A lot of this answer has to do with your current level of fitness. If you are new to exercise, then it is likely that you need to spend some time working on your “base”. You need to make sure your engine is primed and ready to access all the energy storage in your body. This is done by starting out the first month or so at lower intensities and then building onto that with more challenging workloads. It might seem too easy at first but that does not make it a bad thing. One, it gets you into a routine. Two, it’s a way to start out successfully. Three, it gives your body a chance to adapt to the work it is being asked to do. This goes in line with strength training or aerobic training. You don’t just go try to pick up the heaviest weights right off the bat, even if that’s your goal. You start with something doable, get stronger, and build your way up to those heavy weights. It’s no fun to get injured and it sets training back, respect your body’s limits and it should adapt steadily.
Strength training is considered high intensity exercise. I don’t really think it should be monitored for heart rate. It is a great way to increase muscle mass and thus increase your resting metabolic rate. This means that it is a great way to lose weight and keep it off, and in my mind one of the better ways to do it! (eating vegetables, less or no meat or dairy being my other choices but that is a personal preference for myself) Aerobic training is great for your cardiovascular health and regulation of your body’s systems. And of course, it does burn calories too. When using aerobic work as a way to kickstart your metabolism, you can do gauge intensity the easy way. This is the talk test (can I?) or using a perceived exertion scale which is based on 1-10 (1 being rest, 10 being I’m going to collapse). Being around the 6 often times correlates to a person’s actual 60% of their heart rate max. Same goes for 7, 8, etc. But if you want to be more precise about it or just have the personality for it, you can use some common guidelines for aerobic exercise.
First thing to do is find your Max Heart rate. This is just a guideline of course (and can be affected by some medications so check with your doctor) but it a place to start. Take 220 - age to find your estimated max rate. It is advised that you should not go over this number during aerobic training but again, it is just a ballpark. Max heart rate does depend on personal factors (training history, medications, etc) as well. After you find this number, multiply it by 60 and 70%.
220-50= 170 beats per minute (bpm) max heart rate
170 x .6 = 102 bpm, 170 x .7 = 119 bpm If you are quite deconditioned, try 2-6 weeks of walking or biking in this heart rate range. After that, increase the intensity from 70-85% to up the total amount of calories spent, you can always monitor by estimating how hard you are working 1-10. After 6-8 weeks, either keep it there or consider adding bursts to your aerobic routine. Per the ACSM www.acsm.org, recommendations include:
Adults should get at least 150 minutes of moderate-intensity exercise per week. Exercise recommendations can be met through 30-60 minutes of moderate-intensity exercise (five days per week) or 20-60 minutes of vigorous-intensity exercise (three days per week)