Stability gold. Looks easy, humbles everyone.
Don't let your hips tip or your lower back sag. Move slow and stay flat as a table.
Reaching one leg straight back makes the glute on that side hold the hip in extension while the core fights to keep your hips and shoulders from tipping as your base shrinks to two points. The slow, deliberate reach and return is the entire exercise, done well it looks like nothing and feels like work. It earns its spot in warm-ups and spine-friendly core training because it teaches the glutes and trunk to work together before heavier lifts demand it.
It trains your glutes to extend the hip while your trunk holds dead still, which is the foundation underneath deadlifts, squats and running. It doubles as a low-stress core drill that most backs tolerate well.
Because lifting an arm and the opposite leg cuts your support in half, and every lazy stabiliser gets exposed. Slow down, brace before you move, and shorten the reach until you can move without your hips tipping.
Both work. A one to two second hold per rep builds the stability the exercise is famous for, while longer holds of five to ten seconds turn it into a real endurance challenge. Flowing reps with no pause is the least valuable version.
