Decreased contraction economy in mouse EDL muscle injured by eccentric contractions

Abstract

The objective of this study was to find out whether basal and/or active energy metabolism are altered in isolated mouse extensor digitorum longus muscle injured by eccentric (Ecc) contractions. Measurements of basal O2 consumption and isometric tetanus O2 recovery cost were made at 25 degrees C on muscles that had done either 10 Ecc, 10 isometric (Iso), or no contractions (No). In parallel experiments, rates of lactate and pyruvate production were measured to estimate the anaerobic contribution. Basal O2 consumption was unaffected by the type of protocol performed (P = 0.07). However, the tetanus O2 cost per force-time integral was elevated by 30-36% for the Ecc protocol muscles over that for the Iso and No protocol muscles. When including the increased lactate production by the Ecc protocol muscles, the total energetic cost per force-time integral was 53% higher than that for the Iso protocol muscles [2.35 +/- 0.17 vs. 1.54 +/- 0.18 mumol O2/(N.m.s)]. The decreased economy was attributed to two factors. First, in skinned fibers isolated from the injured muscles, the ratio of maximal actomyosin adenosinetriphosphatase activity to force production was up by 37.5%, suggesting uncoupling of ATP hydrolysis from force production. Second, increased reliance on anaerobic metabolism along with the fluorescent microscopic study of mitochondrial membrane potential and histochemical study of ATP synthase suggested an uncoupling of oxidative phosphorylation in the injured muscles.

Repeated muscle damage blunts the increase in heat strain during subsequent exercise heat stress

“…Muscle damaging exercise increases steady state exercising VO2 following downhill running (Braun and Dutto 2003) and rodent models have shown decreased contraction economy in damaged muscle fibres (Warren, III et al 1996). One might therefore anticipate improved running economy during HS on the second EIMD trial.…”

Effects of Eccentric Exercise on Cycling Efficiency

“…O 2 is caused by increased ATP utilisation due to decreased mechanical efficiency and/or reduced efficiency in ATP production, i.e., decreased efficiency in the energy transfer (P/O ratio). In theory, factors such as hyperthermia, increased plasma catecholamines, changes in mitochondrial respiration (Tonkonogi et al, 1998;Willis and Jackman, 1994), alterations in sarcoplasmic reticulum function (Tupling, 2004;Warren et al, 1996), increased recruitment of type II fibers (Krustrup et al, 2004a(Krustrup et al, , 2004b, and impairment of intermuscular coordination could contribute to increase ATP utilisation (Kyrolainen et al, 2000). However, neither hyperthermia (Gonzalez-Alonso et al, 1998) nor adrenaline infusion or betablockade (Mora-Rodriguez et al, 2001) alter V .…”

“…It has also been reported that muscle soreness is associated with decreased running economy in trained subjects (Braun and Dutto, 2003;Calbet et al, 2001). Warren et al (1996) have shown that eccentric exercise reduces concentric contraction economy in the muscle of the mouse. Human experiments also suggest that concentric muscle contractions are likewise impaired following exhaustive eccentric exercise, but to a lesser extent than eccentric contractions (Horita et al, 2003).…”

Eccentric contractions do not induce rhabdomyolysis in malignant hyperthermia susceptible mice

“…A typical response to an acute bout of eccentric contractions can include muscle fiber damage (26,27), increased presence of muscle proteins in the blood, resting cytosolic Ca 2ϩ perturbations (4,21,28,46), mitochondrial disruption (14,44), excitation-contraction (E-C) coupling failure (4,21), and immediate and prolonged functional deficits (4, 20 -22, 27, 29, 41). Usually, injured muscle undergoes a degenerative and regenerative process that repairs the injured muscle fibers and restores function on the order of days to weeks, depending on the age and health status of the individual and the severity of the injury.…”