Skill performance is the key to a successful athlete. Moreover, power, speed, strength, agility, and physical size are emphasized in several types of sports, especially in contact sports such as American football, rugby, and ice hockey. With regard to American football, numerous studies have attempted to compare body composition and physical performance within (6,7,21) and between the divisions (13,14), between drafted and nondrafted players (27), and between players with varying numbers of years in the team (25). These prior studies demonstrated that better teams or players have superior body composition and/or muscular strength and established some useful normative data for football coaches and athletes at each level.
Football is one of the most popular sports in the United States, and its teams included more than 60,000 college-level male athletes in 2008 (23) and >1 million high school male athletes in 2009 (24). On the other hand, according to 2009 data released by the Japan American Football Association, Japan had 402 teams, with approximately 20,000 players participating in 11 junior high school teams, 112 high school teams, 218 university teams, and 61 adult club teams. Despite the significant population size, normative data on physical stature and performance of Japanese football players have not been established. In addition to a lack of data for Japanese players, no study has been conducted to compare body composition and physical performance between players from the 2 countries. One reason for this might be the difficulty in the comparison of strength-related performance (i.e., bench press and back squat) between players with a large difference in body mass. The simplest method to compare different body mass groups is to normalize the strength performance according to body mass. This method is valid only if the relationship between body mass and strength performance is linear (9). However, as results of a few studies contradict this notion (8,11), alternative methods such as the two-thirds power law (2) and second-order polynomial equation (5) have been developed. In particular, Cleather (9) invented a new equation that allows for a comparison in strength performance among different body mass groups, independent of body mass bias.
Given a lack of data on body composition and physical performance for Japanese collegiate football players, it is valuable to collect such data and compare them with the corresponding data of US players. Furthermore, to our knowledge, no study has examined whether physical performance and body composition are associated with team success for Division 1 football teams in Japan. Therefore, this study aimed to establish the physical and performance characteristics of football players in the Japanese Division 1 football program and to compare these characteristics between the Japanese and US Division 1 football players.
Experimental Approach to the Problem
To determine the physical and performance data of Japanese Division 1 football players, surveys were sent to strength and conditioning coaches of 2 Kansai Division 1 collegiate football teams. As for US data, we referred to previously published data (25), which consisted of physical characteristics (height [cm], body mass [kg], percent body fat [%], and fat-free mass [FFM, kg]) and performance characteristics (40-yd dash [seconds], vertical jump height [cm], 1-repetition maximum [1RM] bench press and back squat records [kg], relative bench press and back squat records [%], and power [kg·m·s−1]). The physical and performance data were grouped by projected playing position without kickers and compared accordingly: (a) between a higher-ranked university team vs. a lower-ranked university team in Japan, (b) between different playing positions in Japan, (c) between starters and nonstarters in Japan, and (d) between playing positions in Japan vs. those in the United States When comparing the muscle strength between Japanese and the US players, data were normalized according to body mass based on previously published equation (9).
For Japanese data, we chose 2 teams from the 8 teams in the Kansai Division 1 collegiate football league (n = 208, mean age = 20.2 ± 1.4 years). To compare physical characteristics in the Division 1 teams in the United States and Japan, we used US records (n = 797) assessed by Secora et al. (25). The study has been approved by the ethics committee at Doshisha University. Informed consent was implied when a questionnaire was returned from the participating universities.
After the 2008 season, we sent data collection forms to the strength and conditioning coaches certified by the National Strength and Conditioning Association (NSCA) at 2 universities in Japan. The form requested that the coaches provide physical records to be used in this study. Because the 2 Japanese teams chose to remain anonymous, we will refer to them as universities A and B for the purposes of this study. University A was ranked in second place and university B was ranked in the fourth place in the 2009 season. The physical data requested for each player included height, body mass, and percent body fat. Fat-free mass was calculated using body mass and percent body fat. Performance records for each player included 40-yd dash, 1RM bench press and back squat, and a vertical jump. We divided absolute bench press and back squat records by body mass to get relative scores. Furthermore, we calculated power from vertical jump height and body mass by applying the Lewis equation (12). For purposes of data analyses, players were grouped by playing position into defensive back (DB), linebacker, defensive lineman (DL), offensive lineman (OL), running back (RB), tight end, wide receiver (WR), and quarterback (QB). In the study conducted by Secora et al. (25), a covering letter, data collection form, and instructions were sent to the strength and conditioning coach at each university. However, their procedures for physical and performance data were not detailed, leading to the potential difference for the measuring methods. Furthermore, this methodological weakness has been pointed out by another previous study (18).
Considering the potential differences in the measurement methods for physical and performance data between Japan and the United States, we decided to compare only body mass, bench press, and back squat scores because the procedures for these values, especially the 1RM bench press and back squat, were well established by the NSCA (2), and these values were assessed by NSCA-certified strength and conditioning coaches. Performance records were accepted on the basis of the criteria explained in the description of each test.
One Repetition Maximum Bench Press and Back Squat
The bench press and back squat were included as routine conditioning in each football program, and all participants had previously been tested for 1RM bench press and back squat. Instructions for bench press and back squat were based on NSCA guidelines (2). In the bench press, the athlete was in a supine position with the head, shoulder, and hip on the flat bench, both feet on the floor. The 5-point body contact positions were maintained during both the descent and ascent phases of the lifting movement. The bar had to be in contact with the chest before being pushed upward until the elbow joints were fully extended. In the back squat, the athlete was positioned directly underneath the bar and stood on the floor with his feet positioned at shoulder width or slightly wider apart. The bar was carried on the shoulder, and no footsteps were permitted during the lifting performance. The athlete had to descend until the thighs were parallel to the floor.
The 1RM began with the athlete warming up by lifting weights at 60–70% of the previous 1RM. The weights were gradually increased until the last successful performance was accomplished. All of their performances were visually assessed by an NSCA-certified strength and conditioning coaches.
Instructions were derived from a previous study (3). Briefly, this test consisted of 2 trials in which the athlete sprinted over 40 yd at maximum effort after a warm-up routine. Light gates were integrated to the timing system (Race time 2, Microgate S.r.L, Italy, Bozen) and placed at the 0- and 40-yd marks. The best 40-yd dash time of the 2 trials was used in this study. Time was recorded to 0.01 of a second.
The athletes participated in 2 trials that consisted of jumping vertically without being permitted to shift horizontally. A countermovement was allowed before jumping. The score was decided by measuring the difference between a fully extended standing reach and maximal vertical jump reach. The highest vertical jump score of the 2 trials was used in this study. Additionally, we referred to a prior study regarding detailed instructions (13).
Body Fat Measurement
At university A, body fat was measured using bioelectrical impedance (BC-304, Tanita Ltd, Tokyo, Japan), a measure which is strongly correlated with a Dual-energy X-ray Absorptiometry (DXA) scan results (r = 0.88; Tanita, unpublished data). Nevertheless, several previous studies (10,15,26) have indicated that bioelectrical impedance analysis is not without problems, including issues such as the limitation in prediction equation and difficulties in controlling physiologic condition such as hydration status and skin temperature.
At university B, body composition was determined using skinfold measurements and the formula of Jackson and Pollock (16). Percentage of body fat was calculated using the equation for a Japanese male ([4.570 ÷ body density] 4.142) × 100 (1). The 7 sites for skinfold thickness measurements were triceps, scapula, middle axillary, suprailiac, chest, abdomen, and thigh.
Considering the problems with Bioelectrical Impedance Analysis (BIA) and the different methods available for body fat calculation, we decided to use skinfold measurements along with FFM data derived from body mass for comparison with the US counterparts. We decided not to compare universities A and B on these measures because of the different methods they used for measurement.
Modification Method for the Power Lifting Performance
To compare muscle strength between the US and Japanese football teams, we used the power lifting (PL) coefficient developed by Cleather:
In this equation, x is the average lifter's body mass (kg) for each playing position, and a, b, c, and d are the constants for each lifting performance. For example, in the back squat, a = 1,113.227; b = 2,261.016; c = 0.239; d = 430.645, whereas in bench press, a = 386.722; b = 4,228.725; c = 0.724; d = 274.195 (9). The PL score was computed by multiplying the average lifting performance for each playing position by a PL coefficient. This score allows for a comparison of PL performance for athletes of different body masses.
In this study, the following comparisons were made: (a) between a higher-ranked university team vs. a lower-ranked university team in Japan, (b) between different playing positions in Japan, (c) between starters and nonstarters in Japan, and (d) between playing positions in Japan vs. those in the United States Descriptive statistics were performed to obtain the mean, SD, and range of each variable. Independent t-tests were performed by comparing the mean scores of university A and B football teams. One-way analysis of variance was performed by comparing the mean scores for each playing position. The difference for each variable between the data of Secora et al. (25), and this study was determined using 1-sample t- test. Pairwise differences were examined using Scheffé's method, and the alpha level was set at p ≤ 0.01 to reduce the probability of a type 1 error. Data analysis was performed using the SPSS statistical package (version 17.0; SPSS Inc, Chicago, IL, USA).
Table 1 summarizes the comparison of the Japanese teams from universities A and B. Significant differences (p < 0.01) were found in 4 of the 11 comparisons: body mass, vertical jump, back squat, and power. The players at university A were heavier, stronger in the back squat, jumped higher, and had greater power than the players at university B.
Differences by playing positions are presented in Table 2. Briefly, OLs had the highest score for all of the following outcomes: height, body mass, percent body fat, FFM, bench press, back squat. On the other hand, DBs had the top scores for the 40-yd dash, vertical jump, and relative bench press. Furthermore, the DLs and RBs had the highest score for the power and relative back squat, respectively.
Table 3 summarizes the comparison between starters and nonstarters among the Japanese players. Briefly, the starters were stronger in the bench press in absolute terms, and in the back squat in both absolute and relative terms, plus they were more powerful and carried greater FFM than did the nonstarters (p < 0.01).
Significant differences (p < 0.01) were found in all the comparison criteria between the Japanese and US groups. For instance, US players were significantly heavier than Japanese players (Table 4). Furthermore, US players were significantly stronger in the bench press and back squat for both absolute and modified values than Japanese players (Tables 5 and 6).
In the comparison between the 2 Japanese universities, the players at university A (higher ranked) had more body mass, better vertical jump height, greater strength in the back squat, and more power than the players at university B. Previous studies revealed that the 1RM back squat (4,13), relative back squat (4), 40-yd dash (13), vertical jump (7,13), and power (6,28) are important factors in determining success in American football. Of these factors, power seems to be the most important factor because power is described as force multiplied by speed (28) and is absolutely imperative for explosive movements, such as jumping and throwing (30) and agility (28).
Our findings are partially consistent with those of the study conducted by Berg and Latin (6), where players on the higher-ranked team had more power than players in the lower-ranked team. In this study, power is defined by vertical jump height and body mass. Thus, the significant difference between universities A and B for vertical jump height and body mass indirectly contributed to the significance of power. Furthermore, Barker et al. (4) found that the 1RM back squat and relative back squat are possibly linked to the vertical jump height. In this study, there was no significant difference in the relative back squat between the 2 universities, but there was a trend toward significance (p = 0.03). As for the 1RM back squat, we found that the players at university A had significantly greater strength in the back squat than did those at university B.
With respect to the comparison by playing positions among the Japanese athletes (Table 2), our results indicated that linemen were generally characterized by larger size, greater strength, and more body fat than OL and DBs. On the other hand, backs tended to be faster, relatively stronger, smaller in physical size, and had higher vertical jump height than linemen did.
The linemen position requires a considerable amount of powerful upper body movements, especially in the arms (27). However, these upper body movements mostly derive from lower body strength (27). Our results revealed that OLs were superior to the other positions in most indexes related to body composition, such as height and body mass. Furthermore, OLs had the greatest strength in the bench press and back squat, whereas DLs had the most power.
Agility and speed play an important role in the position of the skill players (WR, DB, and RB) (27). In our study, DBs and RBs were the strongest in relative bench press and back squat, respectively. The DBs were the fastest in the 40-yd dash and had the highest vertical jump. These findings support those of previous studies in showing that strength normalized by body mass was related to the 40-yd dash time (3) and vertical jump height (4).
In the comparison between starters and nonstarters, starters were absolutely stronger in the bench press, both absolutely and relatively stronger in the back squat, had greater power and more FFM than did nonstarters (Table3). We also noted a trend for a difference in height (p = 0.02) and body mass (p = 0.03) between starters and nonstarters. Our findings are in general agreement with those of Fry and Kraemer (13), who reported significant differences in the vertical jump for 5 of 6 playing positions, the bench press and 40-yd dash for 4 of 6 playing positions, and the back squat for 2 of 6 playing positions between starters and nonstarters. As previously explained in the comparison between universities A and B, power is the key factor in defining good sports performance, whereas strength is the ability to generate force, which is an integral part of power (28). Therefore, the results of this comparison between starters and nonstarters reaffirm the importance of both power and strength.
Each of the 40 statistical comparisons between the 2 nationality groups revealed significant differences (Tables 4–6). These large numbers of significant differences may be partially accounted for by factors such as racial difference (22) or the population difference for football (17).
In the comparison of performance related to strength, data revealed that US players were 39.3% stronger in the bench press and 33.8% stronger in the back squat than the Japanese players (Table 5). Despite using a PL coefficient, a large difference between the 2 groups (bench press: 32.0%, back squat: 25.8%) persisted (Table 6). The intensive training programs (25) and the spread of nutritional supplements (29) are most likely related to this difference in strength performance. In addition, Berg et al. (6) reported that 40% of the schools that participated in their study employed an NSCA-certified strength and conditioning coach. On the other hand, a full-time strength coach in college settings is less common in Japan. Furthermore, Japanese coaches tend to place greater emphasis on scrimmage rather than physical training (19). The background described above may also have influenced the results obtained in the performance of the bench press and back squat.
The data for US players (25) demonstrated superior body composition in comparison to Japanese players. Intensive training programs (25) and the prevalence of nutritional supplements (29) may help to explain the relatively low percentage of body fat, higher body mass, and FFM found among the US players. Furthermore, as body composition can have an effect on performance (20), differences in the body composition between the 2 groups may explain the differences in strength, power, and speed-related performances.
The injury rate (IR) per 1,000 athletic exposures in Japan could also be a potential extrinsic factor contributing to the results of this study. Kuzuhara et al. (19) showed that the IR during a practice in Japan is about 6 times higher than the IR in the United States. This may suggest that injured players could not perform some parts of the physical training, which may influence the strength-power components. Furthermore, US players can concentrate on physical training during the spring season because there are no games during that time, whereas a few games are played during training season in Japan. Thus, players in Japan tend to spend more time in skill practice than in physical training.
Our results revealed a few intrinsic and extrinsic factors that are possibly linked to the differences in body composition and performance between the US and Japanese football players on Division 1 teams. Our study validated the results of previous studies showing that the better teams and players in the United States had better body composition and performance. Therefore, the key factors related to success for a football player in Japan are virtually the same as those in the United States. This suggests that an intensive training program to improve strength and power, along with a balanced diet or supplements to increase FFM, may be key factors for developing a successful Japanese football player.
As described above, strength is the most important element of success for an athlete. Absolute strength may be the best indicator when we compare groups within the same weight class. However, a weight difference is present in most cases, especially when comparing the players from different countries such as in this study. This factor is also an issue among sports divided by weight classes (e.g., judo or wrestling) or sports that have relatively large weight differences by playing positions such as football (e.g., backs vs. linemen). Use of the PL coefficient could be one of the best solutions for these situations by being able to compare muscular strength independent of body mass. This calculation is beneficial to the strength and conditioning coaches or scientists who are interested in comparing muscular strength among different body mass classes.
This study established a baseline for Japanese football players. This normative data can be used to compare similar types of data and to examine time-dependent changes in terms of physical status and performance in the future. Also, these data can be used to compare with data collected by other divisions or conferences, even in countries whose physical and performance data are similar to Japan's, such as other Asian countries. Furthermore, strength and conditioning coaches could use this norm when designing strength and conditioning programs that suit individual needs.
Our investigation found a close link between strength and power and elucidated how strength and power play an important role in football. The implication is that the specific training to increase strength will enhance power and eventually lead to better football performance. Further study is needed to confirm whether power and strength are the key factors for a successful football player in a variety of conferences or divisions.
No funding was received for this study.
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