Mark D. Ricard

A comparison of plyometric training techniques for improving vertical jump ability and energy production

This study was done to determine which plyometric training technique is best for improving vertical jumping ability, positive energy production, and elastic energy utilization. Data were collected before and after 12 weeks of jump training and were analyzed by ANOVA. Subjects (N = 28) performed jumps under 3 testing conditions—squat jump, countermovement jump, and depth jump—and were randomly assigned to 1 of 3 groups: control, depth jump training, or countermovement jump training. The 12-week program resulted in significant increases in vertical jump height for both training groups. The depth jump group significantly improved their vertical jump height in all 3 jumps. None of the training methods improved utilization of elastic energy. In activities involving dynamic stretch-shorten cycles, drop jump training was superior to countermovement jump training due to neuromuscular specificity. This study provides support for the strength and conditioning professional to include plyometric depth jump training as part of the athletes overall program for improving vertical jumping ability and concentric contractile performance.

Effects of strength training and vascular occlusion

The purpose of our study was to determine if vascular occlusion produced an additive effect on muscle hypertrophy and strength performance with high strength training loads. Sixteen physically active men were divided into two groups: high-intensity (HI = 6 RM) and moderate-intensity training (MI = 12 RM). An occlusion cuff was attached to the proximal end of the right thigh, so that blood flow was reduced during the exercise. The left leg served as a control, thus was trained without vascular occlusion. Knee extension 1 RM and quadriceps cross-sectional area (MRI) were evaluated pre- and post-8 weeks of training. We only found a main time effect for both strength gains and quadriceps hypertrophy (p < 0.001). Therefore, we conclude that vascular occlusion in combination with high-intensity strength training does not augment muscle strength or hypertrophy when compared to high-intensity strength training alone.

Influence of training background on jumping height.

The aim of this study was to compare the pattern of force production and center of mass kinematics in maximal vertical jump performance between power athletes, recreational bodybuilders, and physically active subjects. Twenty-seven healthy male subjects (age: 24.5 ± 4.3 years, height: 178.7 ± 15.2 cm, and weight: 81.9 ± 12.7 kg) with distinct training backgrounds were divided into 3 groups: power track athletes (PT, n = 10) with international experience, recreational bodybuilders (BB, n = 7) with at least 2 years of training experience, and physically active subjects (PA, n = 10). Subjects performed a 1 repetition maximum (1RM) leg press test and 5 countermovement jumps with no instructions regarding jumping technique. The power-trained group jumped significantly higher (p > 0.05) than the BB and PA groups (0.40 ± 0.05, 0.31 ± 0.04, and 0.30 ± 0.05, respectively). The difference in jumping height was not produced by higher rates of force development (RFD) and shorter center of mass (CM) displacement. Instead, the PT group had greater CM excursion (p > 0.05) than the other groups. The PT and BB groups had a high correlation between jumping height and 1RM test (r = 0.93 and r = 0.89, p > 0.05, respectively). In conclusion, maximum strength seems to be important for jumping height, but RFD does not seem relevant to achieve maximum jumping heights. High RFD jumps should be performed during training only when sport skills have a time constraint for force application.

Limitations of Ordinary Least Squares Models in Analyzing Repeated Measures Data

PURPOSE To a) introduce and present the advantages of linear mixed models using generalized least squares (GLS) when analyzing repeated measures data; and b) show how model misspecification and an inappropriate analysis using repeated measures ANOVA with ordinary least squares (OLS) methodology can negatively impact the probability of occurrence of Type I error. METHODS The effects of three strength-training groups were simulated. Strength gains had two slope conditions: null (no gain), and moderate (moderate gain). Ten subjects were hypothetically measured at five time points, and the correlation between measurements within a subject was modeled as compound symmetric (CS), autoregressive lag 1 (AR(1)), and random coefficients (RC). A thousand data sets were generated for each correlation structure. Then, each was analyzed four times--once using OLS, and three times using GLS, assuming the following variance/covariance structures: CS, AR(1), and RC. RESULTS OLS produced substantially inflated probabilities of Type I errors when the variance/covariance structure of the data set was not CS. The RC model was less affected by the actual variance/covariance structure of the data set, and gave good estimates across all conditions. CONCLUSIONS Using OLS to analyze repeated measures data is inappropriate when the covariance structure is not known to be CS. Random coefficients growth curve models may be useful when the variance/covariance structure of the data set is unknown.

Intermittent exercise as a conditioning activity to induce postactivation potentiation

Postactivation potentiation (PAP) is defined as a short-term increase in voluntary muscle activation following a previous conditioning activity (CA). Controversy about PAP is mostly attributed to the characteristics of the CA and the training status of the subjects. While some studies have found that PAP can be induced by series of 5–10 second maximal voluntary isometric contractions or near maximal dynamic contractions (e.g., 3–5 repetition maximum), others have failed to do so. On the other hand, some studies suggest that intermittent contractions can also induce PAP. However, even though PAP was observed, its duration was not taken into account, leaving ground for further investigations. The purpose of this study was threefold: (a) to verify if PAP can progressively enhance performance of voluntary actions throughout a set of intermittent contractions; (b) to verify PAP duration when induced by an intermittent contractions protocol; and (c) to verify if PAP effects were reproducible in different sessions when induced by intermittent contractions. Ten physically active men, not engaged in strength training, underwent 5 randomized experimental sessions, during which they performed a set of 10 unilateral knee extensions (KE) (1 every 30 seconds) at 60°·s-1 in an isokinetic dynamometer. Peak torque was evaluated over the 10 unilateral KE and at the randomized intervals of 4, 6, 8, 10, and 12 minutes post CA. Peak torque was potentiated 1.3 (±0.79) N·m per unilateral KE, and the potentiation effect persisted for 12 minutes after the last contraction. These findings were reproduced in all 5 experimental sessions. Thus, intermittent conditioning activities seem to be an effective way to produce PAP. However, these activities should be tested in a more real world situation to verify the applicability as a warm-up routine.

A randomized cross-over study of the quality of cardiopulmonary resuscitation among females performing 30:2 and hands-only cardiopulmonary resuscitation

BackgroundHands-Only cardiopulmonary resuscitation (CPR) is recommended for use on adult victims of witnessed out-of-hospital (OOH) sudden cardiac arrest or in instances where rescuers cannot perform ventilations while maintaining minimally interrupted quality compressions. Promotion of Hands-Only CPR should improve the incidence of bystander CPR and, subsequently, survival from OOH cardiac arrest; but, little is known about a rescuers ability to deliver continuous chest compressions of adequate rate and depth for periods typical of emergency services response time. This study evaluated chest compression rate and depth as subjects performed Hands-Only CPR for 10 minutes. For comparison purposes, each also performed chest compressions with ventilations (30:2) CPR. It also evaluated fatigue and changes in body biomechanics associated with each type of CPR.MethodsTwenty healthy female volunteers certified in basic life support performed Hands-Only CPR and 30:2 CPR on a manikin. A mixed model repeated measures cross-over design evaluated chest compression rate and depth, changes in fatigue (chest compression force, perceived exertion, and blood lactate level), and changes in electromyography and joint kinetics and kinematics.ResultsAll subjects completed 10 minutes of 30:2 CPR; but, only 17 completed 10 minutes of Hands-Only CPR. Rate, average depth, percentage at least 38 millimeters deep, and force of compressions were significantly lower in Hands-Only CPR than in 30:2 CPR. Rates were maintained; but, compression depth and force declined significantly from beginning to end CPR with most decrement occurring in the first two minutes. Perceived effort and joint torque changes were significantly greater in Hands-Only CPR. Performance was not influenced by age.ConclusionHands-Only CPR required greater effort and was harder to sustain than 30:2 CPR. It is not known whether the observed greater decrement in chest compression depth associated with Hands-Only CPR would offset the potential physiological benefit of having fewer interruptions in compressions during an actual resuscitation. The dramatic decrease in compression depth in the first two minutes reinforces current recommendations that rescuers take turns performing compressions, switching every two minutes or less. Further study is recommended to determine the impact of real-time feedback and dispatcher coaching on rescuer performance.

Effects of a 4-Week Exercise Program on Balance Using Elastic Tubing as a Perturbation Force for Individuals With a History of Ankle Sprains

STUDY DESIGN Randomized controlled trial with pretraining, posttraining, and follow-up repeated measures. OBJECTIVE To determine the effectiveness of a 4-week elastic resistance exercise program on balance in subjects with and without a history of sprained ankles. BACKGROUND Several researchers have suggested that improving balance may help alleviate the symptoms of functional ankle instability and reduce the rate of recurrent ankle sprains. METHODS AND MEASURES Forty subjects (20 males, 20 females; 20 subjects with chronic ankle instability [CAI], 20 healthy) participated in the study. Ten subjects (5 males, 5 females) from each CAI and healthy group were randomly assigned to either the exercise or control group, resulting in a total of 4 groups. Total travel distance of the center of pressure, monitored using a force platform, was measured before training, after 4 weeks of training, and at a 4-week follow-up. RESULTS There were no interactions between gender, ankle sprain history, or training groups. Balance significantly improved in subjects with and without a history of ankle sprains following 4 weeks of elastic resistance exercises. Mean improvement in balance for the exercise group following training, reflected through a decrease in total travel distance, was -11.1 cm (95% confidence interval: -14.0 to -8.2 cm). These improvements in balance were retained 4 weeks after training. CONCLUSIONS Balance was improved after 4 weeks of elastic resistance exercise in subjects with and without a history of lateral ankle sprains. Balance improvements persisted 4 weeks following the treatment cessation.

A counterbalanced cross-over study of the effects of visual, auditory and no feedback on performance measures in a simulated cardiopulmonary resuscitation

BackgroundPrevious research has demonstrated that trained rescuers have difficulties achieving and maintaining the correct depth and rate of chest compressions during both in and out of hospital cardiopulmonary resuscitation (CPR). Feedback on rate and depth mitigate decline in performance quality but not completely with the residual performance decline attributed to rescuer fatigue. The purpose of this study was to examine the effects of feedback (none, auditory only and visual only) on the quality of CPR and rescuer fatigue.MethodsFifteen female volunteers performed 10 minutes of 30:2 CPR in each of three feedback conditions: none, auditory only, and visual only. Visual feedback was displayed continuously in graphic form. Auditory feedback was error correcting and provided by a voice assisted CPR manikin. CPR quality measures were collected using SkillReporter® software. Blood lactate (mmol/dl) and perceived exertion served as indices of fatigue. One-way and two way repeated measures analyses of variance were used with alpha set a priori at 0.05.ResultsVisual feedback yielded a greater percentage of correct compressions (78.1 ± 8.2%) than did auditory (65.4 ± 7.6%) or no feedback (44.5 ± 8.1%). Compression rate with auditory feedback (87.9 ± 0.5 compressions per minute) was less than it was with both visual and no feedback (p < 0.05). CPR performed with no feedback (39.2 ± 0.5 mm) yielded a shallower average depth of compression and a lower percentage (55 ± 8.9%) of compressions within the accepted 38-50 mm range than did auditory or visual feedback (p < 0.05). The duty cycle for auditory feedback (39.4 ± 1.6%) was less than it was with no feedback (p < 0.05). Auditory feedback produced lower lactate concentrations than did visual feedback (p < 0.05) but there were no differences in perceived exertion.ConclusionsIn this study feedback mitigated the negative effects of fatigue on CPR performance and visual feedback yielded better CPR performance than did no feedback or auditory feedback. The perfect confounding of sensory modality and periodicity of feedback (visual feedback provided continuously and auditory feedback provided to correct error) leaves unanswered the question of optimal form and timing of feedback.

The Comprehensive Muscular Activity Profile (CMAP): Its High Sensitivity, Specificity and Overall Classification Rate for Detecting Submaximal Effort on Functional Capacity Testing

Introduction A traditional problem faced by clinicians attempting to objectively measure musculoskeletal disorders such as low back pain, where there is often primarily soft tissue involvement, is that psychosocial factors (e.g., fear-avoidance, secondary gain) frequently influence the experience/reporting of pain. Nevertheless, there is still a great need for the quantification of physical function, with appropriate criteria in place, in order to help assess both physical impairment and therapeutic endpoint following treatment. One such potentially objective measure is surface electromyographic (sEMG) recordings during purposeful muscular activity and resting states. The present randomized controlled study assessed the potential validity of a new sEMG approach—the comprehensive muscular activity profile (CMAP)—by addressing the following question: can the CMAP accurately document whether a subject is exerting appropriate muscular effort during range-of-motion and lifting testing, or is submaximum effort being exerted? Methods Eighty healthy volunteers were randomly assigned to either: (1) an instruction group encouraging maximum effort on the tests; or (2) an instruction group encouraging “faking” and not putting in maximum effort on the tests. Therapists, who then administered the CMAP protocol (range-of-motion and lifting tests), were kept blind to subject group assignment. They were also asked to complete a rating scale evaluating whether subjects were exerting maximum effort after all the tests were completed. Results In differentiating between the two instruction groups, the CMAP demonstrated high levels of sensitivity [predicting maximum effort on all tests (ranging from 84.6 to 94.9%)]. In contrast, the sensitivity of the therapists’ ratings was much lower (ranging from only 72.5 to 80.0%). Most importantly, when the CMAP data and therapists’ ratings were combined, logistic regression analyses revealed high rates of sensitivity (94.4–97.2%), specificity (84.6–92.3%), and overall classification (90.7–93.3%). Conclusion The results of this study demonstrate the potential utility of the CMAP, combined with therapist ratings, as a valid method of objectively quantifying subject muscular performance and effort during lumbar range-of-motion and lifting tasks.

The impact of state policy on teen dating violence prevalence.

Teen dating violence (TDV) is a serious public health concern that is associated with many negative effects. Studies on TDV prevention most often focus on the evaluation of prevention programs in school and community settings. Much less is known about the effects of policy on TDV prevalence. This study tests a model to explain whether stronger laws regarding TDV, specifically civil protection orders, have an impact on TDV rates in states. Results show that stronger policy, Democratic party control of the governors office, and higher state median income are associated with lower rates of TDV. This study provides solid information regarding the role of civil protection orders as a means of TDV prevention and adds to our knowledge of the efficacy of state-level TDV policy. The information can lead to increased vigor on the part of advocates to strive for specific provisions in the law and to work for gubernatorial candidates who will support such laws.