Association and Agreement between Reactive Strength Index and Reactive Strength Index-Modified Scores

Evaluation of the impact of a 3-week specific-sport rehabilitation program on neuromotor control during single-leg countermovement-jump tests in professional soccer players with lower-limb injuries

Purpose

This study investigated the evolution of neuromotor control during a typical short sport-specific rehabilitation program (SSR) in professional soccer players who had incurred a major lower-limb injury (n = 15, chondral and muscle injuries, ACL-reconstruction).

Methods

All injured participants (n = 15) were in the on-field rehabilitation phase of their specific sport rehabilitation process, prior to return to play. An experimental group (EG, chondral and muscle injuries, ACL-reconstruction) followed a 3-week SSR-program composed of muscular and core strengthening (weightlifting, functional stability, explosivity and mobility exercises), running and cycling, neuromotor reprogramming, cognitive development and specific soccer on-field rehabilitation (acceleration, braking, cutting, dual-contact, high-speed-running, sprint, jump, drills with ball). Neuromotor control via analysis of movement kinematics, muscle activation and kinetic parameters was evaluated using a single-leg Countermovement-Jump, pre- and post- rehabilitation program. A control group (n = 22) of healthy soccer players of similar standards performed the same single-leg Countermovement-Jump to provide reference values regarding the level to be attained by the injured players for return to play.

Results

In the experimental group, almost all kinetic analyses values progressed during the program and significantly for concentric Rate-of-Force-Development (p < 0.05), height jump (p < 0.001) and Reactive-Strength-Index Modified (p < 0.001) but remained lower than control group values for RSI-Mod (p < 0.05) and RFDconcentricLate (p < 0.001). Activation changed (p < 0.05) for all muscles except for rectus femoris and medial gastrocnemius in the pushing phase and rectus femoris during landing in the EG. Activation of all muscles decreased for EG, except for semitendinous which increased. Regarding kinematic analyses during the landing phase, there were a significant decrease in peak trunk flexion (p < 0.001) and lateroflexion (p < 0.001) and an increase in peak knee flexion (p < 0.001) for both legs. Trunk flexion (p < 0.001) and lateroflexion (p < 0.001) values were again higher for EG while knee flexion remained significantly lower than the CG (p < 0.001).

Conclusion

The SSR generally improved neuromotor control suggesting that the present specific sport rehabilitation program, albeit of only three weeks duration, was effective in aiding elite footballers recover their neuromotor qualities although this was potentially insufficient to return to the values observed in healthy players.

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 38(8): 1428-1432, 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.

Unsupervised Machine Learning in Countermovement Jump and Isometric Mid-Thigh Pull Performance Produces Distinct Combat and Physical Fitness Clusters in Male and Female U.S. Marine Corps Recruits

INTRODUCTION

Several challenges face the U.S. Marine Corps (USMC) and other services in their efforts to design recruit training to augment warfighter mobility and resilience in both male and female recruits as part of an integrated model. Strength and power underpin many of the physical competencies required to meet the occupational demands one might face in military. As the military considers adopting force plate technology to assess indices of strength and power, an opportunity presents itself for the use of machine learning on large datasets to deduce the relevance of variables related to performance and injury risk. The primary aim of this study was to determine whether cluster analysis on baseline strength and power data derived from countermovement jump (CMJ) and isometric mid-thigh pull (IMTP) adequately partitions men and women entering recruit training into distinct performance clusters. The secondary aim of this study is then to assess the between-cluster frequencies of musculoskeletal injury (MSKI).

MATERIALS AND METHODS

Five hundred and sixty-five males (n = 386) and females (n = 179) at the Marine Corps Recruit Depots located at Parris Island and San Diego were enrolled in the study. Recruits performed CMJ and IMTP tests at the onset of training. Injury data were collected via medical chart review. Combat fitness test (CFT) and physical fitness test (PFT) results were provided to the study team by the USMC. A k-means cluster analysis was performed on CMJ relative peak power, IMTP relative peak force, and dynamic strength index. Independent sample t-tests and Cohen's d effect sizes assessed between-cluster differences in CFT and PFT performance. Differences in cumulative incidence of lower extremity %MSKIs were analyzed using Fisher's exact test. Relative risk and 95% confidence intervals (CIs) were also calculated.

RESULTS

The overall effects of cluster designation on CMJ and IMTP outcomes ranged from moderate (relative peak power: d = -0.68, 95% CI, -0.85 to -0.51) to large (relative peak force: d = -1.69, 95% CI, -1.88 to -1.49; dynamic strength index: d = 1.20, 95% CI, 1.02-1.38), indicating acceptable k-means cluster partitioning. Independent sample t-tests revealed that both men and women in cluster 2 (C2) significantly outperformed those in cluster 1 (C1) in all events of the CFT and PFT (P < .05). The overall and within-gender effect of cluster designation on both CFT and PFT performance ranged from small (d > 0.2) to moderate (d > 0.5). Men in C2, the high-performing cluster, demonstrated a significantly lower incidence of ankle MSKI (P = .04, RR = 0.2, 95% CI, 0.1-1.0). No other between-cluster differences in MSKI were statistically significant.

CONCLUSIONS

Our results indicate that strength and power metrics derived from force plate tests effectively partition USMC male and female recruits into distinct performance clusters with relevance to tactical and physical fitness using k-means clustering. These data support the potential for expanded use of force plates in assessing readiness in a cohort of men and women entering USMC recruit training. The ability to pre-emptively identify high and low performers in the CFT and PFT can aid in leadership developing frameworks for tailoring training to enhance combat and physical fitness with benchmark values of strength and power.

Comparing autoregulatory progressive resistance exercise and velocity-based resistance training on jump performance in college badminton athletes

Objectives

Jumping ability has been identified as a key factor that influences the performance of badminton athletes. Autoregulatory progressive resistance exercise (APRE) and velocity-based resistance training (VBRT) are commonly used approaches to enhance muscle strength and have been shown to accurately monitor the development of explosive power to improve jumping ability. This study aims to investigate the effects of APRE and VBRT on badminton athletes' jumping ability and to provide practical insights into improving their jumping performance during competitions.

Methods

Upon completing familiarization and pretesting, 18 badminton athletes were included and completed the training intervention (age, 21.4 ± 1.4 years; stature, 170.1 ± 7.3 cm; body mass, 65.9 ± 12 kg); they were randomly divided into the APRE group (n = 9) and VBRT group (n = 9). Jumping performance was assessed during the countermovement jump (CMJ), squat jump (SJ), and drop jump (DJ) via SmartJump, with CMJ 's and SJ's jump height, eccentric utilization ratio (EUR), and reactive strength index (RSI). All participants then completed a 4-week in-season resistance training intervention.

Results

(1) The results of the within-group indicated that only the CMJ (pre: 41.56 ± 7.84 vs post: 43.57 ± 7.85, p < 0.05) of the APRE group had significant differences, whereas the SJ, EUR, and RSI were not significantly different (p > 0.05). (2) The results of the intergroups revealed that all indicators had no significant differences (p > 0.05), but APRE had a moderate effect size on the improvement of the CMJ (η2 = 0.244) and EUR (η2 = 0.068) when compared with VBRT.

Conclusions

The results showed that, compared to VBRT, APRE can effectively improve the performance of the reactive athletes' lower limb explosive power in the CMJ in a shorter period of time. The findings indicate that APRE may be useful for coaches seeking to improve the CMJ performance of athletes in the short term.

Kinetics of Depth Jumps Performed by Female and Male National Collegiate Athletics Association Basketball Athletes and Young Adults

The depth jump (DJ) is commonly used to evaluate athletic ability, and has further application in rehabilitation and injury prevention. There is limited research exploring sex-based differences in DJ ground reaction force (GRF) measures. This study aimed to evaluate for sex-based differences in DJ GRF measures and determine sample size thresholds for binary classification of sex. Forty-seven participants from mixed-sex samples of NCAA athletes and young adults performed DJs from various drop heights. Force platform dynamometry and 2-dimensional videography were used to estimate GRF measures. Three-way mixed analysis of variance was used to evaluate main effects and interactions. Receiver operating characteristic (ROC) curve analysis was used to evaluate the combined sensitivity and specificity of dependent measures to sex. Results revealed that reactive strength index scores and rebound jump heights were greater in males than females (p < 0.001). Additionally, young adult females showed greater peak force reduction than young adult males (p = 0.002). ROC curve analysis revealed mixed results that appeared to be influenced by population characteristics and drop height. In conclusion, sex-based differences in DJ performance were observed, and the results of this study provide direction for future DJ investigations.

Acute effects of foam rolling and dynamic stretching on angle-specific change of direction ability, flexibility and reactive strength in male basketball players

The purpose of our study was to determine the acute effects of dynamic stretching (DS), foam rolling (FR) and foam rolling combined with dynamic stretching (Combo) protocols on angle-specific change of direction (COD) ability, drop jump (DJ) performance and flexibility. Using a counterbalance crossover study design, eleven male basketball collegiate players (20.7 ± 0.6 years) were randomly assigned to one of the four protocols - control (CON), DS, FR, Combo - for each session, for a total of four sessions. A more aggressive foam cylinder with raised nodules, which is thought to be effective in stimulating the deep layer of muscle tissue, was used to observe for changes in their performance during sit and reach (SAR), DJ and COD tasks in 45 and 180 degrees. One-way repeated measures ANOVA was used to identify differences of each variable separately between interventions. The SAR after three interventions compared to the CON was significantly improved (F (3,30) = 5.903, P = 0.003, η2 = 0.371). In the 505 test, both limbs failed to show a significant improvement in COD deficit. The non-dominant limb showed a significant improvement of 6.4% after FR when performing the Y-shaped agility (F (3,30) = 4.962, P = 0.0065 < 0.05, η2 = 0.332). In the DJ, the reactive strength index and contact time changed significantly by 17.5% and -17.5% (η2 = 0.518, η2 = 0.571), respectively, immediately after FR. The current research suggested that FR may have an enhancing effect on COD speed in a 45° cutting task and neuromuscular function, while having the potential to improve non-dominant limb deficits in both COD tasks. In contrast, the Combo warm-up protocol did not produce a cumulative effect, suggesting the need for coaches to remain cautious about excessive warm-up duration.