Related Experiment Video
Updated: May 30, 2026
07:09
Assessment of Pulmonary Capillary Blood Volume, Membrane Diffusing Capacity, and Intrapulmonary Arteriovenous Anastomoses During Exercise
Published on: February 20, 2017
Reliability of cycling gross efficiency using the Douglas bag method
James G Hopker1, Simon A Jobson, Hannah C Gregson
1Centre for Sports Studies, University of Kent, Kent, United Kingdom.
Medicine and Science in Sports and Exercise
|July 29, 2011
Summary
The Douglas bag method reliably measures gross efficiency (GE), a key indicator of exercise efficiency. Collecting larger gas samples minimizes potential errors, establishing this method as a gold standard.
Area of Science:
- Exercise Physiology
- Metabolic Measurement
- Biomechanical Analysis
Background:
- Gross efficiency (GE) is a critical measure of metabolic and mechanical energy utilization during physical activity.
- Accurate and reliable measurement of GE is essential for understanding exercise performance and training adaptations.
- The Douglas bag method is a traditional technique for collecting expired gases for metabolic analysis.
Purpose of the Study:
- To determine the reliability of the Douglas bag method for measuring gross efficiency (GE).
- To identify and quantify potential sources of error in the Douglas bag method for GE assessment.
- To establish the day-to-day variability of GE measurements in trained cyclists.
Main Methods:
- The study involved two parts: assessing potential errors in the Douglas bag method and evaluating within-subject day-to-day GE variability.
- Part 1 analyzed errors from gas concentration analysis, bag residual volume, and gas leakage/diffusion.
- Part 2 involved 10 trained male cyclists performing repeated GE measurements at various work rates (150-300 W) on separate days.
Main Results:
- Gas sampling reliability was high (CV <0.5% for O2 and CO2).
- Bag residual volume introduced a potential error of ~0.4 L (CV ~15%), which is reduced by collecting larger volumes.
- Within-subject day-to-day GE measurement showed a mean CV of 1.5% with limits of agreement of ±0.6% around a mean GE of 20.0%.
Conclusions:
- The Douglas bag method demonstrates very high reliability for measuring expired gases and calculating GE.
- This method is considered a gold standard for evaluating changes in gross efficiency.
- Minimizing errors in GE measurement is achievable by collecting larger expired gas samples.
Related Concept Videos
01:26Carnot Cycle and Efficiency
The Second Law of Thermodynamics asserts that it's impossible for any heat engine to achieve 100% efficiency. While contemplating the maximum possible efficiency, Nicolas Sadi Carnot conceptualized an ideal heat engine. This engine gets its energy from a high-temperature reservoir. It then performs some work and releases the remaining energy into a low-temperature reservoir.The Carnot cycle, named after Sadi Carnot, is fully reversible. The cycle consists of four distinct stages. In the first...
01:16Efficiency of The Carnot Cycle
The hypothetical Carnot cycle consists of an ideal gas subjected to two isothermal and two adiabatic processes. Since the internal energy of an ideal gas depends only on its temperature, which is the same before and after the completion of the Carnot cycle, there is no change in its internal energy. Hence, using the first law of thermodynamics, the total heat exchanged by the ideal gas equals the total work done. Thus, we can quantify the efficiency of the Carnot cycle via the heat exchanged...