Lark is a great free app that makes use of Health app using the HealthKit API. Lark uses the lower power sensors in the iPhone 5s, iPhone 6, and iPhone 6 Plus to track your activity, eating and sleep data without draining your battery. No extra sensors are required, but it does require you to have your iPhone on you every time you move to collect data. Something that I am not too good at.
You can authorize Lark to share its data with Health app. This will allow you to use Health app’s simple and informative graphs and charts to analyze the health and fitness data gathered by Lark.
Heart Rate Monitor is exactly what one would expect from a heart rate monitor app. It makes it easy check your heart rate by placing your finger on the rear camera lens or aiming the front facing camera at your face from about 15-20 cm away. I used my finger on the rear camera primarily during my tests. I found this mode to be easier to use and it seemed to provide more consistent test results. It was also less awkward then staring at my face in the gym while waiting for my pulse to be taken.