Instruments of torture?

I have read recently that a runner's greatest asset (sic) is a strong behind.  Yes, a tough butt makes for a better runner.  So, with this knowledge in hand I have decided to widen my fitness horizons and join a 'Body Blast' class at my local Y.  I'm ready to sculpt, lift, strengthen and otherwise torture my behind.  Pictured above is a deceitfully cheery colored array of fitness tools.  It was not until our hour class closed, that I realized  these should more accurately be described as 'instruments of torture'.  I repeatedly lifted my 6 pound hand weights over and under, up and down, in and out....  I bobbed up and down grunting through hundreds (yes, you've read that correctly, hundreds!) of abdominal crunches while balancing my wobbly body on a large ball.  I wrapped my feet with obnoxiously slippery resistance bands and kicked 'to the beat' of a girls rock band screaming "we are strong!".  All of these exercises were making me feel less than "strong".  But none of these exercises compared to the partnered squats I conquered today.  After balancing a ball between my back and friend's, we squatted up and down courageously.  After warming our quads up with several of these lovely moves, we performed heel rises while in squatting position.  Ouch!  My poor legs and butt burned worse than hot sauce, seriously.   But, in the journey of marathon training, a tough tushy is must!