Internal vs External in CMA
I've been told in the past that 'internal' arts are not about strength, but as far as I can tell IMA practitioners who actually do any fighting definitely do train to strengthen their bodies.
I've been told that IMA are about relaxed power and body structure, but as far as I can tell all martial arts that do a good job of teaching how to hit hard teach you to relax (for speed) and to use your bodyweight intelligently (e.g. put your hips into it).
Whilst Tai Chi (and probably other IMAs) have a slow form, people who want to use them to fight certainly don't do most of the other drills or sparring in slow motion.
I've read that Tim Cartmell of Shenwu (a BJJ blackbelt who teaches a blend of chinese IMA for standup) considers BJJ to be an IMA. Perhaps boxing is an IMA too ? (All that training to weave, bob and slip rather than attempt to 'block' incoming blows, generating power through relaxed and coordinated bodymechanics rather than 'arm punching').
So given that chinese IMAs, when used for fighting, seem to involve sparring and strength/stamina training as much as so-called 'external' arts used for fighting, what's the real difference between Internal and External types of CMA ?
Is it that IMAs don't seem to go in for the 'Iron Body' type conditioning exercises which increase bone density which I've heard of other kung fu styles doing ? (I may be wrong about this, I'm a Tai Chi newb and may have just not seen it yet).
Your thoughts appreciated.