Lactate has been implicated as a potential signaling molecule. In myotubes, lactate incubation increases mTORC1- and ERK-signaling and induces hypertrophy, indicating that lactate could be a mediator of muscle adaptations to resistance exercise. However, the potential signaling properties of lactate, at rest or with exercise, have not been explored in human tissue. In a cross-over design study, 8 men and 8 women performed one-legged resistance exercise while receiving venous infusion of saline or sodium lactate. Blood was sampled repeatedly, and muscle biopsies were collected at rest and at 0, 90,180 min and 24 h after exercise. The primary outcomes examined were intracellular signaling, fractional protein synthesis rate (FSR), and blood/muscle levels of lactate and pH. Post-exercise blood lactate concentrations were 130% higher in the Lactate trial (3.0 vs 7.0 mmol×l^-1_, p<0.001) whereas muscle levels were only marginally higher (27 vs 32 mmol×kg^-1 d.w., p=0.003) compared to the Saline-trial. Post-exercise blood pH was higher in the Lactate-trial (7.34 vs 7.44, p<0.001), with no differences in intramuscular pH. Exercise increased the phosphorylation of mTOR^S2448 (~40%), S6K1^T389 (~3-fold), and p44^T202/T204 (~80%) during recovery, without any differences between trials. FSR over the 24-h recovery period did not differ between the Saline (0.067 %/h) and Lactate (0.062 %/h) trials. This study does not support the hypothesis that blood lactate levels can modulate anabolic signaling in contracted human muscle. Further in vivo research investigating the impact of exercised versus rested muscle and the role of intramuscular lactate is needed to elucidate its potential signaling properties.

中文翻译：

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通过外源性乳酸输注增加的血浆乳酸水平不会改变抗性运动诱导的人骨骼肌信号或蛋白质合成。

乳酸被认为是潜在的信号分子。在肌管中，乳酸孵育会增加mTORC1和ERK信号传导并诱导肥大，这表明乳酸可能是抵抗运动的肌肉适应性的介质。然而，尚未在人体组织中探索静止或运动时乳酸的潜在信号传导特性。在一项交叉设计研究中，有8名男性和8名女性在接受静脉输注生理盐水或乳酸钠的同时进行了单腿抵抗运动。重复采样血液，并在休息后以及运动后0、90、180分钟和24小时收集肌肉活检。检查的主要结果是细胞内信号传导，蛋白质合成分数（FSR）以及血液/肌肉中的乳酸和pH值。^-1 _， p <0.001），而与盐水试验相比，肌肉水平仅略高（27 vs 32 mmol×kg ^-1 dw，p = 0.003）。乳酸试验中的运动后血液pH较高（7.34 vs 7.44，p <0.001），肌内pH没有差异。运动增加了mTOR ^S2448（^〜40％），S6K1 ^T389（^〜3倍）和p44 ^{T202 / T204}的磷酸化（〜80％）的恢复期间，试验之间没有任何差异。盐水（0.067％/ h）和乳酸（0.062％/ h）试验之间，在24小时恢复期内的FSR没有差异。这项研究不支持血乳酸水平可以调节人的收缩肌肉中合成代谢信号的假设。需要进一步的体内研究来研究运动肌肉与休息肌肉的影响以及肌内乳酸的作用，以阐明其潜在的信号传导特性。