Free gait in a shallow pool accelerates recovery after exercise in model mice with fibromyalgia

Abstract

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.

Keywords: Behavior analysis; Fibromyalgia-induced model mouse; Shallow pool gait.

Fig. 1

A flow chart of the experimental group, intervention, and experimental protocol. (A) A flow chart of the group classification for the experiment. (B) The intervention protocol for the control and pool gait groups. (C) The experimental protocol for fibromyalgia (FM)-induced model mice. ECG, electrocardiogram.

Fig. 2

Electrostimulation- and heat-evoked sensory threshold in the control group. A sensory threshold using a 5-Hz sine wave (Ai), a 250-Hz sine wave (Aii), and a 2,000-Hz sine wave (Aiii, **P<0.01). A sine wave is an electrical stimulation used to determine the sensory threshold. The sensory threshold with heat stimulus (5°/sec) (Bi, *P<0.05) and heat stimulus (2°/sec) (Bii).

Fig. 3

Weekly changes in locomotive behavior in the control group. (A) An example of gait tracking in the FM-induced model mice. Changing the gait distance (B; *P<0.05, **P<0.01), maximum speed (C; *P<0.05, **P<0.01), and average speed (D; *P<0.05, **P<0.01) in the control group.

Fig. 4

Weekly changes in the sensory threshold in the control and pool gait groups. (Ai) A comparison of the sensory threshold with a 5-Hz sine wave between the control and the pool gait groups. (Aii) A comparison of the sensory threshold with a 250-Hz sine wave between the control and the pool gait groups. (Aiii) A comparison of the sensory threshold with a 2,000-Hz sine wave between the control and the pool gait groups. (Bi) A comparison of the sensory threshold with heat stimulus between the control and the pool gait groups (5°/sec). (Bii) A comparison of the sensory threshold with heat stimulus between the control and the pool gait groups (2°/sec).

Fig. 5

Weekly changes in locomotive behavior in the control and pool gait groups. Changing the gait distance (A), maximum speed (B), and average speed (C) for the control and the pool gait groups.

Fig. 6

Comparison of the motor recovery in the control and pool gait groups after exercise in shallow water. (Ai and Aii) An example of gait tracking in the control and pool gait groups after the exercise in shallow water. (Aiii) The difference in time of onset of movement after the exercise between the control and the pool gait groups (**P<0.01). (Aiv) The time course of the gait distance following the completion of the exercise. (Av) The time course of the average speed following the completion of the exercise. (Avi) The gait distance at time (1, 2, 5, 10, 20, and 30 sec) following the completion of the exercise (*P<0.05). (Avii) The maximum speed at the point of the time (1, 2, 5, 10, 20, and 30 sec) following the completion of the exercise (*P<0.05).

Fig. 7

Comparison of the cardiac function in the control and pool gait groups after exercise in shallow water. (Ai) Three examples of gait tracking during the exercise in shallow water. (Aii) Gait distance between the control and the pool gait groups during the exercise (ns). (Aiii) The maximum speed of the control and the pool gait groups during the exercise (ns). (Bi) An example of electrocardiogram (ECG) signals in the control group before and after the exercise. (Bii) A second example of ECG signals in the pool gait group before and after the exercise. (Biii) A third example of ECG signals in the pool gait group before and after the exercise. (Biv) The change in heart rate before and after the exercise in the control and pool gait groups. (Bv) Changes in the heart rate irregularity score before and after the exercise in the control and pool gait groups. ns, not significant difference.