Loose/release the shackles

To loose or release the shackles, or to say 'the shackles have come off' are figurative uses of shackle, which means that one is free, and can cut loose, express oneself, often in a sporting context. This figurative usage dates from 1738, according to the OED, but it gives an earlier date of 1641 for its usage in 'to die fighting rather than live in shackles.' A shackle, of course, is an Old English word for a circular fetter, usually made of iron, that fits around the neck, ankles, or wrists (or all three in some instances). Shackles are usually attached to chains, and were, and still are, used to restrain captives or prisoners. This usage dates from before the 12th century. Again, according to the OED, to shackle or hobble a horse dates from 1814.