PMC

Partitioning of consumed food energy. Note that energy going to the thermic effect of food is not available for ATP production or biosynthesis, but it can be used for thermoregulation. In addition, a considerable portion of the chemical potential energy in absorbed food molecules is lost as heat during the production of ATP (but again, some of this heat may be used for thermoregulation).

Relationship between estimated energy expenditure during inactivity and during moderate-to-vigorous physical activity (MVPA) in 125 human males and 152 females aged 18–24 years [data from Wickel and Eisenmann ()]. On days when MVPA was relatively high, DEE was also relatively high [see fig. 3 in Wickel and Eisenmann ()], but, as shown here, some compensation occurred in that the energy expended during inactive behaviours was reduced. However, the slope (–0.25) is much shallower than –1 (dashed line), indicating that compensation was incomplete.

Western diet increased voluntary wheel running of mice from High Runner (HR) lines by ∼52% (+36% duration of running, +18% average speed of running) during days 17–30 of wheel access, whereas it had no effect on control lines [standard diet (Std)] [data from Meek et al. ()]. This stimulation of voluntary exercise is remarkable in particular because the lines have been at an apparent selection limit for ∼35 generations (see ). Data are adjusted means + s.e.m.

(A,B) Partitioning of daily energy expenditure (DEE) when the amount of voluntary exercise is extraordinarily high. For humans, this occurs during the Tour de France cycling race () and for mice it represents the High Runner lines housed with wheel access (; ; ; ). For the mice, some of the heat produced during wheel running is used for thermoregulation, thus reducing costs of thermoregulation per se. SPA is still a substantial part of the energy budget for mice (). SPA may also appreciable for these human ultra-racers, but it has not been directly measured to our knowledge. In general, larger-bodied mammals are predicted to expend a larger fraction of their DEE on costs of locomotion, based on previous allometric analyses (; ). For additional literature sources, see legend.

(A,B) Partitioning of daily energy expenditure in a sedentary human and a sedentary laboratory mouse. The human engages in negligible voluntary exercise, and the mouse is housed without a wheel. At room temperature (∼21°C), people wear appropriate clothing and so do not have any extra energy expenditure to maintain body temperature. For mice, however, 21°C is below their thermoneutral zone, so they have a substantial cost of thermoregulation (e.g. see ; ; ). The values depicted are approximations, based on the synthesis of a number of sources (e.g. http://www.fao.org/docrep/007/y5686e/y5686e04.htm) [Garland and others (; ; ; ; ; ; ; Westerterp, 2004; ; ; ; Johanssen and Ravussin, 2008; ; ) and references therein]. BMR, basal metabolic rate; NEAT, non-exercise activity thermogenesis; SPA, spontaneous physical activity; TEF, thermic effect of food.

SPA (and resulting NEAT) regulatory brain areas and associated neuropeptides/transmitters [updated from fig. 1 in Kotz ()]. Colors correspond to specific neuropeptides/hormones as follows: blue, orexin; purple, CCK; pink, NMU; orange, Agrp; brown, POMC; green, ghrelin; yellow, leptin. Areas with these colors indicate site of synthesis (e.g. AgRP, POMC and ARC; orexin, LH), peripheral source (NMU, ghrelin, leptin and CCK), areas in which the neuropeptide/hormone has been injected and effects on SPA reported, or proposed site(s) of action (see text). Signals from all of these areas have the potential to influence cortical premotor neurons. Brain areas are not to scale, and connections and neuropeptides/transmitters indicated are not all-inclusive. Outline of rat brain was modified from Paxinos and Watson (). For an alternative depiction, see fig. 2 in Castaneda et al. (). 5HT, serotonin; Agrp, Agouti-related protein; ARC, hypothalamic arcuate nucleus; CCK, cholecystokinin; CRH, corticotrophin releasing hormone; DA, dopamine; LC, locus coeruleus; LH, lateral hypothalamus; MCH, melanin concentrating hormone; NAccSH, shell of nucleus accumbens; NE, norepinephrine; NMU, neuromedin U; NPY, neuropeptide Y; POMC, proopiomelanocortin; PVN, hypothalamic paraventricular nucleus; VTA, ventral tegmental area; rLH, rostral LH; SN, substantia nigra; TMN, tuberomammillary nucleus.