HIIT training

You need to work at 80%+ of your max heart rate for it to count as ‘high-intensity’. Go all out, rest, then repeat

LISS training

65%: The percentage of your max heart rateto aim for during LISS to reach the fat-burning zone.

Both are great and very useful. HIIT can be seen as exercise that stresses the body and isn't necessary be performed everyday; as it may lead to overtraining. Overtraining can have a counter effect, instead of enabling to keep calories down in a fat loss phase or expending to much energy while building muscle.

LISS is at a lower intensity so can be performed everyday. It is good for active recovery on days where you're not performing any resistance training and also helps maintain muscle while still being able to burn fat.

It would be advisable for beginners to use LISS as a starting point then build up to HIIT training alongside resistance sessions. For the average person, two days of LISS and a shorter HIIT combined in a resistance session makes a good balance. LISS cardio is more effective after resistance training.

Lastly, remember, rest days are key! As much as reaching a certain goal might be on your mind and you want to be summer ready it doesn't have to be rushed as training should always be sustainable. Always ensuring your body gets enough rest and sleep is essential. This is important for muscle growth and/ or weight loss.