Muscle Mass and Training Status Do Not Affect the Maximum Number of Repetitions in Different Upper-Body Resistance Exercises

Method: Thirty participants, 15 trained (T) and 15 untrained (UT) men, volunteered to participate in this study and attended six separate occasions, each separated by at least 48 h. In the first three sessions, familiarization and 1RM tests were evaluated. The last three sessions were designed to assess the performance of the RM’s at 60%, 75%, and 90% 1RM. The exercise order and intensities performed in each session were randomized. Muscle action velocity for each repetition was controlled by an electronic metronome.


INTRODUCTION
One of the most important variables to consider in the development of the resistance training prescription is exercise intensity [1], which is considered one of the program variables that dictate the magnitude of training-induced neuromuscular adaptations [2].Depending on an individual's training experience and current level of fitness, proper loading encompasses one or more of the following loading schemes: increasing load based on a percentage of 1RM, increasing absolute load based on a targeted repetition number, or increasing loading within a prescribed zone (e.g., 8-12 RM) [3].
Based on the inverse relationship between the amount of weight lifted and the maximum number of repetitions (RM's) performed [4 -6], the prescription of resistance exercise intensity is usually based on a percentage of one repetition maximum test (%1RM) [7].Previous studies investigating the relationship between RM`s and %1RM have shown that different factors influence the RM's during resistance exercises: the amount of muscle mass used [4,5,8], the training status of participants [5,8,9] and the movement velocity of each repetition [10,11].Hoeger et al. [5] reported that at 80% of 1RM an individual can perform 10-15 RM's for exercises such as the bench press, leg extension, lat pulldown, and leg press (i.e., multi-joint exercises); while at the same intensity the same individual can perform only 6-8 RM's for the leg curl, and for the arm curl (i.e., single-joint exercises).
Regarding the training status of participants, controversial results have been found.Pick and Becque [9] reported that trained individuals are able to perform more repetitions in the squat exercise at 85% 1RM compared to untrained subjects.In contrast, Shimano et al. [8] showed that untrained participants performed a significantly greater number of repetitions than trained subjects during bench press at 90% 1RM, although no differences between groups at 60 or 80% 1RM for bench press were found.In addition, previous studies have demonstrated that the RM's can vary with different movement velocities, with a higher number of RM's produced under faster conditions, and this effect becomes greater with lower intensities [10 -12].Although the relationship between the percent of 1RM and the RM's performed is affected by the movement velocity, the previous above-mentioned studies did not control this variable [4,5,8,9].Consequently, studies on the relationship RM`s and %1RM that controlled the movement velocity are scarce [13].In addition, controversial results have been shown in studies comparing this relationship in trained and untrained participants [8,9].Therefore, the purpose of the present study was to compare the number of repetitions performed at 60, 75%, and 90% of 1RM in 4 different upper-body free weight exercises, controlling the movement velocity of each repetition.The working hypothesis was that, using the same percentage of 1RM, trained and untrained subjects would perform similar number of repetitions in four different muscle groups of upper-body exercises.

Participants
Thirty participants (15 trained and 15 untrained men) volunteered to participate in this study.The trained group (T) had been engaged in regular resistance training in the last 2 years at least three times per week using free weight exercises.The untrained participants (UT) were physically active but had not engaged in any resistance-training program before the study.All participants were free of any musculoskeletal, bone and joint, or cardiovascular diseases.Moreover, the participants reported that were not taking steroid anabolic medications.In order to participate in this study all subjects were informed about the procedures and potential risks and gave their written informed consent.The study was approved by the local Research Ethics Committee and is in accordance with the Declaration of Helsinki.Sample size was calculated based in a previous study [8] using PEPI software (version 4.0) and determined that a sample size of n=15 subjects would provide a statistical power of 90% and a correlation coefficient of 0.8 for all variables.

Experimental Design
In order to evaluate the efficacy of resistance exercise prescription based on percentages of 1RM, the number of repetitions performed at 60%, 75%, and 90% of 1RM in 4 different upper-body free weight exercises (i.e., bench press, barbell triceps extension, unilateral dumbbell elbow flexion, unilateral bent knee dumbbell row -Fig.( 1)) were determined.The loads corresponding to 60, 75, and 90% of 1RM were used due its potential to maximize adaptations in local muscular endurance, hypertrophy, and muscular strength, respectively [7].Participants attended six separate occasions, each separated by at least 48 h.The tests and experimental protocols were performed at the same time of day to avoid variations related to circadian rhythms and under the same conditions (i.e., no resistance exercise for at least 24 h and no stimulants for 12 h before each experimental session).In the initial session, body mass, height and body composition using a 7-sites skinfold prediction technique [14] were assessed.After that, participants performed a familiarization in order to practice the resistance exercises and standardize the technique and range of motion of the resistance exercises.The next two sessions were randomly performed (i.e., exercise sequence and the percentages) to determine 1RM in four upper-body free weight exercises: bench press, bilateral triceps extension, unilateral dumbbell elbow flexion and unilateral bent knee dumbbell row.The participants warmed up for 5 min on a cycle ergometer, and performed specific movements with 1 set of 10 repetitions with light load (50% of the first test load) in the exercise tests.Two 1RM tests were performed each day (bench press or barbell triceps extension and unilateral dumbbell elbow flexion or unilateral bent knee dumbbell row) and a ten-minute recovery was used between exercises.Each subject's 1RM was determined with no more than five attempts with a three-minute recovery between each.Participant performance characteristics are reported in (Table 1).The last three sessions were designed for the performance the maximum number of repetitions (RM's) tests, in which three different percent of 1RM were used in each exercise (i.e., 60%, 75%, and 90% of 1RM).Each day the participants performed one exercise; the exercise order and intensities performed in each session were randomized.In order to perform the RM's tests, the participants warmed up for 5 min on a cycle ergometer, and performed a warm up set of ten repetitions using 50% of 1RM [15,16].Thereafter, each participant performed a maximal attempt using the load corresponding to the selected percentage of 1RM.Movement velocity for each muscle action (i.e., concentric and eccentric) was two seconds and was controlled by an electronic metronome (MA-30, KORG; Tokyo, Japan).If the individuals could not maintain the controlled velocity the exercise was interrupted and the test was ended and considered completed.

Statistical Analysis
Results are reported as mean ± standard deviation (SD).Normal distribution of data was checked with Shapiro-Wilk.The comparison between performance characteristics by group was performed using Student's independent ttests.Statistical comparisons regarding the number of repetitions among different exercises in each load and between groups were tested using a mixed model two-way ANOVA, using repeated measures for different exercises in each percentage evaluated.Significance was accepted when P <0.05 and the SPSS statistical software package (version 22.0) was used to analyze all data.

RESULTS
The performance characteristics presented in Table 1 showed higher 1RM values for all exercises in trained subjects (p<0.001), which reinforce the different training status of participants in the present study.
The number of repetitions performed at 60, 75, and 90% of 1RM on bench press, barbell triceps extension, unilateral dumbbell elbow flexion and unilateral bent knee dumbbell row are described in (Table 2).There was no significant difference between T and UT in any of the exercises and loads evaluated.The number of repetitions during the row exercise was significant lower when compared to other exercises at 60 and 75% 1RM.However, comparing exercises with different muscle mass (i.e., bench press vs. triceps extension, and dumbbell row vs. elbow flexion), the same number of repetitions in each percentage was performed in those that utilize greater muscle mass (i.e., bench press and dumbbell row) compared to the exercises with less amount of muscle mass.

DISCUSSION
The primary finding of the present study was that, independent of the muscle group exercised, there was no difference on the number of repetitions performed by different upper-body free weight exercises at 60%, 75% and 90% 1RM.In addition, the training status of subjects does not affect the number of repetitions performed in each percentage of 1RM.To the best of our knowledge, this was the first study design that controlled all main factors that could potentially interfere in the number of repetitions performed at a given percentage of 1RM (i.e., training status, amount of muscle mass, and movement velocity of each repetition).The present results showed that RM's performed at a given percentage of 1RM, when movement velocity is controlled, is not dependent on the absolute muscle mass involved during free weight upper-body exercises.However, previous studies have found that large muscle mass exercises allow a higher RM's when compared small groups [4,5,8].
Hoeger et al. [5] investigate the relationship between RM's at different percentages of 1RM and reported that at 80% of 1RM an individual can perform 10-15 RM's for bench press, leg extension, lat pulldown, and leg press exercises, while for the same intensity the individual can perform 6-8 RM's for the leg curl, and for the arm curl exercises.Likewise, Shimano et al. [8] try to determine the RM's that trained and untrained men could perform at 60, 80, and 90% of 1RM in 3 different exercises: hack squat, bench press, and arm curl.The authors also concluded that the RM's performed during free weight exercises are influenced by the amount of muscle mass used.It has been shown that faster velocities allow performing a higher RM's during resistance exercises [10,11,16].However, the previous abovementioned studies did not describe how the movement velocity of each repetition was controlled, which can potentially explain these controversial findings.Because the movement velocity influences the number of repetitions achieved, it is not possible to compare properly different exercises, as well as different intensities with no velocity control.In addition, the number of repetitions performed at a given intensity influences the mechanical overload, and consequently, the neurophysiological, hormonal, and metabolic responses, which can also influence the strength gains and muscle hypertrophy resulted from resistance training [17].Besides, it has been suggested that increasing the repetition duration without changes in the repetition numbers per set could increase the metabolic response provided by resistance training [18].
Another interesting result of the present study was that the training status of participants does not affect the number of repetitions performed in each percentage of 1RM.Previously, Pick and Becque [9] demonstrated that trained individuals performed a higher RM's in the squat exercise at 85% 1RM compared to untrained.In contrast, Shimano et al. [8] showed that untrained participants performed a significantly greater number of repetitions than trained during bench press at 90% 1RM, although no differences between groups at 60 or 80% 1RM for bench press were found.Methodological differences, especially regarding the movement velocity of each repetition during the RM's tests and the use of different resistance exercises could be an explanation for those discrepancies.
Our findings have an important implication for resistance exercise intensity prescription, since the use of a specific percentage of 1RM can be used for target the same maximum number of repetitions in different free weight upper limb exercises.Second, movement velocity of each repetition throughout each set should be standardized in order to allow the same goal using the same percentage of 1RM, facilitating the exercise prescription and management of a group of athletes or recreational weight lifters.However, some limitations should be taken into account in order to interpret the results.Our sample consisted of men only, therefore limiting the generalization of our findings to the female population.Moreover, lower limb resistance exercises were not evaluated and should take into account in future studies.

CONCLUSION
In conclusion, the amount of muscle mass used during upper-body resistance exercises does not influence the number of repetitions performed at 60, 75 and 90%1RM.Likewise, the training status of participants does not affect the maximum number of repetitions performed when the movement velocity of each repetition is controlled and maintained constant throughout the set.