obobskivich
Headphoneus Supremus
With my limited knowledge, hearing damage relates to a number of different conditions. NIHL can be gradual or acute, includes cilia death and can include tinnitus, nerve damage and PTS; a TTS (acoustic reflex) become permanent. PTS can be quite pernicious because after a TTS event the ear recovers but may not totally recover, resulting in a small PTS which isn't noticed. Subsequent TTS events can result in further, cumulative PTS's to the point of it becoming noticeable but because of the gradual cumulative effect of these small PTS's the damage can be quite severe before it's noticed. There's a lot of concern currently about the use of portable music players by youngsters and a possible epidemic of NIHL.
G
From what I've read (and understood, ha), NIHL is an over-arching symptom/problem that can have different root causes. Like it isn't just limited to music listening - factory workers and miners can also experience it due to loud industrial noises, as can people who regularly use firearms, etc. Its like saying "traumatic brain injury" - there isn't a single cause or prognosis behind it. But as I understand it, the actual "loss of hearing" is due to cochlear damage, not muscle injury, and the threshold shift is an expression/result of over-exposure is basically how one is "getting there" (the TS is like the whiplash, the NIHL is like the TBI from the whiplash) - other maladies, like tinnitus, are (as I understand it) co-present symptoms/syndromes common to hearing damage but not the cause of it (probably am wrong on this). Based on that, as I understand it, the acoustic reflex is not, itself, the "threshold shift" but an involuntary response to the initial over-exposure, which (depending on exposure) may occur prior to the threshold shift (as in, there's probably some safety margin wherein you're exposed to something really loud, and while you're fleeing the area the reflex occurs which helps to protect your hearing, and due to that + leaving the exposure, you either don't experience a threshold shift or it is a very temporary/minor experience, as opposed to permanent damage). What would be more likely as a "muscles are damaged" is an impact on the Acoustic Reflex Threshold (ART) which apparently is mediated by hearing loss, and basically is what its name describes - the threshold at which the reflex actually occurs vs intensity of exposure. Wiki has an article on this (https://en.wikipedia.org/wiki/Acoustic_reflex - it has citations), which also includes another piece of the puzzle that is relevant to the original poster's question - this (the acoustic reflex) is an involuntary muscle response that "cannot be maintained in response to continued stimulation." (That's quoted out of: http://www.tandfonline.com/doi/abs/10.3109/00016486409134576 - which is behind a paywall) If I'm reading that right, that completely deflates the "bodybuilder" idea - it cannot be trained or coached.
Something else that your (and @bigshot's) points made me think of is I remember reading an article a while ago talking about young people partially getting NIHL in higher numbers due to using their portable music players for acoustic masking of background noises they don't want to hear (e.g. turn up their iBuds to block out the noise of a subway) and that the acoustic masking effect somewhat "hides" the over-exposure (which goes to what @bigshot is talking about). I'm not sure if this is absolutely "a thing" but certainly I'd agree with the premise: don't just use higher volume to try and compensate for a lack of legitimate isolation in your headphones/listening environment.