Thanks, scvdiver! Yes, I've compiled research from over 40 studies on diving and exercise, and I dedicate a chapter in "Fitness for Divers" to the issue of dive day exercise. Bottom line, it seems to be much safer to exercise before diving than after. Strenuous lifting after diving is much riskier than moderate cardio. Cardio before diving might even be advantageous, but more research needs to be done here before any recommendations are made about this.
DAN's recommendation to wait 6 hours after diving seems to be safe, as it has been difficult for me to find any cases of DCS in someone who felt fine after a dive and waited that long before exercise. More significantly, it has also been difficult for me to find any cases of DCS in someone who exercised at any point *before* a dive that wasn't attributed to dehydration rather than bubble nucleation.
Cameron