FORCE, VELOCITY, AND POWER ADAPTATIONS IN RESPONSE TO A PERIODIZED PLYOMETRIC TRAINING PROGRAM

This study assessed kinetic, kinematic and temporal adaptations to the countermovement jump in response to a 6 week periodized plyometric training program. Twenty recreationally active women were randomly assigned to a plyometric training or control group. Testing consisted of 3 maximal countermovement jumps on a force platform prior to and after the six weeks of training. A two-way repeated measures ANOVA was used to assess differences between pre- and post-testing sessions and between groups. Post-test eccentric and concentric velocity, power and jump height were significantly greater (p < 0.05) in the training group. Periodized plyometric training is effective for increasing jump height, and augmentations are likely due to enhanced eccentric velocity

THE EFFECT OF REMOTE VOLUNTARY CONTRACTIONS 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

Kinetic Analysis of Lower Body Resistance Training Exercises

This study evaluated and compared the peak vertical ground reaction force (GRF) and rate of force development (RFD) for the eccentric and concentric phases of 4 lower body resistance training exercises, including the back squat, deadlift, step-up, and forward lunge. Sixteen women performed 2 repetitions of each of the 4 exercises at a 6 repetition maximum load. Kinetic data were acquired using a force platform. A repeated measures ANOVA was used to evaluate the differences in GRF between the exercises. Results revealed significant main effects for GRF both the eccentric (p ≤ 0.001) and concentric (p ≤ 0.001) phases. Significant main effects were also found for RFD for the eccentric (p ≤ 0.001) and concentric phases (p ≤ 0.001). Force and power requirements and osteogenic potential differ between these resistance training exercises

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 &#8804; 0.001), but no significant interaction between time period and CAP non-responders and responders (p > 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

GENDER DIFFERENCES IN KNEE EXTENSOR AND FLEXOR PERFORMANCE

The purpose of this study was to evaluate gender differences in peak torque (PT), rate of torque development (RTD), power, and work during isometric (ISOM) knee extension and isokinetic (ISOK) knee extension and flexion. Forty-four university women and men volunteered to perform the test exercises on a computerized dynamometer. Data were reduced with manufacturer software and were analyzed with an independent-samples t-test in order to determine gender differences. Results revealed significant differences (P &#8804; 0.001) for ISOM PT and ISOK PT, RTD, power, and work. Gender differences in knee extensor and flexor performance are present, with women demonstrating a range of 68.9 to 76.9% of their male counterparts. Conversely, the rate of force production is not gender specific during ISOM knee extension

ECCENTRIC MUSCLE ACTIONS PRODUCE 36% TO 154% LESS ACTIVATION THAN CONCENTRIC MUSCLE ACTIONS

This study evaluated the differences in eccentric and concentric phase muscle activation of variety of muscles during lower body resistance training exercises. Surface electromyography data (EMG) from 12 subjects was analyzed for the eccentric and concentric phases of the squat, deadlift, step-up, and lunge. Data from the test exercises were averaged for the eccentric and concentric phase for each muscle group to produce a comprehensive measure of activation differences between the eccentric and concentric phases. A paired samples t-test revealed differences between eccentric and concentric phase activation for all muscles assessed (p &#8804; 0.05). Results demonstrated that during lower body multi-joint exercises the eccentric phase produced 36% to 154% less muscle activation that the concentric phase

GROUND REACTION FORCE AND RATE OF FORCE DEVELOPMENT DURING LOWER BODY RESISTANCE TRAINING EXERCISES

This study quantified the differences in the kinetic profiles of the back squat, deadlift, step-up, and lunge. Eleven subjects performed 2 repetitions of their 5 repetition maximum in each of the 4 exercises. Kinetic data were collected using a force platform. The exercises were compared based on their peak vertical ground reaction force (GRFP) and rate of force development (RFD) in both the eccentric and concentric phase. A repeated measures ANOVA indicated differences (p &#8804; 0.001) in GRFP attained for the different exercises in both the eccentric and concentric phase. No significant differences (p &#8805; 0.05) were found for RFD for any of the exercises in either the eccentric or concentric phase. Results can guide the development of training programs that are specific to strength, explosiveness, or osteogenesis

ELECTROMYOGRAPHICAL ANALYSIS OF LOWER EXTREMITY MUSCLE ACTIVATION DURING VARIATIONS OF THE LOADED STEP UP EXERCISE

This study evaluated the biceps femoris, gluteus maximus, gluteus medius, rectus femoris, semitendonosus, vastus lateralis, and vastus medialis activation during four variations of the step up exercise. 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 four exercises with 6RM loads on a 45.72cm plyometric box. Data were collected with a telemetered EMG system, and RMS values were calculated for EMG data for eccentric and concentric phases. Results of a repeated measures ANOVA (p&#8804;0.05) revealed a variety of differences in muscle activation between the exercises

Genome-wide analyses of cassava Pathogenesis-related (PR) gene families reveal core transcriptome responses to whitefly infestation, salicylic acid and jasmonic acid.

BACKGROUND:Whiteflies are a threat to cassava (Manihot esculenta), an important staple food in many tropical/subtropical regions. Understanding the molecular mechanisms regulating cassava's responses against this pest is crucial for developing control strategies. Pathogenesis-related (PR) protein families are an integral part of plant immunity. With the availability of whole genome sequences, the annotation and expression programs of the full complement of PR genes in an organism can now be achieved. An understanding of the responses of the entire complement of PR genes during biotic stress and to the defense hormones, salicylic acid (SA) and jasmonic acid (JA), is lacking. Here, we analyze the responses of cassava PR genes to whiteflies, SA, JA, and other biotic aggressors. RESULTS:The cassava genome possesses 14 of the 17 plant PR families, with a total of 447 PR genes. A cassava PR gene nomenclature is proposed. Phylogenetic relatedness of cassava PR proteins to each other and to homologs in poplar, rice and Arabidopsis identified cassava-specific PR gene family expansions. The temporal programs of PR gene expression in response to the whitefly (Aleurotrachelus socialis) in four whitefly-susceptible cassava genotypes showed that 167 of the 447 PR genes were regulated after whitefly infestation. While the timing of PR gene expression varied, over 37% of whitefly-regulated PR genes were downregulated in all four genotypes. Notably, whitefly-responsive PR genes were largely coordinately regulated by SA and JA. The analysis of cassava PR gene expression in response to five other biotic stresses revealed a strong positive correlation between whitefly and Xanthomonas axonopodis and Cassava Brown Streak Virus responses and negative correlations between whitefly and Cassava Mosaic Virus responses. Finally, certain associations between PR genes in cassava expansions and response to biotic stresses were observed among PR families. CONCLUSIONS:This study represents the first genome-wide characterization of PR genes in cassava. PR gene responses to six biotic stresses and to SA and JA are demonstrably different to other angiosperms. We propose that our approach could be applied in other species to fully understand PR gene regulation by pathogens, pests and the canonical defense hormones SA and JA

THE EFFECT OF ANTAGONIST CONDITIONING CONTRACTIONS ON LOWER AND UPPER BODY POWER TESTS

This study assessed the effect of antagonist conditioning contractions (ACC) on lower and upper body power tests. Six subjects performed the bilateral countermovement jump and the supine medicine ball chest throw on a force platform in baseline conditions and after ACC. A repeated measures ANOVA was used to compare performance between the baseline conditions and the ACC condition. Analysis demonstrated no significant main effects for GRF (p = 0.41) or RFD (p = 0.55) for the countermovement jump. Additionally, there were no significant main effects for GRF (p = 0.85) or RFD (p = 0.95) for the medicine ball throw. This study demonstrated that maximal short term ACC do not enhance multi-joint power tests such as the countermovement jump and medicine ball throw