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Communications to the Editor |

Measuring the Work of Exercise FREE TO VIEW

Carl M. Kirsch, MD, FCCP
Author and Funding Information

Affiliations: Santa Clara Valley Medical Center, San Jose, CA,  University of Vermont College of Medicine, Burlington, VT

Correspondence to: Carl M. Kirsch, MD, FCCP, Chief, Division of Respiratory and Critical Care Medicine, Santa Clara Valley Medical Center, 751 S Bascom Ave, San Jose, CA 95128; e-mail: danjosh2@aol.com



Chest. 2004;126(3):1006-1007. doi:10.1378/chest.126.3.1006
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Published online

To the Editor:

Drs. Irvin and Kaminsky (January 2004)1 have stated that “… often there is a discordance between work (watts) and [oxygen uptake] V̇o2 in clinical testing, making the interpretation and final determination of exercise tolerance difficult.” The authors suggested that normal exercise should be predicted as the maximal number of watts rather than the maximal V̇o2.

Our exercise laboratory uses the predicted maximal V̇o2 based on ideal body weight, and we have had good agreement between the percent predicted values for these two measurements in our patient population. I think that discrepancies in these two measurements may be due to the usage of inappropriate predicted equations or weights, especially in obese patients. It makes sense that the measured work on a cycle ergometer (expressed in watts) is only part of the patient’s total work done. Additional work by the muscles of respiration and upper arm musculature cannot be measured at the pedals but can be measured as V̇o2. If there are no technical errors, a discrepancy between maximal work done at the pedals (watts) and V̇o2 may actually be important information indicating a significant component of nonleg work. Therefore, I suggest that readers not necessarily abandon the use of maximal V̇o2 as a measure of total work done.

Irvin, CG, Kaminsky, DA (2004) Exercise for fun and profit.Chest125,1-3. [CrossRef] [PubMed]
 
To the Editor:

We thank Dr. Kirsch for his comments regarding the use of work vs oxygen uptake (V̇o2) to assess exercise tolerance. Most of the time, these two measures are in close agreement in terms of percent predicted and can be used interchangeably as objective measures of exercise tolerance. Dr. Kirsch correctly points out some of the reasons for the discrepancies between these two measures, such as the selection of appropriate predicted values, especially in obese individuals, and the performance of different types of exercise. Most studies relating exercise capacity to important outcomes such as survival or the ability to tolerate lung resection surgery use V̇o2 as the measure of exercise capacity because it reflects the physiologic health of the individual in terms of their global ability to utilize oxygen. Our suggestion that work may be a more appropriate measure of exercise tolerance is based on our view of exercise expressed as power output (work per unit of time) rather than oxygen utilization. Indeed, many subjects achieve a percent predicted for work that is higher than their maximal percent predicted V̇o2, likely indicating a motivational ability to sustain exercise beyond the anaerobic threshold. In real-world terms of the ability to perform various tasks and activities, the amount of work someone is able to do seems more relevant than the amount of oxygen they can consume. In this regard, defining exercise tolerance in terms of work is also more appropriate when prescribing exercise or explaining the results of exercise testing to patients. As we stated in the editorial, we invite more discussion in this area of the definition of exercise tolerance.


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References

Irvin, CG, Kaminsky, DA (2004) Exercise for fun and profit.Chest125,1-3. [CrossRef] [PubMed]
 
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