ROS Scavenging Activity and Muscle Damage Prevention in Eccentric Exercise in Rats

Abstract

Depending on intensity, eccentric exercise is experimentally and clinically documented to have opposing dual effects on skeletal muscle, intense eccentric exercise damages muscle while daily low-load eccentric exercise prevents damage. To clarify mechanisms of this dual effect, microscopic damage and oxidative stress were studied in rat quadriceps muscle. Oxidative stress was estimated from immunostaining of advanced glycation end-products (AGE) and measurement of muscle tissue preparations, ability to scavenge reactive oxygen species (ROS). Intense eccentric downhill running (IEE) induced muscle damage, apparent microscopically 3 days after IEE. Since AGE-positive cells and decreased ROS scavenging activity were observed earlier (on the day after IEE), microscopically visible damage may be related to ROS production. Intense concentric uphill running (ICE) induced an immediate but transient decrease in ROS scavenging activity, which recovered within a day. Neither AGE-positive cells nor microscopic damage was observed after ICE. Since each contracting muscle fiber develops greater tension during eccentric than concentric exercise, the initial trigger of IEE-induced muscle damage may be damage at the subcellular level to muscle fibers and connective tissues. Daily low-load training of eccentric downhill running (LET) but not concentric uphill running efficiently prevented muscle damage after subsequent IEE. No evident elevation of ROS scavenging activity was evident after LET. We concluded that LET prevents IEE-induced muscle damage not through elevated ROS scavenging activity, but through suppression of initial subcellular damage that triggers subsequent ROS-producing processes resulting in microscopically visible delayed damage.