Heinemeier K M, Olesen J L, Schjerling P, Haddad F, Langberg H, Baldwin K M, Kjaer M
Institute of Sports Medicine, Bispebjerg Hospital-Bldg. 8, 1st Floor, 23 Bispebjerg Bakke, DK-2400 Copenhagen NV, Denmark.
J Appl Physiol (1985). 2007 Feb;102(2):573-81. doi: 10.1152/japplphysiol.00866.2006. Epub 2006 Oct 12.
In skeletal muscle, an increased expression of insulin like growth factor-I isoforms IGF-IEa and mechano-growth factor (MGF) combined with downregulation of myostatin is thought to be essential for training-induced hypertrophy. However, the specific effects of different contraction types on regulation of these factors in muscle are still unclear, and in tendon the functions of myostatin, IGF-IEa, and MGF in relation to training are unknown. Female Sprague-Dawley rats were subjected to 4 days of concentric, eccentric, or isometric training (n = 7-9 per group) of the medial gastrocnemius, by stimulation of the sciatic nerve during general anesthesia. mRNA levels for myostatin, IGF-IEa, and MGF in muscle and Achilles' tendon were measured by real-time RT-PCR. Muscle myostatin mRNA decreased in response to all types of training (2- to 8-fold) (P < 0.05), but the effect of eccentric training was greater than concentric and isometric training (P < 0.05). In tendon, myostatin mRNA was detected, but no changes were seen after exercise. IGF-IEa and MGF increased in muscle (up to 15-fold) and tendon (up to 4-fold) in response to training (P < 0.01). In tendon no difference was seen between training types, but in muscle the effect of eccentric training was greater than concentric training for both IGF-IEa and MGF (P < 0.05), and for IGF-IEa isometric training had greater effect than concentric (P < 0.05). The results indicate a possible role for IGF-IEa and MGF in adaptation of tendon to training, and the combined changes in myostatin and IGF-IEa/MGF expression could explain the important effect of eccentric actions for muscle hypertrophy.
在骨骼肌中，胰岛素样生长因子 -I 亚型 IGF-IEa 和机械生长因子（MGF）的表达增加，同时肌肉生长抑制素下调，被认为是训练诱导的肌肉肥大所必需的。然而，不同收缩类型对这些肌肉因子调节的具体影响仍不清楚，并且在肌腱中，肌肉生长抑制素、IGF-IEa 和 MGF 与训练相关的功能尚不清楚。雌性 Sprague-Dawley 大鼠在全身麻醉期间通过刺激坐骨神经，对腓肠肌内侧进行 4 天的向心、离心或等长训练（每组 n = 7 - 9）。通过实时 RT-PCR 测量肌肉和跟腱中肌肉生长抑制素、IGF-IEa 和 MGF 的 mRNA 水平。所有类型的训练均使肌肉中肌肉生长抑制素 mRNA 减少（2 至 8 倍）（P < 0.05），但离心训练的效果大于向心和等长训练（P < 0.05）。在肌腱中检测到肌肉生长抑制素 mRNA，但运动后未见变化。训练后，肌肉中 IGF-IEa 和 MGF 增加（高达 15 倍），肌腱中增加（高达 4 倍）（P < 0.01）。在肌腱中，不同训练类型之间未见差异，但在肌肉中，离心训练对 IGF-IEa 和 MGF 的作用均大于向心训练（P < 0.05），对于 IGF-IEa，等长训练的作用大于向心训练（P < 0.05）。结果表明 IGF-IEa 和 MGF 在肌腱适应训练中可能发挥作用，肌肉生长抑制素和 IGF-IEa/MGF 表达的联合变化可以解释离心运动对肌肉肥大的重要影响。
