Influence of endurance exercise training and sex on intramyocellular lipid and mitochondrial ultrastructure, substrate use, and mitochondrial enzyme activity

Abstract

Impaired mitochondrial function and structure and intramyocellular lipid (IMCL) accumulation have been associated with obesity and Type 2 diabetes. We examined whether endurance exercise training and sex influenced IMCL and mitochondrial morphology using electron microscopy, whole-body substrate use, and mitochondrial enzyme activity. Untrained men (n = 5) and women (n = 7) were tested before and after 7 wk of endurance exercise training. Testing included 90 min of cycle ergometry at 60% Vo(2 peak) with preexercise muscle biopsies analyzed for IMCL and mitochondrial size/area using electron microscopy and short-chain beta-hydroxyacyl-CoA dehydrogenase (SCHAD) and citrate synthase (CS) enzyme activity. Training increased the mean lipid area density (P = 0.090), the number of IMCL droplets (P = 0.055), the number of IMCL droplets in contact with mitochondria (P = 0.010), the total mitochondrial area (P < 0.001), and the size of individual mitochondrial fragments (P = 0.006). Women had higher mean lipid area density (P = 0.030) and number of IMCL droplets (P = 0.002) before and after training, but higher individual IMCL area only before training (P = 0.013), compared with men. Women oxidized more fat (P = 0.027) and less carbohydrate (P = 0.032) throughout the study. Training increased Vo(2 peak) (P < 0.001), %fat oxidation (P = 0.018), SCHAD activity (P = 0.003), and CS activity (P = 0.042). In summary, endurance exercise training increased IMCL area density due to an increase in the number of lipid droplets, whereas the increase in total mitochondrial area was due to an increase in the size of individual mitochondrial fragments. In addition, women have higher IMCL content compared with men due mainly to a greater number of individual droplets. Finally, endurance exercise training increased the proportion of IMCL in physical contact with mitochondria.

High-fat diet overrules the effects of training on fiber-specific intramyocellular lipid utilization during exercise

“…In agreement with previous findings by others (16a, 19) and van Loon et al (61), fiber-specific IMCL degradation was positively correlated with initial IMCL content, particularly at the higher range of IMCL levels seen in the posttest. By analogy, elevated IMCL hydrolysis during exercise in females compared with males probably also is largely driven by higher basal IMCL content (54,60). Such interpretation is also supported by the observation that 5 days of a HFD were sufficient to enhance HSL activity during moderate-intensity exercise by ϳ20 -30% (58).…”

Effect of exercise training on insulin sensitivity, mitochondria and computed tomography muscle attenuation in overweight women with and without polycystic ovary syndrome

“…Men have lower IMCL than women despite being more IR [38]. With endurance exercise, men exhibit lower lipid oxidation than women [39], and an acute exercise bout leads to muscle triacylglycerol breakdown in women but not in men [40]. Furthermore, PCOS women have more visceral fat than non-PCOS women, which decreases with exercise training in PCOS women only [26], again mimicking the response of visceral fat to exercise that occurs in men when compared with non-PCOS women [41].…”

Heritability and genetic etiology of habitual physical activity: a twin study with objective measures

“…High-intensity physical activity is known to increase skeletal muscle PGC-1a protein content (Franks and Loos 2006;Pilegaard et al 2003), mitochondrial capacity (Tarnopolsky et al 2007;Tonkonogi and Sahlin 2002) and maximal oxygen uptake (Gavin et al 2007). Hence, the GA/AA genotypes could be anticipated to reduce the risk for cardiovascular diseases and type 2 diabetes mellitus.…”