Work/Rest Cycles for Heat Stress

Overseen By Riana R Pryor, PhD

Age: 18 - 65

Sex: Any

Trial Phase: Academic

Sponsor: State University of New York at Buffalo

Must not be taking: Beta blockers, Statins, Aspirin, others

Disqualifiers: Cardiovascular, Metabolic, Respiratory, others

No Placebo Group All trial participants will receive the active study treatment (no placebo)

Compensation: Varies

Number of Visits: 4

24 Participants Needed

Trial Summary

What is the purpose of this trial?

The overall goal of this project is to identify a work/rest cycle that allows for faster mission completion needed in emergency situations, compared to current Army heat guidance, while mitigating heat strain and neuromuscular fatigue. This project will determine the trade-off between faster mission completion and risk of heat strain and physical performance decrements. Completion of this project will allow military leaders to make informed decisions by understanding the impact of their choices on the magnitude of physical performance decrements and expected heat casualties, setting up hot weather missions for success.

Do I have to stop taking my current medications for the trial?

Yes, if you are taking medications or supplements that affect exercise or thermoregulation, like beta blockers, omega-3 fatty acids, statins, or aspirin, you cannot participate in the trial.

What data supports the idea that Work/Rest Cycles for Heat Stress is an effective treatment?

The available research shows that Work/Rest Cycles for Heat Stress can help maintain physical work capacity in hot conditions. In one study, workers who used work/rest cycles were able to keep their heart rates and body temperatures within safe limits, even in hot environments. This suggests that taking regular breaks can prevent excessive strain on the body. Another study found that work output decreased less when using work/rest cycles compared to continuous work in hot conditions, indicating that these cycles help sustain energy levels and performance. ^{1 2 3 4 5}

What safety data exists for work/rest cycles in heat stress conditions?

The safety data for work/rest cycles in heat stress conditions includes several findings: (1) Self-regulation of work-rest cycles can effectively protect workers from excessive physiological strain in hot conditions, provided the task is not urgent and workers are well-trained. (2) Heat stress risk can be managed through environmental control, mandatory work-rest regimens, and self-paced working. (3) Regional heat stress management practices are recommended to account for local climatic conditions and worker acclimatization. (4) In South Korea, mandatory rest times based on WBGT thresholds are necessary for outdoor workers during hot summer months to prevent heat-related illnesses. ^{1 3 6 7 8}

Is the 30/30 work-rest cycle a promising treatment for managing heat stress?

Yes, the 30/30 work-rest cycle is a promising treatment for managing heat stress. It helps maintain physical work capacity by allowing regular breaks, which can prevent exhaustion and keep workers' body temperatures within safe limits, even in hot conditions. ^{2 3 9 10 11}

Research Team

Riana R Pryor, PhD

Principal Investigator

University at Buffalo

Eligibility Criteria

This trial is for individuals who are healthy and can safely perform physical tasks in hot conditions. Specific eligibility criteria were not provided, so it's important to contact the study organizers for detailed requirements.

Inclusion Criteria

Healthy individuals

Physically active

Exclusion Criteria

I have a history of heart, metabolic, lung, nerve, or kidney disease.

Tobacco or nicotine use currently or in the past six months

I can understand and follow the study's instructions.

Timeline

Screening

Participants are screened for eligibility to participate in the trial

2-4 weeks

Work/Rest Cycle Testing

Participants complete various work/rest cycles to assess heat strain and neuromuscular fatigue

180 minutes per session

4 sessions (in-person)

Follow-up

Participants are monitored for safety and effectiveness after completing the work/rest cycles

4 weeks

Treatment Details

Interventions

• 20/12 work/rest cycle
• 30/20 work/rest cycle
• 30/30 work/rest cycle
• 40/30 work/rest cycle

Trial Overview The PREPARED trial is testing different work/rest cycles (30/30, 30/20, 20/12, and 40/30 minutes) to see which allows for faster completion of missions in heat without causing too much strain or fatigue.

Participant Groups

Group I: 40/30 work/rest cycle first Experimental Treatment 4 Interventions

Participants will first complete the 40/30 work/rest cycle, and then complete the other three conditions in a randomized fashion

Group II: 30/20 work/rest cycle first Experimental Treatment 4 Interventions

Participants will first complete the 30/20 work/rest cycle, and then complete the other three conditions in a randomized fashion

Group III: 20/12 work/rest cycle first Experimental Treatment 4 Interventions

Participants will first complete the 20/12 work/rest cycle, and then complete the other three conditions in a randomized fashion

Group IV: 30/30 work/rest cycle first Active Control 4 Interventions

Participants will first complete the 30/30 work/rest cycle, and then complete the other three conditions in a randomized fashion

Who Is Running the Clinical Trial?

State University of New York at Buffalo

Lead Sponsor

Trials

279

Recruited

52,600+

United States Department of Defense

Collaborator

Trials

940

Recruited

339,000+

Findings from Research

In a study involving 12 male participants aged 28 to 40, it was found that short-term alterations in work-rest cycles (lasting 1 to 3 days) can help maintain work capacity when frequently changing schedules.

The transition back to a normal work-rest cycle was smoother when the participants had not fully adapted to the altered cycles, suggesting that incomplete adaptation may facilitate quicker readjustment.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

[Characteristics of human sleep, circadian periodicity of physiological functions and of work capacity indices in the 1st 24 hours after the transition from an altered to a usual sleep and wakefulness cycle]. Litsov, AN.[2006]

In a study involving nine healthy males, it was found that physical work capacity (PWC) decreased during a simulated work shift with repeated heat exposure, showing a 16% reduction in very hot conditions compared to cool environments.

The research suggests that existing models predicting PWC based on short-term heat exposure may need adjustments to account for the cumulative effects of heat stress over longer work shifts, especially after breaks.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Quantifying the impact of heat on human physical work capacity; part IV: interactions between work duration and heat stress severity. Smallcombe, JW., Foster, J., Hodder, SG., et al.[2022]

In a study of seven masonry workers in a hot environment, their self-pacing during work-rest cycles was found to be effective in keeping heart rates and rectal temperatures within safe limits, despite varying physical capacities.

The workers' ability to self-regulate their work time to about 25% of the shift, along with alternating tasks in pairs, contributed to their safety, suggesting that self-regulation can protect against heat stress when conditions allow for it.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Workers self-pacing in hot conditions: a case study. Mairiaux, P., Malchaire, J.[2019]

Heat acclimation (HA) can be maintained for up to 26 days without significant decay in physiological responses, allowing individuals to return to hot environments without extensive re-adaptation.

In a study with 16 participants, re-induction of heat acclimation (RA) was achieved in just 2 days after 12 days of cooler conditions, indicating that previous acclimation can be quickly regained.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Quantification of the decay and re-induction of heat acclimation in dry-heat following 12 and 26 days without exposure to heat stress. Weller, AS., Linnane, DM., Jonkman, AG., et al.[2018]

The study developed new guidelines for work-rest cycles during training, particularly in military settings, using the Environmental Stress Index (ESI) and Physiological Strain Index (PSI) to assess heat strain more effectively.

The PSI, which focuses on heart rate and rectal temperature, is easier to measure and integrate with the ESI, potentially reducing the risk of heat injuries by providing real-time assessments of physiological strain.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Combined environmental stress and physiological strain indices for physical training guidelines. Moran, DS., Pandolf, KB., Heled, Y., et al.[2019]

During the period from 2010 to 2014, Russian crewmembers on the International Space Station experienced a hard work schedule 69% of the time, primarily due to demanding tasks like extravehicular activities and docking operations.

The analysis indicated that the distribution of work was more balanced in 2013-2014 compared to 2010-2012, which may have reduced the risk of critical workload levels during important operations, potentially enhancing crew health and performance.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

[WORK-REST CYCLE OF COSMONAUTS IN MISSIONS 22/23-39/40 OF THE INTERNATIONAL SPACE STATION]. Stepanova, SI., Karpova, OI., Galichiy, VA., et al.[2016]

Climatic heat stress significantly impacts construction site safety, leading to accidents due to heat-induced illness and fatigue, necessitating a complete overhaul of safety management systems rather than just incremental improvements.

The authors propose a three-level methodology for managing heat stress that includes controlling environmental exposure, regulating work time with mandatory breaks, and empowering workers to manage their own pace, emphasizing the need for region-specific practices tailored to local climatic conditions.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Management of climatic heat stress risk in construction: a review of practices, methodologies, and future research. Rowlinson, S., Yunyanjia, A., Li, B., et al.[2014]

Outdoor workers in South Korea experience heat stress during about 30% of their working hours in the summer, highlighting the need for effective heat management strategies.

The study found that the recommended minimum rest time for workers with moderate workloads should increase significantly during mid-summer, with a rise of up to 31% (18 minutes per hour) around noon, indicating a critical need for adjustments in work-rest schedules to ensure worker safety.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Spatio-temporal patterns of the minimum rest time for outdoor workers exposed to summer heat stress in South Korea. Lee, SW., Kim, IG., Kim, HM., et al.[2020]

A new method based on limiting metabolic rate has been developed to compare various heat stress indices, addressing the confusion caused by the lack of a universally accepted index.

This comparison reveals significant discrepancies in recommended heat stress limits across different indices, even for similar groups of acclimatized workers, highlighting the need for a standardized approach to occupational heat stress assessment.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

A valid method for comparing rational and empirical heat stress indices. Brake, R., Bates, G.[2022]

Exercise-rest cycles during outdoor activities in extreme heat did not improve physiological tolerance to uncompensable heat stress, as core temperatures at exhaustion remained similar across different exercise intensities and rest conditions.

Field study participants showed greater physiological tolerance to heat stress compared to laboratory participants, indicating that long-term acclimatization in real-world conditions may enhance heat tolerance more effectively than short-term acclimation in controlled environments.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Physiologic tolerance to uncompensable heat: intermittent exercise, field vs laboratory. Sawka, MN., Latzka, WA., Montain, SJ., et al.[2019]

In a study with 17 male volunteers performing heavy work while wearing the chemical defense ensemble (CDE) at 21°C, most participants stopped working due to fatigue or high body temperature rather than heat storage limits, indicating that fatigue and temperature management are critical factors in work performance under these conditions.

The findings suggest that existing U.S. Air Force guidelines for managing heat stress may not accurately reflect the actual work tolerance of personnel in CDE, highlighting the need for revised recommendations to ensure safety and effectiveness during heavy work tasks.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Limitations to heavy work at 21 degrees C of personnel wearing the U.S. military chemical defense ensemble. Bishop, PA., Pieroni, RE., Smith, JF., et al.[2008]

References

1. Russia (Federation) pubmed.ncbi.nlm.nih.gov

[Characteristics of human sleep, circadian periodicity of physiological functions and of work capacity indices in the 1st 24 hours after the transition from an altered to a usual sleep and wakefulness cycle]. [2006]

2. United States pubmed.ncbi.nlm.nih.gov

Quantifying the impact of heat on human physical work capacity; part IV: interactions between work duration and heat stress severity. [2022]

3. England pubmed.ncbi.nlm.nih.gov

Workers self-pacing in hot conditions: a case study. [2019]

4. Germany pubmed.ncbi.nlm.nih.gov

Quantification of the decay and re-induction of heat acclimation in dry-heat following 12 and 26 days without exposure to heat stress. [2018]

5. Germany pubmed.ncbi.nlm.nih.gov

Combined environmental stress and physiological strain indices for physical training guidelines. [2019]

6. Russia (Federation) pubmed.ncbi.nlm.nih.gov

[WORK-REST CYCLE OF COSMONAUTS IN MISSIONS 22/23-39/40 OF THE INTERNATIONAL SPACE STATION]. [2016]

7. England pubmed.ncbi.nlm.nih.gov

Management of climatic heat stress risk in construction: a review of practices, methodologies, and future research. [2014]

8. United States pubmed.ncbi.nlm.nih.gov

Spatio-temporal patterns of the minimum rest time for outdoor workers exposed to summer heat stress in South Korea. [2020]

9. England pubmed.ncbi.nlm.nih.gov

A valid method for comparing rational and empirical heat stress indices. [2022]

10. United States pubmed.ncbi.nlm.nih.gov

Physiologic tolerance to uncompensable heat: intermittent exercise, field vs laboratory. [2019]

11. United States pubmed.ncbi.nlm.nih.gov

Limitations to heavy work at 21 degrees C of personnel wearing the U.S. military chemical defense ensemble. [2008]