Effect of preconditioning exercise on biceps brachii myotendinous junction displacement during elbow flexor eccentric exercise.

The present study tested the hypothesis that 30 low-intensity (10%) eccentric contractions (10%EC) or two maximal voluntary isometric contractions at a long muscle length (2MVIC) that were performed at two days before maximal eccentric exercise of the elbow flexors consisting of five sets of six maximal eccentric contractions (MaxEC) would reduce increases in biceps brachii distal myotendinous junction displacement (MTJd) over the eccentric contractions during MaxEC. 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 20° elbow flexion at two days prior to 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. The average MTJd from the start to the end of six eccentric contractions 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 < .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 < .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. These results supported the hypothesis that protective effect was associated with less MTJd changes, suggesting that this is associated with the mechanisms underpinning the preconditioning effect on muscle damage.

Low-intensity eccentric contractions attenuate muscle damage induced by subsequent maximal eccentric exercise of the knee extensors in the elderly.

This study investigated whether low-intensity eccentric contractions of the knee extensors would attenuate the magnitude of muscle damage induced by maximal eccentric exercise of the same muscle performed 7 days later using elderly individuals. Healthy older men (66.4 ± 4.6 years) were assigned to control or experimental (Exp) group (n = 13 per group). The control group performed six sets of ten maximal eccentric contractions (MaxECC) of the knee extensors of non-dominant leg. The Exp group performed six sets of ten low-intensity eccentric contractions of the knee extensors on a leg extension machine by lowering a weight of 10 % maximal voluntary isometric knee extension strength (10 %ECC) 7 days prior to MaxECC. Changes in maximal voluntary isokinetic concentric torque (MVC-CON), angle at peak torque, range of motion (ROM), upper thigh circumference, muscle soreness, plasma creatine kinase activity and myoglobin (Mb) concentration and B-mode ultrasound echo-intensity before and for 5 days after MaxECC were compared between groups by a mixed factor ANOVA. No significant changes in any variables were observed following 10 %ECC. Following MaxECC, all variables changed significantly, and changes in all variables except for angle at peak torque were significantly different between groups. MVC-CON and ROM decreased smaller and recovered faster (P < 0.05) for Exp than control group, and changes in other variables were smaller (P < 0.05) for Exp group compared with control group. These results suggest that preconditioning knee extensor muscles with low-intensity eccentric contractions was effective for attenuating muscle damage induced by subsequent MaxECC of the knee extensors for elderly individuals.