Wiktionary
phr. 1 difficult of progress 2 boring, tedious 3 (context of horse racing English) the going is wet and muddy (qualifier: difficult to gallop on)
Usage examples of "heavy going".
The Kushans, encumbered with armor and gear, had made heavy going of the march.
The royal nephews made heavy going of the effort, despite the assistance of several kshatriya.
The hairy-fetlocked animal made heavy going, but easier than with Loial on its back.
The men in the lead, breaking trail, had heavy going in the deep fluffy snow.
I should have been condemned as heavy going, would-be clever, even unpleasant or dangerous.
The bitter cold and the heavy going had nearly knocked the wind out of me, and I could feel the horse's side ticking like a clock under my hand.
Fired and disgruntled employees received an especially heavy going over.
The snow and heavy going had deprived his own people of any sort of formation, as well, and what had been intended as a nice, neat ambush turned into an ugly, sprawling melee.
The heavy going against the flood of noontime traffic did nothing to ease his spirits.
The stuff looked to be pretty heavy going, too, with many pages of closely written script.