For example, when your training plan assigns you a certain pace for a workout, it's simply an estimation of how fast you need to run to elicit a certain effort based on your abilities, fatigue levels and progression in the training plan. When the body isn't operating on all cylinders, the assigned pace is no longer a correct estimation of the effort level needed to accomplish the workout. By slowing the pace, you give yourself a chance to run within the physiological parameters of the workout, and still get some benefit.
On the other hand, the rest and interval length are usually a factor of the race distance or the physiological system you're working on. For example, a threshold interval workout like 4 x 1 mile at 10K pace with a short, one-minute rest, allows you to work on your lactate threshold. Lengthening the rest allows you to recover fully, and thus takes you out of the primary lactate threshold training zone. As a consequence, you diminish the benefits of the workout. If you had simply slowed the pace, you'd still be in your lactate threshold zone, just not running as fast as you would like.
Stopping the Workout
Some days, everything feels off. How do you know the difference between having a bad day, and feeling the general training fatigue described above? If you feel sick to your stomach, you're getting headaches, or you're running more than 30 seconds slower than your goal pace for the workout, it's a bad day. Stop the run, and jog back slowly to the car or house.
It's definitely not an easy mental task for a runner to stop a workout, but sometimes it's actually the best way to move forward and get faster. When you're struggling this much to hit times for a workout, it's better to regroup, put the workout behind you, and just move forward with the training.
You need to have the courage and mental toughness to realize that a day off and missing one workout isn't going to ruin your entire training segment.
This is easy advice to dispense in an article, but it's difficult for many runners to swallow. However, the legendary coach Alberto Salazar sums it up perfectly:"You've got to have the mental toughness and confidence in yourself where you believe that you can take those days off, and you can recover and run great. A lot of what we see in athletes [who] just train all the time and never give themselves adequate recovery is often portrayed as toughness. What I've realized over the years is it really is a weakness. It's an insecurity that you're not good enough to recover like other athletes: I'm not good enough to do that; I need to keep training; I can't take time off; I can't take easy days."
It's important that you do not try to make up a workout the next day.
This throws off the balance of the training program, and could lead to injury or overtraining. This is the number one training mistake I see new runners commit.
Instead, evaluate why you had a bad workout—was it the heat? Stressful day at work or with the family? Went too hard on your easy day? Look for an answer and try to improve that problem for the next workout, then put the bad day behind you. This can be difficult mentally, but in the long term, it will keep you more consistent.
Bad runs happen to the best of runners, and it's bound to happen once or twice in every runner's training cycle. However, if you adjust the pace on the rough days and stop the workout on the really bad runs, you can stay consistent and ensure that the off day is merely a blip on the training schedule.race.