The inverse relationship between the maximum number of repetitions (MNR) and relative intensity [eg, % 1 repetition maximum (%1RM)] has been frequently utilized for training monitoring (18). Regarding this relationship, some formulae have been calculated for 1RM prediction from the MNR with submaximal loads (30,32,33) or from the loads associated to the MNR (1,12,15).
Also factors like experience, subjects genre, exercise type, and performing rate are demonstrated to affect this relationship (6,37,39). Moreover, some studies show performance differences when exercises are performed with machine or free weight, as the later demands a greater contribution of synergistic musculature (11,18). From these considerations, MNR is proposed as the best parameter for training monitoring (18).
Previous studies have shown the existence of potentiation and fatigue processes simultaneously after high-intensity exercises (8,23,34), pointing out the predominance of potentiation in resistance-trained subjects (9,20,23). In this regard, it is also suggested that the positive influence of endurance capacity on potentiation as a better load endurance capacity promotes a higher potentiation effect of preactivation processes (23). Positive influence of endurance and strength on potentiation could suggest the existence of some association between maximum strength and muscular endurance. Moreover, taken into consideration that high-load training improves high-load endurance capacity (9,40), it could be speculated an association between MNR with high loads and 1RM.
On the other hand, some studies presented evidence that performing series without muscular failure is an appropriated method in power training (3,21,22,36). Also, this method results in improvements in maximum isometric strength similar to maximum fatigue methods (19). As high-load endurance capacity has been suggested to be training volume dependent (40), it could be interesting to research into methods that allow achieving a higher training volume during training session. Cluster training (21,22) could be an approach to this objective, but we did not find references of assessment MNR at high relative intensity with cluster set configuration.
The main purpose of this investigation was to evaluate the association between 1RM and MNR and to assess the influence of exercise mode and load on this relationship. In this regard, MNR was evaluated at 90% and at 70% of 1RM in bench press (BP) and biceps curl (BC). Cluster set configuration with an interrepetition rest of 30 seconds (20,21) was used at 90% of 1RM because effectiveness of interrepetition rest for achieving a high training volume at high load was a secondary objective of this study. Likewise, correlations between 1RM and velocity along set were evaluated.
Experimental Approach to the Problem
One repetition maximum in BP and BC were evaluated in a resistance training experienced subject sample. These exercises were selected for testing exercise-type influence on MNR as BP involves various muscle groups (pectoralis majoris and triceps brachii), whereas BC involves less muscle mass (biceps brachii). Moreover, these exercises could be considered opposites as they are performed in different body positions (supine vs. seated); involve antagonistic muscle groups (extensor vs. flexor arm muscles); and are performed with different implements (free weight vs. machine).
During the following 2 weeks, all subjects performed MNR at 90% 1RM as high-intensity condition and MNR at 70% of 1RM as medium-intensity condition in both exercises. In attempt to test the training volume hypothesis, 2 set configurations were established in each intensity condition in both exercises. Cluster configuration (21,22), with an inter-repetition rest interval of 30 seconds, was used for high-intensity condition. Traditional or continuous set configuration was used for medium-intensity condition. The design was balanced for exercise and load factors.
Thirteen male subjects volunteered for this study. All subjects were familiarized with the research procedures and gave their informed consent. The experimental procedure was approved by the local ethics committee of the University of A Coruña. All of them had at least 6 months of experience in weight training, with a minimum of 3 training days per week, as they were preparing for police or fire fighter trials in a fitness center. Training regimens were designed according to concurrent model (14). Subjects' characteristics are shown in Table 1.
One repetition maximum tests were performed in the week before MNR tests. After a warm-up of 10 minutes on a cyclergometer at a freely chosen load, subjects were evaluated in 1RM in BC with dominant arm and BP according to a previously described incremental protocol (29).
The election of upper-body resistance exercises was based on subjects' training regimen. Police and fire fighter trials require the development of upper-body muscular endurance, whereas lower body resistance training is oriented toward explosive strength. Therefore, subjects were more experienced in upper-body activity that would be demanded in MNR assessment. Evaluated exercises were frequently used in subjects' training, so they were familiarized with them.
Tests were performed on separated days by at least 48 hours. One repetition maximum relative to body mass (1RM/body mass) was also calculated. The subjects were helped with bar loading before starting the BP tests. Repetitions were considered valid when the bar clearly touched the chest in eccentric phase and when full extension was totally achieved at the end of concentric movement. During BC tests (ie, “preacher curl”), the subjects started with a maximum elbow flexion (hand-to-shoulder) and with the arm totally leaned on a sloping bench at 45° while they maintained the other arm behind the back. Repetitions were considered valid when they fully extended the elbow before a new full flexion. The handgrip was connected to a low pole by a steel cable (X-Pression, Panatta Sport, Italy).
During 2 weeks after 1RM tests, the subjects performed MNR tests of both exercises with high and medium loads. The design was balanced for exercise and load factors. Before starting the tests, they performed a 10-minute warm-up on the cycle ergometer and some calisthenics during 5 minutes. Immediately after this general warm-up, they performed 10 repetitions at 50% of 1RM and 5 repetitions at 70% of 1RM with 3 minutes of rest as special warm-up for the following test.
Medium-intensity tests consisted of performing MNR with the 70% of 1RM in BC and BP. In this case, continuous set configuration was used with interrepetition stops of 2 seconds at final positions, which the load was self-maintained by the subjects. High-intensity tests consisted of performing MNR with the 90% of 1RM in a cluster set configuration. Inter-repetition rest interval was 30 seconds as suggested by Haff et al. (20,21). Subjects maintained their normal training regimens that consisted of a great variety of training methods (including running training), as they had a wide range of experience and personal objectives. They were advised against training the involved muscle groups the day before data recordings. Each recording was separated by at least 48 hours.
During test execution, the subjects were suggested to perform all repetitions with maximum volitional velocity. The velocities of the bar in BP and of the load in BC were measured with a linear encoder (MuscleLab, Bosco Systems, Norway) connected to a PC. Signal were recorded at a frequency of 100 Hz. Maximum mean velocity in 1 repetition; mean velocity of the first repetition; mean velocity of the last repetition; minimum mean velocity in one repetition and mean velocity during all repetitions were considered for analysis.
Descriptive parameters are shown as mean ± SD or range. Normal distribution of parameters was tested with Kolmogorov-Smirnov (Lilliefors) test. Repeated measures Analysis of variance (ANOVA) of 2 levels (load × exercise) were employed for variance analysis. Simple effect of exercise factor for each load was analyzed with Bonferroni adjustment in critical level. Significance level was set at p ≤ 0.05. Spearman rank order correlation was employed on test correlations among parameters. Larger correlation of 0.553 would be significant because of sample size (13 subjects; 11 freedom degrees) and significance level (α = 0.05, 2 tailed). The statistical power (α = 0.05, 2 tailed) for ANOVA ranged between 16.2% for interaction and 92% for load. Although statistical power for simple effect of exercise at 70% of 1RM was 99%, large variability caused a low statistical power for 90% of 1RM (9.5%).
One repetition maximum performances are shown in Table 1.
ANOVA 2 × 2 (load × exercise) revealed a significant effect of load (p < 0.01), and a tendency in exercise factor (p = 0.096), whereas the interaction effect was not significant (p = 0.315). We did not find significant differences in MNR among exercises in high-intensity condition (21.85 ± 11.06 vs 18.54 ± 12.84 repetitions in BP and BC, respectively; p > 0.05). As can be seen from Figures 1 and 2, simple effect of exercise was significant in MNR at medium-intensity condition (16.31 ± 2.59 vs 8.77 ± 3 in BP and BC, respectively; p < 0.05). Interpolation lines among MNR performances in both exercises are shown in Figure 3. The coefficients of variation (CVs) in the high-intensity condition were 50.6% and 69.3% for BP and BC, whereas CVs of 15.9% and 34% were calculated at 70% of 1RM for BP and BC, respectively.
Correlations between 1RM and MNR parameters are shown in Table 2 for bench press and Table 3 for biceps curl. The correlation between 1RM and MNR was only significant and negative for medium-intensity in biceps curl (Table 3). Neither 1RM nor 1RM relative to body mass correlated with velocity. Individual mean velocity data points during MNR assessment are shown in Figure 4.
A novel approach in this study was to evaluate correlations between 1RM and MNR in various conditions as a function of exercise type, set configuration, and relative intensity. From these considerations, it is interesting to note that only a tendency (p = 0.096) was detected by ANOVA for exercise, whereas a significant interaction was not found (p = 0.315). Nevertheless, differences in MNR among exercises at 70% of 1RM were significant (p < 0.001). This is clearly represented in Figure 3 as the slopes of the interpolation lines are similar but with MNR differences at 70% of 1RM point.
This finding is similar to other studies in the way that the longer the involved muscle mass is, the higher the MNR are performed (17,25,28). On this matter, Shimano et al. (38) found significant differences in MNR between BP and BC at 60% of RM in untrained subjects but not for the rest of the conditions (60% for trained; 80% and 90% of 1RM for both trained and untrained). Consequently our data are only partially coincident with the results from these authors (39). One possible explanation for this divergence is the heterogeneous training status of our subjects as it is reflected in the high CVs in MNR, higher in the high-intensity conditions as previously observed in another study for 90° squat (26). Moreover, there are also some differences between both studies regarding the medium intensity selected (60% vs. 70% of 1RM) and the BC exercise mode (bilateral biceps vs. “preacher curl”).
Another interesting finding of our study was the achieving of a high volume of repetitions at high-intensity condition in both exercises allowed by cluster set configuration (21,22). In fact, in some cases of MNR at 90% of 1RM, we decided to stop the experiment when some subjects reached 35 repetitions and they could have been continuing. If we consider the 4 repetitions performed at 90% of 1RM in the study of Shimano et al. (38), it could be considered as highly effective to introduce rest intervals between repetitions in achieving a high volume of high-intensity training.
A diminished MNR index (number of repetitions/MNR) has been suggested previously by some authors (13,19) for strength development. If we consider the effectiveness of performing series without muscular failure for power development (3,21,22,36), and the dependence of high-intensity performance on training volume of high-intensity loads (40), it seems that inter-repetition rest could be an appropriate approach in resistance training. Further studies are needed for testing the effectiveness of pause magnitude between different MNR index series (7,13,35) or the employment of pauses between repetitions as reflected in our study.
As it can be seen in Figure 4, the cluster method allowed subjects to perform a high-repetition number and also to keep mean velocity along set. Regarding this, we suggest the use of cluster set configuration for the development and assessment of high-intensity muscular endurance. This would be an interesting approach for such sports as wrestling, judo, or weightlifting, which demand to repeat high-intensity muscular actions. We think this could open new perspectives on investigation and practical applications.
Significant correlations were detected between 2 intensity conditions in each exercise (0.632 and 0.582 for BC and BP, respectively; p < 0.05) in a similar manner as previously described for 90° squat exercises (26). These data suggest a link between high- and medium-intensity muscular endurance performance that is constant across different exercises.
One of the principal purposes of this investigation was to evaluate the relationship between 1RM and MNR and to assess the influence of exercise mode, relative load, and set configuration on this link. Regarding this, the correlation between maximum strength and MNR was only significant at medium intensity in BC for 1RM (r = −0.574; p < 0.05) and normalized 1RM (1RM/body mass) (r = −0.574; p < 0.05). In contrast, no significant correlations were found between MNR and 1RM in BP. These data are consistent with previously described for 90° squat exercise (26). However, Shimano et al. (38) found a negative correlation between MNR and 1RM in BP at 90% of 1RM. This absence of agreement between studies could be attributable to experimental design differences such as allometric scaling for maximum force characterization (5) in the study of Shimano et al. (38) or different BC exercise selections and set configuration employed in our study for 90% of 1RM load.
Previously, an inverse relationship between the percentage of type II fibers and MNR at a given intensity was suggested (16,24). Furthermore, a relationship between the percentage of type II fibers and maximum torque (2,4,41) or strength performance in athletes of different levels (25) has also been suggested. Although this relationship could be controversial (10,31,38), we suggest taking it into consideration for the understanding of the correlation between 1RM and MNR in BC at 70% of 1RM in our study. Unfortunately, muscular biopsies were not performed.
On the other hand, some authors suggest a relationship between maximum strength and endurance capacity, especially in high-intensity conditions (9,40). In this regard, the negative correlation between 1RM and MNR in BC at 70% of 1RM was surprising. Otherwise, these later studies focused on the relationship between explosive tasks and medium-intensity loads (40).
Another possible explanation about this correlation could be related to the subjects' training background as the training methods in BC are typically based on medium loads, whereas high loads are more often utilized during training in BP. Further studies are needed for clarifying the relative influence of fiber composition, maximum strength, training background, and endurance performance in resistance training.
Neither 1RM nor 1RM relative to body mass correlated with velocity along set, so velocity seems to be similar for different maximum strength levels. Otherwise, MNR only correlated in curl biceps at 70% of 1RM with maximum mean velocity in 1 repetition (r = 0.764; p = 0.005) and mean velocity of the last repetition (−0.564; p = 0.045). The correlation was also significant between MNR in curl biceps at 70% of 1RM and coefficients: minimum mean velocity in 1 repetition/maximum mean velocity in 1 repetition (r = −0.670; p = 0.017), mean velocity of the last repetition/ mean velocity of the first repetition (r = −0.618; p = 0.024); minimum mean velocity in one repetition/mean velocity of the first repetition (−0.623; p = 0.021); mean velocity of the last repetition/maximum mean velocity in one repetition (r = −0.670; p = 0.017); and minimum mean velocity in one repetition / maximum mean velocity in one repetition (r = −0.670; p = 0.017). Taking all of them into consideration, it could be interpreted that those who achieved a higher MNR, had a greater velocity drop in this exercise and at this load. These associations were not significant for the rest of the exercises and loads. In this regard, Izquierdo et al. (26,27) found that the significant velocity loss during MNR was later in parallel squat than in BP (48% MNR vs. 34% MNR). From these considerations, we suggest the existence of an exercise-dependent pattern in velocity loss.
In summary, the results of this study indicated the existence of relationship between 1RM and MNR only in medium-intensity condition in BC. Neither 1RM nor 1RM relative to body mass correlated with velocity along set, so velocity seems to be similar for different maximum strength levels. Also the influence of exercise type on MNR was confirmed. Regarding to set configuration, cluster set configuration would be an interesting method to achieve a high upper-body work amount at high intensities in the same training session (ie, 90% RM). So assessment of MNR and training at high intensities with interrepetition rest could be interesting for sports with the objective of high-load muscular endurance.
From our results, we suggest the employment of MNR instead of the percentage of 1RM for training monitoring as MNR is influenced by different factors such as exercise type.
Also, we recommend the introduction of cluster set configuration for upper-body assessment of MNR and upper-body training muscular endurance at high-intensity loads (ie, 90% 1RM), as it seems an efficient approach for seeking greater sessions training volumes. This could be an interesting approach for such sports as wrestling or judo.
We would like to recognize the collaboration of the Spanish representative of Panatta Sport for his donation for subject recruitment. Conflicts of interest: none identified.
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