The Effect of Concurrent Activation Potentiation During Fast Stretch Shortening Cycle Activity

This study evaluated the effect of remote voluntary contractions (RVC) on depth jump performance. Subjects performed the depth jump in a RVC condition and a condition without RVC (NO-RVC). Ground reaction force (GRF), impulse (I), and reactive strength index (RSI) were assessed with a force platform. Data were analyzed using a two way ANOVA. Analysis of GRF showed no significant main effects for RVC condition (p = 0.46) and no interaction for RVC condition and gender (p = 0.11). Analysis of I showed no significant main effects for RVC condition (p = 0.99) and no interaction for RVC condition and gender (p = 0.61). Analysis of RSI showed no significant main effects for RVC condition (p = 0.78) and no interaction for RVC condition and gender (p = 0.20). Remote voluntary contractions appear to offer no performance benefits for exercises such as the depth jump

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 ≤ 0.05) and for knee flexion tests for peak torque and power (P ≤ 0.05). All subjects produced higher peak torque and power during knee extension in the RVC condition (P ≤ 0.05). Men produced a higher rate of torque development and work during knee extension (P ≤ 0.05) and a higher peak torque and power during knee flexion in the RVC condition (P ≤ 0.05). Prime mover activation was greater in the RVC condition for most tests (P ≤ 0.05). Women demonstrated lower bilateral flexor digitorum superficialis activation than men during all tests in the RVC condition (P ≤ 0.05). Conclusions: RVC increased the performance of several outcome variables assessed, which coincides with the concomitant increase in EMG of the prime movers

The Acute Time Course of Concurrent Activation Potentiation

This study evaluated the acute time course of the ergogenic effect of concurrent activation potentiation (CAP). Forty-two men and women, including CAP non-responders and responders, performed a 5 second isometric knee extension on a dynamometer with the use of remote voluntary contractions (RVC). Mean torque was assessed in seven 500 millisecond (ms) time periods. A two-way repeated measures ANOVA revealed significant main effects for time period (p ≤ 0.001), but no significant interaction between time period and CAP non-responders and responders (p \u3e 0.05). The ergogenic effects of CAP are accrued during the first 1000ms. Concurrent activation potentiation responders produce greater initial force than the CAP non-responders, without a concomitant acceleration in force decay throughout the time course

The Effect of Concurrent Activation Potentiation on the Knee Extensor and Flexor Performance of Men and Women

This study evaluated the effect of remote voluntary contractions (RVC) during isometric and isokinetic knee flexion and extension tests and evaluated gender differences therein. Subject peak torque, rate of torque development, and power were assessed with a dynamometer in RVC and no RVC’s conditions. A two way mixed ANOVA with repeated measures for condition was used to evaluate the interaction between conditions and gender, and to assess the main effects. Main effects were evaluated with a paired samples t-test. Results revealed a significant interaction between all but one test condition and gender as well as significant main effects for all of the variables assessed (P ≤ 0.05). Men attained 9.2% to 19.7% greater performances in the RVC condition for all variables whilst women demonstrated no significant differences between test conditions

Quantifying the onset of the concentric phase of the force–time record during jumping

Thirteen college students performed a drop jump from height equal to their peak vertical jump, single leg jumps from the left and right legs, and a counter movement jump. Vertical ground reaction force (GRF) obtained via an AMTI force plate and video analysis of markers placed on the hip, knee, lateral malleolus, and fifth metatarsal were used to estimate reaction forces on the knee joint. One-way Repeated Measures ANOVA indicated no differences for knee joint reaction forces relative to body weight or peak GRF for any of the jumps (p \u3e 0.05). Average measures Intraclass Correlation Coefficients ranged from r = 0.90 to 0.97. Results indicate that peak GRF and knee joint reaction forces during the drop jump, counter movement jump, and single leg left and right leg jumps are reliable measures

Kinetic Quantification of Plyometric Take Off, Flight, and Landing Characteristics

This study assessed the kinetic characteristics of a variety of plyometric exercises and assessed gender differences therein. Twenty-six men and 23 women performed a variety of plyometric exercises including line hops, 15.24 cm cone hops, squat jumps, tuck jumps, countermovement jumps, loaded countermovement jumps equal to 30% of 1 RM squat, depth jumps normalized to the subjects jump height, and single leg jumps. All plyometric exercises were performed on a force platform. Outcome variables associated with the takeoff, airborne, and landing phase of each plyometric were assessed including the peak ground reaction force during takeoff, time to takeoff, jump height, peak power, peak ground reaction force during landing, and landing rate of force development. A number of differences were found between plyometric exercises

Dynamic Stabilization During the Landing Phase of Plyometric Exercises

This study examined the differences in and the reliability of time to stabilization (TTS) of several plyometric exercises. Twenty six men performed a variety of plyometric exercises representing a continuum of intensities of landing instability, including line hops, cone hops, squat jumps, tuck jumps, countermovement jumps, dumbbell countermovement jumps, and single leg countermovement jumps on a force platform. A repeated measures ANOVA with Bonferroni post hoc corrections was used to evaluate the differences in TTS between plyometric exercises. Practitioners who use plyometrics to train dynamic stability and balance should create programs that progress the intensity of the exercises based on the results of this study. This study also demonstrates that TTS reliability is fair to excellent for a variety of jumping conditions

Electromyographical Analysis of Lower Extremity Muscle Activation During Variations of the Loaded Step-Up Exercise

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 (

Gender-Based Analysis of Hamstring and Quadriceps Muscle Activation During Jump Landings and Cutting

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 subject\u27s 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 subject\u27s 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

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