Anyone who's trained with me, done my classes or been in ear shot whilst I'm doing either would have heard me speak continually of intensity & efforts.
Changes in body composition & fitness come from a reaction to stress. Eg. I attempt to lift a heavy weight for a desired number of reps, I push as hard as I can but still struggle to perform the desired work load (weight x reps) so the human body, being the highly adaptable machine it is, grows me some muscles to better deal with this stress in future.
Another example is I want to run a certain distance at a certain pace, however my body can't perform to the desired level(this time) so I push as hard as I can to try & get through, this results in the body finding a way to store more oxygen in your blood increasing our cardio fitness, which eventually leads to greater performance output(longer distances, faster speeds etc) this is a very simplistic explanation of the process as theres other factors involved, but the point being effort/intensity is going to get results.
Comfort Zone training will not do this, ever! I'm not calling anyone out here & never would, knowing that only 8-12% of the population are involved in any kind of regular physical activity, anyone in this modern society prepared to take the time out of their day to go to the gym already has my admiration & respect, but you're only half way there, you need to make your time count otherwise why are you training in the first place?
Do you ever try to find a way to make exercises you don't like easier? Make excuses or fake an injury to avoid certain exercises you don't like? Skip workouts & classes regularly? If this is you, you're selling your results short & will more than likely just go through the motions you're comfortable with, without any progression which will keep you looking the same as long as this attitude persists.
Intensity is a mindset, it gives us the drive & motivation to push through barriers, giving us the desired results which in turn lead to more motivation to get even more positive results, these types get the job done, they turn up consistently, don't make excuses & try to get a bit better at something everytime they're in the gym. Be this person!
Happy Training & as always if you have any questions pertaining to this article or anything else for that matter, feel free to hit me up in the gym, you know I love a chat!