Cycle Core is a back and core workout that alternates high-rep movement with low-rep control, cycling between the front and back of your trunk the whole way through. Climbers and knee-to-elbow crunches supply the volume in blocks of ten; plank crunches, back extensions and leg circles slot between them in deliberate sets of four.

The structure runs on two gears, and the gear changes are the point. Each high-rep block - climbers in the plank phase, knee-to-elbow crunches in the floor phase - drives heart rate and accumulates fatigue through the abs and obliques. Then the workout downshifts: four plank crunches, four back extensions, four leg circles, each demanding precision exactly when precision is hardest to supply. The back extensions matter most in this rotation - they are the only exercise here working the posterior chain directly, balancing all the flexion around them, which is what earns this session its title as a back workout. The closing leg circles ask the deep core to stabilize against movement in every direction at once, four slow orbits to end the set honestly.

Keep your hips low through the climbers and draw each plank crunch knee in with control rather than bouncing it. On the knee-to-elbows, rotate shoulder to hip and keep the tempo unhurried. Lift modestly on the back extensions - a controlled rise with a squeeze beats altitude every time. During leg circles, press your lower back into the floor and shrink the circle the moment that contact starts to slip.

Front, back, fast, slow - around the cycle again. Your trunk is strongest when the loop stays unbroken.

Make it Harder: Double every four-rep block to eight without changing the tens.

Make it Easier: Slow the climbers to a march and halve the leg circle diameter.