The primary objective of most resistance training programs in college football is to gain muscular strength, whereas the secondary objective may be the acquisition of short-term muscular endurance. Considerable time and effort may be spent during off-season training programs to maximize strength and muscular endurance in a variety of dynamic movements. To evaluate the strength level of players, the most widely accepted method has been the one repetition maximal (1RM) lift in various exercises (4). Perhaps the exercise receiving the most attention for assessing upper-body strength level of football players has been the supine bench press. Although the capability of the 1RM for determining player success may be largely anecdotal, it seems to receive the most notoriety when discussing player potential. However, owing to its use by the National Football League (NFL) Combine, the muscular endurance test known as the NFL-225 test has prompted many National Collegiate Athletic Association Division IA programs to adopt it as a primary evaluator of upper-body muscular performance. Although the 1RM bench press may still be used to assess players at selected points in the yearly training cycle, the NFL-225 test may be frequently used to check progress of upper-body strength performance.
The NFL-225 test requires a player to perform as many bench press repetitions as possible without rest using a weight of 225 lbs (102.3 kg). Because of the high number of repetitions produced, especially by larger players, the test may be more appropriately categorized as an evaluation of muscular endurance. Numerous investigations have attempted to determine the association of NFL-225 repetitions with 1RM performance in college players, typically producing high correlations (r > 0.95) with standard errors of estimate ranging from 5.6–9.4 kg (5,7,14,16,17–19,21,24). Similar findings have also been noted with B. Allenheilegen (B. Allenheilegen, personal communication, June 2003). What has not been evaluated is the potential of the NFL-225 test to track changes in 1RM performance over a training period. The strong correlation between repetitions and 1RM suggests that the NFL-225 test could be used to assess changes in upper-body strength after training (14,16,17–19). If this premise holds true, strength and conditioning specialists might be able to use the NFL-225 test to track changes in upper-body strength performance in a safe and time-efficient manner. Therefore, the purpose of this study was to evaluate the degree of accuracy of the NFL-225 test for determining the changes in 1RM bench press after a short-term resistance training program in college football players.
Experimental Approach to the Study
The NFL-225 test is widely used at all levels of college football as a primary determinant of muscular endurance and prediction of muscular strength. Information is lacking, however, which documents how well the NFL-225 test is able to track changes in maximal bench press strength after a short training program. This study was designed to assess the accuracy of the NFL-225 test to gauge the change in 1RM bench press performance after a short-term training program among major college football players. Players were tested before and after a 6-week off-season resistance training program for maximum repetitions completed using 225 lbs and for 1RM bench press, with each test occurring within 1 week of each other. Comparisons were made between the changes in both tests and the ability of selected NFL-225 prediction equations to estimate 1RM changes after training.
The subjects (n = 203, age range 18–24 years) for this study were the members of a successful Division IA program and selected over a period from 2007 to 2011. The 4-year team record was 40 wins vs. 14 losses and 4 bowl game appearances. The testing program was part of the regular training procedures for the team, and all players provided a waiver of consent to participate. No players younger than 18 years were included in the study. All testing protocols were approved by the university's Institutional Review Board for Studies Involving Human Subjects.
One Repetition Maximum Test
A spotter assisted the player in lifting the bar from support racks. The 1RM attempt required the player to lower the bar slowly to touch the chest before pressing it immediately to full-arm extension in the “touch-and-go” method. The head, shoulders, and buttocks remained in contact with the bench throughout the lift. Players were not allowed to bounce the bar off their chest.
Each player was allowed to warm up according to personal preference using light weights of approximately 60–80% of the estimated 1RM. Testing protocol allowed the player to select a starting weight that would permit completion of one repetition. Depending on the player's perception of difficulty for that lift, weight was added, a minimum of 5-minute rest was allowed, and the second repetition was attempted. The objective was to have most players reach their 1RM within 3–5 attempts. Standard Olympic bars and plates were used for all lifts, and the player used a grip of their preference (typically 15–35 cm greater than shoulder width). All testing was performed between 1500 and 1800 hours. No player was allowed to perform either test if he had any upper-body injury within the previous 3 months of the test date. A registered dietitian provided regular advice to insure adequate nutrition for each player. Players were encouraged to be well hydrated before testing and had personal water bottles in the facilities at all times. Reliability for the 1RM procedure has been established at greater than 0.99 (11).
National Football League 225 Test
During the week after the 1RM testing, each player performed the NFL-225 test using a load of 225 lbs (102.3 kg), attempting to complete as many repetitions as possible without pause. After individual warm-ups, the player grasped the bar at the same position used during the 1RM procedure. No mandatory cadence was imposed for the repetition test, although each player was encouraged to maintain a constant pace of his own choosing. No more than a 2-second pause between each repetition was allowed. The bar was required to touch the chest on each repetition (but not allowed to bounce off it) and be returned to full-arm extension. The head, upper back, and buttocks were required to remain in contact with the bench throughout the test. The test was terminated when the subject could not complete a repetition with proper form. Reliability for this procedure had previously been determined to be 0.987 (13).
The training program used an autoregulatory progressive resistance exercise protocol throughout (15). The program called for players to perform 4 sets of upper-body exercise using progressively heavier loads 2 times per week; the other 2 days per week, the players concentrated on lower-body exercise. The program progression involved using 6RM and 3RM sets across the 6 weeks. The typical daily plan called for players to perform the first set with 6 repetitions using 50% of the estimated 6RM load. The second set was performed with 6 repetitions at 75% of the 6RM load. In the third set, players performed as many repetitions as possible using 100% of the load for the 6RM-level. The fourth set load was adjusted based on the number of repetitions completed (15). During the second 3-week period, the same procedure was used, substituting the 3RM load for all sets. In addition, heavy dumbbell bench presses (>85% of the estimated 1RM) were performed one time per week with 3 sets of 6 repetitions. On the other upper-body exercise day, players selected one or 2 exercises from among body-weight pull-ups, lat pull-downs, overhead barbell presses, barbell rows, and triceps extensions and performed several sets.
Paired t-tests were used to assess the change with training in the composite group. Effect size was determined using Cohen d-statistic (6) and interpreted according to the scale given by Batterham and Hopkins (1). One-way analysis of variance was used to assess differences among position groups, body mass groups, and repetition groups, with Bonferroni post hoc follow-up testing in which significance was noted. Pearson's correlations were used to determine the relationship among selected variables. A contingency coefficient determined from a 3 × 3 Chi-Square design was used to determine the correlation among variables measured on a nominal scale where increases, constancy, and decreases in repetitions and 1RM were considered as discrete variables. Linear regression analysis was used to determine the predictive potential between NFL-225 repetitions and 1RM bench press before and after training. In addition, 6 previously developed NFL-225 prediction equations were selected for evaluation of accuracy before and after training using paired t-test and intraclass correlation coefficients (ICCs). Constant error was assessed as the difference between predicted and actual 1RM performances. Total error was estimated using:
Coefficient of variation (CV) was determined by dividing the SD diff by mean of the actual 1RM. The significance level for all analyses was set at p ≤ 0.05.
Pretraining and posttraining differences for the entire team are shown in Table 1. After training, there was a significant improvement in 1RM bench press (4.2 ± 8.6 kg; 2.9 ± 6.2%) and NFL-225 repetitions (1.0 ± 3.2 repetitions; 11.6 ± 32.7%) over the 6-week training period. Given the increase in 1RM, the load represented by 225 lbs (i.e., %1RM) decreased significantly (70.7 ± 9.9% to 68.8 ± 10.0%). The combination of load and repetitions produced a significant increase in work capacity (11.6 ± 32.7%).
The change in 1RM was not significantly related to initial 1RM (r = −0.05), initial body mass (r = −0.11), or change in body mass (r = 0.07). Pretraining and posttraining work capacities were significantly correlated with initial 1RM (r = 0.95 and 0.89, respectively) but not with the change in 1RM (r = −0.16 and −0.22, respectively). There was no difference in the magnitude of change in these variables because of training when players were divided into groups based on player position (Table 2), NFL-225 repetitions completed (Table 3), and body mass (Table 4).
A prediction equation to estimate 1RM from pretraining NFL-225 repetitions was developed (equation 1) and produced a predicted 1RM (147.5 ± 20.6 kg) that was not statistically different from the actual 1RM (147.5 ± 19.5 kg), with a high intraclass correlation between the 2 values (ICC = 0.972) and a moderate standard error of estimate (SEE; 6.5 kg) and CV (4.5%). This equation predicted 71% of the players within ±4.5 kg (3.1%) of their actual 1RM. The Bland-Altman plot (Figure 1) shows this good agreement but also indicates a tendency for considerable heteroscedasticity at higher 1RM (>150 kg).
Applying equation 1 to the posttraining data produced a predicted 1RM (150.3 ± 20.1 kg) that was not significantly different (p = 0.20) from the actual 1RM (151.7 ± 22.0 kg), with a high intraclass correlation between the 2 values (ICC = 0.852) but with a high SEE (14.7 kg) and CV (9.8%). Forty-seven percent of the group had predicted 1RM values within ±3.9 kg (±5%) of their actual 1RM, whereas 23% had predicted values ± 10.7 kg (±5%) greater than their actual values, and 30% had predicted values ± 8.0 kg (±5%) lower than their actual values. The Bland-Altman plot of these data shows the variation and lack of agreement in the posttraining prediction when using equation 1 (Figure 2A).
Equation 2 was produced using posttraining NFL repetitions to predict 1RM. Applying equation 2 to posttraining data produced an estimated 1RM (150.3 ± 20.1 kg) that was not significantly different (p = 0.20) from the actual 1RM (151.7 ± 22.0 kg), with a moderate intraclass correlation between the 2 values (ICC = 0.833) and a high SEE (15.1 kg) and CV (10%). Forty-seven percent of the group had predicted 1RM values within ±5.3 kg (±5%) of their actual 1RM, whereas 23% had predicted values ± 10.5 kg (±5%) greater than their actual values, and 30% had predicted values ± 7.5 kg (±5%) lower than their actual values. As with using equation 1, the Bland-Altman plot shows variability and little agreement when trying to predict posttraining 1RM using either posttraining (equation 2; Figure 2B) or pretraining (equation 1; Figure 2A) data.
The regression lines comparing the %1RM represented by the NFL-225 load with the number of repetitions completed at pretraining and posttraining were curvilinear, with posttraining regression line shifted from the pretraining relationship (Figure 3). Additionally, there was considerable variability in direction and magnitude of change in 1RM ranging from a 24-kg decrease (−18%) to a 31-kg increase (25%). To assess this variability and its impact on 1RM prediction, the change in 1RM performance was evaluated by grouping players according to the direction of change in measured 1RM: 154 players increased, 12 remained the same, and 37 decreased (Table 5). For the Increase group, 1RM (ES = 0.36), 1RM/body mass (ES = 0.24), NFL-225 repetitions (ES = 0.09), and work capacity (ES = 0.10) increased significantly, while the relative load represented by 225 lbs decreased significantly (ES = 0.34). The change in 1RM was not significantly correlated with initial 1RM (r = −0.09), initial body mass (r = −0.06), initial NFL-225 repetitions (r = −0.14), change in body mass (r = 0.10), change in repetitions (r = −0.05), or change in work capacity (r = −0.05).
For the Decrease group, 1RM decreased significantly (5.7%; ES = −0.43) while body mass increased significantly (ES = 0.05; Table 2). This resulted in a significant decrease in 1RM/kg (ES = −0.51). The decrease in 1RM caused the %1RM for repetitions to increase significantly (ES = 0.47), yet repetitions (ES = 0.09) and work capacity still increased significantly (ES = 0.32). The change in 1RM was not significantly correlated with initial 1RM (r = 0.23), initial body mass (r = 0.31), initial NFL-225 repetitions (r = 0.18), change in body mass (r = −0.09), change in repetitions (r = −0.04), or change in work capacity (r = −0.04).
Using equation 1 to estimate posttraining 1RM, it significantly underpredicted 1RM in the Increased 1RM group (Predicted: 148.5 ± 19.1 kg; Actual: 155.2 ± 21.5 kg) and significantly overpredicted 1RM in the Decreased 1RM group (Predicted: 161.7 ± 22.9; Actual: 142.6 ± 22.4 kg). Similarly with equation 2 to estimate posttraining 1RM, it significantly underpredicted 1RM in the Increased 1RM group (Predicted: 150.2 ± 15.1; Actual: 155.2 ± 21.5 kg) and significantly overpredicted 1RM in the Decreased 1RM group (Predicted: 161.0 ± 18.6; Actual: 142.6 ± 22.4 kg). Within each group, there was no difference in predicted 1RM between the 2 equations. Although the ICC's were high in both groups for predicting 1RM with each equation (ICCs ranged from 0.885 to 0.976), the SEE (range, 11–13.4 kg) and CV (7–9%) were also high.
Given the variation and high SE when predicting 1RM from within-team data (pretraining and posttraining), the 1RM was also predicted using previously accepted equations to assess applicability. Table 6 illustrates the efficacy of 7 NFL-225 equations previously identified to produce accurate estimates of 1RM in college players.
This is the first attempt to assess the accuracy of the NFL-225 test for tracking changes in 1RM strength over a short resistance training period in a large sample of elite-level college players. Based on the present results, it appears that the NFL-225 test does not track or accurately predict acute changes in muscular strength in elite-level players after a 6-week, high-intensity training program despite the considerable information detailing the efficacy of the test for predicting 1RM bench press at various levels of competition (3,5,7,14,16,17–19,21,24).
A major point of interest noted in this study was the considerable variability in the change scores of both major variables; 1RM and NFL-225 repetitions. Although the majority of players increased their 1RM, only 44% improved in both variables. Even in the players who increased in 1RM, the average change in NFL-225 repetitions was not greater than the smallest worthwhile difference (2 repetitions) previously established to indicate more than random variation in performance (13). To address the variation, players were divided into groups based on the direction of change in 1RM, which did not improve the ability of the NFL test to track changes in muscular strength. In fact, the NFL test predictions were opposite of the actual direction of change. Players who increased 1RM after training were predicted to have decreased their 1RM by an average of 7 kg, whereas players who decreased 1RM were predicted to have increased 1RM by an average of 19 kg. Interestingly, these predictions, rather the error in prediction, were very consistent with ICCs >0.890.
Attempting to predict posttraining 1RM using previously published NFL-225 equations provide equally questionable and variable results. Predicted 1RM was not significantly different from the actual 1RM for the same 3 equations at pretraining and posttraining (Table 6). The correlations between the predicted and actual 1RM for each equation at pretraining were significantly greater than that of after training. In addition, there was a precipitous drop in the number of players who had predicted values within ±4.5 kg of actual 1RM after training with all equations.
The variation and error in prediction in the present study indicates that after the resistance training, the number of completed repetitions on the NFL test are not indicative of the changes in 1RM indicating a very specific adaptation to the training program. There is an apparent absolute dissociation between muscular strength and muscular endurance with a singular emphasis on development of muscular strength almost to the exclusion of work capacity and muscular endurance. Undoubtedly, the interaction of the low-repetition, high-load training program used and the acute nature of the training resulted in this very specific impact on muscular strength. The reduced prediction accuracy at posttraining is an indication that estimating 1RM with repetitions to failure may have limited success when programs exclusively emphasize strength development. Although the lack of association between the changes in each variable supports the possible dissociation between muscular strength and endurance after this type of training program, this outcome may be common since most short-term resistance programs used in college football center around heavy resistance and low repetitions designed predominantly to improve strength (8,10,22). Thus, it is unlikely that the NFL-225 test accurately reflects strength changes resulting from such short-duration, high-intensity programs. Training programs of longer duration or more emphasis on muscular endurance could increase the accuracy of the NFL-225 test for estimating 1RM performance. However, it is probable that absolute load tests, such as the NFL-225 test, are a reflection of muscular strength only at the lower end of the repetition continuum, i.e., <10 repetitions or loads >80% of 1RM (2), which is verified by the higher correlation between NFL-225 repetitions and 1RM in the current players completing <10 repetitions (r = 0.97) compared with those completing >20 repetitions (r = 0.71). In addition, it is worth noting that both correlations decreased significantly after training (r = 0.45 and 0.26, respectively), again emphasizing the greater improvement in strength than endurance in these players.
In a previous study on Division II players (2), 35 individuals who performed NFL-225 repetitions had their pretraining 1RM accurately predicted with an average error of only 0.2% (±3.8%). After a 12-week linear periodization program using decreasing intensity (90–80% of 1RM) and increasing repetitions (1–5 repetitions in 4–8 sets), 94% of the players increased their 1RM by 11.6 ± 5.3 kg (8.5 ± 3.9%) and their NFL-225 repetitions by 1.8 ± 1.9. Sixty-eight percent of the 35 players increased their NFL-225 repetitions by 3.0 (±1.4), which was comparable with the 60% of the current sample that increased by 2.2 (±1.6) repetitions. In the Division II players, an NFL-225 equation underpredicted posttraining 1RM by only 1.8 ± 7.9 kg (p = 0.27). Comparison of the Division II results with those from the current study underscores the importance and impact of the type and duration of the training program in this sport.
If' work capacity (i.e., repetitions × load) was considered before (1,438 ± 673 kg·repetitions) and after training (1,535 ± 691 kg·repetitions), players generally made a significant gain of approximately 12%. The change in volume load was not significantly different among body mass or repetition groups, and initial 1RM (r = −0.10) and NFL-225 repetitions (r = −0.09) were not significantly related to the change in volume load, indicating that all players had equal potential to enhance their work output. This could be a positive factor allowing each player to sustain more force over the course of an average football play because the latter typically lasts only 6 seconds (20). Furthermore, given that the average recovery between plays is approximately 34 seconds (20), the enhanced work capacity would be important for players to be able to repeat high-level force generation frequently to maintain performance in game situations.
In the previous study on Division II players, it was suggested that muscular strength is typically controlled or limited, to a large degree, by neural factors while the expression of work capacity is determined by an interaction between neural factors and energy supply. Since maximal motor unit activation occurs only during a maximal effort or near the conclusion of endurance repetitions (25), training may improve the order of motor unit activation thus requiring fewer motor units to complete a given task. Therefore, fatigue might be delayed by having a greater motor unit reserve pool which would allow a greater number of repetitions to be achieved with an absolute load. However, the degree to which a high-load, low-repetition training program might modify the neural activation of muscle compared with a low-load, high-repetition program remains to be elucidated.
A major complication in analyzing changes in strength among college football players may lie in the diverse nature of their training programs. Rarely does a major emphasis on resistance training last longer than 10 weeks in major college programs (10,22). Furthermore, the emphasis in these programs is usually on strength rather than endurance. Longer training programs in the off-season might offer a slightly better opportunity to determine the ability of NFL-225 repetitions to track changes in 1RM. Thus, the best opportunity to evaluate the association of muscular strength with muscle endurance may be over the entire college career of players (9,23). Stodden and Galitski (23) found that NFL-225 repetitions increased significantly each of the 4 years in Division I players, with the number of repetitions doubling in the first year and increasing only by 2 repetitions in the fourth year. Jacobson et al. (12) noted gains in 1RM bench press of 18–34% over a 4-year period, while NLF-225 repetitions increased by 68–193%, and the latter was influenced greatly by the average of 8 repetitions gained from 4 to 12 by backs compared with the 11 repetitions gained by linemen from 15.8 to 26.5.
The findings of this study suggest that the NFL-225 test may not be an adequate method for tracking acute changes in upper-body maximal strength after short-term, high-intensity resistance training in college football players. Although previous studies have shown fairly strong correlations between NFL-225 repetitions and 1RM, the predictions were completed after longer duration or higher repetition training. After training, our results showed that the correlation between NFL-225 repetitions and 1RM decreased in all repetition groups and prediction error was more than doubled.
Muscle performance operates on a continuum from absolute strength to absolute endurance with various combinations of the 2 elements between the extremes. Resistance training is a multifaceted domain, and it may be difficult to emphasize both aspects of the continuum simultaneously. Hence, the limited ability to predict muscular strength using tests of muscular endurance, especially, when the test generates more than 10 repetitions. Thus, there may not be a perfect program for all individuals even in the same sport. Therefore, until further long-term analysis can be performed, caution should be exercised in using the NFL-225 test as an indicator of gains in upper-body muscular strength after short-duration, high-load, low-repetition resistance training programs.
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Keywords:Copyright © 2015 by the National Strength & Conditioning Association.
muscular strength; absolute muscular endurance; strength prediction