to the laboratory in a 3-hr post-absorptive state and were provided either the supplement (SUP; commercially marketed as Amino Impact) or placebo (P). During each laboratory visit subjects performed a treadmill run (70% VO2 max) to exhaustion. Mean VO2 was measured during each endurance exercise protocol. Subjects were required to complete visual analog scales for subjective measures of energy, focus and fatigue at the onset of exercise (PRE), 10-mins into their run (EX10) and immediately post-exercise (IP).

RESULTS

Time to exhaustion was significantly greater (p = 0.012) during SUP than P. Subjects consuming the supplement were able to run 12.5% longer than during the placebo treatment. Subjects consuming SUP reported significantly greater focus (p = 0.031), energy (p = 0.016), and less fatigue (p = 0.005) at PRE. Significant differences between groups were seen at EX10 for focus (p = 0.026) and energy (p = 0.004), but not fatigue (p = 0.123). No differences were seen at IP for either focus (p = 0.215), energy (p = 0.717) or fatigue (p = 0.430).

CONCLUSIONS

Results of this study indicate that the supplement Amino Impact can significantly increase time to exhaustion during a moderate intensity endurance run and improve subjective feelings of focus, energy and fatigue.

The effects of caffeine during exercise in fire protective ensemble

To examine the effects of caffeine during exercise in fire protective ensemble (FPE), 10 healthy males completed 3 x 10 min bouts of treadmill exercise on two separate days. Sixty minutes prior to exercise either 6 mg/kg of caffeine (CAFF) or dextrose placebo (PLA) capsules were ingested (randomly assigned, double blind). End-exercise gastrointestinal temperature (T(gi)) was higher in CAFF compared to PLA (38.80 +/- 0.08 degrees C vs. 38.43 +/- 0.11 degrees C, p < or = 0.01). Ventilation (V(E)) and tidal volume (V(t)) were also significantly higher in CAFF, which resulted in higher consumption of air from the self-contained breathing apparatus. While perceived exertion in the caffeine condition was decreased (p < or = 0.05) compared to placebo, the higher T(gi) values increased calculated physiological strain index in CAFF (p < or = 0.01). Caffeine appears to alter the physiological and psycho-physical responses to exercise in FPE and may influence factors related to work tolerance in firefighting. These findings are relevant to occupations such as firefighting where workers are encapsulated during exposure to heavy physical work and/or environmental heat. The results indicate that workers may be more susceptible to heat-related fatigue, illness or injury with ingestion of significant amounts of caffeine. To the authors' knowledge this is the first study involving humans and exercise to detect an increase in body temperature with caffeine ingestion.

No effect of prior caffeine ingestion on neuromuscular recovery after maximal fatiguing contractions

The purpose of this study was to test the hypothesis that prior caffeine ingestion would enhance neural recovery after isometric fatiguing maximal intermittent plantar flexions, and thus would enhance the recovery of voluntary muscle strength. After a familiarisation session, 13 males randomly participated in two experimental trials where they ingested either caffeine (approximately 6 mg/kg) or identical placebo pills 1 h prior to testing. Subjects were tested for electromyogram (EMG) activity and evoked V-waves in the soleus and gastrocnemius medialis muscles. These measurements were obtained during brief plantar flexion maximum voluntary isometric contractions (MVICs), and normalised by the superimposed maximal M-wave (EMG/M(SUP) and V/M(SUP), respectively), before and after (20 s, 10 min and 20 min) a fatigue protocol (seven 25 s MVICs, 5 s rest). There were no effects (P > 0.05) of caffeine ingestion on EMG/M(SUP), V/M(SUP), MVIC or M(SUP). The central neural modulation (EMG/M(SUP) and V/M(SUP)) and voluntary strength changes followed a similar time-course with a substantial reduction 20 s post-fatigue and a gradual return towards baseline values.

Examination of a pre-exercise, high energy supplement on exercise performance

BACKGROUND

The purpose of this study was to examine the effect of a pre-exercise high energy drink on reaction time and anaerobic power in competitive strength/power athletes. In addition, the effect of the pre-exercise drink on subjective feelings of energy, fatigue, alertness and focus was also explored.

METHODS

Twelve male strength/power athletes (21.1 +/- 1.3 y; 179.8 +/- 7.1 cm; 88.6 +/- 12.1 kg; 17.6 +/- 3.3% body fat) underwent two testing sessions administered in a randomized and double-blind fashion. During each session, subjects reported to the Human Performance Laboratory and were provided with either 120 ml of a high energy drink (SUP), commercially marketed as Redline Extreme(R) or 120 ml of a placebo (PL) that was similar in taste and appearance but contained no active ingredients. Following consumption of the supplement or placebo subjects rested quietly for 10-minutes prior to completing a survey and commencing exercise. The survey consisted of 4 questions asking each subject to describe their feelings of energy, fatigue, alertness and focus for that moment. Following the completion of the questionnaire subjects performed a 2-minute quickness and reaction test on the Makoto testing device (Makoto USA, Centennial CO) and a 20-second Wingate Anaerobic Power test. Following a 10-minute rest subjects repeated the testing sequence and after a similar rest period a third and final testing sequence was performed. The Makoto testing device consisted of subjects reacting to both a visual and auditory stimulus and striking one out of 30 potential targets on three towers.

RESULTS

Significant difference in reaction performance was seen between SUP and PL in both average number of targets struck (55.8 +/- 7.4 versus 51.9 +/- 7.4, respectively) and percent of targets struck (71.9 +/- 10.5% versus 66.8 +/- 10.9%, respectively). No significant differences between trials were seen in any anaerobic power measure. Subjective feelings of energy (3.5 +/- 0.5 versus 3.1 +/- 0.5) and focus (3.8 +/- 0.5 versus 3.3 +/- 0.7) were significantly higher during SUP compared to PL, respectively. In addition, a trend towards an increase in average alertness (p = 0.06) was seen in SUP compared to P.

CONCLUSION

Results indicate a significant increase in reaction performance, with no effect on anaerobic power performance. In addition, ingestion of this supplement significantly improves subjective feelings of focus and energy in male strength/power athletes.

Multiple-Sprint Work: Methodological, Physiological, and Experimental Issues

Tests of repeated-sprint ability provide a simple way to evaluate the basic physical characteristics of speed and endurance necessary to excel in various multiple-sprint sports. Furthermore, such tests help overcome the complications associated with field-based evaluations of this type of exercise. Nevertheless, despite over 40 y of research, many issues regarding our understanding of multiple-sprint work remain unresolved. This commentary aims to raise awareness of issues relating to methodology, physiological responses, and the effectiveness of various ergogenic and training strategies; to promote a greater understanding; and to drive future research.

Effects of acute caffeine administration on NOS and Bax/Bcl2 expression in the myocardium of rat

Caffeine is the most frequently ingested neuroactive drug in the world and it is largely used to delay fatigue and improve physical activity. Caffeine can modulate NO synthesis in cells and may influence muscular function by modifying the cellular cycle life-death. There is little data concerning the relationship between caffeine in the heart, NOS expression and apoptosis and no data regarding the acute effect of high doses of caffeine in the in vivo myocardium. We therefore studied hemodynamic NOS and Bax/Bcl2 expression in the rat myocardium after a single cafffeine administration. Thirty-two male rats were divided into six groups: the first was iv-injected with caffeine (16 mg/kg), the second with caffeine + L-NAME (30 mg/kg), the third with caffeine + L-arg (0.5 g/kg), the fourth with caffeine + L-NAME + L-arg and finally the fifth with saline. Mean arterial blood pressure (MAP) was monitored for 30 min, then the animals were killed. The sixth group was injected with caffeine and killed after 2 h. The hearts were isolated and processed by immunohistochemistry. We found that caffeine increased MAP temporarily while caffeine + L-NAME increased it for a longer period. In the control myocardium, all NOS isoforms were expressed. The Bcl2 were strongly expressed inside the perinuclear cytoplasm whereas Bax was very faintly detectable in the peripheral cytoplasm. In caffeine and caffeine + L-NAME treated animals, NOS expression disappeared. Bax and Bcl2 expression did not vary. The l-arg administration reversed these caffeine and L-NAME effects on NOS expression. Two hours after caffeine, NOS expression increased and Bax and Bcl2 expression did not vary, although Bcl2 was mainly expressed in the peripheral cytoplasm. We conclude that improved caffeine-induced physical performance could also be related to caffeine's ability to interfere with endogenous myocardial NO synthesis. Furthermore, we suggest that myocardial cell plays an effective anti-apoptotic role against acute caffeine administration.

Central excitability does not limit postfatigue voluntary activation of quadriceps femoris

After fatigue, motor evoked potentials (MEP) elicited by transcranial magnetic stimulation and cervicomedullary evoked potentials elicited by stimulation of the corticospinal tract are depressed. These reductions in corticomotor excitability and corticospinal transmission are accompanied by voluntary activation failure, but this may not reflect a causal relationship. Our purpose was to determine whether a decline in central excitability contributes to central fatigue. We hypothesized that, if central excitability limits voluntary activation, then a caffeine-induced increase in central excitability should offset voluntary activation failure. In this repeated-measures study, eight men each attended two sessions. Baseline measures of knee extension torque, maximal voluntary activation, peripheral transmission, contractile properties, and central excitability were made before administration of caffeine (6 mg/kg) or placebo. The amplitude of vastus lateralis MEPs elicited during minimal muscle activation provided a measure of central excitability. After a 1-h rest, baseline measures were repeated before, during, and after a fatigue protocol that ended when maximal voluntary torque declined by 35% (Tlim). Increased prefatigue MEP amplitude ( P = 0.055) and cortically evoked twitch ( P < 0.05) in the caffeine trial indicate that the drug increased central excitability. In the caffeine trial, increased MEP amplitude was correlated with time to task failure ( r = 0.74, P < 0.05). Caffeine potentiated the MEP early in the fatigue protocol ( P < 0.05) and offset the 40% decline in placebo MEP ( P < 0.05) at Tlim. However, this was not associated with enhanced maximal voluntary activation during fatigue or recovery, demonstrating that voluntary activation is not limited by central excitability.