Estimation of metabolic equivalent (MET) of an exercise protocol based on indirect calorimetry

Abstracts

OBJECTIVE: Determine the energy expenditure (EE) in terms of caloric cost and metabolic equivalents (METs) of two sessions of an exercise protocol. METHODS: Fifteen subjects (51.0 ± 5.5 years) performed the exercise sessions (80min), composed of warm-up, walking and flexibility exercises (Session A) and warm-up, walking and local muscular endurance exercises (Session B). Heart hate (HR) was measured during each part of the sessions. In laboratory environment, maximal oxygen consumption (VO2max) and oxygen uptake at rest and exercise conditions (using mean HR obtained in classes) were measured on different days, using indirect calorimetry. Exercise METs were obtained by dividing VO2 in exercise (mL.kg-¹.min-¹) by VO2 at rest (mL.kg-¹.min-¹). The EE of the exercises was calculated by the formula: MET x Weight (kg) x Time (min)/60. The results were analyzed by ANOVA with Tukey post hoc test (p < 0.05). RESULTS: One MET for this group was 2.7 ± 0.1mL.kg-¹.min-¹. The METs means in the exercises were 4.7 ± 0.8 (warm-up); 5.8 ± 0.9 (walking) and 3.6 ± 0.7 (flexibility) in session A, and 4.6 ± 1.2 (warm-up); 5.6 ± 1.0 (walking) and 4.8 ± 1.0 (local muscular endurance exercises) in Session B. The training sessions showed similar energy cost (A: 398 ± 86.72 kcal and B: 404 ± 38.85 kcal; p > 0.05). None of the activities were classified as having vigorous intensity (> 7 METs). There were no differences in VO2 between walking (15.6 ± 2.8 or 15.4 ± 2.6 mL.kg-¹.min-¹) and local muscular endurance exercises (13.2 ± 2.9 mL.kg-¹.min-¹), although both were higher (p > 0.05) than flexibility exercises (10.1 ± 2.2 mL.kg-¹.min-¹). CONCLUSION: The proposed protocol achieves the physical activity needed by healthy adults to improve and maintain health, by their structure, moderate intensity, duration, frequency and caloric expenditure.

exercise; energy expenditure; MET

OBJETIVO: O objetivo do estudo foi determinar o gasto energético (GE) em termos de gasto calórico e equivalente metabólico (MET) de duas sessões de um protocolo de exercício. MÉTODOS: Quinze indivíduos adultos (51,0 ± 5,5 anos) realizaram as sessões de exercício (80min), compostas por (aquecimento, caminhada e flexibilidade; Sessão A) e (aquecimento, caminhada e resistência muscular local; Sessão B). A frequência cardíaca (FC) foi medida durante cada parte da sessão. Em laboratório, foram medidos, em dias diferentes, o consumo máximo de oxigênio (VO2max), durante repouso e exercício (usando a FC média obtida nas aulas), por calorimetria indireta. O MET dos exercícios foi obtido dividindo VO2 em exercício (mL.kg-¹. min-¹) pelo VO2 em repouso (mL.kg-¹.min-¹). O GE dos exercícios foi calculado por: MET x Peso (kg) x Tempo (min)/60. RESULTADOS: Os resultados foram analisados por ANOVA com teste post hoc de Tukey (p < 0,05). Resultados: Um MET para este grupo foi de 2,7 ± 0.1mL.kg ¹. min-¹. O valor médio de MET nos exercícios foi de 4,7 ± 0,8 (aquecimento), 5,8 ± 0,9 (caminhada) e 3,6 ± 0,7 (flexibilidade) na sessão A, e 4,6 ± 1,2 (aquecimento), 5,6 ± 1,0 (caminhada) e 4,8 ± 1,0 (resistência muscular localizada) na sessão B. O custo de energia foi similar entre as sessões (A: 398 ± 86,7 kcal e B: 404 ± 45 kcal; p > 0,05). Nenhuma atividade foi classificada como vigorosa (> 7 METs). Não houve diferença no VO2 entre caminhada (15,6 ± 2,8 ou 15,4 ± 2,6 mL.kg-¹.min-¹) e resistência muscular localizada (13,2 ± 2,9 mL.kg-¹.min-¹) embora ambos tenham sido superiores (p > 0,05) aos exercícios de flexibilidade (10,1 ± 2,2 mL.kg-¹. min-¹). CONCLUSÃO: O protocolo proposto atinge a atividade física necessária para adultos saudáveis, para melhorar e manter a saúde, por sua estrutura, intensidade moderada, duração, frequência e gasto calórico.

exercício físico; gasto energético; MET

ORIGINAL ARTICLE

EXERCISE AND SPORTS SCIENCES

Estimation of the metabolic equivalent (MET) of an exercise protocol based on indirect calorimetry

Christianne de Faria Coelho-Ravagnani^I,III; Flávia Carolina Lemos Melo^I; Fabricio C. P. Ravagnani^I,II; Franz Homero Paganini Burini^III; Roberto C. Burini^III

^INucleus of Physical Fitness, Informatics, Metabolism Sports and Health (NAFIMES) - Physical Education School – Federal University of Mato Grosso – UFMT – Cuiabá, MT, Brazil

^IIFederal Institute of Education, Science and Technology of Mato Grosso – IFMT- Bela Vista Campus – Cuiabá, MT, Brazil

^IIICenter of Metabolism in Exercise and Nutrition (CeMENutri) –Department of Public Health -Júlio de Mesquita Filho São Paulo University – UNESP – Botucatu, SP, Brazil

Mailing address

ABSTRACT

OBJECTIVE: This study aimed to determine the energy expenditure (EE) in terms of caloric cost and metabolic equivalents (METs) of two sessions of an exercise protocol.

METHODS: Fifteen subjects (51.0 ± 5.5years) performed the exercise sessions (80min), which were composed by (warming, walking and flexibility exercises; Session A) and (warming, walking and local muscular endurance exercises; Session B). Heart hate (HR) was measured during each part of the sessions. In laboratory environment, maximal oxygen consumption (VO_2max) and oxygen uptake in rest and exercise conditions (using mean HR obtained in classes) were measured on different days, using indirect calorimetry. Exercise METs were obtained by dividing VO₂ in exercise (mL.kg^-1.min^-1) by VO₂ in rest (mL.kg^-1.min^-1). The EE of the exercises was calculated by the formula: MET x Weight(kg) x Time(min)/60. The results were analyzed by ANOVA with Tuckey post hoc test (p < 0.05).

RESULTS: One MET for this group was 2.7 ± 0.1mL.kg^-1.min^-1. The mean METs of exercises were 4,7 ± 0,8 (warming), 5,8 ± 0,9 (walking) and 3,6 ± 0,7 (flexibility) on session A, and 4,6 ± 1,2 (warming), 5,6 ± 1,0 (walking) and 4.8 ± 1,0 (local muscular endurance exercises) on Session B. The training sessions showed similar energy cost (A: 398 ± 86.72 kcal and B: 404 ± 38.85 kcal; p > 0,05). None of activities were classified into vigorous intensity (> 7 METs). There were no differences on VO₂ between walking (15,6 ± 2,8 or 15,4 ± 2,6 mL.kg^-1.min^-1) and local muscular endurance exercises (13,2 ± 2,9 mL.kg^-1.min^-1), although both were higher (p > 0.05) than flexibility exercises (10.1 ± 2.2 mL.kg^-1.min^-1).

CONCLUSION: The proposed protocol achieves the physical activity needed by healthy adults to improve and maintain health, by their structure, moderate intensity, duration, frequency and caloric expenditure.

Keywords: exercise, energy expenditure, MET.

INTRODUCTION

Regular physical activity plays an important role in the body weight control¹ and in the prevention of countless non-transmissible chronic diseases². However, some variables should be assessed and manipulated in order to boost the benefits of physical activity, variables as intensity and duration of performed activities.

The accurate determination of the physical activity intensity which is also expressed in relation to the energy expenditure (EE), has become crucial in epidemiological studies^1,3-6. The exercise intensity is usually determined by the percentage of the VO₂max or of the maximum heart rate, scale of perceived exertion and metabolic equivalent (MET)⁷.

The metabolic equivalent (MET), multiple of the baseline metabolic rate, is equivalent to the energy needed by an individual to remain at rest, represented in the literature by the oxygen consumption (VO₂) of approximately 3.5 ml/kg/min^8,9. When the energy expenditure is expressed in METs, the number of times by which the rest metabolism was multiplied during an activity is represented^8-10. For example, cycling at four METs implies in caloric expenditure four times higher than what it is at rest¹¹.

The American College of Sport Medicine suggests that the MET unit is used as a method to indicate and compare the absolute intensity and energy expenditure of different physical activities. Therefore, the MET concept is applied in the general guidelines to the population concerning energy expenditure of the activities; thus, MET is a measurement of exertion intensity^12,13.

In the compendium of physical activities^9,14 translated to Portuguese ¹¹, the different activities are classified concerning the energy expenditure and metabolic equivalent. However, until the present moment, we have not found in the literature any study which quantified these variables in a traditional physical training protocol.

Thus, this study had the aim to determine the energy expenditure in terms of caloric expenditure and metabolic equivalent of two physical exercise sessions performed in a traditional physical training protocol.

METHODS

Subjects

15 (12 women and three men) moderately trained participants of a university extension program with individual supervised physical exercises and eating counseling, conducted by the Center of Metabolism in Exercise and Nutrition (CeMENutri) of the Medicine School – UNESP – Botucatu, were selected.

The study was carried out within the standards required by the Declaration of Helsinki (1975), modified in 1983 and approved by the ethics in research committee of the Medicine School of Botucatu (# 112/protocol 209/2003).

The adult individuals (age range of 40 to 60 years) were selected. Normal menstrual cycles was a pre-requisite for inclusion in the experiment. Vegetarians, renal, digestie and metabolic diseases patients, who made use of hormones or similar medication and drugs which interfere in the normal metabolism, besides corticoids, ,HMG-CoA reductase inhibitors (beta-hydroxy-beta-methyl-glutaryl CoA) or statins, diuretics and individuals with osteoarticular problems which made exercise practice impossible, were excluded.

Physical exercise protocol

The physical exercises protocol was conducted by Physical Education professional from the Center of Metabolism in Exercise and Nutrition (CeMENutri) of the Medicine School of UNESP in Botucatu. It included aerobic, local muscular resistance and flexibility exercises, in five weekly sessions with duration of 80 min/session, where session A was performed on Mondays, Wednesdays and Fridays and session B on Tuesdays and Thursdays.

Session A was composed of 20 minutes of warm-up, 40 minutes of walking and 20 minutes of flexibility exercises. Session B was composed of 20 minutes of warm-up, 30 minutes of walking and 30 minutes of local muscular resistance exercises. The target zone for walking was set between 70 and 80% of maximum heart rate (220 – age). The local muscular resistance activities (Session B) consisted of two sets of 10-15 repetitions, where load was progressively adjusted according to the group's adaptation. Nine exercises for muscle groups were performed, namely: chest, latissimus dorsi muscle, shoulder, biceps, triceps, quadriceps, thigh posterior, abductors and abdominals.

The exercises proposed for flexibility and balance should be performed for at least 30 seconds for the main joints: neck, elbow, shoulder, wrist, hip, knee and ankle.

During the articular warm-up, recreational and/or stretching activities were performed.

Anthropometric evaluation

Body weight and height were measured according to the procedures described by Heyward and Stolarczyk¹⁵. Body weight and height were evaluated with the use of an anthropometric scale (Filizola, Brazil) with precision of 0.1 kg for weight and 0.1 cm for height. The body mass index (BMI) was calculated from the weight and height measures through the body weight quotient (kg)/height² (m).

In order to estimate the fat-free mass (FFM) and fat percentage values, the bioelectric impedance test (Byodinamics) was used according to the procedures described by Lukaski et al.¹⁶. The formula used for the fat-free mass calculation was proposed by Gray et al.¹⁷.

The nutritional diagnosis was performed using the classification proposed by the World Health Organization (2002) and the Latin American Consensus in Obesity (1998).

Metabolic rate, heart rate and metabolic equivalent at rest (MET)

The individuals remained at dorsal decubitus on the stretcher for tem minutes for the test performance. After that period, the evaluation was performed for 30 consecutive minutes. The individuals were at 12-hour fast and without physical exercises in the 24 hours preceding the evaluation. Room temperature and relative humidity were kept between 21 and 23°C and 40 and 60%, respectively, in all the tests performed.

In order to determine the metabolic rate at rest (MRR) and the metabolic equivalent at rest (MET), the oxygen consumption volume (VO₂) and the produced carbonic gas volume (VCO₂) were continuously measured in an one-circuit ergospirometric system (QMC^TM 90 model Metabolic Cart, Quinton^®, Bothell, USA) using indirect calorimetry. Energy expenditure at rest was calculated with the formula proposed by DeWeir mentioned by Branson¹⁸:

The mean of the oxygen consumption at rest (VO₂ rest) during the 30 minutes of the test was calculated. This value was considered the metabolic equivalent art rest (MET). The heart rate at rest was measured in a heart rate monitor (Polar^® Edge NV) during the 30 minutes of the test. The mean value of all the measurements was calculated.

Evaluation of maximum aerobic power (VO_2max) and maximum MET

Maximum aerobic power (VO_2max) was evaluated in the ergospirometry on treadmill (inclination of 1%), with initial velocity of 4.5 km/h and increase of 0.5 km at each minute until voluntary exhaustion or when one of the following criteria was reached: increase in the VO₂ lower than 2 ml.kg^-1.min^-1 for the increase in the exercise intensity (plateau); expiratory exchange ratio higher than 1,1; maximum heart rate expected for the age was reached, calculated by the formula (220 – age). Prior to the beginning of the test, the individuals performed three minutes of warm-up at the 3.1 km/h velocity. Heart rate (HR) was monitored in the electrocardiogram. The respiratory parameters were measured in an open-circuit ergospirometric system using the Mix-Chamber Technique. MET was determined at the end of the test (MET maximum) by the ratio:

Cardiorespiratory fitness of the individuals was determined using the classification proposed by the American Heart Association mentioned by Marins and Gianichi¹⁹.

Calculation of the metabolic equivalent (MET) and calorie expenditure of the exercises

HR measurements during training sessions A and B were monitored through the heart rate monitor (Polar^® Edge NV) and recorded. It was possible to determine the mean HR of each part of the training sessions (warm-up, walking, LMR and flexibility/balance) with these data. They were later sent to the ergospirometry laboratory. At the laboratory, the individuals performed 30 continuous minutes of walk on treadmill at the same mean frequency reached during the parts of the exercise sessions, to precisely determine in the ergospirometry the oxygen consumption in each part of the sessions.

The evaluation of the intensity (MET and % of VO_2max) and the energy expenditure (kcal) was performed in each part of the class.

In order to calculate the MET value in each part of the class, the following formula was used:

Concerning intensity, according to the model proposed by Pate et al.¹⁸ the METs are classified in: < 3 METs – light activity; 3 to 6 METs – moderate activity; > 6 METs – vigorous activity.

Caloric expenditure of the exercises which compose each part of sessions A and B was calculated with the formula:

DATA ANALYSIS

Data were expressed in mean and standard deviation (± SD). The comparison between exercises in each part of the class was done with one-way ANOVA with Tukey post hoc. The significance level accepted was p < 0.05. The statistical treatment was performed by the BioEstat 5.0 software (Brazil).

RESULTS

The data expressed on table 1 reveal that mean and women are classified as overweighed and obese, according to BMI and fat percentage data, respectively. ,

Table 2 evidences that the mean values of oxygen relative consumption (ml.kg^-1.min^-1) classified the individuals of both sexes within good status concerning the expectation for the age. The VO₂ at rest equivalent to 1 MET (2.7 ml.kg^-1.min^-1 for men and women) was lower than the one described in the literature (3.5 ml.kg^-1.min^-1). In the test of aerobic power, men and women increased the oxygen consumption 8.7 and 10.3 times compared to at rest (MET_max).

Table 3 presents the values of metabolic and equivalent and total energy expenditure of the sessions and of the exercises which compose the different parts of the class. There was no significant difference in the total of energy spent between sessions A (398 kcal) and B (404 kcal). The oxygen consumption (15.6 ± 2.8 ml.kg^-1.min^-1) of the walking and local muscular resistance exercises was not different from each other. However, both were statistically higher than the ones obtained in the warm-up and flexibility/balance exercises (p < 0.05).

DISCUSSION

In the present study, similarly to others performed with indirect calorimetry^1,19 the metabolic equivalent at rest value was lower than the one which is used as reference in the literature (3.5 ml/kg^-1/min^-1)¹⁰. These data corroborate the study performed by Fardy and Hellerstein²⁰, where the use of indirect calorimetry has demonstrated that the conventional 1MET value overestimates the energy expenditure and the real oxygen consumption at rest.

Concerning the maximum exercise intensity (MET maximum), Fletcher et al.²¹ and the ACSM¹³ determined some reference values for this variable, which is different according to sex and age of the subjects (nine to 11 METs for men and eight to nine for women in the age range from 40 to 69 years). The data obtained by our subjects were within these normal zones, namely, from 10.3 and 8.75 for men and women, respectively, which also corroborates another study ²² similar to ours.

In the present study, for each type of exercise which was part of the sessions, individual analysis of the MET and caloric expenditure values was performed, which were classified as moderate, obtaining values range between 3.6 and 5.8 METs.

Almeida et al.²³, in their study with mail carriers, found values of 4.0 METs during walk to deliver the mail (moderate activity) and values of 2.5 METs for the triage activity (light activity). The research with adult men practitioners of yoga, the MET values ranged from 1.3 to 2.1 METs, according to the given position characteristics of the activity²⁴.

Farinatti¹¹in their study, which had the aim to design a complete version of the Compendium of Physical Activities, based on the values present in the compendia designed by Ainsworth et al.⁹ and Ainsworth et al.¹⁴, determines that for conditioning activities such as general circuit or exercises in health fitness clubs and/other health centers, approximately 8.0 and 5.5 METs are spent, respectively, values close to the ones found by us during the LMR activity (4.8 METs). The same author proposes values of 2.5 METs for light stretching activities and of 3.3 for walk on flat surface (moderate walk) to 5.0 METs (very fast walk), values which are also very similar to the ones obtained by us in the present study, in both variables.

According to Fletcher et al.²¹, the physical activity intensity necessary to improve conditioning varies among the individuals. However, the exercise intensity and duration ratio suggests that exercise of lower intensity requires more time to increase functional capacity, but with lower probability of complications concerning the exercise of higher intensity.

Thus, the classification of the physical activities intensity and the estimation of the caloric expenditure aassociated to it are important aspects of the exercise prescription and the exercise physiology, due to the need to adequate the activities proposed to the performance ability of the practitioner. Therefore, our training protocol prioritized the performance of exercises of moderate intensity, with low risk of injury onset or possible collateral cardiovascular effects, in a trial to minimize the risks and maximize benefits.

Concerning the training sessions of the present study, they were standardized about the total duration time (80 minutes) and aimed at improving the health-related physical fitness components (cardiorespiratory, flexibility and muscular resistance) and promoting increase of daily energy expenditure. Thus, the training proposed and applied in the Tuesday and Thursday sessions (Session B) obtained caloric expenditure of 404 ± 38.9 kcal, while caloric expenditure of session A was of 398 ± 86.7 kcal, that is, the difference between them was of only 6 kcal.

Although the population recommendations for adults^7,13 and older subjects²⁵ recommend 30 minutes of daily physical activities, five days per week (total of 150 min/week) for reduction of cardiovascular diseases and cancer, the recommendations for obesity control support the use of longer durations (200 to 300 weekly minutes) and energy expenditure with physical activity of about 2,000 kcal/week for individuals with free diet²⁶.

Therefore, the protocol of the present study would meet the expenditure for maintenance and/or prevention of non-transmissible chronic diseases and obesity control, since it presents caloric expenditure of approximately 400 kcal/session, which would come to an end of 2,000 kcal/week if performed in the frequency it is offered, that is, 5x/week.

The energy expenditure during the activity could determine higher or lower alteration in the body fat supplies. Therefore, the manipulation of the type of exercise would be necessary. However, there is considerable controversy concerning the impact of the many types of physical training on the energy expenditure and, consequently, on the body composition of the practitioners.

Thus, when resistance and aerobic resistance exercises are compared, some studies^1,22,27 evidence that both were efficient in promoting benefits to body composition and VO_2max.

Another factor which corroborates for the indefinition on which activity is the most effective in caloric expenditure and fat loss is the EPOC effect (excess post-exercise oxygen consumption) provided by the physical activities²⁸. Probably, resistance exercises of high intensity could require more energy expenditure during and/or immediately after exercise^29,30.

Nonetheless, in the present study, the LMR training was not different from walking concerning the oxygen consumption during exertion, and the metabolic equivalent values (MET) of both classified them as activities of moderate intensity. The LMR energy expenditure in the present study (144 kcal/30 minutes) was slightly lower than in the walk (168 kcal/30 minutes).

The protocol of the present study would hence meet the expenditure for maintenance and/or prevention of non-transmissible chronic diseases, since it is performed with weekly frequency of five times and it has its structure based on and aimed at the improvement of the health-related physical fitness components and caloric expenditure above the minimum recommendation for prevention of these diseases.

As a summary, our study reveals that the two exercise sessions applied could promote expressive increase in daily energy expenditure, but it is worth mentioning that the association of resisted, aerobic and flexibility exercises is essential in the promotion and/or maintenance of physical fitness, as well as for prevention and rehabilitation of cardiovascular diseases in adults of all ages².

Limitations were found when we tried to compare our data with the ones in other studies, since great part of the research available considers in their evaluations only the total daily energy expenditure. No study which analyzed the metabolic equivalent of an exercise protocol, the way ours did, was found.

Moreover, these studies are based on pre-existing data from physical activity compendia to estimate the energy expenditure or exercise intensity, that is, the existing individual differences between sexes and perceived exertion, in some cases, may be big, which represents a difficulty in establishing comparison between values.

CONCLUSION

Thus, the protocol performed in this study meets the recommendations for health due to its intensity of 3 to 6 METs (moderate exercises) structure, time longer than sixty minutes, frequency (5x/week) and caloric expenditure of 1,200 to 2,000 kcal/week, meeting the minimum demands of energy expenditure recommended by the WHO, AHA and ACSM.

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Publication Dates

• Publication in this collection
  03 June 2013
• Date of issue
  Apr 2013