Temperature is just the starting point

When comparing two cryotherapy systems, the first piece of information that is usually taken into account is the temperature. One device reaches 5 °C, another 3 °C, whilst yet another claims to be able to reach as low as 0 °C.

It is natural to assume that the system capable of reaching the lowest temperature is also the most effective. From a thermodynamic point of view, however, the comparison is much more complex.

The temperature shown on the display actually represents the system’s setpoint – that is, the value the device is designed to reach and maintain. It does not automatically correspond to the temperature on the surface of the band, on the skin, or, even less so, in deep tissues. The new ZAMAR White Paper highlights precisely this distinction as one of the key points for correctly interpreting a cryotherapy system.

From the device to the patient: a chain of exchange

There are several stages between what we read on the display and what actually happens in the tissues.

The fluid is cooled inside the equipment, reaches the applicator, passes through the fascia and exchanges energy with the body’s surface. Heat must therefore pass through several elements before the cooling produces a change in skin temperature and, progressively, in the underlying tissues.

Experimental research confirms that cryotherapy modalities with different thermodynamic properties can generate different temperatures on the surface and within the muscle, even when used with the same general objective. Merrick and colleagues, when comparing different cooling modalities, observed significant differences both at the skin level and one centimetre beneath the adipose tissue. (PubMed)

This makes it clear why it is incorrect to use the value set on the machine alone as a proxy for the temperature actually reached by the patient.

Let us imagine two devices both set to 5 °C.

In the absence of the patient, they may reach exactly the same temperature. However, once the band is applied to the body, the system begins to continuously absorb heat from the tissues.

From that moment on, what matters is not only how cold the device has managed to become, but how much heat it is able to remove as the treatment progresses.

This is where other parameters come into play: cooling capacity, fluid volume and flow rate, the surface area of the wrap, the quality of contact, and the ability to maintain the set conditions over time. The White Paper V1.1 examines precisely how the interaction between these elements underpins overall thermal performance.

Device temperature and skin temperature

A recent randomised study on a continuous-flow cryocompression system provides a clear understanding of this difference.

With device settings of 6, 8, 10 and 12 °C, after thirty minutes the median skin temperatures were 12.8, 14.3, 16.1 and 17.7 °C respectively. In other words, the temperature set on the device and that measured on the skin were clearly different. (PubMed)

This is not an anomaly: it is the natural result of heat transfer.

For a professional, a more useful question than ‘what is the minimum temperature?’ might be:

Is the system capable of reaching and maintaining the set temperature under actual treatment conditions?

It is from this question that the whole process of exploring thermodynamics as applied to cryotherapy begins.

And the first parameter to understand, apart from temperature, is cooling capacity – that is, the system’s ability to extract heat over time.

Sources

Merrick M.A., Jutte L.S., Smith M.E. Cold Modalities With Different Thermodynamic Properties Produce Different Surface and Intramuscular Temperatures. Journal of Athletic Training. 2003;38(1):28–33. (PubMed)

Belsey J., Gregory R., Paine E., Faulkner J. Skin temperature of the knee was effectively reduced when using a new continuous cold-flow cryocompression device. Physiotherapy. 2024;123:11–18. (PubMed)

Nadler S.F., Weingand K., Kruse R.J. The physiological basis and clinical applications of cryotherapy and thermotherapy for the pain practitioner. Pain Physician. 2004;7(3):395–399. (PubMed)

ZAMAR. Comparative Engineering Analysis of Active-Control Cryotherapy Technologies – Version 1.1. Technical White Paper.