Pretty much every kick-ass fitness move has this sequence (and there’s a reason why)

The other week at the Well+Good office, an editor found out about a fitness test that requires you to go from standing—with your ankles crossed—to sitting on the floor, then standing back up, all without uncrossing your ankles, which supposedly predicts your longevity. Everyone tried it, and about half of us (give or take) could actually do it without falling over.

It’s deceptively hard to do. Then it led me to realize that there are other moves in fitness that are somewhat similar: like burpees (ugh) and Turkish get-ups. Both of these require moving between the floor and standing upright—which happens to be a very challenging maneuver. It’s such a foundational part of fitness, so why the heck isn’t getting up from the floor a breeze?

“Getting from the floor to standing in general takes hip mobility and strength, glute activation, and core strength all firing at once,” says Lacee Lazoff, creator of Bells Up at Neou Fitness. Your entire body’s working really hard to support the movement.

On a physiological level, it has to do with your blood flow. “There are a few different components going on in these moves,” says Heather Milton, MS, RCEP, CSCS, an exercise physiologist and clinical specialist at NYU Langone’s Sports Performance Center. “One is that if you’re in a supine or prone position, meaning that you’re lying on your back or your stomach, then your body doesn’t have to work as hard to return blood to your heart because you’re not really fighting against gravity—you’re in a horizontal plane. This is versus being vertical, when blood is flowing all the way from your heart to your fingertips and the brain and your toes, throughout your body’s muscular pump, then returns that blood flow to the heart.”

So when you’re moving between the two positions, your heart has to step up its job and transition. “When you’re moving from a position where it’s much easier to maintain a homeostasis where blood is moving through your system, then moving quickly to upright, your body has to react by maintaining blood pressure to keep that blood flowing,” says Milton. “When you’re doing that movement really quickly, not only is your body responding by altering your blood pressure, but also your heart rate is going to respond by increasing. Your body has to maintain that constant blood flow and blood pressure.”

Your heart and your blood are doing all sorts of complex things on top of the fact that you’re involving almost all of your muscles to get up and then back down. “These are relatively demanding exercises, meaning they require a lot of muscles,” adds Milton. “That inherently makes it more difficult anyway—so it does require a higher level of fitness to be able to perform the movements with good form, which is why it feels more challenging than like a jumping jack where it’s not involving as many muscle groups.”

What can make it even worse is having tightness in your muscles. “Tight hips are common in a culture where people sit for hours a day,” says Lazoff, who notes that you really need mobile hips to do burpees and Turkish get-ups (on top of upper body strength).

These maneuvers are beneficial, though—as dreaded as they may be. “I like the Turkish get-up for challenging core strength and lumbopelvic stability,” says Milton. “And the burpee is really great for inducing those increases in heart rate.”

On the other hand, the skills required in transitioning from supine to standing are something that decrease as you age—hence why you see the older population having trouble swiftly standing up. “The older we get, the less quickly our body is responding,” says Milton. “That’s why when an older adult that gets out of bed or goes from seated to standing quickly might feel a little lightheadedness.” So while you can, try to embrace that skill of moving between planes…with proper form, of course.

There are burpee modifications out there, though, to help things out a little. And here are burpee alternatives, if you’re really opposed to them (I feel you).