Retired veteran Mark Martin (left) was impressed, to say the least, by Kevin Harvick (right) on Sunday.

Revered by many observers as one of the toughest men to ever strap in a NASCAR stock car, Mark Martin isn't all that easily impressed.

But the retired veteran of 882 top series NASCAR starts understandably recognizes toughness when he sees it.

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Such was clearly the case on Sunday when Martin, widely touted for his robust workout regimen and the physical fitness of his slender, 5-foot-6 frame, took to Twitter to sing the praises of Kevin Harvick.

Martin, who watched the Texas Sprint Cup race from afar, was in awe of how the 2014 Sprint Cup champion managed to drive the final 94 laps with only his left hand, while holding his shifter -- which had popped out of gear -- with his right hand.

Here's what Martin, a five-time Sprint Cup Series championship runner-up and winner of 40 Cup races, had to say: