I want to make sure I understand what you mean by "internal load" and "external load."
Let "Bob" be our fictional runner for the example.
If Bob is performing workouts with a major competition still months away, Bob should be concerned with INTERNAL LOAD. Meaning; say he wanted to perform 5x 1000m repeats at 5000m pace with 3 minutes recovery, but due to extreme heat (>40 Degree Celsius), he was far from his ideal pace. (Bob isn't a good hot weather runner). BUT Bob's EFFORT would equal the proper time in better conditions. Since his internal load was still great, the workout was still effective.
Bob is nearing a major competition. The weather is ideal and very similar on how it will be on race day. Bob should be concern with EXTERNAL LOAD. So, if he decides to do the same workout as before, his 1000m's should be at 5000m pace.. not slower! At this point in training, he needs to see the times unlike a few months ago....
I really hope I understand these two concept. If not, I apologize for the misinterpretation and please correct me. Thank You