Sports Medicine Biodynamics Center and Human Performance Laboratory, Cincinnati Children's Hospital Medical Center, and with the Department of Pediatrics, College of Medicine, University of Cincinnati, Cincinnati, OH.
The purpose of this study was to identify alterations in preparatory muscle activation patterns across different drop heights in female athletes. Sixteen female high school volleyball players performed the drop vertical jump from three different drop heights. Surface electromyography of the quadriceps and hamstrings were collected during the movement trials. As the drop height increased, muscle activation of the quadriceps during preparatory phase also increased (p < .05). However, the hamstrings activation showed no similar increases relative to drop height. Female athletes appear to preferentially rely on increased quadriceps activation, without an increase in hamstrings activation, with increased plyometric intensity. The resultant decreased activation ratio of the hamstrings relative to quadriceps before landing may represent altered dynamic knee stability and may contribute to the increased risk of ACL injury in female athletes.
"It has been suggested that hamstrings activation reduces anterior tibial translation which is associated with anterior cruciate ligament injury (Ford, Myer, Schmitt, Uhl, & Hewett, 2011). Recent investigations have found that when the height of landing increases, quadriceps but not hamstrings EMG activity increases (Ford et al., 2011; Peng, Kernozek, & Song, 2011). These results are interpreted as a neuromuscular deficit in utilising the hamstrings, which is suggested to predispose an individual to anterior cruciate ligament injury. "
[Show abstract][Hide abstract] ABSTRACT: Hip extensor strategy, specifically relative contribution of gluteus maximus versus hamstrings, will influence quadriceps effort required during squat exercise, as hamstrings and quadriceps co-contract at the knee. This research examined the effects of hip extensor strategy on quadriceps relative muscular effort (RME) during barbell squat. Inverse dynamics-based torque-driven musculoskeletal models were developed to account for hamstrings co-contraction. Net joint moments were calculated using 3D motion analysis and force platform data. Hamstrings co-contraction was modelled under two assumptions: (1) equivalent gluteus maximus and hamstrings activation (Model 1) and (2) preferential gluteus maximus activation (Model 2). Quadriceps RME, the ratio of quadriceps moment to maximum knee extensor strength, was determined using inverse dynamics only, Model 1 and Model 2. Quadriceps RME was greater in both Models 1 and 2 than inverse dynamics only at barbell loads of 50-90% one repetition maximum. The highest quadriceps RMEs were 120 ± 36% and 87 ± 28% in Models 1 and 2, respectively, which suggests that barbell squats are only feasible using the Model 2 strategy prioritising gluteus maximus versus hamstrings activation. These results indicate that developing strength in both gluteus maximus and quadriceps is essential for lifting heavy loads in squat exercise.
"It may have implications for the mechanism of injuries as ACL prevents anterior translation of the tibia (Amis, 2012). This finding is in agreement with previous studies reporting that in female athletes quadriceps activity but not hamstrings activity increases with increasing height during the prelanding (Ford, Myer, 2011) and landing phases (Peng, Kernozek, 2011 "
[Show abstract][Hide abstract] ABSTRACT: ACL tear is a major concern among athletes, coaches and sports scientists. More than taking the athlete away from training and competition, ACL tear is a risk factor for early-onset of knee osteoarthritis, and, therefore addressing strategies to avoid such injury is pertinent not only for competitive athletes, but for all physically active subjects. Imbalances in the prelanding myoelectric activity of the hamstrings and quadriceps muscles have been linked to ACL injuries. We investigated the effect of landing from different heights on prelanding myoelectric activity of the hamstrings and quadriceps muscles in recreational athletes. Thirty recreational athletes (15 male and 15 female) performed three bilateral drop jumps from two different heights; 20 cm and 40 cm while myoelectric activity of the vastus medialis, rectus femoris, biceps femoris and medial hamstrings were collected. When increasing the height of drop landing tasks prelanding normalized myoelectric activity of the quadriceps was increased by 15-20% but no significant changes were found for the hamstrings. Female athletes exhibited higher activity of the medial hamstrings compared to their male counterparts. We concluded that increasing the height of drop landing tasks is associated with increased myoelectric activity of the quadriceps but not the hamstrings in recreational athletes. These differences in muscle activity may be related to increased risk for ACL injury when the height is increased. Female athletes demonstrated higher recruitment of the medial hamstrings.
Journal of Electromyography and Kinesiology 08/2014; 24(4). DOI:10.1016/j.jelekin.2014.04.009 · 1.65 Impact Factor
"The drop vertical jump (DVJ) is a dynamic movement that has frequently been used to identify biomechanical characteristics that contribute to ACL injury risk in athletic populations (Ford et al., 2011; Hewett et al., 2005; McNair and Prapavessis, 1999). DVJs mimic the rapid deceleration followed by maximal vertical jump observed in a rebounding task, which happens to be the task most commonly associated with ACL injury in basketball (Powell and Barber-Foss, 2000). "
[Show abstract][Hide abstract] ABSTRACT: Rapid impulse loads imparted on the lower extremity from ground contact when landing from a jump may contribute to ACL injury prevalence in female athletes. The drop jump and drop landing tasks enacted in the first and second landings of drop vertical jumps, respectively, have been shown to elicit separate neuromechanical responses. We examined the first and second landings of a drop vertical jump for differences in landing phase duration, time to peak force, and rate of force development.
239 adolescent female basketball players completed drop vertical jumps from an initial height of 31cm. In-ground force platforms and a three dimensional motion capture system recorded force and positional data for each trial.
Between the first and second landing, rate of force development experienced no change (P>0.62), landing phase duration decreased (P=0.01), and time to peak ground reaction force increased (P<0.01). Side-by-side asymmetry in rate of force development was not present in either landing (P>0.12).
The current results have important implications for the future assessment of ACL injury risk behaviors. Rate of force development remained unchanged between first and second landings from equivalent fall height, while time to peak reaction force increased during the second landing. Neither factor was dependent on the total time duration of landing phase, which decreased during the second landing. Shorter time to peak force may increase ligament strain and better represent the abrupt joint loading that is associated with ACL injury risk.
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