# Effect of Moderate-Intensity Endurance Exercise on Inflammatory Cytokines in Leukocytes of Dogs
## 1 Introduction  
Dogs have long shared environments and lifestyles with humans [1]. In modern society, they are recognized as members of the family beyond the concept of companion animals [2]. Dogs also reveal unique behavior patterns that induce human care and affection [3], resulting in a stronger bond between humans and dogs. Accordingly, many dog owners are striving to improve the welfare of their companions by providing them with a variety of physical activities in daily life, including walks and trotting for obesity prevention, health care, and stress relief [4]. However, it is unclear whether these activities can provide sufficient exercise levels for dogs. The American College of Sports Medicine (ACSM) provides scientific and detailed guidelines for health benefits that take into account individual characteristics (i.e., gender, age, fitness level, presence or absence of disease, etc.) by comprehensively analyzing numerous studies in the field of human exercise science [5]. The ACSM suggests \(\geq\) 30 min/day\({}^{-1}\) moderate and higher exercise intensity with \(\geq\)50-70% maximal oxygen uptake (VO\({}_{\text{max}}\)) \(\geq\) 3 day/wk to improve or maintain physical fitness and health in humans [5]. However, there are no established exercise guidelines for dogs, and it is challenging to measure exercise intensity with VO\({}_{\text{2 max}}\) due to the problem of using the equipment under experimental control conditions. Maximal heart rate (HR\({}_{\text{max}}\)) is often used to determine exercise intensity in dogs as an alternative measure [6]. Previous studies have demonstrated that the HR\({}_{\text{max}}\) of dogs is 220-230 beats per minute (bpm) by measuring the heart rate during progressive exercise [6, 7]. According to former exercise databased on HR\({}_{\text{max}}\)[6; 7; 8], dogs who participated in aerobic exercise on a treadmill, reaching 50-70% HR\({}_{\text{max}}\), for four weeks showed positive changes in white blood cell count (WBC) and serum alkaline phosphatase (ALP) levels [8]. In another study, walking (3.8 km/h, 10 min) followed by running (7.2 km/h, 20 min) then walking again (3.8 km/h, 10 min) resulted in a significant change in lactate and glucose levels in the blood serum of dogs [9]. Meanwhile, in a survey of the frequency and duration of walks regarding overweight dogs, 82.5% of respondents said that their dog walks at least once a day, and 63.2% said that their dog walks for more than 30 min per day [10]. Although overweight dogs were often walked, their weight seems to be stagnant. The enforced or voluntary exercise of appropriate frequency, intensity, time and type may be more essential for achieving health and fitness goals for dogs, as suggested in human studies [11; 12]. Recent research has focused on the role of exercise in the positive regulation of cytokines [13]. Cytokines are a control system of intercellular signaling molecules produced by various cells for immune and inflammatory reactions with complex mechanisms [14; 15]. Without stressful stimuli, cytokines are usually regulated at low levels through autocrine or paracrine action [16], but they also serve as physiological protection against tissue damage, injury, and disease [17; 18; 19]. In the cytokine response to exercise, moderate levels of exercise induce anti-inflammatory mechanisms, and intense levels of exercise stimulate pro-inflammatory pathways [20]. Interleukin (IL)-6, a pro-inflammatory cytokine, was significantly increased following high-intensity interval exercise (VO\({}_{\text{2 max}}\) 90%) compared to low-intensity exercise [21]. In addition, moderate-intensity aerobic exercise over four weeks induced a decrease in tumor necrosis factor-alpha (TNF-\(\alpha\)) [22]. On the other hand, other studies have reported that walking at -60% VO\({}_{\text{2 max}}\) intensity in healthy female subjects did not affect immune-related parameters [23].