THIS barely keeps Maribeth off welfare. Reading fortunes for a living barely keeps Maribeth off welfare. You lift weights every day. THIS has improved your looks. Some people drive trucks in the summer.
Some people clean homes in the summer.
You proofread your paper. Stroke victims swim an hour every day. Doctors advise THIS for stroke victims. Till now, when making a gerund of the minor sentence's verb you just deleted its subject. The subject was unnecessary because clearly implied in the major sentence.