|What is your brain doing during exercise?|
|[Untitled cartoon of an exercising brain]. Retrieved March 26,2013 from:
The brain and its ability to perceive and react to stimuli is very important in the world of sport and exercise. Even more amazing and being highly researched is the brain's acute ability to adapt to stressful situations, in the form of sports and exercise, and alter perception. These exercise-induced modulations involve a wide range of neuronal networks such as the limbic, opioidergic, and somatosensory systems in order to change mood, pain, and exertion perception. The mechanisms behind elevated mood, decreased pain perception, and changes in perceived exertionare being deciphered and its details are hotly pursued. Perhaps more relatable to the general public is the effect of one of the most accessible and commonly used drugs on these exercise-induced mechanisms, caffeine. During exercise and sport, it is the careful balance of these perceptions and manipulations of these perceptions that can differentiate between a successful athlete and non-professional exercisers.
Table of Contents
1.1 Mood Modulations during Exercise
1.1a Euphoria from Runner's High
Over the last few decades the details and mechanism of the Runner's High phenomenon experienced by long distance runners has eluded the understanding of scientists and lay people alike. Even controversies of the existence of the experience arose due to its inconsistency to occur, variability of occurrence among runners, and its subjectivity. Only recently have there been reviews and studies that attempted to scientifically define and deduce its mechanism. The runner's high has been defined as a change in mental state as a result of exercise mainly "analgesia, sedation (post-exercise calm), anxiolysis, and a sense of well being" (Dietrich & McDaniel, 2004). The sense of well being, or feeling of euphoria, has since been studied and the evidence linking the mood modulation to exercise has been mounting. For example, in a study of endurance runners, levels of euphoria were measured via Visual Analog Mood Scales (VAMS) before and after a 2 hour session of endurance running and were found to be significantly elevated after running [see above 1]. In another paper, the amount of change in affect during exercise was found to correlate with the current activeness of the individual along with other physical and cognitive factors in which more active subjects experienced more of a positive affective change. Perhaps it is this difference between individuals that predisposes a person to be a "superior athlete". Although there is relatively clear data in terms of the functions of endogenous opioids and cannabinoids in the central nervous system, it is more difficult to discern its relationship to exercise and sport if any. The following theories were proposed in order to attempt to provide support for the connection between exercise and perception modulations: the endorphin/opioid theory and the endocannabinoid hypothesis.
The Runner's High: A Quick Overview
Your choice, exercise or marijuana?
1.1b The Opioid/Endorphin Theory
The endorphin/opioid theory was first introduced in 1985 relating the positive affects of exercise to endorphin release seen during exercise. It was met with criticism and eventually rejected mostly due to the indirect measurement of endorphins in the peripheral nervous system as opposed to the central nervous system and the fact that endorphins cannot freely diffuse across the blood brain barrier [see above 4]. However, in a previously mentioned recent study involving endurance runners, positron emission tomography (PET) ligand activation scans were done during the experiment tracking an opioidergic ligand which allowed the monitoring of endorphins in the central nervous system. Results showed that levels of euphoria measured were inversely associated with opioid binding in specific regions of the brain namely frontolimbic regions involved in mood and affect providing the first pieces of evidence that supports the criticized endorphin theory[see above 1].
1.1c The Endocannabinoid Hypothesis
As an alternative to the endorphin theory which was troubled at the time, the endocannabinoid hypothesis was suggested. Endocannabinoids are lipid-based thereby freely diffusing across the blood brain barrier and exerting its modulating effects on emotion and cognition. The endocannabinoid system was shown to activate owing to exercise which led to its candidacy in the runner's high phenomenon. In recent times, evidence of a correlation between positive affect and increased levels of anandamide, a recognized endocannabinoid, due to exercise further fuels the debate between the two theories.
2.1 Pain Perception During Exercise
2.1a Decreased Pain-Related Brain Activity
The measurement of pain is often highly subjective and takes away from the strength of data obtained from pain surveys concerning exercise. However, a novel study involving functional magnetic resonance imaging (fMRI) was able to track brain activations during thermally induced pain during and after low and high intensity exercise. Interestingly enough, pain pathways were shown in all conditions to be activated but less so after the exercise condition particularly in pregenual anterior cingulate cortex which projects to the pariaqueductal gray, a key component in the pain pathway [see above 2] (refer to figure 1). Also argued in this study was that although peripheral endorphins are an indirect measure of central nervous system endorphins, the resulting increase in endorphins across all subjects implied opioidergic pain modulations[see above 2]. Evidence, however, of interaction between the endocannbinoid and opioidergic systems in pain modulation is increasing. Despite the vague mechanism, there is a clear link between exercise and pain modifications.
3.1 Percieved Exertion
3.1a Visual Stimuli Effects
|Figure 2 Ratings of perceived exertion vs normalized power output. Note
that slow optic flow resulted in a lower RPE despite cyclists biking the same
distance. Adapted from Figure 2 of Parry et al., (2012).
One of the biggest, if not most important, challenges an athlete or an active individual must face is overcoming exertion. Astonishingly, the brain is able to alter its ability to perceive exertion depending on the input it receives. This ability was wonderfully demonstrated in a study conducted by Parry, Chinnasamy, and Micklewright (2012) who looked at the effects of visual stimuli. Parry et al. (2012) had fifteen cyclists ride a 20 km virtually simulated course under three conditions following a baseline course-run in which participants were told to go through it as fast as they could and their power output and cadence information were continually provided to the riders. Afterwards, they manipulated the optic flow, the visual input of their world around them as they cycled passed it, into slow, normal, and fast conditions. Participants were also told to attempt to match their baseline power output and cadence to their baseline so as to give them voluntary control. Finally, heart rate and ratings of perceived exertion (RPE) were taken at 4 km intervals throughout trials. There was no difference between the normal and fast conditions in terms of RPE and power output and in heart rate and cadence across all conditions, but the slow condition resulted in a lower RPE but higher power output [see above 3] (refer to figure 2). During exercise, the brain's awareness of the body's resources, its relationship relative to the world, and of motivational goals all influence perceived exertion.
3.1b Parasympathetic Autonomous Nervous System Effects
As a further link of the brain's influence to perceived exertion is research conducted using transcranial direct current stimulation (tDCS). By stimulating brain regions that controlled the autonomous nervous system, specifically the parasympathetic nervous system, RPE was shown to increase at a slower rate than it would have in a sham stimulation throughout exercise (cycling in this case). It was hypothesized that the increase in parasympathetic influence, particularly the vagus nerve and its cardiovascular control, is able to decrease the perception of tiredness[see above 11].
4.1 Caffeine and Exercise
4.1a Caffeine's Effects
Caffeine has many brain enhancing effects and, along with being highly accessible, is widely consumed among athletes before and during sports and activities. In fact, after caffeine's removal from the World Anti-Doping Agency list, 3 out of 4 athletes had consumed caffeine before or during an event. However, there are a multitude of conflicting studies about the effects of caffeine on perception during exercise. Caffeine was thought to elevate mood and decrease RPE possibly as a result of its ergogenic effect. It was also supposed that acute caffeine ingestion reduced muscle pain perception in exercise to failure tasks. However, separate studies looking at men and women found that caffeine improved mood but had no effect on RPE or pain perception in men and improved performance in women but, again, had no effect on pain or RPE. In spite of the inconsistency and uncertainty of caffeine's effects on perception, it remains a valued drug and is continually used routinely in exercise regimes.
|Do you really? Or is that what your brain is perceiving?|
|[Untitled cartoon of running coffee cup]. Retrieved March 27,2013 from: