The CaloBox – A letter from Prof. Heldmaier

The CaloBox is the result of several decades of development by the German physiologist and zoologist Professor Gerhard Heldmaier. After a  professorship in metabolic physiology at  Goethe University Frankfurt from 1976, Heldmaier was appointed to the chair for animal physiology at Marburg University in 1982.

His entire career was devoted to the study of animal metabolism – specifically regarding seasonal adaptions of temperature and body mass regulation in mammals and birds. Decades of own calorimetric measurements with traditional devices taught him the dire need for a new technology with push-button simplicity. Using his rich experience from the lab, the field, and with numerous novice students he designed his own measurement device – the CaloBox.


Multiple generations of the CaloBox have been used by him and various colleagues as their metabolic measuring instrument of choice for research and for teaching. The successive refinements and improvements have led to an instrument he considers nearly perfect. Here is what Prof. Heldmaier says about his CaloBox:

“Standard setups for indirect calorimetry require gas analysers for oxygen, for carbon dioxide and water vapour, plus pumps for cage ventilation and flowmeters to measure the air flow through the cage, all mounted in a 19’’ rack offering an impressive number of displays and knobs for handling. This makes indirect calorimetry a complex method and its installation expensive. Calculating results is cumbersome. Calibration of the gas analysers requires considerable efforts, with calibration gases and expensive calibration pumps for gas mixtures.

In most setups water vapour is not measured but removed from air by drying air with freeze traps or chemicals. Most are not user friendly (phosphor pentoxide, magnesium perchlorate) and are not reliable for long term use.

After having configured and used such setups for many years myself, and introducing students into the secrets of direct and indirect calorimetry, I am confident about the validity of the first law of laboratory work: anything that can go wrong, will. This showed me the dire need for the development of a small, portable, simple, reliable and user-friendly technology – the CaloBox.

The CaloBox combines sensors for oxygen, carbon dioxide, water vapour and air pressure in a single unit at  the size of a document bag. It includes pumps and flowmeters for the ventilation of an animal cage. The combination of multiple sensors in a single, small volume provides the basis for rapid responses and high accuracy of measurements. No drying of the air is required since water vapour is measured and included in the calculation.

The now mature software guarantees a maximum of user-friendly operation. The zero adjustment of sensors,  as well as the calibration of the oxygen sensor operates automatically in 15 min intervals, without user interaction. The measurement is continuous. Calculated results and sensor voltages are stored continuously. Measurement cycles and data storage can be varied by the user between 4 sec and 1 minute. The final results for metabolic rate (oxygen consumption, carbon dioxide production, water vapour production) are displayed on the computer screen, together with the respiratory exchange ratio (RER) and heat production calculated from metabolic rate and the RER.

For curious and advanced users, the CaloBox software allows access to detailed information on sensor voltages as well as semi-automatic calibration procedures for all gas sensors and flowmeters.

The first prototypes of the CaloBox were tested in field studies with alpine marmots at high altitude mountain locations even in winter and with lemurs on tropical Madagascar. These field studies were an important test for the robustness of the CaloBox technology as well as a prerequisite to keep everything as simple as possible.

For measuring with the CaloBox almost no action of the user is required.  The CaloBox is connected with an animal cage, turned on and immediately auto-collects sample air and reference air. Pushing the “Start” button on the computer screen starts measurements. The CaloBox does all the rest by itself.”


– Professor Gerhard Heldmaier