Use the Ring-Con and leg strap, to track body movement.

Attach your Joy-Cons to the included Ring-Con and leg strap.
Then set off into the game world,
tracking your body movements and measuring the power in your arms, shoulders, chest, core, back, glutes, legs and more.

The Ring-Con™

with integrated "Strength Sensor"

This is the ring-shaped controller you grip with both hands and use to move your character.
Made with a special springy material, the Ring-Con always returns to its original form but includes a high-sensitivity force sensor to detect you squeezing and pulling it out of shape. By using the Joy-Con sensor as well, it can also detect a variety of other movements, including vertical/horizontal shaking and tilting.

Review your exercise results

Measure your pulse after exercising, using the Joy-Con (R) IR Motion Camera*.
Knowing how long you exercised and how many calories you burned lets you better understand your training results and know what exercises best suit your individual requirements. By reviewing your exercise load, you'll avoid overdoing things.
* Reported values are estimates only, and not for medical use.

Leg Strap

“Accelerometer and gyroscope monitoring

This is another controller, which attaches to your left thigh using a band.
Similar to the Ring-Con, it employs the Joy-Con's built-in accelerometer and gyroscope to measure your lower body movements, in the form of steps and knee bends.
* Fits thighs with a circumference of approximately 34 - 70 cm.