**Background:** Firefighters responding to large-scale disasters perform diverse, high-intensity activities under harsh conditions, yet no studies have established standard energy expenditure values for each type of disaster relief operation. Previous methods (doubly labeled water, expired gas analysis) are impractical for field settings. Wearable devices combining accelerometry and heart rate monitoring offer a less invasive alternative. This study aimed to estimate hourly energy expenditure for specific disaster relief activities using a combined accelerometer-heart rate method.
**Methods:** Thirty male firefighters were randomly selected from participants in a two-day large-scale disaster simulation drill in Kanagawa Prefecture, Japan (30 November–1 December 2018). Two subjects were excluded due to data defects, leaving 28 (mean age 34.0 ± 7.4 years, height 173.4 ± 5.4 cm, weight 68.7 ± 5.6 kg, BMI 22.9 ± 1.5, basal metabolic rate 1544 ± 89 kcal). Participants wore a tri-axial accelerometer (Omron HJA-750C, 23 g) taped inside the left breast pocket and a wearable heart rate monitor (myBeat WHS-1, 14 g) fastened to the chest. Data were recorded every 10 seconds (accelerometer) and per minute (heart rate). MET values were calculated using an individually optimized estimation formula based on two reference points: the 10th percentile heart rate during nap (assigned 0.95 METs) and the 90th percentile heart rate during the most intense activity (matched to MET table values). Activities were self-reported every 30 minutes using activity logs. The drill simulated an earthquake (magnitude 7.3, depth not clearly reported) causing building collapse, fire, road damage, and landslides, with 2323 total participants. Six groups of 4–5 firefighters each performed different scenarios: gas leak rescue (Groups 1–2), high-rise building rescue (Groups 3–4), and landslide/tunnel collapse rescue (Groups 5–6).
**Key Results:** METs for each activity type ranged from 4.3 to 7.0 across groups. The 10 classified activity types with hourly energy expenditure (for an average 71 kg adult male, excluding resting metabolism) were: Rescue from a Small Place (4.5 ± 1.2 METs, 249 kcal/h, n=14), Rescue from a Vehicle (4.7 ± 1.5 METs, 263 kcal/h, n=5), Rescue Personnel Transportation (4.8 ± 1.4 METs, 270 kcal/h, n=5), Search Activities (4.9 ± 1.3 METs, 277 kcal/h, n=10), Fire Fighting Activities (5.1 ± 0.6 METs, 291 kcal/h, n=5), Gas-related Accidents (5.6 ± 1.3 METs, 327 kcal/h, n=14), Excavation Activities (5.7 ± 1.4 METs, 334 kcal/h, n=9), Rescue Operations (6.0 ± 0.7 METs, 355 kcal/h, n=10), Tunnel Collapse Accident (6.0 ± 1.1 METs, 355 kcal/h, n=4), and Rescue from a High Ground (6.9 ± 1.0 METs, 419 kcal/h, n=20). Total energy expenditure across all activities was estimated at 4838 ± 508 kcal/day. The authors applied their reference data to a real disaster (Atami, Japan, July 2021) and estimated a total energy expenditure of approximately 5436 kcal on the second day of rescue operations.
**Clinical Implications:** This study provides the first standardized hourly energy expenditure values for 10 types of large-scale disaster relief operations, enabling more accurate estimation of total energy needs during disaster response. These data can inform nutritional planning (caloric replenishment) and crew rotation scheduling to prevent exhaustion. The combined accelerometer-heart rate method captured energy expenditure that may be underestimated by accelerometry alone, particularly during activities involving static exertion or psychological stress. Limitations include the all-male sample (no female firefighters were available in the participating units), the simulated rather than actual disaster setting, potential self-report bias in activity logs, and the lack of consideration for fatigue effects and circadian rhythm. The authors note that activities such as mountain rescue and water rescue were not included and require further study. Despite these limitations, the approach is practical for field use and applicable not only to firefighters but also to other disaster response personnel (e.g., Japan Self-Defense Force, police).