Basketball is a multifaceted team sport that requires a well-developed physical fitness to be played successfully (29). Many authors have suggested that strength, power, agility, and speed are important characteristics for elite basketball players (18,25). However, several research studies showed that the aerobic involvement during competitive basketball, either played at youth or professional level, is higher than previously thought (6,7,9,29,30).
Recently, Ben Abdelkrim et al. (7) showed that in junior basketball players, aerobic fitness is related to match performance and that the aerobic pathway is progressively heavily stressed during the course of the game. These findings are supported by studies that reported an important cardiovascular involvement during men's basketball competitions (6,7,29). Narazaki et al. (30) using direct oxygen consumption (VO2) assessment showed that players during scrimmage attained 65% of individual VO2max suggesting aerobic-fitness training to improve game performance. This VO2 involvement and the reported blood-lactate concentration [La]b suggest that submaximal aerobic fitness may play a role in basketball conditioning (30,31). This hypothesis was supported by the Laplaud et al. (24) findings that showed improvement in submaximal aerobic fitness in professional male basketball players during the competitive season (i.e., sensitivity). As a consequence of that, the determination of the submaximal components of aerobic fitness such as lactate threshold (LT) may be of some help in training monitoring and exercise prescription in modern basketball (36).
Although laboratory LT detection is the optimal choice for the determination of reliable results, the procedures involved are time consuming and require highly trained personal (16). Furthermore, laboratory testing requires exercise modes such as cycling or line running that are not basketball specific (11). Consequently, LT results may have doubtful relevance to specific basketball training, and the protocol used may limit players' motivation to testing. Therefore, the possibility to implement a basketball exercise mode-specific field test for the determination of LT would be of interest for coaches and basketball fitness trainers. The assessment of aerobic fitness via submaximal protocol in the field may also have a positive impact on player's motivation to testing having less impact on training fatigue compared to maximal aerobic-fitness tests (3-5,10,13). This may be the case before major competitions and after an injury has occurred.
Given this, the aim of this study was to assess the validity of a newly devised exercise mode-specific field test for LT detection in young basketball players. We hypothesized an association between court (surrogate) and laboratory (gold standard) submaximal aerobic-fitness values (criterion validity).
Experimental Approach to the Problem
Recently, aerobic fitness (31) has been proposed as a performance component in basketball conditioning (35,42) and team sports (36). During basketball, the majority of the actions affecting the match outcome are performed at near-maximal intensities involving players' anaerobic-power abilities. However, medium-to-low intensity activities (∼50 and 40% of game time, respectively) and post high-to-maximal exercise game recovery (∼10% of game time) are accomplished through aerobic-pathway involvement (36). Consequently, aerobic-fitness training and tests are suggested to be included in basketball-specific test batteries to complement anaerobic power and agility performance assessment (34,36,42,43). In this study, the assessment of aerobic fitness was performed using a progressive intermittent submaximal test that involved shuttle running (Intermittent Shuttle-Running Test [ISRT]) on a 20-m base of the basketball court. This is to provide logical validity and feasibility (39). Criterion validity was tested comparing ISRT results with LT values assessed in the laboratory during a progressive treadmill test (i.e., gold standard) (23). Lactate threshold was considered as the speed attained at a [La]b 1 mmol·L−1 above the resting level (13,41). Speed at LT was calculated using the best fit line method for each individual's [La]b vs. speed data using a custom-made visual-basic program.
Fourteen well-trained basketball players (age 15.3 ± 0.6 years, height 182 ± 5 cm, and body mass 72 ± 6.3 kg) were randomly chosen within a population of basketball players of an elite basketball-academy team (Stamura Basket, Ancona, Italy). To be included in the study, players had to possess official medical clearance at the beginning of the season according to national law, to ensure that they were in good health. This medical examination, which includes electrocardiogram, blood and urine analysis, and spirometry, was performed in medical centers certified by the National Ministry of Health. Written informed consent was received from all participants and parents/guardians after a detailed explanation about the aims, benefits, and risks involved in this investigation. Participants were told they were free to withdraw from the study at any time without penalty. The study was approved by the local Institutional Research Board and the local ethics committee before the commencement of the assessments. The study protocol followed the guidelines laid down by the World Medical Assembly Declaration of Helsinki.
Before the testing session, players were advised to maintain a high carbohydrate diet and not to eat food or drink beverage containing caffeine. The testing session took place at least 3 hours after the main meal. All testing sessions were undertaken with well-rested players. Players at the time of the investigation were experiencing a midseason break (Christmas holidays). During this period of the season, players trained 4 times a week with a tournament or friendly game played during the weekend. Training sessions were mainly devoted to tactical and technical skill development (∼90 minutes) in the form of ball drills. Strength and conditioning was provided with 2 45-minute sessions a week involving explosive strength and aerobic and anaerobic-fitness development (circuit training, and interval training). Inclusion in the study required at least 3 years of experience in competitive basketball, regular participation in championship competitions, absence of muscle-tendon injuries during the 2 months preceding the experimentation, and regular adherence to training schedule during the same period of time. During the training period considered for the physiological measurements of this study, the players scored 40.3 ± 5.7 cm in the countermovement jump and 26.7 ± 1.3 seconds in the line drill, respectively (11). These measurements were taken to assess the fitness level of the basketball players that volunteered in this study and to assess the external validity of this study population (11).
Lactate threshold was detected using a progressive intermittent running protocol (TM) on a motorized treadmill (Technogym Run Race 1400 HC, Gambettola, Italy) consisting of bouts of 4 minutes interspersed with 1 minute of passive rest. Running speeds were set at 8, 10, 12, and 14 km·h−1. After a 5-minute recovery, subjects performed an incremental short-term (4-7 minutes) continuous protocol to determine maximal heart rate (HR) and peak [La]b (23). In this second testing phase procedure, players ran at 14 km·h−1 with speed increments of 1 km every 30 seconds until 16 km·h−1. Thereafter, treadmill inclination was increased every 30 seconds by 1% until exhaustion (23). Lactate threshold was assessed taking blood samples at rest and immediately after each of the 4 running bouts. Peak [La]b was assessed by sampling blood 3 minutes after the all-out progressive run.
On a separate occasion and in random order, players were submitted to an incremental ISRT over a 20-m base. This consisted of 3 4-minute bouts of shuttle running performed at 9, 10, and 11 km·L−1, respectively. These shuttle-running speeds were selected according to a preliminary pilot study that showed a progressive submaximal physiological stress in this selected population of athletes. Between each shuttle-running bout, players rested passively for 1 minute. During ISRT, [La]b was determined by analyzing blood samples taken at rest and immediately after each continuous shuttle-running bouts. Shuttle-running speeds over 20 m were dictated with CD-recorded audio cues broadcasted by a CD player (Philips AZ1030, Best, The Netherlands). During the ISRT, players had to run between 2 lines set 20 m apart stepping on the front line in time with the prerecorded audio cues.
During all testing procedures, [La]b was determined using the Biosen 5030 enzymatic-amperometric lactate analyzer (EKF Industrie, Barleben, Germany). Earlobe blood samples were collected using 20-μL glass sodium heparinized capillaries. Blood samples were immediately stored in heparinized test tubes and analyzed within 5 hours.
Exercise HRs were monitored throughout each test using short-range telemetry (Polar NV, Kempele, Finland). Heart rate profiles were analyzed using dedicated software (Polar NV, Kempele, Finland).
Subjective effort perception was assessed immediately after exercise using the 1-10 Börg rate of perceived exertion (RPE) scale (8).
Testing sessions took place on separate days, at least 2 days apart and at the same time of the day (between 14.00 and 17.00 h) to avoid circadian variation of physiological variables.
Reliability of the ISRT reported as intraclass correlation coefficient (ICC) and coefficient of variation (CV) were calculated in 18 players tested 1 week apart. The ICC and CV values for the HR and [La]b during the ISRT ranged between 0.89 and 0.92 and 1.8-2.3%, respectively (n = 18).
Data are presented as mean ± SD. The power for the statistical calculations for the sample size used (n = 14) in this study was of 0.86. Comparison between 2 variables has been performed with paired t-tests and effect size (ES) as Cohen's d was calculated. When comparisons between >2 variables were necessary, analysis of variance designs were used (simple 1-way or repeated measurements) with Bonferroni post hoc test. Association between variables was assessed using Pearson's product-moment coefficient of correlation and providing confidence interval at 95% (95%CI). According to Hopkins (21), magnitude for correlation coefficients was considered as trivial (r < 0.1), small (0.1 < r < 0.3), moderate (0.3 < r < 0.5), large (0.5 < r < 0.7), very large (0.7 < r < 0.9), nearly perfect (r > 0.9), and perfect (r = 1). Significance was set at p ≤ 0.05. All calculations were performed with Statistica package (Statsoft, Tulsa, CA, USA, 6 version).
Results showed that the speed at LT during ISRT and TM was significantly related (r = 0.82, p < 0.001, 95%CI 0.51-0.94, Figure 1); this relationship is deemed to be very large according to Hopkins (21). Speed at ISRT-LT showed to be significantly lower than the TM-LT speed (10.1 ± 1.7 vs. 12 ± 2.3 km·h−1, p < 0.001).
Heart rates during ISRT were 80 ± 4.7, 87 ± 4.4 and 92 ± 3.0% of HRmax at 9, 10, and 11 km·h−1, respectively (p < 0.001). Mean %HRmaxs at 8, 10, 12, and 14 km·h−1 were 71 ± 4.2, 80 ± 4.0, 85 ± 3.9 and 91 ± 2.9% during TM. No significant differences were detected between %HRmax at LT in the ISRT and TM tests (84 ± 5.1 and 83 ± 5.1%, p = 0.23, respectively, ES = 0.33). Rate of perceived exertion at LT was significantly higher during TM than during ISRT (4.4 ± 0.7 vs. 3.6 ± 1.6, p < 0.05, ES = 0.80). The [La]b, RPE, and %HRmax during ISRT and TM are reported in Tables 1 and 2, respectively.
The main finding of this study was the significant association (r = 0.82, p < 0.001) existing between ISRT and TM lactate thresholds, which confirms our research hypothesis. The ISRT was devised in the attempt to limit the technical, economical, and logistic constraint usually associated with laboratory testing.
The ISRT test involving intermittent shuttle running performed over a 20-m base possesses a good logical validity because it mimics the exercise pattern that usually takes place during basketball training and competitions (11,12,26,27). The physiological and perceptual responses to ISRT showed a progressive involvement of aerobic and anaerobic metabolism with attainment of submaximal effort throughout the test. Indeed, test end [La]b was only 33% of the peak values obtained by the involved basketball players at exhaustion during the laboratory all-out test. Similar pattern was observed for effort perception at 11 km·h−1 that was 55% of RPE experienced at exhaustion. Heart rate during the ISRT peaked to 92% of HRmax showing an important aerobic involvement during the last stage of the test. Interestingly, the HR at LT in the 2 test conditions showed no significant differences when expressed as a percentage of the individual maximal. Despite this, RPE resulted in being significantly lower during the ISRT as per the speed at LT. This result shows that shuttle running induced higher physiological stress on players compared to line running. Indeed, at the same running speed (10 km·h−1), [La]b, RPE, and HR resulted in being 29, 24, and 9% higher in the shuttle-running condition than in line running (i.e., treadmill running). This is similar to what was previously reported by Reilly and Bowen (32) in nonorthodox directional running modes such as backward and sideward motions.
Shuttle running like backward and sideward running are directional modes heavily involved in basketball competitions (7,29). Consequently, because of the unique physiological demands imposed, nonorthodox directional modes should be used to implement basketball-specific training drills. In this regard, the [La]b and HR responses found during the 11-km·h−1 shuttle running bout may suggest the use of such a speed to induce metabolic adaptation in young basketball players using game exercise mode-specific drills (i.e., shuttle running). This option may parallel the use of ball drills (i.e., scrimmage and rule-modified games) to implement metabolic training in basketball (10,30,38). In this regard, soccer studies showed that significant enhancements in aerobic fitness (31) may be achieved using ball or running drills (4-minute length) that elicit HR in the range of 90-95% of maximal (17,22).
This is the first study that assessed the LT in young nonelite basketball players. The HR and [La]b at LT are similar to those reported to occur during age-matched basketball competitions (10), suggesting that exercise intensities at LT may result in being functional to aerobic conditioning of young basketball players (36). However, basketball anaerobic fitness should not be neglected because the majority of the technical tactical relevant activities are performed at high to maximal intensities in basketball competitions (7,29). In this regard, training studies that addressed concurrent training in basketball showed that combining strength and endurance was more effective in promoting aerobic fitness than endurance or strength training programs only (2). Although the direct effect of improvement in aerobic and strength fitness on game performance was not investigated, this study finding suggests the value of concurrent training in basketball (2).
Apostolidis et al. (1) detected in elite level junior basketball players (age 18.5 years) ventilatory threshold occurrence at 86% of the individual maximal HR. This figure is similar to that reported here showing that the randomly chosen nonelite players were as much aerobically fit as their elite level junior counterparts. These results may indicate that young well-trained basketball players should be able to at least manifest LT or VT at approximately 86% of their maximal HR to be considered conditioned for competitive basketball. As this %HRmax has been reported to be typical of most part of basketball competitions (7,11,29,30), it can be assumed that this study players were aerobically fit to cope with demands of the game. However, the speed attained at LT in these young basketball players was lower than that reported in French professional basketball players that was found to be 15 km·h−1 (33). Nevertheless, difference in testing protocols and LT and or anaerobic threshold definitions make comparisons difficult to be performed (28,37,40).
The values for the countermovement jump and the line-drill performances of this study players were similar or even higher to that reported in elite basketball teams of the same age (14,15,42). Specifically, Apostolidis et al. (1) and Hoffman et al. (19) reported line-drill performances of 27.9 ± 1.0 and 28.3 ± 0.9 seconds for junior players of the Greek and Israeli National teams, respectively. Moreover, the countermovement jump performance of the players in this study was similar to those reported in professional adult players (43.9 ± 4.0) and in junior elite players (40.1 ± 3.7 cm) (42). Given the good physical performances showed by this sample of basketball players, the IRST test performance reported here may represent a valid reference for competitive basketball.
The very large correlation between (i.e., r = 0.82, p < 0.001) ISRT and TM lactate thresholds showed that only 33% of the common variance resulted in being unexplained. Probably, the difference in the ability to perform shuttle running may have affected the strength of the relationship (12).
The ISRT may be safely used by strength and conditioning coaches to evaluate submaximal aerobic fitness in basketball players in field conditions within just 15 minutes. The assessment of the relevant variables may be achieved with trend analysis (see Methods) or just plotting the [La]b against speeds to examine the aerobic efficiency of players (23). The submaximal nature of the test should be considered as an added value of ISRT being convenient for in-season fitness assessment.
The data reported here showed that LT, irrespective of exercise mode (i.e., line or shuttle running), occurs at approximately HR 83-84% of HRmax. Consequently, this result may guide coaches and strength and conditioning professionals in aerobic-fitness prescription when maximal HR is known and HR monitoring is available. If this is not the case, as in schools and nonprofessional basketball teams, a viable surrogate of HR cues may be RPE. Using the 1-10 Börg Scale, an RPE score of approximately 4 may be reasonably considered as the exercise intensity at LT (unpublished data of this study). Continuous 20-m shuttle running performed at 11 km·h−1 revealed to elicit HR in the range of those reported to induce aerobic-fitness development in trained subjects; this induces [La]b in the range of those reported in youth basketball games (10).
The ISRT may be considered in the basketball-specific testing batteries as per anaerobic performance and agility abilities (14,15,42,43). Test sensitivity (i.e., ability to detect fitness changes during the season) studies should be undertaken to test the full applicability of ISRT in youth basketball (20). Furthermore, direct validity should be tested comparing ISRT results with match physical performance (10).
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Keywords:© 2010 National Strength and Conditioning Association
submaximal testing; team sports; anaerobic capacity