Accuracy of 1-RM Prediction Equations for the Bench Press and Biceps Curl

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Accuracy 1-RM Prediction Equations

Sports Physiology

Accuracy of 1-RM Prediction Equations for the Bench Press and Biceps Curl

Matthew Hutchins, Randall Gearhart Jr

1Indiana State University, Terre Haute IN, USA,2Ashland University, Ashland OH, USA

ABSTRACT

Hutchins MD, Gearhart RF. Accuracy of 1-RM Prediction Equations for the Bench Press and Biceps Curl. JEPonline2010;13(3):32-39. Few studies have examined the validity of 1-RM prediction methods with smaller muscle groups. The researchers hypothesized that the prediction methods would yield valid estimates of 1-RM and accuracy of the prediction methods would not be affected by type of lift. Young (23.6 ±3.5 yrs.), recreationally trained males (n=27) were recruited. Experimental procedure: During trial 1, subjects completed 1-RM testing for the bench press and biceps curl. During the second trial, subjects completed repetitions to fatigue at a weight load equal to 85% of measured 1-RM. One-repetition maximums and number of repetitions performed at 85% measured 1-RM were recorded. Correlations between measured and predicted 1-RMs demonstrated a moderate to strong relationship (r = .81 - .97 bench press; r = .70 - .91 biceps curl). The means of the predicted 1-RMs for the bench press were 94.2 ± 24.2 kg and 94.9 ±24.5 kg. Both were lower than the mean of the measured 1-RMs (95.5 ± 26.5 kg). The means of the predicted 1-RMs for the biceps curl were 51.1 ±12.3 kg and 51.4 ± 12.4 kg. Both were higher than the mean of the measured 1-RMs 49.4 ± 11.8 kg. These differences were not significant. Error of prediction was between 5.4 and 6.8 kg for the bench press and between 5.3 and 6.9 kg for the biceps curl. The Total Error of Estimate was between 10.6% and 13.5% of the means.Employing either prediction equation appears to be appropriate for predicting bench press and biceps curl maximums.

Key Words: Resistance Training, Strength Testing, Dynamic Strength.

INTRODUCTION

Intensity for strength training is often based on a percentage of 1-repetition maximum (1-RM). The most widely accepted method of determining a person’s 1-RM is a direct one in which the maximum is actually achieved through a series of trials. This direct method is detailed by the American College of Sports Medicine (10). The second means of obtaining 1-RM is an indirect method in which an individual performs multiple repetitions at a specified weight load and those results are entered into one of many prediction equations (1, 2, 3, 4, 5, 7, 8, 13, 14, 15, 17, 18, 19, 20, 21, 23, 24). The 1-RM is a critical variable for the purpose of prescribing exercise in various populations. Actual 1-RM testing may not be appropriate with certain populations. These groups may benefit from the use of prediction equations aimed at estimating maximal strength. The use of multiple repetitions to predict 1-RM is beneficial. Most notably, the method is considered to be a safer method especially in the presence of known injury (1). The current study examined the validity of the Berger (2, 3) and O’Conner et al. (20) non-exercise specific 1-RM prediction methods for the bench press and biceps curl when compared to the determined 1-RM. These equations were chosen because they are two of the more commonly cited equations.

Knight (12)was one of the first to develop load specific exercise programs based on a person’s 1-RM. His method was known as the Daily Adjustable Progressive Resistance Exercise (DAPRE) and was used primarily for training persons on an individual basis and for patients recovering from injury. Knight (12) was one of the first to determine that prediction of 1-RM from lesser loads offers added safety for beginners and for those recovering from injury. This may prove beneficial for individuals hesitant to lift a maximal weight or those who are medically restricted from maximal exertion (13). As resistance training involves a variety of exercises performed for different muscle groups, it is critical to examine the nature of prediction equations as they relate to the various exercises. Most previous work has focused on core lifts or used exercise specific equations for smaller muscle groups (1, 7, 15, 17, 18, 19, 21). Core lifts are generally considered to be the bench press, deadlift, and squats. Research suggests that exercise specific equations are more accurate than non-specific equations in estimating 1-RM and that the accuracy of prediction decreases at higher repetitions (1, 5, 7, 15, 17, 18, 19, 24). Accuracy of prediction equations have also been shown to vary over different resistance exercises, particularly when linked to the size of the muscle groups and the range of the movement (4, 8, 10). As most resistance exercise sessions involve both core and accessory lifts, it is important to examine the accuracy of prediction during both types of lifts. The cumbersome process of using different prediction equations for each exercise makes this practice impractical. The examination of predictability from a single equation increases the likelihood that such equation would be most useful in the development of multi-RM testing procedures. This, combined with the ever increasing focus on the resistance training component of physical activity, prompted the current investigation.

Several investigations have indicated that dynamic muscular strength can be accurately estimated from multiple repetition testing with much of the research focusing on what are considered to be core lifts (1, 2, 3, 4, 5, 7, 8, 9, 12, 17, 18, 19). However, research does show that prediction equations may yield valid results with smaller muscle group lifts, especially when used with four to six RM loads (9, 24). Four to six- repetition maximum prediction equations improved the predictive accuracy of 1-RM strength compared to seven to ten-repetition maximum prediction equations (8, 9, 21, 24). There is general agreement that no more than ten repetitions should be used to estimate 1-RM regardless of the type of lift (8, 9, 24). Therefore, for the purpose of multiple repetition testing, the present research effort used a load equal to 85% of the measured 1-RM. Berger (3) indicates that a participant should be able to perform six to eight repetitions at this load. Stated differently, it is assumed that there is a 2 – 2.5% decrease in a person’s 1-RM mass for each single increase in repetition maximal (3). This difference could be much higher or lower depending upon previous training experience, learning phenomenon associated with proper technique and even certain psychological influences. In an effort to decrease the effects of learning phenomenon and training effects, recreationally trained males were chosen to participate in the current study.

Research shows that only one in five Americans meet minimum recommended activity guidelines as set forth by the Centers for Disease Control and Prevention (CDC) and the American Heart Association (AHA) (6). Current recommendations state that adults should engage in moderate-intensity aerobic physical activity on five or more days a week for a minimum of 30 minutes each day or in vigorous-intensity aerobic physical activity three days a week for a minimum of 20 minutes each day. Combinations of moderate and vigorous intensity activities can be combined to meet these recommendations. Recommendations further state adults should perform activities that maintain or increase muscular strength and endurance at least two days each week (6, 8, 10). These recommendations are supported by the American College of Sports Medicine (ACSM) (9) and by the CDC (6). As varying populations are being prescribed resistance exercise, this has led to a need to better understand the accuracy of prediction equations with different muscle groups. Resistance training using all major muscle groups has been shown to enhance the five health related components of fitness when performed properly. These components are 1) body composition 2) cardiorespiratory endurance 3) muscular strength 4) muscular endurance 5) muscular flexibility (9). Accurate estimation of the 1-RM for each major muscle group is a key aspect of proper exercise prescription and to the development of safe and effective resistance training programs.

The nature of the relationship between maximal and submaximal strength is a primary factor influencing the prediction of 1-RM. Brzycki (5)argues that there is a distinct relationship between anaerobic endurance and strength. Brzycki (5) goes on to state that it appears this relationship is not quite linear beyond ten repetitions. It is also possible that individual muscle groups have different relationships between maximal and submaximal strength. Therefore, the validity of prediction equations with the bench press and biceps curl may be different. Another consideration is the effect of increasing strength. Changes in muscular strength, in a given subject or population, has been shown to have little effect on prediction of 1-RM using submaximal loads (4).

For comparison purposes, the current study tested the validity of two prediction methods with a small muscle group as well as a large muscle group using non-exercise specific equations. It was hypothesized that the prediction methods would yield valid estimates of 1-RM and accuracy of the prediction methods would not be affected by type of lift.

METHODS

Subjects

Permission for the current investigation was approved by the Human Subjects Review Boards at Indiana State University and at Southern Illinois University-Carbondale. Twenty-seven male volunteers currently participating in recreational physical activity agreed to participate in this study. Mean age of the group was 23.6 ± 3.5 years. Twenty-two of the subjects identified themselves as Caucasian. Five subjects identified themselves as African-American. Subjects chosen for this study reported that they were currently incorporating resistance training as part of their physical activity regimen. Subjects additionally reported resistance training an average of 3.56 + 1.11 days per week. Subjects were excluded if they had recently, or were currently using a personal trainer. The subjects did not report skeletal muscle or cardiovascular complications during testing. Signed informed consent and a medical history were obtained from each subject prior to participation. Subjects were given instructions concerning test day procedures and what would be expected during each trial. Subjects reported they had a “good night’s rest“, maintained adequate hydration, avoided alcohol and tobacco prior to testing and avoided strenuous exercise the day of testing. This protocol was observed for both days of testing.

Procedures

Upon arrival to the laboratory, subjects read and signed informed consent forms before any testing took place. All questions were answered regarding the study procedures at this time. Height, weight, and training history were recorded. A brief medical history was obtained at this time. The subjects then underwent the first of two experimental trials beginning with 1-RM testing. The trials were separated by at least 48 hr. apart, but not more than one week.

As part of the initial session, testing was performed to assess the 1-RM for both the bench press and biceps curl exercises. A flat bench and an adjustable 45 degree curl bench were used for the respective lifts. The protocol developed by the American College of Sports Medicine was followed during this trial to determine 1-RM (9). Participants were allowed a light warm-up of 5 to 10 repetitions at 40% to 60% of perceived maximum. Following a 1-minute rest period, the participants performed 3 to 5 repetitions at 60% to 80% of perceived maximum. Additional weight was added in small increments until concentric failure occurred. 3 to 5 minutes rest occurred between attempts. To date there is no standard for minimal rest interval between successive 1-RM attempts (24). Several studies have used a two to three minute rest period (11, 22, 23). Other investigations indicate a rapid return in maximal force production following a fatiguing task (22, 23). The practical applications are that rest intervals, even relatively short ones, are not a major factor in the success of 1-RM attempts (23). Subjects were encouraged to lift additional resistance to be sure the maximal muscle force was achieved. Only when it was clear from their effort that no further resistance could be added was a non-failure trial accepted. The 1-RM was determined to be the most resistance the subject could concentrically lift once. Testing consisted of an average of 3 to 4 attempts with a maximum of 6 attempts. All lifts were conducted with an experienced spotter present.

Proper technique for the bench press was as follows. The subject lay horizontally on the back with arms flexed at approximately a 90 degree angle at the elbow. The hands were placed in a horizontal position and the width of the grip was set at shoulder width. Each subject started the lift at full extension of the elbows. The barbell was lowered to the chest, held 1 sec. before the arms were fully extended back to the starting position. Subjects were instructed that both portions must be completed in a controlled fashion.

Proper technique for the biceps curl was as follows. Subjects were seated at a 45 degree curl bench. The height was set so that the top of the curl bench was at mid-sternal level. Seat height allowed for both feet to be planted on the ground and for the back to remain straight. A spotter assisted the subject to a starting position at the top part of the lift. At this point, the bar was just below the chin with elbows flexed at approximately a 90 degree angle. The bar was then lowered by slowly extending the elbows to a point of 180 degree elbow extension. The concentric portion of the contraction consisted of raising the bar back to the starting position. Subjects were instructed to complete the lift in a controlled fashion with the back remaining straight and without the weights being swung or bounced. A repetition was counted when the protocol was met.

The second day of testing consisted of an experimental trial at 85% of the previously measured 1-RM. After an appropriate warm-up consisting of 3-5 repetitions at 60.4% to 80.7% 1-RM, a weight load equal 85% ± 1.3% of the previously obtained 1-RM was loaded onto the bar. The subject was asked to complete one set of repetitions to concentric failure. The number of repetitions recorded was equal to the number of concentric lifts completed with proper technique as determined by the researcher. The Berger (2,3) and the O’Conner et al. (20) prediction methods were then used to determine predicted 1-RMs. The Berger and O’Conner equations are listed below.

Statistical Analyses

All data were analyzed using Statistical Package for the Social Sciences (SPSS) version 11(IBM Company, Chicago, IL).Data are presented as means and standard deviations. Alpha was set at .05 which was accepted as significant. Differences in measured and predicted 1-RMs were determined using one-way ANOVA with actual resistance or predicted 1-RM as the dependent variable. The two assumptions of the ANOVA were met. The analysis showed that the data had a normal distribution and the variances were not significantly different (p 0.05). Correlations between measured and predicted 1-RMs were determined using Pearson’s Product Moment analysis. The Total Error of Estimate was also determined to analyze the magnitude of the prediction error. The equation for Total Error of Estimate is listed below (16).

RESULTS

Descriptive data for the two groups are found in Table 1.Bench press was not different (p > 0.05; actual p = .982) between the measured 1-RM and the two predicted 1-RMs.Data are presented in terms of means and standard deviations. The Total Error of Estimate was lower for the O’Conner et al. equation (20) than the Berger equation (2, 3) during the bench press. Mean number of repetitions completed at 85% measured 1-RM was 8.6 (Table 2).

Biceps curl was not different (p > .05; actual p = .824) between the measured 1-RM and the two predicted 1-RMs.Data are presented in terms of means and standard deviations. The Total Error of Estimate was lower for the O’Conner et al. equation (20) than the Berger equation (2, 3) during the biceps curl exercise. The Total Error of Estimate was lower for the O’Conner et al. equation (19). Mean number of repetitions completed at 85% measured 1-RM was 9.3 (Table 3).

DISCUSSION

The primary finding of the current investigation was that the prediction methods were equally effective in predicting bench press and biceps curl 1-RMs. There are numerous equations used to predict 1-RMs.The current study focused on two well known prediction equations. The equations chosen were the Berger equation (2, 3)and an equation from O’Conner et al. (20). The correlations (.84 - .98) and the lack of significant differences and similar error rates between measured and predicted 1-RMs strongly suggest that these equations produce valid estimates of 1-RMs, even when used with smaller muscle groups. In addition, these data suggest that exercise specific equations are not needed to yield accurate estimates of 1-RM when either of the two aforementioned equations is used. This finding is important in that using a single equation allows for a reduction in testing time and makes 1-RM testing simpler and more practical. Other research efforts suggest that theequations are capable of yielding valid estimates for lower body exercises (13) and can be used with machine lifts or with free weights (15). The prediction method showed little bias in whether the measured 1-RM is over or underestimated.

The Total Error of Estimate suggests that while they are valid, the equations are not without some error. The current findings are consistent with the work of others (1,8,11). The equation with the lowest Total Error of Estimate for both the bench press and the biceps curl was the O’Conner et al. equation (20). The fact that the error rates for the biceps curl show nearly a twofold difference in the amount of error associated with prediction is most likely because the equations were initially designed and tested with large muscle groups.

One limitation of the current study was the use of only two upper body lifts. Future investigations could test a variety of both upper and lower body lifts. Also, the current study selected recreationally trained male subjects. Potential differences may be noted if training status and gender are not controlled.Additional research should be conducted with different participant groups and varying percentages of 1-RM loads.