I think long distance running is a bad thing to do. There’s little point losing leg mass if your strength goes as well. Why dont you carry on squatting and deadlifting, but do only 3-5reps with 3-5 minutes of rest. ie train for pure strength, not size
This will make him bigger. You can see this with most powerlifters. Not too many are small yet strong. Most are big and strong. Strength comes with size. They are related.
OP- I would start eating a normal diet of 3 meals a day with lots of medium - long distance running. Just keep the upper body work up and the best peri & post workout nutrition you can to keep most of your upper body mass.
To those that don’t know anything about rock climbing, it’s mostly upper body work. Lots of mass on the legs will mean there’s more weight for the upper body to support. Most good climbers have massive lats and no legs at all. This is a specific adaptation to the demands of their sport. [/quote]
Your not thinking straight. Eric Cressey is extremely strong yet weighs about 165 i think. Pavel Tsatsouline is very strong yet is not heavily muscled. If you wanna get big you need to get stronger, but you can can very strong without getting bigger.
One or two sets of squats with 3-5 reps and long rests is not going to build any significant muscle in most people…the volume is not there. However, that rep range and low volume should allow strength to be maintained