Low-frequency fatigue is fibre type related and most pronounced after eccentric activity in rat medial gastrocnemius muscle

Abstract

Effects of fibre type composition and type of contraction on low-frequency fatigue (LFF) were investigated in isolated rat medial gastrocnemius (GM) muscle. Fast oxidative or fast glycolytic GM muscle parts of anaesthetised male Wistar rats (n=18) were activated selectively by maximal electrical stimulation of the nerve after selective cutting of sub-branches. LFF was induced by a series of 40 isometric, concentric or eccentric contractions. Post exercise (55 min), the force-frequency curves differed significantly from the pre-exercise curves. Decreased forces were exerted mainly at the lower frequencies. This effect was significantly greater for glycolytic than oxidative muscle parts and following eccentric compared to isometric and concentric exercise. Seventy minutes following eccentric exercise, the relative values of the 60:200 Hz force ratios for the oxidative compared to the glycolytic parts were 65.6+/-2.2% and 43.6+/-4.6% (mean+/-SE) of the pre-fatigue values (=100%), respectively. In conclusion, for conditions of identical activation, eccentric exercise led to significantly more LFF than isometric and concentric exercise. In addition, and independent of the exercise type, fast glycolytic muscle parts were more susceptible to LFF than fast oxidative muscle parts.

Low-frequency fatigue at maximal and submaximal muscle contractions

“…www.bjournal.com.br the force-pCa 2+ curve, whereas high frequencies relate to the horizontal part (25). Therefore, according to the forcefrequency relationship, little variations in intra-muscular Ca 2+ concentrations result in greater changes in the force produced with low stimulation frequencies compared to that produced with high stimulation frequencies (3,33).…”

“…The submaximal exercise in this study could have been accomplished with predominantly slow-twitch motor unit activation. Rijkelijkhuizen et al (25) studied regions of the rat's gastrocnemius muscle with different fiber type distribution and found greater levels of LFF in the fast glycolytic compared to the fast oxidative muscle fibers. Some investigators attribute such results to the greater susceptibility of fast contraction fibers to fatigue and injury (26,27) compared to the slow fibers.…”

“…As eccentric exercise is known to be more destructive to the muscle fibers than other types of contraction (29,30), damage to the sarcoplasmic reticulum leading to diminished Ca 2+ release, as well as sarcolemmal damage that could interfere with Ca 2+ homeostasis (22,25), might have been greater in the maximal eccentric fatigue test. However, as we did not examine Ca 2+ concentrations, we cannot say which effects each one of our four protocols had on these variables.…”

Muscle Fatigue Increases the Probability of Developing Hyperalgesia in Mice

“…50 It can occur as a result of concentric, eccentric, or isometric contractions. 35 However, muscle damage and delayed onset muscle soreness occur predominately with eccentric contractions. Eccentric induced soreness is generally associated with inflammatory changes in exercised muscle that includes infiltration of leukocytes, increases in lactate, increases in phosphate, fatigue, and pain.…”

Low-Frequency Fatigue in Individuals With Spinal Cord Injury

“…However, it has been reported that fast-glycolytic fibers show greater LFF than do fast-oxidative fibers (18,19). Powers and Binder (18) reported that fatigueresistant motor units from cat flexor digitorum muscles exhibited less pronounced LFF than fast intermediate and fast-fatigable motor units after electrically stimulated contractions.…”