The Modified Reactive Strength Index Is a Valid Measure of Lower-Body Explosiveness in Male and Female High School Athletes.

ABSTRACT: Witte, BC, Schouten, TC, Westphal, JA, VanZile, AW, Jones, DD, Widenhoefer, TL, Dobbs, WC, Jagim, AR, Luedke, JA, and Almonroeder, TG. The modified reactive strength index is a valid measure of lower-body explosiveness in male and female high school athletes. J Strength Cond Res XX(X): 000-000, 2024-The modified reactive strength index (mRSI) is a commonly used metric to quantify lower-body explosiveness during countermovement jump (CMJ) performance. However, few studies have attempted to examine its validity as a measure of explosiveness, particularly among high school athletes. The purpose of this study was to examine the validity of the mRSI as a measure of lower-body explosiveness among a relatively large sample of male and female high school athletes from various sports. As part of this study, male (n = 132) and female (n = 43) high school athletes performed CMJs, while ground reaction forces were recorded using a force platform. The vertical ground reaction force data collected during the CMJs were used to derive the following variables: peak force (PF), peak power, time to PF, time to take-off, peak rate of force development, and the mRSI. Principal component analysis was applied and reduced these variables into 2 components related to "force" and "speed." The mRSI loaded on both the force (loading = 0.82) and speed (loading = -0.46) components, indicating that it incorporates elements of both force and speed, although it loaded more strongly on the force component than the speed component. The observed pattern of cross-loading suggests that the mRSI is generally a valid measure of lower-body explosiveness for male and female high school athletes.

Predicting First-Time National Physical Therapy Examination Performance for Graduates of an Entry-Level Physical Therapist Education Program.

INTRODUCTION: The National Physical Therapy Examination (NPTE) is a standardized examination designed to assess competence after graduation from an entry-level physical therapist education program. REVIEW OF LITERATURE: Previous studies have identified applicant and student variables that are related to NPTE performance, with applicant variables reflecting performance before admission and student variables reflecting performance after admission. However, there are very few articles describing how these variables can be combined to predict NPTE performance. The purpose of this study was to develop, evaluate, and describe models to predict first-time NPTE scores and NPTE outcomes (pass vs fail), based on various applicant and student variables related to academic performance. SUBJECTS: Pre- and postadmission data and NPTE scores were recorded for 185 individuals who graduated from an entry-level physical therapist education program. METHODS: Multiple linear regression was used to develop a model to predict NPTE scores, and binary logistic regression was used to develop a model to predict NPTE outcomes (pass vs fail). RESULTS: A model including undergraduate prerequisite grade point average, grade point average in basic science courses taken during the program, and comprehensive examination scores combined to explain 30.9% of the variance in NPTE scores and accurately predicted NPTE outcomes (pass vs fail) 81.1% of the time. DISCUSSION: In general, our findings support the notion that prediction of NPTE performance should be based on a combination of applicant and student variables. The models described in this article could be used to identify students who may be likely to struggle on the NPTE, making it possible to provide additional support to these students. CONCLUSION: Various applicant and student variables related to academic performance can be combined to predict NPTE performance. The results of this study provide a framework for programs interested in applying models to predict NPTE performance.

Kinetic Asymmetry During a Repetitive Tuck Jump Task in Athletes with a History of Anterior Cruciate Ligament Reconstruction.

BACKGROUND: Athletes who have undergone anterior cruciate ligament reconstruction typically exhibit relatively high/rapid loading of their uninvolved limb during bilateral landing and jumping (vs. their limb that underwent reconstruction), which may place their uninvolved limb at risk for injury. However, previous studies have only examined forces and loading rates for tasks involving an isolated land-and-jump. PURPOSE: The purpose of this study was to examine bilateral landing and jumping kinetics during performance of a repetitive tuck jump task in athletes who had undergone anterior cruciate ligament reconstruction and completed rehabilitation. STUDY DESIGN: Cross-sectional study. METHODS: Nine athletes (four males, five females) participated in this study. All participants had undergone successful unilateral anterior cruciate ligament reconstruction, had completed post-operative rehabilitation, and were in the process of completing return-to-sport testing. Athletes performed a repetitive tuck jump task for 10 seconds, while ground reaction forces were recorded for their uninvolved and involved limbs via separate force platforms. Two-way analysis of variance, for within-subjects factors of limb and cycle, was performed for the impact forces, loading rates, and propulsive forces from the first five land-and-jump cycles completed. RESULTS: There was not a limb-by-cycle interaction effect or main effect of cycle for the impact forces, loading rates, or propulsive forces; however, there was a main effect of limb for the impact forces (F(1, 8) = 14.64; p=0.005), loading rates (F(1, 8) = 5.60; p=0.046), and propulsive forces (F(1, 8) = 10.38; p=0.012). Impact forces, loading rates, and propulsive forces were higher for the uninvolved limb, compared to the involved limb, over the five land-and-jump cycles analyzed. CONCLUSION: The athletes in this study consistently applied higher and more rapid loads to their uninvolved limb over multiple land-and-jump cycles. This may help to explain the relatively high injury rates for the uninvolved limb in athletes who have returned to sport following anterior cruciate ligament reconstruction.

The effects of drop vertical jump technique on landing and jumping kinetics and jump performance.

The drop vertical jump is a popular plyometric exercise. Two distinct techniques are commonly used to initiate the drop vertical jump. With the 'step-off' technique, athletes step off a raised platform with their dominant limb, while their non-dominant limb remains on the platform. In contrast, with the 'drop-off' technique, athletes lean forward and drop off the platform, with both feet leaving the platform more simultaneously. The purpose of this study was to compare landing and jumping kinetics, inter-limb kinetic symmetry, and jump performance when individuals used the step-off and drop-off techniques, and to examine whether potential differences between these techniques are affected by platform height. Sixteen subjects completed drop vertical jumps with the drop-off and step-off techniques, from relatively low and high platform heights. Ground reactions forces were recorded for the dominant and non-dominant limbs during the land-and-jump phase of the drop vertical jump. Subjects demonstrated greater inter-limb asymmetry in peak impact forces when using the step-off technique, vs. the drop-off technique. This difference between the techniques was consistent across platform heights. The step-off technique appears to result in greater asymmetry in limb loading, which could contribute to the development of neuromuscular asymmetries between the limbs and/or asymmetric landing patterns.

Verbal Instruction Reduces Patellofemoral Joint Loading During Bodyweight Squatting.

CONTEXT: The bodyweight squat exercise is a common component for treatment and prevention of patellofemoral pain; however, it can also place a high load on the patellofemoral joint. Restricting anterior motion of the knees relative to the toes during squatting appears to reduce patellofemoral loading. However, exercise professionals typically rely on verbal instructions to alter squat technique. OBJECTIVE: To evaluate the influence of verbal instructions regarding squat technique on patellofemoral joint loading. DESIGN: Cross-sectional study. SETTING: Motion analysis laboratory. PARTICIPANTS: Eleven uninjured females. INTERVENTION: Participants performed bodyweight squats before (baseline) and after receiving verbal instructions to limit anterior knee motion. Two different types of verbal instruction were used, one intended to promote an internal focus of attention and the other intended to promote an external focus of attention. Three-dimensional kinematics and kinetics were recorded using a multicamera system and force plate. MAIN OUTCOME MEASURES: Sagittal plane patellofemoral joint forces and stress were estimated using a musculoskeletal model. RESULTS: Participants demonstrated a reduction in patellofemoral joint forces (35.4 vs 31.3 N/kg; P = .01) and stress (10.7 vs 9.2 mPa; P = .002) after receiving instructions promoting an internal focus of attention, compared with their baseline trials. Participants also demonstrated a reduction in patellofemoral joint forces (35.4 vs 32.3 N/kg; P = .03) and stress (10.7 vs 9.6 mPa; P = .04) after receiving instructions promoting an external focus of attention (vs baseline). However, there were no significant differences in patellofemoral forces (P = .84) or stress (P = .41) for trials performed with an internal versus external attentional focus. CONCLUSION: It appears that verbal instruction regarding knee position influences patellofemoral joint loading during squatting.

Training rugby athletes with an external attentional focus promotes more automatic adaptions in landing forces.

Training to reduce landing forces is a common component of anterior cruciate ligament injury prevention programmes. The purpose of this study was to compare the effects of training incorporating instructions promoting an internal versus external attentional focus on landing forces in adolescent rugby athletes. Twenty-two rugby athletes were randomly allocated to groups that received instructions promoting an internal versus an external focus during a two week training programme. Landing forces were recorded before and after completion of the programme. During follow-up testing, landings were performed with and without a secondary cognitive task. Both groups exhibited a similar reduction in landing forces following training for trials performed without the secondary cognitive task. However, the groups responded differently when the secondary cognitive task was imposed. Athletes who were trained with an internal focus demonstrated a prominent increase in landing forces for trials that included the secondary cognitive task (vs. trials performed without the secondary cognitive task), whereas the secondary cognitive task had minimal influence for athletes who were trained with an external focus. It appears that training with an external focus may promote adaptations in landing mechanics that can be implemented more automatically.