The role of skeletal muscle contractile duration throughout the whole day: reducing sedentary time and promoting universal physical activity in all people

• Published in: The Journal of physiology Vol. 596; no. 8; pp. 1331 - 1340
• Main Author: Hamilton, Marc T.
• Format: Journal Article
• Language: English
• Published: England Wiley Subscription Services, Inc 15.04.2018; John Wiley and Sons Inc
• Subjects: Activity patterns; Cardiovascular system; Energy Metabolism; Exercise; Feasibility studies; Humans; Life span; Metabolic rate; metabolic regulation; Metabolism; muscle activity; Muscle Contraction; Muscle, Skeletal - metabolism; Muscle, Skeletal - physiology; Musculoskeletal system; Physical activity; Physical fitness; Physical training; Sedentary Behavior; Skeletal muscle; Symposium Review; Symposium reviews: Physiological approaches to study the science of human sedentariness; skeletal muscle; muscle activity; metabolic regulation
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/JP273284

A shared goal of many researchers has been to discover how to improve health and prevent disease, through safely replacing a large amount of daily sedentary time with physical activity in everyone, regardless of age and current health status. This involves contrasting how different muscle contractile activity patterns regulate the underlying molecular and physiological responses impacting health‐related processes. It also requires an equal attention to behavioural feasibility studies in extremely unfit and sedentary people. A sound scientific principle is that the body is constantly sensing and responding to changes in skeletal muscle metabolism induced by contractile activity. Because of that, the rapid time course of health‐related responses to physical inactivity/activity patterns are caused in large part directly because of the variable amounts of muscle inactivity/activity throughout the day. However, traditional modes and doses of exercise fall far short of replacing most of the sedentary time in the modern lifestyle, because both the weekly frequency and the weekly duration of exercise time are an order of magnitude less than those for people sitting inactive. This can explain why high amounts of sedentary time produce distinct metabolic and cardiovascular responses through inactivity physiology that are not sufficiently prevented by low doses of exercise. For these reasons, we hypothesize that maintaining a high metabolic rate over the majority of the day, through safe and sustainable types of muscular activity, will be the optimal way to create a healthy active lifestyle over the whole lifespan.  The cause and effect influences impacting what is defined as a health active lifestyle. Beginning at the top left, a sedentary lifestyle (with nearly ubiquitous sitting opportunities) results in infrequent skeletal muscle contractile activity. An ensuing deleterious chain of events creates disease, poor ageing, and ultimately compounding influences to create more sedentary behaviour. In contrast to the sedentary lifestyle, the right side of the diagram shows the chain of events linked to high levels of activity.