Purpose: This study aimed to examine the differences in the co-activation of the rectus femoris (RF) and biceps femoris (BF) using the co-contraction index (CI) in aquatic and land environments during a drop-landing task in active and non-active females.

Methods: In this casual-comparison study, 10 active and 10 non-active females volunteered to participate. The CI was calculated from recorded surface electromyographic (SEMG) activity of the RF and BF. To calculate CI, the amount of overlap between the linear envelopes of the agonist and antagonist muscles was found and divided by the number of data points. MathLab software (version 10) was used to process row data. Also, 2-way analysis of variance (ANOVA) assessed differences between groups and environments.

Results: Results indicated that the CI was not affected by activity level in pre- and post-contact (P>0.05) while it was significantly higher (P<0.05) in land environment compared to the aquatic environment.

Conclusion: Our findings show the differences in co-contraction of knee muscles between different environments. Our measure of co-contraction was lower in water compared to land, with no difference between the active and non-active groups. This may indicate that regardless of activity level, an aquatic environment may be an appropriate choice as an early phase in rehabilitation process.

Purpose: Core stability training (CST) has increased among athletes. The study hypothesis is that neuromuscular training and exercises of central area of trunk, pelvis and hip can reduce injury risk, and specifically peak vertical ground reaction forces in drop landing task. Therefore, the objective of this study was to evaluate kinetics during single leg drop landing test following a CST intervention.
Methods: The present research was a quasi-experimental study with pretest/posttest and a control group. After giving their informed written consent, 30 athletes (15 in the experimental group, and 15 in the control group) volunteered to participate in the training program consisting of CST sessions, 3 times per week for 8 weeks. Training group was performed the CST during 8 weeks but control group did not perform these exercises. Kinetics variables in pretest and posttest during single-leg drop landing were measured by motion analysis and force plate device. To compare the obtained data, mixed ANOVA repeated measure at significance level of P<0.05 was used. All analyses were done by SPSS 22.
Results: The results revealed that the peak vertical ground reaction forces, loading rate, and average loading rate significantly reduced following 8 weeks CST intervention (P<0.05).
Conclusion: This study shows evidence that core stability training improves landing kinetics, and may reduce lower extremity injury risk in athletes.

Purpose: Genu varum deformity changes the line of gravity from center of knee towards the medial side. This deviation results in changes in the upper part of the lower extremity that can affect postural control as well as the position and activity of the proximal muscles of the knee joint, like the gluteus medius muscle. Therefore this study aims to investigate the effect of genu varum disorder on the activity of gluteus medius muscle and postural control during single-leg jump-landing exercise.
Methods: A total of 28 male students of Physical Education Major (Mean [SD] age, weight, and height: 21.53[1.65] y, 66.76[7.51] kg, and 173.38[4.54] cm, respectively) were enrolled and studied in two groups of genu varum (14 students) and normal ones (14 students). The activity level of gluteus medius muscle and the ground reaction force were measured using electromyography device and force plate, respectively in single-leg jump-landing exercise. In order to analyze the data, we used the Independent t test at significance level of P<0.05. Participants were asked to perform the single-leg jump-landing exercise with 50% of maximum vertical jump and land on the force plate using one leg. The RMS of gluteus medius muscle was measured using MATLAB software.
Results: There is a significant difference between the genu varum and normal group in terms of mean activity of gluteus medius muscle before and after the landing. There were significant difference between these groups with regard to time to stabilization in anterior-posterior direction, while significantly higher time to stabilization was found in the genu varum group compared to the normal groups in medial-lateral and overall direction. The time to stabilization of the subjects in the directions of medial-laterallateral and anterior-posterior and total Resultant Vector (RV) using the force plate in the jump-landing movement was evaluated. There was no significant difference in the time to stabilization between the two groups of the knee parenthesis and the normal knee in the anterior-posterior direction (P>0.05), but the time to stabilization in the medial-lateral and in resultant vector direction in the genu varum group was significantly more than those in normal knee group (P<0.05).
Conclusion: Participants with genu varum have weakness in postural stability in medial-lateral and total RV direction that might decrease the activity of gluteus medius muscle. This might increase the demand on the muscle for stabilizing hip and pelvis which decreases control of transverse and frontal part of hip and finally affects postural stability in medial-lateral direction (may be due to inappropriate activity of the hip). Thus, improvement of gluteus medius muscle might improve medial-lateral control of the posture in individuals with genu varum.

Purpose: This study aimed to investigate the effect of genu varum abnormality on the activity of the anterior leg calf muscle during single-leg jump-landing task. 
Methods: A total of 28 male students of Physical Education (Mean±SD age: 21.53±1.65 y, weight: 66.67±7.15 kg, height: 173.38±4.54 cm) were assigned into the genu varum (n=14) and normal knee (n=14) groups. Their level of activity of tibialis anterior muscle and ground reaction force were analyzed using an electromyography and force plate in single-leg jump-landing task. In order to analyze the data, the Independent t test was used at the significance level of P<0.05. In jump-landing task, the subjects were required to jump up to 50% of maximum vertical jump and land with one leg on the plate. Root-Mean Square (RMS) level of tibialis anterior muscle was calculated by MATLAB. 
Results: The study results showed no significant differences between genu varum and normal knee groups (P>0.05) in the mean scores of the tibialis anterior muscular activity before and after landing. 
Conclusion: In performing the jump-landing task, tibialis anterior muscular activity of the two groups was similar before and after floor contact. Therefore, activity of tibialis anterior muscle does not seem responsible for differences observed in the balance between people with genu varum and normal knee. In addition to biomechanical reasons, other muscles or muscle groups might responsible for weaker balance observed in people with genu varum.

Purpose: Ankle sprain is one of the most common sports injuries and many people suffer from chronic ankle instability after ankle sprains. Changes in the function of the lower limbs following chronic ankle instability make a person susceptible to re-injury of ankle sprains. This is a systematic review of studies that investigated the kinematic changes of the lower limbs in people with chronic ankle instability during unilateral jump landing tasks.
Methods: Articles in English were searched in Google Scholar, Science Direct, PubMed, Scopus, ProQuest, and Cochrane Library databases without a time limit until 2021 with keywords related to “chronic ankle instability,” “kinematics,” and “single-leg jump-landing.” The inclusion criteria included the subjects being male and female with ankle instability and the type of single-leg jump-landing task. The modified checklist of Downs and Black (1998) was used to evaluate the quality of the studies.
Results: Based on the inclusion and exclusion criteria and the study quality review, 15 articles out of 762 studies, which investigated the kinematics of the lower limbs in the performance of unilateral jump landing, were comprehensively examined.
Conclusion: According to the findings of this study, individuals with chronic ankle instability showed kinematic changes in the lower limbs during various unilateral jump landing tasks. These changes are possible factors for the recurrence of ankle sprain injury. The findings show the necessity of developing and creating a rehabilitation program that comprehensively considers the kinematic changes.