High Intensity Exercise Threshold (0x2B4D): byte layout
GATT characteristic · org.bluetooth.characteristic.high_intensity_exercise_threshold · read from the Bluetooth SIG’s repository on 2026-10-17 · commit 408f4a0 (2026-10-14)
High Intensity Exercise Threshold is Bluetooth GATT characteristic 0x2B4D, org.bluetooth.characteristic.high_intensity_exercise_threshold in the Bluetooth SIG's assigned numbers. The SIG's GATT Specification Supplement file lays its value out as 5 fields: Field Selector, Threshold as Energy Expenditure per Hour, Threshold as Metabolic Equivalent, Threshold as Percentage of Maximum Heart Rate and Threshold as Heart Rate. The SIG's User Data permitted-characteristics list includes it.
- UUID
- 0x2B4D
- Identifier
org.bluetooth.characteristic.high_intensity_exercise_threshold- The SIG’s description
- The High Intensity Exercise Threshold characteristic is used to represent the high intensity exercise threshold of a user.The structure of this characteristic is defined below.
- Service the SIG’s files tie it to
- User Data (0x181C) — listed in uds_permitted_characteristics.yaml
- Source file
- gss/org.bluetooth.characteristic.high_intensity_exercise_threshold.yaml
Byte layout: 5 fields
In the order the SIG’s structure lists them. Type and size are as published; sizes count octets except where a struct is marked as sized in bits. The offset is printed only where every earlier field has a fixed size; where an earlier field can be absent or vary, the cell names what it depends on. “Present when” is read from the field’s own “Present if” line, shown in full in the field notes below.
| Offset | Field | Type | Size | Present when | Unit |
|---|---|---|---|---|---|
| 0 | Field Selector | uint8 | 1 | Always (fixed size) | — |
| 1 | Threshold as Energy Expenditure per Hour | uint16 | 0 or 2 | Present if value of Field Selector field is 1 | energy (joule)org.bluetooth.unit.energy.joule |
| Depends on the size of Threshold as Energy Expenditure per Hour | Threshold as Metabolic Equivalent | uint8 | 0 or 1 | Present if value of Field Selector field is 2 | metabolic equivalentorg.bluetooth.unit.metabolic_equivalent |
| Depends on the size of Threshold as Energy Expenditure per Hour and Threshold as Metabolic Equivalent | Threshold as Percentage of Maximum Heart Rate | uint8 | 0 or 1 | Present if value of Field Selector field is 3 | percentageorg.bluetooth.unit.percentage |
| Depends on the size of Threshold as Energy Expenditure per Hour, Threshold as Metabolic Equivalent and Threshold as Percentage of Maximum Heart Rate | Threshold as Heart Rate | uint8 | 0 or 1 | Present if value of Field Selector field is 4 | period (beats per minute)org.bluetooth.unit.period.beats_per_minute |
Field notes
Each field’s text in the SIG’s file, line by line.
- Field Selector uint8 · 1
- See Field Selector
- Threshold as Energy Expenditure per Hour uint16 · 0 or 2
- Base Unit: org.bluetooth.unit.energy.jouleRepresented values: M = 1, d = 3, b = 0Unit is joule with a resolution of 1000 joulesPresent if value of Field Selector field is 1
- Threshold as Metabolic Equivalent uint8 · 0 or 1
- Base Unit: org.bluetooth.unit.metabolic_equivalentRepresented values: M = 1, d = -1, b = 0Unit is MET with a resolution of 0.1 MET (i.e., kcal/kg/hour)Present if value of Field Selector field is 2
- Threshold as Percentage of Maximum Heart Rate uint8 · 0 or 1
- Unit: org.bluetooth.unit.percentagePresent if value of Field Selector field is 3
- Threshold as Heart Rate uint8 · 0 or 1
- Unit: org.bluetooth.unit.period.beats_per_minutePresent if value of Field Selector field is 4
Flags and value tables
The definitions the SIG’s file gives for its fields, every row as published. On a flags table the last column lists the fields whose “Present if” line names that bit.
Field Selector
The Field Selector field determines the High Intensity Exercise Threshold characteristic field selected to express the high intensity threshold. The selected field is present in the High Intensity Exercise Threshold characteristic, whereas the remaining fields are not present.The values of this field are defined below.
| Value | Description |
|---|---|
| 0 | No field is selected |
| 1 | The Threshold as Energy Expenditure per Hour field is selected |
| 2 | The Threshold as Metabolic Equivalent field is selected |
| 3 | The Threshold as Percentage of Maximum Heart Rate field is selected |
| 4 | The Threshold as Heart Rate field is selected |
| 5–255 | Reserved for Future Use |
Guides on this site
No guide on this site names 0x2B4D yet. The connected-devices guides cover pairing, subscribing and testing for the device types they do name.
Questions
- What is the UUID of the High Intensity Exercise Threshold characteristic?
- 0x2B4D. The Bluetooth SIG's characteristic_uuids.yaml lists High Intensity Exercise Threshold as 0x2B4D with the identifier org.bluetooth.characteristic.high_intensity_exercise_threshold. The SIG's User Data (0x181C) permitted-characteristics list includes it.
- Which High Intensity Exercise Threshold fields are optional?
- 4 of its 5 fields have a published size that can be zero: Threshold as Energy Expenditure per Hour (0 or 2; Present if value of Field Selector field is 1); Threshold as Metabolic Equivalent (0 or 1; Present if value of Field Selector field is 2); Threshold as Percentage of Maximum Heart Rate (0 or 1; Present if value of Field Selector field is 3); Threshold as Heart Rate (0 or 1; Present if value of Field Selector field is 4). Field Selector (1) has a fixed size.
- What units does High Intensity Exercise Threshold use?
- The SIG's text names a unit for 4 of the 5 fields: Threshold as Energy Expenditure per Hour: energy (joule) (org.bluetooth.unit.energy.joule); Threshold as Metabolic Equivalent: metabolic equivalent (org.bluetooth.unit.metabolic_equivalent); Threshold as Percentage of Maximum Heart Rate: percentage (org.bluetooth.unit.percentage); Threshold as Heart Rate: period (beats per minute) (org.bluetooth.unit.period.beats_per_minute).
- Which values does the High Intensity Exercise Threshold Field Selector table define?
- 0: No field is selected; 1: The Threshold as Energy Expenditure per Hour field is selected; 2: The Threshold as Metabolic Equivalent field is selected; 3: The Threshold as Percentage of Maximum Heart Rate field is selected; 4: The Threshold as Heart Rate field is selected. The other rows are reserved for future use or carry no text.
Source
Read on 2026-10-17 from gss/org.bluetooth.characteristic.high_intensity_exercise_threshold.yaml and assigned_numbers/uuids/characteristic_uuids.yaml in the Bluetooth SIG’s public repository (branch main, commit 408f4a0, committed 2026-10-14), by scripts/fetch-bluetooth-gatt.mjs. The file’s notice says it is proprietary to Bluetooth SIG, that furnishing it grants no licence, and that it is subject to change without notice; it is © Bluetooth SIG, Inc., and its text is quoted here for identification. Generated by AIFitnessAPI, which is not affiliated with Bluetooth SIG; the SIG’s file remains the authority. The full notice and the conventions used on these pages are on the reference hub.