Tonight I did 30 minutes on the bike, getting my heart rate up to 182 at one point - up around 95% of my max! As you can see from the graph, I generally like to keep my pulse around 70% of max, but it's crucial for me to really push myself a couple times in a half-hour workout. I learned the importance of pushing hard during my Body for Life workouts, when I had to hit an intensity level of 9/10 for several minutes, and 10/10 for at least a minute, to achieve the best results and the longest afterburn (body burning calories after I get off the bike). Any time I get my pulse over 180, my energy levels go through the roof for days or weeks afterward. It's awesome.
I'm already feeling very energetic -- it's like a shot of caffeine but without the jitters!