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

What You Need to Know Before You Apply

What is the purpose of this trial?

This trial explores different work/rest cycles to determine which helps emergency workers complete tasks faster in hot weather while reducing heat stress and muscle fatigue. Participants will test various cycles, such as 30/20 or 40/30, to find the optimal balance between speed and safety. This research is particularly valuable for military operations in hot climates. The trial seeks healthy, physically active individuals without a history of heart, thyroid, or major health issues. As an unphased trial, it offers participants the chance to contribute to research that could enhance safety and efficiency in challenging environments.

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 prior data suggests that these work/rest cycles are safe for managing heat stress?

Research has shown that balancing work and rest is crucial to avoiding heat stress and related health problems. In the 20/12 work/rest cycle, studies indicate that extreme heat can lead to serious health issues, including heat illness and even death. Monitoring conditions and adjusting tasks are essential to ensure worker safety.

For the 30/20 and 40/30 work/rest cycles, research finds that performing moderate work in high temperatures, such as 108°F, significantly increases the risk of heat-related injuries. Safety guidelines recommend taking at least a 15-minute break every hour in hot conditions to help prevent heat stress.

Overall, these work/rest cycles aim to balance productivity with health. While this trial does not provide new safety data, following established guidelines and adjusting work based on temperature are key to reducing risks. ^{1 2 3 4 5}

Why are researchers excited about this trial?

Researchers are excited about this trial because it explores how different work/rest cycles might prevent or manage heat stress more effectively. Current strategies often focus on hydration and cooling methods, but this approach aims to optimize productivity while ensuring safety by adjusting work and rest durations. By testing various cycles, like 20/12 and 40/30 work/rest ratios, researchers hope to find the ideal balance that minimizes heat stress while maintaining efficiency. This trial could lead to new guidelines that better protect workers in hot environments without compromising output.

What evidence suggests that these work/rest cycles are effective for managing heat stress?

Research shows that different patterns of work and rest affect how people handle heat and perform physically. In this trial, participants will experience various work/rest cycles. The 20/12 cycle, one of the cycles under study, involves shorter work times that help keep body temperature steady, potentially aiding in managing heat stress. The 30/20 cycle, with two parts work to one part rest, is being tested for its ability to maintain physical and mental performance in hot conditions, though more data is needed to confirm its effectiveness. For the 40/30 cycle, research suggests that longer work periods might reduce productivity because people naturally slow down in hot environments. Overall, the trial aims to find the best way to balance work efficiency and safety in hot conditions. ^{6 7 8 9 10}

Who Is on the Research Team?

Riana R Pryor, PhD

Principal Investigator

University at Buffalo

Are You a Good Fit for This Trial?

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.

My doctor agrees I am fit for the study considering my health and medications.

I can't swallow the temperature capsule due to GI issues or past surgery but can use it rectally.

Timeline for a Trial Participant

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

What Are the Treatments Tested in This Trial?

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.

How Is the Trial Designed?

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+

Published Research Related to This Trial

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]

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]

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]

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]

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]

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]

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]

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]

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 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]

Citations

1. withpower.com withpower.com/trial/phase-hyperthermia-7-2024-fc16f

Work/Rest Cycles for 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 ...

2. pmc.ncbi.nlm.nih.gov pmc.ncbi.nlm.nih.gov/articles/PMC10970706/

Plateau in Core Temperature during Shorter but Not Longer ... Core temperature plateaued with a 20/10 work/rest cycle, while it increased with a 40/20 cycle during the second hour of work.

3. clinicaltrials.gov clinicaltrials.gov/study/NCT06475339

Study Details | NCT06475339 | Predicting Responses to ... Participants will walk on a treadmill while wearing a weighted backpack to a work/rest cycle of 20 minutes of work followed by 12 minutes of rest. Participant ...

4. journals.lww.com journals.lww.com/joem/fulltext/2025/11000/air_conditioned_cooling_during_consecutive.6.aspx

Air-Conditioned Cooling During Consecutive Work-Rest ... Evidence suggests that passive rest after exertional heat stress decreases core temperature by an average of −0.004°C/min indicating inadequate cooling.

5. pmc.ncbi.nlm.nih.gov pmc.ncbi.nlm.nih.gov/articles/PMC10215832/

A Systematic Review of Post-Work Core Temperature ... These findings indicate passive rest does not reverse the elevated core temperatures of heat-exposed workers in a timely manner.

6. cdc.gov cdc.gov/mmwr/preview/mmwrhtml/mm6331a1.htm

Heat Illness and Death Among Workers — United States ... Thirteen cases involved a worker death attributed to heat exposure, and seven involved two or more workers with symptoms of heat illness.

7. stacks.cdc.gov stacks.cdc.gov/view/cdc/183128/cdc_183128_DS1.pdf

Heat Illness and Death Among Workers Exposure to heat and hot environments puts workers at risk for heat stress, which can result in heat illnesses and death. This report describes ...

8. osha.gov osha.gov/heat-exposure/hazards

Heat Hazard Recognition | Occupational Safety and Health ... This step allows employers to determine if the work conditions are too hot. Employers should be aware of any heat advisories from the National Weather Service.

9. pmc.ncbi.nlm.nih.gov pmc.ncbi.nlm.nih.gov/articles/PMC11131018/

Heat and health of occupational workers: a short summary ... Globally, occupational workers suffer various health impacts due to extreme heat. In this short review, we examine the literature discussing health impacts ...

10. mgaleg.maryland.gov mgaleg.maryland.gov/cmte_testimony/2020/ecm/2540_02252020_10113-399.pdf

Heat‐related deaths among construction workers in the ... The deaths and work‐relatedness were verified from death certificates, workers' compensation reports, OSHA reports, medical examiner reports, newspaper articles ...