Heart-rate Monitor while lifting weights?

From Men’s Health:

I do intervals and lift weights. Would it be smart to use a heart-rat monitor?

More like brilliant. “Most men (people) don’t know their bodies very well. They think they’re going all out, but they’re not,” says David Jack, general manager at Competitive Athlete Training Zone. “A heart-rate monitor tells you exactly how hard you’re going.” That’s critical whether you’re hammering out intervals or doing strength training. For instance, short intervals are best done at 90% of your Max heart rate and heavy lifts at 60% of your Max, says Jack.