Sweating away depression? : the impact of intensive exercise on depression

Master Thesis


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University of Cape Town

In periods of prolonged stress and pain from strenuous exercise, the body produces chemicals called endorphins that help it endure pain. These natural analgesics are presumably only released when the level of pain intensity is at least moderately high. The PANIC/separation distress system is built on the same pathways as the physical pain system, and is responsible for the ‘mental pain’ (feelings of panic anxiety, loss and sorrow) that is associated with the loss of an attachment object, or separation from it. Given this overlap, it is reasonable to expect that endorphin release can affect depressive symptoms in a positive way. There is existing evidence that exercise has a beneficial effect on depressive symptoms, yet the underlying physiological mechanism has yet to be properly determined. The purpose of this three-armed prospective randomized control pilot study was therefore to try to establish this mechanism by investigating whether intensive exercise can improve the symptoms of moderate depression as a result of demonstrable increases in plasma &#946;-endorphins. It has previously been established that exercise-induced &#946;-endorphin release correlates positively with the intensity of the exercise. There were two central hypotheses for this study. The first was that the mechanism behind the improvements seen in depressive symptoms due to exercise is the same mechanism that is responsible for the established analgesic effect of exercise, namely endorphin release. The second hypothesis was that only high-intensity exercise (i.e. great that 70 of heart rate reserve) will be sufficient to produce a guaranteed endorphin release, whereas moderate-intensity exercise (just under 50% of the heart rate reserve) and very low intensive exercise would not be sufficient to release endorphins, and would therefore not result in an improvement in depressive symptoms. The main aim was therefore to investigate whether intensive exercise (greater than 70% of heart rate reserve) improves moderate depression, and if so, whether this correlates with a demonstrable increase in &#946;-endorphins. This study therefore wished to determine which of low, moderate or high intensity exercise alleviates the symptoms of depression. It also intended to determine whether an increase in &#946;-endorphins correlates to an improvement in the participants’ depression levels, and whether greater &#946;- endorphin release occurs during high-intensity exercise compared to low- and moderate intensity exercise. Male participants (n = 33) with moderate levels of depression were randomly assigned to one of three experimental groups of varying exercise intensities: High-intensity (160 beats per min (bpm)), Moderate intensity ( 140bpm), and a low-intensity control group (under 120bpm). All participants underwent a six-week exercise program that involved participation for three days per week, for one hour per day (i.e.18 sessions in total). Once weekly, the Hamilton Rating Scale for Depression (HAM-D) and the Montgomery Åsberg Depression Rating Scale (MADRS) were administered to each participant. The participants in the High-and Moderate-intensity exercise groups each had 5ml of blood drawn, once per week, before and after exercise, in order to measure their &#946;-endorphin levels, and to track any changes in these levels over time. The participants in the Control group had blood samples taken twice – once at the start of the study (a baseline measure), before and after exercise, and once on completion of the study, before and after exercise. The results indicate that both Moderate- and High-intensity exercise improved the participants’ depression levels, while the Control group also showed some improvement, but not to the same extent as the other two groups. A significant difference (p = < 0.0001) was found when comparing the initial and final HAM-D scores between all three groups. The participants’ MADRS scores also improved between all three exercising groups. A significant difference (p = 0.0182) was found when comparing the initial scores within each of the three groups to their final MADRS scores. No significant difference was found in the serum &#946;- endorphin levels when comparing the Moderate- with the High-intensity group. The differences between the baseline and post-exercise serum &#946;-endorphin measurements were also not significantly different for both the Moderate- and High-intensity groups (p= 0.953 and p= 0.992 respectively), while the Control’s pre- to post levels decreased significantly (p < 0.017). A significant difference between the Control-, Moderate-, and High-intensity groups (p = <0.022) was found when comparing the three groups’ serum &#946;-endorphin concentrations after they engaged in exercise. Overall, the results of this pilot study go against the hypothesis that only High-intensity exercise would improve symptoms of moderate depression, as both high- and moderate-intensity exercise had a clear positive impact on depression scores. However, consistent with this hypothesis, very-low intensity exercise did not seem to have as beneficial an effect. The mechanism underlying the benefit of exercise on the symptoms of depression cannot be conclusively confirmed given the overall &#946;-endorphin results. A larger sample size and more accurate analysis methods of &#946;-endorphin levels are required in order to test these tentative findings more rigorously.

Includes bibliographical references.