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Acute Cardiorespiratory and Metabolic Effects of a Sandbag Resistance Exercise Protocol

Ratamess, Nicholas A.; Kang, Jie; Kuper, Jeremy D.; O'Grady, Elizabeth A.; Ellis, Nicole L.; Vought, Ira T.; Culleton, Emma; Bush, Jill A.; Faigenbaum, Avery D.

The Journal of Strength & Conditioning Research: June 2018 - Volume 32 - Issue 6 - p 1491–1502
doi: 10.1519/JSC.0000000000002415
Original Research
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Ratamess, NA, Kang, J, Kuper, JD, O'Grady, EA, Ellis, NL, Vought, IT, Culleton, E, Bush, JA, and Faigenbaum, AD. Acute cardiorespiratory and metabolic effects of a sandbag resistance exercise protocol. J Strength Cond Res 32(6): 1491–1502, 2018—The purpose of this study was to examine the acute cardiorespiratory and metabolic effects of a sandbag (SB) resistance exercise protocol and compare the responses to time-matched treadmill running protocols. Eight healthy, resistance-trained men (21.1 ± 1.0 years; 86.1 ± 7.8 kg) completed 4 protocols of equal duration in random sequence: (a) SB, (b) treadmill running at 60% of V[Combining Dot Above]O2 reserve (60V[Combining Dot Above]O2R), (c) treadmill running at 80% of V[Combining Dot Above]O2 reserve (80V[Combining Dot Above]O2R), and (d) a control protocol. The SB protocol was 16 minutes in duration and consisted of 3 circuits of 8 multiple-joint exercises (with 11-, 20-, or 48-kg SBs) performed for as many repetitions as possible for 20 seconds followed by a 10-second rest interval before beginning the next exercise. Two minutes of rest was allowed between circuits. Breath-by-breath oxygen consumption (V[Combining Dot Above]O2) and heart rate (HR) were recorded throughout each protocol and for 30 minutes postexercise (PE) and blood lactate was determined before and immediately after each protocol. Blood lactate was significantly higher after SB compared with 60V[Combining Dot Above]O2R and 80V[Combining Dot Above]O2R. Mean and peak HR in SB was significantly higher than 60V[Combining Dot Above]O2R but not different from 80V[Combining Dot Above]O2R. Mean V[Combining Dot Above]O2 and energy expenditure (EE) in SB was significantly lower than 60V[Combining Dot Above]O2R and 80V[Combining Dot Above]O2R during each protocol but significantly higher after SB compared with 60V[Combining Dot Above]O2R and 80V[Combining Dot Above]O2R PE. Compared with 60V[Combining Dot Above]O2R and 80V[Combining Dot Above]O2R, respiratory exchange ratio was significantly higher during SB and through 5 minutes PE, but was significantly lower at 25–30 minutes PE after SB. Sandbag, as performed in this study, provides a superior metabolic stimulus to treadmill running during the PE period; however, the SB results demonstrate inferior EE compared with running at 60V[Combining Dot Above]O2R and 80V[Combining Dot Above]O2R.

Department of Health and Exercise Science, The College of New Jersey, Ewing, New Jersey

Address correspondence to Dr. Nicholas A. Ratamess, ratamess@tcnj.edu.

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Introduction

Metabolic training (i.e., high-intensity interval training) programs have become popular within the strength and conditioning and general fitness communities. Metabolic training programs integrate several modalities including resistance exercise (RE), speed, agility, and plyometric and aerobic forms of exercise that use large muscle-mass exercises performed almost continuously with very little rest in between sets (4,30,41). The integrated, continuous training structure performed with moderate to high intensities yield large cardiovascular and metabolic demands compared with traditional circuit structures (41) and has the capacity to improve several health- and skill-related fitness components (4,26,30). Studies have shown that these types of training programs can increase aerobic fitness, muscle strength, power, and endurance (4,26,30) and are popular, in part, because they are time efficient (11,30). Although many participants use metabolic training programs to increase muscle strength, hypertrophy, endurance, power, and motor performance, another primary goal for trainees is to augment energy expenditure (EE), thereby leading to greater potential body fat reductions. However, only few studies have examined EE during different metabolic training protocols.

The source of resistance for the RE component of metabolic training can vary dramatically. Resistance exercise embodies multiple forms of resistance including the most basic element of one's body weight to more elaborate forms such as free weights and related equipment, machines, elastic bands, whole-body vibration devices, ropes, kettlebells (KBs), and various types of strength implements (10,20,28,34,35). One such implement of resistance is a sandbag (SB).

Sandbags have long been advocated as a unique resistance training (RT) implement beneficial to strength training and conditioning (23,39). Sandbags vary in size and shape, provide unbalanced and unstable resistance, are believed to increase stabilizer muscle activation during exercise, and provide a potent stimulus for grip strength training (23,39). However, a recent study found no difference in core muscle activation between an SB and barbell clean and jerk (6). It has also been suggested that SBs may provide the athlete with a larger transfer of training effect to performance of occupational tasks (39). A large number of exercises can be performed with SBs especially because some models have handles which improve gripping capacity. However, the efficacy of SBs during RT remains relatively unknown. Wright et al. (45) developed an SB throw conditioning test for wrestlers consisting of 7 throws per minute for seven 1-minute rounds. Other studies have examined the use of SBs as a functional assessment tool for various types of timed carrying, dragging, and loading/stacking tasks (12,15,24,25,31,37). However, acute physiological responses and subsequent adaptations to SB training remain understudied.

Given the paucity of scientific information regarding SB RE, the purpose of this study was to quantify the metabolic and cardiovascular responses to a single SB RE protocol. A secondary purpose was to compare these responses to traditional running programs of similar duration at 60 and 80% of V[Combining Dot Above]O2 reserve. It was hypothesized that the SB protocol would elicit potent cardiorespiratory and metabolic responses comparable with running; however, it would provide augmented EE during the PE period.

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Methods

Experimental Approach to the Problem

To examine the primary hypothesis of the present investigation, subjects were pretested for V[Combining Dot Above]O2peak and flat treadmill running performance, and subsequently did a nonexercise control (CT) protocol plus 3 exercise protocols of similar duration (16 minutes): (a) an SB protocol performed for 3 sets of 8 exercises in circuit manner using Tabata intervals (42; where as many repetitions as possible were performed in 20 seconds followed by 10 seconds of rest); (b) treadmill running at 60% of V[Combining Dot Above]O2 reserve (V[Combining Dot Above]O2R); and (c) treadmill running at 80% of V[Combining Dot Above]O2R. Blood lactate was measured pre-exercise and PE, and oxygen consumption (V[Combining Dot Above]O2), heart rate (HR), and performance data were collected during each protocol. This study design enabled us to examine and quantify the acute cardiorespiratory and metabolic responses to an SB circuit RE protocol and compare these responses with 2 treadmill running protocols of similar duration.

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Subjects

Eight healthy, resistance-trained men (18-23 years old) agreed to participate in this study (Table 1). Each subject initiated the study in a trained state (i.e., were RT 2–4 days per week, but had limited experience using SBs) and none were taking any medications/supplements such as anabolic steroids known to affect RE performance. Subjects underwent one session of familiarization with study procedures before testing. Familiarization focused on subjects' ability to perform all the SB exercises with good technique. During this time, height was measured to the nearest 0.1 cm using a wall-mounted stadiometer and body mass was measured to the nearest 0.1 kg using an electronic scale. Percent body fat was estimated through a three-site skinfold test. The sites measured were the pectoral, anterior thigh, and abdominal skinfolds using methodology previously described (21). Body density was calculated using the equation of Jackson and Pollock (21) and percent body fat was calculated using the equation of Siri (40). The same research assistant performed all skinfold assessments. This study was approved by the College of New Jersey and each subject subsequently signed an informed consent document before participation. No subject had any physiological or orthopedic limitations that could have affected exercise performance as determined by completion of a health history questionnaire.

Table 1

Table 1

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Procedures

Peak Aerobic Capacity Testing

All subjects reported to the laboratory for maximal aerobic capacity testing. Subjects refrained from exercise for at least 24 hours before each testing session. V[Combining Dot Above]O2peak was assessed with a progressive, multistage ramp protocol on a treadmill using a metabolic data collection system (MedGraphics ULTIMA Metabolic System; MedGraphics Corporation, Saint Paul, MN, USA). It consisted of 2-minute stages at a speed of 6.0 mph with increments in percent grade of 2.5% per stage. All subjects were verbally encouraged to continue exercise until volitional exhaustion. Breath-by-breath V[Combining Dot Above]O2 data were obtained and V[Combining Dot Above]O2peak was determined by recording the highest measure. Gas analyzers were calibrated before each trial using gases and guidelines provided by the manufacturer (MedGraphics Corporation).

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Running Test

Approximately 48 hours after the V[Combining Dot Above]O2peak test, subjects performed a flat treadmill running test (0% grade) to establish velocities for the running protocols. It consisted of 2-minute stages (starting at 5.0 mph) with increments in velocity of 0.5 mph each stage (after a general warm-up of walking at 3.5 mph) and was terminated when subjects could no longer volitionally continue or achieve at least 90–95% of their V[Combining Dot Above]O2. All subjects were verbally encouraged to volitionally continue or achieve at least 90–95% of V[Combining Dot Above]O2peak. V[Combining Dot Above]O2 was obtained for each breath. Gas analyzers were calibrated before each trial using gases and guidelines provided by manufacturer (MedGraphics Corporation).

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Experimental Protocols

After baseline (BL) testing, each subject reported to the Human Performance Laboratory (HPL) at a standard time of day per subject on 4 occasions (in random sequence) separated by 48–72 hours and at least 2 hours postprandial. On arrival, subjects were weighed, fitted with a mask, and connected to the metabolic system after calibration with known gas levels (MedGraphics ULTIMA Metabolic System, MedGraphics Corporation), fitted with a Polar HR monitor (Polar Electro, Inc., Woodbury, NY, USA), provided a resting blood sample through a finger stick for determination of blood lactate, and sat quietly for 10 minutes for determination of pre-exercise resting V[Combining Dot Above]O2 and HR. Baseline V[Combining Dot Above]O2 data were obtained after the 10-minute resting period and recorded (and averaged) over a 3-minute period. During the familiarization period, V[Combining Dot Above]O2 data were collected on 2 occasions to determine test-retest reliability. Reliability was shown to be high for the metabolic measurements (r = 0.90).

In random sequence, subjects completed 1 of 4 protocols: (a) an SB RE protocol; (b) treadmill running at 60% of V[Combining Dot Above]O2 reserve (60V[Combining Dot Above]O2R); (c) treadmill running at 80% of V[Combining Dot Above]O2R (80V[Combining Dot Above]O2R); or (d) a nonexercise quiet sitting CT protocol. For the CT protocol, subjects remained seated for 46 minutes to match the duration of the exercise protocols (i.e., 16 minutes of exercise plus 30 minutes PE). Oxygen consumption and HR were measured throughout. Breath-by-breath relative V[Combining Dot Above]O2, respiratory exchange ratio (RER), minute ventilation (VE), and HR data were collected and averaged for the 16- and 30-minute periods, respectively.

For the exercise protocols, subjects reported to the HPL at a standardized time of day per subject at least 2 hours postprandial. On arrival, each subject was encouraged to drink water ad libitum to prehydrate and was fitted with a respiratory mask, Polar HR monitor, connected to the metabolic system, and sat quietly for 10 minutes for pre-exercise HR and V[Combining Dot Above]O2 measurements. Subjects subsequently performed a standard 5-minute warm-up consisting of light stretching and 5 minutes of treadmill walking at 4.0 mph.

The SB protocol was 16 minutes in duration and consisted of 3 circuits of 8 SB exercises (front squat, clean, bear hug squat, rotational deadlift [DL], rotational reverse lunge, lateral drag from a push-up position, shoulder-to-shoulder press, and shouldering from the floor) performed at a fast cadence (for as many repetitions as possible) for 20 seconds followed by a 10-second rest interval (RI) before beginning the next exercise (42). Two minutes of rest was allowed after each circuit. Each subject used a 48-kg SB for the first 4 exercises, and 11- or 20-kg SBs for the final 4 exercises (11 kg for the lateral drag and 20 kg for the remaining 3 exercises). The SBs had 5 handles for ease of gripping (Ultimate Sandbags; DVRT Ultimate Sandbag Fitness, Scottsdale, AZ, USA). Subjects were verbally encouraged throughout to maximize repetition performance. Proper exercise technique was used and only those repetitions that met the established criteria were counted. Total numbers of repetitions were counted and recorded, HR, ratings of perceived exertion (RPEs), and metabolic data (V[Combining Dot Above]O2, EE, RER, and VE) were collected. Subjects sat quietly for an additional 30 minutes to quantify the PE response.

The treadmill running protocols were performed at 0% grade and velocities corresponding to 60 and 80% of V[Combining Dot Above]O2R (determined by the flat running test), respectively, for an equal amount of time of 16 minutes to the SB protocol. Velocity was decreased as needed to target the respective V[Combining Dot Above]O2 as the protocol progressed. Breath-by-breath V[Combining Dot Above]O2 and HR were recorded throughout each protocol and for 30 minutes PE.

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Metabolic and Cardiorespiratory Measurements

Heart rate, absolute V[Combining Dot Above]O2, relative V[Combining Dot Above]O2, RER, and VE data were recorded during each protocol. Individual breath-by-breath data points for all metabolic variables were averaged for the entire circuit and for each minute of rest in between sets for the SB protocol and averaged for the entire exercise and 5-minute PE periods during the running protocols. The time corresponding to the initiation of each set, the time of the completion of each set, and the RI length between sets were precisely recorded and used subsequently for determination of each phase of the protocols. Heart rate was measured after each set of each exercise and RI during the SB protocol and each minute during the running protocols. Data were averaged for the entire protocol and for each 5-minute interval PE. Gross EE in kcals per min for each protocol was estimated by multiplying absolute V[Combining Dot Above]O2 (L·min−1) by 5.05 kcal·L−1 when all RER values were ≥1.0. For RER values during exercise or rest ranging from 0.85 to 0.98, V[Combining Dot Above]O2 (L·min−1) was multiplied by 4.86–4.98 kcal·L−1, respectively. Pre-exercise (BL) EE was estimated by multiplying absolute V[Combining Dot Above]O2 (L·min−1) by 4.80 kcal·L−1 to match BL RER. In addition, EE was also expressed in kJ. Aerobic EE was estimated at 1 LO2 = 21.1 kJ (38) for RER values ≥1.00 or 1 L O2 = 20.1–20.8 kJ for resting or PE data where RER values were between 0.86 and 0.95. Anaerobic EE for the entire protocol was estimated from blood lactate concentrations using the following equation (8,38): EE (kJ) = Δ[LA] × body mass (kg) × 3 ml O2. Data were converted to L O2 and multiplied by 21.1 kJ. Total EE was calculated by summing aerobic EE, anaerobic EE, and PE EE. Energy expenditure per minute was calculated by dividing total EE by the protocol (exercise and PE) duration.

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Blood Lactate and Ratings of Perceived Exertion

Whole blood lactate was assessed in duplicate using a portable lactate analyzer (Lactate Plus Meter; Nova Biomedical, Waltham, MA, USA) taken at the fingertip using a sterile lancet. Blood lactate samples were taken at rest and immediately after each exercise/CT protocol. Reliability of this analyzer has been shown to be high (19). After each set of SB exercise, RPE were obtained using a 10-point (0–10) scale. After each min of running RPEs were obtained using a Borg 15-point (6–20) scale. Each RPE scale was used to examine time effects within each protocol and not used to compare the running protocols with the SB protocol.

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Statistical Analyses

Descriptive statistics (mean ± SD) were calculated for all dependent variables. A 2-way (time point × protocol) analysis of variance with repeated measures was used to analyze within-subject performance, V[Combining Dot Above]O2, RPE, HR, and lactate data. Subsequent Tukey's post hoc tests were used to determine differences when significant main effects were obtained. Partial eta-square (η2) effect sizes were determined for treatment effects and interpreted using the following criteria: 0.01 = small; 0.06 = medium; and 0.13 = large. For all statistical tests, a probability level of p ≤ 0.05 denoted statistical significance.

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Results

Exercise Performance

Treadmill running velocities were significantly reduced (p < 0.001) by 12 and 18%, respectively, for 60V[Combining Dot Above]O2R and 80V[Combining Dot Above]O2R, from the start to the completion of each protocol to maintain the targeted V[Combining Dot Above]O2 values. Treadmill running velocities were reduced from 2.5 ± 0.2 (range = 2.2–2.7) and 3.3 ± 0.5 (range = 2.7–3.6) m·s−1 for 60V[Combining Dot Above]O2R and 80V[Combining Dot Above]O2R, respectively, to 2.2 ± 0.3 (range = 1.8–2.4) and 2.7 ± 0.5 (range = 2.1–3.4) m·s−1 from beginning to the end of each running protocol. Repetition performance data are presented in Table 2. A significant time effect (p < 0.001; η2 = 0.50) was observed where repetition performance declined from set 1 to set 3 for most exercises. Most notable reductions were seen in the front squat, bear hug squat, rotational DL, and lateral drag exercises.

Table 2

Table 2

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Blood Lactate

Blood lactate results are presented in Figure 1. A significant time effect was observed (p < 0.001; η2 = 0.96) where blood lactate concentrations were significantly elevated immediately PE after the SB, 60V[Combining Dot Above]O2R, and 80V[Combining Dot Above]O2R protocols. In addition, a significant interaction was observed (p < 0.001) where blood lactate concentrations after the SB protocol were significantly higher than 60V[Combining Dot Above]O2R and 80V[Combining Dot Above]O2R. In addition, blood lactate concentration after the 80V[Combining Dot Above]O2R protocol was significantly higher than 60V[Combining Dot Above]O2R.

Figure 1

Figure 1

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Oxygen Consumption

Mean V[Combining Dot Above]O2 results are presented in Figure 2. A significant protocol effect was observed (p < 0.001; η2 = 0.98) where the 80V[Combining Dot Above]O2R protocol was significantly higher than all protocols. The 60V[Combining Dot Above]O2R protocol was significantly higher than SB and CT and SB was significantly higher than CT. A significant PE effect was observed (p < 0.001; η2 = 0.86) where the SB protocol was significantly higher than all protocols. No significant difference was observed between 60V[Combining Dot Above]O2R and 80V[Combining Dot Above]O2R (p = 0.09); however, both of these protocols were significantly higher than CT.

Figure 2

Figure 2

Mean V[Combining Dot Above]O2 results for the SB protocol are presented in Figure 3. Significant time effects were observed from beginning to completion of the protocol (p < 0.001; η2 = 0.94). All exercise and PE values were significantly higher than BL. V[Combining Dot Above]O2 was significantly highest during each set (S1, S2, and S3) and first min of rest (R1 and PE1) compared with R2. The highest mean value was seen during S2 (p = 0.001). All PE values were significantly higher than BL. V[Combining Dot Above]O2 during PE significantly decreased from PE1 to PE20, whereas no significant further decreases were observed between PE20 and PE30. Peak V[Combining Dot Above]O2 values obtained during SB (38.7 ± 7.5 ml·kg−1·min−1) averaged ∼83% of V[Combining Dot Above]O2peak, whereas mean V[Combining Dot Above]O2 values obtained during the SB protocol (24.6 ± 4.3 ml·kg−1·min−1) averaged ∼53% of V[Combining Dot Above]O2peak.

Figure 3

Figure 3

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Heart Rate

Heart rate values were significantly elevated during all exercise and PE trials (p < 0.001; η2 = 0.97). Compared with CT (65.9 ± 14.0 b·min−1), mean exercise HR values were significantly higher during the SB (169.7 ± 11.2 b·min−1), 60V[Combining Dot Above]O2R (151.8 ± 9.8 b·min−1), and 80V[Combining Dot Above]O2R (170.5 ± 13.5 b·min−1) protocols. No significant differences were observed between SB and 80V[Combining Dot Above]O2R, although both protocols yielded significantly higher HR values than 60V[Combining Dot Above]O2R. Similar results were observed for peak HR (SB = 183.0 ± 8.7 b·min−1; 60V[Combining Dot Above]O2R = 160.4 ± 11.8 b·min−1; and 80V[Combining Dot Above]O2R = 177.4 ± 14.4 b·min−1). Mean HR during the 30-minute PE period in SB (116.7 ± 14.1 b·min−1) was significantly higher than 60V[Combining Dot Above]O2R (87.6 ± 13.1 b·min−1) and 80V[Combining Dot Above]O2R (101.5 ± 9.5 b·min−1) and mean HR in 80V[Combining Dot Above]O2R was significantly higher than 60V[Combining Dot Above]O2R.

The acute HR responses to the SB protocol are presented in Figure 4. A significant time effect was observed (p < 0.001; η2 = 0.94). All exercise and PE values were significantly higher than BL. Heart rate values significantly increased from the first exercise (E1) to completion of the last exercise (E8) for each of the 3 sets. Heart rate values seen during the RIs (R1 and R2) were significantly lower than all exercise values with the exception of the first exercise of the first set. Heart rate values seen during the first set for each exercise were significantly lower than the HR values of corresponding exercise seen during sets 2 and 3. No significant differences were observed for individual exercise HRs between sets 2 and 3. Heart rate decreased significantly from PE1 to PE10, from PE15 to PE 20, and from PE25 to PE30.

Figure 4

Figure 4

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Energy Expenditure

Energy expenditure data are presented in Table 3. Significant exercise (kcals·min−1) protocol (p < 0.001; η2 = 0.98) and PE (p < 0.001; η2 = 0.80) effects were observed. All exercise values were significantly higher than CT. Acute EE during 80V[Combining Dot Above]O2R was significantly higher than 60V[Combining Dot Above]O2R and SB and the EE response during 60V[Combining Dot Above]O2R was significantly higher than SB. During the PE period, EE was significantly higher in SB than in 60V[Combining Dot Above]O2R and 80V[Combining Dot Above]O2R whereas no differences in EE were observed between 60V[Combining Dot Above]O2R and 80V[Combining Dot Above]O2R. All PE exercise EE values were significantly higher than those of CT.

Table 3

Table 3

Significant running EE (kcals and kJ) protocol effects were observed during exercise (p < 0.001; η2 = 0.97), PE (p < 0.001; η2 = 0.86), and total kcals of EE combined (p < 0.001; η2 = 0.96). During exercise, all EE values were significantly higher than those of CT. Acute EE during 80V[Combining Dot Above]O2R was significantly higher than during 60V[Combining Dot Above]O2R and SB and the EE response during 60V[Combining Dot Above]O2R was significantly higher than during SB. During the PE period, EE was significantly higher in SB than in 60V[Combining Dot Above]O2R and 80V[Combining Dot Above]O2R, whereas no differences in EE were observed between 60V[Combining Dot Above]O2R and 80V[Combining Dot Above]O2R. All PE exercise EE values were significantly higher than those of CT. Total EE was significantly higher in 80V[Combining Dot Above]O2R compared with 60V[Combining Dot Above]O2R and SB, whereas no significant differences were observed between 60V[Combining Dot Above]O2R and SB. A significant exercise protocol effect (p < 0.001; η2 = 0.92) was observed for anaerobic EE (kJ) where EE in SB was significantly higher than in 60V[Combining Dot Above]O2R and 80V[Combining Dot Above]O2R and EE in 80V[Combining Dot Above]O2R was significantly higher than in 60V[Combining Dot Above]O2R.

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Ventilation

Significant mean (p < 0.001; η2 = 0.96) and peak (p < 0.001; η2 = 0.97) exercise protocol and mean PE (p < 0.001; η2 = 0.88) responses were observed. Mean exercise VE values for SB (86.7 ± 11.8 L·min−1), 60V[Combining Dot Above]O2R (65.3 ± 9.2 L·min−1), and 80V[Combining Dot Above]O2R (92.0 ± 16.0 L·min−1) were significantly higher than those for CT (8.9 ± 1.2 L·min−1). In addition, peak exercise VE values for SB (102.7 ± 14.1 L·min−1), 60V[Combining Dot Above]O2R (73.3 ± 9.7 L·min−1), and 80V[Combining Dot Above]O2R (101.2 ± 14.1 L·min−1) were significantly higher than those for CT (9.6 ± 1.3 L·min−1). Mean and peak VE values during SB and 80V[Combining Dot Above]O2R were significantly higher than during 60V[Combining Dot Above]O2R, whereas no significant difference was observed between SB and 80V[Combining Dot Above]O2R (p = 0.34 and 0.58, respectively). Mean PE VE values for SB (35.4 ± 8.4 L·min−1), 60V[Combining Dot Above]O2R (17.1 ± 4.4 L·min−1), and 80V[Combining Dot Above]O2R (21.6 ± 3.5 L·min−1) were significantly higher than CT (8.8 ± 1.2 L·min−1). Mean PE VE values after SB were significantly higher than after 60V[Combining Dot Above]O2R and 80V[Combining Dot Above]O2R and PE VE values in 80V[Combining Dot Above]O2R were significantly higher than in 60V[Combining Dot Above]O2R.

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Respiratory Exchange Ratio

Acute RER responses are shown in Figure 5. A significant time and protocol effect was observed (p < 0.001; η2 = 0.85). Respiratory exchange ratio values observed during SB, 60V[Combining Dot Above]O2R, and 80V[Combining Dot Above]O2R were significantly higher than those of CT (and from BL) during exercise and through 15 minutes PE. During exercise and at PE5, RER values seen during SB were significantly larger than the values seen during 60V[Combining Dot Above]O2R and 80V[Combining Dot Above]O2R. No significant differences were observed between 60V[Combining Dot Above]O2R and 80V[Combining Dot Above]O2R during exercise (p = 0.58) or PE5 (p = 0.21). Respiratory exchange ratio values seen between PE10 and PE20 did not significantly differ between exercise conditions. However, RER values obtained during SB at PE25 and PE30 were significantly lower than values obtained during CT, 60V[Combining Dot Above]O2R, and 80V[Combining Dot Above]O2R (with no significant differences observed between 60V[Combining Dot Above]O2R and 80V[Combining Dot Above]O2R).

Figure 5

Figure 5

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Ratings of Perceived Exertion

Data on RPE for the SB protocol are presented in Table 4. A significant time effect was observed (p < 0.001; η2 = 0.65). Values of RPE significantly increased from set 1 to set 3 in all exercises and increased significantly from set 1 to set 2 in all but 2 exercises (clean and bear hug squat). Significant increases in RPE were observed from set 2 to set 3 in all but 1 of the exercises (lunge with rotation). Highest mean RPE values were seen for the bear hug squat, rotational DL, overhead press, and shouldering exercises. The mean RPE for the entire SB protocol was 7.92 ± 1.0. For the running protocols (on a 15-point 6 to 20 Borg RPE scale), mean RPE for the 80V[Combining Dot Above]O2R protocol (12.9 ± 1.1) was significantly higher (p = 0.004; η2 = 0.71) than that of the 60V[Combining Dot Above]O2R protocol (10.1 ± 1.4).

Table 4

Table 4

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Discussion

The salient finding from this study was that the SB protocol elicited a substantial cardiorespiratory and metabolic stimulus. It was hypothesized that the SB protocol would elicit potent cardiorespiratory and metabolic responses comparable with running; however, it would provide augmented EE during the PE period. Although mean V[Combining Dot Above]O2 and EE seen during the SB protocol was significantly lower than those seen during the 60V[Combining Dot Above]O2R and 80V[Combining Dot Above]O2R protocols, mean V[Combining Dot Above]O2 and EE were significantly higher after the SB protocol compared with 60V[Combining Dot Above]O2R and 80V[Combining Dot Above]O2R during the 30-minute PE period. Total EE (exercise and PE) was significantly higher in 80V[Combining Dot Above]O2R compared with 60V[Combining Dot Above]O2R and SB; however, the SB protocol produced similar total EE as 60V[Combining Dot Above]O2R. Mean HR during SB protocol was significantly higher than that during 60V[Combining Dot Above]O2R but not different from 80V[Combining Dot Above]O2R. Compared with 60V[Combining Dot Above]O2R and 80V[Combining Dot Above]O2R, RER was significantly higher during the SB protocol and through 5 minutes PE, but was significantly lower at 25–30 minutes PE. Ratings of perceived exertion observed during the SB protocol increased significantly with each set yielding high mean protocol RPE values comparable with other circuit RE protocols (41). These data show that performing SB RE with Tabata intervals poses a significant cardiorespiratory stress similar to running at 80% of V[Combining Dot Above]O2R and provides superior EE during the PE period. However, continuous running protocols seem to maximize EE observed during exercise.

The blood lactate response seen during the SB protocol was 4.9 times greater than 60V[Combining Dot Above]O2R and 1.9 times greater than 80V[Combining Dot Above]O2R. This was not surprising considering the intense anaerobic nature of RE and subsequent greater recruitment of fast-twitch muscle fibers. Previous studies have shown relatively high lactate responses during circuit RE (1,13,41) with the responses lower than the lactate concentrations (∼17.5 mmol·L−1) observed in this study. Wright et al. (45) reported blood lactate concentrations of up to 13.4 mmol·L−1 during a 7-minute SB conditioning test in wrestlers. The lactate response observed during the SB protocol was greater than another study examining a protocol consisting of KB swings using Tabata intervals (11) and previous studies from our laboratory examining traditional RE after aerobic exercise (36) and battling rope protocols (34,36). Although differences in protocol design, subject physical characteristics, and technology of lactate assessment contribute significantly to the lactate responses seen during RE, a critical element to the present SB protocol was the use of Tabata intervals (42). Other studies have examined Tabata intervals during RE primarily using KB swings (11,44) and other KB exercises (44) and reported lower blood lactate concentrations (11) than this study. Our protocol emphasized performance with as many repetitions as possible per set (as opposed to a standard number) and very short 10-second RIs (with the exception of the 2-minute intercircuit RIs). The 20-second set durations coupled with only 10 seconds of rest during each circuit (and use of several large muscle-mass exercises with heavy SBs) likely accounted for the large lactate response and indicates that an SB RE protocol consisting of Tabata intervals (42) provides a substantial anaerobic stimulus to trainees.

The SB protocol yielded a mean EE of ∼11 kcals·min−1, and ∼795 kJ in 16 minutes, slightly higher EE values than a previous study (∼9.5 kcals·min−1) examining a KB protocol using Tabata intervals (44). However, these mean V[Combining Dot Above]O2 and EE data were significantly lower than the running protocols. Mean EE was 17 and 36% lower during the SB protocol compared with 60V[Combining Dot Above]O2R and 80V[Combining Dot Above]O2R, respectively, encompassing a range seen in other studies comparing aerobic exercise to KB protocols (20). This confirms other reports demonstrating the superiority of continuous aerobic exercise in augmenting the acute V[Combining Dot Above]O2 and EE responses to exercise (2,9,16,20). Bloomer (2) compared cycling at 70% of V[Combining Dot Above]O2 max to traditional RE (squats; 60–70% of 1RM with 90–120 seconds RIs) for 30 minutes and reported a 39% difference in EE of 442 and 269 kcal, respectively. Elliot et al. (9) reported EE of ∼432, 362, and 248 kcals during 40 minutes of cycling (80% of HRmax), circuit RE (4 sets of 15 repetitions with 50% of 1RM), and traditional RE (3 sets of 3–8 repetitions with 80–90% of 1RM). Hulsey et al. (20) reported EE of ∼12.5 and 17.1 kcals·min−1, respectively, for a 10-minute KB swing workout (35 seconds of work followed by 25 seconds of rest) compared with a 10-minute treadmill run at a matched RPE.

Although the gap in EE between aerobic and RE was narrowed in this study, the continuity of aerobic exercise seems to be a key variable to maximizing the acute EE responses. Our data (Figure 3) show that relative V[Combining Dot Above]O2 was mostly maintained during RE and the 1st minute of rest; however, it declined significantly during the 2nd minute of rest. Peak V[Combining Dot Above]O2 values obtained during the SB protocol (∼38.7 ml·kg−1·min−1) averaged ∼83% of V[Combining Dot Above]O2peak, whereas mean V[Combining Dot Above]O2 values (∼24.6 ml·kg−1·min−1) averaged ∼53% of V[Combining Dot Above]O2peak. These mean relative V[Combining Dot Above]O2 values were less than a KB swing workout (∼34.1 ml·kg−1·min−1) with no major RI between rounds (20), but higher than a KB protocol (∼22.6 ml·kg−1·min−1) consisting of Tabata intervals with no major RI between rounds (44). It seems that the V[Combining Dot Above]O2 reductions seen during extended RIs during RE may negatively impact total EE. However, when total EE was calculated to include anaerobic contributions and the PE response, no significant differences in EE were seen between the SB and 60V[Combining Dot Above]O2R protocols (despite slightly higher values observed during the SB protocol), thereby indicating that running beyond 60% of V[Combining Dot Above]O2peak was needed to augment EE compared with the SB protocol used in this study.

A noteworthy finding was that V[Combining Dot Above]O2 and EE after the SB protocol was significantly greater than PE 60V[Combining Dot Above]O2R and PE 80V[Combining Dot Above]O2R. Energy expenditure after the SB protocol was 33 and 17.6% greater than 60V[Combining Dot Above]O2R and 80V[Combining Dot Above]O2R, respectively, during the 30-minute PE period. In addition, SB RER values at 25 and 30 minutes PE were significantly lower than CT, 60V[Combining Dot Above]O2R, and 80V[Combining Dot Above]O2R, indicative of greater fat oxidation toward the latter end of the recovery period. These data indicate that the intense anaerobic nature of this SB protocol may have had its largest impact during the PE period. These data support previous findings indicating that the most substantial PE response will be elicited by an anaerobic stress with a high degree of perturbation (3). The rise in PE V[Combining Dot Above]O2 has been attributed to elevated blood lactate levels, reduced pH, glycogen resynthesis, elevated temperature, oxygen replacement in muscle and circulation, ATP-PC resynthesis, sodium-potassium pump activity, cardiovascular demand, increased VE, triglyceride-fatty acid cycling, tissue damage and PE elevations in protein synthesis, elevated sympathetic nervous system activity, and acute hormonal elevations (i.e., catecholamines, cortisol, thyroid hormones, and the superfamily of growth hormones) (3,18,43).

Previous studies have shown that RE elicits a substantial PE response (3,9,27,32), and the response is greater than that of aerobic exercise (5,9,14). The interaction of the RE selection of exercises (and muscle-mass involvement), intensity, volume, and RI length between sets and exercises seems to govern the magnitude of the PE response (9,17,18,29), and the response may be greater with circuit-type protocols. Haltom et al. (18) compared circuit training with 20- or 60-second RI and reported a ∼28% greater PE response over 1 hour for the 20-second protocol. Murphy and Schwarzkopf (29) compared traditional RE with circuit training protocol and reported greater PE response after circuit training. Kelleher et al. (22) reported greater EE during the PE period when supersets were used to reduce workout time compared with a traditional set scheme matched for exercise selection, loading, and volume. However, Elliot et al. (9) reported similar EE during the PE period after circuit and traditional RE. It has been suggested that the lack of recovery in between sets of circuit RE increases the PE EE response (7). Our data confirm the findings of augmented PE EE and demonstrate that a time-efficient SB protocol using Tabata intervals elicits a superior PE EE response to treadmill running of up to 80% of V[Combining Dot Above]O2R; however, further research is warranted examining extended PE periods beyond 30 minutes.

Our results indicated that this SB protocol elicited a substantial rise in mean HR, similar to values observed during the 80V[Combining Dot Above]O2R protocol. The mean HR value seen during the SB protocol is higher (2,9,11,44), similar to (10,41), and lower (16,20) than some HR values seen in other studies examining circuit RE or continuous RE protocols, and is lower than mean HR reported during a 7-minute SB throw test (45). This SB protocol yielded a mean HR equivalent to ∼86% of HRmax in our subject pool, which is similar to or slightly lower than HR observed during 10–12 minutes of continuous or interval KB swings (10,20), a level capable of eliciting cardiovascular improvements over time (20,26). Considering that other studies examining circuit RT have reported improved cardiorespiratory fitness (4,26,30), it is possible that aerobic fitness improvements may occur using a program such as the one used in this study. McRae et al. (26) examined 4 weeks of circuit training consisting of 8 sets of Tabata intervals performed for one body mass exercise per workout (either burpees, mountain climber, squat and thrusts, or jumping jacks) and reported an 8% increase in V[Combining Dot Above]O2max, which was similar to improvements seen with 30-minute treadmill running program. Thus, the intense nature of this training structure seems to be a sufficient stimulus to improve cardiorespiratory fitness in addition to increasing muscle strength, power, and endurance (4,26,30).

Mean exercise VE values for the SB (∼87 L·min−1) and 80V[Combining Dot Above]O2R (∼92 L·min−1) protocols were significantly higher than those of 60V[Combining Dot Above]O2R (∼65 L·min−1). Several studies examining acute VE responses to RE have shown values in the range of 18–70 L·min−1 (2,5,33,43). Williams and Kraemer (44) reported VE values ranging from ∼40 to 65 L·min−1 during a KB protocol consisting of Tabata intervals. The VE data seen in this study were more comparable with studies examining battling rope protocols (34,35). These data indicate that the SB protocol used in this study elicited a substantial VE response comparable with running at 80% of V[Combining Dot Above]O2peak.

A possible limitation of this study was that only a limited number of SBs were available for use (i.e., only 3 weights were used for performance of the 8 exercises). The goal was to study SBs in a way they are commonly used in RT and often facilities may be limited to few SBs of various size. It is likely that the use of lighter or heavier bags per exercise could have influenced the total numbers of repetitions performed and possibly other metabolic or cardiovascular variables. Pilot work from our laboratory indicated that all subjects were comfortably able to tolerate the SB weights per exercise during nonfatigued and partially-fatigued conditions. Given the continuous nature of metabolic training protocols and high levels of fatigue induced, we chose to use an SB mass of ∼55% of body mass for the first 4 exercises and ∼13–24% of body mass for the last 4 exercises. It is important to note that continuous metabolic programs such as the one used in this study make it difficult to use several pieces of equipment, especially when performed in group settings. In fact, other studies using Tabata intervals or similar quasi-continuous protocols during RE (primarily with KBs) have used either one size KB for men and women (11,20) or a narrow range of sizes (44). However, performing as many repetitions as possible per exercise increases the metabolic demand despite the absolute or relative level of loading used per exercise. Thus, the results of this study must be viewed within the context of the exercises selected, the masses of SBs used, and the use of Tabata intervals (42).

In summary, to the best of our knowledge, this was the first study to quantify acute metabolic responses to an RE protocol consisting entirely of SB exercises. The SB protocol using Tabata intervals elicited a substantial cardiorespiratory and metabolic stimulus as indicated by high mean HR, RPE, and blood lactate responses. Although the aerobic treadmill running protocols elicited greater mean V[Combining Dot Above]O2 and EE responses during exercise, the SB protocol elicited a significantly greater EE during the PE period, thereby demonstrating potential advantages for aerobic and anaerobic fitness improvements.

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Practical Applications

Strength and conditioning and fitness professionals constantly seek alternative methods to improve health- and skill-related components of fitness. In some instances, time efficiency may be needed. Therefore, programs that combine multiple exercise modalities may serve as an attractive alternative. The use of metabolic programs, or high-intensity interval training, has increased over recent years because of the combined integration of several modalities that can improve several fitness components in a time-efficient manner (4,26,30). The use of SBs in metabolic training programs has also increased because they provide an unstable form of resistance and could be used to mimic many movements seen in sports, daily living, or in tactical occupations. The results of this study demonstrated that the SB RE protocol provided a large cardiorespiratory and metabolic stimulus that could potentially enhance several components of fitness in resistance-trained adults. It also demonstrated that few SBs can be used to design a time-efficient circuit that could serve as an alternative or supplemental form of RT.

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Acknowledgments

The authors thank a dedicated group of subjects and laboratory assistants for their participation in this study. Funding was provided by The School of Nursing, Health & Exercise Science Seed Grant at TCNJ.

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References

1. Abel MG, Mortara AJ, Pettitt RW. Evaluation of circuit-training intensity for firefighters. J Strength Cond Res 25: 2895–2901, 2011.
2. Bloomer RJ. Energy cost of moderate-duration resistance and aerobic exercise. J Strength Cond Res 19: 878–882, 2005.
3. Borsheim E, Bahr R. Effect of exercise intensity, duration and mode on post-exercise oxygen consumption. Sports Med 33: 1037–1060, 2003.
4. Buckley S, Knapp K, Lackie A, Lewry C, Horey K, Benko C, Trinh J, Butcher S. Multimodal high-intensity interval training increases muscle function and metabolic performance in females. Appl Physiol Nutr Metab 40: 1157–1162, 2015.
5. Burleson MA, O'Bryant HS, Stone MH, Collins MA, Triplett-McBride T. Effect of weight training exercise and treadmill exercise on post-exercise oxygen consumption. Med Sci Sports Exerc 30: 518–522, 1998.
6. Calatayud J, Colado JC, Martin F, Casana J, Jakobsen MD, Andersen LL. Core muscle activity during the clean and jerk lift with barbell versus sandbags and water bags. Int J Sports Phys Ther 10: 803–810, 2015.
7. Da Silva RL, Brentano MA, Kruel LFM. Effects of different strength training methods on postexercise energetic expenditure. J Strength Cond Res 24: 2255–2260, 2010.
8. di Prampero PE, Ferretti G. The energetics of anaerobic muscle metabolism: A reappraisal of older and recent concepts. Respir Physiol 118: 103–115, 1999.
9. Elliot DL, Goldberg L, Kuehl KS. Effect of resistance training on excess post-exercise oxygen consumption. J Appl Sport Sci Res 6: 77–81, 1992.
10. Farrar RE, Mayhew JL, Koch AJ. Oxygen costs of kettlebell swings. J Strength Cond Res 24: 1034–1036, 2010.
11. Fortner HA, Salgado JM, Holmstrup AM, Holmstrup ME. Cardiovascular and metabolic demands of the kettlebell swing using tabata interval versus a traditional resistance protocol. Int J Ex Sci 7: 179–185, 2014.
12. Foulis SA, Redmond JE, Frykman PN, Warr MB, Zambraski EJ, Sharp MA. U.S. Army physical demands study: Reliability of simulations of physically demanding tasks performed by combat arms soldiers. J Strength Cond Res 31: 3245–3252, 2017.
13. Garbutt G, Boocock MG, Reilly T, Troup JD. Physiological and spinal responses to circuit weight-training. Ergonomics 37: 117–125, 1994.
14. Gillette CA, Bullough RC, Melby CL. Postexercise energy expenditure in response to acute aerobic or resistive exercise. Int J Sport Nutr 4: 347–360, 1994.
15. Gillingham RL, Keefe AA, Tikuisis P. Acute caffeine intake before and after fatiguing exercise improves target shooting engagement time. Aviat Space Environ Med 75: 865–871, 2004.
16. Gotshalk LA, Berger RA, Kraemer WJ. Cardiovascular responses to a high-volume continuous circuit resistance training protocol. J Strength Cond Res 18: 760–764, 2004.
17. Haddock BL, Wilkin LD. Resistance training volume and post exercise energy expenditure. Int J Sports Med 27: 143–148, 2006.
18. Haltom RW, Kraemer RR, Sloan RA, Hebert EP, Frank K, Tryniecki JL. Circuit weight training and its effects on excess postexercise oxygen consumption. Med Sci Sports Exerc 31: 1613–1618, 1999.
19. Hart S, Drevets K, Alford M, Salacinski A, Hunt BE. A method-comparison study regarding the validity and reliability of the lactate plus analyzer. BMJ Open 3: e001899, 2013.
20. Hulsey CR, Soto DT, Koch AJ, Mayhew JL. Comparison of kettlebell swings and treadmill running at equivalent rating of perceived exertion values. J Strength Cond Res 26: 1203–1207, 2012.
21. Jackson A, Pollock M. Generalized equations for predicting body density of men. Br J Nutr 40: 497–504, 1978.
22. Kelleher AR, Hackney KJ, Fairchild TJ, Keslacy S, Ploutz-Snyder LL. The metabolic cost of reciprocal supersets vs. traditional resistance exercise in young recreationally active adults. J Strength Cond Res 24: 1043–1051, 2010.
23. Kubik BD. Dinosaur Training: Lost Secrets of Strength and Development. Louisville, KY: self-published by BD Kubik, 1996. pp. 112–120.
24. Lenton G, Aisbett B, Neesham-Smith D, Carvajal A, Netto K. The effects of military body armour on trunk and hip kinematics during performance of manual handling tasks. Ergonomics 59: 806–812, 2016.
25. McLellan TM, Bell DG, Kamimori GH. Caffeine improves physical performance during 24 h of active wakefulness. Aviat Space Environ Med 75: 666–672, 2004.
26. McRae G, Payne A, Zelt JGE, Scribbans TD, Jung ME, Little JP, Gurd BJ. Extremely low volume, whole-body aerobic-resistance training improves aerobic fitness and muscular endurance in females. Appl Physiol Nutr Metab 37: 1124–1131, 2012.
27. Melby C, Scholl C, Edwards G, Bullough R. Effect of acute resistance exercise on postexercise energy expenditure and resting metabolic rate. J Appl Physiol 75: 1847–1853, 1993.
28. Mendes R, Sousa N, Garrido N, Cavaco B, Quaresma L, Reis VM. Can a single session of a community-based group exercise program combining step aerobics and bodyweight resistance exercise acutely reduce blood pressure? J Hum Kin 43: 49–56, 2014.
29. Murphy E, Schwarzkopf R. Effects of standard set and circuit weight training on excess post-exercise oxygen consumption. J Appl Sport Sci Res 6: 88–91, 1992.
30. Myers TR, Schneider MG, Schmale MS, Hazell TJ. Whole-body aerobic resistance training circuit improves aerobic fitness and muscle strength in sedentary young females. J Strength Cond Res 29: 1592–1600, 2015.
31. O'Hara R, Vojta C, Henry A, Caldwell L, Wade M, Swanton S, Linderman JK, Ordway J. Effects of a new cooling technology on physical performance in US Air Force military personnel. J Spec Oper Med 16: 57–61, 2016.
32. Olds TS, Abernethy PJ. Postexercise oxygen consumption following heavy and light resistance exercise. J Strength Cond Res 7: 147–152, 1993.
33. Ratamess NA, Rosenberg JG, Kang J, Sundberg S, Izer KA, Levowsky J, Rzeszutko C, Ross RE, Faigenbaum AD. Acute oxygen uptake and resistance exercise performance using different rest interval lengths: The influence of maximal aerobic capacity and exercise sequence. J Strength Cond Res 28: 1875–1888, 2014.
34. Ratamess NA, Rosenberg JG, Klei S, Dougherty BM, Kang J, Smith C, Ross RE, Faigenbaum AD. Comparison of the acute metabolic responses to traditional resistance, body-weight, and battling rope exercises. J Strength Cond Res 29: 47–57, 2015.
35. Ratamess NA, Smith CR, Beller NA, Kang J, Faigenbaum AD, Bush JA. The effects of rest interval length on acute battling rope exercise metabolism. J Strength Cond Res 29: 2375–2387, 2015.
36. Ratamess NA, Kang J, Porfido TM, Ismaili C, Selamie S, Williams B, Kuper JD, Bush JA, Faigenbaum AD. Acute resistance exercise performance is negatively impacted by prior aerobic endurance exercise. J Strength Cond Res 30: 2667–2681, 2016.
37. Reilly T, Spivock M, Prayal-Brown A, Stockbrugger B, Blacklock R. The influence of anthropometrics on physical employment standard performance. Occup Med (Lond) 66: 576–579, 2016.
38. Scott CB. Contribution of blood lactate to the energy expenditure of weight training. J Strength Cond Res 20: 404–411, 2006.
39. Sell K, Taveras K, Ghigiarelli J. Sandbag training: A sample 4-week training program. Strength Cond J 33: 88–96, 2011.
40. Siri WE. Gross composition of the body. In: Advances in Biological and Medical Physics (Vol. 4). Lawrence JH, Tobias CA, eds. New York, NY: Academic Press, 1956, pp. 239–279.
41. Skidmore BL, Jones MT, Blegen M, Matthews TD. Acute effects of three different circuit weight training protocols on blood lactate, heart rate, and ratings of perceived exertion in recreationally active women. J Sports Sci Med 11: 660–668, 2012.
42. Tabata I, Nishimura K, Kouzaki M, Hirai Y, Ogita F, Miyachi M, Yamamoto K. Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and V[Combining Dot Above]O2max. Med Sci Sports Exerc 28: 1327–1330, 1996.
43. Thornton MK, Potteiger JA. Effects of resistance exercise bouts of different intensities but equal work on EPOC. Med Sci Sports Exerc 34: 715–722, 2002.
44. Williams BM, Kraemer RR. Comparison of cardiorespiratory and metabolic responses in kettlebell high-intensity interval training versus sprint interval cycling. J Strength Cond Res 29: 3317–3325, 2015.
45. Wright GA, Isaacson MI, Malecek DJ, Steffen JP. Development and assessment of reliability for a sandbag throw conditioning test for wrestlers. J Strength Cond Res 29: 451–457, 2015.
Keywords:

resistance training; running; oxygen consumption; circuit training; interval training

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