The influence of marijuana on physiologic processes and exercise

Introduction[edit | edit source]

Cannabis use is widespread, totaling more than 400 possible compounds with the most prevalent compound being Tetrahydrocannabinol (THC). THC has a psychotropic effect on the central nervous system by acting on CB1 and an analgesic by working on CB2 receptors. CB1/CB2 receptors are activated by the attachment of the ligand, Anandamide [1]. Marijuana has been shown to elevate resting heart rate and systolic/diastolic pressure after consumption [2]. Marijuana has also been seen to produce bronchodilation in patients with bronchoconstriction secondary to asthma [3]. Many athletes consume marijuana for their euphoric effects by reducing stress and anxiety. Reducing stress before competition allows for adequate sleep, which allows for optimal performance [1] .

Tetrahydrocannabinol is the primary constituent of marijuana that binds to G-Protein-Coupled CB1 receptors which are found throughout the brain in the frontal and medial temporal lobe[4]. Marijuana is one of the most frequently used drugs among young adults. Marijuana induces tachycardia which can decrease the maximal work capacity after smoking this drug[5]. Marijuana creates an increase in carboxyhemoglobin concentration of blood due to large amount of carbon monoxide created from the smoking of this drug[5]. Some other factors that could affect the maximal work capacity after smoking marijuana are bronchodilation, a decrease in the perception of dyspnoea and an increase in blood flow to exercising muscles[5]. Despite the increase in maximal work capacity, the utilization of marijuana with exercise has a negative correlation that greatly affects overall health. 

Cardiovascular Effects[edit | edit source]

Marijuana use has both acute and prolonged effects on the cardiovascular system, drastically altering the normal functioning of the entire system. The initial intake of THC increases heart rate, causes hypertension during sitting, and hypotension whilst standing[6]. A person may develop a tolerance to these symptoms quickly[7]. Determining how long the patient has been using marijuana and the frequency that he or she uses it can help determine if heart rate and blood pressure is within normal limits. In addition, there are potential risks of orthostatic hypotension and dizziness that can come with frequent marijuana use[6]. A person's blood volume goes up and the circulatory system response decreases. Concerns over the decrease in blood pressure and quick loss of mental orientation should be brought to the attention of the physical therapist during evaluation and treatment of patients using recreational marijuana. The influence of marijuana would affect how a patient responds to standard examinations and exercise during treatment. Patients who have cardiovascular disease are much more likely to have health problems because their heart has to work harder, their catecholamine levels go up, and postural hypotension happens.[8] Prolonged effects of frequent marijuana use could have more adverse effects as tolerance level is increased including alterations to the plasma volume[6].

To provide evidence to this data, Lindsay, Foale, Warren, & Henry (2005) studied two different cases. This first case involved a 48-year-old man who had a terrible history of heart problems: coronary artery bypass 10 years prior, recurrent angina for 18 months, unstable grafts, and a sub-total occlusion of a previous stent to the left main stem. The patient for Case 1 was admitted for urgent coronary angiography. Approximately 24 hours after admission, the patient suffered cardiac arrest while smoking, what was thought to be, a cigarette. Once the medical staff got to his side to resuscitate him, they noticed that the room smelled like cannabis and the ‘tobacco cigarette’ was actually a ‘cannabis cigarette.’ The Case 1 patient survived the cardiac arrest and stayed in the intensive care unit for ten days. The patient also admitted to being a chronic cannabis user for many years[9].

Another case reported by Lindsay, Foale, Warren, & Henry (2005) involved a 22-year-old man who was admitted to the hospital with two episodes of chest pain and shortness of breath. On both occasions, he admitted having smoking cannabis at the beginning of each attack. The patient for Case 2 had no family history or personal history of coronary artery disease or cardiovascular disease. The Case 2 patient admitted to smoking cannabis regularly since his mid-teens and had increased his frequency and potency of his cannabis habit within the two weeks prior to the hospital admission[9].

Both cases provide evidence that prolonged cannabis use is highly detrimental to the cardiovascular system, whether the patient has a history of cardiovascular problems or not. The evidence also defies the myth that heart problems only happen to older individuals.

Marijuana has been shown to increase heart rate and blood pressure while decreasing overall cardiac output[10]. This is important for clinicians to consider when treating patients who use marijuana, as it is an ergolytic drug. When used in combination with exercise it will negatively affect the patient’s exercise performance and overall health.

Neuromuscular Effects[edit | edit source]

Marijuana could positively affect the ability of people with underlying neurological conditions to exercise. Reduction of symptoms could allow these people to exercise more effectively and frequently. A systematic review of patients with neurological disorders including multiple sclerosis, movement disorders, and epilepsy showed that some of the debilitating effects of these diseases were reduced after the intake of cannabis extracts[11]. Most notably, it was found that oral cannabis extract was effective in reducing patient-reported scores of spasticity, allowing them to move freely and have better control of movements. It was also found to be effective in reduction of central pain in patients with multiple sclerosis[11].  Another condition that symptoms could be reduced enough by cannabinoids to promote ease of movement for exercise is rheumatoid arthritis. Rheumatoid arthritis causes inflammation in a joint along with cartilage damage. The long-term effects of inflammation can cause changes in sympathetic activity that continue to cause inflammation. Activation of cannabinoid receptor type 1 (CB1) by cannabinoids can lower sympathetic activity in the brain and can affect the amount of neurotransmitters released, providing anti-inflammatory effects in other regions of the body [12]. Marijuana use has a direct effect on the central nervous system because it contains the receptor sites for THC[10]. Although marijuana does possess some ergogenic effects in certain situations, it impacts the body oppositely during exercise. The drug has a sedative effect during exercise, resulting in decreased exercise and psychomotor performance like slower reaction time[10].

Pulmonary Effects[edit | edit source]

Marijuana also has its effects on the pulmonary system. Specifically, research has shown a high association between marijuana use and certain respiratory issues, such as coughing and wheezing[13]. In addition, the drug causes inflammation, bronchodilation, and diffusion impairment[13]. These conditions would have a negative impact on a person's ability to adhere to a rigorous exercise routine. Diffusion impairment would especially affect the amount of oxygen successfully entering the alveoli of the lungs, decreasing the amount of oxygen available for use during strenuous activity. Therefore, physical therapists would take extra precautions and plan exercise treatment accordingly as to prevent overexertion and fatigue.

A 2002 longitudinal study measured the relationship between long-term marijuana use and lung function. Lung function was measured using spirometry and the ratio of forced expiratory volume in one second/vital capacity (FEV1/VC). The study was conducted over an eight-year period and measured over 900 young adults. The results showed a dose-dependent relationship between marijuana use and decreased lung function [14] 

References[edit | edit source]

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  9. 9.0 9.1 Lindsay, A., Foale, R., Warren, O., & Henry, J. Cannabis as a precipitant of cardiovascular emergencies. International Journal of Cardiology 2005; 104(2), 230-232. doi:10.1016/j.ijcard.2004.10.038
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