He was apparently somewhat disabled, and was once described by a contemporary as "walking with a hirple" (i.e., a limp. Scots word originally used in 1450 by the Scots poet Robert Henryson, perhaps derived from the Old Norse word herpast "suffer from cramps").This, however, is somewhat at odds with the tradition that it was Iain Lom who walked from Brae Lochaber to Cille Chumein (now renamed Fort Augustus) to warn Montrose of the arrival of Argyll at Inverlochy and then guided the Jacobite army up Glen Turret and over the snow-covered hills into Glen Roy to surprise Argyll at Inverlochy on 2 February 1645. John Buchan described this as "that flank march which is one of the great exploits in the history of British arms". Montrose's own son died a month later as a result of this desperate march. It is believed that Iain Lom accidentally killed his own brother at a skirmish on Loch Tayside (Sròn a’ Chlachain), a battle in which his father was also killed. Thereafter he refused to draw a sword. When offered one by Alasdair Mac Colla at Inverlochy he declined saying "Cathaichibh sibhse 's innse mise" (You fight and I'll narrate). His long narrative poem"Là Inbhir Lochaidh" (Day of Inverlochy) is regarded as one of the treasures of the Gaelic language and an important historical source regarding the battle.