The length of rest intervals (RIs) used during resistance exercise is a variable of importance to practitioners. The RI length between sets and exercises has been shown to affect the acute metabolic (17,25) responses to a bout of resistance exercise, as well as performance of subsequent sets (15,22,23,25,34,36). Previous studies have shown that short RI length leads to large reductions in performance but yields a high metabolic demand (25); long RI length results in stable resistance exercise performance but yields low metabolic demand (25); and acute performance reductions with short and long RIs are similar between single- and multiple-joint resistance exercises (31). In addition, short RI length has a more profound negative effect on performance in adults than in children and adolescents (7) and short RI lengths are more tolerable in women compared with men (23) and in men with lower levels of 1 repetition maximum (1RM) strength compared with stronger individuals (22). These studies have been critical in the development of resistance training program design recommendations for RI prescription by major health and fitness organizations (6,18,21).
A fitness component that has the potential to influence acute resistance exercise performance is maximal aerobic capacity (V[Combining Dot Above]O2max). Individuals with a high V[Combining Dot Above]O2max generally have other positive endurance-related phenotypes, for example, smaller skeletal muscle cross-sectional area, higher proportions of slow-twitch fibers, increased aerobic enzyme activity, and greater mitochondrial and capillary densities (33). Although V[Combining Dot Above]O2max may weakly correlate to short-term (30 seconds) anaerobic power fatigue indices (14), a high V[Combining Dot Above]O2max has been shown to improve repetitive sprint performances (2). This finding suggests that improved recovery ability could augment other modalities of anaerobic exercise including resistance training. Thus, it is likely that endurance-trained individuals may have a greater capacity to maintain resistance exercise performance when short RIs are used compared with individuals with moderate or poor aerobic fitness.
The sequence of resistance exercises is another training variable of interest to practitioners. Research has shown that manipulating the sequence of resistance exercises significantly affects acute performance (as determined by repetition number per specific exercise or loading used) (9,23). In addition, other studies have shown significantly larger elevations in acute oxygen consumption and energy expenditure (EE) for large vs. small muscle-mass exercises (13,28). Although a few studies have shown that performance of large muscle-mass exercises along with small muscle-mass exercises may augment small muscle-mass exercise strength gains (11,27), less is known concerning the metabolic effects of sequencing a smaller muscle-mass exercise after a large muscle-mass exercise. Therefore, the primary purpose of this study was to examine the relationship between V[Combining Dot Above]O2max and acute upper- and lower-body resistance exercise performance using different RI lengths. A secondary purpose was to investigate the acute metabolic effects of 2 sequences of exercises involving large and moderate muscle masses.
Experimental Approach to the Problem
To examine the primary hypotheses of this investigation, subjects were tested for V[Combining Dot Above]O2max and maximal strength, matched, and randomly assigned to 1 of the 2 following treatment groups: (a) a group who performed the barbell back squat (S) exercise first in sequence (followed by the bench press) or (b) a group who performed the barbell bench press (BP) exercise first in sequence (followed by the back squat). A between-groups design was used to reduce any potential training effects incurring from performance of several acute resistance exercise protocols. Both groups performed 3 resistance exercise protocols using different (1-, 2-, or 3-minute) RIs. Each protocol consisted of performing 5 sets of up to 10 repetitions of the squat and bench press using 75% of the subjects' predetermined 1RM. Oxygen consumption and performance data were collected during each protocol. Pearson product-moment correlations were calculated between V[Combining Dot Above]O2max and selected performance parameters. This study design enabled us to examine the influence of V[Combining Dot Above]O2max on acute resistance exercise performance using different RIs and to investigate the influence of exercise sequencing on the acute metabolic demands to resistance exercise.
Seventeen healthy resistance-trained men (at least 1 year of consistent resistance training experience) with a wide range of V[Combining Dot Above]O2max values (34.1–59.3 ml·kg−1·min−1) agreed to participate in this study (Table 1). Each subject initiated the study in a trained state (i.e., were resistance trained 2–4 days per week), had relative strength measures of 1.2 and 1.6 × body mass for the bench press and squat, respectively, were current or former athletes, and none were taking any supplements or medications such as anabolic steroids known to affect resistance exercise performance. Subjects underwent 1 week of familiarization with study procedures before testing. Familiarization focused on subjects' ability to perform the squat and bench press exercises comfortably while wearing a respiratory mask. During this time, height was measured using a wall-mounted stadiometer, and body mass was measured using an electronic scale. Percent body fat was estimated through a 3-site skinfold test. The sites measured were the pectoral, anterior thigh, and abdominal skinfolds using previously described methodology (12). Body density was calculated using the equation of Jackson and Pollock (12), and percent body fat was calculated using the equation of Siri (32). The same research assistant performed all skinfold assessments. This study was approved by The College of New Jersey's Institutional Review Board, and each subject subsequently signed an informed consent document before participation. Subjects were 19-22 years old. No subject had any physiological or orthopedic limitations that could have affected lifting performance as determined by completion of a health history questionnaire.
Maximal Aerobic Capacity (V[Combining Dot Above]O2max) Testing
All subjects reported to the laboratory twice at a personally standardized time of day for maximal aerobic capacity testing. Subjects refrained from exercise for at least 24 hours before each testing session. V[Combining Dot Above]O2max was assessed using a progressive multistage ramp protocol on a treadmill (MedGraphics ULTIMA metabolic system; MedGraphics Corporation, St. 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]O2max was determined by recording the highest measure. Gas analyzers were calibrated before each trial using gases provided by MedGraphics Corporation: (a) calibration gas: 5% CO2, 12% O2, balance N2 and (b) reference gas: 21% O2, balance N2. Each subject completed 2 maximal trials separated by at least 48 hours, and the trial resulting in the highest V[Combining Dot Above]O2max was used for further analysis.
One repetition maximum barbell bench press and back squat was assessed before the experimental sessions using a standard protocol (16,24). For each exercise, a warm-up set of 5–10 repetitions was performed using 40–60% of the perceived 1RM. After a 1-minute RI, a set of 2–3 repetitions was performed at 60–80% of the perceived 1RM. Subsequently, 3–4 maximal trials were performed to determine the 1RM with 2- to 3-minute RI between trials. A complete range of motion and proper technique was required for each successful 1RM trial. For the bench press, the bar was lowered until it touched the lower-to-mid sternum (with no “bouncing”) and was lifted to full elbow extension (with no excessive arching of the back). For the back squat, subjects descended with the bar on the rear shoulders until their upper thighs were parallel to the ground. At that point, a “lift” signal was given by a research assistant (to ensure proper depth) and the subject ascended to the starting position. Assessment of 1RM strength enabled calculation of the protocol loads (75% of 1RM). Test-retest reliability for 1RM testing has been high in our laboratory (R > 0.93) (7,24).
Resistance Exercise Protocols
All subjects reported to the Human Performance Laboratory at least 2 hours after their last standardized meal on 3 occasions separated by at least 48 hours. Subjects refrained from caffeine consumption and exercise for at least 24 hours before each testing session. Upon arrival, each subject was encouraged to drink water ad libitum to prehydrate and was subsequently fitted with a respiratory mask that was placed over the subjects' face, fastened, and carefully checked for proper sealing. Subjects were also fitted with a Polar heart rate (HR) monitor (Polar Electro Inc., Woodbury, NY, USA) that was used to measure HR at baseline (BL), after each set of resistance exercise, and after each minute of recovery per RI. Subsequently, each subject was positioned on a reclining chair and sat quietly for 30 minutes before measurement of BL HR and oxygen consumption (which was recorded over a 3-minute period). Breath-by-breath oxygen uptake (V[Combining Dot Above]O2) was measured throughout each protocol through a metabolic system (MedGraphics ULTIMA metabolic system; MedGraphics Corporation). Gas analyzers were calibrated with gases of known composition before collection of metabolic data. Heart rate data presented are the values obtained at rest (after 30 minutes of quiet sitting), mean HR data obtained during performance of each exercise (all 5 sets and RIs were averaged), and mean HR for the total protocol (average of both exercises and RIs combined).
After BL measures, each subject performed a warm-up consisting of 3 minutes of stationary cycling and 2–3 light-to-moderate sets (40–60% of 1RM) of the bench press and squat. Respiratory masks were temporarily removed from each subject during the warm-up to allow subjects to consume water one last time before initiating the protocols. The protocols consisted of performing 5 sets of the bench press and 5 sets of the back squat for up to 10 repetitions using 75% of their predetermined 1RM. The BP group performed the bench press first, whereas the S group performed the back squat first. For all exercises, resistance remained constant while total numbers of repetitions were recorded. Heart rate and oxygen consumption data were collected during the entire protocol. In addition, a linear position transducer (Tendo Sports Machines, Trencin, Slovak Republic) was attached to the bar to measure power and velocity during each completed repetition. A different RI was used during each protocol, for example, 1-, 2-, and 3-minute RIs in randomized order. A standard 2-minute RI was used in between exercises. After each protocol, subjects were seated in a reclined position (same as BL body position) for the measurement of postexercise V[Combining Dot Above]O2 for 30 minutes.
Absolute and relative V[Combining Dot Above]O2, respiratory exchange ratio (RER), and ventilation (VE) data were recorded. Individual breath-by-breath data points for all metabolic variables were averaged for the entire set and for the first 15 seconds of each minute for each RI in between sets (25). 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. Energy expenditure per minute for each protocol was estimated by multiplying absolute V[Combining Dot Above]O2 (L·min−1) by 5.05 kcal·L−1 because all RER values were ≥1.0. Ventilation data are presented as the mean of each entire protocol. Postexercise breath-by-breath data were averaged immediately after the last set of the last exercise, and at 5, 10, 15, 20, 25, and 30 minutes after exercise, that is, a 15-second interval was averaged for each postexercise time period.
Descriptive statistics (mean ± SD) were calculated for all dependent variables. A 2 (group) × 3 (RI) analysis of variance with repeated measures was used to analyze performance and metabolic data. In addition, a 2 × 3 analysis of covariance (ANCOVA) with repeated measures using V[Combining Dot Above]O2max as a covariate was used to examine the influence of V[Combining Dot Above]O2max on resistance exercise performance. Subsequent Tukey's post hoc tests were used to determine differences when significant F ratios were obtained. Pearson product-moment correlations were calculated between V[Combining Dot Above]O2max and selected performance variables. Independent T-tests were used to analyze total repetitions completed between groups for each exercise protocol. For all statistical tests, a probability level of p ≤ 0.05 denoted statistical significance.
Acute resistance exercise performance data are shown in Table 2. Significant main effects were observed for total, squat, and bench press repetitions completed. For total repetitions completed, significantly more repetitions were completed using 2RI and 3RI compared with 1RI in both groups. In the BP group, significantly more repetitions were completed using 3RI compared with 2RI. No difference was observed between groups. For squat repetitions completed, significantly more repetitions were completed using 2RI and 3RI compared with 1RI in both groups. No differences were observed between 2RI and 3RI or between groups. For bench press repetitions completed, significantly more repetitions were completed using 2RI and 3RI compared with 1RI in both groups. In the BP group, significantly more repetitions were completed using 3RI compared with 2RI. The number of bench press repetitions completed using 1RI was significantly greater in the BP than in S group. For each exercise, significant main effects were observed using 1RI, 2RI, and 3RI indicating that repetition number was lower for the last 2–3 sets compared with the first 2 sets (see Table 2 for specific comparisons). For the bench press, a significant interaction was observed using 2RI, and a trend (p = 0.08) was observed using 1RI indicating that the repetitions performed for noted sets were higher in BP than in S.
The results of ANCOVA indicated that V[Combining Dot Above]O2max significantly influenced the total number of repetitions completed for all RIs. V[Combining Dot Above]O2max was significantly negatively correlated to 1RM bench press and squat (r = −0.79 and −0.60, respectively) and was significantly correlated to total squat repetitions performed (r = 0.43–0.57) but did not correlate to bench press performance. Moderate associations were observed between V[Combining Dot Above]O2max and total repetitions performed (r = 0.34–0.48), but these associations did not reach statistical significance (p = 0.06–0.10).
Table 3 presents kinetic and kinematic data averaged per set in both groups for the squat and bench press exercises. For the squat, significant main effects were observed in average power and velocity during 1RI, 2RI, and 3RI, and an interaction was observed during 2RI where the reduction in average power and velocity over 5 sets was significantly greater in the S group. Overall, reductions in average power and velocity were seen over the course of 5 sets (see Table 3 for specific comparisons). The average power per set was significantly lower during 1RI compared with 3RI. For the bench press, significant main effects were observed in average power and velocity during 1RI, 2RI, and 3RI. Reductions in average power and velocity were seen over the course of 5 sets (see Table 3 for specific comparisons). The average power and velocity per set was significantly lower during 1RI compared with 2RI and 3RI.
Acute V[Combining Dot Above]O2 responses to the 1RI, 2RI, and 3RI protocols are shown in Figures 1–3, respectively. In all protocols, V[Combining Dot Above]O2 was significantly elevated compared with BL at all time points. V[Combining Dot Above]O2 during the first minute of rest (R1) was significantly higher than V[Combining Dot Above]O2 obtained during each set. V[Combining Dot Above]O2 data obtained for the squat exercise were significantly higher than the bench press. During 1RI and 2RI, V[Combining Dot Above]O2 during the bench press tended to be higher in the S group when it was performed after the squat exercise (p = 0.07). V[Combining Dot Above]O2 during the postexercise period was significantly elevated at all time points compared with BL. No significant differences in postexercise oxygen consumption were observed between the S and BP groups. Postexercise V[Combining Dot Above]O2 values obtained at 5 minutes after exercise (E5) were significantly higher in 1RI than 3RI. No other significant differences were observed in postexercise V[Combining Dot Above]O2 values between 10 and 30 minutes using 1RI, 2RI, or 3RI.
Mean V[Combining Dot Above]O2 responses for the squat and bench press and mean protocol V[Combining Dot Above]O2 data are presented in Figures 4 and 5, respectively. Mean V[Combining Dot Above]O2 values were significantly higher during 1RI and lowest during 3RI for both exercises. Mean squat V[Combining Dot Above]O2 was similar between groups across all RIs. However, a trend (p = 0.07) was observed where mean V[Combining Dot Above]O2 data for the bench press were higher in the S group using 1RI and 2RI indicating that the metabolic response for the bench press was higher when it followed the squat in sequence. Mean V[Combining Dot Above]O2 data for the squat were significantly higher than the bench press across all RIs. The mean protocol V[Combining Dot Above]O2 was significantly highest during 1RI and lowest during 3RI with no differences observed between the groups (Figure 5). Overall, the 1RI protocols yielded the highest percent of V[Combining Dot Above]O2max when averaged over 5 sets (48.8 ± 8.8% and 47.1 ± 4.7% for the squat and 33.1 ± 10.4% and 26.3 ± 4.5% for the bench press, respectively, in the S and BP groups) compared with 2RI (42.0 ± 7.3% and 43.4 ± 6.1% for the squat and 27.0 ± 7.4% and 23.4 ± 5.1% for the bench press, respectively, in the S and BP groups) and 3RI (34.3 ± 6.4% and 37.7 ± 5.6% for the squat and 24.2 ± 7.1% and 20.7 ± 4.5% for the bench press, respectively, in the S and BP groups).
Minute ventilation (VE) responses are shown in Figure 6. VE values were significantly highest during 1RI and lowest during 3RI. In addition, a trend (p = 0.10) was observed between the groups during 1RI, where the VE values for the S group tended to be higher than the BP group. Energy expenditure data are shown in Figure 7. Energy expenditure values were significantly highest during 1RI and lowest during 3RI. In addition, a trend (p = 0.09) was observed between groups during 1RI, where the EE values for the S group tended to be higher than the BP group.
Respiratory exchange ratio and HR data are presented in Tables 4 and 5, respectively. Significant main effects were observed where RER was higher during each exercise than BL or after exercise for 1RI, 2RI, and 3RI. For all RIs, RER during the bench press was significantly higher than the squat. No significant interactions between groups were observed during 1RI and 2RI. However, a significant interaction was observed during 3RI where RER was higher during the bench press in BP compared with the S group. No differences in RER were observed in either exercise between RIs. For HR, significant main effects and interactions were observed for 1RI, 2RI, and 3RI. Heart rate was significantly higher during each exercise and in total compared with BL. Mean HR was significantly higher during the squat than the bench press. In addition, mean HR was significantly higher in the S group compared with the BP group during performance of the bench press. For both exercises, mean HR values were significantly higher during 1RI than 2RI and 3RI. In addition, mean HR values were significantly higher during 2RI than 3RI for the squat and bench press (in the BP group only), and a trend (p = 0.06) was observed for the bench press in the S group.
The salient findings from this study were (a) V[Combining Dot Above]O2max significantly correlated to squat exercise performance across all RIs (but not bench press performance) and was negatively correlated to 1RM strength; (b) mean V[Combining Dot Above]O2 obtained for the squat was similar independent of exercise sequence; however, mean V[Combining Dot Above]O2 obtained during the bench press tended to be higher when it followed the squat in sequence using 1- and 2-minute RIs; (c) mean squat V[Combining Dot Above]O2 data were significantly higher than bench press V[Combining Dot Above]O2 data across all RIs; (d) squat repetition performance was greatest when 2- and 3-minute RIs were used and limited with 1-minute RIs, whereas bench press repetitions were highest with 3-minute RIs and lowest with 1-minute RI; (e) squat and bench press average power and velocity data were highest during 3-minute RIs; and (f) VE and EE were significantly highest with 1-minute RIs and lowest using 3-minute RIs.
V[Combining Dot Above]O2max was negatively correlated to 1RM bench press and squat (r = −0.79 and −0.60, respectively) and was positively correlated to total squat repetitions across all RIs (r = 0.43–0.57) but did not correlate to bench press performance. These data indicated that individuals with high V[Combining Dot Above]O2max had lower 1RM strength but were able to maintain squat repetition performance to a greater extent than individuals with a lower V[Combining Dot Above]O2max. In addition, our data suggest that V[Combining Dot Above]O2max is another component to consider when prescribing RIs for lower-body exercises. Individuals with a high V[Combining Dot Above]O2max generally have other positive endurance-related phenotypes, for example, smaller skeletal muscle cross-sectional areas, higher proportions of slow-twitch fibers, increased aerobic enzyme activity, and greater mitochondrial and capillary densities (33). Although these qualities contribute poorly to maximal muscle strength, a high V[Combining Dot Above]O2max may improve recovery parameters during lower-body anaerobic exercise such as repeated sprint performance (2). The results of this study support the contention that individuals with a high V[Combining Dot Above]O2max may not require as much rest in between sets to maintain performance during a predominantly lower-body/trunk exercise such as the squat.
However, this was not evident during the bench press. It seems that V[Combining Dot Above]O2max obtained during a predominantly lower-body aerobic exercise mode (treadmill) may correlate more strongly to lower-body resistance exercise performance. deJong et al. (5) showed that elite marathon runners displayed reduced V[Combining Dot Above]O2max values determined using an arm cycle ergometry protocol relative to V[Combining Dot Above]O2max values obtained during a treadmill protocol. V[Combining Dot Above]O2max data obtained using arm cycle ergometry was 41–76% of values obtained using a treadmill protocol (5). The authors concluded that marathon runners had reduced relative arm fitness because of training specificity (5). This divergent V[Combining Dot Above]O2max response between arm and leg exercises agrees in principle with this study in which we found a poor relationship between V[Combining Dot Above]O2max determined through treadmill running and bench press exercise involving upper-body musculature.
Resistance exercise selection significantly affected the acute oxygen consumption responses across all RIs. Mean and peak V[Combining Dot Above]O2 data obtained during the squat were significantly higher than the bench press across all RIs. These data support previous studies indicating that the acute oxygen consumption response is higher during a large muscle-mass exercise such as the squat compared with a smaller muscle-mass exercise such as the bench press (3,19,26,28). Similar findings were reported by Farinatti and Castinhierans Neto (8), who showed that acute oxygen consumption during 5 sets of 10 repetitions (with 15RM loading) and subsequent 1- and 3-minute RIs in between sets was nearly double during performance of the leg press compared with the chest fly. Scala et al. (28) reported that performance of multiple large muscle-mass resistance exercises during a session yielded a stimulus approximately 58% of V[Combining Dot Above]O2max compared with only 34% for small muscle-mass exercises. The results of this study were consistent (since Scala et al. studied multiple exercises) where we found a range of 34–49% of V[Combining Dot Above]O2max for the squat sets and 20–27% of V[Combining Dot Above]O2max for the bench press sets depending on RI length. The back squat exercise involves activation of the ankle, knee, and hip musculature during the ascent and descent phases as well as activation of spine, arm, and shoulder muscles to stabilize the bar in place on/near the posterior deltoid and trapezius muscles, whereas the bench press predominantly involves shoulder adduction/abduction, flexion/extension, and elbow extension/flexion musculature during the “up” and “down” phases, respectively, recruiting a smaller magnitude of muscle mass (4,29). Subjects also had to overcome their body weight, in addition to the similar relative loading on the bar, to perform the squat in comparison with the bench press. Thus, it seems that the combination of muscle mass involvement and loading contributed to the larger acute oxygen consumption response seen during the squat exercise.
A continuum was observed where mean oxygen consumption, VE, and EE values were highest during 1RI, followed by 2RI and 3RI for both exercises. In addition, intra-exercise V[Combining Dot Above]O2 values were higher during the initial segment of the RI than during the set. The acute oxygen consumption response to resistance exercise was similar to previous studies using 1-, 2-, and 3-minute RIs for the bench press (9,10,25) and other exercises such as the shoulder press and triceps extension (9). In addition, Scala et al. (28), Ratamess et al. (25), and Farinatti and Castinhierans Neto (8) reported that acute V[Combining Dot Above]O2 was higher during the RI than during the set for a multitude of exercises. Farinatti and Castinhierans Neto (8) also reported that the acute V[Combining Dot Above]O2 response was higher using 1-minute RI than 3-minute RI for the leg press exercise but not the chest fly. Their results for the leg press support the results of this study and others (25) demonstrating a continuum of responses where short RIs yield a large acute V[Combining Dot Above]O2 response and this response decreases with increasing RI lengths. However, the authors attributed the lack of RI interaction during the chest fly to a smaller amount of muscle mass activation (8). The discrepancy in this regard may be because of differences in muscle involvement between bench press and chest fly. It could be hypothesized that the bench press stimulates a larger amount of muscle mass (as it is a multiple-joint exercise that also involves elbow motion plus a larger stabilizing requirement) compared with the chest fly and could be more susceptible to RI length in between sets. The results of this study support previous research showing greater acute V[Combining Dot Above]O2 response with short RIs. The anaerobic nature of resistance exercise may limit peak V[Combining Dot Above]O2 elevations during a set (8,25,28). Resistance exercise performance may elicit Valsalva maneuvers, rises in intrathoracic and intra-abdominal pressures and cardiovascular demand, increased temperature, increased interstitial potassium, decreased muscle and blood pH, and increased blood lactate, all of which can lead to a compensatory rise in VE and V[Combining Dot Above]O2 during the subsequent RI (28).
Resistance exercise sequence has been shown to affect acute lifting performance (loading and repetitions completed) (20,23) and metabolic response (9,10). Exercises performed first in sequence yield greater repetition total than those exercises performed later especially when similar muscle groups are involved (20,23). Few studies have investigated the effects of resistance exercise sequencing on the acute oxygen consumption response. Farinatti et al. (9,10) compared 2 resistance exercise sequences of the bench press, shoulder press, and triceps extension to the reverse order and found that V[Combining Dot Above]O2 for the bench press and triceps extension was significantly higher when they were performed last in sequence.
However, the effects of performing large muscle-mass exercises before small-mass exercises remain unclear. Although it has been suggested that small muscle-mass exercises may metabolically benefit after larger muscle-mass exercises, few studies have investigated the sequence effects. Some research has indicated that testosterone and growth hormone elevations resulting from large muscle-mass exercises may augment muscle strength gains of subsequent small muscle-mass exercises (i.e., elbow flexors) during resistance training (11,27). In this study, mean squat V[Combining Dot Above]O2 was similar between groups across all RIs. However, a trend (p = 0.07) was observed where mean V[Combining Dot Above]O2 data for the bench press were higher in the S group using 1RI and 2RI indicating that there was a tendency for the oxygen consumption response for the bench press to be higher when it followed the large muscle-mass squat in sequence. These data indicate that sequencing a large muscle-mass exercise before a smaller muscle-mass exercise can augment the oxygen consumption response when 1- or 2-minute RIs are used.
A continuum was observed in this study where acute resistance exercise performance (repetition number, average power, and velocity) was superior during 3RI and inferior during 1RI. Minimal differences were seen between groups although the first exercise performed in sequence tended to yield a larger number of completed repetitions, that is, the number of bench press repetitions completed using 1RI was significantly greater in the BP group. The results of this study support previous research demonstrating a continuum of performance reductions with short RI lengths (15,25,30). Ratamess et al. (25) showed that volume load significantly decreased with each set in succession over 5 sets of the bench press when 30-second and 1-minute RIs were used; and that lifting performance was maintained over 2 sets for 2-minute RIs, 3 sets for 3-minute RIs, and 4 sets for 5-minute RIs with subsequent reductions taking place for the remaining sets. Similarly, Senna et al. (31) used 5 sets of 10RM loads with 1-, 3-, and 5-minute RI for the bench press, machine fly, leg press, and leg extension exercises and reported a continuum of performance reductions with 1-minute RI yielding the greatest reductions and 5-minute RI yielding the least. For the bench press, performance maintenance was observed for first 2 sets and reductions were seen during sets 3, 4, and 5 during 3-minute RI and 5-minute RI similar to Ratamess et al. (25). In addition, Senna et al. (31) reported ∼28.5 and 41 total repetitions performed for the bench press with 1-minute RI and 3-minute RI which is similar to ∼26 and 37 total bench press repetitions performed for the BP group in this study. Willardson and Burkett (34) reported that volume was highest when 5-minute RI was used, followed by 2- and 1-minute RIs when performing 4 sets of the squat and bench press with 8RM loading. They also showed that when performing 5 sets of 15 repetitions, neither 30-second, 1-, or 2-minute RIs were sufficient to maintain performance (36) and 3-minute RI was more effective (i.e., higher repetitions performed) than 2- and 1-minute RIs for maintaining bench press performance over 5 sets with 80% of 1RM (35). The results of this study support previous research showing reduced capacity to maintain repetition performance with short RIs.
Reductions in average velocity and power were observed the most during 1RI and the least during 3RI in this study. These data support 2 of our previous studies in men where average power and velocity per set for the bench press was lowest during 1-minute RI and greater during 3-minute RI (22,23). In addition, Abdessemed et al. (1) studied 10 sets of 6 repetitions of the bench press using 70% of 1RM with 1-, 3-, or 5-minute RIs and reported significant reductions in average power per set (27% between sets 4 and 10) when 1-minute RIs were used but power performance was maintained with 3- and 5-minute RIs. These data, coupled with the data from this study, indicate that power and velocity reductions are most prominent when short RIs are used and support resistance training recommendations of long RI lengths for power training to preserve the quality of each repetition (18,21).
In conclusion, the results of this study indicate that V[Combining Dot Above]O2max is another factor to consider when prescribing RI lengths for lower-body exercises. Individuals with a higher V[Combining Dot Above]O2max have a greater capacity to maintain repetition performance of lower-body exercises when short RIs are used. In addition, acute oxygen consumption for the bench press exercise can be augmented when it follows the squat in sequence when shorter RIs are used as opposed to being performed first in sequence. These data provide further insight into resistance exercise prescription for RI length and exercise sequencing and can be used to enhance the design of resistance training programs.
Rest interval length during resistance exercise is often prescribed based on training goals. One objective in RI prescription is to prescribe a length that allows the individual to maintain loading and/or repetition performance. Previous studies have shown that gender and absolute muscular strength (22,23) significantly affect acute resistance exercise repetition performance. In this study, we have also shown that V[Combining Dot Above]O2max is another variable of consideration when prescribing RIs. Specifically, individuals with a high V[Combining Dot Above]O2max maintained repetition performance to a greater extent during the squat when short RIs were used. The results of this study do not indicate more aerobic training is needed. Rather, these data indicate that aerobically fit individuals may not need as long a RI to maintain the prescribed volume load for acute lower-body resistance exercise. In addition, we showed that acute oxygen consumption during the bench press exercise was higher when it followed the squat in sequence. These data give support to current resistance training guidelines that recommend sequencing large before small muscle-mass exercises to increase the metabolic demands of resistance exercise (21).
We thank a dedicated group of subjects and laboratory assistants for their participation in this study. In addition, we thank the Office of Academic Affairs at The College of New Jersey for funding this study through the Mentored Undergraduate Summer Experience (MUSE) program.
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