Weight loss might not be about maxing out after all, Our friends at Shape  have the full scoop here!
In Fall of 2013, the Vail Vitality Center and the Human Performance Lab at Anschutz Health and Wellness Center in Denver presented a performance test to the public that had previously only been offered to elite and professional athletes. Developed by Basque doctor Iñigo San Millán, it goes beyond discovering VO2 max (an indicator of your aerobic fitness) and the lactate threshold (an indicator of your anaerobic fitness) and does what no other test has done before: it gives you an exact number range for your six heart rate training zones and pinpoints the exact beats per minute (bpm) when you stop burning fat and start burning carbs.
That's a big deal.
For well-trained athletes, it's an exact science that reins in overtraining and prevents injury. In one collegiate team, San Millán and his crew decreased injuries threefold. For the rest of us, it's even more helpful: it proves that most people trying to get in shape push themselves too hard to burn fat.
Here’s how it works: during a 35-minute workout on a treadmill or stationary bike, the speed slowly increases while a technician measures your VO2 max via a face mask and takes a blood sample every five minutes. Those measurements tell the exercise physiologist how your muscles flush out lactate (the gunk that eventually builds up in your bloodstream to slow muscles down during a hard, anaerobic pace), the health and density of your mitochondria, and how your body burns fat and carbs.
When I run through the test with Nick Edwards, assistant director of the Sports Performance Program, I learn that my magic number is 146 bpm. That’s the upper limit of Zone Two for me.
A quick primer: Zones One and Two are for everyday training, while Zones Three through Six are for workouts and racing. The threshold of Zones Two and Three is where the body transitions from aerobic to anaerobic. Outside of pure cardio, these zones are important to remember in high-intensity strength-training classes or in workouts like CrossFit, too. If you're heading north of Zone Two every day, you’re asking for injury, which is why Edwards recommends saving classes that raise your heart rate for hard workout days and only twice a week.
If I want to burn fat — the preferred fuel for going faster, longer — and train at a healthy pace, I have to stay at 146 bpm or below. If I go above that, the only thing I'll burn is what I ate that day, plus I'll end up stressing my muscles. If I had a lot of weight to lose, I might slim down some, but for those looking to drop the last few pounds, there's a higher risk of developing an injury before your fitness base can catch up to match your workload.
Looking at my results, Edwards tells me that I can't run easy three-milers to get in shape like I always have. The minute I transition from walking to running on the treadmill, I become anaerobic, so my prescription is power walking — for two months. For a former Division I all-American runner, it's a hard prognosis to swallow. But if I want to build a fitness base that will allow me to begin running and increase speed safely, my only option is walking or riding pitifully slow on my bike. It's hard to rein in speed, but after three weeks, I'm growing stronger and faster — the watts are increasing on my indoor cycling trainer, but my heart rate is staying the same. And I'm barely sweating.
For recreational athletes, Edwards recommends coming in for a follow-up after six months since numbers will change dramatically when you're improving fitness. In another month, I'll have built enough of an endurance base that I should be able to go for an easy run and stay in Zone Two. After that, it's worth following up to see how my body has adapted to regular exercise. For competitive athletes, Edwards recommends an annual check.
Good things don't come cheap, though: the test is available for $450, and for now, you can only find it in Colorado. Luckily, Edwards says there are four easy things you can do to make sure you're working out at your personal best level.
1. Go to school. Until San Millán's test is more widespread, a lactate threshold test will give you the best estimate of your training zones. (They'll be given in percentages of your threshold, as opposed to an exact bpm range for each.) A good place to find the test is at local universities, where you can have physiological testing done for free if you volunteer for a study. Otherwise, cost at performance centers nationwide ranges from $125 to $300. Edwards suggests avoiding the old standby of calculating your threshold with the equation "220 bpm minus your age." The answers it gives are "all over the map," he says, and often don't come close to your actual threshold.
2. Go slow. Really slow. "The body needs to assimilate to anything you do, so you can't throw it into the fire," Edwards says. So if you haven't worked out regularly in a while, start walking — and not quickly. Without a fitness base, your body burns fat most efficiently without you ever getting out of breath. Begin with 30 to 90 minutes of exercise three times a week, and slowly increase to five days a week from there. After a month or two, add in one or two weekly interval sessions to raise your heart rate, which will improve cardiovascular health in addition to fitness.
3. Don't overtrain. When you begin working out, soreness is only OK if it goes away after three days. If you wake up achy or are constantly tired, you're overdoing it. The same goes for sleeplessness, loss of appetite, big fluctuations in weight (trust your instincts: dropping two pounds could be a lot for a petite woman, but no big deal for someone bigger), or feeling fatigued all day long — they're all classic symptoms of pushing too hard, Edwards says.
4. Change it up. When you first start a workout routine, you're putting your body under stress, which is why you see big gains in fitness and health. But after a while, your body adapts and gets used to the same processes. A good rule of thumb is to change up your routine every four to six weeks, Edwards says. Even hitting refresh for three weeks and then returning to your previous routine is enough to jump-start your body into gaining fitness again.
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The Six-Week, No-Fail Fat-Loss Plan 
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Five Surprising Ways Stress Messes With Your Workout