SophieLion different heart rate zones build different types of fitness, so there isn’t really an ideal number to aim for.
This is a little simplistic as there are more than 2 heart rate zones, but roughly 60-70% of maximum heart rate is good for building base level fitness, strengthening your heart and making your body more efficient at burning fat. Anything over that increases your anaerobic capacity, i.e. your bodies ability to function when it starts to run out of oxygen. That’s what you need to aim for if you want to get better at activities that require shorter bursts of energy, such as sprinting.
Most of the training program I’m following is made up of long, fairly slow paced sessions, with only 1-2 shorter sessions where the focus is on anaerobic training, e.g. 4x5 minutes sprint training. That’s supposed to be a good mix as trying to build anaerobic fitness without having a good level of aerobic fitness is apparently a bit pointless.
That’s my long winded way of saying, aim for a mix of heart rate zones! 😂