Basketball is a multifaceted team sport that requires well-developed physical fitness to be played successfully (30).
Many authors have suggested that strength, power, agility, and speed are important characteristics for elite basketball players (19,26). As a consequence, anaerobic testing has been considered more important than aerobic assessment in evaluating fitness to play basketball (21,32).
In a recent research survey, this belief was shown to be shared by the National Basketball Association (NBA) strength and conditioning coaches who reported extensive use of a variety of Olympic-style lifts, squats, and plyometric exercises to create and test training adaptations in elite-level professional basketball players (24,39).
Maximal strength measured as maximal back squat lift performance (1 repetition maximum [1RM]) has been reported to be strongly related to short sprint (10 to 30 m) and vertical jump ability in elite-level soccer players (46). Furthermore, Baker and Nance (2) reported that squat performance (3RM) was selectively related to short sprint ability (10-40 m) in elite rugby league players.
In basketball, Hoffman et al. (19) reported that 1RM squat strength can be considered a stable performance variable throughout the competitive season and a predictive variable for seasonal playing time (24) in well-trained collegiate basketball players. However, despite the interest in squat performance as a testing and training exercise (19,24,39), no structured study has examined the relationship between squat maximal strength and functional performance (vertical jump, sprint, and agility) in basketball (22,24,42).
Agility has been considered a physiological prerequisite in basketball (22), because players are frequently involved in a variety of sudden directional changes during the game (30). Agility performance is determined by the speed in changing direction and has been reported to be influenced by explosive strength, balance, muscular coordination, and flexibility (37). Several studies have previously shown that agility should be regarded as a major physiological variable in male football players (8,27,46). However, soccer studies have shown that sprint shuttle running (10-m shuttle with a 160° turn) was related to parallel back squat 1RM performance in professional well-trained male soccer players (46). This may suggest that maximal strength, measured as maximal squat performance, might be a performance correlate of agility in team sport players.
Although agility ability is an important factor in basketball (30), the assumption that maximal squat strength would be highly relevant to agility is based on logical reasoning because no information is available regarding the variables that determine agility performance in basketball players.
As a result of this reasoning, the aims of this study were to examine (a) the association between squat 1RM and basketball-relevant performance parameters in elite basketball players (19,23,24,28,30,39,42); and (b) the main variables of agility in basketball players.
As a working hypothesis, it was assumed that there would be a significant association between squat 1RM and vertical jump and both short-sprint performance in elite basketball players (46).
Experimental Approach to the Problem
Fitness profiling is a sport science research method that enables sport scientists together with coaches and fitness trainers to gain normative data helpful in the development of training strategies or to act as stepping stones for further studies involving training interventions (47). The basis of the fitness profiling method in sport science is the representatives of the sample population investigated (3).
In accordance with contemporary fitness profiling research philosophy (44), the present study was performed using elite male professional basketball players, all of whom were current members of the Tunisian national team.
In this study, a nonexperimental, descriptive correlation design was used to examine the relationship between back squat maximal lifting ability (1RM) and a number of relevant basketball tests (24,42). The players' maximal back squat 1RM weight lifted was compared with vertical and horizontal jumps, sprint performance over a series of short distances (5,10,30 m), and agility (T-test) performance. Upper-limb maximal strength (bench press 1RM) was assessed because a previous study showed that bench press performance was significantly related to short sprint times (48). To investigate the components that influence agility in basketball, a stepwise correlation analysis was carried out.
Anthropometric variables were also assessed because Ostojic et al. (32) showed that body size is associated with functional performance in elite male basketball players.
Fourteen healthy male basketball players selected for the Tunisian National Basketball Team volunteered to serve as subjects for this study (Table 1). All players were full-time professionals and had played at a national level and competed internationally. The players performed the assessments for this study shortly before competing in the African Nations' championship. All the players were fully accustomed with the procedures used in this research because they were routine evaluations in the National Centre of Medicine and Science of Sports of Tunis (CNMSS) used for scientific follow-up purposes for elite athletes. The training routine of this study group of basketball players consisted of twice-daily training sessions (approximately 90 minutes each), which were mainly devoted to technical-tactical skills and strength and endurance development. During the months preceding the testing procedures, all the players participated in national tournaments and championship games over most weekends. All players were starters in their teams (12). The Ethics Committee of the CNMSS approved the study, and written informed consent was obtained from each subject before participation.
Subjects reported to the laboratory at 8:00 am. On entering the laboratory, height (m), body mass (kg), and percentage of body fat were measured in each subject. Body mass was obtained to the nearest 0.1 kg using an electronic scale (Seca Instruments Ltd., Hamburg, Germany). Height was measured to the nearest 0.1 cm using a stadiometer (Holtain Ltd., Crymych, UK). Skinfold thickness at 4 sites (biceps, triceps, subscapular, and suprailiac) was measured using a Harpenden calliper (Lange, Cambridge, MA) and from these measurements, percent body fat was calculated using the technique of Durnin and Womersley (15).
The subjects were familiar with the testing protocols because they routinely performed these tests for scientific follow-up and for training prescription purposes. Each player was instructed and verbally encouraged to give a maximal effort during all tests. A standardized warm-up, consisting of jogging, dynamic stretching, and then a series of increasing intensity sprints, was performed before testing. No static stretching exercises were allowed before any test.
Vertical jump performance was assessed using a portable force platform (Quattro Jump; Kisler, Winterthur, Switzerland). Players performed countermovement (CMJ) and squat jumps (SJ) according to the protocol described by Bosco et al. (7). Before testing, players performed self-administered submaximal CMJs and SJ (2N3 repetitions) as a practice and specific additional warm-up. Subjects were asked to keep their hands on their hips to prevent any influence of arm movements on the vertical jumps and to avoid coordination as a confounding variable in the assessment of the leg extensors (6). Each subject performed 3 maximal CMJs and SJs, with approximately 2 minutes recovery in between. Players were asked to jump as high as possible. The best of each type of jump was used for analysis. Vertical jump performance was considered as jumping height and peak power at takeoff (6).
The subjects performed 3 maximal 30-m sprints (with 5- and 10-m split times also recorded) on an indoor synthetic track. During the recovery period between 30-m sprints (2-3 minutes), the subjects walked back to the starting line and then waited for their next sprint. Time was recorded using photocell gates (Brower Timing Systems, Salt Lake City, UT; accuracy of 0.01 second) placed 0.4 m above the ground. When ready, the subjects began the sprint from a standing start 0.5 m behind the first timing gate. Stance for the start was consistent for each subject. The run with the lowest 30-m time (and corresponding 5- and 10-m split times) was selected for analysis.
A quintuple horizontal jump test (5JT) was also performed by each player. The 5JT involved the subject attempting to cover the greatest horizontal distance possible by performing a series of 5 forward jumps with alternated left and right foot contacts. Immediately before the 5JT, players were instructed to begin and end with their feet parallel. The participants were instructed to move forward using their preferred leg. The 5JT performance was measured, with a measuring tape, as the distance from the front edge of the player's feet at the starting position to the rear edge of the feet at the final landing position. The assessor at landing had to focus on the last stride of the player to determine exactly the last feet print, because the players could not always stay on their feet at landing. The starting position was settled on a fixed point. Subjects were allowed 3 trials with the longest distance used for analysis. It has been proposed that the 5JT is an appropriate alternative to traditional jumping exercises for estimating lower limb explosive power in various athletes (13,14,33,40,41). Reliability of 5JT performed in the present study was very high (Table 2).
One repetition maximum half-squat and bench press strength was recorded as the maximal weight subjects were able to raise as described by Chtara et al. (14) and Weiss et al. (45), respectively. In the present study, a free-weight squat exercise was performed allowing players to bend their knees to reach half-squat position (approximately 90° angle in the knee between the femur and the tibia) with the barbell held over the shoulders (back squat). The bar position for the free-weight bench press exercise began in the up position at full elbow extension, moved to chest level for a momentary pause, and finished back at the starting position. Hand and foot positions were determined for each subject during familiarization and were held constant during all testing. No bouncing of the bar off the chest was allowed. After the general warm-up, subjects performed a specific warm-up using 50% (10 repetitions), 75% (6 repetitions), and 85% (3 repetitions) of their estimated 1RM. After the specific warm-up, the subjects' resistance was fixed at a critical value of 5% below the expected 1RM and was gradually increased after each successful performance until failure. Three minutes of recovery were allowed between each attempt (46).
The T-test was administered using the protocol described by Semenick (36). Three test trials were performed, and times were recorded to the nearest one-hundredth of a second using an electronic timing system (Brower Timing Systems; accuracy of 0.01 second) placed 0.4 m above the ground. The subjects began the sprint when ready from a standing start 0.5 m behind the first timing gate. Reliability and validity of the T-test were reported by Pauloe et al. (34).
Players' endurance performance was assessed using the Yo-Yo intermittent recovery test level 1 (Yo-Yo IR1) (25). Maximal aerobic power (o2max) was estimated using Yo-Yo IR1 distance covered according to the data of Castagna et al. (9). The intraclass correlation (ICC) and coefficient of variation (CV) for the Yo-Yo IR1 were reported to be 0.93 and 4.9%, respectively (4).
Results are presented as mean ± SD and range to represent the centrality and spread of data. Data sets were checked for normality using the Shapiro-Wilk's normality test and visual inspection. Relationships between variables were assessed using Pearson's product-moment correlation. Stepwise multiple regression analysis was used to determine the predicting variables of sprinting and agility performance. Reproducibility of data was assessed through the SEM, also called the method error (ME) by Sale (35), and calculated here as the SD of differences (SDdif) between tests 1 and 2 divided by the square root of 2 (the number of tests performed), i.e., ME = SDdif /√2. The CV, which quantifies the relative instability of measurement, was then computed as follows:
These calculations were carried out for all outcome measures supplied by the test. We also calculated the ICC for the same measures (Table 2). Significance was set at 5% a priori (p ≤ 0.05). Statistical analyses were performed using SPSS software statistical package (SPSS Inc., Chicago, IL; Version 14.0).
Players' characteristics and test performances are reported in Table 1. The relationship between the anthropometric and performance variables and agility are detailed in Table 3. T-test performance was significantly related to body mass (r = 0.58, p = 0.03) and percent body fat (r = 0.80, p < 0.001). A significant negative correlation was observed between T-test and 5J test performances (r = -0.61, p = 0.02). Squat 1RM strength was significantly related to 5-, 10-, and 30-m sprint times (Table 4).
Stepwise correlation analysis showed that percent body fat was the best single predictor factor (p < 0.05) of agility (Table 5). Squat 1RM strength was the best single performance predictor for 5- and 10-m sprint times (p < 0.05), whereas 30-m sprint time was best predicted by CMJ performance (p < 0.05).
During the Yo-Yo IR1, players covered 2389 ± 616 m.
This is the first study that has investigated the relationship of squat 1RM with functional tests and the performance determinants of agility in elite male basketball players. The main finding of this study was the existence of significant positive correlations between squat 1RM and sprint times over 5, 10, and 30 m. Surprisingly, agility performance was significantly associated with anthropometric variables such as body mass and percentage of body fat in addition to a negative correlation with the 5JT.
The associations found between squat 1RM and sprint performances (i.e., 10- to 30-m sprint) are in line with that reported by Wisløff et al. (46) in professional male elite soccer players. However, in the present study, significantly lower correlation coefficients were found between squat 1RM and 10-m (r = −0.68 vs. −0.94) and 30-m (r = −0.65 vs. −0.71) performances compared with those reported by Wisløff et al. (46). The difference in correlation coefficient values may be the result of the greater number of subjects used in the study of Wisløff et al. (46) or there may be a sport-specific reason. In this study, no significant difference was observed between 1RM vs. 10-m and 1RM vs. 30-m relationships (−0.68 vs. −0.65, p > 0.80) showing that squat 1RM was equally associated with sprint performances. This means that maximal lower limb dynamic strength is related to a wide range of sprint distances performance in elite basketball. The explained variance (r2) between 1RM and sprint performances suggests that other variables may significantly affect sprinting ability in basketball players.
In this regard, multiple correlation analysis showed that 1RM squat performance was the best single predictor of 5- and 10-m sprints, demonstrating that maximal dynamic lifting ability may positively affect short sprinting in elite basketball. On the other hand, 30-m performance was best predicted by CMJ performance. Further analyses showed that 5JT and CMJ performances were significantly related to 10- and 30-m sprint performances. The relationships were significantly greater for 30-m distance compared with 10-m distance, showing that stretch-shortening cycle tests are more related to longer sprint performance.
Agility is reported to be a multifactorial physical ability affected by strength, speed, balance, flexibility, and muscular coordination (37). In this study, agility considered as performance in a basketball-specific test (i.e., T-test) was only significantly related to 5JT performance (r = −0.61). Interestingly, agility performance was also strongly correlated to percent body fat (r = 0.80, p < 0.001) and to a lesser extent to body mass (r = 0.58, p = 0.03). As expected, line-sprinting performances were not related to agility performance. This study's results seem to support the findings of previously investigations in other team sports such as soccer and field hockey (46,49). As a result, agility may be considered as a per se physiological variable probably more dependent on coordinative aspects of performance (37,38). The existing significant relationship with body composition and agility performance, seen in the present study, may be the result of the high intersubject variability existing for the percent body fat (CV = 26.4%). It is possible that the fattest subjects have more difficulty in moving their heavier bodies in the acceleration/deceleration movements imposed by the agility test.
Interestingly, in this study, T-test results were significantly related to o2max (r = −0.72). This unexpected association may be partly the result of the test used in this investigation to estimate players' maximal aerobic power. Indeed, in this study, according to Castagna et al. (10), the maximal aerobic power that was estimated from the distance covered during a progressive intermittent maximal test that involved continuous shuttle running over 20 m to exhaustion with a 10-second recovery every 40 m (25). Consequently, it could be speculated that agility ability may favor basketball players during the Yo-Yo IR1 in covering more distance through more economic movements.
Profiling studies are appearing more frequently in the literature because they provide valuable information on developing normative data and standardized testing for team sports (16).
The anthropometric and physiological characteristics found in the present study were similar to those of previous researches that studied Serbian and French elite-level professional basketball players (32,35). Indeed, Serbian and French elite players showed heights, body masses, and body fat percentages ranging from 196.4 to 199.5 cm, 93.1 to 96.5 kg, and 11.5 to 12.6% respectively (32,35). However, the estimated aerobic capacity of the elite male basketball players in the present study (54.9-59.1 ml·kg-1·min-1) was greater than those reported in the previous 2 studies (32,35). There are several factors that may contribute to this difference, including methodological differences in the testing procedures, the team's style of play, training regimens, and the time of the season when testing occurred. Nevertheless, several authors have argued that the aerobic capacities of elite basketball players are not as important as their anaerobic or physical characteristics and thus a o2max even lower than 55 ml·kg-1·min-1 may be considered as adequate for elite basketball players (26,32,43).
Strength, power, agility, and running speed are thought to be important for successful participation in basketball (32,35). Indeed, Simenz et al. (39) reported in a survey study conducted on NBA professional strength and conditioning coaches that the most popular strength training exercises were Olympic lifts, squats, and plyometric exercises. This type of training is consistent with the literature that addresses the development of strength, power, agility, and running speed (17,20,29,39). Power is heavily dependent on maximal strength, which, when increased, results in improvements in relative strength and therefore in power abilities (46).
Bench press 1RM absolute (79 kg) and relative (0.84 kg·kg-1 body mass) values in the present investigation were lower than those reported in previous studies (0.9-1.1 kg·kg-1 body mass) for subelite male basketball players (5,18,19,26). Differently from bench press performance, squat 1RM expressed either in absolute (142 kg) or relative (1.5 kg·kg-1) terms resulted within the range (1.35-1.6 kg·kg-1 body mass) reported for subelite basketball players (19,24,26). Unfortunately, previous profiling studies on elite male basketball players have not investigated upper- or lower-body strength (32,35). Consequently, it could be speculated that probably relative upper-body strength is not very important for elite basketball players and that subelite players may be overtraining their upper body. Additionally, 1RM squat to body mass ratio in the range of 1.5 appears to be a sufficient strength prerequisite to play at elite and subelite levels of male basketball (19,24,26). The squat 1RM values reported in this study were lower both in absolute (145 vs. 172 kg) and relative (1.5 vs. 2.2 kg·kg-1) terms with respect to that reported for male professional soccer players. Recently, allometric scaling for strength notations was proposed to account for intersubject body mass differences (1,18). Despite the use of the 0.67 exponent difference in 1RM relative strength differences between the present study, players and the professional soccer players used by Wisløff et al. (46) were still evident (6.76 vs. 9.4 kg·body mass-0.67, respectively). These findings may indicate differences in strength requirements between basketball and soccer players or the efficacy of the different strength training methods adopted by the 2 sports (46).
The vertical jump heights reported in the present study (61.9 ± 6.2 cm) were within the range that have previously been reported (54.6-71.4 cm) for subelite and elite male basketball players (19,24,26).
There have been no previous studies that have profiled sprint or agility times in elite male basketball players. There are, however, several studies that have profiled sprint and agility times in college male basketball players (19,24,26). The most common distance for assessing sprint capability in college basketball players is 27 m with times ranging from 3.8 to 4.1 seconds being recorded (26). The present study reported sprint times for distance of 5 m (0.82 second), 10 m (1.7 second), and 30 m (4.1 seconds). The only comparison that can be made among these studies is to assess average running velocity over the entire distance. The previous studies reported average running velocities of 6.6-7.1 m·s-1 over 27 m. The present study reported a slightly higher average running velocity of 7.3 m·s-1 over 30 m. It appears that elite basketball players are only slightly faster than their nonelite counterparts over a distance of 27-30 m. However, these comparisons between sprint velocities have to be made with caution because of the 3-m difference in distance. However, because basketball is interspersed with many short sprints (<30 m), further research with elite basketball players is necessary to profile the optimal speed required over these distances (20,21,24,30). From the current and previous researches, it could, however, be speculated that an average running velocity above 7.1 m·s-1 (or below 4.2 seconds) for 30 m would be appropriate for elite male basketball players.
As a result of the physical and physiological similarities in the basketball players used in the present study with those of top international-level basketball players, the results obtained in this study may be regarded as representative of elite-level basketball (32,35).
In light of the present study, findings on agility should be regarded as a major physiological ability in male elite basketball players. Consequently, as a result of the documented specificity of agility training outcome (37,49), basketball-specific drills should be stressed in elite basketball training (i.e., line drills and T-drills). Short sprinting (i.e., 5- to 10-m sprint) should be considered as a basketball-related sprint activity (11,30). Because of the association between squat 1RM performance and short sprint times, squat exercises should be considered in basketball conditioning. As a result of the nature of basketball game, the squat exercises may be used emphasizing the maximal force mobilization during the concentric phase of the squat exercise according to Østerås et al. (31) and Wisløff et al. (47).
However, conclusive inference with regard to the exact impact of squat 1RM performance to basketball-relevant performances may only be drawn after further well-designed training studies. Bench press exercise should not be overemphasized in elite basketball players' training.
This study was supported by the Tunisian Ministry of Scientific Research, Technology and Development of Competences. The authors thank the staff of the National Centre of Medicine and Science in Sports as well as the athletes and the staff of the Tunisian National Basketball team. The authors also thank Dr. Leiper Jhon for revising the English grammar of the manuscript.
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