On Lifehacker, we often write about interval training, to which you alternate exercises and bring your cardiovascular system to the limit. We also write about running. But there are excessive loads and insufficient loads. Listening to your ego when "enough is enough" or when "enough is enough" means constantly misleading yourself. You need some measure of sufficiency and progress of your workouts.
For me, the main measure is the number of beats per minute of my heart under various loads. To do this, I use the Wahoo Fitness Blue HR cardio sensor bought half a year ago together with the iPhone 4S and I am a satisfied user.
It is worth saying that I started my regular sports activities for the development of not muscles and wound kilometers — I don't give a damn about all this. The main goal is to give the circulatory system its former strength and flexibility. Here is an example of such tracking. When I started running, at 6 min/km I had 165-170 beats per minute, I was suffocating and literally "dying" at extremely short distances. Today it is ≈140 beats per minute at the same pace. This is my goal and I clearly measure it with this device.
The main reason for buying it was that for it to work with the phone, you don't need to stick anything into the phone. There are a lot of sensors around that can be connected to the phone, but this requires an additional expander/adapter. Because of this, it only works on the bluetooth module of the latest gadgets from Apple: iPhone 4S, iPhone 5, the NEW iPod Nano (8th generation), the NEW iPad (3rd and 4th generations) and iPad Mini. Don't be confused by the fact that it is connected to tablets :) People not only run with cardio sensors, but also do interval training at home, looking at the indicators on the tablet, which are displayed by one of hundreds of programs. Fat burning zone, aerobatic zone, etc. By the way, I was able to connect the sensor with the HTC One X phone running Android 4.1 and the RunKeeper program on it.
Wahoo Fitness Blue HR is worn on the chest. For women, it will not cause discomfort due to the habit of wearing bras, but I had to get used to new sensations. The sensor does not fall or slide while running. Its tape is covered with rubber strips that reliably "stick" to the body covered with the slightest nabout volume.
The sensor is equipped with a removable battery that can be easily replaced. For half a year, she has never sat down. So you don't have to think about her.
To understand if you need a heart sensor, you just need to be honest with yourself — what you are afraid of and what you are striving for, and also undergo a basic diagnosis of your heart. And also, running and practicing with such a gadget allows you to achieve your goals and track them in a timely manner. Remember — what is not measured is simply not there.