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The article reports on research conducted to investigate the within-session, trial-to-trial reliability of a variety of electromyographic data (EMG) which evaluated quadriceps and hamstring muscles during isometric and ballistic activities. Researchers evaluated 24 subjects who performed three repetitions of two exercises. They found that the EMG was a reliable method for assessing the reproducibility of the quadriceps and hamstrings muscle activation.

The article reports on research conducted to evaluate gender differences in the magnitude and timing of hamstring and quadriceps activation during activities that are believed to cause anterior cruciate ligament injuries. Researchers evaluated 12 men and 12 women who performed drop jumps, a sprint and cut at a 45 degree angle. They found that men are lateral hamstring dominant during the postcontact phase of the cut and women sustain rectus femoris activation longer than men during this phase.

The article reports on research conducted to 2010—This study evaluated the effectiveness of a periodized plyometric training program and the impact of the duration of the post-training recovery period on countermovement jump performance. Researchers evaluated 14 women. They found that the training is effective for women and that performance is not influenced by the length of post training recovery.

The article presents the results of a survey which investigated the standard practices used by strength and conditioning coaches of U.S. high school athletes. Question addressed included program design, injury frequency, and physical testing. Responses indicated that most coaches used weightlifting exercises such as the Olympic lifts and the squat, as well as plyometric techniques.

The article presents a study which examined the relationship between quadriceps resistance training exercises and squat exercises when predicting quadriceps exercise loads. Exercises discussed include the dead lift, lunge, leg extension, and step-up. The author presents an equation used to predict the maximum load used for six-repetition exercises.

This study assessed hamstring and quadriceps timing and hamstring to quadriceps activation ratios (H:Q), and gender differences therein, during jump landings and cutting maneuvers. Subjects included 6 boys (age = 17.1 ± 0.9 years) and 6 girls (age = 15.7 ± 1.2 years). All subjects provided informed and parental consent and the study was approved by the university review board. Subjects performed 2 repetitions each of the drop jump from a height equal to their maximum vertical jump (J) as well as a sprint and cut at a 45 degree angle (C). Electromyographic (EMG) data were collected for the rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM), lateral hamstring (LH), and medial hamstring (MH). Root mean square (RMS) signal processing was used on all EMG data which were analyzed to assess the magnitude and timing of the muscles bursts pre and post landing for the J and C, using the average of 2 trials and normalized to maximal voluntary isometric contraction. The H:Q were calculated from the collective average of the hamstring muscles divided by the collective average of the quadriceps muscles. The timing of the foot contact was synchronized with the EMG system using a switch mat. Data were evaluated using an independent samples t-test to assess differences in muscle timing and H:Q for the pre and post foot contact for the J and C, for all muscles assessed. Significant gender differences were found for the timing of the MH activation (p ≤ 0.05) pre and post contact during the J, with boys demonstrating 24.4% earlier MH activation and a 19.8% longer burst after foot contact. Compared to boys, girls demonstrated 17.2% earlier MH activation during the C (p ≤ 0.05). Significant gender differences were also found in the H:Q activation ratios with boys demonstrating a 56.3% higher H:Q ratio after J landing (p ≤ 0.05). No other significant gender differences in the timing of muscle activation or the H:Q ratios were found. Counter-movement jump height was assessed as a measure of gender difference in training status. Girls demonstrated 73.7% of the jumping ability of the boys. This study confirms the existence of gender differences in the timing and magnitude of activation of MH during movements that are similar to those that cause ACL injuries. Strength and conditioning professionals are encouraged to prescribe hamstring training to their female athletes in an attempt to remediate gender differences in hamstring activation during J landings. [ABSTRACT FROM AUTHOR]

This study evaluated the effect of wind speed on 10 and 40 yard sprint times and stride frequency. Twenty-two men and women (Mean ± SD; age, 20.4 ± 1.4 years; body mass, 73.0 ± 12.5 kg) ran 6 sprints into variable speed headwinds, as assessed by wind vane and anemometer. Sprint data from the slowest and fasted wind conditions were kept for analysis. Ten and 40 yard sprint speed was assessed using an infrared timing system, and stride frequency was calculated from video analysis. Differences between 10 and 40 yard sprint times and stride frequency in slow and fast wind conditions were assessed using paired sample t-tests. Additionally, differences in scores were calculated for the slow and fast wind conditions for the 10 and 40 yard sprint times, as well as for wind speeds. Regression analysis was used to determine if a change in wind speed was a statistically significant predictor of changes in sprint times. Paired sample t-tests revealed that slow and fast mean wind conditions of 2.36 ± 1.06 and 6.73 ± 2.52 miles per hour (MPH), respectively, were significantly different (p ≤ 0.001). Mean 10 yard sprint times were 1.97 ± 0.17 seconds and 2.02 ± 0.16 seconds in the slow and fast wind conditions, respectively (p = 0.004). Mean 40 yard sprint times were 5.70 ± 0.52 seconds and 5.88 ± 0.64 seconds in the slow and fast wind conditions, respectively (p = 0.005). There was no significant difference in stride frequency between the slow and fast wind conditions of the 10 (p = 0.50) and 40 (p = 0.11) yard sprint. Results of regression analysis indicated that a change in wind speed is a significant predictor of a change in 40 yard sprint time (R2 = .22; p = 0.034) but not for the 10 yard sprint time (R2 = .05; p = 0.034). From these results, the following regression equation was created: Δ 40 yard sprint time = .054 (wind speed) - 0.055. Running into the wind decreases 10 and 40 yard sprint times, without affecting stride frequency. Changes in 40 yard sprint times can be predicted from wind speed. Running against the wind is an economical resisted speed development strategy. Coaches can use the regression equation from this study to determine the effect of forecasted or assessed wind speeds on resisted running performance, thus quantifying the nature of this training stimulus. Table 1 provides example data.Table 1. Example data based on the regression equation. [ABSTRACT FROM AUTHOR]

Concurrent activation potentiation (CAP) enhances lower body torque and rate of force development, via the contraction of muscles remote from the prime mover. This study assessed the effect of remote voluntary contractions (RVC's) on upper body muscle activation and force. Fifteen women (20.7 ± 2.1yr) and fourteen men (21.4 ± 1.8 yr) performed isokinetic concentric elbow flexion and extension at 60 degrees/sec for 3 repetitions in RVC and NO-RVC conditions. The RVC condition included jaw clenching, plantar flexion, and the Valsalva maneuver. Rate of torque development (RTD), peak torque (PT), and average power (P) were assessed using dynamometry (System IV, Biodex Inc., Shirley, NY). Electromyography (Myomonitor IV, Delsys Inc., Boston, MA) was used to assess activation of muscles potentially involved in the RVC's (gastrocnemius, rectus femoris, hamstrings belly, rectus abdominous, flexor digitorium superficialis, masseter) and the prime mover and its antagonist (biceps brachii, triceps brachii). A two way mixed ANOVA with repeated measures for test condition was used to evaluate the interaction between RVC/NO-RVC conditions and gender, and to assess the main effects. Significant main effects were further evaluated with a paired samples t-test. Significant main effects were found for RVC/NO-RVC condition (p ≤ 0.001) along with significant interaction between test condition and gender (p ≤ 0.05) for tests of peak torque, rate of torque development, and power. Significant main effects were found for RVC/ NO-RVC condition (p ≤ 0.05) without significant interaction between test condition and gender for any test of muscle activation. The RVC condition produced 7.8 to 14.1% higher performance for all variables for men, and 5.5 to 12.7% higher values for women for peak torque and rate of torque development. This performance augmentation appears to be the result of 9.7 to 12.0 % higher prime mover activation for men and 11.5 to 15.3 % higher for women, in the RVC condition. Athletes and exercisers should consider using RVC's to augment upper body force and muscle activation during training. [ABSTRACT FROM AUTHOR]