Same exercise every night should you alternate?

I've been told by numerous trainers that you have to shake up your routines so that you continue to see results. Your body adapts to doing the same exercise over and over again. The last trainer I had said to do no more than two weeks of the same cardio - then switch it up for another two weeks and just keeping switching every two weeks. If you really love the treadmill, switch it up - do some intervals - a couple of minutes until you feel like you just can't go on, then recover and repeat. You want to keep shocking your system so it stays on guard.

The answer is yes, you should definitely alternate. It is your body's job to adapt to what you are putting it through. The first time you run one mile, your body says, "what the crap?". But it makes adjustments in case you do that again. Each time you run, your body makes those small changes so it's easier each time you do it. By doing the same thing consistently, your body adapts and will take less energy (calorie burn) to do the same exercise. You should alternate intensity and vary your workouts to constantly keep your body guessing without giving it the chance to adapt.

Your body does adapt, but you don't necessarily need to change the exercise, you need to increase speed and/or duration and/or intensity.

Exactly^

If you do the same exercise, at the same intensity, for the same amount of time: then you will eventually plateau and stop making any gains. You need to keep pushing yourself. So, try going faster, or doing intervals, or shaking things up as you said.