Energy expenditure (EE) is a critical component to exercise programing particularly for those individuals seeking to reduce body weight or percent body fat. Increasing EE by exercise is an important strategy for weight control. Resistance training is a modality of exercise shown to increase EE (10,21,22,25,26,31) and improving a multitude of health and fitness components (14,24). However, the acute EE response is dependent on several variables including intensity, volume and duration, rest intervals, exercise selection, and sequence (7,21,22,25,26). The appropriate prescription of each of these variables to target increased EE is of great importance to the practitioner. Thus, studies quantifying EE during various resistance exercise programs are warranted.
One acute program variable known to affect the acute metabolic response to resistance exercise is volume. In particular, the number of sets per exercise is a variable of interest that has received much attention in the literature. Studies have shown that multiple-set programs produce superior increases in muscle strength (12,13,15,17) and hypertrophy (16) primarily over long-term training periods. In addition, multiple-set programs elicit a greater acute hormonal response to resistance exercise (6) and augment the metabolic response to resistance exercise (7,8). As a result, major health and fitness organizations such as the National Strength and Conditioning Association and American College of Sports Medicine have recommended multiple-set programs for long-term improvements in muscular fitness (24). In light of these recommendations, little is known concerning acute resistance exercise metabolic responses especially because single-set and multiple-set programs can be constructed in numerous ways.
Another pertinent area of research is gender responses to resistance exercise. Studies have shown conflicting results where some studies have shown greater absolute EE during resistance exercise in men (2,18,20,21) compared with women but some researchers have reported no significant differences between genders (19). When EE is expressed relative to lean body mass (LBM), conflicting results have been reported where studies have found similar relative EE between genders (21) and one study found women had higher EE/LBM when expressed relative to exercise volume (19). Thus, many questions still exist regarding gender differences in the acute EE response to resistance exercise and few studies have examined the responses to single-set and multiple-set protocols. Therefore, the primary purpose of this study was to quantify the EE of a single-set vs. multiple-set resistance exercise protocol. A secondary purpose was to investigate potential gender differences in gross, net, and the rate of EE.
Experimental Approach to the Problem
To examine the primary hypotheses of this investigation, a within design was used where all subjects performed a single-set (SS) and multiple-set (MS) resistance exercise protocol in random order. The subjects performed the protocols at 70% of their 1-repetition maximum (1RM). The protocols consisted of 5 upper-body exercises and 1 or 3 sets per exercise were performed. Metabolic and cardiorespiratory data were recorded over the entire exercise session and during 5 minutes of recovery. This design enabled us to quantify differences in EE when resistance exercise volume was tripled during a MS protocol.
Twenty-four subjects (12 men and 12 women) with a mean age of 21.4 ± 1.3 years volunteered to participate in this study (Table 1 for subject characteristics). All subjects were recreationally weight-trained with a minimum of 1 year of resistance training experience and were accustomed to the exercises selected in this study. Subjects underwent 1 session of familiarization with study procedures before testing. During this time, height was measured using a wall-mounted stadiometer and body mass was measured using an electronic scale. Percent body fat was determined by hydrostatic weighing. Fat mass was calculated as body mass (kg) × body fat percent. Lean body mass was calculated using the following equation: LBM (kg) = body mass (kg) − fat mass (kg). This study was approved by the Bloomsburg University Institutional Review Board and all subjects subsequently signed an institutionally approved informed consent document before participation. A Physical Activity Readiness Questionnaire was used to exclude subjects with known cardiovascular or musculoskeletal problems. The study conforms to the Code of Ethics of the World Medical Association (approved by the ethics advisory board of Swansea University) and required players to provide informed consent before participation.
One-repetition maximum strength was assessed before the experimental sessions using a standard progressive protocol. The exercises assessed were the free weight bench press, military press, biceps curl, and machine lat pull-down and triceps pushdown on a Body-Solid EXM-4000S strength training machine (Body-Solid Inc., Broadview, IL). All 1RMs for each exercise were assessed in the same session in the aforementioned sequence. For each exercise, 1–2 warm-up sets of 10 repetitions were performed using approximately 70–80% of the perceived 1RM. Subsequently, 3–5 maximal trials were performed to determine the 1RM with 3–5-minute rest intervals in between trials. A complete range of motion and proper technique was required for each successful 1RM trial. Assessment of 1RM strength enabled calculation of the protocol loads (70% of 1RM).
Measurement of Energy Expenditure
All subjects reported to the laboratory after a 12-hour fast on two occasions separated by at least 48 hours. Subjects refrained from caffeine consumption for at least 12 hours and from exercise for at least 24 hours before each testing session. On arrival, each subject was encouraged to drink water ad libitum to prehydrate. After equipment calibration, each subject was subsequently connected to the Cosmed K4b2 system (Cosmed, Rome, Italy). The unit was attached to the subject's chest with a harness. A Hans Rudolph face mask (Hans Rudolph, Inc., Shawnee, KS) was attached using a head strap and a disposable gel seal was used to ensure an airtight environment. Subjects sat quietly for 15 minutes while resting preexercise metabolic data were collected during the last 5 minutes. The Cosmed K4b2 system has been shown to be a reliable metabolic system when used during exercise (4,28) and has been used for similar research (8,21).
Resistance Exercise Protocols
After baseline measures, each subject performed a 5-minute warm-up consisting of stationary cycling on a Lifecycle 9100 (Schiller Park, IL) at a workload of 40 W followed by a few light stretches. Subsequently, subjects performed an initial warm-up set of 10 repetitions at a self-selected weight. Testing order was randomized such that half of the subjects began with the SS protocol, whereas the other half began with the MS protocol. The SS protocol consisted of performance of 1 set per exercise with 70% of 1RM for 10 repetitions at a standard cadence (1- to 2-second concentric phase, 2-second eccentric phase). The MS protocol consisted of performance of 3 sets of each exercise for 10 repetitions with the same loading and cadence. The exercise sequence used a large to small muscle-mass strategy (14,24) and included the bench press, lat pull-down, military press, triceps pushdown, and biceps curl. Rest intervals between sets for the MS protocol were 2 minutes, whereas 3-minute rest intervals were used between exercises for both protocols. Volume load per exercise was calculated by the equation: volume load = sets × repetitions × load (kg). Total volume load was summed for all exercises collectively. Protocol loads are presented in Table 2.
Metabolic data were collected for the entire protocol. The beginning and end of each set and exercise were marked on the metabolic system. At the cessation of each protocol, subjects remained connected to the metabolic system for 5 minutes for collection of postexercise data. Energy expenditure of resistance exercise was determined using the following equation: EE (kcal·min−1) = 3.781 × V[Combining Dot Above]O2 + 1.237 × V[Combining Dot Above]CO2 (5). The average EE was multiplied by the protocol time to determine gross EE. Net EE for each resistance exercise session was obtained by subtracting resting EE from gross EE.
Data were analyzed using SigmaStat statistical analysis software (SPSS, Chicago, IL). Descriptive statistics (mean ± SD) were calculated for all dependent variables. Independent t-tests were used to determine significant differences between the SS and MS protocols and gender differences. For all statistical tests, a probability level of p ≤ 0.05 denoted statistical significance.
The total elapsed time for the SS protocol averaged 13 minutes (2.5 minutes of actual lifting time as each set was completed in ∼40 seconds) not including the warm-up. The total time for the MS protocol averaged 37 minutes (7.5 minutes of actual lifting time). Volume load was significantly higher in MS (6,001.1 ± 3,621.3 kg) than SS (2,000.4 ± 1,207.1 kg). Tables 3–5 present the EE and cardiorespiratory data. Significant differences (p < 0.001) were observed between the SS and MS protocols for gross, net, and relative EE where values obtained during MS were greater than SS (Table 3). However, gross, net, and relative EE per min were not significantly different between protocols. In addition, gender differences (p < 0.001) were observed in total gross and net EE and gross and net EE per minute where values in men were significantly higher than women for both protocols (Table 4). Significant gender differences were also observed when EE data were expressed relative to LBM. Relative V[Combining Dot Above]O2, V[Combining Dot Above]CO2, respiratory exchange ratio (RER), minute ventilation (VE), VE/V[Combining Dot Above]O2, heart rate (HR), and respiratory rate (RR) were significantly higher in MS than SS (Table 5).
The salient finding from this study was that the volume of resistance exercise significantly affects the metabolic and cardiovascular responses but not the rate of EE. We were able to examine the EE of resistance exercise using a portable metabolic system and reported that at least 5 exercises were needed for the MS protocol to increase EE to more than the recommended 150 kcals per day standard given the rest intervals used in this study. Thus, the MS upper-body protocol (using 10 repetitions per set with 70% of 1RM) produced more than double the gross and net EE than a SS protocol consisting of the same number of exercises. In addition, we have shown gender differences in response to both protocols where gross and net EE, rate of EE, and EE expressed relative to LBM were higher in men than women.
Energy expenditure during resistance exercise is critical to those individuals striving to lose weight or reduce percent body fat. Our findings indicate that gross and net EE for the MS protocol is more than twice that of the SS protocol (135% increase) used in this study. These results support previous studies showing greater acute EE during MS protocols (8) although comparisons with other studies are difficult because of different resistance exercise protocols used. A few studies have investigated EE during acute SS protocols. Phillips et al. (21) reported an EE of 108.5 ± 30.9 kcal (4.5 ± 1.3 kcal·min−1) for a single set of 8 exercises using 15RM loading on resistance training machines. In a follow-up study, these authors reported lower EE values in older adults using a similar SS protocol (84.2 ± 14.6 kcals in men and 69.7 ± 17.4 in women) (22). These values in both studies (21,22) were greater than those observed in this study most likely because of a higher volume of work, performance of 3 additional exercises, and the inclusion of lower-body resistance exercises.
In direct comparison, Heden et al. (8) compared 1 vs. 3 sets of 10 exercises (total body, 10RM loading) in circuit manner with short rest intervals between sets and reported a mean EE for the SS protocol of 283 ± 38 kJ vs. 849 ± 134 kJ for the MS protocol, i.e., a 3 times greater EE in the MS compared with SS protocol. Haddock and Wilkin (7) reported EE values of 661.9 ± 43.9 kJ for a 3-set protocol versus 234.7 ± 13.4 kJ for a SS protocol. The higher magnitude of response could be attributed to the larger number of exercises, the use of lower-body (large muscle mass) exercises, and shorter rest intervals used compared with this study. Previous studies have shown that rest interval length (11,25,26) and exercise selection, i.e., upper versus lower body (26) significantly affect acute oxygen consumption and EE during resistance exercise. Kelleher et al. (11) reported greater acute resistance exercise EE during a protocol where supersets were used versus a traditional resistance exercise protocol. Ratamess et al. (25,26) have shown greater acute oxygen consumption and EE with short (i.e., 30 sec to 1 minute) vs. long (3–5 minutes) rest intervals and for a large muscle-mass exercise such as the squat compared with a smaller muscle-mass exercise such as the bench press. Thus, a combination of factors needs to be considered when examining acute EE response to resistance exercise.
A critical finding in this study was the lack of difference in the rate of EE between the SS and MS protocols. Our results support the study of Haddock and Wilkin (7) who also reported no difference in rate of EE between SS and MS protocols. These data indicate that the key difference between protocols is the volume and duration of resistance exercise. Interestingly, EE did not increase in proportion to the increase in volume load. The total protocol times were approximately 23 and 47 minutes for SS and MS, respectively, whereas actual lifting time was 2.5 and 7.5 minutes, respectively. The rise in EE was slightly more than doubled while volume load was 3 times higher in MS. This may be explained by the longer rest intervals seen between sets and exercise during the MS protocol. Other studies have shown that when viewing an entire protocol, short rest intervals increase rate of EE, whereas long rest intervals decrease the rate of EE (25,26).
Interestingly, gender differences were observed for all EE variables. Gross and net EE and the rates of EE were all significantly higher in men than women for both SS and MS protocols. In fact, gross EE was 47% and 43% higher (in SS and MS, respectively) and net EE was 61% and 56% higher (in SS and MS, respectively) in men compared with women. In young adults, Phillips et al. (21) reported EE values of 135.2 ± 16.6 kcals for men and 81.7 ± 11.1 kcals for women during a SS protocol. Thus, our results are consistent with previous research demonstrating a larger EE in men compared with women (2,18,20,21) but contrast with those who reported no significant differences between genders (19). A major contributor is LBM differences between genders. When EE is expressed relative to LBM, conflicting results have been reported where studies have found similar relative EE between genders (21) and one study found women had higher EE/LBM when expressed relative to exercise volume (19). In this study, we reported that men still had greater EE when expressed relative to LBM in both SS and MS trials. Our results are consistent with Ortego et al. (20) who examined circuit weight training in men and women and reported greater relative oxygen consumption values to LBM in men than women. These data expand the current literature base showing men may still have higher EE when expressed relative to LBM.
The MS protocol yielded a 10% higher relative V[Combining Dot Above]O2 and 6% higher RER than the SS protocol in this study. The relative V[Combining Dot Above]O2 data for the MS protocol were comparable with studies investigating rest interval lengths of 2–3 minutes during upper-body resistance exercise (25,26) but were lower compared with studies examining short rest intervals, circuit training protocols, or protocols involving large muscle-mass and lower-body exercises (2,25–27). Respiratory exchange ratio data for the MS protocol were similar to other studies investigating upper-body resistance exercise (25,26). Other studies have reported lower RER values during circuit resistance exercise, e.g., 0.91 to 1.01 (2,29). Thus, it appeared that the high anaerobic nature (and possible hypoxia due to breath-holding) of resistance exercise resulted in higher RER values particularly during the MS protocol, which also yielded a significantly higher V[Combining Dot Above]CO2 compared with the SS protocol.
The rise in V[Combining Dot Above]CO2 may have stimulated an increase in VE seen during upper-body resistance exercise. VE, RR, and VE/V[Combining Dot Above]O2 were significantly higher during the MS than SS protocol. Values for VE during the MS protocol fell within the range reported in the literature of 24–64 L·min−1 (1,3,25,26,30) albeit on the lower end. The higher response during the MS protocol may be indicative of greater fatigue induced by higher volume load and increased CO2, H+, temperature, and other neural factors. In addition, the HR response was also significantly higher during the MS protocol. These values were somewhat comparable with studies examining upper-body resistance exercise using at least 3-min rest intervals (26) but were lower than several studies examining resistance exercise using short rest intervals, circuit protocols, different loading and volume, or protocols involving larger muscle mass (9,10,23,25,29). These data indicate that the higher volume load of resistance exercise during the MS protocol provides a more potent cardiorespiratory stimulus than that observed during a SS protocol.
In conclusion, the salient finding from this study indicates that volume significantly affects the metabolic and cardiovascular responses to resistance exercise. The 5-exercise MS upper-body protocol used in this study produced more than double the gross and net EE than the SS protocol and higher RER, VE, relative V[Combining Dot Above]O2, VE/V[Combining Dot Above]O2, and HR. However, the rate of EE was not affected by resistance exercise volume. In addition, gender comparisons showed that men had significantly higher absolute and relative EE than women and these differences remained present when EE was expressed relative to LBM. These findings have direct implications with regard to resistance exercise prescription where increasing EE is a goal to potentially increase weight/body fat reductions. Further studies are warranted investigating EE of other resistance exercise protocols and mixed protocols combining different modalities of training.
This study provides quantitative evidence indicating an approximate doubling of EE when a 5-exercise MS resistance exercise protocol was used compared with a SS protocol. It has been recommended that exercise provide at least 150–200 kcal·d−1 of EE (21). Our data and results of previous studies (21,22) indicate that a typical SS protocol may be insufficient to meet the recommended daily exercise EE requirements unless several additional exercises are added to the program. The upper-body MS protocol used in this study met these requirements despite consisting of only 5 exercises. Thus, exercise professionals may use this information to carefully develop and prescribe resistance training programs targeting weight loss and/or body fat reductions through greater EE.
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