Max HR is very individual, any chart will be unreliable, it is better to use a tested value. Max HR generally decreases with age, and it does not increase with increased fitness, so it doesn't matter if you are in shape or not. One of my strongest friends has a max hr about 30 bpm below my own, but he can ride circles around me.
When trying to find your own personal max HR, use the highest number you can achieve when you are working absolutely as hard as you can. You should be about to pass out or throw up, and you won't be able to sustain your max for very long. You won't just be breathing heavy, you'll be gasping desperately.
Test when you are well rested, not after several days of training.
You might want to check with a doctor to make sure it's safe to exert yourself that hard. Or just figure your max HR is a few bpm higher than what you're seeing when you're working 'pretty hard' and call that good enough to figure your zones.