I know some people despise cardio. I actually have NEVER been a cardio hater and I believe this little tip of advice is why….
I change something every time I do cardio. If that means machines, intensity, time, mileage etc., I am huge on Interval training… or HIIT style training. Go HARD for 30 seconds to a minute then allow time for your heart to recover. You can do that on anything in the gym. Just add speed, incline, resistance etc. Even if you're an outdoor runner. Time yourself to pick up the pace for 'X' amount of minutes then allow some recovery time.
Doing this I am never bored. It's always new, fun and challenging in a new way. That's why I am that crazy girl who says, 'I LOVE CARDIO'.
Make this small change and it alone will boost your metabolism back into gear.