Abstract：
Intramuscular lipids are stored as subsarcolemmal or intramyofibrillar droplets with potential diverse roles in energy metabolism. We examined intramuscular lipid utilization through transmission electron microscopy during repeated high-intensity intermittent exercise, an aspect that is hitherto unexplored. Seventeen moderately to well-trained males underwent three periods (EX1-EX3) of 10 × 45-s high-intensity cycling [∼100%-120% Wattmax (Wmax)] combined with maximal repeated sprints (∼250%-300% Wmax). M. vastus lateralis biopsies were obtained at baseline, after EX1, and EX3. During the complete exercise session, no net decline in either subsarcolemmal or intermyofibrillar lipid volume density occurred. However, a temporal relationship emerged for subsarcolemmal lipids with an ∼11% increase in droplet size after EX1 (P = 0.024), which reverted to baseline levels after EX3 accompanied by an ∼30% reduction in the numerical density of subsarcolemmal lipid droplets compared with both baseline (P = 0.019) and after EX1 (P = 0.018). Baseline distinctions were demonstrated with an approximately twofold higher intermyofibrillar lipid volume in type 1 versus type 2 fibers (P = 0.008), mediated solely by a higher number rather than the size of lipid droplets (P < 0.001). No fiber-type-specific differences were observed in subsarcolemmal lipid volume although type 2 fibers exhibited ∼17% larger droplets (P = 0.034) but a lower numerical density (main effect; P = 0.010) including 3% less droplets at baseline. Collectively, these findings suggest that intramuscular lipids do not serve as an important substrate during high-intensity intermittent exercise; however, the repeated exercise pattern mediated a temporal remodeling of the subsarcolemmal lipid pool. Furthermore, fiber-type- and compartment-specific differences were found at baseline underscoring the heterogeneity in lipid droplet deposition.NEW & NOTEWORTHY Undertaking a severe repeated high-intensity intermittent exercise protocol led to no net decline in neither subsarcolemmal nor intermyofibrillar lipid content in the thigh muscle of young moderately to well-trained participants. However, a temporal remodeling of the subsarcolemmal pool of lipid droplets did occur indicative of potential transient lipid accumulation. Moreover, baseline fiber-type distinctions in subcellular lipid droplet deposition were present underscoring the diversity in lipid droplet storage among fiber types and subcellular regions.
摘要：
肌内脂质作为肌膜下或肌内原纤液滴储存，在能量代谢中具有潜在的不同作用。我们通过透射电子显微镜检查了在重复高强度间歇性运动期间肌内脂质的利用，这是迄今为止尚未探索的一个方面。17名受过中等至良好训练的男性经历了三个阶段（EX1-EX3）的10x45s高强度自行车运动（最大功率约100-120％瓦），并进行了最大重复冲刺（最大功率约250-300％瓦）。在基线时获得了股外侧肌活检，在EX1和EX3之后。在完整的练习期间，肌膜下和肌原纤维间脂质体积密度均未出现净下降。然而,在EX1后，肌膜下脂质的时间关系出现了〜11％的液滴大小增加（P=0.024），与基线（P=0.019）和EX1后（P=0.018）相比，EX3后恢复至基线水平，同时肌膜下脂滴的数值密度降低约30％。1型肌原纤维间脂质体积比1型肌原纤维间脂质体积高约2倍。2型纤维（P=0.008），仅由较高数量而不是大小的脂滴介导（P<0.001）。在肌膜下脂质体积中没有观察到纤维类型特异性差异，尽管2型纤维表现出〜17％的较大液滴（P=0.034），但数值密度较低（主要影响；P=0.010），包括基线时少3％的液滴。总的来说，这些发现表明，在高强度间歇性运动中，肌内脂质并不是重要的底物，然而,重复运动模式介导了肌膜下脂池的时间重塑。此外，在基线时发现纤维类型和隔室特异性差异，强调了脂滴沉积的异质性。
