I am 76 going on 77 years old. I want start dividing my cardio workouts. It could be 3 10 minute, 2 15 Minute or 2 20 Minute sessions. For the shorter workout what should my intensity target be ? My max heart rate is 155 BPM using the new formula. and how long should I rest between sessions?
Even when shortening your cardio into smaller bouts you should continue to aim for 60-70% of your heart rate max. It is not necessary to perform higher intensities when you are splitting 3o minutes into 2 or 3 smaller sections.
Are you splitting the sessions because you are limited on time or are you tired after completing 30 min? If you are able to do the 30 min without rest I would suggest that you try to maintain that level and mix in intervals into your training. That will provide you with small bursts of higher intensity exercise within your current routine.
If you have to split your training take the time that you need between bouts. You can take 30 minutes to 5 hours between bouts and still see benefits.