Exercise, illness and drug use: guiding principles for approaching a complex triad

Abstract

Regular, low to moderate intensity exercise is considered beneficial to the human body, not only having ergogenic advantages, but also being anti-inflammatory, cardio- and neuroprotective.1 On the other hand, although high intensity training (HIT) is able to exaggerate cardiac conditions, e.g., hypertension2 as well as exacerbate inflammatory and oxidative stress responses,1,3 such exercise programs are becoming more popular as they too have shown demonstrable health benefits if performed appropriately. Indeed, various studies have reported on the superior beneficial cardiac and vascular effects of high intensity exercise programs over that of moderate intensity continuous training (MICT),4-7 contributing to the growing popularity of such time-efficient programs. As such, exercise can accurately be described as a double-edged sword - able to induce positive, beneficial physiological effects when performed chronically at lower intensities, but generating harmful effects when performed at high intensities without sufficient recovery periods. From a toxicological point of view, exercise mediates hormesis, i.e., the biphasic dose response to an environmental agent characterized by a low dose stimulation or beneficial effect and a high dose inhibitory or toxic effect.8 Clinical illness on the other hand, most notably those conditions that are associated with significant peripheral inflammation and interfering with cardiovascular, pulmonary, and skeletal muscle function, generally reduce the maximum exercise capacity of individuals.9 As clinicians and pharmacists are often confronted with questions related to uncertainties of whether patients may or may not exercise while being ill - here we will refer to illness as those acute conditions that transpire in most individuals over time, e.g., common colds and upper respiratory infections -and considering that such individuals are generally being treated for their symptoms, the current review will address broad principles that may provide some direction in this regard. Instead of focusing on certain specific conditions and drugs per se, we will summarise key points for consideration when advising patients with respect to exercising while they present with clinical symptomology and/or are undergoing drug treatment. In terms of exercise, HIT will be applied as a reference to explain potential illness-drug-exercise interactions. For this purpose, HIT will be defined as exercising at a level which will result in a heart rate ranging between 70-100% of an individual's maximum theoretical heart rate for at least 30 minutes,10 where the maximum theoretical heart rate is roughly calculated by subtracting age from 220. Further, although a number of organ systems are involved in and influenced by HIT, e.g., the central nervous system, the gastro-intestinal system and the endocrine system as broadly referred to, the current review will be written against the backdrop of the major organ systems that are directly functionally involved in training, i.e. the cardiovascular, pulmonary and skeletal-muscular systems