You've probably heard it a million times: It's a great idea for your workout motivation to have a specific fitness goal. That could mean running a 5k or a marathon, reaching a high score at your indoor cycling class, or crushing a 30-day plank challenge.

That said, not all goals need to rely on a race, peer competition, or require a month's worth of sore abs. Sometimes, the mental and physical rewards of mastering a new, difficult skill can top that of training for hours on end just to cross a finish line. If you're looking to challenge yourself in a new way, this is for you: three boutique fitness studios picked the hardest move they offer in their classes, and give you the tips to try it for yourself below.

Work on mastering each one, then put them all together for a crazy-person workout that will surely challenge you to the max.

The preztel

When you're sitting on the floor with one leg bent behind you and the other bent in front of you, you might think the instructor is downright crazy when she tells you to lift that back knee and start pulsing. Lift it...how? No, you're not being punked. That's the pretzel, infamous for being confusing to most and seemingly impossible to some.

The main reason it's so difficult is that you have to get the alignment just right to target the correct spot. Once you get the position just right, you might find it easier to target the glute.

How to do the pretzel:

A. Start seated with the right leg at a 90-degree angle in front of body (knee pointing to the right) and left leg at a 90-degree angle behind body (knee pointing to the left). (FYI this is also called the 90-90 stretch.)

B. Place hands in front of right shin, framing right knee. Bring left thigh as far behind you as possible, making sure the knee is behind the hip bone. Internally rotate the left thigh so knee is tilted lower than foot, then raise the lower leg off the floor.

C. Lift leg up for 20 to 30 pulses, then hold leg up and press it back (think: moving left foot away from glutes) for 20 to 30 pulses. Then combine the two moves by doing one press back and one lift up for 20 to 30 reps. Repeat on the other side.

Twisted half moon

Just when you finally master the super-challenging half moon pose, you learn about an even more challenging variation, the twisted half moon.

In order to master this pose, you need to be warmed up through the hamstrings, pelvis, and lower back, as this pose demands a lot of those areas. Once you're warmed up, think about being rooted strongly through the foot, which is the base of the pose. Try not to focus on lifting the raised leg, but rather on rotating through the pelvis. The more you rotate, the more your raised leg will move with it.

How to do twisted half moon:

A. Start standing with weight in left foot. Lift right leg behind body and lean forward, placing right fingertips on the floor (or a yoga block) next to the left foot.

B. Using left leg and core to balance, twist upper body to the left (it should feel awkward!), keeping right fingertips on the floor to steady you. Attempt to open chest and left arm up as much as possible, extending left leg long.

C. Attempt to hold the pose for a few deep breaths in and out, then switch sides.

Medicine ball burpee

It's the high-intensity, full-body move you love to hate. In fact, many people are so tired after the first few burpees that they end up flubbing form big time and causing strain to other muscles. People often sink into their lower back and overuse their neck and traps.

To counteract that and keep the focus on the legs, upper back, and core, experts recommend positioning your hands on top of a medicine ball instead of the floor. Also, don't look up: Keep your chin tucked down to your chest when you are coming in and out of the plank, which will help you align your body correctly from the top of your head to your heels. And when you return to standing, try stepping backward instead of jumping so you don't tweak your lower back.

Once you learn to keep your energy up and your form tight, you can add the jump back in and try the move with your palms on the floor instead of the ball.

How to do a medicine ball burpee

A. Begin in a plank position with hands balancing on a medicine ball.

B. Jump feet in, landing on either side of the ball, and lift chest up to assume a squat position. Jump up into the air, landing back in a squat.

C. Place hands back on the ball in front and step back into a plank. To make the move harder, jump back into the plank instead of stepping into it, and perform one push-up on the ball before jumping feet back in to a squat.

D. Do as many reps as possible for 30 to 60 seconds.