Effect of Rapid Heat Stress on Firefighters Musculoskeletal Injury Risk

Heat Stress Clinical Trial

Official title:

The Impact of Rapid Heat Stress on Firefighters' Strength, Dynamic Balance, and Movement Quality

Clinical Trial Details — Status: Not yet recruiting

Administrative data

• NCT number: NCT06442956
• Other study ID #: STUDY00002549
• Status: Not yet recruiting
• Phase: N/A
• Start date: July 2024
• Est. completion date: May 2026

Study information

• Verified date: June 2024
• Source: Louisiana State University Health Sciences Center Shreveport
• Contact: Erin McCallister, DPT
• Phone: 3188133502
• Email: erin.mccallister[@]lsuhs.edu
• Is FDA regulated: No
• Study type: Interventional

Clinical Trial Summary

This study will examine the effect of heat stress on factors that influence musculoskeletal injury risk in firefighters. Participants will attend 4 data collection sessions. 1: informed consent, screening, and familiarization. 2: pre-tests (strength, balance, and movement quality). 3: heat stress (rapid or gradual) followed by post-tests (strength, balance, and movement quality). 4: heat stress (rapid or gradual) followed by post-tests.

Description:

This study utilizes a crossover design, with participants acting as their own controls and participating in both the control (gradual uncompensable heat) and experimental (rapid heat stress (RHS)) conditions. The independent variable is the type of heat stress (uncompensable or rapid). The dependent variables are: peak concentric muscle torque (hip abductors, hip adductors, knee flexors, knee extensors), dynamic balance (Y-Balance Test, Firefighter-Specific Functional-Balance Test (FFSFBT)), and frontal plane movement quality (Forward-Step-Down Test (FSDT)). These will be measured three times, once during pre-testing and twice during post-testing as described below.

The study will consist of four visits. Visit one will be the informed consent and familiarization to the outcome measures. Participants will be educated on filling out the 24-hour food/drink diary, and asked to standardize their diet as close as possible to this record the 24 hours before visits 2, 3, and 4. Injury history and demographic data will be collected at visit 1.

Visit two will be the pre-test data collection, which will occur at approximately 22°C. Participants will complete all outcome measures (torque, balance, movement quality measures). Body composition will also be measured in the BodPod at this time.

Before visits 2, 3, and 4, participants will follow the safety guidelines outlined below to ensure proper hydration:

• 48 hours before: no heat stress (will contact participant to determine if they have been called out to a live fire. Data collection will be postponed if so)

• 24 hours before: no alcohol consumption, no energy drink consumption (normal coffee/tea is allowed)

• 24 hours before: no physical activity (exercise or vigorous play)

• 24 hours before: drink 3.7L of total water to make sure to be well-hydrated

• 2 hours before: eat last meal

Visits three and four will consist of a steady-state treadmill protocol inside the environmental chamber (37-38°C, 50% humidity) followed by post-test measures. During either session three or four, the participant will don his/her firefighting gear (jacket, pants, hood, boots, gloves) and perform the treadmill test with the gear on. This is the RHS trial and will be denoted GEAR. In the other session, the participant will wear exercise clothes (shirt and shorts) plus a weighted backpack to replicate the weight of the gear. This is the gradual uncompensable heat stress trial and will be denoted NOGEAR. The order of the GEAR and NOGEAR sessions will be randomized and counterbalanced to prevent crossover effects.

Upon arrival for the pre-testing visit (session two), participants will be measured for height using a stadiometer and weight. Body composition will be measured once with the BodPod (Cosmed, USA). They will warm up for five minutes on an exercise bike or treadmill then proceed with taking the outcome measures.

Upon arrival for visits three and four, participants will be weighed again. A urine sample will be collected to assess hydration status. They will swallow the core temperature (Tc) capsule 40-45 minutes prior to the start of the session using a small amount of 20°C water, with no further water ingestion throughout the protocol to avoid artificially lowering Tc. Participants will be fit with the Equivital EQLife Monitor (Equivital, NY) system to record heartrate (HR) and Tc. They will then perform the treadmill protocol, and post-test measures will be completed immediately following the cessation of the treadmill test with removal of their gear. They will be weighed following exercise to determine changes in body weight due to sweating.

Sessions three and four will be separated by at least seven days to reduce the influence of heat acclimatization and fatigue. Continuous monitoring of Tc and HR will help ensure participant safety.

The treadmill exercise protocol begins with a graded approach to reach aerobic steady state. The treadmill protocol includes an initial five-minute stage at 3 miles per hour and a 0% grade, followed by increases in percent grade of 4% at minute 5 and 8% at minute 10 and continued throughout the test. Following the final planned incremental increase in treadmill incline, the incline will then be adjusted to ensure that the subject remains at steady-state for the duration of the protocol, defined by a respiratory exchange ratio between 0.9-0.99 using the lab's metabolic cart (Parvomedics, USA). HR, rating of perceived exertion (RPE), thermal comfort, and thermal sensation will be recorded at each 0.5°C interval. The treadmill test will be stopped when participants either reach a Tc of 39°C or a volitional maximum (participant is unable to continue exercise). The investigators will also halt the test if signs of excessive heat stress are present (unsteady gait, confusion, dizziness, slurred speech, etc.) Should the participant not meet either termination criteria, there will be a 50 minute time limit for the treadmill protocol for the GEAR condition and 2 hour limit for the NOGEAR condition. Both GEAR and NOGEAR sessions will begin with the same treadmill test.

Following the treadmill test, the participants will complete the post-test outcome measures. These consist of isokinetic torque of the hip abductors and adductors, isokinetic torque of the knee flexors and extensors, the Y-Balance Test, the FFSFBT, and FSDT. Participants will doff their gear immediately following cession of the treadmill test. For unilateral tests, the dominant leg will be recorded and used for these tests; this is the leg used to kick a ball. Outcome measure order will be standardized for each participant with testing order based on primary outcomes and difficulty of each test. The FSDT will be performed first, as this is the primary outcome and previous research showed that recovery after a maximal exertion stimulus happens quickly. The FFSFBT will be performed next, followed by the Y-Balance Test. Isokinetic testing will be last due to the fatiguing nature of this testing. Hip muscles will be tested first, followed by thigh muscles. Three minutes will be allotted for rest and instruction between each outcome measure. Five minutes of rest will be given between isokinetic tests to allow for machine set-up and instructions. One minute of rest will be given between each isokinetic speed, with three speeds tested for the hip (30°, 60°, and 120° per second) and knee (60°, 180°, and 300° per second) muscles.

Participants will be followed for 2 years, with 6-month follow-up calls to track injury status. Details on type of injury, location of injury, and time lost to work will be collected.

Recruitment information / eligibility

• Status: Not yet recruiting
• Enrollment: 28
• Est. completion date: May 2026
• Est. primary completion date: July 2025
• Accepts healthy volunteers: Accepts Healthy Volunteers
• Gender: All
• Age group: 18 Years to 57 Years

Eligibility

Inclusion Criteria:

• professional firefighter

• healthy per the Physical Activity Readiness Questionnaire+ screening

Exclusion Criteria:

• unable to swallow core temperature capsule

• unable to follow pre-testing hydration criteria

• musculoskeletal injury in the past 3 months that limits ability to perform outcome measures

• females with known pregnancy (risk of hyperthermia to fetus)

Related Conditions & MeSH terms

• Back Injuries
• Heat Stress
• Heat Stress Disorders
• Leg Injuries
• Leg Injury
• Occupational Injuries
• Wounds and Injuries

Intervention

Other:
• Rapid Heat Condition
The heat condition is the intervention. Personal protective equipment will be used to create the rapid heat stress condition, resulting in a rapid rise in core temperature. This will be in combination with the physiological heat produced by the treadmill protocol.
• Gradual Heat Condition
The gradual heat condition is the control. Physiological heat will be produced by exercise on a treadmill, and light exercise clothing will help moderate the rise in core temperature.

Locations

Country	Name	City	State
United States	LSUHSC-Shreveport	Shreveport	Louisiana

Sponsors (1)

Lead Sponsor	Collaborator
Louisiana State University Health Sciences Center Shreveport

Country where clinical trial is conducted

United States, 

References & Publications (27)

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* Note: There are 27 references in all — Click here to view all references

Outcome

Type	Measure	Description	Time frame	Safety issue
Primary	Forward-Step-Down Test	a step-down task that is performed off a 20 cm box. Five repetitions are performed to give one score (minimum score 0, maximum score 6). A higher score is worse.	Familiarization trials (session 1, recruitment); pre-testing (baseline, session 2 (approximately day 7)); post-control and post-experimental sessions (session 3 (approximately day 14) & 4 (approximately day 21)).
Primary	Y-Balance Test	A dynamic balance test that is performed on the dominant leg, reaching in the anterior, posteromedial, and posterolateral directions. The length of reach is standardized to participants' leg length. A higher score is better, with 0 being the minimum distance and the maximum distance in anterior reach being 126cm, and the maximum posteromedial and posterolateral directions being 149cm.	Familiarization trials (session 1, recruitment); pre-testing (baseline, session 2 (approximately day 7)); post-control and post-experimental sessions (session 3 (approximately day 14) & 4 (approximately day 21)).
Primary	Firefighter Specific Functional Balance Test	A dynamic balance test performed by stepping down from a 15cm box, walking across a low beam (4cm high), and stepping up onto a 10cm box, turning around, and returning to the original box. 8 Trials are performed. In 4 trials, a bar is placed at 75% of the participant's height for them to negotiate while on the beam. A faster time with fewer errors is better.	Familiarization trials (session 1, recruitment); pre-testing (baseline, session 2 (approximately day 7)); post-control and post-experimental sessions (session 3 (approximately day 14) & 4 (approximately day 21)).
Primary	Knee Flexor/Extensor Isokinetic Test	Knee flexor/extensor isokinetic strength will be tested at 60°, 180°, and 300° per second from the seated position with 5, 10, and 10 concentric contractions for each speed. A higher reading of strength is better.	Familiarization trials (session 1); pre-testing (baseline, session 2); post-control and post-experimental sessions (session 3&4).
Primary	Hip Abductor/Adductor Isokinetic Test	Hip abductor/adductor strength will be tested at 30°, 60°, and 120° per second from the standing position. A higher reading of strength is better.	Familiarization trials (session 1, recruitment); pre-testing (baseline, session 2 (approximately day 7)); post-control and post-experimental sessions (session 3 (approximately day 14) & 4 (approximately day 21)).
Secondary	Injury Occurrence	Participants will be contacted after sessions 1-4 to follow up on occurrence of musculoskeletal injuries, with 0 representing no injury and numerical values indicating presence of injury.	6 months, 12 months, 18 months, 24 months after session 4.