Poll Results

Total votes: 3987

Swim: 1140 (28.6%)
Manual labour: lifting, carrying, digging: 766 (19.2%)
Jog outdoors: 593 (14.9%)
Play tennis: 393 (9.9%)
Play some form of football: 392 (9.8%)
Use various weight machines in the gym: 369 (9.3%)
Jog on a treadmill: 205 (5.1%)
An aerobics class: 129 (3.2%)

I deliberately omitted bicycling, because I thought it would probably dominate the responses. It certainly dominated my mailbox with people wanting to vote for it, even though it wasn't an option.