in basketball, balance ability is important to reduce non-contact injuries. The purpose of the present study was to investigate the effect of training on balance.

thirty-two healthy male volunteers were recruited from amateur basketball teams. They were asked to perform the Balance Error Scoring System BESS test in order to measure the number of stability errors in six conditions. The test was performed at the beginning of the season (T0) and after 12 weeks (T1). In both cases the test was carried out before (pre-session) and after a training session (post-session).

the comparison of the total BESS scores both pre- and post-session showed a statistically significant increase of stability errors at both T0 and T1 (T0: pre-session 8.6±6.1 errors, post-session 10.7±6.3 errors; t=−4.03; p=0.002) (T1: pre-session 7.2±3.8 errors, post-session 9.1±5.4 errors; t=−1.93; p=0.03). Between T0 and T1 we noticed a reduction of errors which reached a statistical significance during the pre-session time (t=2.75; p=0.0049).

stability improved after 12 weeks of training, even for those conditions for which no specific training was done to improve, such as on the soft surface and feet aligned in a tandem stance.

Keywords: balance, exercise, instability, sport

Balance or postural stability is a necessary component in both daily activities and sport1,2. While “balance” is a commonly used term to describe the ability to maintain an upright position, “postural stability” is a more specific description of human balance3. Postural stability can be defined as the ability of an individual to maintain their center of gravity within the base of support4. It involves feedback from the sensorial systems which determine continual neuro-muscular changes4. This allows better sport performance and reduces the risk of injury5,6. Because of this, sports training, as well as focusing on improving sporting skills, also develops balance. However, the athlete must take into account the fact that fatigue can compromise stability5,6.

From the literature, an evidence-based relationship between balance ability and the risk of injury is clear7,8. In fact, studies have demonstrated that exercise training is effective in reducing the risk of injuries7,8. The training improves proprioception and protect athletes from forthcoming injuries. Proprioceptive information from lower limbs is important in the maintenance of equilibrium in basketball due to the nature of the game9. Proprioception is even more significant for basketball because the basketball skills are composed by complex movements demanding high balance ability9. It was observed that when balance training was implemented during competitive season, the occurrence of injury rate was reduced by 38%10. However, the link between balance ability and athletic performance is not fully clear and required further evidence11,12. There are, in fact, very few studies that specifically investigated balance training as approach to improving performance11,12.

Basketball is a high-demand sport activity with a high prevalence of lower limb injuries, namely knee and ankle sprains13. It is a sport which involves mainly jumping and landing14. Disequilibrium can be found in every specific movement of basketball, such as in the twisting movement of feet, jump shots as well as offensive and defensive rebounds9. Besides which, basketball requires the players to habitually address physical contact and various situations involving balance instability, such as basketball-specific accelerations and decelerations, changes in direction, penetrations into the defensive perimeter, boxing out, dribbling and defense position recovery15. These actions are often performed in a very limited space and require very fast movement, high coordination ability and appropriate strength. It is very important to have good balance while executing these skills.

Until now, no study has ever been carried out looking at the effects of training on balance in basketball. Thus, the aim of this study is to verify balance improvement in basketball players. At the same time we also monitored whether fatigue after a training session has compromised balance.

We set up a clinical longitudinal observational study designed to recruit 32 volunteer healthy male basketball players from amateur teams. The parents of all subjects read and signed the informed consent form approved by the local Ethics Committee, which also approved the study procedures16. The observation period lasted for 12 weeks, from September (pre-season) to December 2013 (mid-season). Participants were selected on the following criteria: young male basketball players of different Under Fifteen Basketball, currently participating in basketball at least 1 year before, no lower extremity musculoskeletal injuries, no history of head injury or of pre-existing visual, vestibular, or balance disorders. Anthropometric data was recorded (age=13.6±0.5 years; weight= 55.4±5.8 kg; height=166.5±5.2 cm; previous basketball practice=2.8±1.2 years). Eighty percent of players were right-handed.

All subjects followed the same athletic training programme, three times a week. Each training session consisted of 30 minutes warm-up, isotonic training and proprioceptive exercises and of 90 minutes technical-tactical training. The warm-up was composed of three phases: 5 min of jogging at a comfortable speed; 2 min of static stretching for the lower limb muscles; and 5 min of shooting, from both sides of the court. The isotonic training used the leg press and leg extension isotonic machines. Each subject performed the following: 5 sets of 12 leg press repetitions at 70% 1 RM (Repetition Maximum) with 3 min of recovery and 4 sets of 10 leg extension repetitions at 70% 1 RM with 3 min of recovery. Following, the balance training was performed. First, subjects performed 8 sets of 20 s of Swiss ball kneeling hold balancing with 30 s of recovery; subjects were told to maintain balance on the Swiss ball while keeping their knee at an approximate angle of 90°. Then, they performed 6 sets of 20 repetitions of the two-handed chest pass balance exercise with 30 s of recovery; subjects were instructed to maintain balance on the trial half-sphere while performing 20 chest passes to a teammate in front of them at a distance of approximately 10 m. After these exercises, subjects completed 90 min technical-tactical training session with their head coach.

Postural stability was evaluated using BESS. The test was carried out four times: at the beginning of competitive preparation before training (T0 pre-session); at the beginning of preparation after training (T0 post-session); after 12 weeks before training (T1 pre-session); after 12 weeks after training (T1 post-session). Postural stability was measured using BESS (Balance Error Scoring System) error scores17–20. The BESS consisted of 6 separate 20-second balance tests that the subject performed in different stances and on different surfaces. The test consisted of 3 stance conditions (double-leg, single-leg, and tandem stance) and 2 surfaces (firm and foam). The firm surface was the floor of a gym. The foam surface consisted of a 46 × 46 × 13-cm block of medium-density foam on a 10-cm-thick. A stopwatch was used to time each of the 20-second trials. Subjects were instructed to assume the required stance by placing their hands on their iliac crests and were informed that when they closed their eyes, the test would begin. Errors were recorded as the quantitative measurement of postural stability under different testing conditions. Before the test, subjects were allowed to familiarize themselves with the different conditions. They were first allowed to try standing on the firm surface. Once they were comfortable standing on each surface, we instructed them in the correct positioning for each of the 6 conditions. The double-leg stance conditions consisted of the subject standing with feet together. The single-leg stance was performed on the non-dominant leg, as determined by which limb the subject would not preferentially use to kick a ball. The dominant leg was positioned so that the hip was flexed to approximately 30° and the knee flexed to 90°, leaving the foot approximately 25 cm off the ground. We instructed the subjects not to lean the dominant leg on the non-dominant leg. The non-dominant foot was positioned behind the dominant foot in the tandem stance, and the subject was instructed to maintain the stance with the big toe of the non-dominant foot touching the heel of the dominant foot. For each condition, we instructed the subject to remain still with their eyes closed and hands on their hips. After instruction, each subject was given 2 familiarization trials on each condition before the actual data collection. During the familiarization and testing sessions, each condition lasted 20 seconds, and at no point was the clock stopped. We instructed the subject to remain as still as possible; if he moved from the test position, he was to return to it as soon as possible. One BESS error was scored if the subject engaged in any of the following: (1) lifting the hands off the iliac crests; (2) opening the eyes; (3) stepping, stumbling, or falling; (4) moving the hip into more than 30° of flexion or abduction; (5) lifting the forefoot or heel; (6) remaining out of the test position for longer than 5 seconds. Performance was scored by adding 1 error point for each error committed. Error scores were calculated for each of the 6 conditions and summed to obtain the total BESS score17–20. During the testing, the examiner was positioned 3 m away from the subject, so the subject’s eyes, hands, and feet could all be observed.

Given the previous data in literature related to mean and standard deviation of the number of BESS errors at recruitment and follow-ups17–20, we established al-fa=0,05 and power=0,90 and yielded a minimum number of 24 subjects.

For each subject recruited we filled in a form showing personal data, weight, height, dominant limb, years of taking part in sport activity and the scores performed at each time. Leg dominance was determined by methods used in previous studies21,22. The completed forms were inserted into a database created using FileMaker pro and analysed using STATA MP11 software. To evaluate the differences between the average values of the results at T0 pre- and post-session and at T1 pre- and post-session we used the t-student test for paired samples (T0 pre- vs T0 post-session; T1 pre- vs T1 post-session; T0 pre- vs T1 pre-session; T0 post- vs T1 post-session). To evaluate the results of the tests at T1 pre-session we built multiple regression models which investigate age, gender, weight, height, dominant limb, values at T0 both pre-and post-session. To evaluate results at T1 post-session we built multiple regression models which investigate age, gender, weight, height, dominant limb, values at T0 both pre- and post-session and at T1 pre-session. For each test a value of p<0.05 was considered statistically significant.

The results of each test, expressed as number of errors, and the statistical evaluations are shown in the Tables 1 and 2.

Table 1 Values expressed as averages (± standard deviation) of the various BESS tests, at both times in the study pre-and post-session.

Table 2 Statistical comparison of each BESS test showing the comparisons between the pre-and post-session score at each time and between each pre- and post-session score respectively at both times in the study.

The number of errors increased significantly from pre-to post-session at both T0 and T1. In comparing T0 and T1 we found a statistically significant reduction only in the pre-session scores.

We found a trend to increase the number of errors from pre- to post-session at T0 and T1. A statistically significant reduction was recorded in the pre-session from T0 to T1.

At T0 and T1 we recorded a statistically significant increase of errors from pre- to post-session. At T1 pre-session the number of errors has been reduced significantly respect to T0 pre-session.

The total score of the firm surface at T1 pre-session was influenced by the total score of the firm surface at T0 post-session (coef 0.25; t=4.71; p<0.0001). The total score of the firm surface at T1 post-session was influenced by age expressed in years (coef 2.75; t=2.61; p=0.015). The total score of the foam surface at T1 pre-session was influenced by the total score of the foam at T0 pre-session (coef 0.51; t=4.66; p<0.0001) and post-session (coef 0.35, t=2.89; p=0.008). The total BESS score at T1 pre-session was influenced by age (coef −2.34; t=−2.27; p=0.032) and by the total BESS score at T0 pre-session (coef 0.78; t=5.51; p<0.0001). The total foam score at T1 post-session was influenced by age (coef 5.7; t=4.15; p<0.0001), height (coef −0.35; t=−2.99; p=0.006), dominant right limb (coef 4.1; t=2.69; p=0.013), total foam score at T0 pre-session (coef 0.51; t=2.11; p=0.045). The total BESS score at T1 post-session was influenced by age (coef 7.6; t=3.11; p=0.005), by height (coef −0.53; t=−3.08; p=0.005), by dominant right limb (coef 5.33; t=3.11; p=0.005), by the total BESS score at T1 pre-session (coef −1.7; t=3.91; p=0.001).

The BESS total scores demonstrate that after 12 weeks (at T1) there was an improvement in balance, with a statistically significant difference in the pre-session test. At both times in the study (recruitment and revaluation at 12 weeks, T0 and T1) the postural stability of the post-session was statistically worse compared to the pre-session.

BESS is a standardized, rapid, inexpensive screening test of postural stability that can be helpful for documenting stability17–20. It has been used in many studies with healthy athletes, and as an outcome measure relating to low limb instability or those completing neuromuscular training17–20, 23, 24. At the beginning this test was used to study balance stability23. The average number of BESS errors depends on the stance and surface23. Very few errors are associated with the double-limb stance on either the firm or foam surfaces9. The single-leg stance is the most responsible for adding errors to the total BESS score on the firm and on the foam surface18. Less number of errors are added to the total BESS score during the tandem stance on the two surfaces18. The errors of stability linked to position and surface were the same that we found in literature17–20.

We found that training improved balance stability. In basketball, athletic training focuses on functional strengthening, agility training, and balance training25. This specific physical training supports the improvement of balance control25. Postural control is obtained by the interaction of three principal systems: the musculoskeletal system, the sensorial system and the central nervous system6. The musculoskeletal system is represented mainly by the triceps surae muscle, particularly trained in basketball13. In fact, repeated vertical jumping reinforces the ankle muscles and allows a better and more stable joint12. As far as the sensorial system is concerned, basketball players have a particularly developled visual system, which compensates for the decreased stress mechanoreceptors and vestibular receptors26. The central nervous system reacts by regulating the muscular activity neccessary to maintain good posture and to restore balance when thrown off, based on information received from the sensorial systems27.

A recent review underlined that there are no significant differences in postural stability between athletes of different specializations and physically active individuals27. Various sport disciplines differ for different postural strategies employed: for example, there is a greater stimulation of mechanoreceptors in gymnastics28, a more specific development of proprioceptive and vestibular receptors in swimming29, peculiar development of muscular fibres of the trunk in volleyball30, a decrease in the centre of gravity in martial arts31, a reduction in the center of pressure frequency in football32,33, and stability of the support base with the use of hard boots in skiing34.

The second result of the study is that balance decreases due to fatigue. Sport particularly tired fast muscular fibres, that have an anaerobic metabolism, that come into play not only during speed and power activities, but also during sudden postural changes35. Moreover, muscle fatigue may alter the proprioceptive afferents, causing further instability36,37.

It has also been discovered in other sports that motory overload reduces stability. In elite gymnasts, the fatigue due to exercises performed in training leads to a reduction of trunk stability38. In soccer, high-level players experience fatigue in the last 15 minutes of each half time of a match39,40 and players may also experience deficits in postural balance during these 15 minutes, as it has been suggested that soccer-specific fatigue can influence the functional stability of players in match play5. In volleyball, the fatigue induced by a match has a marked effect on knee joint position sense in elite female volleyball players. Knee joint position sense was less accurate and less consistent after the volleyball match6. However in tennis no loss of stability was recorded at the end of the game, consistent with a lower level of muscle fatigue41.

Due to further study of the results in each test carried out in our case, we found a pattern which was similar to the BESS total, except in some conditions. The first variation is that of the tandem feet test on a firm surface for which we found no statistically significant improvement between T0 and T1. This could be due to the lack of training for this specific position. Training is specific for conditions of bi-podalic support with feet side by side. The second exception is the data found on the foam surface (at T0 and T1, both on one leg or feet in tandem). In the post-session we discovered a decrease in stability even though the values did not reach a significant difference. We hypothesize that this is due to a fatigue-related failure in the neuro-muscular system involved in this particular position. As a matter of fact, training has always taken place on the firm surface of a gym floor. The third variable is that found on the foam surface, when the test was carried out with feet in a tandem position, for which from T0 to T1 balance improved in the post-session. We suppose that this improvement was determined by athletic preparation, even if it was not specific to the stand evaluated in the test, and this justified the lower level of fatigue at the end of the training session.

The analysis of the multiple regression model showed that right dominance could be a confounding factor and it increases the number of errors. This can be explained by the notion that humans are generally right-footed for mobilization tasks, but left-footed for tasks requiring postural stabilization42–44. Other confounding factors are height and age. Indeed, in taller subjects, the centre of gravity is higher and this increases the risk of instability45. Furthermore, younger subjects have a less mature postural system which accounts for this greater instability46. As for the pre-session values at T1, we also found that they were influenced by the values at T0 which can be justified considering that balance is an innate skill for each individual which can be worked on and improved46.

There are some weak points in our study which need to be pointed out. In our study we analysed the link between training and postural stability. It would also be interesting to analyse the effects of a match, considering that in a match pyscho-physical fatigue conditions can take over which can alter the player’s performance. The use of a stabilometry could allow us to quantify the direction (medial-lateral or anterior-posterior) of the deviations. A control group using sedentary subjects could give us a reference to quantify the effects of taking part in sport. It would be interesting to be able to compare the effects of training in other sports.

Despite limitations, the study has deepened our knowledge of the effects made by training and fatigue on balance. We also discovered that predominantly in basketball, even when a pose was not specifically worked and the work surface were not specifally trained on, balance improved. On the other hand, the loss of stability is specifically connected to fatigue in sport.

The findings of this study could have important implications for basketball players and their coaches. It could be useful to ration training loads, allowing for any neccessary recovery time. Furthermore, it could be appropriate to differentiate programmes administered, varying work and support surfaces and in order to train balance in different conditions. Further studies could look at the effects if these different training programmes.