Despite remarkable advancements in modern medicine, muscular atrophy remains as an unsolved problem. It is well known that pathological characteristics of different atrophy types could vary according to the pathophysiological causes. In fact, the lesion of atrophy is not always homogenously distributed but often predominantly evident in either fast or slow myofibers. As the focalization of the atrophic lesions, the existence and the functional impairment of each fast and slow progenitor/satellite cell (SC) are suspected though there are still controversies about this hypothesis. In this study, we isolated Pax7 positive (Pax7^+ve) SCs from the tibia anterior (fast) and soleus (slow) muscles respectively and successfully demonstrated, for the first time, the difference between optimal exposure durations of photobiomodulation (PBM) which was known as low level laser irradiation (LLLI) in promoting proliferation of Pax7^+ve SC which were acquired from fast and slow muscles respectively. Moreover, a hypertrophy-accompanied bidirectional change in myofiber composition with neuromuscular junction alteration, either from slow to fast or fast to slow, were achieved by applying different PBM durations. Simultaneously, PBM exhibited a synergistic effect with muscle exercise on the increase in myofiber size. Our data suggested the existence of at least two different populations of Pax7^+ve SC which possess distinct sensitivities towards PBM. As our data revealed the capability of PBM in bidirectional changes of skeletal muscle composition and neuromuscular junction constitution thereby strengthen its contractility through altering the irradiation condition, we believe PBM showed the potential to be as a promising clinical treatment for muscular atrophy.

尽管现代医学取得了显着进步，但肌肉萎缩仍然是一个尚未解决的问题。众所周知，不同的萎缩类型的病理特征可根据病理生理原因而变化。实际上，萎缩的病灶并不总是均匀分布的，而是在快速或缓慢的肌纤维中通常很明显。作为萎缩性病变的聚焦点，尽管仍存在关于该假说的争议，但怀疑每个快速和慢速祖细胞/卫星细胞（SC）的存在和功能受损。在这项研究中，我们分离了Pax7阳性（Pax7 ^{+ ve}）分别来自胫骨前肌（快速）和比目鱼肌（慢）的SC并成功地首次证明了光生物调节（PBM）的最佳照射持续时间之间的差异，这被称为低水平激光照射（LLLI）在促进增殖中Pax7 ^{+ ve} SC分别来自快肌和慢肌。此外，通过应用不同的PBM时间，可以实现肌纤维组成的肥大伴有双向变化，从慢到快或从快到慢。同时，PBM与肌肉运动对肌纤维大小增加具有协同作用。我们的数据表明存在至少两个不同的Pax7 ^{+ ve}种群对PBM具有独特敏感性的SC。由于我们的数据揭示了PBM在骨骼肌组成和神经肌肉接头组成的双向变化中的能力，从而通过改变辐照条件而增强了其收缩能力，因此我们认为PBM显示出了作为有望治疗肌肉萎缩的潜力。