May 1st, 2021
Started in 2017, National Fitness Day™ is celebrated the first Saturday of May in the US as a single day to celebrate strength and empowerment through fitness. It's the ideal time to re-embrace fitness aspirations and resolutions made earlier in the year. Fitness can come by way of gym membership, walking, biking, or engaging in any cardiovascular or strength-training activity.
Source: http://holidayinsights.com/moreholidays/May/national-fitness-day.htm