Athletes use caffeine as an ergogenic aid for performance, focus, and fat loss. There are countless studies that prove it’s effectiveness for increases in power output, mental alertness, and the increased rate of metabolism. But the effects of caffeine really aren’t that simple. Actually that’s just a piece of it’s effects on the individual. Caffeine is the most widely used drug in the world today. It’s use ranges from a cup of coffee in the morning to high concentrations in supplements, energy drinks, and weight loss products. Most people associate the negative risks of caffeine use with just blood pressure issues (and all things stemming from them) and sleep issues. The truth is it goes deeper and is more far reaching than that. Caffeine can be a useful ergogenic aid, that’s proven. But at what amounts, frequency of use, and duration of daily use are the effects more positive than negative? It turns out that it doesn’t take a lot of caffeine for the negative effects to start wreaking havoc on your body. And for the athletes who don’t care about the health concerns, that havoc reaches all the way to impacting your performance and recovery. Caffeine can be an aid in training but can also create an issue in training and recovery.
Hormonal Response To Caffeine
Caffeine acts by blocking the action of adenosine, a hormone released to control nerve activity in the brain, causing an excitement of nerve action. Adenosine is also responsible for dilation of blood vessels and an increase of blood flow in the brain. So with the constriction of blood flow and the increased excitement, or firing, of neurons the body reads this as the beginning of the “fight or flight” response. Then the signal goes to the adrenals and cause adrenaline to be released. Blood flow is directed away from the skin and away from the digestive tract to muscle tissue. It also causes a release of glucose into the bloodstream for meeting higher energy needs. In short, it’s your body getting ready for a fight. That chain reaction that gives you the desired feeling of focus, alertness, aggression, and energy isn’t the end of the process. If that was all I wouldn’t be writing this and would tell all of my athletes “the more the better” when I get the question about caffeine intake. But let’s look at the hormonal responses that follow that initial phase.
Cortisol, a hormone also produced in the adrenals, is released in response to the adrenaline release. This hormone increases the rate of gluconeogenesis (creation of glucose from protein and fat) which is responsible for that release of glucose into the bloodstream mentioned. Along with the increase in blood sugar levels it’s also responsible for inhibiting the uptake of glucose from all cells except those of the central nervous system. Remember this for when insulin is discussed later.
Cortisol is typically supposed to surge in the early morning hours but with caffeine intake this cortisol release can happen throughout the day even surging in the afternoon. Cortisol is also thought to disrupt the slow-wave sleep cycle, which is normally a time of low cortisol level, and this phase of sleep is thought to be where memory consolidation takes place primarily.
It’s also an anti-inflammatory hormone which when needed by the body for short term effects is essential. The problem is with chronically elevated cortisol levels the immune system is suppressed. The body needs an inflammatory response for healing and recovery. When the inflammatory response is suppressed long term you heal slower, are more susceptible to infection, among a few other consequences. There is also a link between elevated cortisol levels and cancer due to this impairment of cell immune function.
Insulin / Insulin Resistance
Ok so along with the release of cortisol and spike in blood sugar levels, you have an inhibition of cellular uptake of the glucose to be converted to energy. What we end up with is a bunch of blood sugar in circulation not able to enter cell walls, due to the decrease in insulin sensitivity (insulin resistance), as well as a spike in insulin levels. One study found a decrease of 35% in insulin sensitivity (https://www.ncbi.nlm.nih.gov/pubmed/17998023) with a 200mg dose of caffeine administered twice daily. That’s a few cups of coffee, about 2 energy drinks, or 1 serving of some of the heavy duty preworkout supplements on the market. Point being, it really isn’t a massive amount for most daily caffeine users. So what does this mean? Basically glucose has a tougher time entering muscle tissue and cells for conversion to energy, where we would like it, and is sent where we don’t want it. The excess blood sugar is converted into fats and stored. Insulin resistance means muscular recovery from exercise will be slower and fat gain (or difficulty losing fat) becomes more likely. It also has many negative effects on the way you feel overall not to mention the extreme end of insulin resistance being type 2 diabetes.
Aldosterone is a hormone that helps the body regulate blood pressure. Constriction of blood vessels due to caffeine intake (vasoconstriction) signals the release of renin which is the first in the chain for aldosterone release. Aldosterone signals the body to release more sodium into the bloodstream (by reuptake instead of being excreted through urine) and the release of potassium in the urine. This imbalance is the perfect environment for sharp increase in water retention. There are many other things that can cause release of aldosterone. Caffeine specifically has been shown to increase plasma renin activity (the precursor for aldosterone) 57% in some studies. http://www.nejm.org/doi/full/10.1056/NEJM197801262980403
Caffeine and Adrenal Fatigue
Like most glands of the body the adrenals can’t be taxed hard repeatedly every day and still keep up their normal level of function. Tolerance to caffeine doesn’t seem to be related to any change in the way it blocks adenosine from acting. The decrease in effectiveness is likely not related to tolerance to caffeine itself but the inability of the adrenals to produce adrenaline as efficiently over time. Adrenal fatigue can effect everything from your mood, energy levels during the day, appetite and cravings, sleep, recovery/immunity, to your strength and motivation in the gym. When you have less adrenaline available in times you need it, as you would in an intense training session, the intensity suffers and you notice you have a hard time getting “fired up” before a big lift or for the workout. “Just not in it mentally”. You have a feeling of just going through the motions and don’t have the aggression to tap into. This brings me into the last part.
Increased Stress on the Central Nervous System
People view overtraining as the inability of the body to recover from workouts. Most think of it as a muscular recovery issue when it’s bigger than that. That can be part of it but what most don’t recognize is the overtraining effect that stems from the central nervous system (CNS). Your CNS is what sends all the signals to the muscles to fire during lifting. The higher the workload the more stress the CNS is under to recruit all the muscle fibers for the lift. This is the main reason lifters with a max of 400 on the squat can handle more volume than someone with a max of 700. 85% is 340 for one and 595 for the other. Although the intensity (85%) is the same for both, the 595 is much harder for the CNS to handle. It’s doesn’t have as much to do with muscular recovery between sessions but with ability of the CNS to recover. When your CNS is burnt out (overtrained) your body can feel fine. But when you get in the gym everything feels heavy and moves slow. Your movement will be off and inconsistent and you may be shaky during lifts. So what does this have to do with caffeine/stimulants? Caffeine places more stress on the CNS by exciting motor neurons and increasing the rate at which they fire. So add a moderate to high daily intake of caffeine to heavy lifting and intense training, and you are digging that hole faster and deeper.
I recommend my clients never have more than 200mg/day. It’s best if the people who are using caffeine as a training aid only use it for training. Limit it’s frequency as much as possible and use it for a specific purpose. If you are a coffee drinker, 1 small cup of coffee in the morning and then no more than 100mg before training. If you can go without caffeine in the morning than just use 100-200mg before a training session. You are trying to use it as a training aid and not something to get you lit up like a Christmas tree. The more you use, the more it taxes your body, the more it effects your progress negatively. Less is more.