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research goal, and can be designed with reproducible parameters such as distances
and speed. But oftentimes the experimental conditions are stressful and the stimulus
to exercise is unpleasant, which may confound outcomes of exercise research goals.
3.2.2 Swimming
Swimming exercise may result in high alternating loads to the cardiovascular sys-
tem [ 1 , 3 , 38 , 52 ]. This exercise can be performed spontaneously with a relative
amount of animal and a range of intensities, and it requires a simpler apparatus
compared to treadmill running and spontaneous wheel exercise [ 20 , 52 ].
After a shorter period of familiarization, animals are able to perform exercisewith less attention [ 29 ]. Swim exercise-induced cardiac hypertrophy model was
generated to study the susceptibility to arrhythmias and determine molecular mech-
anisms underlying exercise-induced cardiac hypertrophy in small rodents (rats,
mice) [ 52 , 54 ]. Interestingly, exercise model using swimming apparatus to control
duration, load, and frequency of exercise applied to mice with or without the weight
workload attached to the tail of the mouse was designed [ 52 ]. The findings demon-
strated that duration- and frequency-controlled exercise training similarly induces a
significant conditioning response similar with the study done in humans, and the
optimal conditioning protocol to induce physiological hypertrophy was 90 minutes,
two times a day, 5 days a week for 4 weeks without overload [ 52 ]. In the swimming
exercise, moderate intensity exercise consists of 1 hour per day and 5 days per week
for 8–10 weeks was the optimal protocol [ 20 , 34 ]. In another study, swimming
induced cardiac hypertrophy and hemodynamic changes, but it does not protect the
heart against the induction of ventricular fibrillation [ 49 ]. Either moderate or high
intensity swim training can have an effect on intrinsic calcium current characteris-
tics in rat myocardium [ 20 ]. In addition, swim training can prevent changes in ace-
tylcholinesterase and butyrylcholinesterase activities in hypertensive rats exposed
to 6 weeks interval swimming training, trained 5 times per week in an adapted
swimming system for 60 minutes a day, gradually increasing the workload up to 5%
of animal's body weight [ 29 ]. In contrast, the susceptibility to ventricular fibrillation
was either reduced [ 54 ] or unaltered [ 49 ] in the isolated, non-ischemic heart of the
swimming-trained rats.
Lack of graded workload protocols and the interference of water in the recordingequipment can be disadvantageous for swimming exercise. In exercise research,
control or sedentary animals are normally placed in shallow water (about 5 cm in
depth) at the same temperature and for the same duration as the experimental group,
but without a workload to exclude the effect of water [ 29 ]. However, there is a need
for closer examination on the ways in which stress-induced modulation of behavior
in the force swimming test is employed [ 38 ].
4 Acute and Chronic Exercise in Animal Models