At this point in our fitness-crazed world, heart rate monitors and fitness trackers and even Bluetooth scales have been somewhat normalized for civilian use. Which made us wonder: What kind of measurements and tools do the pros have that we still don't? What's the really good stuff? So we called up San Francisco exercise physiologist Stacy Sims and asked her to tell us about four different kinds of pro-caliber technology—and to let us know if we actually need to be using any of them.

1. VO2 MAX

What it is: How we measure a person's aerobic capacity. Lance Armstrong's ridiculous VO2 Max as a young Texan, before he was doped to the gills in the late 1990s, is the stuff of urban legend in cycling circles. His score: 84, which is nearly 30 points higher than what would be considered Excellent for a 26-35 year-old-guy sitting at his computer reading this article.

What it measures:"The maximum rate and volume at which oxygen is taken up and used by lungs, heart and muscles during exercise."

Who uses it: Endurance athletes. Think: Runners, cyclists, Nordic skiers. "It's used to quantify an athlete's fitness status, to determine their ability to work at a certain level of sustained exercise—the higher your VO2, presumably the faster you can go and higher intensity you can maintain for longer duration."

Can I do it myself?: You can ballpark it. "To get an accurate number, you need to have it done in the lab. But you can estimate it from a 5k or 10k race time using charts and online calculators."

Should you try it?: Sure! If you're a swimmer, marathoner, or long-distance cyclist, it could be a useful metric to chart and try to improve.

2. LACTATE THRESHOLD

What it is:"The point during exercise of increasing intensity at which blood lactate begins to accumulate above resting levels, where lactate clearance is no longer able to keep up with lactate production." Translation: When your legs feel like they are filled with cement and you begin to hyperventilate, that's your lactate threshold.

What it measures:"The point at which your body produces more lactate than it can clear—shifting from predominantly aerobic metabolism to predominantly anaerobic energy production." Under stress your body is going to produce lactate much, much faster and you are going to want to go much, much slower as a result.

Who uses it: Endurance athletes. A lot of professional runners and cyclists do lactate threshold workouts to increase their aerobic capacity.

Can I do it myself?:"The most accurate and reliable method is through exercise testing with blood sampling," Sims says. But there are ways to test it in time trials.

Should you try it?: Unless you're trying to break a three-hour marathon, it's more hassle than it's worth. Stay in your lane and live your life.

3. MUSCLE OXYGEN SATURATION

What it is is: The percentage of hemoglobin (the protein that carries oxygen from the lungs to your muscles) in your muscle tissue

What it measures:"The balance between increased oxygen demand in the capillaries of the muscle and the cardiovascular delivery of oxygen."

Who uses it: The kind of athletes who need to deliver lots of oxygen from their lungs to their legs. We're talking again about cyclists and runners. (Yes, the simplest sports—running and riding a bike—utilize the most hardcore tests.)

Can I do it myself?:"Yes, there are several new devices out on the market that measure muscle oxygen saturation." Moxy is the most popular, but it'll cost you.

Should you try it?: Hard pass, unless you're having a mid-life crisis and doing one of those bike trips that takes you on the Tour de France course one week ahead of the race. In which case: Knock yourself out.

4. URINE SPECIFIC GRAVITY

What it is:"The ratio of urine density compared with water."

What it measures: Hydration status

Who uses it: Ultramarathoners, triathletes, and other crazies

Can I do it myself?:"Yes, you can use urine dipsticks for a rough result. To be more accurate, you can invest in a refractometer."

Should you try it?: While the prospect of using a urine dipstick may be enticing, you probably don't need this unless you're training for a race that lasts longer than the Godfather trilogy. Just drink enough water and you'll be fine.