Honestly I wouldn't worry about it and just do a workout. Use headphones instead of cranking music. Unless your morning starts at 3 AM, as long as it starts near a regular morning time (5 AM or later), you won't be doing it for very long, and your neighbor can just deal. It's part of the price of living in multi-unit housing. Everyone has to be noisy at times, and you just get it over with and deal and be as quiet as possible at other times.
I can hear my downstairs neighbor cough, pee, and snore. The neighbor across the hall comes in at 3AM every morning (restaurant shift, I think). The family below him has little kids that have tantrums almost every afternoon right after school and right before being fed dinner. Below that is a little yappy dog that barks for hours. Sharing my back steps area are several friendly partier-types that hang out and smoke and talk loudly all night long. My apartment is on a busy street that is a major route for emergency vehicles to other parts of the neighborhood, and it gets used for that purpose several times in every 24 hour period at all hours of the day and night.
I commend your desire to be a considerate good neighbor, but shortchanging yourself on your workout only hurts you and probably won't appreciably improve your downstairs neighbor's quality of life.
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