Effect of Ankle Joint Contact Angle and Ground Contact Time on Depth Jump Performance

Reactive strength index during single-limb vertical continuous jumps after anterior cruciate ligament reconstruction: cross-sectional study

BACKGROUND

The association of the reactive strength index (RSI) during single-limb vertical continuous jumps (SVCJs) with single-limb hop tests in athletes after anterior cruciate ligament reconstruction (ACLR) is unclear. Thus, this study aimed to confirm the measurement properties of the RSI during SVCJs in athletes with ACLR at the phase of determining the timing of their return to sport.

METHODS

RSI during SVCJs and single-limb hop (single, triple, and crossover) tests were measured for post-ACLR and healthy athletes. The limb symmetry index (LSI) was calculated using the measurements of each parameter. For each test, patients were divided into two subgroups according to their LSI score (≥ 90%, satisfactory; < 90%, unsatisfactory). Fisher's exact test was used to examine the association of single-limb hop tests with RSI during the SVCJs.

RESULTS

A total of 21 post-ACLR and 17 healthy athletes completed all the tests. RSI during SVCJs was significantly lower on the involved limb than on the uninvolved limb in post-ACLR athletes (P < 0.001). The LSI of RSI during SVCJs of post-ACLR athletes was significantly lower than that of the healthy athletes (P < 0.01). Among the post-ACLR athletes, < 30% of those with LSIs > 90% in the single-limb hop tests had an LSI > 90% of the RSI during SVCJs.

CONCLUSIONS

RSI during SVCJs of post-ACLR athletes was significantly lower on the involved limb than on the uninvolved limb, and the asymmetry was more remarkable in the SVCJs than in the single-limb hop tests.

Association and Agreement between Reactive Strength Index and Reactive Strength Index-Modified Scores

Since the reactive strength index (RSI) and reactive strength index-modified (RSI-mod) share similar nomenclature, they are commonly referred as interchangeable measures of agility in the sports research literature. The RSI and RSI-mod are most commonly derived from the performance of depth jumping (DJ) and countermovement jumping (CMJ), respectively. Given that DJ and CMJ are plyometric movements that differ materially from biomechanical and neuromotor perspectives, it is likely that the RSI and RSI-mod measure distinct aspects of neuromuscular function. The purpose of this investigation was to evaluate the association and agreement between RSI and RSI-mod scores. A mixed-sex sample of NCAA division I basketball athletes (n = 21) and active young adults (n = 26) performed three trials of DJ from drop heights of 0.51, 0.66, and 0.81 m and three trials of countermovement jumping. Using 2-dimensional videography and force platform dynamometry, RSI and RSI-mod scores were estimated from DJ and CMJ trials, respectively. Linear regression revealed moderate associations between RSI and RSI-mod scores (F = 11.0–38.1; R² = 0.20–0.47; p < 0.001–0.001). Bland–Altman plots revealed significant measurement bias (0.50–0.57) between RSI and RSI-mod scores. Bland–Altman limit of agreement intervals (1.27–1.51) were greater than the mean values for RSI (0.97–1.05) and RSI-mod (0.42) scores, suggesting poor agreement. Moreover, there were significant performance-dependent effects on measurement bias, wherein the difference between and the mean of RSI and RSI-mod scores were positively associated (F = 77.2–108.4; R² = 0.63–0.71; p < 0.001). The results are evidence that the RSI and RSI-mod cannot be regarded as interchangeable measures of reactive strength.

A novel prophylactic Chinese parachute ankle brace

Background

The objective is to compare the effects of a self-designed and self-manufactured novel prophylactic ankle brace [Chinese parachute ankle brace (CPAB)] and two ordinary ankle braces on the ankle joint during a half-squat parachute landing (HSPL) via biomechanical assessment.

Methods

Twenty elite paratroopers were in four different conditions: no brace, elastic brace, semi-rigid brace, and CPAB. Each participant was instructed to jump off a platform with three different heights, 40, 80, and 120 cm, and land on the force plate in a half-squat posture. The vertical ground reaction forces (vGRFs), joint angles, moments, powers, and works were calculated. After the experiment, every participant completed the questionnaires designed for this study.

Results

Increasing the dropping height increased all of the parameters significantly (P<0.01), except for time to peak vGRF (T-PvGRF). Applying three braces can all slightly increase vGRF (P=0.237) and reduce T-PvGRF by 6–10 ms, as well as decrease the joint angles, velocities, and moments on the sagittal and coronal planes. Wearing CPAB and a semi-rigid brace more efficiently restricted dorsiflexion and inversion (P<0.05), and they both significantly reduced ankle work (t=5.107, P<0.01; t=3.331, P<0.01) and peak power (t=7.237, P<0.01; t=6.711, P<0.01) at 120 cm. The total scores from low-to-high were semi-rigid brace (19.20±2.99), elastic brace (21.91±3.25), and CPAB (23.37±3.08).

Conclusions

The CPAB was more effective at restricting ankle joint motion on the coronal and sagittal planes than the other two prophylactic ankle braces. Therefore, the CPAB had the advantages of a novel appearance, high efficiency, and superior comfort, providing a reliable choice for parachute jumping and training in China.

Difference of neuromuscular responses by additional loads during plyometric jump

Plyometric training is a training method to increase the motor output, stretch-shortening cycle which could be associated with power output. To increase the neuromuscular output, various training variables have been incorporated in training programs. Weight vest is one of the variables to develop it. However, how much load can effectively develop the neural response is still not clearly understood. The aim of this study was to identify the effects of additional external loads on neuromuscular response of lower body during plyometric jump. Total 19 men performed jump tests with weight vest (two jumps in each additional load; 0%, 10%, 15% and 20% of bodyweight [BW]). During the tests, neuromuscular responses of lower extremity were measured. In vertical jump, 0%BW group was higher than the other heavier loads. In rate of force development (RFD), 10%BW was higher than 15%BW and 20%BW. In 0-30 msec of interval RFD, the heavier load groups were greater than 0%BW and in 0-50 msec, 15%BW and 20%BW were higher than 0%BW. In neuromuscular efficiency (NME), 15%BW and 20%BW were greater than 0%BW in ankle joint. This research indicated that plyometric jump with additional load causes greater RFD and NME of lower extremity compared with jump training without additional load. During weight vest plyometric jump, 10%-20% of BW load is advantageous to NME of lower body and 10% of BW load is effective to develop RFD of lower extremity.