Effects of eccentric exercise-induced muscle damage on intramyocellular lipid concentration and high energy phosphates

Thirty minutes of moderate-intensity downhill or level running has no effect on postprandial lipemia: A randomized controlled trial

Elevated postprandial triglyceride (TG) concentrations are linked to a relatively high risk of cardiovascular disease. Eccentric endurance exercise, such as downhill walking and running, can provide metabolic benefits similar to concentric exercise. However, whether eccentric exercise affects postprandial lipemia remains unknown. Nine healthy young men performed level running (trial) or downhill running (DR trial, -15% slope) at 60% [INSIDE:1]O_2max or rest (CON trial) for 30 min in a randomized crossover design. The participants were fed a high-fat meal the next day. Blood and expired gas samples were collected before and 0.5, 1, 2, 3, 4, 5, and 6 h after the meal. Muscle soreness was measured using a visual analog scale. The DR trial induced mild muscle damage. During the 6-h postprandial period, serum TG concentrations and area under the curve (AUC) were similar across the three trials. The DR trial had a significantly higher AUC of nonesterified fatty acid concentrations and a significantly lower AUC of glucose concentrations than the CON trial. The results suggested that neither moderate-intensity DR nor running a level surface had a significant effect on lipemia after a high-fat meal. However, DR improved the postprandial glycemic response.

Eccentric Training Improves Body Composition by Inducing Mechanical and Metabolic Adaptations: A Promising Approach for Overweight and Obese Individuals

Skeletal muscle generates force by either shortening (concentrically) or lengthening (eccentrically). Eccentric (ECC) exercise is characterized by a lower metabolic demand and requires less muscle activity than concentric (CON) exercise at the same level of exerted force. However, the specific effect of ECC training vs. CON training on lean and fat mass remains underexplored. The first aim of this paper was to review the available evidence regarding the effects of ECC training on whole body and segmental lean and fat mass and, when possible, compare these with the effects of CON training. The second aim was to provide some insights into the main mechanical, physiological, and metabolic adaptations of ECC training that contribute to its effects on body composition. The third aim was to determine the beneficial effects of ECC exercise on health-related parameters in overweight and obese patients. ECC training is an effective modality to improve lean mass, but when matched for load or work, the difference between ECC and CON trainings seems unclear. A few studies reported that ECC training is also efficient at reducing fat mass. By increasing post-exercise resting energy expenditure, modifying metabolic substrate, and improving both blood lipid profile and insulin resistance, ECC training is a potential exercise modality for individuals with chronic conditions such as those who are overweight and obese. Further investigations using standardized experimental conditions, examining not only segmental but also whole body composition, are required to compare ECC and CON trainings.

Similar substrate oxidation rates in concentric and eccentric cycling matched for aerobic power output

This study investigated substrate oxidation in concentric and eccentric cycling matched for aerobic power output in the postprandial state. Energy expenditure, respiratory exchange ratio, and fat and carbohydrate oxidation rates were measured at rest and after 15, 30, and 45 min of eccentric and concentric cycling in 12 men. Absolute and relative aerobic power output and energy expenditure were similar during concentric and eccentric exercise. No effect of exercise modality was observed for substrate metabolism.

Early metabolic changes measured by 1H MRS in healthy and dystrophic muscle after injury

Skeletal muscle injury is often assessed by clinical findings (history, pain, tenderness, strength loss), by imaging, or by invasive techniques. The purpose of this work was to determine if in vivo proton magnetic resonance spectroscopy ((1)H MRS) could reveal metabolic changes in murine skeletal muscle after contraction-induced injury. We compared findings in the tibialis anterior muscle from both healthy wild-type (WT) muscles (C57BL/10 mice) and dystrophic (mdx mice) muscles (an animal model for human Duchenne muscular dystrophy) before and after contraction-induced injury. A mild in vivo eccentric injury protocol was used due to the high susceptibility of mdx muscles to injury. As expected, mdx mice sustained a greater loss of force (81%) after injury compared with WT (42%). In the uninjured muscles, choline (Cho) levels were 47% lower in the mdx muscles compared with WT muscles. In mdx mice, taurine levels decreased 17%, and Cho levels increased 25% in injured muscles compared with uninjured mdx muscles. Intramyocellular lipids and total muscle lipid levels increased significantly after injury but only in WT. The increase in lipid was confirmed using a permeable lipophilic fluorescence dye. In summary, loss of torque after injury was associated with alterations in muscle metabolite levels that may contribute to the overall injury response in mdx mice. These results show that it is possible to obtain meaningful in vivo (1)H MRS regarding skeletal muscle injury.