COMPARISON OF THE EFFECTS OF ISOKINETIC VS ISOTONIC ECCENTRIC TRAINING ON MUSCLE STRENGTH AND MASS.

Introduction Eccentric (ECC) training has been shown to induce higher improvements than concentric training on muscle strength and mass (Roig, 2009). The majority of the studies have used isokinetic (ISOK) dynamometers for investigating the acute and chronic effects of ECC training. However, isotonic (ISOT) devices are more commonly available in real sport setting. Aim of the study was to compare ISOK to ISOT ECC training by assessing the effects on muscle strength and mass. Methods Forty-nine healthy sport science students were randomly divided in 3 groups: isokinetic eccentric training (ISOK, n=14), isotonic eccentric training (ISOT, n=17) and control group (CON, n=18). Both training groups performed 50 ECC repetitions of knee extension at 120% of their maximal strength measured in concentric modality (1RM for ISOT and peak concentric torque for ISOK), for a total of 14 times in 6 weeks. Isometric maximal voluntary contraction (MVC), concentric and eccentric strength at 60 °/s, 1RM, and muscle mass (using DEXA) were measured pre and post training. All dependent variables were analyzed after log transformation using ANCOVA, entering the baseline values as covariate and factor “group” as independent variable. Results Compare to CON, the ISOK group showed higher 1RM (12%, CI95% 6 to 19%), concentric (15%, 8 to 22%), eccentric (35%, 25 to 45%) and isometric (25%, 18 to 34%) maximal strength (P<0.001). Compare to CON, ISOT showed higher 1RM (14%, 9 to 20%), concentric (17%, 11 to 24%), eccentric (25%, 16 to 34%) and isometric (22%, 15 to 29%) maximal strength (P<0.001). No differences between ISOK and ISOT were found in 1RM (2%, -3 to 7%), concentric (-2%, -4 to 8%) and isometric (-3%, -8 to 3%) maximal strength. Only eccentric strength was higher in the ISOK compare to the ISOT group (8%, 1 to 14%). No differences between groups were found in muscle mass (0.419<P<0.769). Discussion This study showed that ECC training using both ISOK and ISOT improved maximal strength in physically active people. The lack of muscle mass changes suggests that the increase in muscle strength waw mainly due to neural adaptations (Hortobagyi, 1996). ISOK showed higher improvement in ECC strength measured on the isokinetic dynamometer but this may be due to similarity between testing and training conditions. Nevertheless, considering ISOT devices are more easily available this training modality seems to be a good alternative to ECC training using isokinetic dynamometers. References Roig et al., 2009, Br J Sports Med 43(8): 556-68. Hortobágyi et al., J Appl Physiol. 1996 Oct;81(4):1677-82.