*Corresponding author: Beong-Suk Kim Department of Companion Animal Health and Science, Tongmyong University, 428 Sinseon-ro, Nam-gu, Busan 48520, Korea Introduction
Coronavirus disease 2019 (COVID-19) lockdown restrictions worldwide prompted dog owners to implement lifestyle changes for their dogs. Outdoor physical activity among dogs decreased, particularly during the COVID-19 lockdown. Many household dogs had additional playtime with their owners during lockdown [1]. Although shorter-than-usual walks during the pandemic could negatively affect dog health and behavior, dog owners in Spain [2] and the United Kingdom [1] took shorter walks with their dogs [3].
Dog owners have previously focused on physical activity interventions for dogs primarily aimed at reducing body weight [4]. However, most dog owners have recently focused on caring for their dog’s health and improving their physical strength. Dog owners are particularly interested in well-being and preventive medicine such as physical rehabilitation therapy, maintenance of muscle strength and cardiopulmonary fitness, and body-weight reduction [5]. Many human studies have shown that exercise is a powerful intervention with important benefits for maintaining and promoting health and fitness [6-9].
A previous study reported that thigh (hindlimb) circumference increased considerably in dogs that jogged on a treadmill twice weekly for 12 weeks [4,10]. Increased thigh (hindlimb) circumference may be associated with increased muscle mass due to myofibrillar hypertrophy caused by treadmill training [11]. Muscle mass represents limb use and is associated with muscle strength. Limb circumference measurement is an inexpensive, rapid, and easily applicable indirect method for assessing changes in muscle mass and thigh (hindlimb) circumference in clinical patients, showing a significant correlation with actual muscle mass [12,13]. Because muscles act as shock absorbers in joints, strengthening the muscles around the joints can help protect them. Lightweight-bearing exercises also help stimulate cartilage metabolism and increase nutrient diffusion in joints [14]. Core exercises are defined as those that strengthen the core muscles, specifically those of the torso proximal to the ball-and-socket joints [15].
Although overweight and obesity have become increasingly common in companion dogs, affecting their physical activity and health, positive physical activity—such as maintaining a standing position on a compressible surface like an air mattress or exercise ball—tends to increase muscle strength [16]. Basic exercises for dogs, such as sitting, lying down, planking, pivoting, and squats, actively help develop this physical strength [5]. A well-designed and properly balanced exercise program can achieve therapeutic goals safely and effectively [17,18], thereby improving balance and proprioception [19]. In this context, exercise balls or rolls can be utilized to enhance balance and proprioceptive function in dogs to improve muscle strength, joint mobility, and functional limb use [20].
Therefore, the specific purpose of this pilot study was to determine whether a 6-week home-based fitness exercise (HFE) program utilizing an exercise roll affected limb circumference as an indicator of brachial (forelimb) and thigh (hindlimb) muscle mass and body weight. We hypothesized that the HFE program would increase limb circumference in dogs while maintaining stable body weight, comparing active participants with companion dogs that did not participate in any exercise program. Ultimately, this study is expected to promote functional physical strength and metabolic health, providing valuable baseline data for the future development and optimization of canine exercise programs.
Materials and Methods
Ethical approval
The study protocol was approved by the Bioethical Committee of the Research Center (202507-HR-005) of Tongmyong University (Busan, Korea).
HFE program design
The HFE program presented in this study was designed as a companion dog fitness program that allows dog owners to exercise their dogs easily at home using a simple exercise roll. To confirm the effectiveness and safety of the exercise program, 2 veterinarians and 2 canine physical therapists evaluated the program’s composition, exercises, and content validity for the entire session, time, and structure. Dog owners in the exercise group received instruction about the exercise program, including exact posture and movements, through video demonstrations. To ensure measurement reliability and minimize intra-observer variability, owners were pretrained by researchers on how to identify anatomical landmarks (femur [hindlimb] and humerus [forelimb]) and instructed to apply consistent tension on the measuring tape over the fur, following standardized measurement guidelines. The weekly exercise frequency and daily exercise time criteria of the structured HFE program were clarified to the dog owners.
Participants
All dog owners were briefed on the purpose of the study and provided written informed consent. Demographic information of the participating dogs included their name, age (months), animal registration status, body weight, breed, sex, and sterilization status. The dogs included in this study were vaccinated annually.
The study group was initially randomly divided into an exercise and non-exercise group, with 8 owners and dogs in each group. The exercise group received HFE intervention. We also asked the owners in the non-exercise group not to let their dogs participate in special activities, such as obedience training, agility, International Prüfungs-Ordnung, frisbee sports, herding, and jogging during the study period. Dogs in the non-exercise group were remeasured at the end of the HFE program, 6 weeks later.
Participating dogs were selected according to the following criteria: The dogs had to be over 12 months old and in healthy physical condition to participate in the HFE program. Dogs with known systemic or orthopedic conditions such as ataxia, lameness, paw scuffing, and stumbling were excluded. Sixteen dogs were included in this study. However, 2 dogs were excluded: one from the exercise group because of hip problems and one from the non-exercise group because of periodontitis. Thus, 14 dogs were evaluated, with 7 in each group. The brachial (forelimb) and thigh (hindlimb) circumferences and body weight of each dog were measured.
HFE program
Dog owners participated in the study for 6 weeks. The HFE program consisted of one workout session 4 times per week. The sessions consisted of 4 exercises: plank for hind limb exercise, plank for forelimb exercise, super-stand exercise, and squat (posture sit-to-down-stand). Each exercise was performed for 120-180 seconds. The entire exercise session lasted 10-20 minutes, including the break time. The height, length, and transverse diameter of the exercise rolls used in the HFE program were 30 × 70 × 40 cm. Owners were asked to feed their dogs as usual. Reinforcers, such as small treats, were allowed during the exercise sessions to motivate the dogs. The HFE program did not impose any caloric restrictions on the participating dogs.
Plank for forelimbs exercise
The plank for the forelimbs exercise involved placing the dog’s hind limbs on an exercise roll while the forelimbs remained on the ground, with the primary objective of shifting the body weight forward to strengthen the brachial muscles of the forelimbs. The dogs were required to hold the position for 10 seconds, take a 5-10 second break and then repeat the exercise. With the head and neck facing front, the forelimbs were placed on the floor, the hind limbs were placed on the exercise roll, and balance was maintained. The owner rewarded the dog while maintaining correct posture on the exercise roll (Fig. 1A).
Plank for hindlimbs exercise
The plank for hindlimb exercise involved placing the dog's forelimbs on an exercise roll with the hindlimbs on the ground, which was designed to shift the center of gravity backward, thereby increasing the load on and strengthening the thigh muscles of the hindlimbs. With the head and neck facing front, the hindlimbs are on the floor, the forelimbs are placed on the exercise roll, and balance is maintained (Fig. 1B). The owner should reward the dog while maintaining correct posture on the exercise roll.
Super-stand exercise
The super-stand exercise was performed with all 4 limbs on an exercise roll. Rhythmic stabilization can be achieved by supporting the dog in a standing position on an exercise roll and rhythmically pressing it to stimulate contraction of the extensor muscles and maintain body posture [16]. The dog is required to hold the position for 10 s, take a 5-10-second break and then repeat. When performing the super-stand exercise, the owner must help the dog to prevent injury. The owner rewards the dog while maintaining correct posture on the exercise roll. With the head and neck facing the front, the hindlimbs and forelimbs are on the exercise roll, and balance is maintained (Fig. 1C).
Squat (posture sit-to-stand) exercise
Sit-to-stand exercises can strengthen the hip and stifle extensor muscles, enhance the active range of motion, and improve the strength of the glutes, quadriceps, and hamstrings [21]. Dogs can sit or stand on the exercise roll. It may be prudent to let the dog stand upright without tilting to one side when sitting or standing, and it is important to ensure that both hindlimb joints are symmetrically bent so that the dog sits upright on its hips. The sit-to-stand exercise can be repeated up to 15 times, 3-4 times per session [21]. For dogs, the duration in the sit-and-down postures may be as short as 1-2 seconds [5]. The owner rewards the dog while maintaining correct posture on the exercise roll (Fig. 1D and E).
The HFE program is summarized in Supplementary Table S1, with reference to the fitness modality goals and recommended reward methods presented by Farr et al. [5].
Data collection
Thigh (hind limb) and brachial (forelimb) circumferences and body weights were measured before and after the 6-week HFE program by the same dog owner using the same devices. Limb circumferences were measured and recorded in millimeters by the same owner using a consistent measuring tape (Growgrow; Growgrow Company, China). The limb circumferences of the participants in the study groups were recorded before and after the HFE program. The right and left thigh circumferences of the hindlimbs were measured at 70% of the femur length, from the proximal end of the femur to the center of the outer fabella [12]. The 70% point was determined by measuring the total straight-line distance between the 2 landmarks. Measurements were performed on both right and left limbs, and the mean value of both sides was used for the final statistical analysis to enhance data reliability. During measurement, the dogs were positioned in lateral recumbency (lying on their sides) [22]. Similarly, the right and left brachial circumferences of the forelimbs were measured at 20% of the humeral length from the proximal part of the lateral epicondyle [4,12,22], and the mean value was recorded. Body weight was measured to the nearest kilogram using a digital scale (X24; CAS, China) [4].
Data processing and statistical analysis
Data processing and statistical analyses were performed using Excel 2019 (Microsoft Corp., USA) and IBM SPSS Statistics ver. 22.0 (IBM Corp.). Results are presented as mean ± standard deviation. Normality of data distribution was assessed using the Shapiro-Wilk test. Given the small sample size (n = 12) and violations of normality assumptions for several variables, nonparametric tests were employed to ensure robust statistical inferences. Owing to nonrandom attrition in the control group, the original allocation structure was compromised, and the final analysis was conducted using a per-protocol approach. Accordingly, this study was analyzed as a pilot prospective exploratory study rather than a formal randomized controlled trial. Although covariate-adjusted modeling, such as analysis of covariance, was considered to account for baseline differences between the groups, it was not applied because the extremely small sample size limited the stability and interpretability of the adjusted parametric models. Instead, nonparametric methods were prioritized to provide a more conservative analysis. The Wilcoxon signed-rank test was used to compare limb circumferences and body weights within each group before and after the 6-week HFE program. Statistical significance was set at p < 0.05.
Results
The study was conducted between May and August 2025. Fourteen owner-dog pairs participated in the 6-week study, with 7 participants each in the exercise and non-exercise groups. Data were self-reported by the dog owners. However, 2 dogs in the non-exercise group were excluded because they participated in special dog-sport activities (obedience training and jogging) that were not permitted during the study period. As a result, data on changes in limb circumferences and body weights of 12 dogs were collected, of which 7 dogs were in the exercise group and 5 were in the non-exercise group.
Table 1 shows the summarized characteristics of the dogs in the 2 groups; no statistically significant differences in mean age (Mann-Whitney U-test, p > 0.05) or sex (chi-square test, p = 0.558) between the exercise and non-exercise groups were observed; however, limb circumferences and body weights were significantly different. Homogeneity of limb circumference and body weight between the study groups was not confirmed. Therefore, the Wilcoxon signed-rank test was performed to examine the changes in limb circumferences and weights before and after the HFE program in each group. Comparative tests were not performed between the exercise and non-exercise groups.
Description of the dog population
Among the dogs in the exercise group, no reports were made from owners that negative effects, such as physical symptoms, lameness, and problematic behaviors, developed during or after the HFE program.
Baseline characteristics
Table 1 shows the general characteristics of dogs in the exercise and non-exercise groups after completion of the HFE program. The dogs that participated in the study belonged to 7 breeds, including mixed breeds, and small- and medium-sized dogs. The breeds included Maltese (n = 2), Toy Poodle (n = 1), Pomeranian (n = 1), Bichon Frise (n = 1), Shih Tzu (n = 1), Shiba Inu (n = 1), and mixed breeds (n = 5). The exercise dog group's mean age was 77.1 ± 27.9 months, and that of dogs in the non-exercise group was 78.6 ± 40.3 months. At baseline, the non-exercise group had a significantly higher mean body weight (7.6 ± 1.8 kg) compared to that of the exercise group (4.5 ± 1.8 kg) (p < 0.05). Due to this baseline imbalance, intragroup changes were primarily analyzed using the Wilcoxon signed-rank test.
Differences in limb circumferences before and after the intervention
Table 2 and Fig. 2 show the changes in limb circumference of dogs in the exercise and non-exercise groups. All the dogs that participated in the HFE program showed an increase in limb circumference after the intervention. In the exercise group, there were significant increases in brachial (forelimb) circumferences (from 9.2 ± 0.7 to 9.9 ± 1.2 cm, p = 0.018) and thigh (hindlimb) circumferences (from 14.2 ± 2.1 to 15.3 ± 2.7 cm, p = 0.018). However, the non-exercise group showed no significant changes in limb circumference (thigh [hindlimb]: from 14.4 ± 2.6 to 14.3 ± 2.4 cm; brachial [forelimb]: from 21.9 ± 2.4 to 21.9 ± 2.2 cm, p > 0.05).
Differences in body weight before and after the intervention
All dogs in the exercise and non-exercise groups maintained a stable body weight. The body-weight differences between the 2 groups of dogs are shown in Table 3 and Fig. 3. Dogs in the exercise group did not show a significant difference in body weight after the intervention (4.5 ± 1.7 kg) compared with before the intervention (4.4 ± 1.8 kg). Also, dogs in the non-exercise group showed no significant difference in body-weight change after the intervention (7.6 ± 1.6 kg) compared with before the intervention (7.6 ± 1.8 kg).
Discussion
This study investigated the effects of a structured HFE program on limb circumference in dogs. Although the study was initially designed as a randomized trial, nonrandom attrition in the control group compromised the original allocation structure, resulting in a nonrandom pattern of missing data. The final analysis was conducted using a per-protocol approach rather than an intention-to-treat framework. Accordingly, this study should be interpreted as a pilot prospective exploratory study rather than a formal randomized controlled trial, and the findings should be regarded as preliminary and hypothesis generating.
Effects of HFE program on canine limb circumference and body weight
Muscle development generally requires adequate protein intake combined with appropriate resistance and aerobic exercise, along with sufficient recovery. A previous study reported a significant increase in thigh (hindlimb) circumference when healthy dogs jogged on treadmills twice weekly for 12 weeks, and this increase in circumference was indirectly associated with increased muscle mass [4,11]. Söder et al. [4] reported a numerical increase in the thigh (hindlimb) circumference after physical activity in all dogs, regardless of sex or size. Muscle mass has been proposed as an indicator of the effectiveness of aerobic exercise in dogs [4,10].
All the dogs that participated in the current study had a normal body weight. Therefore, intramuscular or subcutaneous fat in the limbs may not significantly affect the circumference. No caloric restrictions were imposed in this study. The exercise program was performed 4 times weekly, once daily, for 10-20 min per session, with each exercise lasting 2-3 minutes with rest intervals. Dogs were fed their usual diets and provided with treats as rewards for exercising. In this study, the dogs maintained a stable body weight and demonstrated an increase in limb circumference. A significant increase in limb circumference without a corresponding increase in body weight may suggest favorable changes in musculoskeletal parameters. These findings were consistent with those reported by Söder et al. [4]. However, because limb circumference is an indirect proxy for muscle mass, the results should be interpreted cautiously as potential indicators of muscular adaptation rather than as definitive evidence of muscle hypertrophy. Although these findings are encouraging, direct body composition measurements (e.g., dual-energy X-ray absorptiometry) were not performed; therefore, changes in fat or lean mass remain speculative. Further studies are required to investigate the influence of dog-specific characteristics, as dogs may respond differently to exercise depending on their sex, size, and physical condition.
All dogs had their limb circumferences measured without clipping the thigh fur. Previous research has reported that clipping results in a mean difference of approximately 3 mm [22], whereas intra-observer variability in repeated thigh measurements may reach approximately 1 cm [23]. In this study, the observed increase in thigh (hindlimb) circumference in the exercise group was 1.1 cm, which is numerically close to the previously reported measurement variability. Although statistical significance was achieved (p < 0.05), the magnitude of the change should be cautiously interpreted. The absence of study-specific reliability indices such as the intraclass correlation coefficient, standard error of measurement, and minimal detectable change represents a methodological limitation. Future studies should incorporate standardized measurement protocols and formal reliability testing to improve the precision and interpretability of limb circumference measurements.
Seven dogs in the exercise group were examined at the end of the HFE program. No injuries, adverse events, or problematic behaviors were observed during the study period. However, given the small sample size and short duration of the intervention, definitive conclusions regarding its safety cannot be drawn. A potential concern with canine exercise programs is that repetitive movements may adversely affect skeletal structures, joints, or epiphyseal plates [14,24,25]. Previous studies have suggested that adding physical activity to weight management programs may help preserve lean body mass [4,26]. Over the 6-week period, limb circumference increased, whereas body weight remained stable, even with the treats provided during exercise. These findings provide preliminary evidence supporting the feasibility of structured home-based exercise programs for dogs.
Limitations and future research
Our study had several limitations. First, as previously mentioned, the original randomized allocation was compromised because of nonrandom attrition in the control group. Accordingly, this study was analyzed as a pilot prospective exploratory study rather than a formal randomized controlled trial, and the findings should be interpreted with caution. Second, the baseline imbalance in body weight prevented a robust between-group comparison, necessitating a focus on intragroup longitudinal changes. Regarding baseline imbalance, the higher body weight in the non-exercise group may reflect inherent breed or size differences, which could influence the absolute values of limb circumferences. However, by focusing on intragroup longitudinal changes, we observed the specific impact of the HFE program regardless of the initial weight gap. Finally, because the measurements were self-reported by the owners, the potential for observer bias and measurement variability cannot be entirely ruled out.
We suggest that the effect of intrinsic dog factors merits further investigation, as it is possible that dogs of different sexes or sizes, independent of their body condition, may respond differently to physical exercise with regard to the distribution of body weight and muscle mass [4]. An inherent limitation of this approach is the potential for errors associated with owner-administered tape measurements. Therefore, future studies should incorporate additional measurement approaches including assessments conducted by trained researchers or independent observers.
Individual owners’ adherence to the HFE program could not be assessed. As the participants in the exercise group were veterinary nursing students, their motivation to adhere to the HFE program was likely higher than that of the general population. Therefore, similar results may not be generalizable to the general public.
Beyond the selection of exercises, further research is required to determine the optimal parameters, including weekly frequency, session duration, interval timing, and rest periods. Recently, canine sports, such as agility, disc dogs, dog dances, flyballs, and the International Prüfungs-Ordnung, have gained popularity. Therefore, structured exercise programs designed to improve strength and range of motion may help prevent injuries and promote safe participation in canine sports. This study highlighted the importance of promoting canine well-being through structured home-based exercise programs aimed at addressing muscle loss and obesity. In addition to its potential physical benefits, home-based exercises may facilitate positive owner-dog interactions. Structured home-based exercise programs may therefore contribute to improved canine welfare by supporting musculoskeletal health.
Although standardized training was provided to the owners to minimize measurement variability, future studies should incorporate more objective assessments, such as ultrasonography or computed tomography, to accurately quantify changes in muscle cross-sectional area and overall body composition. Furthermore, larger, adequately powered, randomized controlled trials with standardized measurement protocols are required to confirm the efficacy and safety of structured home-based exercise programs for dogs. In addition, long-term follow-up studies are required to determine whether the observed increases in limb circumference are sustained after cessation of the HFE program. Establishing the durability of these adaptations is essential to clarify the clinical relevance and practical value of structured home-based fitness interventions for companion animals.
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