Have been running a few years, first on roads before moving into the mountains in the past year. My training is a bit undisciplined, lots of running and hiking around where I live so would be reasonably fit. In recent weeks I'm getting in a 20-30km lsr along a trail at weekends and then maybe a gym session midweek where I usually pound out about an hour on treadmill speeding it up and slowing down, or mix it up with some cycling or rowing.

Joined the gym for 3 months last night so would like to maximise the facilities with a view to improving times on the mountains early next year. Anyone got any good gym programme, maybe some handy YouTube clip with suggestions, or maybe a link to some article? This might sound all very basic, but don't want to waste time on something that is of no use. Thinking of concentrating on core work, so looking at simple stuff like Russian Twists, the Plank etc. Are they directly beneficial for running? Or would I get more benefit from maybe upping time on the machines, the bicycles and rowing etc.?