Below are some terms you may come across while using the app:

  • accelerometer: an instrument for measuring acceleration or for detecting and measuring vibrations*
  • aerobic: occurring only in the presence of oxygen
  • anaerobic: occurring, or existing, in the absence of free oxygen
  • body fat percentage (BFP): fat mass expressed as a percentage of total body mass
  • body mass index (BMI): a measure of body fat that is the ratio of the weight of the body in kilograms to the square of its height in meters*
  • cardiac: pertaining to the heart**
  • cardiorespiratory: of or relating to the heart and the respiratory system*
  • cardiovascular: relating to the heart and the blood vessels or the circulation**
  • heart rate:
    • heart rate reserve: the difference, expressed in beats per minute, between your resting heart rate and your maximum heart rate
    • maximum heart rate (age-related): the age-related number of beats per minute of the heart when working at its maximum*
  • kilocalorie (kcal): a measuring unit of energy, often used interchangeably with “calorie”
  • mass:
    • fat mass: the portion of the human body that is composed strictly of fat***
    • lean body mass: body mass, primarily of muscle and bone, devoid of storage fat, also known as fat-free mass***
  • percentile: a measure used in statistics indicating the value below which a given percentage of observations in a group of observations fall (for example, the 20th percentile is the value (or score) below which 20% of the observations may be found)ˣ
  • PPG: photoplethysmography, a simple and low-cost optical technique that can be used to detect blood volume changes - often used non-invasively to make measurements at the skin surface⁺
  • proprioception: a sense or perception, usually at a subconscious level, of the movements and position of the body and especially its limbs, independent of vision**
  • RR intervals: typically refers to the intervals between successive pulse peaks in an electrocardiogram (ECG)

A note on RR intervals and PPG used by LifeQ

LifeQ uses a PPG sensor instead of a traditional ECG. Therefore, in this context, RR intervals really refer to time delay between successive pulse peaks in the PPG signal.

See the image below:

Image: JMIR Publications (

Additional sources

*Merriam-Webster Online Dictionary (

**MediLexicon (

***Medical Dictionary for the Health Professions and Nursing (2012)

⁺PubMed (

ˣWikipedia (