Maximal power output can be defined as the explosive nature of force production (11). The importance of power output on athletic performance has long been established because many sport movements (e.g., jumping, sprinting, changes of direction, throwing) require the production of force over short time intervals (22). Consequently, several authors have shown differences in power output development (and dynamic performance) in a variety groups such as well-trained athletes vs. untrained controls (5), power-type athletes vs. endurance athletes (4), rugby players involved in national vs. state competitions (2), as well as stronger vs. weaker individuals in a pool of resistance-trained men (36).
Among the wide range of factors affecting power training prescription, including volume, intensity, velocity or rest interval (RI) between sets, the last RI has received less attention. As consecutive power output performance has been linked to the phosphagen system (which requires a minimum of 4 minutes for its full replenishment) (14), some authors have recommended a RI of at least 3 minutes when training for power development (1,26). For instance, Ratamess et al. (27) showed that at least 3 minutes of RI is necessary to maintain bench press performance over 3–4 sets. Nevertheless, other authors have shown that a 2-minute RI is enough to maintain both the number of repetitions completed (34) and power output production (15) when using the bench press exercise. In addition, Nibali et al. (23) showed no differences in acute power output production when comparing long (4 minutes) with short (1 minute) RIs across multiple sets of jump squats, whereas Robinson et al. (30) did not find any differences in vertical jump power output adaptations after 5 weeks of training with different RIs (30 vs. 90 vs. 180 seconds). However, all of these studies used homogeneous samples and did not study the possible influence of strength level on the power output responses to different RIs.
The discrepancies showed in the previously mentioned studies can be partially explained by differences in experimental design, such as the variable used to quantify fatigue (i.e., volume completed vs. power output), or the intensities employed (i.e., body mass vs. 70% of 1 RM). Although training with the load that maximized power output (i.e., 40% of 1RM in the bench press throw exercise) (16–18) has been suggested to be an effective stimulus to optimize power output adaptations and improve dynamic athletic performance (41), very few studies have previously analyzed the influence of different RIs during an upper-body power training session, much less taken into account the subjects' strength level. It has been shown in the literature that individuals with higher strength levels have clearly superior ability to develop power output than those with lower strength levels (4,5,21,36,38). The superior capability of stronger individuals to generate greater power output has been linked to both mechanical and neuromuscular characteristics. For instance, greater muscle pennation angle and larger muscle cross-sectional area (especially more pronounced hypertrophy of type II fibers) lead to greater level of strength (3,19) and consequently, because of this greater maximal strength, it strongly determines power ability (7). In addition, several neural factors, such as firing frequency, motor unit recruitment and intermuscular coordination, are partially responsible for the difference seen in power output production between stronger and weaker individuals (12,22). All of these variables may affect not only power output production, but also the RI required to maintain power output over consecutive sets.
Thus, despite the influence of strength level on the magnitude and mechanisms of adaptations after strength training has been widely studied (9,13,31,40), to the best of the authors' knowledge, no previous studies have examined the influence of strength level on the ability to maintain power output production or the RI required during a power training session based on subjects' strength level. Therefore, the aim of this study was to check the influence of strength level on the ability to sustain power output and both the physiological and perceived exertion responses during the bench press throw exercise when different RIs are used.
Experimental Approach to the Problem
The study used a within-subjects study design that evaluated the influence of strength levels on the ability to maintain power output and measured psycho-biological responses when using different RIs in the bench press throw exercise. Each subject attended 4 testing sessions in a 4-week period. The first session consisted of a 1RM bench press test, whereas the other 3 sessions consisted of the same protocol (i.e., 5 sets × 8 reps of bench press throw exercise) using 40% of 1RM, but differing in the RI used (i.e., 1, 2, or 3 minutes). During testing sessions, peak power (PP) output, lactate concentration ([La−]), and rating of perceived exertion (Borg 0–10 scale) were measured. In addition, delayed onset muscular soreness (DOMS) 24 hours and 48 hours postsession was recorded. To avoid experimental variability, the same researcher conducted all testing sessions, and subjects were scheduled at the same time for each session.
Eighteen physically active men and 20 physically active women took part in the study. For statistical analysis, both men and women were divided into a “stronger” and “weaker” group based on their peak power output, establishing 4 different groups: stronger males (SM; n = 9), weaker males (WM; n = 9), stronger females (SF; n = 8), and weaker females (WF; n = 12). Sample size estimation based on subjects' power output performance (80% power, p = 0.05) revealed that a sample size of 4 subjects was needed to find significant differences. Subjects were classified into each group by dividing the entire sample in 2 halves (the stronger and the weaker) and then reorganizing (if necessary) to achieve the following criteria. The difference in PP between subjects of each group had to be at least 10% (Table 1). All subjects had at least 12 months of experience in strength training and were currently carrying out strength training sessions at least 2 d·wk−1. All subjects completed a health history questionnaire to document that they were free of cardiovascular diseases, physiological disorders, or any other illness that may have increased the risk of participation or introduced unwanted variability into the results. All subjects were instructed to maintain their normal life habits. Throughout the investigation, participants were requested to maintain their regular diets and normal hydration state, not to take any nutritional supplementation or anti-inflammatory medications, and to refrain from caffeine intake in the 3 hours before each testing session. Strength training sessions were not allowed at least 72 hours before the experimental sessions. Before participation, each subject provided written informed consent approved by the Ethics Committee of the Miguel Hernandez University of Elche in accordance with the Declaration of Helsinki. All subjects were over 18 years old.
Maximal Dynamic Strength Assessment
The 1RM test for the bench press was performed using a Smith machine (Multipower M953; Technogym, Gambettola, Italy). The 1RM bench press was assessed using a previously established protocol (8), which requires that subjects progressively increase resistance across attempts until the 1RM is achieved. The rest period between trials was at least 5 minutes. Subjects began by lying horizontally with the feet, gluteus maximus, lower back, upper back, and head firmly planted on the bench with elbows fully extended and gripping the bar. Subjects lowered the bar until it lightly touched the chest, approximately 3 cm above the xiphoid process. The elbows were extended equally with the head, hips, and feet remaining in contact with the floor throughout the lift. No bouncing or arching of the back was allowed. Testing was conducted by the same researcher and all conditions were standardized.
Power Output Measurements
Three minutes after a warm-up consisting of 2 sets of 10 repetitions with the individual participant using 50% of 1RM, subjects performed 5 sets of 8 repetitions with a load representing 40% of 1RM. Subjects performed the experimental protocol in 3 sessions that varied the RI between sets (1, 2, or 3 minutes). The order of the sessions was randomized. Through each set, subjects were encouraged to throw the barbell as high as possible, and during each throw, they were required to keep their head, shoulders, and trunk in contact with the bench and their feet in contact with the floor. No bouncing of the barbell was allowed. Kinematic data were recorded by linking a rotary encoder to one end of the bar (T-Force system, Ergotech, Spain), which recorded the position of the bar with an analog-to-digital conversion rate of 1,000 Hz and an accuracy of 0.0002 m. The linear transducer was interfaced to a personal computer by means of a 14-bit analog-to-digital data acquisition board, where a specialized software application (T-Force Dynamic Measurement System) automatically calculated the relevant kinematic and kinetic parameters. Bar velocity was calculated by differentiation of bar displacement data with respect to time; then, instantaneous acceleration (a) was obtained through differentiation of velocity–time data. Instantaneous force (F) was calculated as F = m (a + g), where m is the moving mass (in kilograms) manually entered into the software, and g is acceleration because of gravity. Finally, instantaneous mechanical power output (P) was calculated as the product of vertical force and bar velocity (P = F × V). Peak power was taken as the maximum value of the power–time curve. The validity and reliability of this system have been previously established, with ICC values ranging from 0.81 to 0.91 and a coefficient of variation 3.6% (10). For the data analysis, the following variables were calculated: PP in each set, and PP of each repetition.
[La−] was determined from 25 ml capillary blood samples drawn from the earlobe and analyzed with a portable device (Lactate Scout; Senselab, Leipzig, Germany), with an accuracy of 0.1 mmol·L−1 (37). Samples were taken 1 minute before and after each protocol and analyzed at these time points by the portable lactate analyzer. For statistical analysis, the difference between prevalues and postvalues was used.
The Borg category scale (CR-10) aimed at determining the degree of heaviness and strain experienced in physical work (35) and was used to determine the subjects' localized (upper body musculature) rating of perceived exertion during exercise. The CR-10 scale was defined by the following anchor points: “rest” (0) and “maximal (10).” Subjects were asked, “How hard do you feel the exercise was?” immediately after the last set of each protocol. Before participation, all perceived exertion scales were conscientiously explained and all subjects declared themselves to be familiarized with the CR-10 scale.
Delayed onset muscular soreness was reported by the subjects 24 hours and 48 hours after each session. Subjects were asked, “How painful do your muscles feel?”, giving their subjective feeling on a 0–10 scale (0 = no pain; 10 = a lot of pain) (25). All subjects reported no DOMS before all testing sessions.
All data were analyzed using the statistical package SPSS 18.0 (SPSS Inc., Chicago, IL, USA). The normality of the outcome measures was tested using the Kolmogorov–Smirnov test. In each male and female strength level group (stronger and weaker), a single-way ANOVA was used to evaluate the physiological ([La−]) and perceptual (RPE and DOMS) variables with each RI, whereas a repeated measures ANOVA was used to evaluate interset and intraset mechanical (PP) data. Statistical significance was set at p ≤ 0.05. In addition, to better evaluate the treatment effect (different strength levels and RIs), Cohen's d and the standardized mean difference were used to calculate effect sizes (ES; mean difference/pooled SD) and interpreted for a recreationally trained sample (subjects with strength training experience ranging from 1 to 5 years) according to Rhea (28), as d < 0.35 (trivial), 0.35–0.80 (small), 0.80–1.50 (moderate), and 1.5 (large) aiming at determining the relative magnitude of the ES calculated.
Peak Power Output
Peak power data for each RI in each group are showed in Figure 1 (WM and SM groups) and 2 (WF and SF groups). In men, when comparing the values between RIs, the WM group showed lower PP values with the 1-minute RI in the second (p = 0.015, d = 0.37; p = 0.007, d = 0.59), third (p = 0.007, d = 0.45; p = 0.007, d = 0.75), fourth (p = 0.019, d = 0.49; p = 0.01, d = 0.88), and fifth (p = 0.013, d = 0.65; p = 0.013, d = 1.03) set than the 2-minute and 3-minute RI, respectively. In addition, when using 2-minute RI, PP values were significantly lower than with the 3-minute RI in the second (p = 0.005, d = 0.23) and third (p = 0.028, d = 0.33) set. Similarly, the SM group showed lower PP values with the 1-minute RI in the second set (p = 0.026, d = 0.43) than the 3-minute RI, and in the third (p = 0.022, d = 0.46; p = 0.022, d = 0.47), and fourth (p = 0.004, d = 0.66; p = 0.002, d = 0.65) set than the 2-minute and 3-minute RI respectively, whereas no differences were found between the 2- and 3-minute RI.
In women, the WF group showed lower PP values in the second (p = 0.005, d = 0.37), third (p = 0.019, d = 0.54), fourth (p = 0.003, d = 0.83), and fifth (p = 0.002, d = 1.08) set when comparing the 1-minute RI with the 3-minute RI. In the SF group, only the fifth set (p = 0.017, d = 0.69) showed lower PP values when comparing the 1-minute RI with the 3-minute RI (Figure 2).
When comparing PP values over the sets within groups, with the 1-minute RI, the SM group showed lower PP output (p = 0.005, d = 0.35; p = 0.005, d = 0.51; p = 0.004, d = 0.74; p = 0.004, d = 0.58) in the second, third, fourth, and fifth set, respectively, compared with the first set. Nevertheless, when using both 2-minute and 3-minute RIs, the SM group did not show significant differences over the 5 sets. In the WM group, compared with the first set, PP values were significant lower in the second set (p = 0.035, d = 0.4) in the 1-minute RI, and in the third (p = 0.009, d = 0.75; p = 0.001, d = 0.47), fourth (p = 0.001, d = 1.11; p = 0.005, d = 0.73), and fifth (p = 0.001, d = 1.38; p = 0.001, d = 0.93) set in both the 1-minute and 2 minute RI, whereas no significant differences were found with the 3-minute RI (Table 2).
In women, when comparing PP values over the sets within groups (Table 3), with the 1-minute RI, the SF group showed lower PP output (p = 0.043, d = 0.24; p = 0.035, d = 0.6) in the second and fifth set, respectively, compared with the first set. When using both the 2-minute and 3-minute RI, no differences were found over the sets. In the WF group, compared with the first set, when using the 1-minute RI, PP values were significantly lower in the second (p = 0.003, d = 0.47), third (p = 0.017, d = 0.78), fourth (p = 0.006, d = 1.23), and fifth (p = 0.003, d = 1.49) set. In addition, when using the 2-minute and 3-minute RI, significantly lower PP values were found in the fourth (p = 0.034, d = 0.54; p = 0.03, d = 0.51) and fifth (p = 0.016, d = 0.73; p = 0.043, d = 0.63) set compared with the first set.
When comparing the same repetition over the sets when using the 1-minute RI, all groups showed significant differences in the 8 repetitions, independently of the group. Thus, ES ranged from 0.38 (p ≤ 0.05) to 1.56 (p < 0.01) (WM), from 0.19 (p ≤ 0.05) to 0.83 (p < 0.01) (SM), from 0.28 (p ≤ 0.05) to 1.75 (p < 0.01) (WF), and from 0.4 (p ≤ 0.05) to 1.03 (p < 0.01) (SF).
Comparisons in PP by repetition over the sets with the 2-minute RI are shown in Figure 3 (WM and SM groups) and Figure 4 (WF and SF groups). Both WM and WF groups showed significant decreases in PP commencing from the first repetition, whereas these decreases were only significant commencing from the sixth (SM group) and the fifth repetition (SF group). Moreover, ES were considerably greater in both weaker groups, ranging from 0.27 (p ≤ 0.05) to 1.18 (p < 0.01) (WM) and 0.23 (p ≤ 0.05) to 0.95 (p < 0.01) (WF), whereas for the stronger groups they ranged from 0.18 to 0.35 (p ≤ 0.05) (SM) and from 0.26 to 0.39 (p ≤ 0.05) (SF).
When the 3-minute RI was used, the WM group showed significant PP decreases commencing from the second repetition, whereas these decreases commenced from the first repetition in the WF group. ES values ranged from 0.37 (p ≤ 0.05) to 0.7 (p < 0.01) in the WM group and from 0.25 (p ≤ 0.05) to 0.75 (p < 0.01) in the WF group. Contrarily, the SF group did not show any differences in PP output independently of the repetition analyzed, whereas the SM group only showed slight PP decreases in the second repetition and in the last repetitions of the set, with trivial ES (d = 0.14–0.34; p ≤ 0.05).
Physiological and Perceptual Variables
Data of physiological and perceptual variables are shown in Table 4. No difference between groups (stronger vs. weaker) was found in any variable in the men. Nevertheless, the WF group showed significantly greater [La−] increase in both the 2-minute RI (d = 1.17; p < 0.01) and the 3-minute RI (d = 1.8; p < 0.01) compared with SF group. In addition, the WF group experienced greater DOMS48h after the 3-minute RI (d = 1.07; p < 0.01) compared with the SF group. When comparing the influence of the different RIs within the same group, greater [La−] were found with the 1-minute RI compared with both the 2-minute (d = 0.99 SM; 1.48 SF; 1.37 WF; p < 0.01) and the 3-minute RI (d = 1.39 SM; 1.72 WM; 1.73 SF; 1.77 WF; p < 0.01). Furthermore, [La−] was also higher in the WM group when comparing the 2-minute RI with the 3-minute RI (d = 1.11; p < 0.01). RPE values were significantly higher in the SM, WM, and WF groups between 1-minute and 3-minute RI protocols (d = 1.03, 1.02 and 0.81, respectively; p < 0.01) and in both SM and WM groups between the 1-minute and the 2-minute RI (d = 0.62 and 0.8, respectively). For DOMS 24 hours, only the WM group showed greater values when comparing the 1-minute RI with the 3-minute RI, and the 2-minute RI with the 3-minute RI in the SF group (d = 1.0; p < 0.01). Finally, only the WM group showed significantly greater values of DOMS 48 hours when comparing the 1-minute RI with the 3-minute RI (d = 0.9; p < 0.01).
The primary finding of this study was that subjects' strength level highly influences the rest interval required to sustain power output production. This was shown by the ability of both the male and the female stronger groups to maintain peak power output over the sets when using both the 2-minute and the 3-minute RI, whereas weaker male and female groups needed at least a 3-minute RI to maintain it. In addition, physiological variables ([La−]) also showed greater values when comparing weaker and stronger groups (although only in women). Nevertheless, perceptual variables (RPE and DOMS) seemed to be a less sensitive tool for strength level comparisons in the protocol (and sample) used in the current study, as it only showed clear differences between the 1-minute RI and both the 2-minute and the 3-minute RI, independently of subjects' strength level.
Despite a couple of studies showing that 1-minute RI did not entail PP production impairments (20,23), the results of the present study agree with several authors who showed significant performance reductions when short (1 minute) RIs were used (1,34,39). Thus, over the sets, significant PP output decreases were found with the 1-minute RI independently of the strength level and gender analyzed, commencing from the second set in all groups. However, when using longer (2 minutes and 3 minutes) RIs, the results differ depending on strength level, as the stronger male (SM) group did not show PP decreases, whereas the weaker male (WM) group showed decreases commencing from the third set (2 minutes RI) (Table 2). Similarly, the weaker female (WF) group also showed significant PP decreases commencing from the fourth set (with both the 2-minute and 3-minute RI), whereas the stronger female (SF) group showed significant decreases commencing from the second set (1-minute RI), but did not show impairments when using the 2-minute RI (Table 3). Therefore, stronger subjects seemed to have a superior ability to recover and repeat power output performance, which may be hypothetically explained by an optimized neuromuscular behavior such as enhanced motor unit recruitment and intermuscular coordination (6,31). Even so, other neuromuscular mechanisms such as changes in neural functions (e.g., muscle coactivation) may also be responsible for the impairments found when short (1 minute) RIs were used (24,32). Analysis of intraset PP is of great importance when comparing stronger and weaker groups. For instance, when the same repetition of each set was compared over the sets, both WM and WF groups showed significant PP decreases even from the first and second repetition (and commencing from the second and third set), even while using the 3-minute RI. Nevertheless, these PP decreases were found much later (i.e., fifth repetition in the SF group and sixth repetition in the SM group) when using the 2-minute RI. Furthermore, no differences were found between any repetitions over the sets when the SF group rested for 3 minutes. Previous studies revealed that PP decrements within a set increase as the number of performed repetitions in a set approaches the maximum predicted number (16,33) although these studies showed much greater values of performance decreases, probably due to the lighter load (40% of 1RM) used in the current study.
Strength level seems to play a role in lactate responses, at least in women, because the WF group showed greater [La−] increases compared with the SF group when using 2-minute and 3-minute RIs (Table 4). From a physiological perspective, the greater decreases found in PP output with the 1-minute RI compared with both 2-minute and 3-minute RI were accompanied by significantly greater [La−] increases in all groups, these results being in line with those showed by Abdessemed et al. (1) and reflecting a greater contribution of the glycolytic system as a source of energy production. The use of rating of perceived exertion scales has been described previously as a sensitive tool to control the intensity of training sessions (29). Thus, RPE values were significantly higher in the SM, WM, and WF groups when the 1-minute RI was used compared with the 3-minute RI, and compared with the 2-minute RI in both SM and WM groups. These results are in line with Scudese et al. (34) who showed greater RPE values when using 1-minute RI in comparison with 3-minute RI. Nevertheless, no differences between stronger and weaker groups were found with the 3 different RIs used in the current study, neither in DOMS24h or DOMS48h (with the exception of greater DOMS48h after the 3-minute RI in WF). Consequently, in spite of the sensitivity of these tools in measuring the intensity of training sessions, it seems that strength levels do not highly influence subjects' perceptual responses when practitioners of recreational/intermediate strength levels performed a bench press throw power training session (5 × 8 at 40% of 1RM). It should be tested if these kinds of perceived scales could show differences between groups of broader strength levels (e.g., novice vs. elite athletes).
The current study presents some limitations including both the lack of direct measures of central/neural fatigue (i.e., electromyography) and the lack of hormonal response measurements that could provide additional information. Furthermore, the effect of different strength/power levels on the RI required should be further investigated with different ranges of loads and in different and more complex exercises (e.g., weightlifting/power movements).
The results of the present study highlight the influence of subjects' strength level on the ability to maintain power output production during a session of bench press throw exercise with a power load. Thus, scientists and coaches should take into account athletes' strength level when designing research experiments or when programming power training sessions, as a 2-minute RI could be enough to maintain power output over 5 sets in the stronger population, whereas with the weaker population, even when using the long (3 minutes) RI, significant power decreases can be expected after the third set. Nevertheless, these considerations should be investigated in other exercises (e.g., lower body, weightlifting movements) and populations (e.g., elderly).
No funding was received to carry out this study.
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