Caffeine Does Not Alter the Acute Testosterone Response to Resistance Exercise
by Benjamin Bunting BA(Hons) PGCert
Written by Ben Bunting: BA, PGCert. (Sport & Exercise Nutrition) // British Army Physical Training Instructor // S&C Coach.
Caffeine, a central nervous system stimulant belonging to the methylxanthine class, is widely consumed through beverages such as coffee, tea and energy drinks. Furthermore, caffeine occurs naturally in some plants.
This study investigated the effects of caffeine consumption on acute testosterone and cortisol responses following one bout of resistance exercise.
Pre-exercise Caffeine Dose
Studies on caffeine's effects on muscle endurance and strength have been widely conducted; however, few compared its effects at various dosage levels. This research focused on low doses (1 mg/kg bodyweight), taken one hour before endurance cycling time trial performance on cycling time trial performance.
Results show that caffeine significantly improved time-trial performance across all groups, without altering acute testosterone response to exercise. This supports previous research which demonstrated that lower doses are equally as effective.
Although caffeine consumption does not alter initial increases in testosterone concentration, it appears to prevent its initial decrease during resistance exercise and blunt its subsequent decline in ratio with cortisol. This could be related to its antagonizing adenosine receptors which in turn reduce inhibition of protein kinase A from being stimulated.
A previous study also demonstrated that low doses of caffeine increase the rate at which muscle glycogen is utilized as energy during resistance exercise, supporting this result and other research findings.
The authors found that, although caffeine significantly enhanced exercise-induced increases in testosterone and cortisol, it did not seem to alter the ratio between them.
This may be a result of the fact that an increase in testosterone was offset by a decline in cortisol production.
The authors of this study also noted that sleep-deprived with caffeine conditions exhibited similar patterns of hormone release as those without sleep deprivation, in terms of both testosterone and cortisol release (as was predicted in previous research) to those not depriving themselves.
Furthermore, as other research has demonstrated anabolic hormone secretion during sleep can be maximized with adequate rest, therefore adequate rest is vital to ensure optimal levels of these key hormonal markers.
Another study investigated the effects of a moderate dose (4 mg*kg-1) of caffeine ingestion on various measures of strength and power in resistance-trained females during the early follicular phase of the menstrual cycle.
Ingestion of caffeine significantly improved squat and bench press one-rep maximum (1RM) performance, squat and bench press maximal vertical jump height, and squat and bench press muscular endurance compared to placebo.
These improvements were accompanied by no changes in intra-set ratings of perceived exertion (RPE) or at-failure perceived pain.
Interestingly, ingestion of caffeine also increased total testosterone concentration by a small percentage (15-21%; P0.05), but resulted in a decline in the squat and bench press testosterone:cortisol ratio.
It is possible that the acute increases in squat and bench press 1RM and muscular endurance observed with caffeine supplementation are mediated through non-genomic effects on mTOR signaling (e.g., phosphorylation of mTOR and its downstream targets).
Increases in the amount of resistance exercise contractions during the test battery could potentiate the effects of caffeine on these cellular events since increased contractile volume is known to increase epinephrine concentrations.
This would result in an increase in cAMP which then activates protein kinase A (PKA) which has hundreds of identified substrates including MAPK and steroid receptors.
Studies examining caffeine's acute effects have generally demonstrated dose-dependent increases in testosterone levels following exercise as well as elevated cortisol levels; yet the mechanisms underlying such responses remain unknown.
Caffeine's most well-documented ergogenic effect is its ability to enhance aerobic endurance performance.
Studies have shown that when taken between 2-6 mg/kg body weight prior to engaging in prolonged endurance activities such as running or cycling, performance improves. Furthermore, males and females alike experienced similar increases.
Although caffeine's benefits for aerobic exercise are well documented, their effect on anaerobic activities such as sprinting or lifting heavy weights in a gym are less clear.
A handful of studies have revealed that when consumed prior to such activity caffeine can improve sprint performance and power output with men seeing greater benefits than women.
Studies also demonstrated that when consumed, caffeine has an ergogenic effect; one study demonstrated this by showing how taking it at 7:00 AM had greater ergogenic benefits than doing so at 12:00 PM.
Caffeine may exert its ergogenic properties by increasing epinephrine activity. Stimulation of beta2 adrenergic receptors results in accumulation of intracellular cyclic adenosine monophosphate (cAMP) and activation of PKA; the latter of which has numerous substrates spanning both steroid receptors and non-steroid receptors.
Researchers have recently reported that caffeine ergogenic effects are increased among individuals who possess the CYP1A2 T allele.
These individuals can rapidly metabolize caffeine, providing full experience from high dose caffeinated energy drinks. It remains to be determined if this finding can be replicated across more genotypes in future research studies.
Effects of Caffeine on Testosterone Levels
Caffeine is an addictive stimulant that stimulates the nervous system by speeding up connections between brain and body, leading to increased alertness.
Caffeine has also been shown to boost testosterone levels when consumed first thing in the morning, including increasing anaerobic performance for those exercising when consumed prior to workouts and raising total testosterone by 21%; an important boost for those experiencing low levels.
As increased testosterone has many beneficial impacts on body such as increasing bone density, decreasing fat storage and encouraging muscle mass growth when increased, making this substance a must for anyone suffering low levels!
Coffee's ability to increase testosterone can be explained by its effect on aromatase, an enzyme responsible for breaking down hormones such as testosterone into estrogen - something aromatase does.
Without aromatase breaking it down into estrogen levels drop, as does its positive benefits for you.
Furthermore, caffeine may increase expression of gene encoding sex factor 1, an essential transcription factor which promotes testosterone synthesis while decreasing cortisol secretion.
Researchers conducted one experiment in which they compared the effects of high doses (800mg) vs low doses (2 cups per day) of caffeine to see which would result in greater increases of testosterone following physical exercise.
Both groups experienced an increase in testosterone production after exercise, with higher caffeine doses leading to a decrease in cortisol/testosterone ratios after exertion.
Another study examined the effects of various levels of caffeine intake on testosterone concentration in men.
This research utilized NHANES data to analyze recall caffeine consumption and total testosterone concentrations using multivariable linear modeling
There was a significant inverse relationship between total testosterone concentrations and 1-methyluric acid, but not between total testosterone concentrations and either uric acid or 3-methyluric acid concentrations.
Caffeine may help increase testosterone through these mechanisms.
However, there's always the chance that increased cortisol secretion due to higher dosage of caffeine could eat away at testosterone synthesis and may prevent 11ssHSD-1 enzyme from protecting testosterone against its harmful effects and thus decrease overall levels.
This study showed that caffeine supplementation did not alter the acute response to resistance exercise.
This is despite widespread usage as an ergogenic aid in pre-workout supplements and prior research showing increased testosterone after both rest and RE contraction when combined with caffeine supplementation along with an increase in cortisol.
Our results demonstrated that these effects of caffeine on testosterone and cortisol levels are caused by non-genomic mechanisms, including changes in AR/GR phosphorylation; further investigation will need to take place as to their impact on skeletal muscle performance.