Heat does more than make us uncomfortable. It quietly chips away at human performance and shortens the life of devices and materials.

The challenge has been measuring that damage cleanly and comparing it across very different systems. A fresh framework now shows how temperature rise pulls down reliability and speeds wear.

How heat harms systems

The physics here sits inside thermodynamics, the study of how energy moves and changes form.

When a system runs, a slice of useful energy turns into heat, and that heat can reorganize a material’s microstructure in ways that add up to damage over time.

This work comes from Dr. Jude A. Osara, an assistant professor in the Faculty of Engineering Technology at the University of Twente.

His project asks a simple question with big consequences, how much of what fails in real systems comes from temperature rise itself.

Heat also raises entropy, a measure of internal disorder, and entropy links to both performance and degradation.

The key is to separate what heat does from what the main job of the system is doing, whether that is moving a bike crank, storing charge, or sliding a bearing.

Measuring heat damage

Osara introduces microstructurothermal (MST) entropy, a term that captures the specific contribution of temperature rise to change inside a system.

In tests with a lithium-ion cell, the framework found that temperature rise accounted for about 37 percent of total degradation during discharge.

That number matters because it is easy to ignore heat when the main signal feels dominant.

A battery’s current looks big compared with its heat, and an athlete’s power meter looks louder than their skin temperature, yet the thermal side still bites into durability.

The framework also distinguishes transformation, how performance is changing right now, from degradation, the lasting loss of health.

Keeping those threads apart makes it easier to see when cooling restores capacity and when it only slows the slide.

Heat in bodies and batteries

“My calculations show that heat is not just a by-product, but an active mechanism that impairs performance and accelerates degradation,” said Dr. Osara.

In the same analysis, elite cyclists training at 32°C (89.6°F) showed a 27 percent higher cardiovascular load than at 23°C (73.4°F).

Exercise studies back up that picture with measured outcomes. A classic study of 11 elite road cyclists recorded roughly a 6.5 percent drop in power output during a 30 minute time trial at 32°C compared with 23°C.

The battery world tells a similar story, and it is not just the average temperature that matters.

Even small thermal gradients speed damage, with one study showing that a 3°C (37.4°F) difference inside a single cell drove a 300 percent increase in degradation.

Heat in mechanical systems

In mechanical systems like journal bearings, friction creates both wear and heat. When cooling is poor, that heat raises local temperatures, changes material properties, and speeds the breakdown of the surfaces in contact. 

Tests have shown that once the temperature rise passes certain thresholds, the damage rate grows far more quickly than expected from friction alone.

Greases and lubricants face similar problems. Their microstructures soften or chemically change when exposed to elevated temperatures.

Even when the load or pressure is constant, heat shifts the balance toward earlier failure, shortening service life. 

By applying the MST framework, these small but steady losses can be tracked and managed with more precision.

Keeping systems cool

The stakes are growing, fast. Globally, electricity use for cooling is projected to more than double by 2050, according to a UN report.

For engineers, the takeaway is straightforward. Keep the MST term small by limiting heat generation, improving heat spread, and holding temperature in the device’s sweet spot.

For clinicians and athletes, the same logic applies. Cooler skin and steadier core temperature reduce cardiovascular strain, support output, and lower risk.

For operators and maintainers, the numbers help prioritize actions. If a third of a battery’s degradation rides on temperature rise, smarter tribology choices, better airflow, or active cooling are not add-ons, they are life-extenders.

For students, the framework shows how to make a clean energy balance that includes both the useful work and the thermal side.

It also shows why reversible, near-isothermal steps can act like “healing” in rechargeable cells, because they add energy while holding dissipation near zero.

The study is published in Applied Mechanics.

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