Mechanical Demands of the Hang Power Clean and Jump Shrug: A Joint-level Perspective

The purpose of this study was to investigate the joint- and load-dependent changes in the mechanical demands of the lower extremity joints during the hang power clean (HPC) and the jump shrug (JS). Fifteen male lacrosse players were recruited from an NCAA DI team, and completed three sets of the HPC and JS at 30%, 50%, and 70% of their HPC 1-Repetition Maximum (1-RM HPC) in a counterbalanced and randomized order. Motion analysis and force plate technology were used to calculate the positive work, propulsive phase duration, and peak concentric power at the hip, knee, and ankle joints. Separate three-way analysis of variances were used to determine the interaction and main effects of joint, load, and lift type on the three dependent variables. The results indicated that the mechanics during the HPC and JS exhibit joint-, load-, and lift-dependent behavior. When averaged across joints, the positive work during both lifts increased progressively with external load, but was greater during the JS at 30% and 50% of 1-RM HPC than during the HPC. The JS was also characterized by greater hip and knee work when averaged across loads. The joint-averaged propulsive phase duration was lower at 30% than at 50% and 70% of 1-RM HPC for both lifts. Furthermore, the load-averaged propulsive phase duration was greater for the hip than the knee and ankle joint. The jointaveraged peak concentric power was the greatest at 70% of 1-RM for the HPC and at 30% to 50% of 1-RM for the JS. In addition, the joint-averaged peak concentric power of the JS was greater than that of the HPC. Furthermore, the load-averaged peak knee and ankle concentric joint powers were greater during the execution of the JS than the HPC. However, the loadaveraged power of all joints differed only during the HPC, but was similar between the hip and knee joints for the JS. Collectively, these results indicate that compared to the HPC the JS is characterized by greater hip and knee positive joint work, and greater knee and ankle peak concentric joint power, especially if performed at 30 and 50% of 1-RM HPC. This study provides important novel information about the mechanical demands of two commonly used exercises and should be considered in the design of resistance training programs that aim to improve the explosiveness of the lower extremity joints

Effect of onset threshold on kinetic and kinematic variables of a weightlifting derivative containing a first and second pull

This study sought to determine the effect of different movement onset thresholds on both the reliability and absolute values of performance variables during a weightlifting derivative containing both a first and second pull. Fourteen men (age: 25.21 ± 4.14 years; body mass: 81.1 ± 11.4 kg; and 1 repetition maximum [1RM] power clean: 1.0 ± 0.2 kg·kg) participated in this study. Subjects performed the snatch-grip pull with 70% of their power clean 1RM, commencing from the mid-shank, while isolated on a force platform. Two trials were performed enabling within-session reliability of dependent variables to be determined. Three onset methods were used to identify the initiation of the lift (5% above system weight [SW], the first sample above SW, or 10 N above SW), from which a series of variables were extracted. The first peak phase peak force and all second peak phase kinetic variables were unaffected by the method of determining movement onset; however, several remaining second peak phase variables were significantly different between methods. First peak phase peak force and average force achieved excellent reliability regardless of the onset method used (coefficient of variation [CV] 0.90). Similarly, during the second peak phase, peak force, average force, and peak velocity achieved either excellent or acceptable reliability (CV 0.80) in all 3 onset conditions. The reliability was generally reduced to unacceptable levels at the first sample and 10 N method across all first peak measures except peak force. When analyzing a weightlifting derivative containing both a first and second pull, the 5% method is recommended as the preferred option of those investigated

Predicting morphotropic phase boundary locations and transition temperatures in Pb- and Bi-based perovskite solid solutions from crystal chemical data and first-principles calculations

Using data obtained from first-principles calculations, we show that the position of the morphotropic phase boundary (MPB) and transition temperature at MPB in ferroelectric perovskite solutions can be predicted with quantitative accuracy from the properties of the constituent cations. We find that the mole fraction of PbTiO$_3$ at MPB in Pb(B$'$B$''$)O$_3$-PbTiO$_3$, BiBO$_3$-PbTiO$_3$ and Bi(B$'$B$''$)O$_3$-PbTiO$_3$ exhibits a linear dependence on the ionic size (tolerance factor) and the ionic displacements of the B-cations as found by density functional theory calculations. This dependence is due to competition between the local repulsion and A-cation displacement alignment interactions. Inclusion of first-principles displacement data also allows accurate prediction of transiton temperatures at the MPB. The obtained structure-property correlations are used to predict morphotropic phase boundaries and transition temperatures in as yet unsynthesized solid solutions.Comment: Accepted for publication in J. Appl. Phy

Comparison of methods of calculating dynamic strength index

Purpose: To determine the reliability and variability of dynamic strength index (DSI) calculated from squat jump (SJ) (DSI-SJ) versus countermovement jump (CMJ) (DSI-CMJ) peak force (PF) and to compare DSI values between methods. Methods: Male youth soccer and rugby league players (n = 27; age = 17.2 ± 0.7 years; height = 173.9 ± 5.7 cm; body mass = 71.1 ± 7.2 kg) performed 3 trials of the SJ, CMJ and isometric mid-thigh pull (IMTP), on two separate days. DSI was calculated by dividing the PF during each jump by the IMTP PF. Results: DSI-SJ exhibited moderate (intraclass correlation coefficient (ICC) = 0.419) within-session reliability and high variability (percentage coefficient of variation (%CV) = 15.91) during session one; however, this improved noticeably during session two (ICC = 0.948; %CV = 4.03). Contrastingly, DSI-CMJ showed nearly perfect within-session reliability (ICC = 0.920-0.952) and low variability (%CV = 3.80-4.57) for both sessions. Moreover, DSI-SJ values demonstrated a small yet significant increase between sessions (P = 0.01, d = 0.37), whereas only a trivial and non-significant increase was observed for DSI-CMJ between sessions (P = 0.796 d = 0.07). Between-session reliability was very high for the DSI-SJ (ICC = 0.741) and nearly perfect for the DSI-CMJ (ICC = 0.924). There was no significant or meaningful difference (P = 0.261; d = 0.12) between DSI-SJ (0.82 ± 0.18) and DSI-CMJ (0.84 ± 0.15). Conclusions: Practitioners should use DSI-CMJ as it is a more reliable measure than DSI-SJ, although it produces similar ratios

One-repetition-maximum measures or maximum bar-power output: which Is more related to sport performance?

Purpose: This study compared the associations between optimum power loads and 1-repetition maximum (1RM) values (assessed in half-squat [HS] and jump squat [JS] exercises) and multiple performance measures in elite athletes. Methods: Sixty-one elite athletes (fifteen Olympians) from four different sports (track and field [sprinters and jumpers], rugby sevens, bobsled, and soccer) performed squat and countermovement jumps, HS exercise (for assessing 1RM), HS and JS exercises (for assessing bar-power output), and sprint tests (60-m for sprinters and jumpers and 40-m for the other athletes). Pearson’s product moment correlation test was used to determine relationships between 1RM and bar-power outputs with vertical jumps and sprint times in both exercises. Results: Overall, both measurements were moderately to near perfectly related to speed performance (r values varying from -0.35 to -0.69 for correlations between 1RM and sprint times, and from -0.36 to -0.91 for correlations between bar-power outputs and sprint times; P< 0.05). However, on average, the magnitude of these correlations was stronger for power-related variables, and only the bar-power outputs were significantly related to vertical jump height. Conclusions: The bar-power outputs were more strongly associated with sprint-speed and power performance than the 1RM measures. Therefore, coaches and researchers can use the bar-power approach for athlete testing and monitoring. Due to the strong correlations presented, it is possible to infer that meaningful variations in bar-power production may also represent substantial changes in actual sport performance

THE EFFECT OF ANTAGONIST CONDITIONING CONTRACTIONS ON LOWER AND UPPER BODY POWER TESTS

This study assessed the effect of antagonist conditioning contractions (ACC) on lower and upper body power tests. Six subjects performed the bilateral countermovement jump and the supine medicine ball chest throw on a force platform in baseline conditions and after ACC. A repeated measures ANOVA was used to compare performance between the baseline conditions and the ACC condition. Analysis demonstrated no significant main effects for GRF (p = 0.41) or RFD (p = 0.55) for the countermovement jump. Additionally, there were no significant main effects for GRF (p = 0.85) or RFD (p = 0.95) for the medicine ball throw. This study demonstrated that maximal short term ACC do not enhance multi-joint power tests such as the countermovement jump and medicine ball throw

An investigation into the effects of excluding the catch phase of the power clean on force-time characteristics during isometric and dynamic tasks

The aims of this study were to compare the effects of the exclusion or inclusion of the catch phase during power clean (PC) derivatives on force-time characteristics during isometric and dynamic tasks, after two 4-week mesocycles of resistance training. Two strength matched groups completed the twice-weekly training sessions either including the catch phase of the PC derivatives (Catch group: n = 16; age 19.3 ± 2.1 years; height 1.79 ± 0.08 m; body mass 71.14 ± 11.79 kg; PC 1 repetition maximum [1RM] 0.93 ± 0.15 kg·kg-1) or excluding the catch phase (Pull group: n = 18; age 19.8 ± 2.5 years; height 1.73 ± 0.10 m; body mass 66.43 ± 10.13 kg; PC 1RM 0.91 ± 0.18 kg·kg-1). The Catch and Pull groups both demonstrated significant (p ≤ 0.007, power ≥0.834) and meaningful improvements in countermovement jump height (10.8 ± 12.3%, 5.2 ± 9.2%), isometric mid-thigh pull performance (force [F]100: 14.9 ± 17.2%, 15.5 ± 16.0%, F150: 16.0 ± 17.6%, 16.2 ± 18.4%, F200: 15.8 ± 17.6%, 17.9 ± 18.3%, F250: 10.0 ± 16.1%,10.9 ± 14.4%, peak force: 13.7 ± 18.7%, 9.7 ± 16.3%), and PC 1RM (9.5 ± 6.2%, 8.4 ± 6.1%), before and after intervention, respectively. In contrast to the hypotheses, there were no meaningful or significant differences in the percentage change for any variables between groups. This study clearly demonstrates that neither the inclusion nor exclusion of the catch phase of the PC derivatives results in any preferential adaptations over two 4-week, in-season strength and power, mesocycles

THE OSTEOGENIC POTENTIAL OF SUPERMAXIMAL SQUAT LOADS

This study evaluated the ground reaction force (GRF) and rate of force development (RFD) of the back squat at 3 different loads. Twelve subjects performed the back squat with 80%, 100%, and 120% of their 1 repetition maximum (RM) on a force platform. A two way repeated measures ANOVA revealed significant main effects for GRF for both the eccentric (p &#8804; 0.001) and concentric (p &#8804; 0.001) phases but no interaction between phase and GRF or RFD (p < 0.05). No significant main effects were found for RFD for the eccentric (p = 0.09) and concentric phases (p = 0.38). Post hoc analyses demonstrated that back squats at 120% produced the highest GRF in the eccentric and concentric conditions. Mean RFD was highest, and trending toward significance, during the eccentric phase at 100% of 1 RM condition

ELECTROMYOGRAPHICAL ANALYSIS OF LOWER EXTREMITY MUSCLE ACTIVATION DURING VARIATIONS OF THE LOADED STEP UP EXERCISE

This study evaluated the biceps femoris, gluteus maximus, gluteus medius, rectus femoris, semitendonosus, vastus lateralis, and vastus medialis activation during four variations of the step up exercise. The exercises included the step up, crossover step up, diagonal step up, and lateral step up. Fifteen women who regularly engaged in lower body resistance training performed the four exercises with 6RM loads on a 45.72cm plyometric box. Data were collected with a telemetered EMG system, and RMS values were calculated for EMG data for eccentric and concentric phases. Results of a repeated measures ANOVA (p&#8804;0.05) revealed a variety of differences in muscle activation between the exercises