In the current issue of Acta Physiologica, Lawrence et al1 provide a rigorous investigation into the effects of mechanical massage therapy on skeletal muscle during normal weight bearing (WB) and unloading conditions. One week of hindlimb suspension (HS) in rats was used to determine if massage is an effective therapy to blunt disuse associated muscle loss. Massage therapy increased the muscle protein turnover compared to HS control, though muscle atrophy still occurred following massage and muscle disuse. Interestingly, massage therapy increased muscle protein turnover in the contralateral, non‐messaged limb compared to HS control.

Prolonged periods of muscle disuse occur following bone fractures, surgeries and bed rest; and lead to a rapid loss of muscle mass and a decrease in quality of life.2 Developing therapies for the prevention of muscle atrophy are hindered by the ability of disuse atrophy to cause anabolic resistance independent of other disease states.3 Resistance training methods to counteract disuse‐associated muscle atrophy may not be safe, practical or even effective for patients as hypertrophy and atrophy signalling are not reciprocal.4 Massage, in the form of cyclic compressive loading (CCL), is a potential therapy that can be implemented during and/or following periods of forced muscle disuse as an anabolic stimulus to prevent or reduce muscle atrophy.

Rhythmic or cyclic massage as a therapy has not been well‐studied, however the data that exist are promising. Following exercise‐induced muscle damage in humans, massage therapy attenuated intramuscular inflammatory signalling and triggered an increase in mitochondrial biogenesis pathways.5 Cyclic mechanical compressions have also been shown to enhance muscle regeneration, reduce fibrosis and decrease inflammation following both toxin‐induced muscle injury and hindlimb ischemia in mice.6 A single bout of CCL massage in unperturbed muscle has significant immunomodulatory effects, but is not a strong enough stimulus to alter protein synthesis rates.7, 8 However, multiple bouts of massage during a reloading period do stimulate protein synthesis and muscle growth, with a significant cross over effect occurring in the non‐massaged limb. The current study is a natural extension of the group's previous work7, 8 with the goals of determining if massage has an anabolic effect on muscle: (a) under normal, WB activities; (b) during disuse atrophy caused byHS; and (c) of the contralateral limb.

Briefly, rats were randomly assigned into one of four groups, normal WB, WB with massage (WBM), HS for 7 days (HS), or HS for 7 days with massage (HSM). Following euthanasia, the right gastrocnemius was used to investigate the effects of message under WB and HS conditions. Importantly, the non‐messaged, contralateral left limb could be used to investigate potential crossover effects of message in WB and HS (WBM‐L and HSM‐L) conditions. Contrary to the authors’ hypothesis, there were no differences in any measure of muscle mass or protein regulation in the messaged or contralateral muscle under normal, WB conditions.

Massage therapy provides a mechanical stimulus that alters intracellular muscle signalling through mechanotransduction. Integrin receptors transmit mechanical stimuli from the extracellular matrix (ECM) to the muscle cytoskeleton via focal adhesion complexes (FACs). Integrin activation results in focal adhesion kinase (FAK) phosphorylation which in turn triggers the activation of pro‐growth signalling pathways inside the muscle fibre. The present study found no differences in phosphorylation of FAK during HS and HSM compared to WB. While massage was unable to blunt muscle atrophy during HS, massage therapy did generate a robust myofibrillar protein synthesis response suggesting increased myofibrillar protein turnover could maintain or even improve myofibrillar protein quality and muscle function. There were no differences between HS and HSM for myofibrillar protein degradation or cytosolic protein synthesis rates, however massage attenuated the HS induced increase in cytosolic protein degradation. The precise implications of these changes in muscle protein regulation in response to message are unclear. Future work utilizing proteomics could help elucidate the benefits by identifying specific proteins altered by massage.

An unexpected finding of the present study was that the reduction in ribosome content during HS and HSM is a byproduct of increased ribosomal degradation and not a change in ribosome biogenesis. In fact, there were no differences in ribosomal biogenesis between HS and HSM or HS compared to WB. While ribosomal degradation was greater in both HS and HSM compared to WB, the greater ribosomal degradation rate in HS was attenuated in HSM. These data suggest massage is able to stimulate muscle protein and ribosomal turnover during disuse. However, the lack of massage‐induced attenuation of muscle loss suggests either a different massage dosage or massage in combination with other therapeutic interventions would be needed to preserve muscle mass during muscle disuse.

One of the exciting findings of the current study was the strong crossover effect found in the non‐massaged, contralateral limb during muscle unloading conditions. Benefits of CCL massage––improved myofibrillar protein synthesis and decreased cytosolic protein degradation––were replicated in the contralateral limb not receiving massage. This is consistent with earlier work in which multiple bouts of CCL during a regrowth protocol following disuse‐induced muscle atrophy produced a crossover effect in the non‐massaged limb.9 Similar to results during muscle regrowth following disuse, the mechanism responsible for the increase in myofibrillar protein synthesis was different in the non‐massaged limb than it was in the massaged limb. In Lawrence et al,1 the unloaded, contralateral, non‐massaged limb had greater rpS6 phosphorylation and higher ribosomal degradation compared to unloaded control.

Neural adaptations likely participate in the crossover effect, as contralateral changes occur only in the same muscle group receiving the original stimulus.9 However, greater attention is being given to the role of circulating muscle produced factors such as myokines and exosomes acting as endocrine regulators. Intramuscularly injected fluorescent labelled exosomes are found in muscle of the contralateral limb.10 Blood flow‐restricted resistance exercise alters circulating exosomes such that these exosomes are able to enhance S‐phase entry of satellite cells and suggesting that exosomes are capable of mediating local and systemic effects.11 Regardless of the precise mechanism, the crossover effect found in the work from Lawrence et al provides critical insight into treating unilateral muscle pathologies or injuries. A deeper investigation utilizing the models employed in the current work could enhance our understanding of muscle protein regulation.

While well conducted, there are some limitations in the current study. The calculation of protein and RNA changes utilized average changes, yet muscle unloading induced atrophy results in dynamic changes in muscle protein turnover over time.12 Measuring dynamic protein turnover could provide important insight into the optimal dosage and timing of massage to counteract muscle loss. Second, massage therapy may prove selectively beneficial in maintaining muscle mass during unloading in females. The current work studied only male rats, however female rats demonstrate greater soleus mass loss with unloading than male rats.13

In conclusion, the study conducted by Lawrence and colleagues represents a significant step forward in identifying the impact of massage therapy on intramuscular signalling during normal WB conditions and during periods of muscle disuse in mice. The major findings were while 1 week of massage during HS does not abrogate disuse‐induced muscle atrophy; massage does increase myofibrillar protein synthesis, decrease cytosolic protein degradation, and decrease ribosomal degradation as well as cause a strong crossover effect in the contralateral non‐massaged limb. Massage holds promise as an effective therapy to improve protein turnover during periods of muscle disuse. Future work employing different dosages of massage or massage combined with other interventions to attenuate disuse‐associated muscle atrophy could prove insightful and beneficial.

在当前一期《生理生理学》中，Lawrence等人1对机械按摩疗法在正常负重（WB）和无负荷条件下对骨骼肌的影响进行了严格的研究。使用大鼠后肢悬吊（HS）一周来确定按摩是否是一种有效的疗法，以钝化废用的相关性肌肉丢失。与HS对照相比，按摩疗法增加了肌肉蛋白质的转化率，尽管在按摩和停用肌肉后仍然出现肌肉萎缩。有趣的是，与HS对照相比，按摩疗法可增加对侧，未患肢的四肢肌肉蛋白质更新。

骨折，手术和卧床休息会导致长时间的肌肉衰竭。并导致肌肉质量的快速丧失和生活质量的下降。2废用萎缩引起与其他疾病状态无关的合成代谢抵抗的能力阻碍了开发预防肌肉萎缩的疗法。3由于肥大和萎缩信号互不相干，抵抗与废用的肌肉萎缩有关的阻力训练方法可能不安全，不实用，甚至无效。4以循环压缩负荷（CCL）形式进行的按摩是一种潜在的治疗方法，可以在强迫肌肉废止期间和/或之后实施，作为合成代谢刺激物，以预防或减少肌肉萎缩。

有节奏的或循环的按摩疗法尚未得到很好的研究，但是已有的数据很有希望。在运动引起的人类肌肉损伤之后，按摩疗法减弱了肌内炎性信号传导并触发了线粒体生物发生途径的增加。5循环机械压迫也被证明可以增强小鼠的肌肉再生，减少纤维化并减少炎症，这既是由毒素引起的肌肉损伤，也是后肢缺血。6在不动的肌肉中单次CCL按摩具有明显的免疫调节作用，但不足以改变蛋白质的合成速率。7、8但是，在重装期间多次按摩确实会刺激蛋白质合成和肌肉生长，在未按摩的肢体中会产生明显的交叉效应。当前的研究是该小组先前工作7，8的自然延伸，其目的是确定按摩是否对肌肉具有合成代谢作用：（a）在正常的WB活动下；（b）在因HS造成的废用萎缩期间；（c）对侧肢体。

简而言之，将大鼠随机分为四组之一：正常WB，带按摩的WB（WBM），HS进行7天（HS）或HS进行7天进行按摩（HSM）。安乐死后，右腓肠肌用于研究WB和HS条件下信息的影响。重要的是，没有消息的对侧左肢可用于调查WB和HS（WBM-L和HSM-L）情况下消息的潜在交叉效果。与作者的假设相反，在正常的WB条件下，消息或对侧肌肉的肌肉质量或蛋白质调节的任何量度均无差异。

按摩疗法提供了一种机械刺激，通过机械转导改变了细胞内肌肉的信号传导。整联蛋白受体通过粘着斑复合物（FAC）将机械刺激从细胞外基质（ECM）传递到肌肉细胞骨架。整联蛋白的激活导致粘着斑激酶（FAK）磷酸化，进而触发肌肉纤维内促生长信号通路的激活。本研究发现与WB相比，HS和HSM期间FAK的磷酸化没有差异。尽管在HS期间按摩不能使肌肉萎缩变钝，但是按摩疗法确实产生了强大的肌原纤维蛋白合成反应，这表明肌原纤维蛋白更新率的增加可以维持甚至改善肌原纤维蛋白的质量和肌肉功能。HS和HSM在肌原纤维蛋白降解或胞浆蛋白合成速率方面没有差异，但是按摩减弱了HS诱导的胞浆蛋白降解增加。这些肌肉蛋白调节响应信息变化的确切含义尚不清楚。利用蛋白质组学的未来工作可以通过鉴定经按摩改变的特定蛋白质来帮助阐明其益处。

本研究的意外发现是，HS和HSM期间核糖体含量的减少是核糖体降解增加的副产物，而不是核糖体生物发生的变化。实际上，与WB相比，HS和HSM或HS之间的核糖体生物发生没有差异。尽管与WB相比，HS和HSM的核糖体降解都更大，但HSM中的HS更大的核糖体降解率却减弱了。这些数据表明，按摩在停用期间能够刺激肌肉蛋白和核糖体更新。但是，缺乏按摩引起的肌肉损失的减弱表明，在肌肉停用期间，可能需要使用不同的按摩剂量或与其他治疗干预措施相结合来保持肌肉质量。

本研究令人兴奋的发现之一是在肌肉卸载状态下未按摩的对侧肢体中发现了强大的交叉效应。CCL按摩的好处-改善了肌原纤维蛋白的合成，减少了胞浆蛋白的降解-在没有接受按摩的对侧肢体中得到了复制。这与早期的工作相吻合，在早期的研究中，停用引起的肌肉萎缩后，在再生过程中多次出现CCL循环，在未按摩的肢体中产生交叉效应。9与停用后肌肉再生长的结果相似，非按摩肢体与按摩肢体引起肌原纤维蛋白合成增加的机制不同。在劳伦斯等人，1 与未加载对照相比，未加载，对侧，未按摩的肢体具有更高的rpS6磷酸化和更高的核糖体降解。

神经适应可能参与交叉效应，因为对侧变化仅发生在接受原始刺激的同一肌肉群中。9然而，人们越来越关注循环肌肉产生的因子，例如肌动蛋白和外泌体作为内分泌调节剂的作用。在对侧肢体的肌肉中发现了肌内注射的荧光标记外泌体。10限制血液流动的抵抗运动会改变循环中的外泌体，从而使这些外泌体能够增强卫星细胞的S期进入，并暗示外泌体能够介导局部和全身效应。11不管精确的机制如何，劳伦斯等人的工作中发现的交叉效应为治疗单侧肌肉病变或损伤提供了重要的见识。利用当前工作中使用的模型进行更深入的研究可以增强我们对肌肉蛋白质调节的理解。

虽然进行得很好，但当前的研究存在一些局限性。蛋白质和RNA变化的计算利用平均变化，但是肌肉卸载引起的萎缩导致肌肉蛋白质更新随时间动态变化。12测量动态蛋白质更新可以为了解最佳剂量和按摩时间以抵消肌肉损失提供重要信息。其次，按摩疗法可能被证明在女性卸载过程中选择性地有益于维持肌肉质量。当前的研究仅研究雄性大鼠，但是雌性大鼠表现出比雄性大鼠更大的比目鱼质量减轻。13

总而言之，劳伦斯及其同事进行的研究代表了向前迈出的重要一步，该过程在确定正常WB条件下以及小鼠肌肉停用期间对肌肉内信号传递的按摩疗法的影响方面具有重要意义。主要发现是在HS期间进行1周的按摩不会消除因滥用引起的肌肉萎缩。按摩确实增加了肌原纤维蛋白的合成，减少了胞浆蛋白的降解，并减少了核糖体的降解，并在对侧未按摩的肢体中产生了强大的交叉效应。按摩有望成为一种有效的疗法，可在肌肉停用期间改善蛋白质更新。未来采用不同剂量的按摩或按摩结合其他干预措施以减轻与废用相关的肌肉萎缩的工作可能证明是有见地和有益的。