Submitted by Garrett M. Hester, Bert H. Jacobson, Ty B. Palmer, Doug B. Smith and Matthew S. O’Brien
The ultimate goal of strength and conditioning practitioners is to improve performance on the field. To date, little data exist that provides evidence of strong relationships between selected exercises and sport-specific tasks. PURPOSE: The purpose of this study was to compare the performance of a position-specific task on the MAXX Football Sled Device (MX) between NCAA Division I offensive (OL) and defensive linemen (DL) and to determine the associations among selected strength and performance variables with results on the MX. METHODS: Offensive (n = 12) and defensive linemen (n = 14) (age 20.11 ±1.49 yrs) performed 10 “fire-off-and-drive” repetitions on the MX from a three-point stance. Data relative to force (N) and movement time (MT) was collected for each repetition on the MX. The duration between each repetition was automatically randomized between 6 to 10 sec. Strength and performance data including 1 RM of the squat, bench press, and power clean, along with vertical jump, 10 yd sprint, 40 yd sprint, and body fat percentage were gathered as part of seasonal standard assessment. RESULTS: Results yielded significant differences in body weight, sprint performances, 1 RM squat, and a near significant difference in MT (p = 0.052) between OL and DL. With respect to performance on the MX, there were no significant associations among selected strength and performance measures and MT on the MX. Although insignificant, force on the MX was found to have moderate associations with the 10 yd sprint (r = .457) and 1 RM power clean (r = .463). CONCLUSIONS: Primarily, these results point out that little carry over exists between the standard exercises performed and the task performed on the MX. Further research for the purpose of finding exercises that correlate with a position-specific task in these athletes is warranted. APPLICATION IN SPORT: A priority among practitioners is to remain cognizant of the positional role differences and distinct physical characteristics between OL and DL. The OL and DL positions should be categorized separately so that specific evaluative and training needs can be met for each position.
American football is a game largely dependent on strength and power. Due to the physical demands of the game, a great deal of time and effort is spent on the development and implementation of strength and conditioning programs designed to optimize athletic development. The primary focus for most collegiate strength and conditioning programs is directed at improving physical performance characteristics such as strength, power, and speed, therefore maximizing the ability of each athlete to contribute to the success of the team (8). Comparatively, the roles of the offensive (OL) and defensive linemen (DL) are considerably different than the roles associated with the ‘skill’ positions. Consequently, strength and conditioning professionals have access to an evaluative tool that provides a practical, position-specific assessment of playing ability in collegiate linemen so that focused exercises can be prescribed for the enhancement of speed and power.
Previous efforts have sought to analyze relationships between selected physical attributes and specific game performance (11). Typically, strength is assessed as one repetition maximum (1 RM) using free weights while speed and power are determined by the 40 yd sprint and vertical jump (VJ), respectively. Although 1 RM strength, speed, and power tests are not direct measures of football ability, these assessments reflect physical performance characteristics representative of football playing potential (7). Many studies have investigated relationships between 1 RM performance and various field tests inclusive of speed and power. However, many of these commonly used field tests are limited to movements that generally occur through a single plane of motion, involve isolated musculature, or do not challenge the proprioception or kinesthetics necessary for the football environment (13). Therefore, the existence is unclear of a known field test that provides strength and conditioning professionals with a practical, position-specific assessment of playing ability in collegiate linemen.
Strength and conditioning professionals are required to effectively evaluate playing ability in collegiate football players on an individual basis. Currently, many of the techniques used for evaluating playing ability in collegiate linemen are poor indicators of skill in these athletes due to a lack of specificity in these tests. Specific to linemen, the development of an explosive start is essential since these athletes are lined up so close to each (3). A position-specific tool that evaluates these characteristics in OL and DL has yet to be established in the literature. Many of the techniques used for evaluating playing ability in collegiate OL and DL provide a poor assessment since these tests lack mechanical specificity with respect to these positions. For instance, the backward overhead medicine ball (BOMB) throw has been proposed as an effective field test for the evaluation of total body explosive power (13). Mayhew et al. (10) studied the relationship between the BOMB throw, the 1 RM hang clean, and power production in college football players. The BOMB throw was only found to be moderately related to either peak or average jump power (p = 0.59 and p = 0.63, respectively). Furthermore, neither of these correlations accounted for more than 40% of the common variance between the two measures. The correlation between the hang clean and the BOMB throw was not significant (r = 0.33). The hang clean when combined with the best BOMB throw to predict average power accounted for only 7% of the common variance. Currently, there is no position-specific tool in the literature that serves the purpose of evaluating playing ability in OL and DL. A more accurate assessment of OL and DL playing ability could be gained through a position-specific evaluation that involves a task specific to these positions. Therefore, the two-fold purpose of the study was to compare the performance of a position-specific task between NCAA Division I offensive and defensive linemen and to determine the association among selected strength and performance variables.
This study utilized a convenience sample of Division 1 offensive (n=12, Wt = 137.51 ±9.09 kg Ht = 193.52 ± 3.48 cm) and defensive (n=14, Wt = 125.08 ± 12.82 kg Ht = 189.38 ± 3.51 cm) linemen between the ages of 18 and 22 with an overall mean Wt of 131.6 ± 5.2 kg and Ht of 191.0 ± 5.3 cm. IRB approval and permission from the Athletic Department were obtained prior to any volunteer participation in this study. An informational meeting in which consent was obtained from all volunteers of the study was held prior to any testing. All subjects completed a medical history questionnaire and physical examination prior to testing by a licensed physician as part of requirements for participation on the university football team. Medical history showed that none of the subjects had suffered or been affected by any musculoskeletal injuries within the past 6 months.
The MAXX Football Sled Device (MX) (Shoot-A-Way, Upper Sandusky, Ohio) was used to assess force (N) and movement time (MT) through a “fire-off”, punch maneuver performed on the contact dummy component of the device. This maneuver is very similar to the game-like action observed for both OL and DL in the game of football. Familiarization for this task was unnecessary since the subjects in the study frequently use the MX as a part of training. The MX measures time from auditory/visual stimulus to contact and displays this value in milliseconds along with the force rating on an integrated display/control panel. For the purpose of analysis the force data were converted to Newtons.
Test-retest reliability of the MX was assessed using 10 randomly selected OL and DL of the football team. Subjects performed the testing protocol for two sessions separated by 48 hours. Results of this analysis demonstrated strong reliability with the device for both force (ICC = .813; SEM = 93.4) and MT (ICC = .828; SEM = .022).
1 RM assessments for the bench press, squat, and power clean were performed using an olympic-style barbell. VJ height was assessed using a Vertec (Perform Better, Cranston, RI), and 40 yd sprints were electronically timed on an artificial turf surface. The proper testing protocols for 1 RM testing and VJ testing using the have been previously published (1). Body fat percentage was analyzed using the BOD POD (COSMED, Chicago, IL).
All testing on the MX occurred at the University Strength and Conditioning facility. To assure similar training conditions the study included two testing sessions, with the OL testing on a Wednesday and the DL testing exactly one week later at the same time of day. Each group performed a 5 minute dynamic warm-up conducted by the team strength and conditioning staff prior to testing. The dynamic warm-up focused on major muscles of the legs, hips, and back. The dynamic stretches performed included high knees, butt kicks, leg swing, and inch worms. Prior to testing, each subject performed two ¾ speed “fire-offs” into the MX. Testing on the MX began by having the subject positioned in a standard three-point football stance at a distance of 12” from the device, as measured from contact dummy to hand. A simultaneous auditory and visual signal delivered by the device served as the initiation of the test. Upon these signals, the subject explosively accelerated out of the three-point stance to make contact with the dummy located on the front of the device. The subject contacted and punched the breast plate region of the dummy, similar to the maneuver observed in the game of football. Each subject was instructed to perform this action as explosively and forcefully as possible. Once the subject completed the punch maneuver the subject disengaged the dummy and repositioned to the original starting position in preparation for the next repetition. The device randomly varied the time between each repetition giving each subject approximately 6 to 10 seconds between repetitions. Each subject performed 10 consecutive repetitions.
Data were analyzed using separate t-tests (position x trial) with Bonferroni adjustments using SPSS version 20.0 (SPSS Inc., Chicago, IL) for Windows. Pearson Correlation Coefficients were used to determine any relationships associated with all assessments (MX data, body mass, percent fat, VJ, 10 and 40 yd sprint, bench press, squat, and power clean). An alpha level of p < 0.05 was used to determine statistical significance for all analyses.
Analysis of physical characteristics revealed that OL were significantly heavier (p = 0.02) and taller (p = 0.01) than DL, but no significant difference was found for body fat percentage (p = 0.21). With respect to selected strength and performance measures, DL were significantly (p = 0.02) stronger in the 1-RM squat and faster in the 40 yd sprint (p = 0.02) and simultaneous 20 yd and 10 yd segments than OL. No significant differences were found between the groups for any of the remaining strength and performance variables (Table 1). Results of the MX field-related “fire-off” technique yielded a near significant difference (p = 0.052) in the average MT, stimulus to dummy contact, between DL and OL. The average MT for DL and OL were 0.430 sec and 0.465 sec, respectively. There were no significant differences in force output on the MX between the two groups.
Table 2. Correlations of selected variables for Division I offensive and defensive linemen
Pearson Correlation Coefficients determined a significant relationship between body mass and body fat percentage. Also, VJ, 10 yd, 20 yd, and 40 yd sprint performances were found to have a significant inverse relationship with body fat percentage. There were no strong associations among selected strength and performance measures and MT on the MX. Although non-significant, force on the MX was found to have moderate positive associations with the 10 yd sprint (r = .457) and 1 RM power clean (r = .463), suggesting that few of the tested variables are related to the on-field technique of “firing off” the line. Additionally, analysis revealed that body mass and VJ demonstrated a non-significant (p > 0.05) moderate relationship with the 1 RM power clean and VJ (r = .448 and r = .472, respectively), while the 1 RM back squat had a slightly stronger (r = .589), but significant (p < 0.05) relationship with the 1 RM power clean.
OL and DL positions are unique in comparison to ‘skill’ positions; however, dissimilarities exist between the OL and DL positions and the roles carried out by these two positions. Previous research has indicated that OL are typically more massive (4, 5, 11) and, although contrary to the present data, likely to possess more adipose tissue (4, 11) when compared to DL. The distinct positional role differences between these two positions most likely play a key role in this regard. Generally, OL must either screen the DL from the ball carrier or quarterback, or attempt to drive the DL away from the running lane. Contrastingly, DL must attempt to outmaneuver OL in an effort to avoid being screened or blocked, thus the need for speed at the DL position comes at the cost of body mass. Present data reflect these positional role differences with the OL being found significantly more massive and, although insignificant, slightly slower than DL on average with regard to MT performance. Additionally, as would be expected, DL performed significantly better than OL in the 40 yd, 20 yd, and 10 yd sprint.
The aim of University strength and conditioning programs is to determine the best possible exercises in the weight room to enhance play on the field. Finding exercises that have the strongest association with techniques required on the field involves extensive testing of those exercises. However, little has been done in the way of quantifying a field-related technique and assessing the relationship with exercises assumed to be related to activity on the playing field. According to Fry et al., (7) strength, speed, and power tests are indirect measures of football ability. However, strength and performance measures are critical for a better understanding of which measures reflect the physical performance characteristics representative of football playing potential. There have been only a few studies that have examined associations between select strength and performance and a practical field-based evaluation. Furthermore, to the knowledge of the authors this is the first study to evaluate the performance of a task specific to the OL and DL positions. The present study failed to find any strong evidence of relationships between selected strength and performance measures and a position-specific task on the MX. Previously, Davis et al. (6) found a weak relationship between the 1 RM power clean and VJ performance in collegiate football players. Additionally, Mayhew et al. (10) examined the relationship between VJ, 1 RM power clean, and performance on a practical, total body BOMB throw assessment in collegiate football players. The authors reported the 1 RM power clean to be a weak predictor (r = 0.33) of the best BOMB throw performance due to a lack of specificity between the movements. Although a diverse group of selected strength and performance measures were used for comparison in the present study, the VJ and PC require dynamic, total body explosiveness much like the performance on the MX. However, none of the strength and performance measures strongly correlated with MT on the MX, while force on the MX only had a modest relationship with the 1 RM power clean (r = .463). Thus, this finding parallels those of Mayhew et al. (10) and are indicative of the weak relationship between the 1 RM power clean and the performance of a dynamic, total body field test. Not surprisingly, VJ performance had a weak relationship with force on the MX. This could be expected as VJ performance is concerned with the ability to explosively move the body vertically, while the MX performance examined absolute force.
In the present study, DL demonstrated significantly faster sprint means and near significantly faster MT means during a position-specific performance on the MX. There was no difference in performance on the MX in regards to force between OL and DL. The OL were found to be significantly more massive than DL, thus slower acceleration produced by the OL may minimize meaningful difference in force. Data indicated that none of the strength and performance measures correlated with performance measures on the MX, thereby adding to the conundrum that few exercises carry strong correlations to the basic movement and strength of OL and DL as expressed through an on-the-field technique. The task performed on the MX may be too complex to have a high degree of association with selected strength and performance measures (10). Thus, although the MX provides an evaluation of a position-specific task, the degree of complexity of the task may make increase the difficulty of high levels of associations with selected strength and performance measures.
To our knowledge, the present study was the first to use a device for evaluative purposes specific to the nature of the linemen position in the game of football. There were no significant differences found in MT and force measures between OL and DL when a position-specific task was performed on the MX. Additionally, there were no strong associations found among selected strength and performance measures and performance on the MX. Future research is warranted for the purpose of identifying exercises that provide a strong relationship to position-specific activity in OL and DL. Although, the MX was found to be reliable, it would be worthwhile for future research to include other tools that provide a more sensitive assessment of a position-specific task.
APPLICATION IN SPORT
Cognition of the differences in the positional roles and distinct physical characteristics between OL and DL is important. These two positions should not be categorized as one group so that training and evaluation can be specifically tailored to benefit both positions. In regards to training, tradition and observation are many times factors that dictate the exercises performed in the weight room. Although more research is needed for the purpose of finding exercises that carry strong relationships with position-specific activity in these athletes. Practitioners should keep an open mind in regards to exercise selection and keep in mind the specific needs of each position.
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