AI Tutor
Have you ever tried skipping across the playground, only to suddenly feel totally clumsy and off-balance? It usually happens not because of your feet, but because your arms get confused!
Skipping is a continuous fundamental movement pattern built from an uneven, rhythmic step-hop sequence on alternating feet (extStepR→HopR→StepL→HopL ext{Step}_R \rightarrow \text{Hop}_R \rightarrow \text{Step}_L \rightarrow \text{Hop}_L).
Once your feet master the step-hop, how do you keep from tipping over with every jump?

The Opposite Rule

Mature skipping relies on contralateral arm and leg action (opposition). As one knee drives upward, the opposite arm swings forward flexed at roughly 90∘90^\circ, providing vertical lift and dynamic rotational balance.
When you switch feet, your arms switch too: left knee up means right arm swings forward.
Why do our bodies love moving in opposites? In the 1600s, scientist Giovanni Borelli studied how animals and humans move, discovering that our limbs act like levers to counter-balance each other.
When a heavy knee lifts forward, it twists your body; swinging the opposite arm forward creates an equal twist in the other direction, canceling out the spin so you fly straight forward.
So what happens if you accidentally lift the arm and leg on the exact same side?

The Robot Trap

A common mistake is same-side swinging, where your right arm swings forward with your right knee. This makes you wobble side-to-side like a stiff robot because both heavy limbs pull on the same side at once.