Kyle T. Ebersole

Resistance training is accompanied by increases in hip strength and changes in lower extremity biomechanics during running

BACKGROUND Movement and muscle activity of the hip have been shown to affect movement of the lower extremity, and been related to injury. The purpose of this study was to determine if increased hip strength affects lower extremity mechanics during running. METHODS Within subject, repeated measures design. Fifteen healthy women volunteered. Hip abduction and external rotation strength were measured using a hand-held dynamometer. Three-dimensional biomechanical data of the lower extremity were collected during running using a high-speed motion capture system. Measurements were made before, at the mid-point, and after a 6-week strengthening program using closed-chain hip rotation exercises. Joint range of motion (rearfoot eversion, knee abduction, hip adduction, and internal rotation), eversion velocity, eversion angle at heel strike, and peak joint moments (rearfoot inversion, knee abduction, hip abduction, and external rotation) were analyzed using repeated measures analysis of variance (P <or= 0.05). The independent variable was time (pre-, week 3, and week 6). A separate analysis of variance was conducted with the dependent variables of peak hip abduction and external rotation strength. FINDINGS Hip abduction (P=0.009) and external rotation strength (P<0.0005) increased by 13% and 23%, respectively. Eversion range of motion decreased (P=0.05), hip adduction range of motion increased (P=0.05), and a trend of decreased hip internal rotation range of motion (P=0.08) were found. Rearfoot inversion moment (P=0.02) and knee abduction moment (P=0.05) decreased by 57% and 10%, respectively. INTERPRETATION The hip abductors and external rotators were strengthened, leading to an alteration of lower extremity joint loading which may reduce injury risk. These exercises could be used in the rehabilitation, or prevention, of lower extremity injuries.

Mean power frequency and amplitude of the mechanomyographic and electromyographic signals during incremental cycle ergometry

The purpose of this investigation was to determine the relationships for mechanomyographic (MMG) amplitude, MMG mean power frequency (MPF), electromyographic (EMG) amplitude, and EMG MPF versus power output during incremental cycle ergometry. Seventeen adults volunteered to perform an incremental test to exhaustion on a cycle ergometer. The test began at 50 W and the power output was increased by 30 W every 2 min until the subject could no longer maintain 70 rev min(-1). The MMG and EMG signals were recorded simultaneously from the vastus lateralis during the final 10 s of each power output and analyzed. MMG amplitude, MMG MPF, EMG amplitude, EMG MPF, and power output were normalized as a percentage of the maximal value from the cycle ergometer test. Polynomial regression analyses indicated that MMG amplitude increased (P<0.05) linearly across power output, but there was no change (P>0.05) in MMG MPF. EMG amplitude and MPF were fit best (P<0.05) with quadratic models. These results demonstrated dissociations among the time and frequency domains of MMG and EMG signals, which may provide information about motor control strategies during incremental cycle ergometry. The patterns for amplitude and frequency of the MMG signal may be useful for examining the relationship between motor-unit recruitment and firing rate during dynamic tasks.

Gender comparisons of the mechanomyographic responses to maximal concentric and eccentric isokinetic muscle actions.

PURPOSE The purpose of this study was to determine whether there is a gender difference in the velocity-related patterns of mechanomyographic (MMG) responses to maximal isokinetic concentric (CON) and eccentric (ECC) muscle actions. METHODS Adult males (N = 15) and females (N = 16) performed maximal CON and ECC muscle actions of the leg extensors on a calibrated Cybex 6000 dynamometer at velocities of 30, 90, and 150 degrees.s-1. MMG was detected by a piezoelectric crystal contact sensor placed over the vastus lateralis muscle. RESULTS The results indicated that there were decreases in CON peak torque (PT) across velocities, while ECC PT remained constant with increasing velocity for both genders. MMG amplitude increased significantly (P < 0.05) with velocity in both the males and females for CON and ECC muscle actions. There was a gender difference in the velocity-related patterns of MMG responses to maximal isokinetic CON muscle actions; however, there was no gender difference in the pattern of ECC MMG responses. CONCLUSIONS The gender difference in CON MMG responses may be attributed to the greater percent decline in CON PT across velocity for the females than the males. In addition, the males displayed greater CON and ECC MMG amplitudes at all muscle action velocities than the females, possibly because of gender differences in muscle mass and/or thickness of the adipose tissue layer.

UNILATERAL BALANCE PERFORMANCE IN FEMALE COLLEGIATE SOCCER ATHLETES

Thorpe, JL and Ebersole, KT. Unilateral balance performance in female collegiate soccer athletes. J Strength Cond Res 22(5): 1429-1433, 2008-The Star Excursion Balance Test (SEBT) is a unilateral balance task designed to evaluate dynamic postural control. This investigation explored the relationship between limb preference, strength, and performance on the SEBT in NCAA Division I, female collegiate soccer athletes (nonsoccer, n = 11; soccer, n = 12). Each participant completed maximal, concentric test efforts at a velocity of 90°·s−1 for supine ankle dorsiflexion (ADF) and plantarflexion (APF) and at 60°·s−1 for the seated leg extension (LE) and flexion (LF) and supine hip extension (HE) and flexion (HF). In addition, participants performed maximal SEBT reaches in the anterior, medial, and posterior directions. All testing was completed on both limbs. These results indicate that SEBT performance is similar for both limbs in both groups. The soccer group, however, reached significantly farther than the nonsoccer group, suggesting that the SEBT may be sensitive to training status and/or sport-related adaptations. The concentric strength results indicate that despite group differences in all strength tests, strength in general was not highly correlated to SEBT performance. Thus, neuromuscular factors above and beyond strength may have accounted for the group differences in SEBT performance. The SEBT may be a useful tool for determining the relative effectiveness of an intervention designed to improve postural control.

Mechanomyographic amplitude and mean power output during maximal, concentric, isokinetic muscle actions.

The purpose of this study was to determine the velocity‐related patterns for mechanomyographic (MMG) amplitude, electromyographic (EMG) amplitude, mean power output (MP), and peak torque (PT) of the superficial muscles of the quadriceps femoris (vastus lateralis [VL], rectus femoris [RF], and vastus medialis [VM]) during maximal, concentric, isokinetic leg extensions. Twelve adult women (mean ± SD: 22 ± 3 years of age) performed such leg extensions at velocities of 60°, 120°, 180°, 240°, and 300°/s on a Cybex 6000 dynamometer. PT decreased (P < 0.05) across velocity to 240°/s. MP and MMG amplitude for each muscle (VL, RF, and VM) increased (P < 0.05) with velocity to 240°/s and then plateaued. EMG amplitude increased (P < 0.05) to 240°/s for the VL, remained unchanged across velocity (P > 0.05) for the RF, and increased (P < 0.05) to 300°/s for the VM. The results indicated close similarities between the velocity‐related patterns for MMG amplitude and MP, but dissociations among EMG amplitude, MMG amplitude, and PT. These findings support the recent hypothesis that MMG amplitude is more closely related to MP than PT during maximal, concentric, isokinetic muscle actions and, therefore, may be useful for monitoring training‐induced changes in muscle power.

Anticipatory effects on anterior cruciate ligament loading during sidestep cutting

BACKGROUND A key to understanding potential anterior cruciate ligament injury mechanisms is to determine joint loading characteristics associated with an injury-causing event. However, direct measurement of anterior cruciate ligament loading during athletic tasks is invasive. Thus, previous research has been unable to study the association between neuromuscular variables and anterior cruciate ligament loading. Therefore, the purpose of this study was to determine the influence of movement anticipation on anterior cruciate ligament loading using a musculoskeletal modeling approach. METHODS Twenty healthy recreationally active females were recruited to perform anticipated and unanticipated sidestep cutting. Three-dimensional kinematics and kinetics of the right leg were calculated. Muscle, joint and anterior cruciate ligament forces were then estimated using a musculoskeletal model. Dependent t-tests were conducted to investigate differences between the two cutting conditions. FINDINGS ACL loading significantly increased during unanticipated sidestep cutting (p<0.05). This increase was primarily due to a significant increase in the sagittal plane ACL loading, which contributed 62% of the total loading. Frontal plane ACL loading contributed 26% and transverse plane ACL loading contributed 12%. INTERPRETATION These results suggest that anterior cruciate ligament loading resulted from a multifaceted interaction of the sagittal plane shear forces (i.e., quadriceps, hamstrings, and tibiofemoral), as well as the frontal and transverse plane knee moments. Additionally, the results of this study confirm the hypothesis in the current literature that unanticipated movements such as sidestep cutting increase anterior cruciate ligament loading.

Balance performance in male and female collegiate basketball athletes: influence of testing surface.

Sabin, MJ, Ebersole, KT, Martindale, AR, Price, JW, and Broglio, SP. Balance performance in male and female collegiate basketball athletes: Influence of testing surface. J Strength Cond Res 24(8): 2073-2078, 2010-The Star Excursion Balance Test (SEBT) is a simple and cost-effective balance test. Information on SEBT performance in athletic populations and under varying testing surfaces is needed to fully elucidate the clinical and training utility of this task. The purpose of this study was to examine SEBT performance in division I, collegiate basketball athletes (men = 9, women = 7) and in a healthy nonathlete control group (men = 7, women = 9). Each participant performed the SEBT with their dominant and nondominant limbs on stable and unstable testing surfaces while reaching in the anterior, medial, and posterior directions. No significant differences resulted between the dominant and nondominant limbs (p > 0.05). Significant differences were found between the basketball and control groups in all directions (p < 0.01) and the average reach score (p < 0.01) with the control group reaching 6-7% farther than the basketball group. A significant main effect for gender (collapsed across group and limb) was present in the posterior direction (p = 0.02). The SEBT performance in the medial and posterior directions and the average score were significantly (p < 0.01) reduced during testing on the unstable surface. These results suggest that athletic status may be a factor to consider when interpreting SEBT reach performance. Future research should examine the influence of SEBT testing in other athletic populations. Further, use of an unstable surface provided a greater challenge to balance. Additional research may provide insight into the role of using an unstable surface with the SEBT as part of an injury risk assessment and its use in identifying limb differences between injured and uninjured limbs.

Reduced hamstring strength increases anterior cruciate ligament loading during anticipated sidestep cutting.

BACKGROUND Dynamic knee stability is considered a critical factor in reducing anterior cruciate ligament loads. While the relationships between hamstring force production and anterior cruciate ligament loading are well known in vitro, the influence of hamstring strength to anterior cruciate ligament loading during athletic maneuvers remains unknown. Therefore, the purpose of this study was to determine the influence of hamstring strength on anterior cruciate ligament loading during anticipated sidestep cut. METHODS Seventeen recreationally active females were recruited to perform sidestep cutting maneuvers pre/post an acute hamstring strength reduction protocol. Kinematics and kinetics were calculated during the cut and a musculoskeletal model was used to estimate muscle, joint, and anterior cruciate ligament loads. Dependent t-tests were conducted to investigate differences between the two cutting conditions. FINDINGS Anterior cruciate ligament loading increased by 36% due to reduced hamstring strength. This was mostly due to a 44% increase in sagittal plane loading and a 24% increase in frontal plane loading. Post strength reduction sidestep cuts were also performed with decreased anterior tibiofemoral shear force, an outcome that would theoretically reduce anterior cruciate ligament loading. However, the overall decrease in hamstring force production coupled with a more axial hamstring line of action yielded a net increase in anterior cruciate ligament loading. INTERPRETATION These results suggest that decreased hamstring strength significantly increases anterior cruciate ligament loading during anticipated sidestep cutting. Additionally, these results support the premise that preseason screening programs should monitor hamstring strength to identify female athletes with potential deficits and increased injury risk.

The Effect of Fluid Replacement on Endurance Performance

The purpose of this study was to examine the effects of fluid replacement on power output (PO), rating of perceived exertion (RPE), heart rate (HR), body weight (BW), urine osmolarity (Uosm), and urine electrolyte concentrations ([UNa+], [UK+], [UCl-]) in physically active men (n = 4) and women (n = 7). The participants were asked to generate their highest possible PO during 60 minutes of cycling under 3 randomized conditions: ingestion of (a) no fluid (trial 1); (b) 1200 ml of distilled water (trial 2); and (c) 1200 ml of Gatorade (trial 3). BW and urine volume (Vu) were measured before and after the ride to determine sweat rate [(SR = ΔBW + Vfluid intake + Vu)/time]. The results indicated that there were no significant differences between trials for PO (123–127 W), RPE (14), HR (140–142 b·min−1), and SR (11.9–12.4 ml·min−1). However, [UNa+] was significantly (p < 0.05) lower postexercise for all 3 trials, and [UCl-] was significantly reduced following trials 2 and 3. There was a significant increase (p < 0.001) in BW postexercise for trials 2 and 3 when compared with the no-fluid trial; however, the effects of water and Gatorade were similar. These results suggest that fluid replacement during 1 hour of moderately intense cycling does not enhance performance in physically active men and women who are normally hydrated.

Validity of bioelectrical impedance equations for estimating fat-free weight in high school female gymnasts

The present study examined the validity of bioelectrical impedence (BIA) equations for estimating fat-free weight (FFW) in female gymnasts by comparing the values to those obtained from underwater weighing (UWW). Ninety-seven female Caucasian high school gymnasts (mean age +/- SD = 15.7 +/- 1.1 yr) participated in the study. FFW from UWW was calculated from percent fat using the revised formula of Brozek et al. (mean FFW +/- SD = 43.8 +/- 4.5 kg) and the age-specific constants of Lohman (mean FFW +/- SD = 44.8 +/- 4.6 kg). Cross-validation analyses included examination of the constant error (CE), SEE, r, and total error (TE). The results indicated similar trends between equations when based on either the Brozek or Lohman conversions; however, the CE, SEE, and TE values were consistently lower for the majority of the equations using the revised formula of Brozek et al. Based upon the results of the cross-validation analyses, the equation of Houtkooper et al. and the interlaboratory equations of Van Loan et al. and Lohman, which resulted in identical TE values of 2.4 kg are recommended for use with young high school gymnasts.