Jomilto Praxedes

INFLUENCE of HIP EXTERNAL ROTATION on HIP ADDUCTOR and RECTUS FEMORIS MYOELECTRIC ACTIVITY DURING A DYNAMIC PARALLEL SQUAT

Pereira, GR, Leporace, G, Chagas, DV, Furtado, LFL, Praxedes, J, and Batista, LA. Influence of hip external rotation on hip adductor and rectus femoris myoelectric activity during a dynamic parallel squat. J Strength Cond Res 24(10): 2749-2754, 2010-This study sought to compare the myoelectric activity of the hip adductors (HAs) and rectus femoris (RF) when the hip was in a neutral position or externally rotated by 30° or 50° (H0, H30, and H50, respectively) during a parallel squat. Ten healthy subjects performed 10 repetitions of squats in each of the 3 hip positions and the myoelectric activities of the HAs and RF were recorded. The signal was then divided into categories representing concentric (C) and eccentric (E) contractions in the following ranges of motion: 0-30° (C1 and E1), 30-60° (C2 and E2), and 60-90° (C3 and E3) of knee flexion. From those signals, an root mean square (RMS) value for each range of motion in each hip position was obtained. All values were normalized to those obtained during maximum voluntary isometric contraction. We found that HAs showed a significant increase in myoelectric activity during C3 and E3 in the H30 and H50 positions, as compared with H0. Meanwhile, RF activity did not significantly differ between hip positions. Both muscles showed higher activation during 60-90° (C3 and E3) of knee flexion, as compared with 0-30° (C1 and E1) and 30-60° (C2 and E2). The results suggest that if the aim is to increase HA activity despite the low percentage of muscle activation, squats should be performed with 30° of external rotation and at least 90° of knee flexion.

Ativação muscular do quadril e do joelho em duas aterrissagens realizadas por atletas do sexo masculino

OBJECTIVE: To compare the myoelectric activity before and after ground contact between single leg (SL) and double leg (DL) landings in male athletes. PARTICIPANTS: Fifteen male volleyball athletes without signs and symptoms of lesions in the lower extremities, with a minimum of three years experience in the sport (13 ± 1 years, 1.70 ± 0.12 m, 60 ± 12 kg). MEASUREMENTS: Participants performed two vertical jumps, landing unilaterally and bilaterally. The myoelectric activity of the rectus femoris (RF), biceps femoris (BF), hip adductors (HA) and the BF/RF ratio were compared between the two landings and between the phases characterized by 100ms before (PRE) and after 100 ms (POST) ground contact using ANOVA two-way test with post hoc test of Bonferroni (α = 5%). RESULTS: In both landings activation of RF was higher in the POST in relation to the PRE (p <0.0001). Comparing the landings in the same phase statistical differences (p = 0.2212) were not found. Although the BF did not present significant differences between the PRE and POST in each landing (p = 0.2321), its activation was higher in SL (p = 0.0051). The HA showed greater activation in the POST during the SL (p = 0.0013), however there were no differences when comparing the two landings (p = 0.9233). The BF/RF ratio was higher in both landings during PRE (p = 0.0012). Nevertheless, no differences between the landings (p = 0.7037) were found. CONCLUSION: The results suggest that each muscle has a different role during landing tasks in men. While RF has the main function to decelerate the knee and the downward movement, characterized by increased activation in the POST, BF seems to attenuate the loads on the knee in activities of higher impact, staying more active throughout the cycle in the SL. The increased activation of HA after ground contact in the SL highlights the importance of core region in stabilizing the pelvis in situations of great instability. Further studies are needed to determine the effects of muscle activation at the imposition of mechanical load on the knee that are potentially harmful to male athletes.

Influence of a preventive training program on the lower limbs kinematics and vertical jump height of male volleyball athletes

Background The effectiveness of preventive training programs (PTP) aiming at changing the biomechanical behaviour related to anterior cruciate ligament injuries is subject to pre-existing risk. However, these assumptions are based on studies in females. Moreover, it is unclear what influence this training has on performance of young male athletes. Objective To examine the influence of a PTP on changes in kinematics during landings and in maximum vertical jump height (VJH) in males. Design 6 weeks prospective exercise intervention. Setting Young male volleyball athletes. Participants 15 male volleyball athletes (13±0.7 years, 1.70±0.12 m, 60±12 kg). Interventions PTP consisting of plyometric, balance and core stability exercises three times per week for 6 weeks. Bilateral vertical jumps with double leg (DL) and single leg (SL) landings were performed to measure the effects of training. Main outcome measurements Kinematics of knee and hip before and after training and VJH attained during both tasks after training. The hypothesis was that the PTP would produce improvements in VJH, but would not generate great changes in biomechanical behaviour. Results The only change revealed for the SL was the longest duration of landing (p=0.0273), while in the DL was the largest angular displacement of the knee (p=0.0371). The training did not significantly alter the VJH in the SL (diff: 2.7 cm, p=0.3054) or DL condition (diff: 3.5 cm, p=0.3635). Conclusion Despite the alterations in the kinematics behaviour, the changes observed are specific for each landing task, which highlights the importance of the principle of specificity. Despite the absence of significant increases in the VJH after training, the absolute differences pre to post training showed an increase consistent with other studies that compared the results with control groups. The present study showed that short time PTP in low-risk populations, although generating little influence on the kinematics, are capable of enhancing performance.