I'm a middle distance runner (8 and 15) and regularly incorporate the gym into my routine twice a week, this consists of core - crunches, sit ups, weighted twists, dead bugs. Arms - pull ups, push ups etc and legs - squats, deadlines, calf raises, and leg press. Usually with about 3x8 reps for all exercises. I also do a fair amount of mileage, running almost everyday, be it track or road/country. What I want to know is, physiology is there any benefit to doing a run of half an hour or 40 minutes steady before hitting the gym straight after, and with other situations, would there be point in doing a threshold run for 20-30 minutes before hitting the gym? This winter season my coach proposes a workout like this: 10x1k at 5k of quicker pace then straight indoors to do circuits which involves body weight, weights and core exercises. I am aware there are adaptation made for specific things you do, so if you do an aerobic run straight before the gym what adaptation are you gaining? Is it bad to mix up different energy systems right away? Would it be better to wait a few hours before going to the gym? Any insight physiologically or opinions welcome, would love to know more. Thanks!