Lifting too much weight
There’s no shame in wanting to lift as much weight as humanly possible, but it won’t do you much good if you get hurt, says Tom Holland, MS, CSCS, exercise physiologist and author of The 12-Week Triathlete  (Fair Winds Press, 2011). “Being attached to the numbers is more of a workout for your ego than anything else.”
Fix it: Instead of busting out the calculator app on your iPhone to add up all that poundage, ease up and focus on the quality of the movement instead, Holland suggests. “Keep in mind that gains happen during the eccentric (stretch) portion of the lift—plus you’ll be less likely to injure yourself.” Use a two-second up (concentric) and five-second down/stretch (eccentric) focus so you control the weight the entire way—and use a weight that works within this range for you.