Luke R. Garceau

Gender-based analysis of hamstring and quadriceps muscle activation during jump landings and cutting

Ebben, WP, Fauth, ML, Petushek, EJ, Garceau, LR, Hsu, BE, Lutsch, BN, and Feldmann, CR. Gender-based analysis of hamstring and quadriceps muscle activation during jump landings and cutting. J Strength Cond Res 24(2): 408-415, 2010-This study evaluated gender differences in the magnitude and timing of hamstring and quadriceps activation during activities that are believed to cause anterior cruciate ligament (ACL) injuries. Twelve men (age = 21.0 ± 1.2 years; body mass = 81.61 ± 13.3 kg; and jump height = 57.61 ± 10.15 cm) and 12 women (age = 19.91 ± 0.9 years; body mass = 64.36 ± 6.14 kg; and jump height = 43.28 ± 7.5) performed 3 repetitions each of the drop jump (jump) normalized to the subjects vertical jump height, and a sprint and cut at a 45-degree angle (cut). Electromyography (EMG) was used to quantify rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM), lateral hamstring (LH), and medial hamstrings (MH) activation, timing, activation ratios, and timing ratios before and after foot contact for the jump and cut and normalized to each subjects hamstring and quadriceps maximum voluntary isometric contraction. Data were analyzed using an analysis of variance with results demonstrating that during the postcontact phase of the cut, men demonstrated greater LH and MH activation than women. In the precontact phase of the jump, men showed earlier activation of the VL and VM, than women. Women produced longer RF and VM muscle bursts during the postcontact phase of the cut. Additionally, men showed a trend toward higher hamstring to quadriceps activation ratio than women for the postcontact phase of the cut. This study provides evidence that men are LH dominant during the postcontact phase of the cut compared with women, whereas women sustain RF activation longer than men during this phase. Men activate quadriceps muscles earlier than women in the precontact phase of the jump. Training interventions may offer the potential for increasing the rate and magnitude of hamstring muscle activation. These outcomes should be evaluated using EMG during movements that are similar to those that cause ACL injuries to determine if gender differences in muscle activation can be reduced.

Reliability of Surface Electromyography During Maximal Voluntary Isometric Contractions, Jump Landings, and Cutting

Fauth, ML, Petushek, EJ, Feldmann, CR, Hsu, BE, Garceau, LR, Lutsch, BN, and Ebben, WP. Reliability of surface electromyography during maximal voluntary isometric contractions, jump landings, and cutting. J Strength Cond Res 24(4): 1131-1137, 2010-The reliability of electromyographic (EMG) data has been examined for isometric and slow dynamic tasks, but little is known about the repeatability of this data for ballistic movements. The purpose of this study was to examine the within-session, trial-to-trial reliability of a variety of quadriceps and hamstrings muscles during isometric and ballistic activities. Data were analyzed by way of intraclass correlation coefficients (ICC), intersubject coefficients of variation (CVinter), and intrasubject coefficients of variation (CVintra). Twenty-four subjects performed 3 repetitions each of 2 randomly ordered test exercises, including landing from a depth jump (J) and cutting after a 10-m sprint (C). Data were acquired and processed with root mean square EMG for the muscles assessed, and data were analyzed for each exercise using a repeated measures analysis of variance. Results revealed that all ICC values were greater than 0.80, with most values greater than 0.90, CVinter values ranged from 5.4% to 148.7%, and CVintra values ranged from 11.5% to 49.3%. This study indicates that EMG is a reliable method for assessing the reproducibility of both the quadriceps and hamstrings muscle activation during either isometric or ballistic exercises.

EMG Analysis of Concurrent Activation Potentiation

PURPOSE This study evaluated the effect of remote voluntary contractions(RVC) on concentric isokinetic knee extensor and flexor peak torque, rate of torque development, power, and work, the activation of the affected muscles, and gender differences therein. METHODS Eleven men and 12 women were evaluated with EMG and isokinetic dynamometry during knee extension and flexion tests in RVC and baseline (NO-RVC) test conditions. The RVC condition included jaw clenching, hand gripping, and the Valsalva maneuver. A two-way mixed ANOVA with repeated measures for test condition was used to evaluate the main effects for each isokinetic measure, as well as the EMG of the prime movers, their antagonist,and the muscles involved in the RVC, and the interaction between test condition and gender. RESULTS Significant interactions between test condition and gender indicate differences in response to RVC during knee extension tests for power and work (P < or = 0.05) and for knee flexion tests for peak torque and power (P < or = 0.05). All subjects produced higher peak torque and power during knee extension in the RVC condition (P < or = 0.05). Men produced a higher rate of torque development and work during knee extension (P < or = 0.05) and a higher peak torque and power during knee flexion in the RVC condition (P < or = 0.05). Prime mover activation was greater in the RVC condition for most tests (P < or = 0.05). Women demonstrated lower bilateral flexor digitorum superficialis activation than men during all tests in the RVC condition (P < or = 0.05). CONCLUSIONS RVC increased the performance of several outcome variables assessed, which coincides with the concomitant increase in EMG of the prime movers.

Electromyographical analysis of lower extremity muscle activation during variations of the loaded step-up exercise.

Abstract Simenz, CJ, Garceau, LR, Lutsch, BN, Suchomel, TJ, and Ebben, WP. Electromyographical analysis of lower extremity muscle activation during variations of the loaded step-up exercise. J Strength Cond Res 26(12): 3398–3405, 2012—The loaded step-up exercise allows strength and conditioning practitioners to incorporate a unilateral resistance for athletes while performing extension at the hip, knee, and plantar flexion at the ankle. This study evaluated the activation of the biceps femoris (BF), gluteus maximus (GMx), gluteus medius (GMe), rectus femoris, semitendinosus (ST), vastus lateralis, and vastus medialis during 4 variations of the step-up exercise to assess the specific muscle training stimulus of each exercise variation. The exercises included the step-up, crossover step-up, diagonal step-up, and lateral step-up. Fifteen women who regularly engaged in lower body resistance training performed the 4 exercises with 6 repetition maximum loads on a 45.72-cm (18-in.) plyometric box. Data were collected with a telemetered electromyography (EMG) system, and root mean square values were calculated for EMG data for eccentric and concentric phases. Results of a repeated-measures analysis of variance revealed a variety of differences in muscle activation between the exercises (p ⩽ 0.05). The results indicated that the crossover step-up elicited the greatest concentric muscle activation for the GMe, whereas the step-up elicited greatest eccentric activation for the GMe and greatest activation for the GMx, BF, and ST in both concentric and eccentric phases. These findings can be used by practitioners to inform exercise selection to best target and maximally activate a variety of hip and thigh musculature.

Kinetic Quantification of Plyometric Exercise Intensity

Ebben, WP, Fauth, ML, Garceau, LR, and Petushek, EJ. Kinetic quantification of plyometric exercise intensity. J Strength Cond Res 25(12): 3288–3298, 2011—Quantification of plyometric exercise intensity is necessary to understand the characteristics of these exercises and the proper progression of this mode of exercise. The purpose of this study was to assess the kinetic characteristics of a variety of plyometric exercises. This study also sought to assess gender differences in these variables. Twenty-six men and 23 women with previous experience in performing plyometric training served as subjects. The subjects performed a variety of plyometric exercises including line hops, 15.24-cm cone hops, squat jumps, tuck jumps, countermovement jumps (CMJs), loaded CMJs equal to 30% of 1 repetition maximum squat, depth jumps normalized to the subjects jump height (JH), and single leg jumps. All plyometric exercises were assessed with a force platform. Outcome variables associated with the takeoff, airborne, and landing phase of each plyometric exercise were evaluated. These variables included the peak vertical ground reaction force (GRF) during takeoff, the time to takeoff, flight time, JH, peak power, landing rate of force development, and peak vertical GRF during landing. A 2-way mixed analysis of variance with repeated measures for plyometric exercise type demonstrated main effects for exercise type and all outcome variables (p ≤ 0.05) and for the interaction between gender and peak vertical GRF during takeoff (p ≤ 0.05). Bonferroni-adjusted pairwise comparisons identified a number of differences between the plyometric exercises for the outcome variables assessed (p ≤ 0.05). These findings can be used to guide the progression of plyometric training by incorporating exercises of increasing intensity over the course of a program.

Teaching practices of the undergraduate introductory biomechanics faculty: a North American survey

Instruction and assessment strategies of undergraduate introductory biomechanics instructors have yet to be comprehensively examined. The purpose of this study was to identify the current instruction and assessment practices of North American undergraduate introductory biomechanics instructors and equipment needed for effective instruction in lecture and laboratory sessions. One hundred and sixty-five respondents (age: 42.5 ± 10.3 years) who currently teach or have taught an introductory biomechanics course in North America were recruited by electronic mail. Subjects completed a web-based survey, consisting of 60 open- and closed-ended questions. Pearsons correlation coefficients were used to assess relationships between instructors familiarity with either the Biomechanics Concept Inventory or the NASPE Guidelines for Undergraduate Biomechanics, and instructor and course characteristics (number of years teaching, age, faculty rank, number of quizzes given, etc.) A number of variables were significantly (p < 0.05) correlated. Answers to open-ended questions were processed using content analysis, with results categorized in content areas including: instructor and course characteristics; lecture instruction; assessment and equipment; laboratory instruction; assessment and equipment; and instructors perspectives. Many active learning strategies for lecture and laboratory instruction were identified by faculty. Limited student preparation and limited resources were noted as the instructors most common challenges.

A proposed novel function of the psoas minor revealed through cadaver dissection.

There is sparse information about the anatomy and function of the psoas minor, specifically the extent and frequency to which the muscle attaches into the iliac fascia that drapes over the iliopsoas. This information may help clarify the function of the psoas minor, especially regarding the possibility of controlling the position and mechanical stability of the underlying iliopsoas. This descriptive, semiquantitative cadaveric study sought to clarify the gross anatomic detail of the psoas minor, particularly the muscles distal attachments. Thirty‐two embalmed cadaver hips were examined. Hips that presented with a psoas minor underwent further anatomic measurements. The psoas minor was present in 65.6% of the 32 hips. All of the psoas minor tendons attached firmly into iliac fascia, while 90.5% also had a firm bony attachment to the pelvis. On average, the muscle belly occupied the proximal 37.5 ± 6.0% of the entire musculotendinous unit, while the muscle bellys average anatomical cross‐sectional area was 52.5 ± 34.3 mm2. The psoas minors firm and consistent distal tendinous attachment into the iliac fascia may allow this muscle to partially control the position and mechanical stability of the underlying iliopsoas as it crosses the femoral head and adjacent regions. This hypothesized function may be clinically related to inflammation and pathology involving the iliopsoas tendon and adjacent tissues in the anterior region of the hip. Further study is now warranted to determine the clinical relevancy and biomechanical validity of this proposed function of the psoas minor. Clin. Anat. 28:243–252, 2015.

The Optimal Back Squat Load for Potential Osteogenesis

Abstract Ebben, WP, Garceau, LR, Wurm, BJ, Suchomel, TJ, Duran, K, and Petushek, EJ. The optimal back squat load for potential osteogenesis. J Strength Cond Res 26(5): 1232–1237, 2012—The osteogenic potential of exercise is reported to be partially a function of the magnitude of training loads. This study evaluated the ground reaction force (GRF) and rate of force development (RFD) of the eccentric and concentric phases of the back squat at 3 different loads. Twelve subjects performed the back squat on a force platform with loading conditions of 80, 100, and 120% of their 1 repetition maximum (RM). Back squats performed at 120% of the 1RM produced the highest GRF in both the eccentric and concentric conditions. No significant differences were found between RFD for any of the loading conditions. Performing the back squat at loads of 120% of the estimated 1RM, accomplished with reduced range of motion, results in higher GRF than the back squat performed at 80 or 100% of the 1RM. Thus, supermaximal back squat loads in excess of the 1RM, with decreased range of motion, may be a useful part of a resistance training program designed to maximize osteogenic potential.