Jumping Asymmetries and Risk of Injuries in Preprofessional Ballet

BACKGROUND

Preprofessional ballet dancers are exposed to the risk of injuries, primarily in the lower extremities, with most injuries occurring during jumping and landing activities. Interlimb asymmetry during jumping and landing activities has been associated with the injury risk in adolescent athletes, but this has not been examined in dancers.

PURPOSE

To investigate associations between interlimb asymmetry during a double-leg countermovement jump (DL-CMJ) and single-leg jump (SLJ) and the injury risk in adolescent preprofessional ballet dancers.

STUDY DESIGN

Cohort study; Level of evidence, 2.

METHODS

Adolescent preprofessional ballet dancers (N = 255) performed 3 DL-CMJs and 3 SLJs on force plates during annual screening. Absolute and directional (separate values for left and right limb dominance) asymmetries in a set of kinetic variables during a DL-CMJ and in jump height during an SLJ were calculated. Each variable was characterized as having "high" or "normal" asymmetry according to the percentage of asymmetry (greater than or less than or equal to, respectively, the mean ± 0.5 SD) based on the present sample. Risk ratios (RRs) and 95% CIs were calculated based on the injury incidence in the subsequent academic year.

RESULTS

Of the 242 dancers that satisfied the inclusion criteria, 128 injuries were observed in the subsequent academic year. In the whole sample, 3 absolute, 7 left limb-dominant, and 1 right limb-dominant kinetic asymmetry in the eccentric, concentric, and landing phases of the DL-CMJ as well as left limb-dominant jump height asymmetry in the SLJ were associated with a significant (P < .001) increase in the injury risk (RR, 1.28-1.69 [95% CI, 1.02-2.37]). Separating by sex, asymmetries in the eccentric and landing phase of the DL-CMJ were not significant in boys, while in girls, RRs for asymmetries in the eccentric and landing phase of the DL-CMJ increased, and SLJ jump height asymmetry was not significant.

CONCLUSION

Higher asymmetries in certain kinetic variables during the DL-CMJ and in jump height during the SLJ were associated with an elevated risk of injuries in elite preprofessional ballet dancers with some sex-specific differences. Associations were mainly identified for high left limb-dominant asymmetry in the takeoff phase, suggesting that the injury risk may be specific to a relative right limb deficit.

Novel Use of an Accelerometer to Assess Load Asymmetry Over Time After Hip Resurfacing Arthroplasty

INTRODUCTION

There is limited knowledge regarding usage of wearable technology to guide return to sport after hip resurfacing arthroplasty (HRA). This study evaluated the use of accelerometers to identify when symmetry is restored between operative and non-operative limbs.

METHODS

A total of 26 primary HRA patients performed five validated physical tests before, 3 and 6 months after HRA: broad jump, double leg vertical jump (DLVJ), hop test, lateral single leg jump (LSLJ), and vertical single leg jump (VSLJ). Impact load and average intensity data (g-force units) were collected using accelerometers. Strength data (pounds (lbs.)) for internal and external rotation was collected with a dynamometer. Univariate and correlation analyses analyzed interlimb asymmetries.

RESULTS

At pre-operation, there were significant impact load asymmetries for DLVJ (P=.008), hop test (P=.021), and LSLJ (P=.003), and intensity asymmetry for DLVJ (P=.010) and LSLJ (P=.003). At 3 months, there was impact load asymmetry for DLVJ (P=.005) and LSLJ (P=.005), and intensity asymmetry for broad jump (P=.020), hop test (P=.042), and LSLJ (P=.005). There were significant strength asymmetries at pre- and 3 months post-operation for internal (P=.013) and external rotation (P=.037). All significant asymmetries indicated the non-operative leg had greater output. No significant asymmetries were found for any exercises at 6 months post-operation. An increase in Harris Hip Score was significantly associated with a decrease in impact asymmetry (r_s = -0.269, P=.006).

DISCUSSION AND CONCLUSION

Impact loads and strength reach interlimb symmetry at 6 months post-HRA. Wearable accelerometers provide useful metrics to distinguish limb asymmetries for recovery monitoring.

Single leg drop jump performance identifies functional deficit in collegiate athletes who have returned to sports after ACL reconstruction: A case-control study

Despite its apparent functional importance, there is a general lack of data in explosive strength in individuals recovering from an anterior cruciate ligament reconstruction (ACLR). Hence, we wonder if single leg drop jump (SLDJ) can be an effective testing since drop jump is a commonly used testing which rely on adequate development of explosive strength and stretch shortening cycle function. The purpose of this study was to determine if SLDJ test can identify functional deficit in collegiate athletes who have returned to sports (RTS) after ACLR when comparing it with the common return to sport testing. Nine collegiate athletes who had undergone a unilateral ACLR and returned to their primary sport with at least 10 months post-surgery were recruited and assigned into the injured group and compared with 9 matched non-injured athletes as the control group. Both groups underwent an identical battery testing in 1 session with the sequence of first modified star excursion balance test (SEBT), second single hop and bound test, third SLDJ and lastly 1 repetition maximum (1RM) single leg press. A 2-way mixed model analysis of variance showed that there is no significant interaction effect on common RTS testing which include modified SEBT, single hop and bound tests, and 1RM single leg press, but significant interaction effect on SLDJ jump height (P = .03), reactive strength index (P = .03) and mean propulsion force (P = .03). For the injured group, ACLR leg jump height (10.35 ± 2.71 cm) was significantly lower than non-ACLR leg (12.86 ± 3.51 cm) with a mean difference of 2.51 (95% confidence interval [CI]: 0.55-4.47). ACLR leg reactive strength index (0.29 ± 0.10 m/s) was significantly < non-ACLR leg (0.39 ± 0.16 m/s) with a mean difference of 0.1 (95% CI: 0.03-0.17) and ACLR leg mean propulsion force (1087.49 ± 287.26 N) was significantly < non-ACLR leg (1157.40 ± 299.80 N) with a mean difference of 69.91 (95% CI: 16.04 to 123.78). SLDJ was able to identify jump height, reactive strength and propulsion force deficit in the involved limb of collegiate athletes who have returned to sports after ACLR.

Effects of blood-flow restricted resistance training on mechanical muscle function and thigh lean mass in sIBM patients

Sporadic inclusion body myositis (sIBM) is an idiopathic inflammatory muscle disease associated with skeletal muscle inflammation and a parallel progressive decline in muscle strength and physical function. Eventually, most sIBM patients require use of wheelchair after about 10 years of diagnosis and assistance to perform activities of daily living. This study presents data from a randomized controlled intervention trial (NCT02317094) that examined the effect of 12 weeks low-load blood-flow restricted (BFR) resistance training on maximal muscle strength, power, rate of force development (RFD), thigh lean mass (TLM), and voluntary muscle activation (VA) in sIBM patients. A time-by-group interaction in knee extensor strength was observed in the stronger leg (p ≤ 0.033) but not the weaker leg. Within-group changes were observed with BFR training (BFR) manifested by increased knee extensor strength in the strongest leg (+13.7%, p = 0.049), whereas non-exercising patients (CON) showed reduced knee extensor strength (-7.7%, p = 0.018). Maximal leg extensor power obtained for the stronger leg remained unchanged following BFR training (+9.5%, p = 0.37) while decreasing in CON (-11.1%, p = 0.05). No changes in TLM were observed. VA declined post-training (p = 0.037) in both BFR (-6.3% points) and CON (-7.5% points). The present data indicate that BFR resistance training can attenuate the rate of decline in mechanical muscle function typically experienced by sIBM patients. The preservation of muscle mass and mechanical muscle function with BFR resistance training may be considered of high clinical importance in sIBM patients to countermeasure the disease-related decline in physical function.

Rate of Force Development Remains Reduced in the Knee Flexors 3 to 9 Months After Anterior Cruciate Ligament Reconstruction Using Medial Hamstring Autografts: A Cross-Sectional Study

BACKGROUND

Anterior cruciate ligament (ACL) rupture is a serious injury with a high prevalence worldwide, and subsequent ACL reconstructions (ACLR) appear to be most commonly performed using hamstring-derived (semitendinosus tendon) autografts. Recovery of maximal muscle strength to ≥90% of the healthy contralateral limb is considered an important criterion for safe return to sports. However, the speed of developing muscular force (ie, the rate of force development [RFD]) is also important for the performance of many types of activities in sports and daily living, yet RFD of the knee extensor and flexor muscles has apparently never been examined in patients who undergo ACLR with hamstring autograft (HA).

PURPOSE

To examine potential deficits in RFD, maximal muscle strength (ie, maximal voluntary isometric contraction [MVIC]), and functional capacity of ACLR-HA limbs in comparison with the healthy contralateral leg and matched healthy controls 3 to 9 months after surgery.

STUDY DESIGN

Cross-sectional study; Level of evidence: 3.

METHODS

A total of 23 young patients who had undergone ACLR-HA 3 to 9 months earlier were matched by age to 14 healthy controls; both groups underwent neuromuscular screening. Knee extensor and flexor MVIC and RFD, as well as functional capacity (single-leg hop for distance [SLHD] test, timed single-leg sit-to-stand [STS] test), were assessed on both limbs. Furthermore, patient-reported knee function (Knee injury and Osteoarthritis Outcome Score) was assessed.

RESULTS

Knee extensor and flexor MVIC and RFD were markedly compromised in ACLR-HA limbs compared with healthy contralateral limbs (MVIC for extensor and flexor, 13% and 26%, respectively; RFD, 14%-17% and 32%-39%) and controls (MVIC, 16% and 31%; RFD, 14%-19% and 30%-41%) (P < .05-.001). Further, ACLR-HA limbs showed reduced functional capacity (reduced SLHD and STS performance) compared with contralateral limbs (SLHD, 11%; STS, 14%) and controls (SLHD, 20%; STS, 31%) (P < .01-.001). Strength (MVIC) and functional (SLHD) parameters were positively related to the duration of time after surgery (P < .05), although this relationship was not observed for RFD and STS.

CONCLUSION

Knee extensor and flexor RFD and maximal strength, as well as functional single-leg performance, remained substantially reduced in ACLR-HA limbs compared with noninjured contralateral limbs and healthy controls 3 to 9 months after reconstructive surgery.

A case of hypomelanosis of Ito accompanied by unilateral abnormal limb overgrowth and delayed speech

Hypomelanosis of Ito (HI) is characterized by unilateral or bilateral hypopigmented skin lesions and usually presents as a multisystemic disorder. Skin lesions may develop in different textures, such as linear, whorled, or patchy, and are often accompanied by abnormalities of the central nervous system, skeletal system, eyes, and teeth. HI is associated with sporadic gene mutations but not gender. Presentation of the current case may be of use in reminding practitioners of the common extracutaneous findings of HI, along with some rare manifestations, such as delayed speech and asymmetric limb growth.

Contribution of Neuromuscular Factors to Quadriceps Asymmetry After Anterior Cruciate Ligament Reconstruction

CONTEXT

  To quantify quadriceps weakness after anterior cruciate ligament reconstruction (ACLR), researchers have often analyzed only peak torque. However, analyzing other characteristics of the waveform, such as the rate of torque development (RTD), time to peak torque (TTP), and central activation ratio (CAR), can lend insight into the underlying neuromuscular factors that regulate torque development.

OBJECTIVE

  To determine if interlimb neuromuscular asymmetry was present in patients with ACLR at the time of clearance to return to activity.

DESIGN

  Cross-sectional study.

SETTING

  Laboratory.

PATIENTS OR OTHER PARTICIPANTS

  A total of 10 individuals serving as controls (6 men, 4 women; age = 23.50 ± 3.44 years, height = 1.73 ± 0.09 m, mass = 71.79 ± 9.91 kg) and 67 patients with ACLR (43 men, 24 women; age = 21.34 ± 5.73 years, height = 1.74 ± 0.11 m, mass = 77.85 ± 16.03 kg, time postsurgery = 7.52 ± 1.36 months) participated.

MAIN OUTCOME MEASURE(S)

  Isokinetic (60°/s) and isometric quadriceps strength were measured. Peak torque, TTP, and RTD were calculated across isometric and isokinetic trials, and CAR was calculated from the isometric trials via the superimposed burst. Repeated-measures analyses of variance were used to compare limbs in the ACLR and control groups.

RESULTS

  No between-limbs differences were detected in the control group ( P > .05). In the ACLR group, the involved limb demonstrated a longer TTP for isokinetic strength ( P = .04; Cohen d effect size [ES] = 0.18; 95% confidence interval [CI] = -0.16, 0.52), lower RTD for isometric ( P < .001; Cohen d ES = 0.73; 95% CI = 0.38, 1.08) and isokinetic ( P < .001; Cohen d ES = 0.84; 95% CI = 0.49, 1.19) strength, lower CAR ( P < .001; Cohen d ES = 0.37; 95% CI = 0.03, 0.71), and lower peak torque for isometric ( P < .001; Cohen d ES = 1.28; 95% CI = 0.91, 1.65) and isokinetic ( P < .001; Cohen d ES = 1.15; 95% CI = 0.78, 1.52) strength.

CONCLUSIONS

  Interlimb asymmetries at return to activity after ACLR appeared to be regulated by several underlying neuromuscular factors. We theorize that interlimb asymmetries in isometric and isokinetic quadriceps strength were associated with changes in muscle architecture. Reduced CAR, TTP, and RTD were also present, indicating a loss of motor-unit recruitment or decrease in firing rate.

Performance on the Functional Movement Screen Is Related to Hop Performance But Not to Hip and Knee Strength in Collegiate Football Players

OBJECTIVE

To define the relationship between Functional Movement Screen (FMS) scores and hop performance, hip strength, and knee strength in collegiate football players.

DESIGN

Cross-sectional cohort.

PARTICIPANTS

Freshmen of a Division I collegiate American football team (n = 59).

MAIN OUTCOME MEASURES

The athletes performed the FMS, and also a variety of hop tests, isokinetic knee strength, and isometric hip strength tasks. We recorded total FMS score, peak strength, and hop performance, and we calculated asymmetries between legs on the different tasks. Spearman correlation coefficients quantified the relationships between these measures, and χ analyses compared the number of athletes with asymmetries on the different tasks.

RESULTS

We observed significant correlations (r = 0.38-0.56, P ≤ 0.02) between FMS scores and hop distance but not between FMS scores and hip or knee strength (all P ≥ 0.21). The amount of asymmetry on the FMS test was significantly correlated to the amount of asymmetry on the timed 6-m hop (r = 0.44, P < 0.01) but not to hip or knee strength asymmetries between limbs (all P ≥ 0.34).

CONCLUSIONS

Functional Movement Screen score was positively correlated to hop distance, and limb asymmetry in FMS tasks was correlated to limb asymmetry in 6-m hop time in football players. No significant correlations were observed between FMS score and hip and knee strength or between FMS asymmetry and asymmetries in hip and knee strength between limbs. These results indicate that a simple hop for distance test may be a time-efficient and cost-efficient alternative to FMS testing in athletes and that functional asymmetries between limbs do not coincide with strength asymmetries.

Force production during maximal effort bend sprinting: Theory vs reality

This study investigated whether the "constant limb force" hypothesis can be applied to bend sprinting on an athletics track and to understand how force production influences performance on the bend compared with the straight. Force and three-dimensional video analyses were conducted on seven competitive athletes during maximal effort sprinting on the bend (radius 37.72 m) and straight. Left step mean peak vertical and resultant force decreased significantly by 0.37 body weight (BW) and 0.21 BW, respectively, on the bend compared with the straight. Right step force production was not compromised in the same way, and some athletes demonstrated substantial increases in these variables on the bend. More inward impulse during left (39.9 ± 6.5 Ns) than right foot contact (24.7 ± 5.8 Ns) resulted in 1.6° more turning during the left step on the bend. There was a 2.3% decrease in velocity from straight to bend for both steps. The constant limb force hypothesis is not entirely valid for maximal effort sprinting on the bend. Also, the force requirements of bend sprinting are considerably different to straight-line sprinting and are asymmetrical in nature. Overall, bend-specific strength and technique training may improve performance during this portion of 200- and 400-m races.