Measurements

Calories burned through activity

Typical range: 0 - 5000 kcal

Minutes of moderate to vigorous activity

Typical range: 0 - 300 min

Calories burned represents total daily energy expenditure (TDEE), comprising basal metabolic rate (BMR), thermic effect of food, and activity energy expenditure. Wearables estimate calories using heart rate, motion, and user demographics (age, weight, height, sex). Accuracy is typically ±15-25% compared to doubly-labeled water or indirect calorimetry. Heart rate-based estimation improves accuracy over accelerometer-only methods. Significant individual variation exists in metabolic efficiency. Calorie data is useful for relative comparisons (yesterday vs. today) rather than absolute values. For weight management, tracking trends over weeks is more meaningful than daily figures. Exercise calories are often overestimated, leading to compensatory overeating. Energy expenditure decreases with weight loss through metabolic adaptation.

Distance traveled

Typical range: 0 - 100 mi

Elevation gain equivalent to floors

Typical range: 0 - 200 floors

Number of steps taken

Typical range: 0 - 50000 steps

Total daily energy expenditure

Typical range: 1200 - 6000 kcal

VO2 max represents maximal oxygen uptake—the maximum rate at which the body can consume oxygen during intense exercise. Expressed in mL/kg/min, it is the gold-standard measure of cardiorespiratory fitness. Average values are 35-40 mL/kg/min for men and 27-31 for women, declining with age. Elite endurance athletes may exceed 70-85 mL/kg/min. Higher VO2 max correlates strongly with reduced all-cause mortality and cardiovascular disease risk. Wearables estimate VO2 max using heart rate response during submaximal exercise, age, and sometimes running pace—accuracy is ±10-15% compared to laboratory testing. Improvements of 10-20% are achievable with consistent aerobic training. Clinical applications include assessing cardiac rehabilitation progress and surgical risk stratification.

Percentage of body mass that is fat

Typical range: 5 - 60 %

Estimated skeletal muscle mass

Typical range: 20 - 200 lbs

Body weight

Typical range: 50 - 500 lbs

Pressure between heartbeats

Typical range: 60 - 120 mmHg

Variation in time between heartbeats (RMSSD)

Typical range: 10 - 150 ms

Pressure when heart beats

Typical range: 90 - 180 mmHg

Blood sugar level

Typical range: 40 - 400 mg/dL

Tracked by 0 sensors.

Tracked by 0 sensors.

Tracked by 0 sensors.

Tracked by 0 sensors.

Tracked by 0 sensors.

Tracked by 0 sensors.

Tracked by 0 sensors.

Tracked by 0 sensors.

Time in deep/slow-wave sleep stage

Typical range: 0 - 4 hrs

Time in light sleep stages

Typical range: 0 - 8 hrs

Time in REM sleep stage

Typical range: 0 - 4 hrs

Total time asleep

Typical range: 0 - 14 hrs

Percentage of time in bed spent asleep

Typical range: 50 - 100 %

Overall sleep quality score

Typical range: 0 - 100 pts

Sleep stages classify sleep into light sleep (N1/N2), deep sleep (N3/slow-wave), and REM (rapid eye movement) sleep. A typical night cycles through stages 4-6 times, with more deep sleep early and more REM later. Deep sleep is critical for physical restoration, immune function, and memory consolidation. REM sleep supports emotional processing, learning, and creativity. Adults should get 1-2 hours of deep sleep and 1.5-2 hours of REM per night. Wearables estimate sleep stages using heart rate variability patterns and movement, but accuracy is limited compared to polysomnography (the clinical gold standard using EEG). Consumer devices may misclassify stages by 20-30%. Trends are more reliable than individual night data. Alcohol, medications, and sleep disorders significantly alter stage distribution.

Energy level estimation

Typical range: 0 - 100 pts

Electrodermal activity (EDA), also known as galvanic skin response (GSR) or skin conductance, measures electrical conductance changes in the skin caused by sweat gland activity. The sympathetic nervous system controls eccrine sweat glands, making EDA a direct window into autonomic arousal states. Skin conductance is measured in microsiemens (μS), with tonic levels (baseline) typically 1-20 μS and phasic responses (event-related) showing rapid increases during stress, emotional arousal, or cognitive load. Wearables detect EDA through electrodes contacting the skin, commonly on the wrist or fingers where eccrine gland density is high. EDA is used for stress detection, emotional state monitoring, sleep quality assessment, and biofeedback applications. Accuracy can be affected by electrode contact quality, skin moisture, ambient temperature, and movement artifacts.

Readiness for physical activity

Typical range: 0 - 100 pts

Estimated stress based on HRV and other metrics

Typical range: 0 - 100 pts

Peripheral oxygen saturation level

Typical range: 90 - 100 %

Beats per minute measured at rest or during activity

Typical range: 40 - 200 bpm

Breaths per minute

Typical range: 8 - 30 brpm

Heart rate measured during periods of rest

Typical range: 40 - 100 bpm

Temperature measured at skin surface

Typical range: 90 - 104 °F