Does it help to use a weight belt to increase endurance, or should weight only be added when training strength and power?
—Jason Grubb | Carbondale, CO
The answer to your question lies in the type of climbing that you are training for, and specifically, the type of endurance you need to develop.
The obvious use for weight belts is system training, where you make each move progressively harder each session simply by adding weight in small increments (of say 1 or 2 pounds) at a time.
Endurance training, in contrast to system, or power training, is all about maximizing volume (or number of moves). Clearly, the use of a weight belt would compromise the goal in favor of boosting intensity.
If you are training for a 30-pitch vertical marathon on El Cap, there is no point weighing yourself down so that you can only climb for bursts of two minutes before burning out. In this case, the goal would be to maximize the volume of training at all costs, so go easy and do the longest possible stints. It can be tedious work but you may need to do five or six stints of 30 minutes of climbing to train this type of slow-burn stamina.
That said, a weight belt of 4 or 5 pounds might be just the ticket to prepare you for that unruly big-wall rack, but reduce the difficulty of the climbing so that you can keep going for the required time.
If, on the other hand, you're training for hard single-pitch sport routes at Rifle or the Red River Gorge then you must maintain a potent blend of intensity and volume, and using a weight belt can be a useful tool. You could increase intensity simply by trying harder routes or circuits, but this is the same old method.
The beauty of weight belts is that they can jolt you out of a plateau, but it's important to note that they should be used with caution. If you train with a weight belt routinely (for example, an hour or so every session) then you are running the risk of injury.
Use weight belts occasionally in a strategic and targeted way; for example, for the last three or four consecutive sessions during the final week or two of a power-endurance training phase. This way your body will be ready to cope with the extra strain and you can obtain that final edge to your performance with a lower risk of injury.