Preconditioning Exercise Effect On Biceps Brachii Myotendinous Junction Displacement During Elbow Flexor Eccentric Contractions

Abstract

The extent of biceps brachii distal myotendinous junction displacement (MTJd) during maximal eccentric contractions (MaxEC) of the elbow flexors (EF) increased over 10 sets in the first MaxEC bout, but did not increase during the second MaxEC bout that was performed 4 weeks later (Lau et al. AJP-RICP 2015). This suggests that the repeated bout effect (RBE) is associated with a reduction in muscle lengthening during MaxEC. However, it has not been investigated if this is also the case for the RBE conferred by low-intensity (10%) 30 eccentric contractions (10%EC) or two maximal isometric contractions at a long muscle length (2MVIC). These two exercises were shown to attenuate the magnitude of muscle damage induced by subsequent MaxEC (Chen et al. MSSE 2012). PURPOSE: This study tested the hypothesis that 10%EC or 2MVIC that was performed at two days before EF MaxEC consisting of 5x6 MaxEC would reduce increases in MTJd over MaxEC, and it would be associated with the protective effect by preconditioning exercise. METHODS: Sedentary young men were randomly placed (n = 12/group) to a control group that performed two bouts of MaxEC (CONT-1st, CONT-2nd) separated by two weeks, or one of two preconditioning groups that performed 10%EC or 2MVIC at 20o elbow flexion at two days before MaxEC. All exercises were performed by the non-dominant arm. MTJd of each contraction was assessed by B-mode ultrasound, and its changes over sets were compared among the groups. Several muscle damage markers were measured before to 2 or 5 days after each bout, and the changes were compared by a mixed-design two-way ANOVAs. RESULTS: The average MTJd from the start to the end of six MaxEC in the first set was similar among the groups (6.4 ± 0.7 mm). The MTJd increased from the first to fifth set, but the increase was smaller (P < 0.05) for the 10%EC (13 ± 6%) and 2MVIC (16 ± 9%) groups, and CONT-2nd (3 ± 6%) when compared with CONT-1st (60 ± 12%). Both 10%EC and 2MVIC groups showed smaller (P < 0.05) changes in all muscle damage markers after MaxEC similarly when compared with CONT-1st, but the changes were greater than those after CONT-2nd. CONCLUSIONS: These results supported the hypothesis, suggesting that less MTJd changes are associated with the mechanisms underpinning the preconditioning effect on muscle damage. Supported by MOST, TAIWAN (MOST108-2410-H-003-116-MY3).