Background Fibromyalgia patients experience cardiovascular complications in addition to musculoskeletal pain. This study aimed to investigate the cardiac effects of a prolonged shallow water gait in a fibromyalgia-induced young mouse model. Methods To produce a fibromyalgia mouse model, wild-type mice were administered an intraperitoneal injection of reserpine once a day for three days, and two primary experiments were performed. First, three types of gait tests were performed before and after the reserpine injections as follows: (i) 5 minutes of free gait outside the water, (ii) 1 minute of free gait in shallow warm water, and (iii) 5 minutes of free gait in shallow warm water. Second, electrocardiogram recordings were taken before and after the three gait tests. The average heart rate and heart rate irregularity scores were analyzed. Results Exercise-induced cardiac arrhythmia was observed at 1-minute gait in shallow water during the acute stage of induced FM in young mice. Further, both cardiac arrhythmia and a decrease in HR have occurred at 5-minute gait in shallow water at the same mice. However, this phenomenon was not observed in the wild-type mice under any test conditions. Conclusion Although a short-term free gait in shallow warm water may be advantageous for increasing the motor activity of FM-model mice, we should be aware of the risk of prolonged and excessive exercise-induced cardiac arrhythmia. For gait exercises in shallow water as a treatment in FM patients. We suggest a gradual increase in exercise duration may be warranted.

This study aimed to determine the effect of pool gait exercise using fibromyalgia-induced model mice. The sensory threshold, locomotive behavior, electrocardiogram, and onset time after the gait test in shallow water using male C57BL/6J mice (weight, 30-35 g; n= 21) were investigated. To induce fibromyalgia in model mice, reserpine was injected intraperitoneally into wild-type mice once a day for 3 days. Subsequently, the fibromyalgia-induced model mice were randomly classified into two groups as follows: the control group (n= 11) and the pool gait group (n= 10). The mice in the pool gait group walked in the same cage containing shallow warm water 5 times per week. Both groups underwent sensory thresholds and video recordings to determine locomotive behaviors weekly. Further, both heart rate and video recordings for observation of a recovery after the gait test in shallow water were undertaken (control group; n= 5, pool gait group; n= 5). The pool gait did not affect sensory thresholds and locomotive behavior; however, in the pool gait group, both the recovery after the test, such as onset time and gait distance, were considerably better than those of the control group. Furthermore, changes in heart rate and heart rate irregularity after the test were more apparent in the control group than in the pool gait group. The free gait in a shallow pool accelerated recovery after exercise, unlike the sensory threshold.