Petal is an ergonomically designed bra insert, resting against the skin of the left breast above the nipple. Petal quietly and unobtrusively captures data while it is worn and features a sensor suite that includes a three-axis accelerometer— a tiny motion sensor that records acceleration, movement, and the body's angular sway many times a second. Petal's advanced algorithms translate this data into meaningful, everyday measures of how a person walks — step cadence, walking speed, and step variability. 

Petal's position on the chest brings several practical advantages over the wrist, finger, or waist placements used by many other wearables. A sensor on the wrist or finger, by contrast, mostly measures what the hands and arms are doing. Your hands may be busy carrying bags, holding a handrail, gesturing, or being tucked into your pockets. All of that movement is unrelated to walking and has to be filtered from the data. In contrast, the upper body stays relatively free of excess movement. Petal’s chest placement provides a stable and repeatable frame of reference and more accurate metrics.

The Three Measures

Step cadence is the tempo of walking — how many steps a person takes each minute. Two people can move at the same speed while one takes longer, slower strides and the other shorter, quicker ones; cadence captures that difference in tempo.

Walking speed is how fast a person walks at their own comfortable, everyday pace. It reflects ordinary, relaxed walking rather than a person's top speed.

Step variability describes how even a person's walking is from one step to the next. Each step takes a slightly different amount of time; this measure captures how much that timing varies. A steadier, more metronome-like rhythm is an indicator of strength and balance, while  more variability may reflect recovery from an injury and an elevated level of fall risk .

Why These Measures Matter

These three metrics can be repeatedly measured during your daily routine , and combined give a clear picture of how smoothly and comfortably a person moves through daily life — how fast, how far per step, and how evenly they walk. Published research helps explain why each one is worth following.

Walking speed as an everyday marker. Self-selected walking speed is often described as a kind of "vital sign" of movement, reflecting overall functional capacity, lower-body power, and cardiovascular efficiency (Studenski et al., 2011). Across adulthood it tends to stay relatively stable through the younger and middle years — highest through the forties and fifties in the reference data for women — and then eases gently downward in the later decades as muscle power gradually shifts (Rössler et al., 2024).

Step variability as a window on steadiness. Fluctuations in step-to-step timing reflect how automatically and smoothly the body controls walking. A low, even rhythm is a sign of steady balance and control, whereas a more variable rhythm reflects the small moment-to-moment adjustments the body makes to stay sure-footed. Younger and mid-life women typically show very even walking, and greater variability tends to emerge from midlife onward — often appearing as an early sign of changing balance before any noticeable change in pace. Research has associated higher stride-to-stride variability with reduced balance control and elevated fall risk in older adults (Verghese et al., 2009).

Step cadence as a measure of rhythm and effort. Cadence captures the rhythm and intensity of walking, and it tracks closely with physical-activity intensity and energy use. Women naturally tend to keep a somewhat higher cadence than men across age groups, in part because of shorter average stride length, and a cadence of roughly 100 steps per minute is a widely used practical marker of moderate-intensity activity in adults (Tudor-Locke et al., 2019). Reference data for healthy women show cadence drifting gradually upward with age, with each step covering slightly less ground (Rössler et al., 2024).

Two large studies of healthy adults anchor these everyday reference points across the whole adult age range: the COmPLETE Cohort study (Rössler et al., 2024), which reported values for women from their twenties into their nineties, and the NONAN GaitPrint study (Wiles et al., 2025), which focused on the often-overlooked middle years of adulthood and showed that these walking patterns are consistent and personal enough to characterize how an individual moves.

How Petal Derives Walking Metrics

The quality check that comes first

Every walking number is only as good as the walking it is built from, so Petal applies a carefully and prudently designed “walking detector” ensuring Petal’s walking metrics are always reliable and stable.Petal records in short sessions through the day. Within each one, the detector picks out sessions i.e continuous stretches of walking, and a session contributes to the day's numbers only if it contains enough sustained walking. Movement that isn't steady-state walking is set aside: running, because it follows a different step model, and shuffling or stop-start gait, where the steps don't form a clean rhythm. . What the trends look like. The figures below show about four weeks of one representative user's daily values. Each point is a day's session-level result; the shaded break at the end of July marks a day that did not pass the quality check above, illustrating the graceful gap state rather than a guessed number.

Step cadence — steps per minute

Cadence is calculated directly: the total number of steps taken during walking, divided by the walking time. In plain terms, it captures how quickly the feet are moving — a brisk walk lands around 100–120 steps per minute, a stroll nearer 80.

Figure 1. Daily step cadence (spm) over four representative weeks. 

Walking speed — distance covered over time

Speed is estimated as step length multiplied by cadence, and then adjusted for the user's height so that people of different stature are compared fairly. In plain terms it captures how much ground a person covers. Petal displays it as a familiar pace, pairs it with cadence each week — covering more ground through longer strides versus quicker steps are different stories worth telling apart — and tracks its direction over several weeks, treating a rising trend as a genuine improvement worth celebrating.

Figure 2. Daily step speed (m/s) over the same period.

Step variability — fluctuations in your steps

Step variability is calculated as the variation in the time between consecutive steps: a low value means even, metronomic walking, a higher value means a more uneven rhythm. In Petal's own data the typical value sits around 22%, with most people falling between roughly 11% and 37%. Petal’s algorithms factor in pace as walking slowly naturally makes the rhythm look less even.

Figure 3. Daily step variability (%) over the same period.

From measurement to everyday insight

Across all three measures, Petal's approach is the same: establish what is normal for each woman, then surface gradual, meaningful shifts against her personal baseline — weekly for near-term changes and monthly for slower trends — always in supportive, everyday language.

References From Pubmed by National Institutes of Health (NIH)

Rössler R, Wagner J, Knaier R, et al. Spatiotemporal gait characteristics across the adult lifespan: Reference values from a healthy population – Analysis of the COmPLETE cohort study. Gait & Posture. 2024;109:101–108.

Wiles TM, Kim SK, Kalaitzi Manifrenti M, et al. NONAN GaitPrint: An IMU gait database of healthy middle-aged adults. Scientific Data. 2025;12:1603.

Studenski S, Perera S, Patel K, et al. Gait speed and survival in older adults. JAMA. 2011;305(1):50–58.

Verghese J, Holtzer R, Lipton RB, Wang C. Quantitative gait markers and incident fall risk in older adults. Journals of Gerontology Series A. 2009.

Tudor-Locke, Catrine, et al. "Walking cadence (steps/min) and intensity in 21–40 year olds: CADENCE-adults." International Journal of Behavioral Nutrition and Physical Activity 16.1 (2019): 8.

Calculation methods, thresholds, and typical operating values reflect Petal's own measurement pipeline. This document is provided for general informational purposes; Petal surfaces everyday wellness trends and is not intended to diagnose, treat, or predict any medical condition.