Are trunk stability and endurance determinant factors for whole-body dynamic balance in physically active young males? A multidimensional analysis.

OBJECTIVES: Determine if (a) a better trunk stability and endurance are associated with an improved whole-body dynamic balance, and if (b) the assessment tests can be interchanged within each capability. METHODS: Sixty-three physically active young males performed three trunk stability (i.e., the lumbopelvic stability, the unstable sitting and the sudden loading sitting tests), three trunk muscle endurance (i.e., the Biering-Sørensen, the side bridge and the front bridge tests) and four whole-body dynamic balance (i.e., the tandem and the single-leg stance, the Y-Balance, and the single-leg triple hop tests) tests two times. After assessing the reliability of the variables, a Pearson correlation analysis was performed. RESULTS: The correlations between trunk stability and endurance tests with dynamic balance tests were non-significant except for the unstable sitting test with both the tandem (r = 0.502) and the single-leg stance (r = 0.522) tests. Moreover, no relationships were observed between the trunk stability and the trunk muscle endurance tests. Interestingly, no relationships were found between most tests within each capability (i.e., trunk stability, trunk endurance, and dynamic balance) except: (i) the front bridge stability test and the back (r = 0.461) and the side (r = 0.499) bridge stability tests; (ii) the two side bridge endurance tests (r = 0.786); (iii) the tandem and the single-leg stance tests (0.439 ≤ r ≤ 0.463); (iv) the Y-Balance and the single-leg triple hop tests (0.446 ≤ r ≤ 0.477). CONCLUSION: Better trunk function does not seem to be a relevant factor for dynamic balance in young active males. In this population, specific measures are needed as the test interchangeability is questioned.

Comparison of hip extension and rotation ranges of motion in young elite tennis players with and without history of low back pain.

BACKGROUND: Although low back pain (LBP) is known to be multi-factorial, certain studies have suggested that a deficit in hip extension and rotation range of motion (ROM) may be associated with LBP in athletes. OBJETIVE: The purpose of this study was to compare hip extension and rotation ROMs in elite tennis players with and without a history of LBP. METHODS: Forty-two male and 22 female young elite tennis players completed this study. Participants were divided into two groups: (1) 32 with history of LBP and (2) 32 without history of LBP. Descriptive measures of passive hip extension and rotation ROMs of the dominant and non-dominant limbs were taken. Active hip rotation ROMs were also assessed. Magnitude-based inferences on differences between groups and legs were made by standardizing differences. RESULTS: The inter-group statistical analysis reported no significant differences (p> 0.05; trivial effect with a probability higher than 95%; d⩽ 0.4) in any ROM measure analyzed. Further, neither LBP group nor control group reported significant bilateral or side-to-side differences (p> 0.05; trivial effect with a probability higher than 99%; d< 0.3) between legs regarding hip extension and rotation ROM measures. CONCLUSION: No relationship between hip extension and rotation ROM and history of LBP was found.

Different neuromuscular parameters influence dynamic balance in male and female football players.

PURPOSE: To analyse the relationship between several parameters of neuromuscular performance with unilateral dynamic balance measured through the Y-Balance test, as well as to determine the possible sex-related differences. METHODS: The Y-Balance test, isokinetic (concentric and eccentric) knee flexion and extension strength, isometric hip abduction and adduction strength, lower extremity joint range of motion (ROM) (hip, knee and ankle) and core stability were assessed in male (n = 88) and female (n = 44) professional football players. A stepwise multivariate linear least square regression with backward elimination analysis was carried out to identify a group of factors that were independently associated with balance performance in both sexes. RESULTS: Passive hip flexion and ankle dorsiflexion with knee flexed ROM were the main factors that retained a significant association to dominant (R2 = 23.1) and non-dominant (R2 = 33.5) balance scores for males. For females, core stability, hip abduction isometric peak torque, passive hip abduction and ankle dorsiflexion with knee flexed ROM variables retained a significant association with balance scores for both, dominant (R2 = 38.2) and non-dominant (R2 = 46.9) legs. CONCLUSIONS: Training interventions aimed at improving or maintaining unilateral dynamic balance in male football players should include, among other things, stretching exercises for the posterior chain of the lower extremity. However, females should also include exercises for strength and mobility of the hip abductors and core stability (especially in the frontal plane). This knowledge would allow clinicians and sport practitioners to develop more effective and tailored unilateral dynamic balance training interventions in male and female football players, possibly improving performance and reducing the risk of injury. LEVEL OF EVIDENCE: III.

A COMPARATIVE STUDY OF PASSIVE SHOULDER ROTATION RANGE OF MOTION, ISOMETRIC ROTATION STRENGTH AND SERVE SPEED BETWEEN ELITE TENNIS PLAYERS WITH AND WITHOUT HISTORY OF SHOULDER PAIN.

BACKGROUND: Glenohumeral internal rotation deficit and external rotation strength have been associated with the development of shoulder pain in overhead athletes. OBJECTIVE: To examine the bilateral passive shoulder rotational range of motion (ROM), the isometric rotational strength and unilateral serve speed in elite tennis players with and without shoulder pain history (PH and NPH, respectively) and compare between dominant and non-dominant limbs and between groups. STUDY DESIGN: Cohort study. METHODS: Fifty-eight elite tennis players were distributed into the PH group (n = 20) and the NPH group (n = 38). Serve velocity, dominant and non-dominant passive shoulder external and internal rotation (ER and IR) ROM, total arc of motion (TAM: the sum of IR and ER ROM), ER and IR isometric strength, bilateral deficits and ER/IR strength ratio were measured in both groups. Questionnaires were administered in order to classify characteristics of shoulder pain. RESULTS: The dominant shoulder showed significantly reduced IR ROM and TAM, and increased ER ROM compared to the non-dominant shoulder in both groups. Isometric ER strength and ER/IR strength ratio were significantly lower in the dominant shoulder in the PH group when compared with the NPH group. No significant differences between groups were found for serve speed. CONCLUSION: These data show specific adaptations in the IR, TAM and ER ROM in the dominant shoulder in both groups. Isometric ER muscle weakness and ER/IR strength ratio deficit appear to be associated with history of shoulder injuries in elite tennis players. It would be advisable for clinicians to use the present information to design injury prevention programs. LEVEL OF EVIDENCE: 2.

Comparisons of hip strength and countermovement jump height in elite tennis players with and without acute history of groin injuries.

BACKGROUND: Despite the high groin-injury (GI) prevalence in tennis, no studies have assessed the extent to which intrinsic groin injury risk factors, such as hip muscle strength, have recovered in elite tennis players with a history of previous GI. OBJECTIVE: To investigate whether elite tennis players with a history of GI show differences in hip strength and jump height between injured and uninjured limbs and compared with dominant limb in tennis players without history of acute groin-injuries (NGI). DESIGN: Cohort study. PARTICIPANTS: Sixty-one tennis players completed this study: 17 in the GI group and 44 in the NGI. Isometric adductor and abductor hip strength were assessed with a handheld dynamometer, and unilateral counter-movement jump tests were performed on a contact mat connected to an Ergo tester. Paired t-tests were conducted to identify differences between injured and non-injured limbs in the GI group, and independent measures t-tests were conducted to compare between GI and NGI groups. RESULTS: Isometric adductor strength and adductor/abductor strength ratios were lower in the injured limb (16.4% and 20.1%, respectively) compared with uninjured side within the GI group, and lower than the dominant side in the NGI group. No significant differences were found for unilateral jump heights between sides in the GI, nor isometric abductor strength, when comparing GI to NGI groups. CONCLUSIONS: Isometric adductor weakness and adductor/abductor strength ratio deficits suggest that adductor muscle strength is not fully recovered in these athletes, potentially increasing their risk of a repeat groin injury.

Short-term effect of crunch exercise frequency on abdominal muscle endurance.

Despite core exercise programs are broadly used to increase muscle function and to promote low back health, there is a lack of scientific evidence on some of the most important characteristics of trunk exercise programs, as for example training frequency. This study aimed to compare the short-term effect of training frequencies of 1, 2 and 3 days per week (d/wk) on abdominal muscle endurance in untrained adolescents. One hundred and eighteen high-school students (59 men and 59 women) with no previous experience in structured abdominal exercise programs were assigned randomly to groups that trained 1 d/wk (G1; N.=21), 2 d/wk (G2; N.=27), 3 d/wk (G3; N.=23), or to a control group (CG; N.=47) that did not train. The training groups performed crunch and cross-crunch exercises 1, 2 or 3 d/wk during six weeks. Before and after the training period, the bench trunk-curl test (BTC test) was carried out to assess abdominal muscle endurance. Men obtained higher BTC test scores than women before and after training. Training frequencies of 1, 2 and 3 d/wk provided a significant increase in BTC test scores; however, no significant differences between the three groups' scores were found after training. Therefore, a small dose of crunch exercise training (1 d/wk) may be sufficient stimulus to increase abdominal endurance in untrained male and female adolescents, at least during the first weeks of an abdominal exercise program, which seems a very relevant finding in terms of time-cost efficiency.

Subtalar joint kinematic correlations with footprint arch index in race walkers.

AIM: The aim of the paper was to analyze the relationship between footprint arch index and subtalar joint movement in race walkers. METHODS: Thirteen young, highly skilled race walkers volunteered to participate. We obtained dominant-foot footprints in a bipedal stance. The arch index was measured to classify arch height. We also conducted a photogrammetric video-3D study on a running track. The support phase was recorded while subjects race walked at their individual competition speed. We calculated 4 angle time series describing the ankle joint kinematics during the support phase. Five specific step instants were calculated for each angle and correlated with the arch index. Race walkers were grouped according to arch height to compare. We also correlated the arch index with the time in medial support, and time to change from lateral to medial support during the stance phase. RESULTS: In the calcaneal angle we found correlations with the footprint (r=0.81; P<0.01) and statistical differences when grouped (P<0.01). In this angle we also found a moderate-high correlation between footprint arch index and the time in medial support (r=0.77; P<0.01), and also in the time to change from lateral to medial support during the stance phase (r=-0.73; P<0.01). Data also show that the race walkers adopt a characteristic propulsion technique in the end of the support. No statistical differences were found in the rearfoot angle, which has been previously associated to specific injuries in running. CONCLUSION: In conclusion, race walkers with higher arches exhibit a more pronounced support with the lateral side of the foot and they do so for a longer time. Conversely, subjects with flatter feet support with the medial side of the foot. The footprint has been found to be a good predictor for the technique employed with respect to the medial and lateral strike of the foot reflected by the calcaneal angle. Coaches should keep this in mind from both performance and injury prevention viewpoints.

Abdominal muscle response during curl-ups on both stable and labile surfaces.

BACKGROUND AND PURPOSE: With the current interest in stability training for the injured low back, the use of labile (movable) surfaces, underneath the subject, to challenge the motor control system is becoming more popular. Little is known about the modulating effects of these surfaces on muscle activity. The purpose of this study was to establish the degree of modulating influence of the type of surface (whether stable or labile) on the mechanics of the abdominal wall. In this study, the amplitude of muscle activity together with the way that the muscles coactivated due to the type of surface under the subject were of interest. SUBJECTS: Eight men (mean age=23.3 years [SD=4.3], mean height=177.6 cm [SD=3.4], mean weight=72.6 kg [SD=8.7]) volunteered to participate in the study. All subjects were in good health and reported no incidence of acute or chronic low back injury or prolonged back pain prior to this experiment. METHODS: All subjects were requested to perform 4 different curl-up exercises-1 on a stable surface and the other 3 on varying labile surfaces. Electromyographic signals were recorded from 4 different abdominal sites on the right and left sides of the body and normalized to maximal voluntary contraction (MVC) amplitudes. RESULTS: Performing curl-up exercises on labile surfaces increased abdominal muscle activity (eg, for curl-up on a stable surface, rectus abdominis muscle activity was 21% of MVC and external oblique muscle activity was 5% of MVC; for curl-up with the upper torso on a labile ball, rectus abdominis muscle activity was 35% of MVC and external oblique muscle activity was 10% of MVC). Furthermore, it appears that increases in external oblique muscle activity were larger than those of other abdominal muscles. CONCLUSION AND DISCUSSION: Performing curl-ups on labile surfaces changes both the level of muscle activity and the way that the muscles coactivate to stabilize the spine and the whole body. This finding suggests a much higher demand on the motor control system, which may be desirable for specific stages in a rehabilitation program.