What the NHS guidelines say about how often to work out
The NHS advises adults to do strengthening activities that work all the major muscle groups on at least 2 days a week, and to do at least 150 minutes of moderate activity or 75 minutes of vigorous activity across the week, spread over 4 to 5 days or every day. It also advises cutting down time spent sitting and breaking up long periods of not moving.
For a commuter, two coached strength sessions cover the first part. The walking between the station, the office and the club, a weekend session and whatever you do outside the gym go towards the second. A day that starts and ends on a train seat is exactly the sitting the guideline warns about, which is one more reason the strength sessions matter.