Those heavy-breathing, sweaty, heart-pumping moments in a workout are challenging, but they're also so rewarding — there's no denying how hard your body is working. Sprinter lunges always get me to ...

(a) Stand with one foot on a towel. Bracing your core, slide that foot back into a low lunge. Go on - lower than that. (b) Explode back up by pushing through the heel of the stationary leg and raise ...