Shaping Hard Sessions
Script
In today’s solo episode we’re tackling the question of how to organize a workout session in light of any high-intensity you plan to do during that session. Should you put intervals at the beginning or at the end, for example. We’ll also apply the same understandings to progression runs.
If the workout session is only for intervals - you warm up, do some intervals, maybe a cool down and you’re done - then the session is the intervals and this is a moot question. But, sometimes intervals are put into a longer run. And the question becomes ‘when should they be done?’.
Critical power declines by the end of a longer session. Recall that critical power is the metabolic rate above which you can not sustain the output by aerobic metabolism at the whole-body level. To put it in simpler terms, we also call it the fatigue threshold. It’s essentially the dividing line between intensity you can sustain for a very long time and that which will bring predictable fatigue…it’s just above what most runners call a maximal steady state or the lactate threshold. Because that value can change during a workout, intervals will require more effort for the intended pace and the intended pace will require more effort if you put them at the end of a long run. If you put high speed intervals into a long run, then you should account for the reduction in capacity that occurs during the run and do them near the beginning.
A quick side-note; strides at the end of a run are not what we’re talking about. Those are so few and so short that they can be done any time.
So, unless the goal is to suffer - which it should never be - those high speed intervals are best completed early in the session when you can perform them well.
It appears you can stave off some of the decline in critical speed/power by ingesting carbohydrate during the run and being sure to start it with plenty of stored glycogen on board.
This is an important discovery for endurance runners in training. It’s not very hard to lower muscle glycogen levels during a run, a moderate 10-mile run can do it. It’s relatively harder to replenish what you’ve used before the next session (see this review). This is all the more reason to put your high-speed intervals early in any session.
What about progression runs? Progression runs are common in the programs of many top runners and they should be in yours as well. If you do a long progression run, say 90-120 minutes, you’ll have a different workout when the progression is based on effort versus pace or power. Again, the research showed no decline in critical power up to 80 minutes of heavy intensity cycling (similar to a marathon pace for a runner) but a 9% decline by 120 minutes. In your training sessions, you should account for that change in metabolic capacity.
Imagine you start at a determined pace and maintain it for 90 minutes. The effort required to maintain that pace is going to progress even without changing pace. That is not a high-quality progression run in my opinion. Rather, progression runs should actually progress in pace or power. The purpose is to train for faster paces not to slog through harder efforts. Basing the progression run on pace or power, you may feel the run become very hard because you are simultaneously increasing the work you’re doing while your maximal sustainable work rate is declining.
It’s also important to point out that progression runs are often compromised if you do a hard or long session the day before. Progression runs should be preceded by relatively easy days to ensure you minimize the impact of the decline in critical power that can occur.
So, you’re generally best off to place high speed intervals, anything near or above critical power, at the beginning of a session and to follow pace (rather than effort) for any long progression runs.
I hope you find this information useful.