HEALTH-PROMOTING EFFECTS OF ECCENTRIC EXERCISE

Abstract

Dear Editor-in-Chief: We read the well-conducted clinical trial by Paschalis et al. (1) about the effects of eccentric and concentric exercise on muscle physiology and blood biochemistry. It was concluded that only 30 min of eccentric exercises per week can induce health-promoting effects and that these effects may be large enough to improve quality of life. Although the authors presented their conclusions as applicable for the general population, we have some doubts about the generalizability of their results. The authors presented training effects of concentric and eccentric training in young, nontrained women. However, compared to all comparable studies from a recent systematic review on concentric and eccentric training in healthy individuals (2), the gain in both concentric and eccentric torque is much higher in the study of Paschalis et al. (1). Studies in untrained women, within the same age range, showed gain in eccentric torque of the knee extensors of 34 N·m in the eccentric training group and around 15 N·m of concentric torque in the concentric training group (2). In comparison, Paschalis et al. (1) reported gains of 54 and 26 N·m for these torques among the same training groups. Moreover, their average gains are both outside the range found in the systematic review, which also included studies among trained men, whereas trained individuals performed better than those untrained and men performed better than women did (2). Unfortunately, the authors did not discuss these findings in their article, and the authors' opinion on possible reasons for these differences in study outcome remains unclear. Probably, a more precise description of some of the exclusion criteria would have resulted in a better interpretation of the results. For instance, the authors required participants to have abstained from activities with "a large eccentric component" for the last 6 months. However, they did not specify these activities or to what extent these activities were allowed. This troubles comparison of their results to other studies, although it may contain a reason for differences in outcome measures. Overall, some ambiguities about the training protocol remain, which complicate interpretation of the results. The authors did not show the level of effort performed by the subjects in both groups during the exercises. So the difference in outcome measures between the groups is not, by definition, due to the different type of exercise but may also be associated with the intensity of the performed exercises. As indicated in the systematic review of Roig et al. (2), no difference between concentric and eccentric training on strength gain exists when intensity was kept equal among the groups. Besides, recreational activities performed during the period of experimental intervention may also be related to the outcome measures. A recent systematic review and meta-analysis showed that nonvigorous activities reduce all-cause mortality (3). This indicates that participants with an active lifestyle, containing nonvigorous activities, probably score better on general health. Because the authors mentioned to have recorded these activities for both exercise groups, we would be very interested in these data. Karen Vermaas Jos Runhaar Department of General Practice Erasmus MC - University Medical Centre Rotterdam, The Netherlands