Research Blog

Does Marijuana Affect Athletic Performance?


Chronic marijuana use is shown by one study to have no effect on aerobic or anaerobic performance. 

Marijuana use has been increasing in popularity over the last several years, especially with the legalization of recreational marijuana in large states such as Colorado and California. A study was recently conducted in Colorado to evaluate the effects of chronic marijuana use on anaerobic and aerobic fitness (Performance and Health Related Characteristics of Physically Active Males using Marijuana, 2018. Lisano JK, et al.).

Marijuana use is especially prevalent in young adults, the age when athletes are in their prime. In fact, 20% of young adults report using marijuana in the last month. In 1999, marijuana was added to the banned substances list by the World Anti-Doping Agency. More recently, marijuana was banned by the NCAA for college athletes in the US. Nonetheless, a one study found that 37% of NCAA Division I athletes reported using marijuana, with the prevalence higher in male athletes compared to female athletes. However, does marijuana really help improve athletic performance?

Marijuana is known to have a number of effects on the body. Marijuana use has been shown to be linked with higher rates of depression and anxiety, but also has successfully treated asthma, migraines, glaucoma and seizures. Marijuana has been used to treat nausea associated with chemotherapy, but its withdrawal can cause whats known as cyclic vomiting syndrome. Medical evidence supports the use of THC, the active ingredient in marijuana, in treating nausea and emesis, muscle spasms in adults with multiple sclerosis and chronic pain. Marijuana is also thought to have prenatal effects when used by pregnant women, although studies out of Jamaica where it used to control morning sickness dispute this. In terms of physiology, marijuana use causes an increase in the resting heart rate and acute use increases airway conductance. Marijuana is known to decrease oxidative capacity of mitochondria in skeletal muscle (and theoretically therefore aerobic performance). Chronic marijuana use decreases testosterone in males and raises cortisol (produced in response to stress).

In regards to performance, the aforementioned study conducted by researchers in Colorado evaluated 24 males, half chronic marijuana users (at least weekly use) and half having abstained from marijuana for the last year. The study found no difference between the groups pulmonary function (assessed with FEV1), cardiovascular function (assessed with VO2 max), muscle endurance (assessed with planks and grip strength) or anaerobic performance (assessed with peak power output). However, there was a trend towards decreased power output in the marijuana users, which may be significant in a larger cohort. The study did find that chronic marijuana users had higher blood levels of CRP (C-reactive protein), a marker of inflammation.

So what does this mean? Despite some athletes having the impression that marijuana can increase athletic performance, this is unlikely. If anything, these results suggest that marijuana may decrease power output, and would therefore not be recommended for athletes in sports were power output is important such as weightlifting. Caution should be utilized in interpreting the results of this relatively small study, further research will be necessary to get a more definitive picture of marijuana’s affect on athletic performance.

Exercise Can Alleviate the Side Effects of Chemotherapy

woman on chemotherapy running on the beach

Chemotherapy produces some nasty side effects, but new research suggests that exercise can alleviate one of the most painful side effects, peripheral neuropathy, in cancer patients.

Unfortunately, cancer treatment produces some very unpleasant side effects for the patients that receive them. The side effects can be so severe that patients are forced to pause or withdraw from potentially lifesaving therapy. One of the most painful side effects of chemotherapy is neuropathy, which produces sharp tingling sensations, numbness and hot or cold feelings. The pain usually manifests in the fingers or toes before progressing up the extremities. The pain, like diabetic neuropathy, likely originates from damage or inflammation to the peripheral nerves although the mechanism is not completely understood. Unfortunately, relieving chemotherapy-induced peripheral neuropathy relies on symptomatic treatment, often requiring opiates that carry their own set of short-term and long-term consequences. 

A clinical trial examining the ability of exercise to alleviate peripheral neuropathy symptoms in cancer patients receiving chemotherapy has yielded promising results (Effects of exercise during chemotherapy on chemotherapy-induced peripheral neuropathy: a multicenter, randomized controlled trial, 2018. Ian Kleckner, et al.). The trial was a large, randomized control trial accruing patients at 20 community cancer centers who were receiving neurotoxic chemotherapy such as taxanes, platinum-based chemotherapy or vinca alkaloid-based chemotherapy. The exercise intervention consisted of 6 weeks of unsupervised walking exercise and 6 weeks of unsupervised exercise with resistance bands. Following exercise just 36.5% of patients reported neuropathic symptoms compared to 49.2% of patients that did not exercise. The patients who exercised reported significantly reduced severity of neuropathic pain as well as less hot and cold symptoms. There was a trend toward reduced numbness and tingling in the exercise group (see figure below). 

Exercise reduces the severity of chemotherapy-induced peripheral neuropathy symptoms per patient-reported numbness and tingling (left; trend-level effect) and hot/coldness in hands/feet (right). Error bars show 95% confidence intervals from 170 exercise patients and 185 control patients. The p-values correspond to differences in exercise and control conditions from linear regression.

The results of this study suggest that walking and resistance exercise can be used to alleviate neuropathic symptoms in cancer patients receiving neurotoxic chemotherapy. The exercise regimens were relatively easy to perform and this allowed the patients to perform the exercises at home. Further studies will need to be conducted to determine the optimal exercise regimens for cancer patients with neuropathic pain. 

Exercise Reduces the Addiction to Smoking

running while smoking

Research finds that a short, intense bout of exercise reduces the urge to smoke, cravings to smoke and withdrawal symptoms.

Can exercise help you quit smoking? According to one recent study the answer is yes. The study (Effect of brief exercise on urges to smoke in men and women smokers, 2018. Alicia Allen, et al.) was published in the journal of Addictive Behaviors. The researchers recruited 38 men and women who were heavy smokers, smoking at least 5 cigarettes per day, for the study. The participants cycled at their maximum VO2 capacity for 6-12 minutes. A questionnaire was completed before and 15 minutes after the cycling exercise to assess smoking addiction. There was a reduction in smoking addiction symptoms after the brief cycling exercise in all categories assessed on the questionnaire: withdrawal, cravings, total smoking urges, intention to smoke and anticipated relief from negative affect. There were no gender differences among groups. 

A mechanism for how smoking reduces smoking addiction has not been elucidated. However, it easy to postulate such a mechanism. Exercise produces a dopamine surge in the brain, producing what is popularly referred to as “runner’s high”. The biology of addiction similarly relies on dopamine surges. Dopamine surges in the brain in response to cigarettes, or other addictive substances such as alcohol or drugs. The addiction strengthens as the brain generates less of a dopamine surge in response to addictive substance. In other words, addiction is simply a yearning for that dopamine surge in the brain produced by the addictive substance. Exercise’s ability to produce that dopamine surge in the brain probably explains the results in the aforementioned study.

Although exercise can reduce addiction symptoms 15 minutes after the exercise session, this may not necessarily translate to hours after the exercise. As exercising every 15 minutes would be impractical, further trials need to be conducted to determine if the effects on smoking addiction have long-term implications. 

Sitting Raises Your Blood Sugar

Standing desk

A recent study finds that individuals who sat for a prolonged period of time had trouble controlling their blood sugar, interestingly intermittent standing brought blood sugar under control.

Advocates for standing desks continue to be backed by further evidence demonstrating the harmful effects of prolonged sitting. The latest research on the subject found that not only was standing beneficial, but it actually was superior to a moderate exercise bout in controlling blood sugar levels after a meal.

The study was published last November in the journal Medicine & Science in Sports & Exercise. The study (Intermittent Standing but not a Moderate Exercise Bout Reduces Postprandial Glycemia, 2017. Benatti FB, et al.) randomized 14 physically inactive healthy adult males to four different physical activity groups: prolonged sitting for 9 hours, 9 hours of alternating between sitting and standing every 15 minutes, prolonged sitting for 8.5 hours with a 30-minute moderate-intensity treadmill run, and a combination group consisting of a 30-minute moderate-intensity treadmill run and sitting with 15 minute standing breaks every half hour for 8 hours. Participants were excluded if they had a known diagnosis of diabetes. The researchers found that glucose levels following breakfast (postprandial) on the day of the intervention were lower in all groups with standing and/or moderate physical activity compared to the group with 9 hours of continuos sitting. Interestingly, when the researchers looked at glucose control after breakfast on the day after the sitting or exercise intervention they found that the group that had intermittent standing, but not the group that had a moderate bout of physical activity, had superior glucose control. This finding may suggest that intermittent standing may have a longer protective effect rather than a single bout of moderate physical activity on glycemic control. 

The mechanism by which standing mediates improvements in glycemic control are thought to originate from the contracting muscle in the legs during standing taking up glucose and fatty acids. This increases the sensitivity of body tissues to insulin, which is the hormone that mediates uptake of glucose from the blood. This study did not find any effect of standing on fat and lipid control in the blood following eating. Further work may be necessary to determine the effect of standing on other health indicators such as hypertension.

Indeed, many individuals follow a schedule of a single daily episode of physical activity followed by prolonged sitting at home and/or work for the remainder of the day. In terms of glucose control, which is a marker of diabetes mellitus, it appears that a trip to the gym in the morning is not enough to cancel out a day of sitting. Intermittent standing appears to be a solution. 

How can one incorporate intermittent standing into their daily lives? In many ways, its easier than a trip to the gym in the morning. A standing desk is probably the most obvious solution, but there are other simple lifestyle changes one can make. For example, while watching TV consider using commercial breaks as an excuse to stand up from the couch. Or, while at the office, set a timer on your phone or watch to remind you to stand up every half hour. Such reminders come standard on many smartwatches now.

With that being said, its time to stand up!

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