Perform as many supersets of pull-ups, sit-ups, and push-ups as possible in twenty minutes.
A superset is done by performing one set of each exercise back to back to back with little or no rest in between. Choose a number of reps that is well below your max to prevent early burnout during the training session. The training effect today will come from the overall volume of exercise combined with short rest periods, not max effort sets. Rest between supersets as necessary.
Intermediate and Basic trainees should substitute assisted, partial, or jumping pull-ups, body rows, crunches, and knee push-ups as necessary.