Energy expenditure during exercise

Energy expenditure during exercise varies over a large range. From a basal metabolic rate (BMR) of approximately 290-340 kJ/h in men and 240-260 kJ/h in women energy expenditure may increase to 45000 kJ/h during heavy exercise. Assuming a mechanical efficiency of around 20%, this permits 1000 kJ/h of work to be performed [24]. During a 10-s bout of exercise more than 10 kJ of work may be performed by a highly trained athlete and during a i-min bout 40 kJ [25].

The total energy expenditure (TEE) of an adult person averages 10000-13000kJ/24h. Individuals with physically very demanding occupations may reach values of 17000-19000kJ/24h. The TEE is made up of three components: the BMR, the dietary-induced thermogenesis (DIT) and the activity-dependent energy expenditure (Table 1.2. i). The BMR is normally the largest component of TEE, averaging 7000-8200 kJ/24 h in men and 5800-6200 kJ/ 24 h in women. The DIT, which is defined as the extra energy consumption resulting from a meal, normally accounts for one tenth of the TEE. DIT is largest after a protein meal, where it amounts to 18-25% of the energy contained in the meal, but considerably smaller for meals containing carbohydrates (4-7%) and fat (2-4%) [24]. The remaining part of the TEE is the activity-dependent energy expenditure (AEE), which can be calculated based on the 19.7 and 21.2 kJ of energy released for each liter of oxygen consumed during fat and carbohydrate oxidation, respectively (for further discussion, see below). When the oxygen uptake is unknown, different approximations are often used to assess the activity-dependent energy consumption, e.g. quiet sitting corresponding to an energy consumption of about 1.2XBMR, office work 1.31.6 X BMR, standing 1.4 X BMR, cycling 4-6 X BMR and various sports activities of the order of 10-20 X BMR (Table i. 2. i) [24]. The energy cost of running is independent of running speed and of the order of 4 kJ/km/kg body weight. For walking at a pace of 4.55 km/h, the corresponding figure is 3 kJ/km/kg: body weight [26]. This means, for example, that the energy content of 100 g fat (3900 kJ) for a 70-kg person covers the energy demand of running approximately 14 km or

Table i .2. i Energy expenditure in adult men and women, given as the total energy expenditure/24 h as a multiple of BMR (equal to the physical activity level, PAL). Data from [72].

BMR = basal metabolic rate (kJ/24 h)

DIT = diet-induced thermogenesis (kJ/24 h)

AEE = activity-induced energy expenditure (kJ/24 h)

TEE = total energy expenditure = BMR + DIT+AEE

PAL = physical activity level (includes DIT)=TEE/BMR

BMR 18-29 years 30-39 years

40-64 years

Males 7500 8200

7000

Females 6200 6000

5800

PAL over 24 h with different living conditions

Chair- or bedbound

1.2

Seated work, low leisure time activity

1.4-1.5

Seated work with moving around,low leisure time

activity

1.6-1.7

Standing work,low leisure time activity

1.8-1.9*

Strenuous leisure time activity (30-60 min,

> 4 times/week)

+0.3+

Strenuous work or high activity in leisure time

2.0-2.4+

* For example, 8 h sleeping (0.95), 4 h sitting (1.2), 12 h walking around (2.5).

t Up to a maximal value of 2.0.

+ 2.4 is considered to be the highest PAL that can be tolerated other than for short periods of e.g.very intensive training.

walking i8 km. It is evident that complex nervous and hormonal regulation is required in order to control the utilization of the different energy substrates during exercise with large variations in energy demand.

Your Metabolism - What You Need To Know

Your Metabolism - What You Need To Know

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