Thanks for writing in with your question. Looks like the test was performed very well. Kudos to your partner. It is not easy to get good samples. The early decrease in lactate is due to the aerobic system gradually coming on line. This is why it so important to get a good warm up, not just in testing but in training. The aerobic engine takes a long time to get to firing on all 12 cylinders. You are exactly right about the dip at 160. You are more economical at that pace/HR so the lactate drops.