# Exercise as it relates to Disease/The Effect of Combination Training on Insulin Secretion and Sensitivity in Overweight Adults
### Insulin Resistance

Insulin resistance is a condition in which the body's insulin is not used efficiently and the cells are not able to absorb glucose from the bloodstream. The body responds by producing more insulin. Overtime the pancreas cannot keep up with the body's need for insulin. Without enough insulin, blood glucose levels increase, which can lead to type 2 diabetes and other health disorders. An individual is at higher risk of developing insulin resistance if they experience:
* Increased amounts of abdominal adiposity.
* Increased levels of physical inactivity.
Therefore, increased levels of physical activity will decrease an individual's insulin resistance. The researchers of the current study aimed to determine which type of training would benefit insulin action the most.

### Aerobic or Resistance Training

* Studies show that following aerobic exercise programs can lead to improved insulin sensitivity.
* Studies that focus on resistance training programs have found that they too can promote an increase in insulin sensitivity.
The aim of the current study was to determine whether aerobic training, resistance training, or a combination of the two is the most effective in reducing an individual's insulin resistance.

## The Current Study
### Where Is The Research From?

The current study was performed at Duke University and East Carolina University. The researchers were from various departments such as, Department of Exercise and Sports Science and Human Performance Laboratory. The article was published in the Journal of Applied Physiology, which is a peer-reviewed medical journal.

### What Kind Of Research Was This?

The current study was a randomised trial that investigated the effects of aerobic training, resistance training, a combination of the two training types on insulin action. Randomised trials aim to distribute participants randomly into different conditions and are often considered as one of the higher standards for clinical research. There were three exercise groups that the subjects were randomly placed into.
* Aerobic Training Program (AT)
* Resistance training Program (RT)
* Combination Training Program, which included both aerobic and resistance training (AT/RT)

### What Did The Research Involve

The experiment involved 88 subjects aged 18–70 years old (M=50yrs), who had been characterised as overweight and sedentary. The wide age range could be problematic, as people of different ages could respond differently to the types of training. Before and after completing their respective program, subjects were asked to complete a variety of assessments:
* Body composition measurements using BOD PODs or DEXA scans. These methods are seen as the gold standard of measurement.
* Insulin measurement, using a 3-hour Intravenous Glucose Tolerance Test (IVGTT). The IVGTT is frequently used in studies that wish to focus on insulin sensitivity.
Therefore, it is evident that a high standard was set in constructing the method, which increased the quality of the study.
The prescribed amount of exercise for each group were as follows:
* The aerobic training group completed approximately 130minutes of aerobic training per week at an intensity of 65-80% of the individual's VO2 max. Exercise and Sport Science Australia (ESSA) recommended that individuals at risk of diabetes and with high insulin resistance complete 210 minutes of moderate physical activity per week. This raises some questions addressing the quality of the method as the researchers failed to prescribe an appropriate amount of exercise to its participants.
* The resistance-training group exercised 3 times a week, completing 8 exercises. They performed 3 sets of each exercise completing 8-12 repetitions per set. Exercise and Sport Science Australia (ESSA) suggest people complete at least 2 sessions of resistance training a week
* The combination-training group completed the full aerobic and the full resistance training schedules.
At the end of the training programs the subjects were instructed to stop training for 14 days. This gives insight into how the body to reacts to a period of detraining, as in the real world this can occur because of injury, illness or other circumstances.

### Results
#### The Main Findings

The results from the study revealed that AT/RT participants experienced a significant increase in insulin sensitivity. Also, approximately 50% of the beneficial effects were maintained after a 14-day detraining period.

#### Other Findings

* BMI of subjects in the AT and AT/RT groups significantly decreased.
* Fat mass of subjects in the AT and AT/RT groups significantly decreased.
* Adipose tissue in the thighs and abdominal significantly decreased for participants in the AT and AT/RT training groups.
These other findings support the ideas constructed by previous research, in that a relationship exists between insulin resistance, adiposity, and physical activity.

## Discussion

The researchers concluded that:
* AT/RT participants reared the greatest health benefits. This suggests that when an individual is trying to improve their insulin sensitivity they should participate in a variety of training types.
* AT/RT participants maintained approximately 50% the benefits of insulin action after detraining. In the real world, if an individual is no longer able to train, it is likely that they will experience a gradual decrease in the health benefits gained through their training program.

### Conclusion and Implications

* This study provided evidence, which supports that increasing levels of physical activity can lead to health benefits.
* The study shows that certain types of training can lead to different outcomes and that a combination of training types appears to produce the greatest number of benefits. A limitation is that it is unknown whether the benefits of the combination-training program were due to the effects of combined training types or due to the greater quantity of training completed.
* For overweight individuals with insulin resistance, a combination-training program appears to be the most effective way to improve insulin sensitivity.
* Another limitation of this study is that the researchers only reveal the types of training the participants completed but failed to provide information on the specific exercises.
* Overall, the researchers used robust scientific methods to construct a study that has provided useful results and information surrounding exercise and insulin resistance.

### Further reading

For further information on insulin resistance and the benefits of exercise read the following:
* Insulin sensitivity: http://www.diabetes.co.uk/insulin/insulin-sensitivity.html
* Physical Activity and Insulin Sensitivity: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2551669/
* Exercise and Insulin Sensitivity: The Parking Lot Analogy http://www.fitscript.com/blogs/news/11575133-exercise-and-insulin-sensitivity-the-parking-lot-analogy

### References

* 1 2 3 National Diabetes Information Clearinghouse. (2014). Insulin Resistance and Pre-diabetes. NIH Publication No. 14-4893
* 1 2 3 Hordern, M.D., Dunstan, D.W., Prins, J.B., Baker, M.K., Singh, M.A., & Coombes, J.S. (2012). Exercise prescription for patients with type 2 diabetes and pre-diabetes: A position statement from Exercise and Sport Science Australia. Journal of Science and Medicine in Sport, 15, 25-31.
* 1 2 3 4 5 6 AbouAssi, H., Slentz, C.A., Mikus, C.R., Tanner, C.J., Bateman, L.A., Willis, L.H., ... Kraus, W.E. (2015) The effects of aerobic, resistance, and combination training on insulin sensitivity and secretion in overweight adults from STRRIDE AT/RT: a randomised trial. Journal of Applied Physiology, 118, 1474-1482.
* 1 2 Ryan, A.S., Blumenthal, J.B., & Ortmeyer, H.K. (2013). Aerobic Exercise + Weight Loss Decreases Skeletal Muscle Myostatin Expression and Improves Insulin Sensitivity in Older Adults. Obesity, 21(7), 1350-1356.
* 1 2 Many, G., Hurtado, M.E., Tanner, C., Houmard, J., Gordish-Dressman, H., Park, J.J., ... Hoffman, E. (2013). Moderate-Intensity Aerobic Training Program Improves Insulin Sensitivity and Inflammatory Markers in a Pilot Study of Morbidly Obese Minority Teens. Pediatric Exercise Science, 25, 12-26.
* 1 2 Mezghanni, N., Mnif, M., Chtourou, H., Chaabouni, K., Masmoudi, L., Lassoued, A., ... Mejdoub, H. (2014). Effect of aerobic training on insulin resistance and C-reactive protein (CRP) levels and subcutaneous abdominal in obese women. Sport Sci Health, 10, 111-118
* 1 2 Sousa, M.S., Saavedra, F.J., Neto, G.R., Novaes, G.S., Souza, A.C., Salerno, V.P., & Novaes, J.S. (2014). Resistance Training in Type 2 Diabetic Patients Improves Uric Acid levels. Journal of Human Kinetics, 43, 17-24.
* 1 2 Shaibi, G.Q., Cruz, M.L., Ball, G.D., Weigensberg, M.J., Salem, G.J., Crespo, N.C., & Goran, M,I. (2006). Effects of Resistance Training on Insulin Sensitivity in Overweight Latino Adolescent Males. Medicine & Science in Sports & Exercise, 1208-1215.
* ↑ Glazerman, S., Levy, D.M., & Myers, D. (2002) Nonexperimental Replications of Social Experiments: A Systematic Review. Mathematica Policy Research discussion paper. 8813-300.
* ↑ Powers, S.K., Howley, E.T., Cotter, J., Pumpa, K., Leight, A. (2014). Body Composition and Nutrition for Health. 361-397. North Ryde, NSW: McGraw Hill Education.
* ↑ Hahn, R.G., Ljunggren, S., Larsen, F., & Nyström, T. (2011). A simple intravenous glucose tolerance test for assessment of insulin sensitivity. Theoretical Biology and Medical Modelling, 8(12).
* ↑ Lobo, A. (2012). Effects of Detraining on Physical Fitness and Cardiovascular Variables in Non-institutionalised Elders. Journal of Medical Science, 1(1), 4-8.