The root from which knackered derives is a "knacker's yard". The following definition was yanked from the web:
The definition of 'knacker's yard' is common to the Slaughterhouses Act 1974, the Meat (Sterilisation and Staining) Regulations 1982 and the Food Act 1984. According to these, a 'knacker's yard' was 'any premises used in connection with the business of slaughtering, flaying or cutting up animals whose flesh is not intended for human consumption'.
source:
http://www.bseinquiry.gov.uk/
Obviously, when one is fit only for the knacker's yard, there isn't much vitality left...
Charlie "philology isn't the study of old Phil Wood hubs"
Young
Honeybrook, PA
> Knackered means tired, shot, dead, otherwise not in good
> shape. You can be knackered (really tired) and parts can
> similarly tired or worn-out.
> (from Cambridge Advanced Learner's Dictionary)
> knacker verb [T] UK SLANG
> 1 to break something:
> Careful or you'll knacker the gears!
>
> 2 to make someone very tired:
> Don't go too fast or you'll knacker yourself in the first
> hour.
> knackered adjective UK SLANG
> 1 broken or too old to use:
> My bike's knackered.
>
> 2 [after verb] very tired:
> I'm too knackered to go out this evening.
>
> David Bilenkey
> Ottawa, Ontario, Canada
>
>
> > -----Original Message-----
> > From: classicrendezvous-bounces@bikelist.org
> > [mailto:classicrendezvous-bounces@bikelist.org]On Behalf
> > Of Tom Sanders Sent: June 11, 2003 12:04 PM
> > To: pariscycles@yahoo.co.uk
> > Cc: classicrendezvous@bikelist.org
> > Subject: [CR]Fag Paper clearance
> >
> >
> > Look forward to seeing you over here, Mick. Thanks for
> > the excellent explanation. Perhaps you can also tell
> > us about "Knackered" parts, too! Any other of these
> > type of things we should know about?
> > Tom Sanders
> > Lansing, Mi