Association between traditional standing vertical jumps and a soccer-specific vertical jump.

The present study aimed to determine the relationships between a soccer-specific vertical jump (ssVJ) test, that included common elements of a soccer VJ (e.g. run-up and intention to head), and three traditional VJ tests using elite soccer players. A secondary purpose of this study was to determine the reliability of the VJs used in the analysis. A randomised order and counterbalanced design was used to assess the relationships between these VJs [countermovement jump (CMJ), drop jump for height (DJh), drop jump for maximum height and minimum ground contact time (DJh/t) and the ssVJ]. Take-off velocity, contact time and flight time were the dependent variables of interest and compared between jumps. Intra-class correlation coefficient (ICC) and coefficient of variation (CV) were used as measures of inter-session reliability. All VJ tests were found to have high ICCs (0.89-0.99) and acceptable within-subject CVs (<7.5%). All the ssVJ dependent variables were not significantly related (r<0.44) with similar variables from the CMJ and DJh tests and only moderately related (r=~0.49) with the DJh/t test variables. In addition, the DJh/t variables were not significantly correlated (r<0.47) with DJh and CMJ test variables. In conclusion, it would seem that the proposed ssVJ test and CMJ or DJh tests assess different leg qualities and thought should be given before using them interchangeably to assess or develop the same performance measures (i.e. velocity at take-off or jump height).

Reliability and validity of a wireless microelectromechanicals based system (keimove™) for measuring vertical jumping performance.

UNLABELLED: The aim of this study was to determine the validity and reliability of a microelectromechanicals (MEMs) based system (Keimove™) in measuring flight time and takeoff velocity during a counter-movement jump (CMJ). As criterion reference, data of a high- speed camera (HSC) and a force-platform (FP) synchronized with a linear position transducer (LPT) was used. Thirty professional soccer players completely familiarized with the CMJ technique performed three CMJs. The second and third trials were used for further analysis. The Keimove™ system, the HSC and the FP synchronized with the LPT (FP+LPT) simultaneously measured the CMJ performance. During each repetition, the Keimove™ system registered flight time and velocity at takeoff. At the same time and as criterion reference, both the HSC and the FP recorded the flight time while the LPT+FP registered the velocity at takeoff. Pearson correlation coefficients for the flight time were high (r = 0.99; p < 0.001) when Keimove™ system was compared with the HSC or the FP+LPT, respectively. For the velocity at takeoff variable, the Pearson r between the Keimove™ system and the FP+LPT was lower although significant at the 0.05 level. No significant differences in mean values were observed for flight times and velocity at takeoff between the three devices. Intraclass correlations and coefficients of variation between trials were similar and ranged between 0.92-0.97 and 2.1-7.4, respectively. In conclusion, the Keimove™ system represents a valid and reliable instrument to measure velocity at takeoff and flight time during CMJ testing. Thus, this MEMs-based system will offer a portable, cost-effective tool for the assessment CMJ performance. KEY POINTS: The Keimove™ system is composed of specific software and a wireless MEMs-based device designed to be attached at the lumbar region of the athlete.The Keimove™ system is a mechanically valid and reliable instrument in measuring flight time and velocity at takeoff during CMJ.The validity of the Keimove™ system was determined by comparing its mean flight time and velocity at takeoff with data obtained simultaneously with both a high-speed camera and a force platform synchronized with a linear position transducer.

Relationship between postactivation potentiation of knee extensor muscles, sprinting and vertical jumping performance in professional soccer players.

Little is known about the relationship between postactivation potentiation (PAP) in human muscles, assessed by enhancement of twitch torque after a conditioning maximal voluntary contraction (MVC), and performance in activities requiring power and speed. Moreover, no studies have assessed PAP in soccer players who train power and endurance simultaneously. The purpose of the present study was to examine the relationship between twitch PAP in knee extensor (KE) muscles, and sprinting and vertical jumping performance in soccer players. Fourteen professional male soccer players with mean (SD) age 20.0 (3.6) years, height 177.9 (6.9) cm and body mass 70.5 (5.7) kg) were tested for 15-m sprint time, vertical jump height in countermovement (CMJ) and squat (SJ) jumps. PAP in KE muscles was induced by a 10-s isometric MVC. Electrically evoked twitches of KE muscles were evoked before and after the conditioning MVC. Immediately after the conditioning MVC, twitch peak torque (PT) and maximal rates of torque development and relaxation were significantly potentiated. A significant negative correlation was found between 15-m sprint time and jump height in CMJ (r = -0.63) and SJ (r = -0.57). PAP of twitch PT correlated significantly positively with jump height in CMJ (r = 0.61) and SJ (r = 0.64), and negatively with 15-m sprint time (r = -0.59). In conclusion, twitch PAP in KE muscles was significantly correlated with performance in vertical jumping and sprinting in male professional soccer players, whereas the magnitude of PAP in soccer players was similar to that observed previously in power-trained athletes.

Vertical jump biomechanics after plyometric, weight lifting, and combined (weight lifting + plyometric) training.

The purpose of this study was to compare the effects of an Olympic weight lifting (OL), a plyometric (PL), and combined weight lifting + plyometric (WP) training program on vertical jump (VJ) biomechanics. Thirty-six men were assigned randomly to 4 groups: PL group (n = 9), OL group (n = 9), WP group (), and control (C) group (n = 8). The experimental groups trained 3 d.wk, for 8 weeks. Sagital kinematics, VJ height, power, and electromyographic (EMG) activity from rectus femoris (RF) and medial gastrocnemius (GAS) were collected during squat jumping and countermovement jumping (CMJ) before and after training. The results showed that all experimental groups improved VJ height (p < 0.05). The OL training improved power and muscle activation during the concentric phase of the CMJ while the subjects used a technique with wider hip and knee angles after training (p < 0.05). The PL group subjects did not change their CMJ technique although there was an increase in RF activation and a decrease of GAS activity after training (p < 0.05). The WP group displayed a decline in maximal hip angle and a lower activation during the CMJ after training (p < 0.05). These results indicate that all training programs are adequate for improving VJ performance. However, the mechanisms for these improvements differ between the 3 training protocols. Olympic weight lifting training might be more appropriate to achieve changes in VJ performance and power in the precompetition period of the training season. Emphasis on the PL exercises should be given when the competition period approaches, whereas the combination of OL and PL exercises may be used in the transition phases from precompetition to the competition period.

Does plyometric training improve strength performance? A meta-analysis.

Majority of the research suggests plyometric training (PT) improves maximal strength performance as measured by 1RM, isometric MVC or slow velocity isokinetic testing. However, the effectiveness of PT depends upon various factors. A meta-analysis of 15 studies with a total of 31 effect sizes (ES) was carried out to analyse the role of various factors on the effects of PT on strength performance. The inclusion criteria for the analysis were: (a) studies using PT programs for lower limb muscles; (b) studies employing true experimental design and valid and reliable measurements; (c) studies including sufficient data to calculate ES. When subjects can adequately follow plyometric exercises, the training gains are independent of fitness level. Subjects in either good or poor physical condition, benefit equally from plyometric work, also men obtain similar strength results to women following PT. In relation to the variables of program design, training volume of less than 10 weeks and with more than 15 sessions, as well as the implementation of high-intensity programs, with more than 40 jumps per session, were the strategies that seem to maximize the probability to obtain significantly greater improvements in performance (p<0.05). In order to optimise strength enhancement, the combination of different types of plyometrics with weight-training would be recommended, rather than utilizing only one form (p<0.05). The responses identified in this analysis are essential and should be considered by the strength and conditioning professional with regard to the most appropriate dose-response trends for PT to optimise strength gains.

Optimal warm-up stimuli of muscle activation to enhance short and long-term acute jumping performance.

The aim of this study was to determine the effect of different types of active warm-up stimuli of muscle activation on explosive jumping performance after short (5 min postwarm-up) and long (6 h postwarm-up) recovery periods following warm-up. Twelve trained volleyball players (21-24 years) performed different types of specific warm-up stimuli (WP) after baseline measurements [e.g., countermovement jump (CMJ) without and with extra load and Drop jump (DJ)] on randomized separate occasions: (1) three sets of five jumps with extra load (WP1), (2) two sets of four reps at 80% of 1RM parallel squat (1RM(PS)) and two sets of two reps at 85% of 1RM(PS) (WP2), (3) two sets of four reps at 80% of 1RM(PS) and two sets of two reps at 90% of 1RM(PS) and two sets of one rep at 95% of 1RM(PS) (WP3), (4) three sets of five DJs (WP4), (5) specified warm-up for a volleyball match (WP5), (6) three sets of five reps at 30% 1RM(PS) (WP6), and (7) an experimental condition of no active warm-up. Height in DJ significantly improved (P < 0.05) after WP1 (4.18%), WP2 (2.98%), WP3 (5.47%), and WP5 (4.49%). Maximal power output during CMJ with extra load significantly improved (P < 0.05) after WP2 (11.39%), WP5 (10.90%), WP3 (9%), and WP1 (2.47%). High-intensity dynamic loading (e.g., 80-95% 1RM), as well as specific volleyball warm-up protocol bring about the greatest effects on subsequent neuromuscular explosive responses. Acute positive effects on jumping performance after warm-up were maintained after long recovery periods (e.g., 6 h following warm-up), particularly when prior high-intensity dynamic actions were performed.