Don't let a workout wall stop you from achieving the body breakthrough you've been sweating for

What makes your muscles cry uncle when you're trying to hold a plank, go the distance on a long run, or do speed drills? New research says they may not actually be tapped out but instead are getting mixed messages from your brain.

In other words, when you're putting in the workout time, it's your mind you need to condition to get past that moment when you want to quit. (Because mental fatigue can seriously affect your workout.) Here's why: With every step or rep, your muscles are sending signals to the brain, telling it what they need in order to keep going-namely, oxygen and other fuel-and reporting their level of fatigue. The brain then responds, adjusting muscle contraction demands accordingly, says Markus Amann, Ph.D., a professor of internal medicine at the University of Utah. "If we can train our brain to respond to muscle signals in a certain way, we can actually push harder and for longer," Amann says.

Know Your Triggers

The first step is to understand your fatigue triggers. The signal to throw in the towel during a workout can come from one of two places: your central nervous system or your muscles. What experts call "central fatigue" originates from the former region, while "peripheral fatigue" originates from the latter. You've likely experienced heavy legs in the last miles of a race or trembling arms as you lower yourself for a final set of push-ups in boot camp. That's peripheral fatigue, a decrease in your muscles' ability to generate power. Until recently, it was assumed that peripheral fatigue dictates a certain threshold at which your muscles give up.

But new research in the journal Medicine & Science in Sports & Exercise found that the brain can actually underestimate how much gas you have left in the tank, and in response, ask your muscles for less effort. In the study, cyclists completed three rides at varying intensities until they reached exhaustion: At sprint speed, they lasted an average of three minutes; at a race pace, they lasted 11 minutes; and at a challenging endurance pace, they lasted 42 minutes. Using a sophisticated electrical stimulation technique, the scientists were able to measure central and peripheral fatigue after each ride to pinpoint which may have triggered the muscles to give up. Peripheral fatigue peaked during the short bouts and central fatigue was the lowest, but central fatigue was at its height in the longer distance, meaning the brain reduced action from the muscles even though they hadn't actually maxed out.

Amann conducted another study that backs up this theory: He injected exercisers with a spinal nerve block that inhibited signals from traveling from the legs to the brain and had them cycle as fast as they could on a stationary bike for 3.1 miles. At the end of the ride, every cyclist had to be helped off the bike because of the exertion; some couldn't even walk. "Because their central fatigue system was blocked, the cyclists were able to push far past their normal limits," Amann says. "Their muscles fatigued nearly 50 percent more than they would have had the communication system warned them they were approaching this state."

Of course, if you ever feel dizzy, nauseated, or like you might pass out, pump the brakes. But a lot of times, your muscles aren't always the boss of your workout, and they will push harder for longer if your brain asks them to. These three methods will help you to game your fatigue systems so you can break through invisible barriers into the next fitness level. (Exercising alone? These tricks will help you challenge yourself when you're flying solo.)

1. Cheat the System

At the start of a long run or race, you feel energized and pumped. But hit mile seven, and every mile feels like a drag and you start to slow. Yes, physical bummers-such as glycogen depletion and buildup of metabolites that make your muscles feel pooped- exacerbate this struggle, but not enough to account for the added difficulty, according to Samuele Marcora, Ph.D., the director of research at the School of Sport & Exercise Sciences at the University of Kent in England. "Performance is not directly limited by muscle fatigue but rather by perception of effort," he says. "We create our own limits in large part because of what our brain thinks we're feeling rather than what may actually be going on deep in the trenches of our muscles."

His research, published in the Journal of Applied Physiology, shows that what matters most is the internal battle between your subjective sense of effort and the mounting desire to just quit. In the study, 16 cyclists rode to exhaustion after 90 minutes of either a demanding cognitive task or a mindless task. The riders who had tired their brains before the workout demonstrated significantly shorter times to exhaustion. The mentally fatigued group also rated their perception of effort much higher during the cycling test, leading them to stop earlier than the rest. The upshot? Any trick that reduces that perception of effort would improve your endurance performance. (And, BTW, having too much on your mind can actually affect your speed as well as endurance.)

First, keep the upbeat thoughts coming as you sweat it out. "Tell yourself powerfully positive statements, like, "You will definitely make it up this hill," Marcora says. Next, make your brain associate exercise with something that feels good. (The "fake it till you make it" approach totally applies; positive thinking really does work). "The muscles that contract to make a frown are actually a reflection of how hard your body feels it's working," he says. "Try to smile during tough stretches of your workout so that the muscles that trigger thoughts of exhaustion are less active." Just as with your muscles, when you lighten your mental load, you can go longer and stronger.

2. Power Through the Burn

During your everyday hustle-and even your average daily workout- your muscles are getting plenty of oxygen from your heart and lungs to help power their movement. But when you go hard, this aerobic system can't keep up with the energy demands and your muscles have to switch to their auxiliary power, eventually blowing through their fuel stores and causing a buildup of those aforementioned metabolites.

Cue: fatigue. But remember, burning legs or quivering muscles are just a heads-up that you're approaching exhaustion-they're not necessarily your real limit. According to Amann, your brain will always keep your muscles from zeroing out to preserve an emergency energy store, but you can teach your brain to respond less aggressively to the metabolite buildup. For example, practice makes you impervious: The more you repeat cycling at sprint speed, the more inured your muscles will be to the burn and the less likely they will be to beg your brain to stop. And raising the motivational stakes of your workout- swapping that Spinning class for a bike race-can preoccupy your brain so it doesn't hit the panic button at the first sign of stiffness. (But guess what? Competition itself might not actually be legit workout motivation.)

3. Quench Your Mind

The right beverage can rev your brain to give you more "go" power during exercise. For a mid workout game changer, swish and spit out a carbohydrate drink such as Gatorade to see a performance boost. According to a study in The Journal of Physiology, cycling participants who wet their mouth with a sports drink finished a time trial at least a minute ahead of the control group. Functional MRI scans showed that reward centers in the brain were activated when drinking the carbo-heavy drink, so the body subsequently thought it was getting more fuel and, as a result, pushed harder.

But for those of you who prefer to swallow your beverages, caffeine can also work wonders on brain drain. "Research shows that having two or three cups of coffee before a workout kicks your head into high gear, requiring less brain activity to produce muscle contractions," Marcora says. Your movement becomes more automatic and seems less daunting, and your workout and body suddenly feel limitless. (If you're hungry and in need of energy, try these coffee-infused snacks that do double duty.)