The acute metabolic demands of strength training (ST) exercise have been investigated by previous studies, and their results have shown significantly larger increases in oxygen uptake (V[Combining Dot Above]O2) and energy expenditure (EE), during and after exercise, depending on variables, such as muscle mass (24), lifting velocities (14), number of sets (13), number of repetitions (31), workload (38), training volume (16), rest intervals (31), or exercise order (7). Similarly, research on the use of aerobic training (AT) exercise showed increases in exercise V[Combining Dot Above]O2, which are concomitant with increases in exercise intensity (26,34) and are larger when AT is preceded by ST exercise (17). Additionally, studies have shown that when performing intermittent aerobic exercise (20,23) and when performing at high and supramaximal intensities (20,30), a significant increase in postexercise oxygen consumption (EPOC) is present.
The combination of AT and ST in the same-session training is very common in physical fitness training programs (1) and athletic programs (5,29) because of time constraints and convenience. However, training including aerobic and strength exercises performed in a single session, known in the literature as concurrent training, presents a specific challenge, especially among different populations (21). Fatigue generated from one mode of exercise may negatively influence the quantity and quality of exercise in the other mode (21).
Few studies have addressed the sequence of AT and ST in the same session and its influence on V[Combining Dot Above]O2 during (27) and postexercise (5). The combination of the ST with AT in the same training session presented higher mean values in V[Combining Dot Above]O2 during exercise, when compared with ST alone (27) but lower mean values postsession (5). Additionally, the inclusion of performing ST before AT increased V[Combining Dot Above]O2 during exercise, when compared with AT alone (17), but postexercise V[Combining Dot Above]O2 was lower, when compared with performing ST after AT (5). To our knowledge, no study has previously compared the effects on V[Combining Dot Above]O2 using different combinations of intermittent AT and ST exercise in the same session, during and postexercise. Because these training methods are often combined, it seems important to assess which combination provides a higher V[Combining Dot Above]O2. If combining each modality into a single training session resulted in a negative impact on aerobic exercise, it would be important to separate the training into different training sessions to allow for optimal aerobic development. However, if little or no impact results from combining the training into one session, no concern would be warranted.
The aim of this study was to examine the differences in physiological demands of workouts comprising differing resistance and cardiovascular demands by assessing V[Combining Dot Above]O2 before, during, and postexercise and comparing the responses in different combinations of ST exercise with AT interval exercise. It was hypothesized that differences would be nonsignificant if the same amount of work was performed in the various sessions.
Experimental Approach to the Problem
To address the question whether combining ST and AT into one training session would hamper the aerobic portion, a series of workouts were performed with physiological measures taken in each workout. The subjects were evaluated in 5 sessions. Session 1 was dedicated to the measurement of body mass, height, and estimated body fat, 1-repetition maximum test (1RM). In session 2 (72 hours later), peak V[Combining Dot Above]O2 was assessed using the cycle ergometer. In sessions 3–5, V[Combining Dot Above]O2, heart rate (HR), and respiratory exchange ratio (RER) were measured 30 minutes before, during, and for 15 minutes after the 3 exercise sessions. The sessions, performed in random order, included 3 combinations of ST with AT in the same session: AT before ST exercises, AT between 2 blocks of 3 ST exercises, and AT after ST exercises.
The session total load and the exercise intensity of both ST and AT were designed to stimulate a high V[Combining Dot Above]O2, to involve all larger muscle groups, and to meet the time available for training in modern societies. Each subject performed the 3 sessions in a randomized order with a 7-day recovery interval between them. Sessions were conducted at the same time of the day, and all the subjects were driven by a researcher into the testing place. In addition, all men were instructed to refrain from any strenuous physical activity (e.g., cycling, running, weight lifting, and recreational activities) for 48 hours before all testing and to record and duplicate their meals for 24 hours before the 3 exercise sessions.
Eight active men (23.6 ± 4.2 years, 178 ± 6.3 cm, 77 ± 7.9 kg, 7.67 ± 1.95% body fat) completed all the established procedures for this study. All the subjects completed a physical activity and medical history questionnaire. Every subject who was selected had been engaged in physical activity (comprising strength and cycling exercises) for at least 3 d·wk−1 over the past 6 months. Additionally, the subjects were informed about the possible risks or discomfort involved in the experiment and provided a written informed consent to participate in the study. The procedures were designed according to the Helsinki Declaration and were approved by the Research Ethics Committee of the Institution.
The 1RM testing protocol has been described previously by Kraemer and Fry (19). The subjects did the familiarization in the 1RM protocol in 4 visits (22), and excellent day-to-day 1RM reliability for each exercise was shown by this protocol in the familiarization 1RM test (36). Intraclass correlation coefficients of half-squat (r = 0.91), bench press (r = 0.94), incline leg press (r = 0.94), and lat pull-down (r = 0.96).
After the familiarization, the 1RM tests were performed for the half-squat, bench press, incline leg press, and lat pull-down (Paramount Fitness®, Los Angeles, CA, USA). The heaviest load achieved was considered the 1RM load. To minimize the error during 1RM tests, the following strategies were adopted (36): (a) standardized instructions concerning the testing procedures were given to participants before the test; (b) participants received standardized instructions on exercise technique; and (c) standard verbal encouragement was provided during the testing procedure. The 1RM was determined in <5 attempts with a rest interval of 5 minutes between them.
Oxygen Consumption Assessment
A maximal cardiopulmonary exercise test was performed to determine the peak V[Combining Dot Above]O2 on a continuous incremental protocol on a cycle ergometer (Model SCIFIT®, ISO1000, Binfield, United Kingdom) with the initial load set at 50 W with each minute increased by 25 W until the subjects could not maintain a 60-rpm cadence or until volitional fatigue. The criteria of interruption of the test followed the recommendations of the American College of Sports Medicine (1). The HR was continuously monitored (Polar Wireless Electrode double, Kempele, Finland), and exhaled gases were measured continuously by a portable gas analyzer (Cosmed® K4b2, Rome, Italy), in which the gas samples were collected and measured every 10 seconds during the test. The analysis was conducted using oxygen and carbon dioxide detectors. The RER, volume of oxygen consumed per minute (V[Combining Dot Above]O2), and volume of carbon dioxide produced per minute (V[Combining Dot Above]CO2) were standardized and calculated directly by the device. The equipment was calibrated before each examination. Ambient temperature and humidity were between 20 and 25°C and 40 and 65%, respectively, for all the tests.
The same environmental conditions were applied, and the same data assessment devices were used for the V[Combining Dot Above]O2 assessment before, during, and after the different sequences on EPOC. The equipment system was calibrated before each individual test according to the manufacturer's guidelines. In the 24 hours before an exercise session day, the subjects were required to (a) avoid caffeine or other metabolic altering supplements and drugs; (b) engage in no physical activity; (c) stay well hydrated and not change their habitual diet; and (d) be well rested.
The subjects recorded food consumption during the day before the first exercise session and were asked to replicate it in the days before the other sessions. The last meal of the day before testing was taken not later than 20:00 hours.
On testing days, 30 minutes before exercise and after the measurement of the resting metabolic rate (RMR), all the subjects received a standardized meal aimed to balance the caloric intake among all the subjects. The meal consisted of 330 ml of water, 350 ml of orange juice and a 35-g energy bar Pro-Plex (All-Stars Fitness products, Peibenberg, Germany), amounting to 150 kcal (6.3 g protein, 12.6 g carbohydrate, and 8.1 g fat).
Resting Metabolic Rate Measurements
Before each exercise session and after a minimum of 12-hour fasting, the RMR was measured by indirect calorimetry using Cosmed® K4b2. The measurement was performed in an isolated room, with the door closed and the lights dimmed. The RMR was then measured for 30 minutes. The RMR was determined from steady-state V[Combining Dot Above]O2 values during the last 25 minutes of measurement. Immediately postexercise, the subjects returned to the room where RMR measurement was repeated.
During each session, expired gases were continuously measured breath by breath with Cosmed® K4b2 and then averaged as 20-second intervals. The HRwas also measured continuously using an HR monitor (Polar Wireless Double Electrode T31, Kempele, Finland).
The subjects performed half-squat, bench press, incline leg press, and lat pull-down with a load of 70% of 1RM. These exercises were chosen to elicit a large muscle mass in the upper and lower limbs. Abdominal crunches and lumbar extensions were also performed without additional load because they are typically included in ST programs. In each exercise, 3 sets of 10 repetitions were performed with a 60-second rest interval between sets and at a 40-b·min−1 cadence, which was controlled by an electronic metronome (Korg MA—30, Korg, Melville, New York, USA). Abdominal crunches and lumbar extensions were performed for 30 and 20 repetitions per set, respectively. The exercise sequence was as follows: half-squat, bench press, abdominal crunch, incline leg press, lat pull-down, and lumbar extension performed on a roman bench (Roman Bench—PFW-5600, Paramount Fitness Corp.).
Interval Aerobic Training
The subjects cycled for 20 minutes, which was divided into 2-minute low-intensity bouts (≈40% of peak V[Combining Dot Above]O2) and interspersed with 1-minute high-intensity bouts (≈75% of peak V[Combining Dot Above]O2).
Strength training and interval aerobic training were sequenced in the following way: (a) For the AT before the ST session, the exercise order was AT, half-squat, bench press, abdominal crunches, incline leg press, lat pull-down, and lumbar extensions; (b) for the AT in the middle of the ST session, the order was half-squat, bench press, abdominal crunches, AT, incline leg press, lat pull-down, and lumbar extensions; and (c) for the AT after the ST session, the order was half-squat, bench press, abdominal crunches, incline leg press, lat pull-down, lumbar extensions, and AT.
Normality assumption was confirmed with the Shapiro-Wilk test, and the homogeneity of variance and covariance was confirmed using Levene's test and Mauchly sphericity test. Differences between the 3 sessions were investigated with a one-way analysis of variance (ANOVA) with Bonferroni post hoc. Differences between values within and between sessions were investigated with ANOVA for repeated measures and one-way ANOVA, with post hoc Bonferroni, respectively. The significance level was maintained at 5%. Results are presented as mean ± SD. The average statistical power for all analyses was calculated to be 0.68.
There were no significant differences in the values of absolute or relative V[Combining Dot Above]O2, in HR, and in RER when the 3 sessions (during) were compared. Analyzing only ST in each session, differences were detected in the RER values between AT before ST and AT in the middle of ST (1.01 ± 0.97 vs. 1.11 ± 0.07, respectively, F = 4.714; p = 0.02; η = 0.308). In all sequences, there was a significant increase in the values of relative and absolute V[Combining Dot Above]O2 and HR, and a significant decrease in the RER values from the first to the second part of the ST session (Table 1). The values of absolute or relative V[Combining Dot Above]O2, HR, and RER did not vary significantly among the 3 sessions as compared with the AT after ST (Table 2).
Oxygen uptake during the 30 minutes postexercise was significantly different when AT was performed before the ST and when AT was performed after ST from the 5th to the 15th minutes. There was also a considerable difference with AT in the middle of the ST session and with AT after the ST session from the 10th to the 15th minutes (Table 3).
Although the current sample size is small (n = 8), and statistical power was not optimal, the repeated measures design of the study appears sufficient to analyze the differences between the conditions. The main finding in this study was that the mean values of V[Combining Dot Above]O2 during exercise were not different between sessions. These data support the hypothesis that ST and AT, when performed in sequence in the same session, does not seem to affect overall oxygen consumption during the exercise session. Thus, combining resistance training and aerobic exercise in one session does not limit the cardiovascular demand of the exercise session.
These data corroborate previous studies that are similar in exercise volume and intensity (15,26). However, the current data contradict those found in the study by Drummond et al. (5). These authors found differences in V[Combining Dot Above]O2 at 15 (36.9 ± 1.3 vs. 37.6 ± 1.3 ml·kg−1·m−1), 20 (38 ± 1.3 vs. 39.3 ± 1.3 ml·kg−1·m−1), and 25 minutes (39.7 ± 1.3 vs. 40 ± 1.3 ml·kg−1·m−1) of exercise, when comparing running on the treadmill before and after the ST. A possible explanation for the differences between our study and that of Drummond et al. (5) is the equipment used for the AT (cycle ergometer and treadmill, respectively). Indeed, Sedlock (34) showed that the V[Combining Dot Above]O2 obtained on the treadmill is higher when compared with the cycle ergometer exercise of the same duration and intensity. Another factor that may have influenced our results was the exercise on the cycle ergometer, which was carried out with a full-seated position, thus mitigating the effect of gravity on the total body mass. When running on the treadmill, the subjects had to bear the effect of gravity on their body mass, and V[Combining Dot Above]O2 (25) tended to be higher.
The order of ST exercises that were performed may have also affected the V[Combining Dot Above]O2 during AT. In this study, lower limb muscle groups were interspersed with upper body exercise (upper limbs or middle zone of the trunk—the abdominal and lumbar). This exercise sequence provided a separation of not <11 minutes between lower limbs ST and subsequent AT. This time period may have been large enough to allow for a recovery of lower limb muscle groups. This phenomenon could also help to explain the lower values of V[Combining Dot Above]O2 in this study, when compared with those observed by Drummond et al. (5). In fact, in the study of Drummond et al. (5), an exercise involving the quadriceps femoris was performed immediately before the start of the aerobic exercise. It has been shown that the V[Combining Dot Above]O2 kinetics are enhanced and the O2 deficit is smaller for a given exercise when a previous bout of exercise is performed (4,11,18,32) involving the same muscle groups (10,39). In short, methodological differences between our study and those by Kang et al. (17) and Drummond et al.(5) may partly explain the discrepancies. Future studies comparing subject's responses during AT treadmill and AT cycle ergometer exercise will help to clarify this issue.
When splitting the ST in 2 parts (half-squat, bench press, and abdominal crunches as part I and incline leg press, lat pull-down, and lumbar extensions as part II), the V[Combining Dot Above]O2 mean values in the first part were lower than those observed in the second part. This seems to reveal an increase of O2 with exercise duration. Moreover, the exercises within each part of ST presented a higher V[Combining Dot Above]O2 relative to the next ST segment. Farinatti et al. (7) observed an increase in V[Combining Dot Above]O2 in the exercises performed at the end of a session of ST. The difference between that study and our current investigation could be explained by the fact that in the study by Farinatti et al. (7) all exercises involved the recruitment of upper limb muscle groups.
The mean values of RER were lower in the second part of the ST and were also lower when the ST was performed before the AT. These data could suggest that the acidosis during ST, caused by the accumulation of the H+, may be lower when AT is performed in advance, which may impair the effectiveness of ST programs addressed to promote muscle mass gains. Fleck and Kraemer (8) state that the blood metabolite accumulation from anaerobic production of adenosine triphosphate can promote the protein synthesis and may assist in muscle hypertrophy. This idea is reinforced by studies that show an increase in muscle mass in the ST methods that promote a decrease of the delivery of O2 to the muscle cells during exercise (35,37). If our results are confirmed, this phenomenon should be taken into account when the purpose of the ST is to address both high-EE during exercise and an increase in muscle mass. However, the difference in the RER between sessions, observed in this study (≤0.1) may be insufficient for such an effect to occur in terms of muscle gain.
In this study, the values of V[Combining Dot Above]O2 recorded in the first 5 minutes postexercise did not differ between the 3 training sessions. This is possibly because of the rapid restoration of phosphagens, oxyhemoglobin and oxymyoglobin, which occurs typically within the first 5 minutes postexercise, regardless of the recovery method used (8). However, during the period between the 5th and 10th (5.79 ± 0.34 vs. 4.90 ± 0.62, respectively, F = 0.252; p = 0.004; η2 = 0.092) and in the period between 10th and 15th minutes (5.30 ± 0.43 vs. 4.57 ± 0.61, respectively, F = 0.305; p = 0.013; η2 = 0.092) postexercise, significant differences between sessions AT after ST and AT before ST were observed. These results corroborate data presented by Drummond et al. (5) (5.7 ± 0 and 5.1 ± 0.2 ml·kg−1·m−1, when the AT was performed before and after ST, respectively) in the first 10 minutes postexercise. In this study, statistically significant differences were found between AT middle of ST and AT before ST (5.40 ± 0.60 vs. 4.90 ± 0.62 ml·kg−1·min−1, respectively, F = 7.112; p = 0.025; η2 = 0.092). These data may suggest that the closer to the end of the session the AT is placed, the quicker the fall in V[Combining Dot Above]O2 in the first 15 minutes postexercise. This might be so because the aerobic exercise (at least when carried out intermittently with high and low-intensity bouts) may act as a method of speeding up the recovery after ST.
Because differences in postexercise V[Combining Dot Above]O2 between different types of exercise are more likely to occur in the first minutes of recovery and tend to be attenuated over time (5,17,28), data were examined to assess recovery V[Combining Dot Above]O2 for the first 30 minutes. The accumulated V[Combining Dot Above]O2 above resting values during this period in this study do corroborate data presented in previous studies (2,3,5,6,9,12,16,26,31,33,38) suggesting further similarities in oxygen consumption.
From the present data, it can be concluded that a combination of ST with AT in young, apparently healthy male subjects may serve to (a) meet the personal preference of the practitioner in terms of exercise sequence; (b) improve space and time management procedures in fitness facilities; (c) provide an additional way to reduce the monotony of training; and (d) knowing that adaptations to physical training are attenuated with repetition over time of the same training methods, the order of combination of ST with AT can be varied without compromising the overall EE during the session. Trainers and coaches should alter the sequencing of strength and AT throughout a training cycle and may incorporate both into one training session without hampering the value of either.
The authors are grateful to Varzim Lazer, EM, for all the support with logistics.
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