Working out in gym vs running outside

[newbie123]

Would exercise be more effecient in a gym vs jogging outdoors? Since in a gym there's air conditioning and exercising seems so much easier compared with the outdoor heat in the summer. In the gym I ran 4 miles on the treadmill and didnt feel that tired, while whenever I go running outside I get tired after maybe 1 mile and Im sweating all over. Also, when you work out in a cooler environment, your body is suppose to burn more fat right?

Also another question I have is that....as one gets more fit...does it require significantly more exercise to burn the same amount of calories? Since the amount of calories used up by the body is measured by respiration rate. A more fit person would not breathe as hard as a out-of-shape person.

[newbie123]

any advice would be appreciated

[Naxis]

It is more work on the body to run on solid ground, but it's not a HUGE difference from running on a treadmill. It's also harder and even dangerous to run to long outside in the heat in the middle of the summer. So feel free to stay in the gym.
And metabolism isn't necessarily tied to respiration. The more one weighs, the more calories they burn. But someone who is more fit and has more muscle mass has a higher metabolism and will burn more calories all day than someone of the same weight with less muscle.