We read with interest the article recently published by Bacchi et al. and would like to provide a few comments on the article.
Nonalcoholic fatty liver disease (NAFLD) is now becoming the most common liver disease in the world and Bacchi et al. were able to demonstrate that exercise per se is effective in decreasing hepatic fat content and improving hepatic steatosis of adults suffering from type 2 diabetes and NAFLD. The data provide an important contribution to the highly relevant “exercise is medicine” paradigm, which further gains ground by evidence presented in the work of Bacchi et al. In our opinion, however, it would be important to match energy expenditure of both interventions. Descriptions of the volume of resistance training (RT) seem inappropriate and difficult to comprehend, leaving some aspects unclear, e.g., was the weight adjusted to match the progress of the subjects? Further, hepatic fat content is ∼20% higher in the RT compared to the aerobic training (AT) group, whereas caloric intake is ∼15% lower.
The point we want to make here is that especially in untrained subjects with a body mass index (BMI) of about 30 with probably little or no previous experience in exercise training, the stimulus of RT resembles more an AT stimulus. Whereas classic RT is characterized by an increase in muscle mass and muscle cross-sectional area, untrained subjects probably do not reach the threshold that is necessary for these adaptations to occur. Therefore, the mild RT carried out provokes a similar response comparable to the AT in this study despite very distinct pathways that are activated during classic RT. The similar effect of both interventions is indicative of a similar stimulus. We want to emphasize that it is necessary to distinguish between mild RT resembling more an AT stimulus and the classic RT that is commonly known when confronted with the term RT. The same phenomenon was observed by our group when conducting a training study with untrained people (BMI ∼26) who were subjected to either strength or endurance training. After 10 weeks of training, we saw similar increases in the capacity to oxidize fatty acids in both groups. In conclusion, RT carried out by well-trained athletes cannot be compared to the mild, resistance-type (circuit) training providing a distinct stimulus.
Dominik Pesta, Ph.D.1,2Martin Burtscher, M.D., Ph.D.3
1Howard Hughes Medical InstituteYale University School of Medicine New Haven, CT2Department of Internal MedicineYale University School of MedicineNew Haven, CT3Department of Sports ScienceUniversity of InnsbruckInnsbruck, Austria