COPD Limitations

The major limitations are the following:
- ‘All’ studies had a small number of enrolled COPD patients, ranging from 16 to 92 participants. A fact possibly due to the strict criteria for patient inclusion and the severity of the disease of the patients evaluated. It could be that if the sample size was larger many papers could have confirmed greater differences.
- 3 studies (Knowles et al., Lewis et al. & Rogers et al.) were +20 years old. Older papers have a weaker methodological quality and it’s a fact that there are more new insights in respiratory rehabilitation. There’s also more known about the underlying processes of the weight loss in patients with COPD, the training principles,...
- 4 studies (Ahnfeldt et al., Sugawara et al. & Vermeeren et al.) reported that the treatment period was too short to achieve a definitive conclusion.
- COPD patients are a very heterogeneous group, which

For example in the study of Lewis the intervention group was unable to tolerate greater than 240 ml of the isocal. HCN per day in addition to their normal diet because of symptoms of bloating and fullness.
- 3 studies (Sugawara et al., Laviolette et al.) were pilot studies and this can be considered as a weakness because of their pilot character.
- There is still so many difference between the results of the different studies, which makes it quite impossible to make a clear and unambiguous decision.
- In a lot of studies, there was a lack of information regarding the methodological quality of the studies. For example: blinding of the subjects and concealment of the allocation weren’t always explicitly mentioned.
- In the study of Creutzberg et al. the control group was taken from the study of Schols et al.. This could be a possible limitation, because each control group has different characteristics. Which can mean if another control group was used other results could have been