Mark A. Guadagnoli

Effect of hamstring-emphasized resistance training on hamstring:quadriceps strength ratios.

A decreased hamstring:quadriceps (H:Q) ratio may put the hamstrings and anterior cruciate ligament (ACL) at increased risk of injury. Therefore, the purpose of this study was to evaluate H:Q ratios of 12 female National Collegiate Athletic Association soccer players, and to test the effects of a 6-week strength training program on these ratios. Each subject completed 2 practice sessions before a pretest. Subjects then completed 6 weeks of strength training that included the addition of 2 hamstring specific exercises, followed by a posttest. Peak torque during concentric and eccentric actions for both hamstrings and quadriceps was measured with an isokinetic dynamometer. Each muscle action was tested at 3 angular velocities in the following order: concentric 240, 180, and 60°·s−1 and eccentric 60, 180, and 240°·s−1. The H:Q strength ratio was evaluated using concentric muscle actions (concentric hamstrings: concentric quadriceps). This method is commonly used and is thus called the conventional ratio. Because concentric actions do not occur simultaneously in opposing muscles, a more functional assessment compares eccentric hamstring actions to concentric quadriceps actions. This functional ratio was also analyzed. Mean conventional and functional H:Q ratio data were analyzed using separate analysis of variance procedures with repeated measures on all factors (2 [Test] × 2 [Leg] × 3 [Angular Velocity]). The results revealed a significant main effect for factor (F test) with the functional ratio (p < 0.05) but not for the conventional ratio. The mean functional ratio increased from 0.96 ± 0.09 in pretest to 1.08 ± 0.11 in posttest. These results suggest that 6 weeks of strength training that emphasizes hamstrings is sufficient to significantly increase the functional ratio. The functional ratio after training exceeded 1.0, which is specifically recommended for prevention of ACL injuries.

Acute Effects of Static and Ballistic Stretching on Measures of Strength and Power

Samuel, MN, Holcomb, WR, Guadagnoli, MA, Rubley, MD, and Wallmann, H. Acute effects of static and ballistic stretching on measures of strength and power. J Strength Cond Res 22(5): 1422-1428, 2008-Preactivity stretching is commonly performed by athletes as part of their warm-up routine. However, the most recent literature questions the effectiveness of preactivity stretching. One limitation of this research is that the stretching duration is not realistic for most athletes. Therefore, the purpose of this study was to determine the effects of a practical duration of acute static and ballistic stretching on vertical jump (VJ), lower-extremity power, and quadriceps and hamstring torque. Twenty-four subjects performed a 5-minute warm-up followed by each of the following three conditions on separate days with order counterbalanced: static stretching, ballistic stretching, or no-stretch control condition. Vertical jump was determined with the Vertec VJ system and was also calculated from the ground-reaction forces collected from a Kistler force plate, which also were used to calculate power. Torque output of the quadriceps and hamstrings was measured through knee extension and flexion on the Biodex System 3 Dynamometer at 60°·s−1. Data normalized for body weight were analyzed using five separate, 3 (stretch condition) × 2 (gender) analysis-of-variance procedures with repeated measures on the factor of stretch condition. The gender × stretch interaction was not significant for any of the four measures, suggesting that the stretching conditions did not affect men and women differently. The results of this study reveal that static and ballistic stretching did not affect VJ, or torque output for the quadriceps and hamstrings. Despite no adverse effect on VJ, stretching did cause a decrease in lower-extremity power, which was surprising. Because of the mixed results, strength coaches would be better served to use dynamic stretching before activity; this has been consistently supported by the literature.

Knowledge of Results for Motor Learning: Relationship Between Error Estimation and Knowledge of Results Frequency

Abstract The authors of the present study investigated the apparent contradiction between early and more recent views of knowledge of results (KR), the idea that how one is engaged before receiving KR may not be independent of how one uses that KR. In a 2 × 2 factorial design, participants (N = 64) practiced a simple force-production task and (a) were required, or not required, to estimate error about their previous response and (b) were provided KR either after every response (100%) or after every 5th response (20%) during acquisition. A no-KR retention test revealed an interaction between acquisition error estimation and KR frequencies. The group that received 100% KR and was required to error estimate during acquisition performed the best during retention. The 2 groups that received 20% KR performed less well. Finally, the group that received 100% KR and was not required to error estimate during acquisition performed the poorest during retention. One general interpretation of that pattern of results is that motor learning is an increasing function of the degree to which participants use KR to test response hypotheses (J. A. Adams, 1971; R. A. Schmidt, 1975). Practicing simple responses coupled with error estimation may embody response hypotheses that can be tested with KR, thus benefiting motor learning most under a 100% KR condition. Practicing simple responses without error estimation is less likely to embody response hypothesis, however, which may increase the probability that participants will use KR to guide upcoming responses, thus attenuating motor learning under a 100% KR condition. The authors conclude, therefore, that how one is engaged before receiving KR may not be independent of how one uses KR.

The application of the challenge point framework in medical education

Medical Education 2012: 46: 447–453

The Magnitude of Tissue Cooling During Cryotherapy With Varied Types of Compression

CONTEXT Certified athletic trainers can choose different types of external compression (none, Flex-i-Wrap, and elastic wrap) when applying an ice bag to the body. However, which type facilitates the greatest magnitude of tissue cooling is unclear. OBJECTIVE To compare the effects of 2 common types of external compression on the magnitude of surface and intramuscular cooling during an ice-bag treatment. DESIGN Randomized controlled trial. SETTING University research laboratory. PATIENTS OR OTHER PARTICIPANTS Fourteen college students (10 women, 4 men; age = 22.4 +/- 1.8 years, height = 169.1 +/- 8.2 cm, mass = 73.3 +/- 18.5 kg, skinfold = 13.14 +/- 1.61 mm) with previous cryotherapy experience and a posterior lower leg skinfold equal to or less than 15 mm. INTERVENTION(S) On 3 different days separated by 24 to 48 hours, an ice bag was applied to the posterior lower leg surface of each participant for 30 minutes with no compression, with elastic wrap, or with Flex-i-Wrap. MAIN OUTCOME MEASURE(S) Posterior lower leg surface and intramuscular (2 cm) temperatures were recorded for 95 minutes. RESULTS At 15 minutes, the elastic wrap produced greater surface temperature reduction than no compression (P = .03); this difference remained throughout the protocol (P range, .03 to .04). At 30 minutes, surface temperatures were 14.95 degrees C, 11.55 degrees C, and 9.49 degrees C when an ice bag was applied with no external compression, Flex-i-Wrap, and elastic wrap, respectively. Surface temperatures between Flex-i-Wrap and elastic wrap and between Flex-i-Wrap and no compression were never different. At 10 minutes, Flex-i-Wrap (P = .006) and elastic wrap (P < .001) produced greater intramuscular temperature reduction than no compression produced; these differences remained throughout the protocol. At 10 minutes, no compression, Flex-i-Wrap, and elastic wrap decreased intramuscular temperature by 1.34 degrees C, 2.46 degrees C, and 2.73 degrees C, respectively. At 25 minutes, elastic wrap (8.03 degrees C) produced greater temperature reduction than Flex-i-Wrap (6.65 degrees C) (P = .03) or no compression (4.63 degrees C) (P < .001 ). These differences remained throughout ice application and until 50 minutes after ice-bag removal. CONCLUSIONS During an ice-bag application, external compression with elastic wrap was more effective than Flex-i-Wrap at reducing intramuscular tissue temperature. Elastic wraps should be used for acute injury care.

The Scheduling of Knowledge of Results

The experiments outlined in this article were performed so that the acquisition effects of KR scheduling on no-KR retention could be determined. In Experiment 1, the group that alternated between 12 KR and 12 no-KR responses produced better retention than both the group that alternated between 6 KR and 6 no-KR responses and an all-KR group. The partial KR group that performed the best on retention also received the least number of reversals from KR to no-KR responses, however. In Experiment 2, when acquisition KR reversals ere held constant for partial KR groups, groups that received either random KR scheduling or all KR produced similar and better retention that groups who received blocked KR scheduling. These results were reconciled with KR frequency experiments by proposing that memory processes invoked by KR protocols decrease from KR frequency, to reversal, to scheduling conditions.

After-contraction phenomenon : influences on performance and learning

Three experiments investigated the influence of an after-contraction phenomenon on the performance and learning of a dynamic force-production task. The after-contraction effect refers to an involuntary potentiation (induced by a sustained precontraction) that is thought to summate with voluntary motor commands to bias subsequent responding. The precontraction involved a brief (20 s) static contraction. The subsequent influence of the precontraction on a dynamic force-production task was assessed. Experiments 1 and 2 were aimed at demonstrating the direct impact of the precontraction intensity on the magnitude and decay of the after-contraction effect. The results indicated that as the intensity of the precontraction increased, the magnitude of the induced bias increased. In Experiment 3, the indirect influence on subsequent retention of varying the precontraction intensity during acquisition was investigated. The results indicated that the performance of subjects experiencing varying precontraction intensities during acquisition was inferior to that of subjects experiencing a constant precontraction intensity, but the performance of the varied precontraction intensities group was superior on the test of retention. It is noted that the paradoxical reversal from acquisition to retention is similar to that found in contextual interference experiments and may arise from similar mechanisms.

On the Use and Misuse of Video Analysis

The popularity of video analysis in sports in general, and golf in particular, has recently risen. However, research in the area of video analysis has lagged well behind these trends in current coaching practice. The current study was designed to assess changes in performance as a result of using video feedback as part of an instructional session. Forty-eight golfers (24 novices; 24 skilled players) performed a pre-test in which twelve swings were recorded using an indoor launch monitor system. The participants were then randomly assigned to a lesson in one of three groups: 1) Verbal coaching (V), 2) Verbal +Video coaching (V+V), and 3) Self-Guided (SG) practice. All groups were then retested to determine the extent to which the various training conditions impacted overall swing characteristics. The results indicated that the positive effects of video feedback were: A) limited in scope, and b) observed to a greater extent in more skilled performers. The results suggest that while more skilled players were able to glean useful timing information from video feedback, these same conditions may in fact impede the learning process in novice performers.

Response Biases: Tonic Neck Response and Aftercontraction Phenomenon

Abstract In the present experiments, an attempt was made to document possible response biases resulting from changes in head position and to determine if this source of bias is additive or interactive in its influence on learned motor responses when paired with response biases arising from the aftercontraction phenomenon (Shea, Shebilske, Kohl, & Guadagnoli, 1991). The results of Experiments 1 and 2 indicated that the influence of head position on response biases was dependent on head position during acquisition and on the direction in which the head was turned with respect to the flexors and extensors involved in the movement; the magnitude of the effect tended to increase as the force of the contraction increased. In Experiment 3, increases in the intensity of a prior contraction were reflected in the magnitude of the response bias and changes in head position were reflected in corresponding changes in response biases. These findings are consistent with the influence of the aftercontraction phenomenon a...

Challenge Point Framework and Efficient Learning of Golf

The current paper overviews a framework for motor learning and uses this framework to suggest efficient means to practice golf. The framework, known as the Challenge Point Framework, was built from years of laboratory and field studies that have been shown to enhance learning. Throughout the paper, the relationship between practice protocols and the learning that results from them are discussed and where appropriate golf-related examples are provided for the reader to be able to translate from motor learning and neuroscience research to the application of golf. Ultimately the aim of the article is to show how the Challenge Point Framework can be used to enhance golf performance