Eccentric Exercise Causes Specific Adjustment in Pyruvate Oxidation by Mitochondria.

INTRODUCTION: The impact of eccentric exercise on mitochondrial function has only been poorly investigated and remains unclear. This study aimed to identify the changes in skeletal muscle mitochondrial respiration, specifically triggered by a single bout of eccentric treadmill exercise. METHODS: Male adult mice were randomly divided into eccentric (ECC; downhill running), concentric (CON; uphill running), and unexercised control groups ( n = 5/group). Running groups performed 18 bouts of 5 min at 20 cm·s -1 on an inclined treadmill (±15° to 20°). Mice were sacrificed 48 h after exercise for blood and quadriceps muscles collection. Deep proximal (red) and superficial distal (white) muscle portions were used for high-resolution respirometric measurements. RESULTS: Plasma creatine kinase activity was significantly higher in the ECC compared with CON group, reflecting exercise-induced muscle damage ( P < 0.01). The ECC exercise induced a significant decrease in oxidative phosphorylation capacity in both quadriceps femoris parts ( P = 0.032 in proximal portion, P = 0.010 in distal portion) in comparison with the CON group. This observation was only made for the nicotinamide adenine dinucleotide (NADH) pathway using pyruvate + malate as substrates. When expressed as a flux control ratio, indicating a change related to mitochondrial quality rather than quantity, this change seemed more prominent in distal compared with proximal portion of quadriceps muscle. No significant difference between groups was found for the NADH pathway with glutamate or glutamate + malate as substrates, for the succinate pathway or for fatty acid oxidation. CONCLUSIONS: Our data suggest that ECC exercise specifically affects pyruvate mitochondrial transport and/or oxidation 48 h after exercise, and this alteration mainly concerns the distal white muscle portion. This study provides new perspectives to improve our understanding of the mitochondrial adaptation associated with ECC exercise.

Eccentric Muscle Contractions: Risks and Benefits.

Eccentric contractions, characterized by the lengthening of the muscle-tendon complex, present several unique features compared with other types of contractions, which may lead to unique adaptations. Due to its specific physiological and mechanical properties, there is an increasing interest in employing eccentric muscle work for rehabilitation and clinical purposes. However, unaccustomed eccentric exercise is known to cause muscle damage and delayed pain, commonly defined as "Delayed-Onset Muscular Soreness" (DOMS). To date, the most useful preventive strategy to avoid these adverse effects consists of repeating sessions involving submaximal eccentric contractions whose intensity is progressively increased over the training. Despite an increased number of investigations focusing on the eccentric contraction, a significant gap still remains in our understanding of the cellular and molecular mechanisms underlying the initial damage response and subsequent adaptations to eccentric exercise. Yet, unraveling the molecular basis of exercise-related muscle damage and soreness might help uncover the mechanistic basis of pathological conditions as myalgia or neuromuscular diseases. In addition, a better insight into the mechanisms governing eccentric training adaptations should provide invaluable information for designing therapeutic interventions and identifying potential therapeutic targets.

Effects of eccentrically and concentrically biased training on mouse muscle phenotype.

INTRODUCTION: The molecular adaptations specifically induced by different muscle contraction types have only been partially elucidated. We previously demonstrated that eccentric contractions in human quadriceps elicited proteome modifications that suggest a muscle fiber typology adaptation. We address this question in a more systematic way by examining here the effects of different running modes on the mouse muscle proteome and the muscle fiber typology. METHODS: Male adult mice (C57BL6) were randomly divided into downhill running (DHR) (quadricipital eccentrically biased contractions), uphill running (UHR) (quadricipital concentrically biased contractions), and untrained control (CONT) groups. Running groups performed five training sessions on an inclined treadmill for 75 to 135 min · d(-1), and the quadriceps muscles were dissected 96 h after the last session. Muscle protein extracts of DHR and UHR groups (n = 4/group) were subjected to a two-dimensional difference in gel electrophoresis (2D-DIGE) analysis coupled with mass spectrometry. The assessment of fiber type, size, and number was performed on the rectus femoris of the three groups (n = 6/group) using myosin heavy chain immunohistochemistry. RESULTS: In the proteomic analysis, eight spots identified as the fast myosin heavy chain isoforms exhibited a lower abundance in DHR compared with UHR (P < 0.05, t-test). In contrast, adenosine triphosphate (ATP) synthase subunit α and tubulin ß were more expressed in DHR (P < 0.05). A significant higher proportion of Type I and IIa fibers was found for DHR compared with UHR or CONT groups (P < 0.05, one-way ANOVA). CONCLUSIONS: Our data suggest that the eccentrically biased contractions in mice induced specific adaptations in protein expression and muscle fiber composition, which may reflect a more oxidative muscle phenotype. The differences in stress placed on the muscle between both trainings may be responsible for some unique adaptations resulting from the eccentrically biased training.

Human muscle proteome modifications after acute or repeated eccentric exercises.

INTRODUCTION: Delayed-onset muscle soreness (DOMS), a condition triggered by eccentric exercise, affects muscle cells at a biochemical level in a poorly understood fashion. The objective of the present study was to examine human muscle proteome modifications induced by strenuous eccentric exercises after a specific training aimed to prevent DOMS. METHODS: Biopsy samples of the rectus femoris were obtained from healthy human volunteers in three successive conditions: 1) at rest, 2) 24 h after an injuring exercise protocol consisting of three series of 30 maximal contractions of the quadriceps on an isokinetic dynamometer, and 3) 24 h after a similar exercise bout preceded either by five eccentric training sessions or by no training. RESULTS: Muscle damage was assessed before and 1 d after each maximal eccentric test by comparing three indirect markers: plasma activity of creatine kinase, muscle stiffness, and subjective pain intensity. Compared with the first eccentric test, those markers were reduced after the second test and further reduced if this second test followed the eccentric training, thus confirming the protective effect of such training. Muscle protein extracts were subjected to a two-dimensional difference gel electrophoresis proteomic analysis coupled with matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry protein identification. Surprisingly, we observed that myosin heavy chains decreased after the first eccentric test and were reduced further with other contractile proteins after the second test. Furthermore, the expression of several glycolytic enzymes decreased only after the second test, which was preceded by a specific training. CONCLUSIONS: These findings suggest that the eccentric training resulted in a switch to oxidative metabolism, which may be associated with protection from DOMS.