Written for MedLab.
Physical activity, by definition, is an umbrella term which encompasses any movement of the human body produced by skeletal muscle contraction, leading to an increase in energy expenditure. Physical activity in daily life can be broken down into exercise, occupational, sports, household, or other activities. Exercise, as a subset of physical activity, is a planned, structured, and repetitive activity that has as a final or an intermediate objective. This is the core business of a personal trainer.
In the world of exercise, there has been an explosion of exercise styles in recent years. People have been experimenting with the way they move their bodies through a myriad of different forms of exercise, everything from Crossfit to Zumba. As far as the literature is concerned, there are essentially three forms of exercise that have been studied: aerobic exercise, High-Intensity Interval Training (HIIT) and resistance training.
Aerobic exercise, synonymous with cardio exercise, is a form of physical activity that is performed at a steady rate, typically within 60-80% of your maximum heart rate. This steady state means that the body uses oxygen to meet its energy demands. This form of exercise can be done for extended periods of time and is the most extensively studied form of exercise. High-intensity interval training (HIIT), synonymous with Intervals, uses alternating periods of intense anaerobic exercise with a less intense recovery period. HIIT is also a form of cardio exercise but generally speaking, participants are only able to perform this type of training for shorter periods than aerobic exercise. Resistance training, synonymous with weight training, induces muscle contraction against high loads of resistance which have the net effect of building the size and anaerobic endurance of skeletal muscles. All three forms of exercise have been shown to improve health. Significant benefits are observed in the prevention and treatment of all -cause mortality, cardiovascular-related mortality, diabetes, cancer, and osteoporosis.
But what about mental health? Does exercise improve outcomes for patients with depression? Doubts were cast over the efficacy of exercise as a therapy for depression when a Cochrane review paper in 2013 concluded that, although there was a moderate benefit in symptom reduction for patients with depression engaged in exercise vs. control groups, there was not a statistically significant difference when the analysis only included high-quality studies. This study received widespread attention at the time and was quick to be countered. A subsequent meta-analysis found large antidepressant effects of exercise on depression when compared to non-active controls. Interestingly, the antidepressant effect of exercise was higher for studies that included participants diagnosed with MDD. The authors of this review highlighted that control groups used in clinical trials often recorded substantial and significant antidepressant effects, which makes the detection of effects in exercise groups much more challenging. Further, they explained the difference in their finding vs. the Cochrane review as being due to three factors: (1) the inclusion criteria, (2) the statistical test used to evaluate the ES, and (3) the inclusion of more recent trials.
Despite the effect on symptom reduction, remission rates in clinical trials are similar to pharmacological interventions and display a significant amount of heterogeneity depending on the amount of exercise performed. One potential explanation to the heterogeneity in response rates can be due the heterogeneity of depression itself. This is an important point for the future researcher to navigate. Despite these difficulties, there does appear to be a dose-response relationship on depression which is a trend seen when examining other physical health conditions. It seems, about half of people with depression will experience significant improvements from exercise with greater improves seen with those who exercise for longer.
Exercise plays an important part in an overall management plan for depression. Given the significant benefits for overall health and its low side effect profile, patients should be encouraged to engage in regular exercise. Regarding which type of exercise is best, in clinical samples, only aerobic exercises had significant effects on depression in clinical studies, though it should be stressed that resistance exercise has only been considered in a handful of studies. Moreover, no RCT was identified when investigating the effects of resistance exercise in samples comprised entirely of participants with MDD. Supervised interventions had the most profound effects. Interestingly, where the exercise takes place may have a small impact on outcomes. It seems that exercise programs that were completed outdoors were more effective than those performed indoors. Mum’s advice to go out and get some fresh air might not be so trite after all. Regardless of where it takes place, we can be confident that seeking professional expertise to oversee the exercise program is of paramount importance. Exercise supervised by professionals with relevant training, including personal trainers and exercise physiologists, was associated with the greatest improvements in patients with depression. This result, added to previous findings of lower dropout rates in interventions delivered by exercise professionals in people with depression, highlights the importance of adequately trained professionals providing exercise interventions. Key considerations for the physician referring to an exercise professional include convenience, cost, and style of program. It is also important to involve social supports into the overall exercise plan. Supports that are educated on the benefits of exercise and gain an understanding of what the patient is trying to achieve can improve outcomes for the patient.
The exact dose of exercise for the management of depression still requires further investigation. Moderate and vigorous-intensity exercises were shown to be more effective than light to moderate intensity exercises. However, this finding needs to be interpreted with caution, since it is based on a small number of studies. That being said, the American College of Sports Medicine (ACSM) released a position stand which recommended 150 minutes per week for maintenance of good health. The ACSM recommends that most adults engage in moderate-intensity aerobic exercise training for 30 minutes a day, five days a week. This recommendation is in alignment with the Australian government's physical activity target's for good health. The ACSM also recommends 2-3 days per week of resistance exercises.
Hippocrates, the father of medicine, once said that walking is man’s best medicine. He might be right indeed.