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

Eccentric exercise is known to cause changes to the ultrastructure of skeletal muscle and, in turn, may alter the ability of the muscle to store and utilise intracellular substrates such as intramyocellular lipid (IMCL). The purpose of this study was to test the hypothesis that exercise-induced muscle damage (EIMD) results in IMCL accumulation. Six males (31 ± 6 years; mean ± SD, and 72.3 ± 9.7 kg body mass) performed 300 unilateral, maximal, isokinetic, eccentric contractions (Ecc) (30° s(-1)) of the quadriceps on an isokinetic dynamometer, followed immediately by an equal amount of work by the contralateral leg but with concentric action (Con). Phosphate compounds and IMCL content of the vastus lateralis of both legs were measured using (31)P and (1)H magnetic resonance spectroscopy. IMCL content was higher in Ecc than Con 24 h post but the reverse was evident 48 h post-exercise (P = 0.046). A significant time × trial interaction for resting [P(i)] (P = 0.045), showed increases in Ecc across time but no change in Con. A significant main effect of trial (P = 0.002) was apparent indicating the Ecc leg had marked metabolic dysfunction. The P(i)/PCr ratio showed a significant effect of trial (P = 0.001) with an increase evident in Ecc leg, primarily due to increases in [P(i)]. The present study highlights changes in IMCL content of skeletal muscle following EIMD.

Aerobic exercise training reduces hepatic and visceral lipids in obese individuals without weight loss.

UNLABELLED: Weight loss remains the most common therapy advocated for reducing hepatic lipid in obesity and nonalcoholic fatty liver disease. Yet, reduction of body weight by lifestyle intervention is often modest, and thus, therapies which effectively modulate the burden of fatty liver but are not contingent upon weight loss are of the highest practical significance. However, the effect of aerobic exercise on liver fat independent of weight loss has not been clarified. We assessed the effect of aerobic exercise training on hepatic, blood, abdominal and muscle lipids in 19 sedentary obese men and women using magnetic resonance imaging and proton magnetic resonance spectroscopy ((1)H-MRS). Four weeks of aerobic cycling exercise, in accordance with current physical activity guidelines, significantly reduced visceral adipose tissue volume by 12% (P < 0.01) and hepatic triglyceride concentration by 21% (P < 0.05). This was associated with a significant (14%) reduction in plasma free fatty acids (P < 0.05). Exercise training did not alter body weight, vastus lateralis intramyocellular triglyceride concentration, abdominal subcutaneous adipose tissue volume, (1)H-MRS-measured hepatic lipid saturation, or HOMA-IR (homeostasis model assessment of insulin resistance; P > 0.05). CONCLUSION: These data provide the first direct experimental evidence demonstrating that regular aerobic exercise reduces hepatic lipids in obesity even in the absence of body weight reduction. Physical activity should be strongly promoted for the management of fatty liver, the benefits of which are not exclusively contingent upon weight loss.

Noninvasive assessment of hepatic lipid composition: Advancing understanding and management of fatty liver disorders.

UNLABELLED: Nonalcoholic fatty liver is frequently observed in obese individuals, yet the factors that predict its development and progression to liver disease are poorly understood. We proposed that proton magnetic resonance spectroscopy ((1)H-MRS) might allow noninvasive assessment of hepatic lipid composition. Lipid saturation (SI) and polyunsaturation (PUI) indices measured by (1)H-MRS were in agreement with those expected in oils of known composition. Hepatic triglyceride concentration (HTGC) and composition were then measured in healthy lean (LEAN) men, obese men with normal HTGC (OB), and obese men with hepatic steatosis (OB+HS). The effect of marked changes in dietary fat consumption on hepatic lipids were also compared in lean men after 67 hours of a normal mixed (NM) diet versus a low-carbohydrate, high-saturated-fat (LCHF) diet. SI was significantly higher in OB+HS (0.970 +/- 0.004) and OB (0.944 +/- 0.008) versus LEAN (0.818 +/- 0.025) (P < 0.01 for both). PUI was significantly lower in OB+HS (0.003 +/- 0.001) and OB (0.022 +/- 0.005) versus LEAN (0.120 +/- 0.021) (P < 0.01), and significantly lower in OB+HS versus OB (P < 0.05). LCHF diet did not alter HTGC, SI, or PUI (P > 0.05). The (1)H-MRS method provides for rapid, qualitative assessment of lipid composition. Application of this technique in the liver produces results that are consistent with biopsy-based approaches demonstrating that relative hepatic lipid saturation increases and polyunsaturation decreases with obesity. Obesity-related hepatic steatosis is characterized by further depletion of polyunsaturated hepatic lipids. CONCLUSION: This readily available and noninvasive approach should promote further study into interactions between hepatic and whole-body lipid metabolism and help to elucidate the pathogenesis of disorders characterized by lipid accumulation within the liver.