The CDC use qualitative, not quantitative definitions.
- The talk test is a simple way to measure relative intensity. In general, if you’re doing moderate-intensity activity, you can talk but not sing during the activity.
- Walking briskly (3 miles per hour or faster, but not race-walking)
- Water aerobics
- Bicycling slower than 10 miles per hour on primarily flat or level terrain without hills
- Tennis (doubles)
- Ballroom dancing
- General gardening
- In general, if you’re doing vigorous-intensity activity, you will not be able to say more than a few words without pausing for a breath.
- Race walking, jogging, or running
- Swimming laps
- Tennis (singles)
- Aerobic dancing
- Bicycling 10 miles per hour or faster that may include hills
- Jumping rope
- Heavy gardening (continuous digging or hoeing)
- Hiking uphill or with a heavy backpack
some exercises that are moderate to me, are totally vigorous and exhausting to my friends and vice versa.
That's to be expected. The same exercise and the same level will have a different intensity to different individuals. E.g. A person with short legs will find it more difficult to match walking pace with a person with longer legs. An out of shape person will struggle to run at the same pace as a fitter person.
In my own personal life, I've used FitBit and Garmin devices to monitor my heart rate, however the CDC does not appear to make these associations with heartrate, therefore it is near impossible for me to know what the actual recommendations would be for me specifically.
You can use heart rate to measure intensity, but it will vary from person to person, and so is usually measured as a percentage of one's estimated maximum heart rate. E.g. The American Heart Association recommends heart rate targets of 50-70% of maximum heart rate for moderate intensity exercise, or 70-85% of maximum for vigorous intensity.
They do suggest trying to talk or sing and using that as a guideline, but I can't sing even if I'm just sitting so that's not useful to me.
The sing test is only for differentiating moderate intensity physical activity from activity that is too low intensity to be counted. It is not for differentiating between moderate and vigorous intensity physical activity, which is apparently what you are trying to do. If you're unable to say more than a few words without pausing for a breath then it is vigorous. If you could, with some difficulty, hold a conversation, it is moderate.