Isometric thermogenesis at rest and during movement: a neglected variable in energy expenditure and obesity predisposition

Abstract

SummaryIsometric thermogenesis as applied to human energy expenditure refers to heat production resulting from increased muscle tension. While most physical activities consist of both dynamic and static (isometric) muscle actions, the isometric component is very often essential for the optimal performance of dynamic work given its role in coordinating posture during standing, walking and most physical activities of everyday life. Over the past 75 years, there has been sporadic interest into the relevance of isometric work to thermoregulatory thermogenesis and to adaptive thermogenesis pertaining to body-weight regulation. This has been in relation to (i) a role for skeletal muscle minor tremor or microvibration -nowadays referred to as 'resting muscle mechanical activity' -in maintaining body temperature in response to mild cooling; (ii) a role for slowed skeletal muscle isometric contraction-relaxation cycle as a mechanism for energy conservation in response to caloric restriction and weight loss and (iii) a role for spontaneous physical activity (which is contributed importantly by isometric work for posture maintenance and fidgeting behaviours) in adaptive thermogenesis pertaining to weight regulation. This paper reviews the evidence underlying these proposed roles for isometric work in adaptive thermogenesis and highlights the contention that variability in this neglected component of energy expenditure could contribute to human predisposition to obesity.

Issues in Continuous 24-h Core Body Temperature Monitoring in Humans Using an Ingestible Capsule Telemetric Sensor

“…The feasibility of using Tc capsules has been shown, particularly for detecting rapid changes in Tc associated with low-intensity dynamic exercise, but not in response to food or low-intensity isometric exercise; while noting that during daily life, dynamic and isometric activities are intertwined pertaining to their impact on EE (35). However, a number of unexpected findings were unearthed which should be considered in future studies: the influence of expulsion time on the duration of measurement and rapid temperature oscillations, particularly among obese subjects, which require appropriate data treatment to avoid misinterpretation of temperature changes.…”

Spontaneous Physical Activity Defends Against Obesity

“…by indirect calorimetry) together with some measurement of activity, which allows linking energy expenditure to specific behavioral states [43]. Yet this method of estimating NEAT is further complicated by the influence of isometric skeletal muscle contraction to energy expenditure [47] which cannot be estimated using the type of analysis outlined. Here, we discuss animal studies that support the concept that SPA and NEAT can protect against obesity, yet we make the distinction where SPA and NEAT have been measured and the components of SPA analyzed in the study.…”

Posture Allocation Revisited: Breaking the Sedentary Threshold of Energy Expenditure for Obesity Management

“…As the skeletal muscles involved in this stabilization and increased tonus are comprised of predominately oxidative fibers, increasing postural muscle activation could present not only an opportunity to increase EE, but also to increase the relative rate of fat oxidation. However, despite daily life activities consisting of a large amount of low-level isometric contraction, compared to dynamic exercise, its energy cost has been much less studied and quantified (Dulloo et al, 2017). …”

“…Furthermore, there is a need to explore human variability in this cost, which may have important implications for the efficacy of the use of low-level physical activity for body weight management. With the majority of daily-life activities consisting of both isometric and dynamic activity (Dulloo et al, 2017), we have recently developed and validated two such standardized methodologies; one involving an isometric leg press protocol of low-intensity (Sarafian et al, 2013), and the other a low-intensity cycle ergometer protocol (Fares et al, 2017). These standardized approaches are applicable to a vast range of population groups (i.e., healthy, elderly, or diseased populations) and pave the way for a more comprehensive examination of inter-individual variability in both our susceptibility to obesity and the efficacy of body weight maintenance strategies.…”