Eric Greska

A functional agility short-term fatigue protocol changes lower extremity mechanics

Abstract The purpose of this study was to evaluate the effects of a functional agility fatigue protocol on lower extremity biomechanics between two unanticipated tasks (stop-jump and sidestep). The subjects consisted of fifteen female collegiate soccer athletes (19±0.7 years, 1.67±0.1 m, 61.7±8 kg) free of lower extremity injury. Participants performed five trials of stop-jump and sidestep tasks. A functional short-term agility protocol was performed, and immediately following participants repeated the unanticipated running tasks. Lower extremity kinematic and kinetic values were obtained pre and post fatigue. Repeated measures analyses of variance were conducted for each dependent variable with an alpha level set at 0.05. Knee position post-fatigue had increased knee internal rotation (11.4±7.5° vs. 7.9±6.5° p=0.011) than pre-fatigue, and a decreased knee flexion angle (–36.6±6.2° vs. −40.0±6.3°, p=0.003), as well as hip position post-fatigue had decreased hip flexion angle (35.5±8.7° vs. 43.2±9.5°, p=0.002). A quick functional fatigue protocol altered lower extremity mechanics of Division I collegiate soccer athletes during landing tasks. Proper mechanics should be emphasized from the beginning of practice/game to aid in potentially minimizing the effects of fatigue in lower extremity mechanics.

A Feedback Inclusive Neuromuscular Training Program Alters Frontal Plane Kinematics

Abstract Greska, EK, Cortes, N, Van Lunen, BL, and Oñate, JA. A feedback inclusive neuromuscular training program alters frontal plane kinematics. J Strength Cond Res 26(6): 1609–1619, 2012—Anterior cruciate ligament (ACL) neuromuscular training programs have demonstrated beneficial effects in reducing ACL injuries, yet further evaluation of their effects on biomechanical measures across a sports team season is required to elucidate the specific factors that are modifiable. The purpose of this study was to evaluate the effects of a 10-week off-season neuromuscular training program on lower extremity kinematics. Twelve Division I female soccer players (age: 19.2 ± 0.8 years, height: 1.67 ± 0.1 m, weight: 60.2 ± 6.5 kg) performed unanticipated dynamic trials of a running stop-jump task pretraining and posttraining. Data collection was performed using an 8-camera Vicon system (Los Angeles, CA, USA) and 2 Bertec (Columbus, OH, USA) force plates. The 10-week training program consisted of resistance training 2 times per week and field training, consisting of plyometric, agility, and speed drills, 2 times per week. Repeated measures analyses of variance (ANOVAs) were used to assess the differences between pretraining and posttraining kinetics and kinematics of the hip, knee, and ankle at initial contact (IC), peak knee flexion (PKF), and peak stance. Repeated measures ANOVAs were also used to assess isometric strength differences pretraining and posttraining. The alpha level was set at 0.05 a priori. The training program demonstrated significant increases in left hip extension, left and right hip flexion, and right hip adduction isometric strength. At IC, knee abduction angle moved from an abducted to an adducted position (−1.48 ± 3.65° to 1.46 ± 3.86°, p = 0.007), and hip abduction angle increased (−6.05 ± 4.63° to −10.34 ± 6.83°, p = 0.007). Hip abduction angle at PKF increased (−2.23 ± 3.40° to 6.01 ± 3.82°, p = 0.002). The maximum knee extension moment achieved at peak stance increased from pretraining to posttraining (2.02 ± 0.32 to 2.38 ± 0.75 N·m·kg−1, p = 0.027). The neuromuscular training program demonstrated a potential positive effect in altering mechanics that influence the risk of incurring an ACL injury.

Effects of a combined resistance-plyometric training program on muscular strength, running economy, and Vo2peak in division I female soccer players.

Abstract Grieco, CR, Cortes, N, Greska, EK, Lucci, S, and Onate, JA. Effects of a combined resistance-plyometric training program on muscular strength, running economy, and V[Combining Dot Above]O2peak in division I female soccer players. J Strength Cond Res 26(9): 2570–2576, 2012—Resistance and plyometric training programs have demonstrated consistent improvements in running economy (RE) in trained and untrained adults in the absence of improvements in maximal oxygen consumption. The purpose of this study was to investigate the effect of a 10-week combined resistance-plyometric training program on the RE and V[Combining Dot Above]O2max in female soccer players. Fifteen Division 1A female soccer players (age 19.0 ± 0.7 years; height 1.67 ± 0.1 m; weight 61.7 ± 8.1 kg) performed a treadmill test for V[Combining Dot Above]O2max and RE at the end of a competitive season (PRE) and after a 10-week training program (POST). Isometric strength was measured in knee flexion and extension. Resistance training was conducted 2 d·wk−1 on nonconsecutive days; plyometric training was conducted separately on different nonconsecutive days. Eleven subjects were included in the PRE-POST analysis (age 19.0 ± 0.8 years; height 1.67 ± 0.5 m; weight 59.9 ± 6.7 kg). Descriptive statistics were compared using analysis of variance with repeated measures with a Bonferroni adjustment, and significance was set at p < 0.05. A significant increase occurred after training in the V[Combining Dot Above]O2peak (10.5%; p = 0.008), time to fatigue (6.9%; p = 0.017), and interpolated maximal speed (3.6%; p = 0.016), despite there being a decrease in the maximal respiratory exchange ratio (2.9%; p = 0.001). There was no significant change in the RE at 9 km·h−1; however, there was a significant decrease in the percentage of the V[Combining Dot Above]O2peak at 9 km·h−1 (−5.6%; p = 0.02). Maximal isometric strength of knee flexors and extensors did not change. The results suggest a plyometric-agility training program may increase the V[Combining Dot Above]O2peak in female soccer players; however, the effect on RE was equivocal.

Anterior cruciate ligament (ACL) loading in a collegiate athlete during sidestep cutting after ACL reconstruction: A case study

BACKGROUND Athletes with anterior cruciate ligament (ACL) injuries usually undergo ACL-reconstruction (ACLR) in order to restore joint stability, so that dynamic maneuvers such as the sidestep cut can be performed. Despite restoration of joint stability after ACLR, many athletes do not return to pre-injury levels and may be at a high risk of a second ACL injury. The purpose of this study was to determine whether or not ACL loading, would increase after ACLR. METHODS One female Division I collegiate athlete performed bilateral unanticipated sidestep cuts both before ACL injury and 27months after ACLR. Musculoskeletal simulations were used to calculate ACL loading during the deceleration phase of the sidestep cuts. RESULTS Twenty-seven months after ACLR, the athlete demonstrated higher total ACL loading in the ipsilateral limb as well as altered joint kinematics, moments, and quadriceps muscle force production. In the contralateral limb, there were no increases in total ACL loading or muscle force production yet altered lower extremity joint kinematics and moments were present after ACLR. CONCLUSIONS Higher total ACL loading in the ipsilateral limb of this athlete may suggest an increased risk of second ACL injury. The results of this study provide an initial step in understanding the effects of ACLR on the risk of second ACL injury in an elite athlete and suggest that it is important to develop a better understanding of this surgical intervention on knee joint loading, in order to reduce the risk of second ACL injury while performing dynamic maneuvers.

Biomechanical differences related to leg dominance were not found during a cutting task.

Previous studies have shown conflicting information regarding leg dominance as an etiological factor for the risk of anterior cruciate ligament (ACL) injuries. It remains unclear if lower extremity neuromechanical limb asymmetries exist in experienced athletes. The purpose of this study was to evaluate lower extremity neuromechanical effects of leg dominance in female collegiate soccer athletes during an unanticipated side‐step cutting task. Twenty female collegiate soccer players completed an unanticipated side‐step cutting task, using their dominant and non‐dominant legs. Kinematic and kinetic data were collected to quantify joint angles and forces, with wireless electromyography (EMG) quantifying muscle activity. MANOVAs were conducted to determine the effect of leg dominance on hip and knee mechanics at and between pre‐contact, initial contact, peak knee adduction moment, and peak stance periods. Dependent variables consisted of peak time occurrences, hip and knee rotations and moments, ground reaction force, EMG amplitudes, stance time, and approach velocity. No significant differences were found for any variables at or between the periods of interest. Collegiate female soccer athletes exhibit similar movement patterns between dominant and non‐dominant legs while performing a side‐step cutting task, suggesting that leg dominance does not adversely influence known biomechanical non‐contact ACL risk factors.

Altered lower extremity joint mechanics occur during the star excursion balance test and single leg hop after ACL-reconstruction in a collegiate athlete

Abstract The effects of ACL-reconstruction on lower extremity joint mechanics during performance of the Star Excursion Balance Test (SEBT) and Single Leg Hop (SLH) are limited. The purpose of this study was to determine if altered lower extremity mechanics occur during the SEBT and SLH after ACL-reconstruction. One female Division I collegiate athlete performed the SEBT and SLH tasks, bilaterally, both before ACL injury and 27 months after ACL-reconstruction. Maximal reach, hop distances, lower extremity joint kinematics and moments were compared between both time points. Musculoskeletal simulations were used to assess muscle force production during the SEBT and SLH at both time points. Compared to the pre-injury time point, SEBT reach distances were similar in both limbs after ACL-reconstruction except for the max anterior reach distance in the ipsilateral limb. The athlete demonstrated similar hop distances, bilaterally, after ACL-reconstruction compared to the pre-injury time point. Despite normal functional performance during the SEBT and SLH, the athlete exhibited altered lower extremity joint mechanics during both of these tasks. These results suggest that measuring the maximal reach and hop distances for these tasks, in combination with an analysis of the lower extremity joint mechanics that occur after ACL-reconstruction, may help clinicians and researchers to better understand the effects of ACL-reconstruction on the neuromuscular system during the SEBT and SLH.

THE EFFECTS OF A 5-WEEK GOLF SPECIFIC STRENGTH AND CONDITIONING INTERVENTION ON SWING PERFORMANCE FACTORS

Background The effects of golf specific strength and conditioning interventions on performance are scarcely researched. However, a multitude of research exists relative to golf related injuries. From those studies, it has been postulated that an increase in the X-Factor Stretch (XFS) variable increases the probability of a lower back injury. As the XF has been identified as a performance variable, it is of interest to determine how it is influenced by a golf specific intervention. Objective To examine the effects of a 5-week strength and conditioning intervention on golf swing performance factors. Design Quasi-experimental. Setting Laboratory and gym. Participants Nine female NCAA Division II collegiate golfers (age 20.7±2.7 yrs; height 175 ±9.81 cm; body mass 76.5 ±9.2 kg), maintaining a handicap of ≤3. Intervention The 5-week strength and conditioning intervention was implemented to improve the subjects golf swing.The majority of the exercises were lower body orientated, and included rotational aspects. Main Outcome Measurements The pre- and post-testing procedures included a biomechanical analysis using 3D motion analysis. The dependent variables were clubhead velocity (CV; m/s), hip velocity (HV; °/s), XFS angle (°), and ball speed (BS; m/s). It was hypothesized that CV, HV, and BS would increase without an increase in the XFS. T-tests were used to define statistical significance (p<0.05). Results From pre- to post-intervention, subjects significantly increased HV (8.2±0.5°/s to 8.8±0.7°/s; p<0.001), and CV (35.8±0.9 m/s to 36.8±2.5 m/s; p=0.018) and significantly decreased XFS (−54.9±10.2° to −47.9±4.2°; p<0.001). We did not detect a significant change in BS from pre- to post-intervention (52.7±2.8 m/s to 53.2±5.1 m/s). Conclusions It was demonstrated that the intervention increased CV, HV, and BS; but decreased the XFS. Thus, it can be suggested that a golf specific strength and conditioning program can increase golf swing performance factors, without increasing the risk of lower back injury.

Associations Between Functional Movement Screening, the Y Balance Test, and Injuries in Coast Guard Training

Tests that have the ability to predict injuries in various military and athletic populations are important because of the role they could play in primary prevention. Functional Movement Screen (FMS) and Y Balance Tests (YBT) may provide this prognostic ability. This study examined the association between injuries and age, physical characteristics, FMS, and upper and lower body YBTs among Coast Guard Maritime Security Response Team (MSRT) candidates. Thirty-one male Coast Guard Maritime Security Response Team candidates were administered the 7 FMS tests and lower- and upper-body YBTs before their intense 2-month training course. Age, height, weight, and body mass index were also obtained. Physical training-related injuries were recorded during the course. Injury incidence was 41%. Older age and lower scores on either FMS or the upper-body YBT were associated with higher injury risk. Performance of the lower-body YBT was not associated with injury risk. This is the first investigation showing that lower scores on the upper-body YBT were associated with higher injury risk and is in consonance with previous investigations demonstrating associations between lower FMS scores and higher injury risk. Certain limitations need to be addressed. Future studies should determine if FMS and the YBTs have prognostic ability in other populations.

Peak Torque as an Indicator of Rapid Torque Production during Screening Examinations

Although the ability to produce force rapidly is an indispensable characteristic of optimal health and performance, screening for this very critical parameter of strength is difficult because of clinician time constraints. The purpose this study was to investigate relationships between peak torque (PT) and rate of torque development (RTD) at 0-30, 0-50, 0-100, and 0-200 ms in female collegiate soccer athletes. Seventeen female collegiate soccer athletes were recruited. Isometric PT and RTD were collected at the hip abductors (AB), hip adductors (AD), knee extensors (KE) and knee flexors (KF). The coefficients of determination were calculated to evaluate the association between PT and RTD. Normalized AB, AD and KF PT were significantly correlated to RTD at 0-30, 0-50, 0-100 and 0-200 ms, while KE PT was only significantly correlated to RTD at 0-100 and 0-200 ms. The results of this study indicate that PT is a viable, indirect indicator of early late phase RTD at separate time intervals at the AB, AD and KF. However, it is likely that other physiological factors coupled with PT are required to provide information on the rapid force production capabilities of the KFs and KEs based on the percent of common variance observed.

Teaching Elementary-age Youth Catching Skills Using Theoretically Based Motor-development Strategies

Participating in general physical activity during childhood may not be the strongest predictor of lifetime physical activity. Children must develop motivation to participate in physically active endeavors and become excited about being active. These feelings toward physical activity may be best obtained by teaching with a more deliberate emphasis on the developmental stages of skill acquisition. This article describes a method for teaching catching skills that is grounded in the cognition and motor-development tenets of refinement and proximodistal development. The preparatory body movement skills — the focus stage — should be a primary objective for physical education teachers and their early elementary-age students during catching instruction. The focus stage includes information gathering, foot movements, body adjustment, and arm motions. Focusing on the actual catch — the control stage — skips vital aspects of a mature catching skill that likely would lead to greater understanding and skill in the future. The control stage involves grasping an object using the hands and fingers. This article describes specific planning characteristics, teaching behaviors, and catching lesson content physical educators can use to revolutionize their elementary physical education programs.