Get into a push-up position.
Retract and lower your shoulder blades, rounding your upper back and squeezing your back muscles.
In addition, tighten your abs, glutes, and hamstrings to retrovert your pelvis and remove the lumbar curvature, this is the hollow body position.
Holding it for as long as possible, try to do push-ups, if necessary, recover the position when you extend your arms again.