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Abstract

BACKGROUND:

Few studies have investigated the variations in body composition and performance in Japanese collegiate American-football players.

OBJECTIVE:

To clarify what characterizes competitors at the highest levels – in the top division or on the starting lineup – we compared players’ body compositions and performance test results.

METHODS:

This study included 172 players. Each player’s body composition and performance (one-repetition maximum bench press, one-repetition maximum back squat, and vertical jump height) were measured; power was estimated from vertical jump height and body weight. Players were compared according to status (starter vs. non-starter), position (skill vs. linemen), and division (1 vs. 2). Regression analysis was performed to determine characteristics for being a starter.

RESULTS:

Players in higher divisions and who were starters were stronger and had more power, greater body size, and better performance test results. Players in skill positions were relatively stronger than those in linemen positions. Vertical jump height was a significant predictor of being a starter in Division 1.

CONCLUSION:

Power and vertical jump may be a deciding factor for playing as a starter or in a higher division.

Keywords

American football performance test body composition muscular strength power

1. Introduction

In the United States, numerous previous studies have reported that greater power, and strength (both absolute and relative), faster performance in the 40-yard dash, and larger body size played important roles in the success of those playing on higher-rank or higher-division teams, as well as in the success of those who were on the starting lineup [1, 2, 3, 4, 5]. As an example, the National Football League (NFL) holds the Scouting Combine every year to draft talented collegiate players based on their performance on tests such as the 225-lb (approximately 102 kg) bench press, 40-yard (approximately 36.6 m) dash, and three-cone drill). These performance tests are designed to measure the abilities of power, strength, speed, and agility. McGee and Burkett [3], who examined how performance test results and draft status were related, successfully predicted the draft status of some positions using prediction equations based on the performance results from the Scouting Combine. This finding suggests that – besides their college careers – power, strength, speed, and agility may play larger roles in contributing to the success of American football players.

In Japan, a few studies examined performance as well as body composition among American football. Iguchi et al. [6] compared Japanese collegiate football players who belonged to two Division 1 teams (ranked 2 ${}^{\text{nd}}$ and 4 ${}^{\text{th}}$ ) with players in the United States and reported that the players on the 2 ${}^{\text{nd}}$ -ranked university team were larger in body size, had greater strength in back squats, and jumped higher in power squats than those who were on the 4 ${}^{\text{th}}$ -ranked team [6]. Additionally, the performances of the players on U.S. teams were superior to the performances of those on the Japanese teams for almost every variable [6]. Furthermore, Yamashita et al. [7] studied Japanese football players who participated in a Combine (performed in the same format as that of the NFL Combine) to select top-level players. They compared (1) Japanese players who were selected with NFL Combine invitees and (2) Japanese players who were selected with those who were not selected by position (skill, big skill, and linemen) [7]. The results showed that Japanese players who were selected were faster, stronger (in bench press performance), and jumped higher and farther than those who were not selected and that NFL Combine invitees were superior to both groups of Japanese players in almost all of the variables [7].

According to world rankings by the International Federation of American Football (IFAF) website [8], Japan ranks 2 ${}^{\text{nd}}$ (in the adult male class); there are 15,917 players and 429 teams registered in Japan. Although Japan has a relatively large population and plays at a high level in the world ranking, to our knowledge, there are only two studies (both of which are described above) regarding the performance and body composition of football players. Furthermore, no study has investigated the differences in body composition and performance between the collegiate divisions in Japan. Thus, the purpose of this study was to compare body composition and the results of American football–related performance tests 1) between starters and non-starters to find the variables that predict being a starter, 2) between skill and linemen positions to clarify the characteristics of each position, and 3) between Division 1 and 2 players to clarify what level of performance is necessary to compete in a higher division. The results from these analyses will allow us to create reference data for each category (starter status, position, and division) that can be used as performance indicators. We hypothesized that starters and players in Division 1 would be stronger, bigger, and jump higher, and consequently exhibit more power, than non-starters and players in Division 2.

2. Methods

2.1 Participants

In Japan, collegiate American football is divided into eight regional leagues subdivided into four groups: 1 (Hokuriku), 2 (Hokkaido, Tohoku, Tokai, Chu-Shikoku, Kyusyu), 3 (Kanto), and 4 (Kansai); each group has at least two divisions but can have up to four. Division 1 is always the highest level. Teams compete to achieve top tier positions. For this study, 172 Japanese collegiate football players from two teams, one team in Division 1 (team A, Kansai league) and one team in Division 2 (team B, Kansai league), were enrolled (mean age $=$ 20.6 $\pm$ 1.01; freshmen, $n=$ 27; sophomores, $n=$ 60; juniors, $n=$ 45; seniors, $n=$ 40). For the 2018 season, team A ranked 1 ${}^{\text{st}}$ in Division 1 of the Kansai league. Team B ranked 1 ${}^{\text{st}}$ in Division 2 of the Kansai league and was promoted to Division 1 (in the league, teams move between Divisions through promotion or relegation based on season or play-off performance).

According to recent studies [7, 9], skill positions can be divided into skill (wide receiver, running back, and defensive back) and big-skill (fullback, tight ends, and linebackers). Compared to players in big-skill positions, those in skill positions generally cover wide areas and have many opportunities to run the ball, as well as many high-speed interactions with other ball carriers. However, in the current study, besides the low number of linebackers, most of the teams did not make a distinction between running backs into tailbacks and fullbacks. Thus, the players were grouped by position as follows: skill ( $n=$ 121) which included defensive back, linebacker, running back, wide receiver, and quarterback, and linemen ( $n=$ 51), which included defensive lineman and offensive lineman. This study was performed according to the Declaration of Helsinki and approved by the ethics committee of Kyoto University of Advanced Science (approval #29–18, December 15 ${}^{\text{th}}$ , 2017). Before participation, each player was informed of the risks and benefits of the study, after which they provided written informed consent.

2.2 Experimental design

Before the 2018 season, we asked the strength and conditioning coach of each team to provide data comprising physical characteristics including height (in centimeters) and body weight (in kilogram-force), as well as data for performance tests that players routinely perform such as one-repetition maximum bench press and squat (in kilograms and percentages), and vertical jump (in centimeters) (Table 1). Both team A and team B strength and conditioning coaches, who were present for all of their teams measurements to ensure they were performed correctly, are strength and conditioning specialists certified by the National Strength and Conditioning Association (NSCA) [10]. We calculated the body mass index (BMI) from height and body weight, and power was estimated from body weight and vertical jump height by applying the Lewis equation: power (kg $\cdot$ -m/s) $=\sqrt{4.9}\times$ body weight (kg) $\times\sqrt{\text{vertical jump height (m)}}$ [11]. This equation has been widely used as a formula for estimating power [1, 12, 13, 14] and thus, we have decided to use it in this study owing to its high reliability.

Table 1
Descriptive statistics for all players

Variables	$n$	Mean	$\pm$ SD	Range	95%CI
	All
Height (cm)	172	174.8	5.72	158.9–188.5	174.0–175.7
Body weight (kg)	172	85.5	15.57	59.7–129.4	83.2–87.9
BMI (kg/m ${}^{2}$ )	172	27.9	4.09	20.7–42.0	27.3–28.5
Bench press (kg)	172	106.8	16.77	50.0–160.0	104.2–109.3
Back squat (kg)	172	156.1	27.04	80.0–230.0	152.0–160.1
Forty-yard dash (s)	172	5.08	0.25	4.58–5.90	5.05–5.12
Vertical jump (cm)	172	62.5	8.72	39.0–87.1	61.1–63.8
Power (kgm $\cdot$ s ${}^{-1}$ )	172	148.4	23.77	103.4–205.4	144.9–152.0
Bench press/BW	172	1.27	0.21	0.75–1.79	1.24–1.30
Back squat/BW	172	1.86	0.34	0.92–2.71	1.81–1.91

Note: BW $=$ body weight.

2.3 Performance test

2.3.1 One-repetition maximum bench press and back squat

Bench press and back squat, performed regularly by all players as part of their daily training, were performed in accordance with NSCA guidelines [15]. Lying on their back, each athlete performed one bench press while maintaining five points of contact (head, shoulder, hip, and feet) with the supporting surface (flat bench or floor). Elbows were fully extended at the end of the ascent phase, and at the end of the descent phase, the Olympic bar made contact with the chest. To perform the back squat, the athlete stood directly under the Olympic bar, with feet placed approximately the same as or slightly wider than shoulder width apart. With the Olympic bar resting on the shoulders, the athletes lowered themselves by flexing their hips and knees until their thighs were parallel to the floor. Each athlete’s tests were visually confirmed to be performed correctly by their respective strength and conditioning coach. The 1RM began with the athlete warming up by lifting weights at 60–70% of the previous 1RM. The weights (kg) 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.

2.3.2 Vertical jump

The athletes participated in 2 trials that consisted of jumping vertically without being permitted to shift horizontally as described in a previous study [6]. 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 (cm) of the 2 trials was used in this study. For the vertical jump, athletes were allowed to make two attempts; the best was retained. Counter movements before jumping were allowed, and the difference between full vertical jump extension from a stationary standing position on the ground was recorded as the jump height. Vertical jump heights were used to assess lower body strength and power [16].

2.4 Statistical analysis

For each physical or performance variable, we calculated the mean, standard deviation (SD), range, and 95% confidence interval (CI). For all variables, the Shapiro-Wilk test was used to verify normality. For comparisons between Division 1 and Division 2, skill position and linemen position players, starters and non-starters, the independent t test was used for normally distributed data and the Mann-Whitney U was used for non-normally distributed data. The effect size ( $r$ ) was calculated for each variable and classified as small (0.20–0.49), moderate (0.50–0.79), or large ( $\geqslant$ 0.80 [17, 18, 19]. We used binomial logistic regression to predict starter status (starter or non-starter) for each division based on players’ physical and performance characteristics. All statistical analyses were performed using IBM SPSS Statistics for Mac (version 25.0; Japanese; IBM Corp, Armonk, NY, USA). We set the level of significance at 0.05.

3. Results

Starters were stronger (in absolute and relative bench press and absolute and relative back squat performance) than non-starters ( $p<$ 0.05) (Table 4).

Players in linemen positions were significantly taller, heavier, and larger, and though they did not jump as high, they exhibited more power than those in skill positions ( $p<$ 0.05). Players in linemen positions had greater absolute strength than those in skill positions (Table 4), but players in skill positions had greater relative strength than those in linemen positions ( $p<$ 0.05).

Players in Division 1 (team A) were significantly taller, jumped significantly higher, and exhibited significantly more power ( $p<$ 0.05) than players in Division 2 (team B). Players in Division 2 were stronger, both absolutely and relative to their own body weight, than players in Division 1 ( $p<$ 0.05) (Table 4). For Division 1, regression indicated vertical jump height was a significant predictor of being a starter ( $p<$ 0.05) (Table 5). No factor was a significant predictor of being a starter for Division 2 (Table 6).

4. Discussion

To the best of our knowledge, this study is the first to compare performance and body composition characteristics by collegiate American-football players’ starter status, position, and division in Japan. We have established reference data for each category.

Overall, starters were stronger than non-starters, both absolutely and relative to their own body weight, for both strength tests (bench press and back squat). Iguchi et al. [6] also found that starters were stronger than non-starters in bench press and both absolute and relative back squat, and had more power and fat-free mass. Additionally, Glaister et al. [20] reported that both absolute and relative back squat performance were closely related to important sports characteristics such as agility. Thus, common findings of our study and of other studies are the importance of lower limb strength, which may suggest that better lower limb strength is a relatively large contributing factor to being a starter.

Between skill positions and linemen, linemen were taller, heavier, larger, stronger in bench press and back squat performance and had more power than those in skill positions. These findings were partially consistent with those of previous studies, especially with respect to larger size and greater absolute strength for bench press and back squat [2, 4, 6]. Wellman et al. [21] explained the characteristics of linemen’s movements. Although there are some differences in positional requirements, usually they accelerate and decelerate for blocking or chasing a ball, requiring quick changes in direction. In particular, their plays begin a few meters behind the scrimmage line and they must start from a static position [22], thus compared with players in other positions such as running backs, defensive backs, and linebackers, they have less time and distance to accelerate. Furthermore, McGee and Burkett [3], who investigated the 2000 NFL Combine to predict draft status from performance tests, reported that height, weight, bench press performance, broad jump distance, and three-cone drill time were the best predictors for the success of offensive linemen and defensive linemen. Considering the findings above, the key components to being a successful lineman seem to be absolute strength and large body size to perform their positional tactics.

Players in skill positions had more relative strength for both bench press and squat and jumped higher than linemen. Some previous studies have pointed out that there is potential link between relative back squat performance with vertical jump height [23]. and sprint time [24]. Compared with linemen, skill positions have more complicated tactics. For example, regarding offensive positions, ball carriers such as running backs and wide receivers do not only carry or catch the ball but also block or contribute to making a pass route [21, 25]. On the other hand, as a defensive position, defensive backs, who are the last line of defense, cover a wide range of defensive positions while mainly matching up with wide receivers [21, 25]. In both positions, players repeatedly run at high speed with quick acceleration and deceleration, meaning that their intermittent sprint ability seems be important for performing their positional requirements.

Regarding the comparison by divisions, we confirmed the players on Division 1 (team A) were taller, jumped higher and had more power than the players on Division 2 (team B). In line with our findings, Willi-

Table 2
Starter vs. non-starter physical and performance characteristics

Variables	$n$	Mean	$\pm$ SD	Range	95%CI	$n$	Mean	$\pm$ SD	Range	95%CI	Difference	Effect size	$P$ value
	Starter					Nonstarter
Height (cm)	55	174.8	5.07	165.2–186.5	173.4–176.1	117	174.9	6.03	158.9–188.5	173.8–176.0	0.09	0.01	0.92
Body weight (kg)	55	88.1	16.01	65.9–129.4	83.8–92.4	117	84.4	15.29	59.7–127.4	81.6–87.2	3.73	0.11	0.75
BMI (kg/m ${}^{2}$ )	55	28.7	4.42	22.8–42.0	27.5–29.9	117	27.5	3.87	20.7–40.2	26.8–28.2	1.28	0.12	0.10
Bench press (kg)	55	114.7	16.81	72.5–160.0	110.2–119.3	117	103.0	15.45	50.0–140.0	100.2–105.8	11.70	0.32	3.1 $\times$ 10 ${}^{-5*}$
Back squat (kg)	55	172.2	23.21	130.0–230.0	165.9–178.5	117	148.5	25.40	80.0–220.0	143.8–153.1	23.72	0.39	2.5 $\times$ 10 ${}^{-7*}$
Vertical jump (cm)	55	61.0	10.04	39.0–87.1	58.3–63.7	117	63.2	7.98	41.0–82.8	61.7–64.6	2.19	0.12	0.12
Power (kgm $\cdot$ s ${}^{-1}$ )	55	150.7	23.60	118.5–202.7	144.3–157.0	117	147.4	23.87	103.4–205.4	143.0–151.8	3.27	0.06	0.40
Bench press/BW	55	1.32	0.20	0.94–1.73	1.27–1.38	117	1.24	0.21	0.75–1.79	1.20–1.28	0.08	0.18	1.8 $\times$ 10 ${}^{-2*}$
Back squat/BW	55	1.99	0.28	1.37–2.51	1.91–2.06	117	1.80	0.34	0.92–2.71	1.73–1.86	0.19	0.27	3.8 $\times$ 10 ${}^{-4*}$

Table 3

Skill position vs. linemen position players’ physical and performance characteristics

Variables	$n$	Mean	$\pm$ SD	Range	95%CI	$n$	Mean	$\pm$ SD	Range	95%CI	Effect size	Difference	$P$ value
	Skill positions					Linemen
Height (cm)	121	173.1	5.28	158.9–183.2	172.1–174.0	51	179.0	4.41	172.0–188.5	177.8–180.3	0.48	5.99	3.0 $\times$ 10 ${}^{-11}$ *
Body weight (kg)	121	77.4	8.16	59.7–99.8	75.9–78.9	51	104.9	11.34	82.2–129.4	101.7–108.0	0.88	27.46	5.3 $\times$ 10 ${}^{-25}$ *
BMI (kg/m ${}^{2}$ )	121	25.8	2.32	20.7–34.0	25.4–26.2	51	32.7	3.22	26.5–42.0	31.8–33.6	0.72	6.86	1.0 $\times$ 10 ${}^{-10}$ *
Bench press (kg)	121	101.6	15.13	50.0–135.0	98.9–104.3	51	119.0	13.94	80.0–160.0	115.1–122.9	0.50	17.43	6.0 $\times$ 10 ${}^{-11}$ *
Back squat (kg)	121	149.2	23.46	80.0–200.0	145.0–153.4	51	172.5	28.10	100.0–230.0	164.6–180.4	0.39	23.28	8.6 $\times$ 10 ${}^{-8}$ *
Vertical jump (cm)	121	65.0	8.16	41.0–87.1	63.5–66.4	51	56.5	7.03	39.0–75.4	54.5–58.5	0.44	8.43	1.2 $\times$ 10 ${}^{-9}$ *
Power (kgm $\cdot$ s ${}^{-1}$ )	121	137.7	15.88	103.4–182.5	134.8–140.6	51	173.9	19.62	131.6–205.4	168.4–179.4	0.88	36.22	1.0 $\times$ 10 ${}^{-10}$ *
Bench press/BW	121	1.32	0.20	0.75–1.79	1.28–1.36	51	1.15	0.18	0.82–1.52	1.10–1.20	0.38	0.17	3.0 $\times$ 10 ${}^{-7}$ *
Squat/BW	121	1.94	0.31	1.10–2.71	1.88–1.99	51	1.66	0.31	0.92–2.13	1.57–1.75	0.38	0.28	3.8 $\times$ 10 ${}^{-7}$ *

Table 4

Division 1 vs. Division 2 players’ physical and performance characteristics

Variables	$n$	Mean	$\pm$ SD	Range	95%CI	$n$	Mean	$\pm$ SD	Range	95%CI	Difference	Effect size	$P$ value
	Japanese Div. 1 school (A)					Japanese Div. 2 school (B)
Height (cm)	116	175.6	6.00	158.9–188.5	174.5–176.7	56	173.2	4.74	163.5–183.0	171.9–174.5	2.4471	0.20	8.2 $\times$ 10 ${}^{-3*}$
Body weight (kg)	116	87.4	16.81	59.7–129.4	84.3–90.5	56	81.7	11.88	65.9–108.4	78.6–84.9	5.6391	0.14	0.06
BMI (kg/m ${}^{2}$ )	116	28.2	4.37	20.7–42.0	27.4–29.0	56	27.2	3.35	22.4–36.4	26.3–28.1	0.9925	0.09	0.24
Bench press (kg)	116	104.1	16.97	50.0–160.0	101.0–107.2	56	112.3	15.05	72.5–160.0	108.2–116.3	8.1538	0.25	9.8 $\times$ 10 ${}^{-4*}$
Back squat (kg)	116	151.4	28.59	80.0–230.0	146.2–156.7	56	165.7	20.59	130.0–225.0	160.2–171.2	14.2564	0.24	1.3 $\times$ 10 ${}^{-3*}$
Forty-yard dash (s)	116	5.11	0.25	4.58–5.74	5.06–5.15	56	5.03	0.25	4.70–5.90	4.97–5.10	0.0754	N/A	N/A
Vertical jump (cm)	116	64.8	8.77	41.0–87.1	63.1–66.4	56	57.7	6.45	39.0–75.0	56.0–59.4	7.0485	0.40	1.3 $\times$ 10 ${}^{-7*}$
Power (kgm $\cdot$ s ${}^{-1}$ )	116	154.2	24.67	103.4–205.4	149.6–158.7	56	136.6	16.47	110.7–186.8	132.2–141.0	17.5710	0.35	6.1 $\times$ 10 ${}^{-6*}$
Bench press/BW	116	1.21	0.20	0.75–1.70	1.18–1.25	56	1.39	0.18	0.95–1.79	1.34–1.43	0.1738	0.39	2.7 $\times$ 10 ${}^{-7*}$
Back squat/BW	116	1.77	0.34	0.92–2.71	1.70–1.83	56	2.04	0.22	1.6–2.6	1.98–2.10	0.2784	0.41	7.3 $\times$ 10 ${}^{-8*}$

Table 5

Logistic regression results for being a starter in Division 1

	B	SE	Wald	$P$ value	Exp (B)
Height (cm)	$-$ 0.05	0.64	0.01	0.94	0.95
Body weight (kg)	0.37	0.57	0.43	0.51	1.45
BMI (kg/m ${}^{2}$ )	$-$ 0.06	1.82	0.00	0.98	0.95
Bench press (kg)	0.24	0.18	1.77	0.18	1.27
Back squat (kg)	$-$ 0.02	0.10	0.05	0.83	0.98
Vertical jump (cm)	0.48	0.19	6.30	1.2 $\times$ 10 ${}^{-2*}$	1.61
Power (kgm $\cdot$ s ${}^{-1}$ )	$-$ 0.26	0.13	3.77	0.05	0.77
Bench press/BW	$-$ 19.31	16.55	1.36	0.24	0.00
Back squat/BW	5.25	9.27	0.32	0.57	191.27

* $p<$ 0.05, Note: BW $=$ body weight.

Table 6

Logistic regression results for being a starter in Division 2

	B	SE	Wald	$P$ value	Exp (B)
Height (cm)	$-$ 0.70	1.21	0.34	0.56	0.50
Body weight (kg)	1.19	1.22	0.96	0.33	3.28
BMI (kg/m ${}^{2}$ )	$-$ 2.48	4.04	0.38	0.54	0.08
Bench press (kg)	$-$ 0.02	0.36	0.00	0.95	0.98
Back squat (kg)	0.49	0.31	2.42	0.12	1.63
Vertical jump (cm)	0.97	0.57	2.90	0.09	2.63
Power (kgm $\cdot$ s ${}^{-1}$ )	$-$ 0.74	0.48	2.37	0.12	0.48
Bench press/BW	$-$ 0.40	27.87	0.00	0.99	0.67
Back squat/BW	$-$ 33.90	23.96	2.00	0.16	0.00

Note: BW $=$ body weight.

ford et al. [26] reported that physical characteristics such as height, body weight, and lean body mass increase as the level of competition increases. It has also been reported that power seems to play the most important role in differentiating between success and failure (e.g., games won or lost; higher or lower ranking) [1, 5]. While Division 2 players exhibited more absolute and relative strength (for bench press and back squat) than Division 1 players, Division 1 players exhibited more power and jumped higher than Division 2 players. Fry and Kraemer [2], who analyzed the differences in performance tests such as one-repetition maximum bench press and back squat and physical characteristics such as height and body weight for Division 1 through 3 players, reported that bench press, power clean, and vertical jump were good differentiators between divisions of play, while back squat was a poor differentiator [2]. Furthermore, Stone et al. [5] stated that sports-related performances such as throwing or jumping which are generated by maximal muscular action are closely related to power, leading to an important determinant for separating level of play. In our study, power and vertical jump effectively differentiated Division 1 from 2. Thus, our findings were mostly consistent with those of the study conducted by Fry and Kraemer [2]. and highlighted the important role of power in the level of play.

While only vertical jump height was a significant predictor of being a starter in Division 1 within this study, power in Division 1 and vertical jump height in Division 2 were almost significant for being a starter. In line with our findings, the findings of some previous studies that examined performance and body composition in relation to playing status (starter vs. non-starter) [27]. or how to determine draft success in NFL combines [3] reported that one of the variables most frequently related to player success was vertical jump height. Power is dependent on vertical jump height and body weight; therefore, power, is one of the essential factors that determine division of play. Rankings within the factors related to physical and performance characteristics such as muscular strength should follow the ranking of divisions (e.g., Division 1 $>$ Division 2 $>$ Division 3) [2, 5]. Therefore, our results may suggest that vertical jump plays an important role in becoming a starter in higher divisions.

Some study limitations must be taken into consideration. First, the number of participants was unevenly distributed between Divisions 1 and 2, and the number of teams was also smaller than that in previous studies, with only one team from each division. Thus, care must be taken when interpreting our results, especially for comparisons between divisions. Future studies should include a greater number of participants and equal in number from each division. Second, we did not use 40-yard dash time because there are methodological differences in how times were measured. However, previous studies have reported that 40-yard dash time was an important determinant for sports performance [2, 24]. Thus, future studies that include 40-yard dash time are needed to better understand performance and body composition differences between the American football divisions in Japan.

5. Conclusions

In this study, as hypothesized, starters and players in the higher division had more strength, more power, greater body size (e.g., height), and better performance test results (e.g., vertical jump). Contrary to the hypothesis, greater absolute strength and greater relative strength were inconsistent in differentiating between divisions. Most importantly, the results of our regression analysis show that vertical jump is an important determinant of being a starter in the higher division. By identifying differences in body composition and performance related to starter status, position, and division, we found determinant factors for collegiate American football players to be successful as a starter or in a higher division, such as power and vertical jump, that will help coaches and conditioning trainers design better training programs or select starters more easily.

Author contributions

CONCEPTION: Junta Iguchi.

PERFORMANCE OF WORK: Junta Iguchi.

INTERPRETATION OR ANALYSIS OF DATA: Junta Iguchi and Kenji Kuzuhara.

PREPARATION OF THE MANUSCRIPT: Junta Iguchi, Kenji Kuzuhara, Yasuhiro Yuasa and Toshiya Kitazawa.

REVISION FOR IMPORTANT INTELLECTUAL CONTENT: Kenji Kuzuhara.

SUPERVISION: Tatsuya Hojo, Yoshihiko Fujisawa and Minoru Matsunami.

Ethical considerations

This study was performed according to the Declaration of Helsinki and approved by the ethics committee of Kyoto University of Advanced Science (approval #29–18, December 15 ${}^{\text{th}}$ , 2017). Before participation, each player was informed of the risks and benefits of the study, after which they provided written informed consent.

Funding

This research was supported by Japan Society for the Promotion of Science KAKENHI Grant Number 17K01648.

Footnotes

Acknowledgments

We thank Coren Walters-Stewart, PhD, from Edanz (https://jp.edanz.com/ac) for editing drafts of this manuscript.

Conflict of interest

The authors have no conflicts of interest to report.

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Physical and performance characteristics related to starter status,position,and division in Japanese collegiate American-football players

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSION:

Keywords

1. Introduction

2. Methods

2.1 Participants

2.2 Experimental design

Table 1 Descriptive statistics for all players

2.3.1 One-repetition maximum bench press and back squat

2.3.2 Vertical jump

2.4 Statistical analysis

3. Results

4. Discussion

Table 2 Starter vs. non-starter physical and performance characteristics

Author contributions

Ethical considerations

Funding

Footnotes

Acknowledgments

Conflict of interest

References

Table 1
Descriptive statistics for all players

Table 2
Starter vs. non-starter physical and performance characteristics