How to design wearables for swimmers
Swimming remains one of the last major sports where elite athletes train without real-time feedback. Runners check pace and cadence mid-stride; cyclists monitor power output continuously. Swimmers get a pace clock on the wall and a coach’s whistle. The opportunity to close this data gap is enormous, but the medium itself fights back. Water blocks all radio frequencies and exerts hydrostatic pressure that changes how sensors contact skin. Every successful aquatic wearable technology accepts that the pool is an RF-shielded, high-pressure environment that inverts standard IoT architecture.
Local Storage Over Connectivity in Submerged Conditions
Mainstream wearable design assumes constant connectivity. Engineers prioritize low-latency Bluetooth transmission to phones, offloading computation to the cloud and treating onboard memory as a buffer rather than a repository. That architecture fails the moment a swimmer submerges. Water attenuates 2.4 GHz signals completely; even the most powerful radio cannot penetrate more than a few centimeters of chlorinated water.
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This physics reality forces a fundamental shift in swimmer performance tracker design. The device must record high-frequency accelerometer, gyroscope, and photoplethysmography (PPG) data continuously for hours, then batch-transfer it during the few seconds a wrist breaks the surface between intervals or after the workout ends. Memory capacity and write-speed endurance become competitive features, not convenience specs. Garmin‘s Swim 2 solved this by optimizing for local storage over cellular redundancy, accepting that a competitive swimming sensor lives in a Faraday cage for 90 percent of its operational life.
How Hydrostatic Pressure Breaks Optical Sensors
The second constraint arrives from fluid dynamics rather than electromagnetics. Hydrostatic pressure increases by one atmosphere for every ten meters of depth. While pool swimmers rarely exceed two meters, the turbulent flow generated during flip turns creates transient pressure spikes that mechanical engineers must account for. An underwater heart rate monitor relies on optical sensors that require consistent skin contact and complete exclusion of ambient light. Water rushing over the wrist during a push-off creates separation forces that break this seal, introducing noise that firmware cannot algorithmically remove.
Whoop addressed this by abandoning the watch form factor entirely, using a high-tension knit band that maintains constant normal force against the radial artery regardless of hand orientation, a design choice that prioritizes signal fidelity over the wrist-worn category that most swimmers expect. For wrist-based pool wearable hardware, the industrial design must solve mechanical contact before the signal processing team can clean the data. The device cannot merely be waterproof; it must be hydrodynamically stable at speeds exceeding two meters per second.
Thermal Drift in Sealed Waterproof Chambers
Waterproofing requires gaskets, O-rings, and conformal coatings that trap heat from the processor and LED drivers. In air, this thermal load dissipates through convection. Submerged, the device becomes a sealed system with no heat sink. This matters because PPG accuracy depends on LED wavelength stability, and photodiode sensitivity drifts with temperature.
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Consider the second turn of a 200-meter interval. The device has been submerged for ninety seconds, the processor has logged thousands of data points, and the LED has fired continuously. Thermal drift peaks precisely when the swimmer needs accurate heart rate zones to pace the final lap. Thermal management in a waterproof wearable for swimming is not a comfort feature; it is a signal integrity requirement that demands thermal vias, low-power microcontrollers, and optical calibration curves that account for junction temperature.
Fluid Damping Changes How Motion Sensors See Strokes
Accelerometers and gyroscopes behave differently in water than in air. Viscous drag filters high-frequency motion, dampening the sharp peaks that algorithms use to detect arm recovery phases in freestyle or the snap of a butterfly kick. A swim stroke analysis device must use fluid damping coefficients in its sensor fusion models rather than the standard kinematic equations developed for running.
Form solved this by moving the sensors to the goggles, fixing the reference frame to the head rather than the wrist, a trade-off that sacrifices wrist-worn convenience for cleaner motion data. For wrist-worn devices, the firmware must distinguish between the laminar flow of a streamline off the wall and the turbulent flutter of a sprint finish. The hardware decision, wrist versus head versus chest, determines which strokes the algorithm can reliably classify and what the athlete actually learns about their technique.
The Unmet Middle: Performance Metrics Without Dive Computer Aesthetics
Current products split into two categories. The Apple Watch Ultra treats swimming as a secondary use case, prioritizing cellular connectivity and bright displays that serve no purpose underwater. Dedicated units like Garmin’s line sacrifice daily-wear aesthetics to survive four-hour training blocks without thermal drift or memory overflow. Whoop captures recovery data but lacks the IMU fidelity for real-time stroke analysis.
The unoccupied middle ground is a device that provides laboratory-grade heart rate and stroke metrics without requiring a chest strap or looking like a dive computer. The team that captures this space will have accepted that water changes every assumption about power budgets, thermal paths, and data transmission. They will have designed for submersion first and connectivity second.
If you’re working through the specific challenges of sealing, thermal management, and signal integrity that define swimmer performance tracker design, Bang Design has spent 25 years taking products from concept to manufactured reality, across consumer, health and life sciences, and technology sectors. Their subscription-based model means you get a full-stack team: design, engineering, visualization, and production without the overhead of a traditional agency. Explore their work or start a project.