I understand the importance of getting pumped as part of your warm-up for onsighting, but what is the best way to warm up?
First, you are right about the importance of getting pumped in your warm-up. The classic mistake is to listen to your natural instinct to save yourself by jumping from an easy warm-up route onto your target onsight for the day. The effect is a “flash pump,” which comes on like an express train and can end your day. If you get moderately pumped first in a controlled and strategic way and then rest, the pump you receive on your target onsight is much easier to control. You will also recruit more muscle fibers and prepare yourself for harder moves, as well as summoning the technique and mindset for the battle. However, getting the formula right for this process is one of the greatest tactical challenges in sport climbing. It is indeed too simple to talk about a primary pump when you really want a primary, a secondary and tertiary pump. For example, your first warm-up route should be so easy that it does not get you pumped at all. Your second warm-up route should get you 30 percent pumped, your third route should get you 60 percent pumped and your final route before your target onsight should take you as close as possible, but not past, the point of peak fatigue. Note that this final warm-up route should induce a higher level of fatigue than the average climber usually dares to allow. You often hear climbers trying to convince themselves that they are not fit enough to warm up in this manner, but this is usually bunk. This strategy (or a version of it) is essential for all climbers, regardless of the grade they climb or their state of fitness. What should vary according to current fitness levels is the number of warm-up routes. For example, if you are feeling very fit then do a total of four or five warm-up routes with a couple at 60 percent pump, whereas if you are feeling less fit then do three, but never any less for sport climbing.
The greatest skill here is to judge the exact grade of your final warm-up route. If you overcook it you may not recover sufficiently but if you underdo it your body won’t be sufficiently prepared for the rigors of your target onsight. A rule of thumb if you are feeling fairly fit is to go one grade less than your target onsight. Shave a grade off both these figures if you are feeling unfit.
The next skill is deciding how long to rest afterward. No matter how long you rest, you are still unlikely to be able to clear the pump completely, but don’t allow this to psyche you out. Even if you do set out with the traces of a slight pump, you will find it easier to manage than setting out fresh and encountering a flash pump. The key is to spot the point when lactic acid levels are no longer lowering and to go before you cool down too much.
A final point regarding the exact sequencing of warm-up routes is that high-level climbers will need to skip grades because they have further to climb up the pyramid. For example, a classic pyramid sequence for someone who is attempting a 5.12b onsight might be a 5.10c > 5.11a > 5.11c > 5.12a before trying the 5.12b. However, someone attempting to onsight a 5.10c might do a 5.6 > 5.8 > 5.9 > 5.10a and then finally the 5.10c. An alternative for both the climbers if they were feeling unfit might be 5.10c > 5.11b > 5.11d for the 5.12b climber and 5.7 > 5.9 > 5.10a for the 5.10c climber. Personally, I believe it is the former combination, with an extra warm-up route, that will produce the best result. Note: choose warm-up routes that mimic your target project. In other words, if your project is 30 moves, pick longer warm-up routes rather than bouldery ones, and vice versa.