GROUND AND KNEE JOINT REACTION FORCES DURING VARIATIONS OF PLYOMETRIC EXERCISES

Six Division-I athletes, who routinely used piyometric exercises, performed drop jumps from 46 and 61 cm, a pike jump, tuck jump, single leg jump, counter movement jump, squat jump, and a squat jump holding dumb ells equal to 30% of 1 RM squat. GRF obtained via an AMTI force plate and video analysis of mar1 0.05). Results indicate that although peak GRF forces of landing from plyometric exercise may not differ, the KRF do possibly due to variability in landing technIques

HAMSTRING ELECTROMYOGRAPHIC RESPONSE OF THE BACK SQUAT AT DIFFERENT KNEE ANGLES DURING CONCENTRIC AND ECCENTRIC PHASES

This study examined mean I-EMG for the hamstring group, during eccentric vs. concentric phases of the back squat at knee angles of 160-150, 140-130, 120-110 and 100-90. A 2X4 Repeated Measures ANOVA of the I-EMG hamstring activity revealed a significant interaction of contraction phase by angle (p.05). Closer analysis of each contraction phase via a One-way (angle) Repeated Measures ANOVA showed hamstring I-EMG during the eccentric contraction at 120-110 and 100-90 to be greater than 160-150 (p.05). In addition, there was no difference between 160-150 and 140-130 during the eccentric phase (p>.05). Furthermore, there were no differences found between mean I-EMG activity for any of the angles during concentric knee extension (p>.05)

IMPULSES AND GROUND REACTION FORCES AT PROGRESSIVE INTENSITIES OF WEIGHTLIFTING VARIATIONS

Five Division-I athletes who routinely performed the hang clean and hang snatch performed a single repetition of each at loads of 50, 60, 70, 80, and 90% of their 1 RM, with 5 minutes rest between each repetition. Movement impulses and peak GRF were evaluated on an AMTI force plate. Two-way ANOVA indicated impulses and peak GRF at 50% 1RM were lower than all other reps (

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 (

THE OPTIMAL PLYOMETRIC EXERCISE HORIZONTAL TO VERTICAL FORCE RATIO FOR SPRINTING

This study determined the horizontal to vertical force ratio (H:V) of two types of sprint starts and a variety of plyometric exercise, for the purpose of determining the exercises which are most biomechanically specific to sprinting. Subjects included 15 men. All subjects’ performed the sprinter start, the standing sprint start, the CMJ, 18 inch hurdle hop, bounding, power skipping, standing long jump, and multiple hops, starting on a force platform. A repeated measures ANOVA was used to determine differences in H:V between the sprinter start, the standing start, and the plyometric exercises. Results reveal significant main effects for sprint start H:V and standing start H:V, and the plyometric exercises H:V (p ≤ 0.001). Post-hoc analyses revealed that bounding and standing long jumps are the most biomechanically for training athletes for sprint starts

FOURTH NORTH AMERICAN SURVEY OF UNDERGRADUATE BIOMECHANICS INSTRUCTION IN KINESIOLOGY/EXERCISE SCIENCE

A web-based survey of introductory biomechanics instructors in Kinesiology/Exercise Science departments from North America was conducted to document current instructor and course characteristics. Responses from 165 faculty from the USA and Canada were compiled and compared to previous surveys. Survey respondents tended to have doctoral training in biomechanics and reported nominally larger percentages, relative to previous surveys, of courses entitled “biomechanics” and mechanical content. The respondents also reported greater diversity of course prerequisites, less emphasis on anatomy, and less familiarity with NASPE guidelines for the course than reported in previous surveys

THE ROLE OF WALKING AND RUNNING VELOCITY ON OSTEOGENIC POTENTIAL

This study assessed the ground reaction forces (GRF) associated with walking and running at a variety of speeds and compared these kinetic values to the landing after a maximum counter-movement jump in order to understand the osteogenic potential for these activities. Twenty-four women walked and ran over a force platform at slow, medium, and fast walking and running speeds, which were assessed using Doppler radar. Landing vertical peak GRF and rate of force development (RFD) were analyzed for all movements using a force platform. In almost all cases, higher walking or running speeds resulted in statistically significant increases in GRF and RFD. Based on the findings of this study, moderate to fast sprints should be prescribed in the training programs for those who seek to maximize their bone health

THE EFFECT OF PLYOMETRIC TRAINING VOLUME ON JUMPING PERFORMANCE

This study compared high and low daily volume periodized plyometric training programs and their effect on countermovement jump (CMJ) performance over a 2 week testing time course after training. Thirty-five male subjects participated. Subjects CMJ was tested on a force platform prior to and at 2, 6, 10 and 14 days post training. Peak vertical ground reaction force (GRF), reactive strength index-modified (RSI mod), jump height (JH), and body mass were assessed. No differences were found between the high and low volume training groups. Subjects GRF, RSI mod, and JH performance was improved in a range of 6 to 14 days post- training. Low and high volume periodized plyometric training programs produced equal results. Six to 14 days of recovery post training was required to accrue the training benefit

GENDER DIFFERENCES IN THE RELATIONSHIP BETWEEN QUADRICEPS MVIC AND HAMSTRING TO QUADRICEPS RATIO

No previous research has evaluated the relationship between degree of Q activation and its’ effect on H:Q ratio, despite the fact that Q dominance and low H:Q ratios are thought to increase the risk of H and ACL injury (Baratta et al., 1988; Hewitt et al., 2001). Compared to males, females may be at greater risk, due to higher Q co-activation (Colliander and Tesch, 1989; White et al., 2003). The purpose of this study was to evaluate gender differences in the relationship between Q activation and it’s effect on H:Q ratios

Diurnal Variation in Stretch Shortening Cycle and Non-Stretch Shortening Cycle Jumping Performance

This study assessed the diurnal variations, as well as the subjects’ perceptions of how time of day affects their jumping performance. Eighteen subjects participated in testing sessions at 7 a.m., noon, and 5 p.m., on the same day. Subjects performed squat jumps (SJ) and countermovement jumps (CMJ) on a force platform with peak ground reaction force (GRF), jump height, and reactive strength index-modified (RSImod) obtained for each jump. Diurnal differences for the CMJ were found for GRF (P = 0.048). Diurnal differences for the SJ were found in RSImod (P= 0.04). Subjective assessment of jumping explosiveness was significantly different across time of day (P = 0. 047). Lower body power training such as plyometrics, may be more effective at mid day than early morning or late afternoon