## 1 Introduction  
Pulsed electromagnetic fields (PEMFs) have been widely employed since the 1970s to treat fractures that do not heal well through the normal bone healing process; PEMF is a safe, non-invasive, and efficacious method for the treatment of diseases associated with fractures and was first approved by the United States Food and Drug Administration (FDA) in 1979 [1, 2]. PEMF has also been suggested as an alternative treatment for osteoarthritis in the clinic [3]. Numerous studies have reported a therapeutic effect on fractures or other diseases in actual clinical use; it is known that PEMF therapy has no significant side effects [4, 5]. Bone growth in children depends on growth plates situated near the end of all long bones in the body. The growth plate (physis) is a thin plate-shaped (narrow disc of cartilage) cartilage that is responsible for longitudinal bone growth and is the result of chondrocyte proliferation and differentiation [6, 7]. These plates consist of cartilage cells and chondrocytes, which form a scaffold that supports the formation of new bone tissue and are generated from stem cells called chondropogenitors [8]. Various biological signals, including growth hormone, directly or indirectly divide and thicken the chondrocytes in the hyperthropic zone, and the cartilage on the side of the bone body is replaced with new bone, resulting in bone elongation [9]. However, it is still not clear how this process is maintained throughout childhood. Recently, a study conducted by a European collaborative research team, including the Karolinska Institute in Sweden, identified the mechanism of origin and differentiation of stem cells, which are the main factors in growth plate activity, using a fluorescent staining method that can differentiate each cell in mice [10]. The postnatal growth plate chondrocytes are divided into three layers that contribute to the longitudinal growth of long bones [11]. The resting zone is located at the top of the growth plate and maintains the integrity of the growth plate structure. Below these are \"proliferating zone chondrocytes\", which are flat and, as the name suggests, divide and proliferate in the longitudinal direction. They resemble a pillar made of bricks. At the bottom are \"hyperthrophic chondrocytes\", which are enlarged cells. These cells do not divide and eventually die, and bone cells fill the empty spots to lengthen the bone body [11]. The resting chondrocytes serve as progenitor cells or stem-like cells to provide a renewable source to populate the whole growth plate. These chondrocytes within the resting zone divide and form proliferating chondrocytes, and the lower proliferating chondrocytes are converted into hypertrophic chondrocytes by terminal differentiation [12]. Thus, the length of growth of the bone body is determined by the extent to which the stem cells in the growth plate undergo symmetric cell division and how smooth the signal exchange is between the three types of chondrocytes. If the chondrocytes stimulate and activate signal exchange and differentiation, growth plate growth is promoted. Accordingly, studies on pulsed magnetic field stimulation for the proliferation of various chondrocytes are being conducted. [PERSON] et al. [13] analyzed the proliferation pattern of human articular chondrocytes after applying PEMs of 75 Hz, 2.3 mT to them for a long time, and observed that the proliferation of chondrocytes was induced. In addition, the effect of electromagnetic fields (EMFs) at 75 Hz and 2.3 mT on bovine articular cartilage cultured in vitro for 24 h was investigated; it was reported that EMFs exert a cartilage protection effect on the in vitro cultured articular cartilage due to the anabolic activity of EMFs and promote the synthesis of proteoglycans in the in vitro culture of small joint cartilage. The continuous application of 75 Hz, 2.3 mT of PEMF in human nasal and knee joint cartilage cells for 6-30 h resulted in increased cell proliferation in both knee articular (joint) cartilage and nasal cartilage cells [14].