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Christopher Thomas, Paul A. Jones and Paul Comfort

Purpose:

To determine the reliability of the Dynamic Strength Index (DSI) in college athletes.

Method:

Nineteen male college athletes performed the squat jump (SJ) and isometric midthigh pull (IMTP) to determine peak force, on 2 separate days. Reliability was assessed by intraclass correlation coefficient (ICC), typical error (TE), percentage change in the mean, smallest worthwhile change (SWC), and coefficient of variation (%CV).

Results:

Peak force for the SJ was 2137 ± 499 N and 2781 ± 435 N for the IMTP, resulting in a mean DSI of 0.78 ± 0.19. Peak forces in the SJ (ICC = .99, TE = 57.22 N, change in mean = 0.2%, SWC = 4.7%, CV = 2.6%) and IMTP (ICC = .95, TE = 104.22 N, change in mean = 0.5%, SWC = 3.1%, CV = 3.8%) were considered highly reliable between sessions. However, IMTP peak force was the only variable with an overall TE < SWC. The DSI was also highly reliable (ICC = .97, TE = 0.03, change in mean = −0.3%, SWC = 5.1%, CV = 4.6%) between sessions.

Conclusion:

This study demonstrates that peak force in the SJ and IMTP are reliable, resulting in a reliable assessment of dynamic-force-production capabilities via the DSI. The DSI may be used to guide individualized training interventions and monitor specific adaptations to training. Changes in SJ peak force, IMTP peak force, and DSI were >4.67%, 3.13%, and 5.13%, respectively, identifying meaningful changes in response to training or competition.

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Kris Beattie, Brian P. Carson, Mark Lyons and Ian C. Kenny

Maximum- and reactive-strength qualities both have important roles in athletic movements and sporting performance. Very little research has investigated the relationship between maximum strength and reactive strength. The aim of this study was to investigate the relationship between maximum-strength (isometric midthigh-pull peak force [IMTP PF]) and reactive-strength (drop-jump reactive-strength index [DJ-RSI]) variables at 0.3-m, 0.4-m, 0.5-m, and 0.6-m box heights. A secondary aim was to investigate the between- and within-group differences in reactive-strength characteristics between relatively stronger athletes (n = 11) and weaker athletes (n = 11). Forty-five college athletes across various sports were recruited to participate in the study (age, 23.7 ± 4.0 y; mass, 87.5 ± 16.1 kg; height, 1.80 ± 0.08 m). Pearson correlation results showed that there was a moderate association (r = .302–.431) between maximum-strength variables (absolute, relative, and allometric scaled PF) and RSI at 0.3, 0.4, 0.5 and 0.6 m (P ≤ .05). In addition, 2-tailed independent-samples t tests showed that the RSIs for relatively stronger athletes (49.59 ± 2.57 N/kg) were significantly larger than those of weaker athletes (33.06 ± 2.76 N/kg) at 0.4 m (Cohen d = 1.02), 0.5 m (d = 1.21), and 0.6 m (d = 1.39) (P ≤ .05). Weaker athletes also demonstrated significant decrements in RSI as eccentric stretch loads increased at 0.3-m through 0.6-m box heights, whereas stronger athletes were able to maintain their reactive-strength ability. This research highlights that in specific sporting scenarios, when there are high eccentric stretch loads and fast stretch-shortening-cycle demands, athletes’ reactive-strength ability may be dictated by their relative maximal strength, specifically eccentric strength.

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Christopher A. Bailey, Kimitake Sato, Angus Burnett and Michael H. Stone

The purpose of this investigation was to determine the existence of bilateral strength and force-production asymmetry and evaluate possible differences based on sex, as well as strength level. Asymmetry was assessed during weight-distribution (WtD) testing, unloaded and lightly loaded static- (SJ) and countermovement-jump (CMJ) testing, and isometric midthigh-pull (IMTP) strength testing. Subjects included 63 athletes (31 male, 32 female) for WtD, SJ, and CMJ tests, while 129 athletes (64 male, 65 female) participated in IMTP testing. Independent-samples t tests were used to determine possible differences in asymmetry magnitude between males and females, as well as between strong and weak athletes. Cohen d effect-size (ES) estimates were also used to estimate difference magnitudes. Statistically different asymmetry levels with moderate to strong ESs were seen between males and females in WtD, 0-kg SJ (peak force [PF]), 20-kg SJ (peak power [PP]), 0-kg CMJ (PF, PP, net impulse), and 20-kg CMJ (PF), but no statistical differences were observed in IMTP variables. Dividing the sample into strong and weak groups produced statistically significant differences with strong ES estimates in IMTP PF and rate of force development, and many ESs in jump symmetry variables increased. The results of this investigation indicate that females may be more prone to producing forces asymmetrically than males during WtD and jumping tasks. Similarly, weaker athletes displayed more asymmetry than stronger athletes. This may indicate that absolute strength may play a larger role in influencing asymmetry magnitude than sex.

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Hayden J. Pritchard, Matthew J. Barnes, Robin J. Stewart, Justin W. Keogh and Michael R. McGuigan

∼50%. Small improvements (effect size, ES = 0.43) in isometric midthigh pull (IMTP) and improvements in 30-m sprint time (ES = −1.61) occurred from pretraining to peak values during the 3-week taper. Together, these findings indicate that reducing training volume while maintaining intensity can be an

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Claire J. Brady, Andrew J. Harrison, Eamonn P. Flanagan, G. Gregory Haff and Thomas M. Comyns

acceleration phase. Therefore, these strength qualities could be different between males and females. 3 Maximum strength has been defined as the ability to produce maximum force against an external resistance. 4 The isometric midthigh pull (IMTP) and isometric squat (ISqT) are 2 tests commonly used to test an

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Kevin M. Carroll, Jake R. Bernards, Caleb D. Bazyler, Christopher B. Taber, Charles A. Stuart, Brad H. DeWeese, Kimitake Sato and Michael H. Stone

questioning by the investigators. Subjects were considered well-trained based on their baseline isometric midthigh pull peak force (IPF; 4403.61 [664.69] N) and allometrically scaled isometric peak force (IPFa; 226.04 [25.81] N/kg 0.67 ), which were similar to or greater than previously reported values for

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Paul Comfort, Christopher Thomas, Thomas Dos’Santos, Paul A. Jones, Timothy J. Suchomel and John J. McMahon

exercises, 2 – 4 , 6 and peak force (PF) assessed during the isometric midthigh pull (IMTP) 5 , 9 , 10 and the isometric squat. 11 While 1-repetition-maximum assessments are easy to conduct, can be incorporated into scheduled training sessions, demonstrate high reliability, 12 , 13 and are regularly used

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We, the Authors, Editors, and Publishers of the International Journal of Sports Physiology and Performance ( IJSPP ), have retracted the following article in whole: Dos’Santos T, Jones PA, Kelly J, McMahon JJ, Comfort P, Thomas C Effect of sampling frequency on isometric midthigh-pull kinetics

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Michael H. Stone, William A. Sands, Kyle C. Pierce, Michael W. Ramsey and G. Gregory Haff

Purpose:

To assess the effects of manipulating the loading of successive sets of midthigh clean pulls on the potentiation capabilities of 7 international-level US weightlifters (4 men, 3 women).

Methods:

Isometric and dynamic peak-force characteristics were measured with a force plate at 500 Hz. Velocity during dynamic pulls was measured using 2 potentiometers that were suspended from the top of the right and left sides of the testing system and attached to both ends of the bar. Five dynamic-performance trials were used (in the following order) as the potentiation protocol: women at 60, 80, 100, 120, and 80 kg and men at 60, 140, 180, 220, and 140 kg. Trials 2 vs 5 were specifically analyzed to assess potentiation capabilities. Isometric midthigh pulls were assessed for peak force and rate of force development. Dynamic lifts were assessed for peak force (PF), peak velocity (PV), peak power (PP), and rate of force development (RFD).

Results:

Although all values (PF, PV, PP, and RFD) were higher postpotentiation, the only statistically higher value was found for PV (ICCα = .95, P = .011, η2 = .69).

Conclusions:

Results suggest that manipulating set-loading configuration can result in a potentiation effect when heavily loaded sets are followed by a lighter set. This potentiation effect was primarily characterized by an increase in the PV in elite weightlifters.

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Lina E. Lundgren, Tai T. Tran, Sophia Nimphius, Ellen Raymond, Josh L. Secomb, Oliver R.L. Farley, Robert U. Newton, Julie R. Steele and Jeremy M. Sheppard

Purpose:

To develop and evaluate a multifactorial model based on landing performance to estimate injury risk for surfing athletes.

Methods:

Five measures were collected from 78 competitive surfing athletes and used to create a model to serve as a screening tool for landing tasks and potential injury risk. In the second part of the study, the model was evaluated using junior surfing athletes (n = 32) with a longitudinal follow-up of their injuries over 26 wk. Two models were compared based on the collected data, and magnitude-based inferences were applied to determine the likelihood of differences between injured and noninjured groups.

Results:

The study resulted in a model based on 5 measures—ankle-dorsiflexion range of motion, isometric midthigh-pull lower-body strength, time to stabilization during a drop-and-stick (DS) landing, relative peak force during a DS landing, and frontal-plane DS-landing video analysis—for male and female professional surfers and male and female junior surfers. Evaluation of the model showed that a scaled probability score was more likely to detect injuries in junior surfing athletes and reported a correlation of r = .66, P = .001, with a model of equal variable importance. The injured (n = 7) surfers had a lower probability score (0.18 ± 0.16) than the noninjured group (n = 25, 0.36 ± 0.15), with 98% likelihood, Cohen d = 1.04.

Conclusions:

The proposed model seems sensitive and easy to implement and interpret. Further research is recommended to show full validity for potential adaptations for other sports.