Many studies have demonstrated the efficacy of strength training in increasing energetic expenditure (EE) both during and after training sessions (6,7,9,12,14,17,18,20,26,27,29,31,35). In these studies, EE during training sessions is found to vary between 64 and 362 Kcal, whereas during recovery it varies from 6 to 52 Kcal, depending on the sample, training intensity, and the length of the measurement period during recovery from the exercise.
After exercise, the oxygen uptake remains above rest levels for a certain period of time, denoting higher EE during this period (13,25). The extra O2 consumption is known as excess postexercise oxygen consumption (EPOC). During recovery from a relatively heavy exercise, it may take approximately 60 minutes or more for the oxygen uptake and the anaerobic metabolic rate to return to pre-exercise levels (3), during which time, 3 phases of recovery can be identified (3): 1) a rapid-action component lasting 30 seconds on average; 2) after supermaximum exercise, a slow but complex component lasting 15 minutes on average; 3) after sustained exercise, a slight rise in the metabolism (ultraslow component), which may persist for up to 38 hours after the completion of a strength exercise session (31).
The magnitude of the EPOC and its duration appears to be related to the intensity of the prior exercise (15,21,23,25,31,35). The ultraslow component of the EPOC appears to only occur after exercise sessions that involve very intense sessions or with an eccentric component (21). Yet, in these studies, the intensity of the sessions was always stipulated by the percentage of 1RM or manipulation of the interval between the sets or the number of sets and number of repetitions.
However, none of the studies focused on “systems” that manipulate the exercise order because of the difficulty of isolating the other variables in strength exercises (load, volume, rest interval, number of sets and repetitions, and session duration). One of these systems is the “pre-exhaustion” (PE), which uses several exercises in rapid succession for the same muscle group, with little or no interval between the sets and exercises (13). Although widely used in gyms, the only information available on this system concerns only neuromuscular aspects in studies involving men (4), whereas there is no information on the EE or studies involving women. Another commonly used system is “circuit training” (CT), which is characterized by several strength exercises performed one after the other with a minimum of rest (15-30 s) while alternating muscle groups. Information regarding the EPOC resulting from this training system is limited (15,28). Halton et al. (15) compared 2 rest intervals (20 and 60 s) between sets, resulting in different workout durations, whereas Murphy and Schwarzkopf (28) compared different loads (50% and 80% 1 repetition maximum [1RM]) and different rest intervals (30 and 120 s), resulting in different total work levels and workout durations.
Therefore, given the lack of information on the above-mentioned training systems and the methodologic limitations of previous studies involving strength training systems and EE, the aim of our study is to verify the effect of the order in which the exercises are performed on the postexercise EE in 2 strength training systems (PE and CT). We hypothesize that performing the exercises for the same muscle group consecutively (PE system) may produce higher EPOC values and higher postexercise energetic demand.
Experimental Approach to the Problem
We used 2 strength training systems that manipulate the exercise order (PE and CT). Exactly the same exercises were used in both systems for the lower (knee extensors) and upper limbs (shoulder horizontal extensors and shoulder horizontal flexors). However, they were performed in different orders. Once the training session had ended, the postexercise expenditure was estimated by EPOC. The values were obtained by subtracting the oxygen uptake (O2) after exercise from that recorded pre-exercise. In both situations (pre- and postexercise), the O2 was collected at rest during 30 minutes, giving a total of 4 measurements per subject.
The sample consisted of 8 nonstrength-trained (at least 1 yr without weight training) women volunteers. None of the subjects had neuromuscular injury or was engaged in any type of competitive exercise and only practiced sports occasionally, at a recreational level (running, walking, or hydrogymnastics). A body mass index below 30, characterizing the sample as nonobese, was the inclusion criterion (1,16). The characteristics of the sample can be seen in Table 1.
Before participation, all subjects were informed about the procedures, risks, and benefits of the study and signed an informed consent document approved by the Ethics Committee of the Universidade Federal do Rio Grande do Sul. The sampled calculation considered a level of significance of 5%, statistical power of 80%, and a correlation coefficient of 0.8 for all the variables. A review of the literature was made to obtain the variability of each dependent variable, and the adopted difference was based on values considered physiologically different in the event that statistically significant differences were found between the training systems.
The data were collected in the weight training room of the School of Physical Education of the Federal University of Rio Grande do Sul, which the subjects attended 5 times. During the first visit, the body mass, height, and skinfolds were measured, and the subjects were introduced to the exercises and apparatus that would be used during the study. During the second visit, the process of familiarization continued, and the load was increased in relation to the first session in accordance with the subjective perception of effort. During the third session, a 1RM test was carried out for the same exercises. During the fourth and fifth sessions, oxygen uptake data were collected pre- (rest) and postexercise while the 2 different methods (PE and CT) were performed in random order. There was a minimum interval of at least 1 week between the last 2 sessions.
Body mass and height were obtained with a scale and stadiometer (Asimed, Barcelona, Spain), following the recommendations of Costa (8). Skinfolds were obtained with a plicometer (Cescorf, Porto Alegre, Brazil) and a metallic measuring tape (Sanny, São Bernardo do Campo, Brazil). The skinfolds were always measured by the same evaluator (8). Each measurement of the skinfolds was taken 3 times, nonconsecutively, and the average value was registered. All the measurements were taken from the right side (22). The sum of the skinfolds was used to estimate the body density of the subjects (19), and the percentage of body mass was estimated using the Siri formula (33).
Weight training apparatus (World, Porto Alegre, Brazil) and free-weight exercises were used. An estimated 1RM test was carried out in each exercise performed in the training sessions. Before the tests, 2 familiarization sessions were held in which the load was incremented by rate of perceived exertion (RPE), using the scale from Robertson et al. (30), so that the load remained between 6 and 8 on the scale, which is considered “difficult.” To carry out the estimated 1RM protocol, the following procedures were performed:
- Warm-up: 1 set of 10 reps with the load used in the last familiarization session.
- Increase of the load to perform 1 to 10 maximum reps.
- The number of reps and the load were used to calculate the 1RM (5).
The interval between each attempt was 5 minutes. During the tests, the muscle groups involved in the action were alternated.
To evaluate oxygen uptake during the at-rest and recovery periods, a portable ergospirometer (Aerosport, KB1-C) was used. The ergospirometer was calibrated before each collection, and the data relating to each analyzed subject were entered together with the atmospheric pressure at the time of collection.
The oxygen uptake of each subject was measured at-rest for 30 minutes before the training session and in the exercise recovery period with the subject in the supine position. For these evaluations, a few points were followed: a) the environment was quiet and dimly lit (10,11); b) the temperature was comfortable (22-24°C) to avoid alterations caused by cold or anxiety (17,27); c) the subjects were instructed not to perform any physical activity the day before the evaluation (9,11,15); d) the subjects fasted for 2 to 3 hours (10); e) the subjects remained at rest on their backs for 30 minutes before the measurements were taken (6,15,17).
After 30 minutes of rest, oxygen uptake measuring began, with the data being collected every 20 seconds until the 30-minute rest period was complete. Once measuring was complete, the sum of the collected data was considered to be the at-rest oxygen uptake for 30 minutes of each subject in the sample.
Soon after the at-rest collection was completed, the subjects in the sample performed the training session. The mask was fitted on the subject at the same time in both the training protocols. During the last set of the “station” (on the bench press exercise), the mask was fitted and the subject performed the last sets in all the apparatus with the collection mask and the ergospirometer functioning, so that when the postexercise collection began, the values obtained were already stable.
At the end of the training session, the subject was taken to a rest area for 30 minutes, and the same procedures used in the at-rest collection were followed. To calculate the EPOC, we used the following formula:
(1) EPOC (L) = O2POST (L) - O2PRE (L),
where EPOC is excess of postexercise oxygen consumption; O2POST is oxygen consumption postexercise; O2PRE is oxygen consumption pre-exercise.
Both while at rest and in recovery, the caloric equivalent used was 4.82 Kcal per liter of oxygen consumed (24). With use of this value, the maximum possible error in the calculation of the energetic metabolism based on the oxygen uptake was approximately 4% (24).
(2) EE (Kcal) = EPOC (L) × 4.82,
where EE is energetic expenditure.
We compared the effect of the exercise order on EE induced by strength training using the PE and CT systems. In both training systems, we used exactly the same exercises; however, they were performed with different orders.
In the present study, in the PE system, on the basis of recent information on the inefficiency of prefatigue when monoarticular exercises are performed first (4), it was decided to perform bi-articular exercises first. The CT was performed by alternating the exercises for lower and upper limbs. The order in which the exercises were performed in the 2 methods can be seen in Table 2. Both training sessions were performed with no rest between either the sets or the exercises. The 2 training sessions were performed randomly.
In the 2 training systems (CT and PE), 3 sets of 12 repetitions were performed for each of the 7 exercises, totaling 36 repetitions of each exercise. The total work of each exercise is presented in Table 3. The training loads used were 50% of 1RM for monoarticular exercises and 55% of 1RM for bi-articular exercises.
The average time taken to complete a session of CT was 23.35 ± 1.15 minutes, whereas in the PE method, it was 23.98 ± 0.96 minutes. There was, therefore, no statistical difference between them.
The velocity of each repetition was controlled using a digital metronome (KORG). The subjects were instructed to perform each phase of the movement (concentric and eccentric) for 2 seconds.
The normality of the data was analyzed using Shapiro-Wilk's test. The reliability of the O2 values was verified using an intraclass correlation coefficient (ICC; alpha test). After this, 2 paired t-tests were used to verify the existence of significant differences within and between the training methods. In all the analyses, the level of significance was p ≤ 0.05.
The ICC of the at-rest O2 values was r = 0.986 (p < 0.05), suggesting that all subjects were in the same metabolic state before each exercise session. In the 2 different training systems, there was a significant difference between the at-rest and postexercise oxygen uptake (Figure 1). However, there were no significant differences either in the at-rest (CT 14.71 ± 4.32 L and PE 15.01 ± 2.76 L) or in the postexercise values (CT 21.91 ± 4.02 L and PE 22.22 ± 6.27 L) between the 2 training methodologies. In terms of EE, these values represent a total of 34.67 ± 29.76 Kcal and 34.77 ± 28.15 Kcal for the CT and PE methods, respectively. The EPOC curve was very similar in the 2 methods, and the EPOC remained above the at-rest values throughout practically the entire recovery period (30 min) (Figure 2).
The main finding of the present study was that both orders of performing exercise were capable of maintaining the postexercise recovery oxygen uptake curve above the at-rest levels for 30 minutes, even when relatively low loads were used (50% and 55% of 1RM). Another important finding of the present study is that, in physically active women, there is no significant difference in the EPOC when strength exercises for the same muscle group are performed in sequence or when the agonist muscle groups are alternated. This result does not support our hypothesis because we expected higher intensity in the PE training.
Many previous studies have found significant differences in the EPOC when more intense strength exercise sessions were compared with less intense sessions (12,28,29,35). Increases in the intensity of the training session produced by the manipulation of load (percent of 1RM) (12,28,29,35), interval between sets (12,15,28), variation of the exercise velocity (17), number of repetitions (12,28), and number of sets (12,14) appear to influence the magnitude of the EPOC. In our study, the duration of the session, the exercise velocity, the number of sets, the number of repetitions, and the recovery interval were controlled so that only the “system” was different.
In the present study, the training sessions using low percentages of 1RM (50% and 55% of 1RM) produced an EPOC curve that remained above at-rest levels throughout the analyzed period (30 minutes) and reached the period that, according to some authors (3), includes the ultraslow component of the postexercise oxygen uptake curve, a period of the EPOC that appears to only occur when the training session is of high intensity or when there is a strong influence of eccentric contractions during the training session. Therefore, because eccentric work was not predominant in our study, it can be concluded that the absence of intervals between the sets of exercises in the 2 systems produced an intense training session, despite the use of low percentage loads, suggesting that little or no rest between exercise or sets increases the EE independently of the exercise order.
Another important factor is that the removal of blood lactate is one of the causes of EPOC. Therefore, the maintenance of the curve above the at-rest levels may indicate high lactate concentrations (3). In our study, using the PE system, 24 repetitions were performed for the same muscle group without interval, which may have produced higher increases in blood lactate concentrations (34). A relationship is suggested between the increases in blood lactate and the energetic demand, which is equivalent to 0.02698 Kcal Kg+1 per millimol of lactate increase postexercise (18). For Hunter et al., the EE in a strength training session and during the recovery needs to take into account the oxidative and metabolic processes. Therefore, when dealing with training methodologies characterized by the accumulation of lactate, perhaps greater precision in the measurement of the EE would be achieved by using the equivalent of the lactate concentrations added to the equivalent of oxygen uptake.
With regard the postexercise EE, the results found in the present study are similar to those of other authors (6,7,12,14,15,27,29) who, although they did not analyze the EE for the same period (30 min), found values varying between 22 and 52 Kcal. Despite reporting similar energy consumption figures, there are important methodologic differences between these studies, which make comparison difficult and leave us with only indications of the postexercise energetic demand.
The fact that only physically active women were used in the present study represents a limitation. Our study design controlled various strength training variables such as total work and exercise duration. Consequently, some characteristics of the training systems were changed. For example, CT is a system commonly applied to untrained individuals (13). However, PE is applied in trained individuals (13) that use much higher loads or more sets than used in present study. Therefore, in adapting the systems to our subjects, it is possible that the PE responses may have been underestimated. According to our statistical power (80%), 8 subjects appear to be sufficient to analyze the EE. However, the high variability of our results represents another important limitation. Therefore, our results must be carefully interpreted, and other studies with highly trained individuals would need to be done to elucidate the effects of the exercise order in strength training.
In conclusion, the results found in the present study indicate that the magnitude of the EPOC, in strength training, is not linked to the order in which the exercises are performed. Furthermore, with the 2 training systems used in this study (PE and CT), we found an ultraslow EPOC curve. Nonetheless, further studies comparing the sex and the training status are required to confirm whether the order in which the exercises are performed influences the EE during a strength training session.
It appears that the order of strength training exercises has no impact on EPOC when using lower loads in physically active women. However, it appears that the strength training systems that use no intervals between strength exercises (such as PE and CT) promote an EPOC similar to that observed with higher loads. Therefore, individuals with limitations in relation to high loads could perform CT and PE systems to obtain a higher EPOC and, consequently, higher EE.
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Keywords:© 2010 National Strength and Conditioning Association
EPOC; circuit training; preexhaustion; energetic expenditure