Running to work is the best option for Rob's heart health.
Running to work instead of driving (20 minutes) is most likely to benefit Rob if he remains in his target heart rate zone. Running at a moderate intensity can help improve cardiovascular fitness by keeping the heart rate elevated within the target zone.
Biking to the convenience store (5 minutes) may not provide enough sustained activity to significantly benefit cardiovascular health compared to running. Swimming after school (10 minutes) is a good aerobic exercise but running or biking would elevate the heart rate more effectively for Rob's goal of maintaining heart health.
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