Control Strategy of Maximum Vertical Jumps: the Preferred Countermovement Depth May Not Be Fully Optimized for Jump Height

The aim of the present study was to explore the control strategy of maximum countermovement jumps regarding the preferred countermovement depth preceding the concentric jump phase. Elite basketball players and physically active non-athletes were tested on the jumps performed with and without an arm swing, while the countermovement depth was varied within the interval of almost similar to 30 cm around its preferred value. The results consistently revealed 5.1-11.2 cm smaller countermovement depth than the optimum one, but the same difference was more prominent in non-athletes. In addition, although the same differences revealed a marked effect on the recorded force and power output, they reduced jump height for only 0.1-1.2 cm. Therefore, the studied control strategy may not be based solely on the countermovement depth that maximizes jump height. In addition, the comparison of the two groups does not support the concept of a dual-task strategy based on the trade-off between maximizing jump height and minimizing the jumping quickness that should be more prominent in the athletes that routinely need to jump quickly. Further research could explore whether the observed phenomenon is based on other optimization principles, such as the minimization of effort and energy expenditure. Nevertheless, future routine testing procedures should take into account that the control strategy of maximum countermovement jumps is not fully based on maximizing the jump height, while the countermovement depth markedly confound the relationship between the jump height and the assessed force and power output of leg muscles

Alternating Consecutive Maximum Contraction as a Test of Muscle Function in Athletes Following ACL Reconstruction

The novel test based on isometric alternating consecutive maximal contractions performed by two antagonistic muscles has been recently proposed as a test of muscle function in healthy subjects. The aim of this study was to evaluate reliability and sensitivity of a novel test as a test of knee muscles function in athletes recovering from anterior cruciate ligament reconstruction. Fifteen male athletes with recent ligament reconstruction (4.0 +/- 0.1 months following the surgery) and 15 sport and physical education students participated in the study. Peak torques of the quadriceps and hamstring muscles assessed both through the alternating consecutive maximal contractions and standard isokinetic test performed at 60 ((degrees) under bar)/s and 180 ((degrees) under bar)/s served for calculation of the hamstrings-to-quadriceps ratio and the bilateral difference in strength. When applied on individuals recovering from anterior cruciate ligament reconstruction, the novel test revealed a high within-day reliability and sensitivity for detecting imbalances both between antagonistic and between contralateral muscles. The present findings suggest that alternating consecutive maximal contractions could be used as a test of muscle function that is either complementary or alternative to the isokinetic test, particularly in the laboratories where the isokinetic devices are not available. Potential advantages of the novel test could be both a brief testing procedure and a possibility to conduct it using relatively inexpensive devices such as custom made kits containing a single one-axis force transducer

Kvantnomehaničeskaja model\u27 myščečnoj konrakcii

Rad predstavlja pokušaj kvantnomehaničkog modeliranja procesa mišićne kontrakcije na molekularnom nivou. Primenjeni formalizam traba da omogući sintezu postojećih teorija mišićne kontrakcije. Prvo je izložen osnovni model Schrödingerove jednačine kontraktilnog procesa za nepertubovano stanje istraživanja mikrosistema, zatim su uključene perturbacije potencijalne prirode iz spoljašnjeg elektrostatičkog polja aktuelne mofibrile, a na kraju su analizirane energetske transformacije i određeni kriterijumi za efikasnost mišićnog rada na kvantnomehničkom nivou.An attempt was made to obtain a quantum mechanical model of process of muscle contraction at the molecular level. The formal approach taken should enable a synthesis to be made of current theories of muscle contraction. First, the basic model of Schrödiner equation for the contractile process in the unperturbed state of the microsystem investigated is presented. Perturbations of a potential nature from a external electrostatic field of the actual myofibril are then included. Finally, energetic transformation and defined criteria for efficiency of muscular work on the quantum mechanical level are analyzed

Anthropometric and Physical Performance Profiles of Elite Karate Kumite and Kata Competitors

Karate tournaments consist of two equally important karate disciplines: the kumite and kata competitions. Due to being based both on the distinctive selection of movement techniques and their kinematic and kinetic patterns, we hypothesized that the elite kumite and kata competitors could differ regarding their anthropometric and physical performance profiles. Thirty-one senior male karate competitors of the national karate team (kumite n = 19; kata n = 12) participated in this study. The tests applied included both the assessment of anthropometric (body height, mass and body mass index) and the following physical performance measurements: the adductor and hamstring flexibility (sideward leg splits test), speed and acceleration (20-m sprint test with 10-m acceleration time), explosive power (countermovement and standing triple jump), agility ("T"- test) and aerobic endurance (20-m multistage shuttle run test). The kumite competitors revealed a larger body size through body height (p = 0.01) and mass (p = 0.03), while the differences in body composition were non-significant. The kumite competitors also demonstrated higher acceleration (p = 0.03) and explosive power (standing triple jump; p = 0.03). A 6-7 degrees higher flexibility of the kata competitors remained somewhat below the level of significance (p = 0.09). The findings could be interpreted by the distinctive differences in the movement techniques. Specifically, a higher explosive power could be beneficial for kumite, while both a smaller stature and higher flexibility (particularly of the lower extremity) could be important for the exceptionally low postures of the kata competitors. Although further elucidation is apparently needed, the obtained finding could be of importance for both the early selection and training of karate competitors

Jump training with different loads: effects on jumping performance and power output

To investigate the selective effects of different types of external loads applied in vertical jump training on both the performance and muscle power output of the squat (SJ) and countermovement jump (CMJ). Physically active males practiced maximum unconstrained vertical jumps over an 8-week period with no load, with either a negative or positive load exerted by a nearly constant external force that altered their body weight, and with a loaded vest that increased both the body weight and inertia. The magnitude of all applied loads corresponded to 30 % of body weight. A similar training-associated increase in jump height was observed in all experimental groups in both CMJ (7.4-11.8 %) and SJ (6.4-14.1 %). The relative increase in power output was comparable to the increase in jump height in SJ (7.4-11.5 %), while the power increase in CMJ was relatively small and load-specific (0.5-9.5 %). The observed differences could originate from the changes in the CMJ pattern, reflected through the depth of the counter movement that particularly increased after the training with negative load (42 %) and no load (21 %). The same participants also revealed increased CMJ duration, reduced ground reaction forces, as well as reduced maximum and average power output when compared with other training groups. Jump training with the applied loads could lead to a comparable improvement in jumping performance. However, the observed load-specific adaptations of CMJ pattern could decouple the training-associated increase in jump height from the increase in muscle power output

Evaluation of isokinetic and isometric strength measures for monitoring muscle function recovery after anterior cruciate ligament reconstruction

Although various strength tests and their outcome measures have been proposed for anterior cruciate ligament (ACL) reconstruction (ACLR), their measurement properties still remain relatively underexplored. The aim of this study was to investigate the longitudinal construct validity of the standard isokinetic (IKT) and isometric test (IMT), and of the IMT of alternating consecutive maximal contractions (ACMC). In addition, the concurrent validity of ACMC was assessed and compared with the validity of IMT. The strength of quadriceps and hamstrings in 20 male athletes with an anterior cruciate ligament (ACL) injury were assessed before ACLR, 4 and 6 months after ACLR, by means of IMT, ACMC, and IKT performed at 60 and 180 degrees s(-1). Significant between-session differences in muscle strength variables were found in the involved quadriceps (F gt 6.5; p lt = 0.05), but not in the uninvolved leg (F lt 2.5; p gt 0.05). Coefficients of variations in the uninvolved leg (all below 13.5%) were lower than the involved leg (11.7-22.1%). Intraclass correlation coefficients were moderate-to-high for the uninvolved leg and low-to-high for quadriceps of the involved leg. The concurrent validity of ACMC with respect to the IKT (r = 0.57-0.92; p lt = 0.05) was comparable with the validity of IMT (r = 0.52-0.87; p lt = 0.05). We conclude that the explored longitudinal construct validity of most of the evaluated variables could be sufficiently sensitive to detect the effects of the applied rehabilitation procedures. In addition, the obtained sensitivity and concurrent validity and the potential advantages of ACMC over IMT, all suggest that ACMC could be a particularly promising method for routine testing of neuromuscular function after ACLR

Contralateral limb deficit after ACL-reconstruction: an analysis of early and late phase of rate of force development

The aim of this study was to assess the effect of a unilateral anterior cruciate ligament reconstruction (ACLR) on maximum voluntary contraction (MVC) and explosive strength of both the involved limb and the uninvolved limb. Nineteen male athletes completed a standard isometric testing protocol 4months post-ACLR, while 16 healthy participants served as a control group (CG). The explosive strength of the knee extensors and flexors was assessed as RFD obtained from the slope of the force-time curves over various time intervals. Both muscle groups of the involved limb had significantly lower MVC compared to the uninvolved. The involved limb also had significantly lower RFD in the late phase of contraction (140-250ms) for both knee extensors and flexors (P lt 0.05). There was no difference in MVC between the uninvolved limb and the CG. However, RFD of the uninvolved limb was lower compared to CG for both knee extensors (0-180ms; P lt 0.01) and flexors (0-150ms; P lt 0.05). ACLR leads to lower MVC and explosive strength of the involved limb. As a consequence of potential crossover (presumably neural-mediated) effects, explosive strength deficits could be bilateral, particularly in the early phase of the contraction ( lt 100ms)

A Novel Two-Velocity Method for Elaborate Isokinetic Testing of Knee Extensors

Single outcomes of standard isokinetic dynamometry tests do not discern between various muscle mechanical capacities. In this study, we aimed to (1) evaluate the shape and strength of the force-velocity relationship of knee extensors, as observed in isokinetic tests conducted at a wide range of angular velocities, and (2) explore the concurrent validity of a simple 2-velocity method. Thirteen physically active females were tested for both the peak and averaged knee extensor concentric force exerted at the angular velocities of 30 degrees-240 degrees/s recorded in the 90 degrees-170 degrees range of knee extension. The results revealed strong (0.960 lt R lt 0.998) linear force-velocity relationships that depict the maximum muscle force (i.e. the force-intercept), velocity (velocity-intercept), and power (their product). Moreover, the line drawn through only the 60 degrees and 180 degrees/s data (the 2-velocity method') revealed a high level of agreement with the force-velocity relationship obtained (0.76 lt R lt 0.97; all power lt 0.001); while the force-intercept highly correlated (0.68 lt R lt 0.84; all power0.01) with the directly measured isometric force. The 2-velocity method could therefore be developed into a standard method for isokinetic testing of mechanical capacities of knee extensors and, if supported by further research, other muscles. This brief and fatigue-free testing procedure could discern between muscle force, velocity, and power-producing capacities

Self-preferred initial position could be a viable alternative to the standard squat jump testing procedure

The purpose of this study was to compare both the magnitude and reliability of different variables (knee angle, squat depth, jump height [Hmax], maximum force [Fmax], and maximum power [Pmax]) between the standardized squat jump (SJ) and the SJ performed from the self-preferred position. Eleven team handball players (age: 19.5 +/- 1.1 years; height: 1.88 +/- 0.06 m; and body mass: 82.1 +/- 8.7 kg) and 13 physically active students (age: 20.5 +/- 0.9 years; height: 1.81 +/- 0.06 m; and body mass: 76.6 +/- 6.6 kg) were evaluated on 2 sessions during the standardized SJ (knee angle fixed at 90 degrees) and the self-preferred SJ (self-selected knee angle to maximize Hmax). Two blocks of both 3 standardized SJ and 3 self-preferred SJ were performed on the first session, whereas only 1 block was performed in the second session. The squat depth was smaller for the self-preferred SJ, whereas the knee angle, Fmax, and Pmax were higher for the self-preferred SJ (p lt 0.025). The magnitude of Hmax did not significantly differ between both jump types. Most importantly, the reliability of the mechanical outputs (Hmax, Fmax, and Pmax) was generally higher for the self-preferred SJ (9 of 12 comparisons), whereas only in 2 of 12 comparisons the reliability was meaningfully higher for the standardized SJ. No differences were observed between presumably more (handball players) and less skilled individuals (physically active subjects). These results suggest that the self-preferred SJ should be recommended over the standardized SJ (90 degrees knee angle) because it is not only quicker and more ecologically valid, but could also provide the performance variables with higher reliability