Can I work out beyond 80% of my max heart rate?

220-41 (my age) = 179. 80% of 179 is approximately 142. However, when my heart rate is 142 BMP I don't feel as though I am getting much of a work out. Is it counter-productive to go beyond the 80% mark? I definitely want to improve my cardio-fitness level, and I also want to improve my resting heart-rate (72 BMP). Thanks.