Eccentric muscle contraction potentiates titin stiffness-related contractile properties in rat fast-twitch muscles.

This study was conducted to examine the effects of an acute bout of eccentric muscle contraction (ECC) on titin stiffness-related contractile properties in rat fast-twitch skeletal muscles. Intact gastrocnemius muscles were electrically stimulated in situ to undergo 200 repeated ECCs. Immediately after the cessation of the stimulation, the superficial regions of the muscles were dissected and subjected to biochemical and skinned fiber analyses. Small heat shock protein αB-crystallin in the muscle fraction enriched for myofibrillar proteins was increased by ECC. ECC resulted in an increase in the titin-based passive force. Protein kinase A-treatment decreased the passive force only in ECC-subjected but not in rested fibers. ECC decreased the maximum Ca-activated force at a sarcomere length (SL) of 2.4 μm and had no effect on myofibrillar-Ca sensitivity at 2.6-μm SL. In both rested and ECC-subjected fibers, these two variables were higher at 3.0-μm SL than at 2.4- or 2.6-μm SL. The differences in the two variables between the short and long SLs were greater in ECC-subjected than in rested fibers. These results indicate that an acute bout of ECC potentiates titin-based passive force, maximum active force at long SLs, and length-dependent activation and suggest that this potentiation may resist muscle fatigue in the muscles of the exercising body. It remains unclear whether eccentric contraction of skeletal muscle affects titin stiffness-related contractile properties. Here, we provide evidence that an acute bout of eccentric contraction can potentiate titin-based passive force, maximum active force at long sarcomere lengths, and length-dependent activation. This potentiation may resist muscle fatigue in the muscles of the exercising body.