You missed a key interval workout in a big training block. As training gets more focused, you start using more two- and three-day blocks to increase overall training stimulus. And often these blocks are arranged in a series, like three two-day blocks separated by two easier days. Each block is dependent on the previous one and impacts the next one, so as you shift your workouts, remember that in the long run, recovery trumps intensity.
Recovery requires time, and you can’t achieve two days’ worth in just one day. It’s better to preserve your scheduled recovery periods than it is to sacrifice recovery for additional intensity. Here’s a real-life example: An athlete had a schedule of hard interval workouts on Wednesday and Thursday (two-day block), easy recovery sessions on Friday/Saturday, and another block on Sunday/Monday. On Friday he learned he had a meeting on Monday that nixed his workout plans, so he moved the interval session to Saturday, making the two-day block Saturday/Sunday.
It didn’t work. By prioritizing intensity over recovery and eliminating one of the two recovery days between his training blocks, he was too fatigued to complete a high-quality workout on Sunday (now the fourth day of intervals in five days). He would have been better off keeping Saturday a relatively easy day and moderately increasing the workload in Sunday’s workout.