Don't make the same mistake I did with too much cardio. Over the past two years I have been running to improve the freediving. At the end of last years dive season (October), I boosted my 3 runs a week from 10Km per run to 15 Km per run. I did this 28 miles a week for 7 months leading up to the new season in April. The first few weeks of diving went great, but as the combination of diving and all of that cardio seemed to take its toll. I began to samba very easily, even on shallow 60-70' dives. I'm not entirely certain if it was the inadequate recoveries between running sessions, the reduced blood pressure, or the formation of more efficient mitochondria to the muscle cells, that caused the problem. After the dive season got under way, and I cut back the running to once a week, the symptoms totally vanished. It took over a month though. I also got into the habit of hook breathing upon surfacing, and to an extent, incorporate it into my breathe-up. Initially, I did not make the connection with excessive cardio training and samba/bo. BTW, I would never run the day before (and usually after) a dive. I don't even like to dive consecutive days due to how thoroughly I like to be hydrated before a session. Also, I would keep the HR to around 90% of maximum. I don't mean to discourage you, but I was kind of discouraged after running almost 1000 miles between seasons, only to find out I did more harm than good. I'm not saying eliminate cardio, just do it in moderation and be prepared to loose lots of hydration and nutrients. Give extreme priority to replenishing them.