Hi Nick,
A couple of us have been training for an Australian record attempt for dynamic no-fins in March - these are my thoughts so far from going from very little no fins training to dedicated no fins training for the last 3-4 weeks.
I am by no means a classic swimmer's build. I am about 5"10 and about 90kg's, which means I am probably about 6-12kg's (8-16 pounds for you non-metric people) overweight. I am also an ex-smoker. I don't think general fitness plays a massive role, but then again you don't see many freedivers who aren't fit. In any case, I think you should maintain some light cardio and some modest weight training at least once per week.
I think heart rate is very individual. My resting is about 65-75 bpm. I have done PB dynamics where my heart rate has been higher than this. It tends to come down as the contractions kick in. The no breathup/no warmup approach suggests that although contractions will come earlier, this will help kick in the dive reflex earlier which should bring your heart rate down. Working the body will make the heart rate rise, though I find that whatever thoughts are swimming through your head can also affect heart rate. Slow thoughts, slow heart. As Happy Gilmore demonstrates, find your happy place
Three weeks ago, I had a 64m PB and a terrible technique. My strokes/kicks were uneven (especially the kicks), I was not gliding long as my body was not in a proper position (arms not together at the top, legs flailing around, apart) and I was not weighted correctly. I was doing around 6 strokes per 25m. Our training for the past 3 weeks has been twice weekly with one night going for a max attempt, then the rest of the time playing with different weights, analysing where I was too buoyant (my arse unfortunately), working on technique and finishing with a few surface laps of freestyle and breaststroke. The technique training involved numerous 25m laps doing arms only, legs only, then combining the two and figuring out what was going wrong. The breaststroke was handy as this utilises most of the muscles you use in a no-fins dive, and as Umberto Pelizzari says, swimming greatly improves your "aquaticity". The second session of the week would be a few 50m's with a lengthy break in between, working mainly again on technique and turns/kicking off turns. By the second week I had my stroke down to 4 and could get it to 3 fairly easily. However this is not necessarily the best approach as you burn a bit of O2 in stretching your body more and keeping it in position, and as you are gliding more, you slow down and end up staying longer underwater. My happy medium is about 4 strokes and a small glide.
The correct weight also plays an important role, this determines your glide length and if you are too buoyant you are constantly fighting it to stay down. In fact, I notice if i'm too buoyant I rise in the glide and I have to kick early which has a double whammy effect - i'm losing part of my glide phase because i'm kicking early and i'm angling down to get back to the correct depth, losing a bit of distance here. Good weighting for me is when I kick off the wall, glide, and don't rise to the surface until i've nearly stopped gliding.
At the gym i'll do some light weights/high rep work on my triceps, lats, and leg muscles, with another random muscle thrown in at each session (eg. chest, abs etc).
Doing all this has seen my pb improve by a bit over 50%, though I think the majority of this was from technique.
The week before the record attempt i'm going to do, as we Australians say, buggar all.
Phew! Apologies for the long post, I think I got sidetracked there.
In summary, don't worry too much about your HR during a dive. The body will do what it has to to keep you conscious, you can assist it by maintaining a level of fitness and working on technique.
Hope this helps.
Cheers,
Ben
