I mean this is the point. If you commute by buìike you get your share of phtysica excecise. Correlation and causation

From the article:

The significant contribution that active commuting makes to total physical activity may explain the positive associations active travel has had with health outcomes. One study found a 44% increase in physical activity levels in individuals who walked to work compared with those who travelled by car. Another Scottish study estimated that 46.5% of all active commuters in 2001 met a daily target of 30 min of moderate intensity activity from their commute alone. Our study did not account for physical activity unrelated to active travel and this may partially explain the larger reduction in all-cause mortality risk associated with cyclist commuting compared with other studies.