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.

Agreement between isokinetic eccentric hamstring strength, Nordic hamstring strength and Nordic break-point angle in a sample of trained and healthy individuals.

Different eccentric strength assessments are used to identifying the risk of hamstring injury in athletes. However, there is scarce information to determine the association between Nordic-based measurements and the gold standard measurement of eccentric hamstring strength in an isokinetic dynamometer. To investigate the relationship of different measures of eccentric hamstring strength (break-point angle and eccentric strength during Nordic exercise) with eccentric hamstring peak torque measured with an isokinetic dynamometer. Forty-six participants volunteered to participate in this study. Eccentric peak force in the Smart-Nordic System and break-point angle measured as trunk lowering at >20°/s and >150°/s2 during the Nordic exercise via high-frequency video-analysis were compared to eccentric hamstring peak torque in an isokinetic dynamometer set to produce knee extension at 30°/s. There was a moderate association between peak eccentric strength with the Smart-Nordic and isokinetic eccentric hamstring peak torque (r = -0.65, p < 0.001, 95%CI = [-0.76-(-0.50)]). The association between Nordic break-point angle measured at 20°/s (r = 0.49, p < 0.001, 95%CI = [0.30-0.64]) and at 150°/s2 (r = 0.52, p < 0.001, 95%CI = [0.33-0.66]) presented statistically significant but lower associations with isokinetic eccentric hamstring peak torque. All Nordic-based measurements presented acceptable associations with the gold standard isokinetic eccentric hamstring peak torque. However, peak eccentric force measured on the Smart-Nordic device had a better agreement with eccentric peak torque measured with an isokinetic dynamometer than the video-based measurements.Highlights Peak eccentric force measured on the isometric strain-gauges device had a better agreement with eccentric hamstring peak torque measured with an isokinetic dynamometer than the break-point angle.The Nordic-based measurements are an alternative cost-effective method to assess eccentric muscle strength and weakness when the access to isokinetic dynamometry is not feasible.Caution should be taken with certain variables such as participants body mass, hip position and movement speed when interpreting the results of Nordic-based measurements.

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.

Kinematic, strength, and stiffness adaptations after a short-term sled towing training in athletes.

One of the most frequently used methods for training the sprint-specific strength is the sled towing. To date, no studies have been conducted to explore the effects of this method after a training period in well-trained athletes. The purpose of this study was to determine the effects of 4 weeks of resisted sprint training with sled towing. Twenty-two trained athletes experienced in the use of weighted sled (WS) participated in the study. They conducted the same 3-week training to level their initial condition. After that they were distributed in two groups, unresisted (UR) and WS training. They carried out the same 4-week, 2 days/week sprint-specific training, only differing in that the experimental group performed sprints with a (WS) which caused a reduction of 7.5% of their maximum velocity. Pre- and posttest were conducted which included the measurement of sprint kinematics, muscular strength (including isoinertial, isokinetic, and jump measurements), and sprinting stiffness (leg and vertical). Results show different adaptations in the groups although no interaction effect was found. The WS group improved the velocity in the transition phase, while the UR group improved the velocity in the maximum velocity phase. No improvements in the height of the jump tests were found.

Muscle morphology and jump performance: gender and intermuscular variability.

AIM: The present study aimed 1) to investigate the gender differences in jump performance and muscle architecture between men and women; and 2) to determine whether the differences in jump performance could be attributed to gender differences in the muscle architecture of the leg extensor muscles. METHODS: Sixty-two subjects volunteered for the study (34 women and 28 men): 19 club-level volleyball players, 20 physical education students, and 23 sedentary individuals. They performed trials of countermovement jumps (CMJ) and the muscle architecture of the vastus lateralis (VL), gastrocnemius medialis (GM), and lateralis (GL) were analyzed at rest by ultrasonography. RESULTS: There were significant differences in jump performance between men and women (CMJ height: 0.388 + or - 0.056 m in men and 0.279 + or - 0.060 m in women, P<0.001). There were also significant gender differences in the VL muscle thickness, while the relative fascicle length was significantly different in the three muscles studied, with longer fascicles in the VL muscle in men and longer fascicles in the gastrocnemii in women. There were significant associations between the VL muscle size and jump performance (r=0.49-0.50, P<0.001), and non linear relationships between muscle size parameters and pennation angles (R(2)=0.67-0.77, P<0.001). CONCLUSIONS: These results confirm that there are gender differences in the muscle architecture of people with a wide physical activity background. The gender differences found in the VL muscle size partially explained the differences in jump performance.

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.

Kinematics of ankle taping after a training session.

This study aimed to test the effectiveness of ankle taping on the limitation of forced supination during a change of direction, as well as the losses of effectiveness after a 30-minute training session. Fifteen young men with no ankle injury volunteered for the study. The static and dynamic ranges of movement (ROM) were measured before and after a training session. The dynamic measurements were recorded using high-speed 3D photogrammetry. The differences between static and dynamic measures of ankle supination and plantar flexion were significant. The losses of effectiveness during supination and ankle plantar flexion restriction were 42.3 % and 47.6 %, respectively. Ankle taping was effective in restricting the maximal static ROMs before a training session, but the effectiveness decreased after 30 min of training. The present study shows the necessity of performing dynamic ROM analysis of sports techniques involved in the ankle sprain mechanism in order to determine the degree of tape restriction after a training session, because there were differences between static and dynamic ankle ROMs. The lack of effects on the restriction of the dynamic plantar flexion would bring into question the necessity of ankle taping in subjects without previous injuries.