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What are the effects of various exercise modalities on insulin resistance and which modality is the most
optimal?
Osman Hussein
Syed Hassan Shah Tirmzi
KIN 3060 (01) F23 Human Development & Ageing
Dr. Kerry Ritchie
November 9th, 2023
Introduction
Our body’s primary source of energy is glucose which typically comes from carbohydrates, but for
the food we intake to enter our muscles, fat, and liver cells so that it can be used for energy and allow the
muscles to follow through on any actions, it requires the hormone called insulin (Basu, 2018). The pancreas
produces and releases the hormone insulin into the bloodstream to function in this manner after a meal
when our blood sugar or blood glucose levels rise (Basu, 2018). At this point, insulin plays a role in aiding
the absorption of glucose and regulating the elevated blood glucose levels at a normal range for the body
so that it always reaches homeostasis (Basu, 2018).
However, in some cases, certain individual’s bodies become unable to adequately respond to
insulin. Further, not being able to absorb glucose efficiently from the blood and use it for energy, these
individuals are deemed insulin resistant (Basu, 2018). Insulin resistance can create problems in the body,
and this is a crucial matter nowadays since there is a higher prevalence of obesity, and diabetes across all
age demographics. The way the body compensates for this lack of responsiveness from the cells is to tell
the pancreas to produce more insulin to maintain homeostasis and normal blood sugar levels. If this
problem of insulin resistance lingers, over time the body can lead to a condition called hyperinsulinemia
which is blood sugar levels that are higher than normal (Basu, 2018). Moreover, this condition does not help
the cells respond to insulin better over time either. The cells continue to resist and are unable to clear the
lingering glucose that is stagnant in the bloodstream which can further lead to hyperglycemia as well (Basu,
2018).
It is known that individuals who are insulin resistant are accompanied by some or several factors
such as physical inactivity, obesity, genetics, sleep disorders, chronic inflammatory conditions, gestational
diabetes, improper diets, etc. It is important to attack this condition as soon as possible because, over a
long period of time, it can also develop into type 2 diabetes (TD2) where the body is then unable to keep
producing high amounts of insulin in response to the high blood sugar and resistance (Basu, 2018).
The purpose of this paper is to research and analyze the effects of various exercise methods and
describe if there are any differences in how they can help decrease insulin resistance in the body, and if
there is a proposed best method for optimal results. Exercise methods such as aerobic, resistance, and a
combination of both under several conditions will be researched to see how each mechanism of action can
counteract or decrease insulin resistance in the body.
Aerobic Exercise and Insulin Sensitivity
Exercise is a fantastic tool for promoting good health and discipline and one popular exercise
method is aerobic exercise which includes activities like running, walking, swimming, or cycling. Aerobic
Exercise has been a great method for improving cardiovascular health and endurance. Aerobic exercise
offers various benefits such as improvements in cardiovascular health, endurance, the efficiency of oxygen
delivery to muscles, increased blood flow throughout the body and enhanced mitochondrial function.
A study by Motahari-Tabari & et al. examined an 8-week aerobic exercise program on the effects of
insulin resistance. The study design observed 53 type 2 diabetic women split into two groups: treatment
(27) and control (26) (Motahari-Tabari & et al., 2014). The participants in the treatment group began a
warm-up 10 minutes prior to walking for 30 minutes with an elevated heart rate of 60% at maximum
intensity. They followed by stretching in a seated position for 10 minutes 3 times per week for 8 weeks
(Motahari-Tabari & et al., 2014). They found significant differences in insulin resistance, fasting glucose,
plasma insulin, changes in BMI and improvements in insulin sensitivity. In addition, waist and hip
circumferences had differences pre- to post-exercise intervention. Researchers did point out that aerobic
exercise influenced insulin after only 8 weeks (Motahari-Tabari & et al., 2014). These findings suggest that
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aerobic exercise improved insulin sensitivity and other physiological changes (Motahari-Tabari & et al.,
2014). Overweight individuals are seen to have higher insulin resistance due to the lack of insulin
stimulating blood glucose to stabilize. They become less receptive to insulin release leading to an elevated
higher blood glucose and converting excess carbohydrates into fat.
Another research study by Gregory, J.M., Muldowney, J.A., Engelhardt, B.G.
et al
observed 11
obese participants with TD2 who performed aerobic exercise. The 11 participants performed treadmill
walking 4-5 days per week for ~15 weeks (Gregory, J.M., 2019).
Each session is followed by 2 x 25 min
bouts at 75% VO2 max and a brief warm-up and cool-down period. They found improvements in muscle
insulin resistance, the ability of insulin to suppress endogenous glucose production, which is the formation
of glucose from the body to contribute to blood sugar levels (Gregory, J.M., 2019). It is crucial to understand
the study design and methods in both studies. Walking is a common exercise type to use for improving
aerobic capacity and was examined in both studies. The method in Gregory, J.M., & et al., had a smaller
sample size that could pose a limitation because of a limited generalizability which makes it hard to apply
the results to different contexts or groups.
Researchers did explain various factors including intensity, frequency, and pre-test - glucose
levels. The frequency and duration are a factor between both studies which can impact results. Motahari-
Tabari & et, al had an 8-week long exercise intervention compared to Gregory, J.M., Muldowney, J.A.,
Engelhardt, B.G.
et al
who were almost double the length at 15 weeks. The changes in an obese individual
are dependent on how their body reacts to the frequency of exercise. It can tell us if there is any
progression or adaptation over time. This furthers our hypothesis, that others may see results on insulin
resistance with aerobic exercise earlier than others and it is best to find researchers to help lead them to the
best course of action.
Resistance Training and Insulin Sensitivity
We can also look at resistance exercises to understand insulin resistance. This type of exercise
involves using weight and/or resistance to stress large muscle groups. The reason we observe resistance
training for insulin resistance is for many reasons. When a muscle contracts due to resistance or weight, it
stimulates an increase in blood glucose to help provide energy to the exercising muscles. After exercise, we
start to use the glucose for energy and allow our blood sugar levels to stabilize due to the continued release
of glucose from the liver (JF, 2000).
Insulin gets signaled to release glucose out into the blood to the
exercising muscles which can be important for peak performance and overall health improvements. A study
by J F Wojtaszewski & et.al observed muscle glucose uptake and insulin signaling after resistance exercise
in seven healthy males (JF, 2000). Subjects performed a one-legged leg extension while the other leg
remained sedentary. Researchers found that there was an increase in insulin release towards the exercising
muscle in seven healthy males (JF, 2000).
Combined Exercise Approaches
In a study by researcher Lana Bell and her team, they assessed exercise alone on insulin
resistance in obese children independently to changes in body composition. The study consisted of 14
children, 8 of whom were boys and 6 girls (Bell, 2007). The subjects participated in an 8-week structured
supervised exercise intervention with outcomes pre- and post-study. The intervention was a circuit-based
exercise with a mix of aerobic training on the cycle ergometer and resistance training composed of 3x
week/1-hour sessions (Bell, 2007). The results showed after 8 weeks, there were improvements in insulin
sensitivity. In addition, subjects showed a decrease in heart rate response during submaximal exercise
which is the physical intensity that increases at regular stages but doesn’t exceed 85% of heart rate max,
indicating cardiovascular fitness improvements (Bell, 2007).
In the study by Lee. S & et. al examines what type of exercise method is the most optimal in
improving insulin sensitivity and reducing fat in overweight and obese adolescents. Specifically focusing on
the impact of the different exercise methods such as aerobic exercise on its own, and resistance exercise
on its own, compared to a combination of both regarding how they impact the factor of interest. The
methodologies of this study were to gather 118 sedentary adolescents who are overweight or obese and
further randomized into one of the following 6-month intervention groups (Lee, 2019). Each group has the
same training duration of 3 days a week exercise and 180 min/week. The main outcome was to assess the
changes in insulin sensitivity with the various modalities. In addition, the secondary outcomes were to
assess changes in liver fat, and intermuscular adipose tissue with the use of CT scanning (Lee, 2019).
What they found was that a combined exercise approach including both aerobic and resistance training had
similar results to the aerobic exercise training as a standalone in improving insulin sensitivity by increasing
insulin-stimulated glucose disposal, and decreasing liver fat (Lee, 2019). However, they found resistance
exercise alone did increase insulin sensitivity but not at the same amount as aerobic exercise alone and the
combined approach.
Discussion
Overall looking across various studies that the paper has mentioned above, one can confidently
say that various exercise modalities that have been researched result in an improvement in insulin
sensitivity which ultimately can help in reducing insulin resistance. However, to say which modality is the
most optimal it is still hard to say. Comparatively speaking looking at the results from the studies that
focused on aerobic exercise and a combination of resistance and aerobic together seem to produce more
optimal results in improving insulin sensitivity. Furthermore, resistance exercise as a standalone option
does not seem to be the best compared to the other methods in decreasing insulin resistance. However, it
must also be considered that each study had its own practical implications such as dropout rates of the
subjects throughout the studies that could have potentially hindered the accuracy of the results.
Conclusion
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In 2023 the obesity epidemic is a significant problem in the world. With obesity, there can be
several factors such as insulin resistance, diabetes, fatty liver disease, etc. that can decrease human
development and the healthy aging process. This paper effectively elaborates on how various types of
exercise modalities such as a combination of resistance training plus aerobic exercise and even aerobic
exercise on its own can be used to improve insulin sensitivity and improve overall health.
References
Bell, L. M., Watts, K., Siafarikas, A., Thompson, A., Ratnam, N., Bulsara, M., Finn, J., O'Driscoll, G., Green,
D. J., Jones, T. W., & Davis, E. A. (2007). Exercise alone reduces insulin resistance in obese children
independently of changes in body composition. The Journal of Clinical Endocrinology and Metabolism,
92(11), 4230–4235. https://doi.org/10.1210/jc.2007-0779
Wojtaszewski, J. F., Hansen, B. F., Gade, B., Kiens, B., Markuns, J. F., Goodyear, L. J., & Richter, E. A.
(2000). Insulin signaling and insulin sensitivity after exercise in human skeletal muscle. Diabetes, 49(3),
325–331. https://doi.org/10.2337/diabetes.49.3.325
Lee, S., Libman, I., Hughan, K., Kuk, J. L., Jeong, J. H., Zhang, D., & Arslanian, S. (2019). Effects of
exercise modality on insulin resistance and ectopic fat in adolescents with overweight and obesity: A
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https://doi.org/10.1016/j.jpeds.2018.10.059
Motahari-Tabari, N., Ahmad Shirvani, M., Shirzad-E-Ahoodashty, M., Yousefi-Abdolmaleki, E., &
Teimourzadeh, M. (2014). The effect of 8 weeks aerobic exercise on insulin resistance in type 2 diabetes: A
randomized clinical trial. Global Journal of Health Science, 7(1), 115–121.
https://doi.org/10.5539/gjhs.v7n1p115
Gregory, J. M., Muldowney, J. A., Engelhardt, B. G., et al. (2019). Aerobic exercise training improves
hepatic and muscle insulin sensitivity but reduces splanchnic glucose uptake in obese humans with type 2
diabetes. Nutrition & Diabetes, 9, 25. https://doi.org/10.1038/s41387-019-0090-0
Basu, T. (2018). Prediabetes & Insulin Resistance. National Institute of Diabetes and Digestive and Kidney
Diseases. Retrieved from https://www.niddk.nih.gov/health-information/diabetes/overview/what-is-
diabetes/prediabetes-insulin-resistance