Stress is your reaction to a challenge or stressor; and it can be helpful when you’re trying to avoid danger or meet a deadline; but also harmful if stressors are chronic or intense. Individuals can experience both good stressors such as a new job and bad stressors such as loss of a loved one; however, most stressors in our life are more routine challenges such as deadlines and arguments, or even physical stressors such as poor sleep or exercise. Stress is a major risk factor for mental health disorders because it influences how your brain perceives challenges as threats and manages emotions; but exercise can help our brains respond to stressors in an adaptive way.
Our body’s main stress mechanism is the hypothalmic pituitary adrenal axis (HPA axis), which releases the stress hormone cortisol to help us interpret and respond to a stressor; so cortisol is helpful
and necessary. The HPA axis has a negative feedback loop whereby the release of cortisol from the adrenals will feedback on the hypothalamus and shut down the HPA axis response, thus facilitating recovery. With intense or chronic stress, the negative feedback loop can become insensitive and fail to shut off the cortisol response. This hypercortisol reaction can cause reduced neuronal communication and even neuron death in the brain. These neural changes particularly impact the centers of the brain associated with threat surveillance and learning.
Evolutionarily speaking, the human brain is “wired” to constantly monitor for threats and respond with an adaptive or learned response through communication among the prefrontal cortex, amygdala, and the hippocampus. The prefrontal cortex is responsible for coordinating emotional responses such as happiness and sadness, and behavioral responses such as activation or avoidance, by interpreting information from the amygdala, the threat center of the brain, and the hippocampus, the learning area of the brain.
Stressors promote a type of re-wiring, termed neuroplasticity, which involves a change in the number and structures of neurons, and the chemical neurotransmitters that provide communication between neurons. In this way, stress is important for learning. Challenging activities can promote a burst of brain changes associated with plasticity; for example, solving a math problem or learning a new sports skill. When we successfully overcome stressors or manage challenges, plasticity can lead to enhanced brain functioning, sense of coping and emotion regulation. Sometimes, though, when challenges are intense, persistent or we perceive that we cannot overcome them, these brain changes are associated with the emotion and behavioral consequences of mental health disorders.
So where does exercise fit into this stress regulatory system? Exercise is a physical stressor for the body and the brain. During exercise, there is a spike in cortisol and other stimulatory hormones such as adrenaline, which among other effects increases heart rate and blood pressure for delivering oxygen to working muscles and the brain. With regular exercise, the HPA axis may become more sensitive so that lower levels of cortisol are needed to respond to the challenge of the exercise, and the HPA axis feedback loop is more efficient, thus recovering the HPA axis more quickly after exercise. This adaptive HPA axis response with exercise may then transfer to other stressors. Additionally, the higher oxygen demand in the brain during exercise leads to an increase in growth factors (Vascular Endothelial and Brain Derived Neurotrophic Growth Factor) that promote blood flow and neuroplasticity. The increase in growth factors from exercise is associated with increased stress resilience and decreased mental health disorders via enhanced neuronal communication. Finally, exercise is associated with optimizing levels of key emotion and behavior regulation neurotransmitters such as serotonin, dopamine, and GABA. On the psychological side, exercise is associated with higher levels of self efficacy, defined as one’s belief in their ability to succeed in a particular situation. One important precursor for high self-efficacy is termed “mastery experiences”, which includes overcoming challenges. When individuals are successful at completing a difficult workout, achieving an exercise goal, or mastering a sports skill, their brain “learns” to be less threatened and more confident that the individual has the capacity to cope with other challenges. Similar to the adaptive HPA axis response, increases in self efficacy from exercise may translate to better coping in other areas of one’s life.
In terms of best exercises for stress, all exercise is helpful, but aerobic exercise or “cardio” is most effective in leading to long term structural and chemical changes in the brain; and mindfulness exercise, such as Yoga and Tai Chi, is best for promoting calming effects in the HPA axis and neurotransmitters. Furthermore, choosing exercise activities that are enjoyable and of appropriate intensity will promote positive stress adaptations. Experienced exercisers and athletes benefit from higher intensities such as high intensity interval training (HIIT), while beginner exercisers and lower fit individuals experience better stress adaptations at low and moderate intensities such as walking and cardio machines.
If you’re interested in learning more about your brain on exercise, register for PE 207/PSY 214!