I guess this is not new, but i will go ahead nevertheless: I am really improving my apnea time doing my weight reps in a slow motion also in apnea!! you will get a heart pounding but it really worths it. Weight training must fit the type of activity. In martial arts training :martial you also hold your breath and do fast and controled reps (traditionaly is called Mushimi), so when you need to hit hard and fast, your fast twitch muscles fibers are trained to do so in an efficient way. That process is called non lactic anaerobia, which mean very low oxigen is involved. That is exactly the focus when freediving and spearfishing. I have lots of friends running a lot miles and miles on a daily basis and they have little or no effect in improving their apnea time. What i do is to run and from time to time ( each 10 minutes, for 6 times at least) hold my breath and make a sudden and short sprint of 20 to 30 yards, then i slow down the pace to slower the heart rate. This training is really succesfull to me, better than just runs for miles and swim a lot.. i hope it would be useful ..
( this training method also improves your speargun cockin' ability
( this training method also improves your speargun cockin' ability