Weight lifting with legs?

Has anyone done heavy weight training with free weight on their legs. mainly heavy squats, i go to the gym a lot but skip the leg work most of the time, never anything heavy, upper body i do heavy weight.

i wondering if heavy leg work will slow me down or mess up my stride, i feel i could benefit from stronger quads and hamstrings, but i would hate to be slowed down by it.

My personal experience is that heavy leg training makes for heavy, dead legs when I go to do my runs.

I do weight train my legs twice per week. 15-20 reps of squats (65% of max), lunges, hamstring ball curls, step ups, and single leg squats.

Otherwise, I build leg strength through hill running and track workouts.

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65 percent of max seems pretty good for squats, im going to give it try, i have a bunch of 5ks coming up so that will be a good speed test, but im putting a lot of miles in because i want to run as many marathons as possible starting in november.

i dont see how it can hurt, thanks for the advice!

10 miles on the bike, tri coming up in a couple weeks...