The specifications that matter most in a sports wearable are usually presented as sensing capabilities. In practice they are downstream of a power budget that the device cannot exceed.
Sampling rate is the largest single cost
Recording position or acceleration more frequently captures more detail and consumes proportionally more energy, both in the sensor and in the processor handling the output. Doubling the rate roughly doubles that portion of the drain.
Designers therefore select the lowest rate that still captures the events of interest, which is why different device categories sample so differently.
A unit intended to run through a full training week cannot sample as aggressively as one recharged after every session, regardless of what its sensors could do.
Transmission costs more than measurement
Sending data wirelessly consumes considerably more power than collecting it, because the radio has to drive a signal across the pitch to a receiver. Live monitoring during a session is expensive in exactly this way.
Devices that store data and transfer it afterwards conserve a great deal of energy, at the cost of removing any possibility of intervening during the session itself.
Many systems compromise by transmitting a reduced summary live and retaining the full record for download, which is why the numbers on a touchline tablet are coarser than the ones reviewed later.
Onboard processing trades power for bandwidth
Calculating metrics on the device reduces how much has to be transmitted, since a summary is far smaller than a raw stream. That calculation itself consumes energy.
Where the balance falls depends on the wireless environment, and a stadium crowded with competing signals makes transmission expensive enough to favour local processing.
This is one reason the same product behaves differently at a training ground and inside a full stadium.
Physical size sets the ceiling
Battery capacity scales with volume, and a device worn during contact sport has strict limits on how large and heavy it can be. Comfort and safety constrain the power source before electronics are even considered.
Miniaturisation has improved sensors faster than it has improved batteries, so power has become the binding constraint on what a wearable can offer.
Devices integrated into clothing or footwear face tighter limits still, which explains why they generally measure narrower quantities.
Practical protocols are built around charging
A unit that fails mid-session produces a partial record, and partial records distort weekly load totals in ways that matter for planning.
Sports science staff therefore run charging routines with the seriousness of a kit operation, because a missing dataset cannot be recovered afterwards.
The most common cause of gaps in a club's physical database is not sensor failure but a device that was not charged, which is a strikingly ordinary limitation on an advanced system.