The goal of the experimental study is to understand the impact of heat stress on core temperature and telomere length. Investigators will recruit rickshaw drivers who use manual power to push their rickshaws and randomly assign half of them to receive battery-powered rickshaws to use for four months. Investigators will assess how this change impacts their core body temperature while they work, the length of their telomeres (caps on the end of DNA that are associated with aging), and kidney function.

Personal exposure to heat may be elevated above ambient temperatures if an individual is very active (which generates metabolic heat) or wears clothing that prevents cooling. Age can influence the consequences of heat stress. Older adults are at elevated risk of adverse impacts from heat stress due to their reduced ability to dissipate heat. Heat stress is particularly high among outdoor workers. South Asia has millions of bicycle rickshaw drivers, who use their muscles or battery power to pull hundreds of pounds of passengers and goods on modified bicycles. When manual rickshaw drivers rest to cool off, they reduce their already meager income. Heat stress not only threatens their livelihoods and thereby their right to an adequate standard of living but also their right to work, given that they have few employable skills other than manual labor. South Asia faces the greatest current and predicted loss in disability-adjusted life years due to heat stress, and heat stress is particularly strong in informal settlements. As such, the investigators plan to conduct this study in Dhaka, Bangladesh. The overall hypothesis is that driving a battery-powered rickshaw will reduce heat strain. The investigators will evaluate the impact of driving a battery-powered rickshaw on core temperature (primary outcome), telomere length, kidney function, heart rate, heart rate variability, sleep quality, self-reported thermal comfort, mental health, wellness, and fatigue (secondary outcomes).

Inclusion Criteria:

• Reports driving a manual rickshaw at least five days per week for at least 8 hours per day for the past 12 months

Exclusion Criteria:

• Reports driving a battery-powered rickshaw in the past 12 months
• Has hypertension, as measured by our study staff
• Has diabetes, as measured by our staff
• Reports diagnosis with cardiovascular disease / chronic cardiac condition
• Reports diagnosis with respiratory disease / chronic respiratory condition

Self-identify as a male. We will use this information about gender only as a proxy for sex, as we will not be assessing sex through chromosomal analysis.

We will post de-identified participant data on our OSF repository (https://osf.io/sd285/)

We expect that data and code will become available by 1 Jan 2027