A Chronic High-Intensity Interval Training and Diet-Induced Obesity Model to Maximize Exercise Effort and Induce Physiologic Changes in Rats

This model allows researchers to investigate many underlying mechanisms related to diet, exercise, and the associated physiology that contribute to health or disease. A key advantage is that animals will always be exercising at maximum intensity because the exercise intensity increases along with the animal's fitness and skill level. This protocol is particularly applicable to the management of metabolic diseases that are often comorbid with obesity as inflammatory pathways are implicated both in exercise and in obesity.

Demonstrating the procedure will be Chris Butler, a research technician from my laboratory. To begin a training session for the Sprague-Dawly rats, turn on the treadmill using the power switch at the back of the control unit. Adjust the treadmill shock to 0.00 milliampere by turning the dial on the control unit counter-clockwise.

To adjust the inclination of the treadmill to 5%first, loosen the locking nut on the bottom of the treadmill. Then, set the incline to the first notch and retighten the locking nut to secure the treadmill incline in this position. Supporting the animal's body with one hand, gently grasp the base of the tail with the other hand and place the animal in an individual lane on the treadmill.

Repeat the process until a rat from the same cohort occupies each of the five individual lanes on the treadmill. Then, adjust the treadmill speed to 45 centimeters per second by rotating the speed dial on the control unit clockwise. Press the Stop/Run button to stop the treadmill and allow it to run for five minutes.

To facilitate learning of how to use the treadmill during the early stages of training, the animals may need encouragement with stiff bristle brushes to stay off the shock grid. Press the Stop/Run button to stop the treadmill after five minutes and allow a two-minute rest before beginning the training bout. Set the initial velocity for the first session of the training bout to 55 centimeters per second.

Once the velocity is set, start the treadmill and have the animals run for one minute. If any animal reaches the shock grid at the rear side of the treadmill, motivate it with a brush to encourage forward motion. If any animal fails to respond to the motivations more than twice per training bout turn on the shock grid to 2.0 milliampere for the remainder of the session.

When the time monitor reads one minute, stop the treadmill by pressing the Stop/Run button and let the animals rest for two minutes. Then, adjust the running speed for the next sprint, depending on the performance of the animals in the previous sprint. If all the animals within a cohort complete the previous one minute sprint without needing motivation or touching the shock grid more than five times, increase the running speed by four centimeters per second.

If not, use the same speed as the previous sprint. If any animal struggles excessively during the previous sprint interval, reduce the speed by four centimeters per second. After setting the speed as described, start the next sprint interval immediately following the two minute rest.

Record the speed and distance run for each bout by transcribing it in a notepad. Repeat the demonstrated high intensity interval training bout consisting of high intensity running, followed by rest 10 times each day. For the first sprint of each subsequent training day, use a starting speed that is four centimeters per second slower than the highest speed achieved on the previous day.

At the end of each training session, remove the animals from the treadmill and place them in their individual cages. The training performance indicated by the running speeds increased over the protocol duration. The final speeds of the exercise trained and high fat diet exercise trained groups were comparable.

The total running distances for the exercise trained and high fat diet exercise trained groups were also similar. Although the average weekly feed intake of the control versus exercise trained groups did not differ from each other, both had greater weekly intake than the high fat diet exercise trained group, which was again more than the high fat diet group. However, the groups being fed a high fat diet had a higher caloric intake than those on the control diet.

The high fat diet exercise trained group showed the highest weekly caloric intake, sequentially followed by the high-fat diet, control and trained groups. Over the training period, the average daily gain of body weight in the high fat diet exercise trained group was greater than in the high fat diet group. No significant differences in average daily gain between the control and exercise trained groups were observed.

Similarly, the average daily gains of the control and high fat diet groups were also comparable. Tissue retrieval after the completion of the training protocol revealed that animals in the high fat diet group had the highest visceral adiposity. The exercise trained groups showed reduced visceral adiposity relative to the non-trained groups, Monitor animals closely while loading and unloading them from the treadmill.

We advise having an assistant available to help during these steps.