What is the maximum heart rate during exercise?

The classic rule of thumb for maximum heart rate is 220 minus age, which gives 190 bpm at 30. It was never derived from a proper study and is off by 10 bpm or more for many people. A 2001 meta-analysis fitted 208 minus 0.7 times age instead. Training zones are usually set at 50 to 70% of maximum for moderate effort and 70 to 85% for vigorous.

Source: Tanaka, Monahan & Seals (2001), Journal of the American College of Cardiology