Resistance training is a well-studied exercise modality that has been shown to increase skeletal muscle strength, muscle mass, bone mass, and connective tissue thickness (14). This modality of exercise is implemented in a variety of settings to improve general fitness and athletic conditioning, along with preventing and rehabilitating injuries. However, these positive health and performance outcomes are dependent on the effectiveness of the resistance training program through proper manipulation of program design variables. One variable that has been given much attention is training volume, which is defined as the product of sets and repetitions (14). A systematic review analyzed the effects of multiple sets vs. one set per exercise found similar increases in skeletal muscle strength across both conditions in untrained and trained individuals (2). However, in the cases when there was a difference in strength improvements, the multiple-set or higher-intensity training programs elicited a greater increase (2,29,30). A meta-regression and meta-analysis also showed a clear dose-response relationship between number of sets performed and increases in both strength and hypertrophy (23,24). These data support the idea that multiple sets are superior to a single set, but in many of these studies, intensity may not have been properly controlled.
In resistance training, intensity is typically defined as a percent of 1 repetition maximum (1RM) (14). However, this may be more appropriately termed “load,” given that the number of repetitions performed at a given repetition maximum may more adequately reflect the actual “intensity” of the stimulus. For example, executing 10 repetitions at a 10RM (which is approximately 75% of 1RM) and achieving momentary muscular failure would be considered an intensity of 100%. Arent et al. (1) evaluated intensity through specific criteria, including performing sets to momentary muscular failure, subsequent physiological responses, and even ratings of perceived exertion. These semantic differences have only managed to contribute to some of the confusion in this area.
Another key variable in designing effective resistance training programs is time under tension (TUT), which comprised repetition duration and total repetitions. Time under tension, although different from training volume, is often disregarded when determining volume or volume load, but it is clear that increased TUT during intensity- and volume-equated resistance exercise induces greater fatigue and causes greater muscular disruption (36). Repetition duration can be increased through increasing the time of the concentric or eccentric muscle action (25), with the eccentric muscle action having been shown to produce 20–60% more muscular force compared with concentric action (16). Accentuated eccentric resistance training has been applied in various studies to investigate its efficacy. This method can be implemented by adding additional resistance during the eccentric phase (5) or increasing repetition duration by extending the duration of the eccentric phase of the repetition (9). Philbin (28) has used this method of accentuated eccentric resistance training in his high-intensity training (HIT) system to increase TUT and maximize training intensity.
Aside from the proper manipulation of program design variables, the hormonal response during and after a resistance training bout may be a key indicator in determining the subsequent adaptations that will occur. A recent study in resistance-trained individuals found a significant correlation between exercise-induced acute testosterone elevations and long-term muscle hypertrophy (26). Another investigation in trained individuals compared the hormonal responses after an arms-then-legs vs. a legs-then-arms protocol and found that testosterone levels were similarly elevated in both groups, although the leg exercises seemed to be the main driver of the hormonal response, represented by a delayed increase in the arms-then-legs group (38). In untrained individuals, multiple studies have found no correlation between the acute testosterone response and post-exercise rates of muscle protein synthesis or improvements in strength and hypertrophy after 8–12 weeks of resistance training (31,39–41). Mechanistically, testosterone has been reported to lead to activation and proliferation of satellite cells, resulting in myonuclear accretion, subsequently increasing the ability to increase rates of muscle protein synthesis to a greater degree than before and also through the formation of new muscle fibers (18). Furthermore, it has been theorized that anabolic androgenic steroids, such as testosterone, act through non-genomic pathways to increase intracellular calcium (37), thus resulting in greater force production (15). When comparing physiological responses in regard to the volume of exercise performed, significantly greater elevations in post-exercise testosterone, growth hormone, and lactate have been found in a 3-set group compared with a single-set group (13) performed with a similar TUT and repetition tempo, which becomes even more apparent when rest periods are shortened (20). Both volume and intensity have been shown to be important factors in determining the magnitude of increase in testosterone after resistance training (21).
Cortisol, although a catabolic hormone, may also be an indicator of the long-term anabolic response to exercise and also reflects acute metabolic stress. After 12 weeks of resistance training, acute cortisol responses showed a positive correlation to improvements in lean body mass (40). In addition, cortisol responses have been shown to be greatest after 4–6 sets compared with just 2 sets (35), indicating high amounts of metabolic stress, as well as being highly correlated with creatine kinase, a marker of muscular damage (21). This analysis shows that cortisol may indicate the magnitude of the training stimulus because cortisol plays a crucial role in mobilizing metabolic substrates during exercise.
Past research has suggested that multiple sets may be superior to a single set of resistance training. However, these findings may be intensity- and TUT-dependent rather than volume-dependent. Thus, the purpose of this study is to use a single-set accentuated eccentric phase protocol and compare this to a traditional 3-set resistance training protocol to determine differences in acute physiological, biochemical, and hormonal responses when matched for TUT and momentary muscular failure (i.e., intensity). It is hypothesized that exercise volume will impact the metabolic responses during resistance training to a greater degree even after controlling for intensity. It is predicted that the 3-set traditional (3ST) and single-set accentuated eccentric resistance training (HIT) sessions will induce physiological responses during and after an acute bout of exercise that will disrupt the homeostatic balance and produce a significant metabolic response. However, because of the unique effects of volume, it is also predicted that the 3-set protocol will result in greater heart rate (HR), lactate, testosterone, and cortisol responses.
Experimental Approach to the Problem
To assess the acute physiological, biochemical, and hormonal responses, a randomized between-subject design was used to compare the acute responses of 2 intensity- and TUT-equated exercise bouts consisting of a single-set HIT vs. a 3ST protocol. Approximately 72–96 hours after 10RM testing, a lower-body, intensity-equated exercise bout was prescribed, and subsequent HR, lactate, testosterone, and cortisol responses were monitored throughout a 60-minute recovery period.
Male college students (between the ages of 18-30 yrs old. N = 19; mean ± SD; age = 21.11 ± 2.5 years; height = 174.33 ± 6.83 cm; body mass = 76.72 ± 10.24 kg; %BF = 5.53 ± 6.35%) participated in the study. Subjects were previously trained, which was defined as participating in a resistance training program for at least 1 year before enrollment. All participants were free from diseases, conditions, or injuries that would prevent them from participation in a resistance training program. All subjects completed a written informed consent approved by the Committee for the Protection of Human Subjects at Rutgers University before participation.
Participants reported to the Rutgers University Center for Health & Human Performance for the initial assessment where informed consent was given, and body composition was measured. On a separate day, 10RM testing was performed. The testing sessions began with a 5-minute warm-up on a stationary bike. The same protocol was used for each of the 6 exercises, and all 10RMs were determined in ≤4 sets for each exercise. Participants were randomly assigned to either a 3ST training group (3ST; N = 9) or a 1-set HIT group (HIT; N = 10) using a computer-generated numbers list. The descriptive statistics for each group are presented in Table 1.
Approximately 72–96 hours after 10RM testing, participants completed the prescribed protocol for their respective group. The traditional 3-set group trained at 100% of their 10RM with 90-second rest intervals between sets and exercises. Concentric and eccentric motions were performed with a 1:1-second duration to regulate the repetition velocity. The HIT group trained at 75–85% of their 10RM with 90-second rest intervals between exercises. The repetition velocity was controlled by taking 2 seconds to perform the concentric motion and 4 seconds to perform the eccentric motion, thereby increasing the TUT of the exercise to be comparable to that of the 3ST group. Both groups performed approximately 60 seconds of work for each exercise, which was evenly split between the concentric and eccentric muscle actions for the 3ST group and split 20 and 40 seconds for the concentric and eccentric muscle actions, respectively, for the HIT group. If a subject deviated from the prescribed repetition tempo, the researcher would instruct the participant to increase or decrease movement speed. To equate for intensity, all participants achieved momentary muscular failure on each set. The exercise selection and exercise order were consistent with the movements performed during the initial testing session. All subjects completed 9–12 repetitions per working set.
Body Composition and 10RM Testing
Body fat percentage (%BF) was calculated from body volume measurements using the Siri equation (17). Body volume was measured through air displacement plethysmography (BODPOD; COSMED, Concord, CA, USA). The BODPOD determines body volume with a roughly 0.02% error, and the subsequent calculation of %BF results in a 0.01% error (8). All testing was conducted according to the manufacturers' guidelines. In addition to body composition, height and body mass were assessed for all participants.
Ten RMs were determined to establish assigned loads for each participant. All 10RM testing followed the protocol described by Haff and Triplett (14) and was performed in the order that the subjects would be completing the exercises during the experimental sessions. The 10RM was chosen to allow for a more accurate loading prescription given the repetition ranges used in this study. The exercises included the 45° leg press, leg extension, Romanian deadlift, prone leg curl, seated adductor, and seated calf raise. Two to 4 minutes of rest was provided between attempts.
Heart Rate, Blood Lactate, and Salivary Hormones
Heart rate was continuously monitored in 5-second sampling intervals using the Polar S610 (Polar Electro, Inc., Woodbury, NY, USA). Average HR (AHR) and peak HR were determined for each group at the following time points: pre-exercise (pre), during exercise (mid), immediately (0post), 15- (15post), 30- (30post), 45- (45post), and 60-minute post-exercise (60post).
Blood lactate samples were collected through finger stick and analyzed using a Lactate Pro (Arkray, Kyoto, Japan) analyzer at pre, mid, 0post, 15post, and 30post.
Saliva samples were collected through passive drool using Salivettes (Sarstedt, Inc., Rommelsdorf, Germany) to be analyzed for testosterone and cortisol at pre, 0post, 30post, and 60post. Saliva samples were stored at −80° C until assayed using commercially available testosterone and cortisol EIA kits (Salimetrics, State College, PA, USA). The CV% for both assays was <7%.
A 2 × 7 group × time analysis of variance (ANOVA) with repeated measures on the second factor was used to analyze changes in the AHR during the workout and throughout the subsequent recovery period. Peak HR during the exercise session was assessed using an ANOVA after adjusting for baseline values. A 2 × 5 group × time ANOVA with repeated measures on the second factor was also used to analyze lactate levels measured before, during, and after workout to gauge responses of the respective HIT and 3ST groups. Testosterone and cortisol responses were analyzed using 2 × 4 group × time ANOVAs with repeated measures on the second factor. Significant univariate effects were followed up with simple-effect analyses and planned simple contrast. In addition, effect sizes (ES) were computed to assess the magnitude of changes in physiological responses compared with baseline and between groups at given time points where appropriate. Significance was set at p ≤ 0.05.
For each univariate analysis, examination of the Hyund-Feldt epsilon general model was used to test the assumption of sphericity. If this statistic was greater than 0.75, sphericity was considered to have been met and the unadjusted univariate statistic was used. If epsilon was less than 0.75, it was considered to be in violation of the assumption of sphericity and the Hyund-Feldt adjusted statistic was used to test significance.
Heart Rate Responses
There was a significant time main effect on AHR (p < 0.001). Compared with baseline, average HR was elevated at all time points for both groups, and a significant elevation in AHR at mid was found (p < 0.001). This elevation remained significant throughout the post-exercise period and did not return to resting values at 60post (p < 0.05; Figure 1).
After adjusting for baseline values, the subjects in the 3ST group had a significantly greater increase in peak HR from pre to mid compared with those in the HIT group (p < 0.02; Figure 2).
Blood Lactate Responses
Analysis of the lactate response to exercise showed a significant time main effect (p < 0.001), and a nearly significant group main effect (p < 0.065). However, these main effects were superseded by a significant group × time interaction (p < 0.01). Follow-up tests indicated a significant time effect within the HIT group (p < 0.001). Lactate was higher at all time points compared with baseline (p < 0.001), and increases were greatest in magnitude at mid (ES = 14.01) and 0post (ES = 15.69). There was a significant time main effect within the 3ST group (p < 0.001). Lactate levels were elevated at all time points because of exercise (p < 0.001) and were greatest at mid (ES = 20.90) and 0post (ES = 17.94). The effect sizes for the simple contrasts of both groups are listed in Table 2, and the time effect of lactate is shown in Figure 3.
The difference in the lactate response between the 2 groups was significant (p < 0.01), with the 3ST group having a higher lactate at mid (ES = 1.70).
A significant time main effect (p < 0.001) for testosterone was seen across both groups, with an increase in testosterone at 0post (p < 0.01), which persisted until 30post (p < 0.05) before returning to baseline at 60post (p > 0.40). The group main effect and group × time interaction failed to reach significance (p > 0.16). Planned contrasts revealed that there was not a significant effect of time in the HIT group, although it did approach significance (p = 0.069), likely due to the transient increase in testosterone at 0post (ES = 0.50). The 3ST group displayed a significant time effect between time points (p < 0.05), with testosterone significantly elevated above baseline at 0post (ES = 1.21) and 30post (ES = 0.76) (Figure 4).
The changes in cortisol showed significant group (p < 0.05) and time main effects (p < 0.001). These main effects were superseded by a significant group × time interaction (p < 0.01) (Figure 5). Cortisol did not rise significantly above baseline values at any time point in HIT (p > 0.07). This can be observed with the low changes in magnitude at 0post (ES = 0.36), 30post (ES = 0.07), and 60post (ES = −0.43). Significant time effects within the 3ST group (p < 0.01) were found, with elevated cortisol at 0post (ES = 1.76) and 30post (ES = 2.23; p < 0.05) before returning to baseline values at 60post (ES = 0.54, p > 0.37). At 0post, there were significant differences between groups (p < 0.05), with the cortisol response significantly higher in the 3ST group (ES = 0.98). This effect persisted through 30post (ES = 1.37, p < 0.001) and 60post (ES = 0.98, p < 0.05), with cortisol significantly higher in the 3ST group.
The purpose of this study was to control for resistance training intensity (i.e., reaching momentary muscular failure) and TUT to compare the potentially unique effects of volume on the acute biochemical, physiological, and hormonal responses. Taken together, HR, lactate, and cortisol responses all suggest that volume serves as a primary driver of physiological demand even after accounting for TUT. Although volume and TUT are conceptually related, these results lend support to the importance of recognizing that they should be treated as distinct variables when designing a training program.
Analysis of the HR data demonstrated significant elevations from baseline in average HR that persisted from the start of exercise and remained elevated throughout the exercise bout and recovery period in both groups. This lack of return to baseline indicates that both the 3ST and HIT groups experienced a significant cardiovascular stressor, leading to an extended metabolic recovery. Peak HR, however, was significantly higher for the 3ST group compared with the HIT group. This may have been due to the greater quantity of work performed and, thus, potentially greater aerobic and metabolic demands of the 3ST compared with the HIT protocol (22).
Similar to the findings of peak HR, there were also significant differences in the lactate response between the 2 groups. Because of the anaerobic nature of resistance training, increases in blood lactate concentrations occur through an increased rate of production through glycolysis compared with clearance through oxidation or gluconeogenesis (6). The lactate response in this study was consistent with the anaerobic demand of this mode of training. The greatest elevations in blood lactate concentrations were observed during exercise followed by a steady decline over the course of the recovery process in both groups. However, even at 30 minutes after exercise, significantly higher blood lactate values compared with resting levels for both the HIT and 3ST groups were seen, although the 3ST group was significantly higher than the HIT group. This response is indicative of the intensity of both protocols, resulting in a high degree of metabolic stress. However, the group main effect shows that the 3-set protocol induced greater metabolic stress through the glycolytic pathway compared with the single-set HIT protocol, most likely due to the greater volume of work performed.
In addition to HR and lactate responses, differences in acute hormonal responses to exercise may also be indicative of substrate mobilization, metabolic stress, and the subsequent physiological adaptations that will occur (26). The assessment of testosterone and cortisol in this study shows the acute endocrine responses of these exercise bouts. Testosterone increased from pre-exercise to post-exercise and remained elevated at 30 minutes after exercise in both the HIT and 3ST groups, although there were no significant differences between the groups. Previous research on testosterone responses to a single-set traditional protocol demonstrated elevated testosterone until 15 minutes after exercise (13). In addition, the acute testosterone response to resistance training may affect the physiological adaptations of skeletal muscle, based on the idea that elevated post-exercise anabolic hormones upregulate several intracellular anabolic pathways (26), while also promoting the synthesis and secretion of GH and IGF-1 (21). However, other research has suggested that acute responses may not predict chronic adaptations to training programs in untrained individuals (31,39–41), although others have suggested that they do appear to provide insight into the long-term response of an extended resistance training program in trained subjects (26). This concept warrants further investigation and clarification given the complexity of hormone and receptor interactions, as well as being a potential reflection of systemic stress.
In addition to the testosterone response, cortisol increased from pre-exercise to post-exercise and remained elevated at 30 minutes after exercise in the 3ST group, whereas the HIT group exhibited no change in cortisol from baseline at any time point. Because cortisol is a catabolic hormone that functions to mobilize substrates during exercise, these results further indicate that the amount of metabolic stress induced was greater in the 3ST protocol compared with the HIT protocol. This is consistent with the findings of Gotshalk et al. (13) who showed that a 3-set resistance training protocol elicits a more robust cortisol response during exercise and recovery compared with a single-set protocol. The acute cortisol response has also been shown to be correlated with long-term adaptations to a resistance training protocol (40), so one may speculate that the 3-set protocol may induce greater muscle remodeling than the HIT protocol, although a longitudinal investigation would be necessary to determine whether acute responses translate to chronic adaptations.
The acute hormonal response to resistance training has been investigated in other studies that tested the effects of varying amounts of training volume (4), durations of rest periods (12), and repetition duration (11). After high- vs. low-volume resistance training bouts, no changes in acute testosterone levels were found in either group (4). Another study compared straight sets with no rest between repetitions to a protocol with a 30-second intraset rest and found no deviations from baseline at any time point with the exception of 30-minute post, where the no-rest group showed a significant decrease in testosterone, although this was not significantly different from the other group (12) and may be indicative of increased receptor binding. Goto et al. (11) compared the hormonal responses between 4 different repetition duration protocols (5:1, 1:5, 3:3, and 1:1 concentric to eccentric, respectively) and found increases in free testosterone immediately after exercise in all groups with no differences between groups. In addition, cortisol increased immediately after exercise in all groups except for the 1:1, whereas the 5:1 condition exhibited the greatest rise in cortisol 15 minutes after exercise. It is important to note that, in addition to varying loads, TUT was not equated between the 1:1 condition and all others (11). Although we did see acute changes in testosterone, there were no significant differences in the magnitude of change following the different resistance training protocols. However, the greater cortisol response seen in the 3ST group may indicate an environment more conducive to promoting structural remodeling following this protocol. The apparently smaller homeostatic disruption associated with the HIT protocol may result in a reduced adaptive response over time.
The markers of metabolic stress and the acute hormonal response measured in this study may potentially predict the long-term adaptive responses to resistance training programs in trained individuals (26,32). Proper manipulation of all program design variables is crucial when attempting to elicit these responses after exercise. Although untrained individuals may see similar increases in muscular strength and hypertrophy after 8–10 weeks of intensity-equated high- vs. low-volume resistance training (3,27), volume seems to be the driver of improvements in muscular strength and hypertrophy in trained individuals. This has been shown in studies prescribing volume-equated programs with varying intensities (19,33,34). Even when training frequency is varied (i.e., training each muscle group once vs. multiple times per week), volume seems to be the driver of the improvements in muscular strength and hypertrophy (10), although some have suggested that higher training frequencies may elicit greater muscular adaptations independent of training volume (7). Further research is needed to adequately test that model; however, along with the results of the current investigation, these data further support the idea that higher volume, multiple-set resistance training bouts may disrupt homeostasis to a greater magnitude and elicit a greater adaptive response than single-set bouts even when intensity is equated and TUT considered.
One limitation of this experiment was the lack of a single-set non-HIT group. If a single-set group that followed a traditional resistance training protocol was included, perhaps there would have been different responses between this group and the HIT group. Also, this investigation explored the acute physiological responses of 2 different resistance training bouts, so it is difficult to extrapolate these results to predict the chronic responses on power, strength, and hypertrophy. Although acute HR, lactate, testosterone, and cortisol responses can be indicative of the adaptations that will take place after exercise, the subsequent physiological adaptations that correlate with these responses require much more research, particularly in trained individuals. For instance, if the “secondary” hormones associated with testosterone (i.e., GH and IGF-1) had also been measured for longer periods, perhaps the anabolic environment after these 2 protocols would have been better understood because these hormones may not peak until 16–28 hours after exercise (21). Future studies should aim to determine the acute physiological responses of both various resistance training protocols, and how these acute responses correlate with the chronic biochemical responses and muscular adaptations.
The results of this study show that a 3 set per exercise traditional exercise bout induces greater metabolic stress and disrupts homeostatic balance to a greater degree than a single set per exercise HIT program as evidenced by greater peak HR, lactate, and cortisol responses. Thus, the 3-set protocol may elicit more favorable adaptations in the long-term as well. In conclusion, this study adds to the growing body of evidence that training volume seems to be the main driver of increases in muscular strength and muscle remodeling in resistance-trained individuals.
This study was funded in part by an Aresty Undergraduate Research Grant from Rutgers University. The results of this investigation do not constitute endorsement of any product by the authors or the National Strength and Conditioning Association. There are no conflicts of interest to declare.
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Keywords:Copyright © 2018 by the National Strength & Conditioning Association.
volume; strength; hypertrophy; metabolic stress