Dragan M. Mirkov

Gender-specific Influences of Balance, Speed, and Power on Agility Performance

Abstract Sekulic, D, Spasic, M, Mirkov, D, Cavar, M and Sattler, T. Gender-specific influences of balance, speed, and power on agility performance. J Strength Cond Res 27(3): 802–811, 2013—The quick change of direction (i.e., agility) is an important athletic ability in numerous sports. Because of the diverse and therefore hardly predictable manifestations of agility in sports, studies noted that the improvement in speed, power, and balance should result in an improvement of agility. However, there is evident lack of data regarding the influence of potential predictors on different agility manifestations. The aim of this study was to determine the gender-specific influence of speed, power, and balance on different agility tests. A total of 32 college-aged male athletes and 31 college-aged female athletes (age 20.02 ± 1.89 years) participated in this study. The subjects were mostly involved in team sports (soccer, team handball, basketball, and volleyball; 80% of men, and 75% of women), martial arts, gymnastics, and dance. Anthropometric variables consisted of body height, body weight, and the body mass index. Five agility tests were used: a t-test (T-TEST), zig-zag test, 20-yard shuttle test, agility test with a 180-degree turn, and forward-backward running agility test (FWDBWD). Other tests included 1 jumping ability power test (squat jump, SQJ), 2 balance tests to determine the overall stability index and an overall limit of stability score (both measured by Biodex Balance System), and 2 running speed tests using a straight sprint for 10 and 20 m (S10 and S20, respectively). A reliability analysis showed that all the agility tests were reliable. Multiple regression and correlation analysis found speed and power (among women), and balance (among men), as most significant predictors of agility. The highest Pearsons correlation in both genders is found between the results of the FWDBWD and S10M tests (0.77 and 0.81 for men and women, respectively; p < 0.05). Power, measured using the SQJ, is significantly (p < 0.05) related to FWDBWD and T-TEST results but only for women (−0.44; −0.41). The balance measures were significantly related to the agility performance for men but not for women. In addition to demonstrating a known relationship between speed and agility in both genders, and a small but statistically significant relationship between power and agility in women, these results indicate that balance should be considered as a potential predictor of agility in trained adult men.

Evaluation of the Reliability of Soccer-Specific Field Tests

Mirkov, DM, Nedeljkovic, A, Kukolj, M, Ugarkovic, D, and Jaric, S. Evaluation of reliability of soccer-specific field tests. J Strength Cond Res 22: 1046-1050, 2008-The soccer-specific field tests are popular among coaches due to their simplicity, validity, and minimal use of equipment. Nevertheless, there is a general lack of data about their reliability, particularly regarding the tests of anaerobic performance. Twenty professional male soccer players performed 3 consecutive trials of the tests of throwing-in and standing-kick performance (the distance measured) as well as on timed 10-m sprint, flying 20-m sprint, running 10 × 5 m, zigzag running with and without the ball, and the skill index (i.e., the ratio of the zigzag running without and with the ball). With the exception of the throwing-in and standing kick, the evaluated tests revealed high intraclass correlation coefficients (i.e., >0.80), small within-individual variations (coefficient of variation, <4%), and sample sizes for detecting a 2% change in the tested performance that are either close to or below the standard size of a professional soccer squad. In addition to simplicity and face validity, most of the evaluated tests revealed high reliability. Therefore, the evaluated tests are recommended for sport-specific profiling and early selection of young athletes as well as for routine testing procedures that could detect effects of various intervention procedures. Regarding the throwing-in and standing-kick tests, direct measurement of the ball velocity (e.g., with a standard radar gun) is recommended.

Development of Anthropometric and Physical Performance Profiles of Young Elite Male Soccer Players: A Longitudinal study

Mirkov, DM, Kukolj, M, Ugarkovic, D, Koprivica, VJ, and Jaric, S. Development of anthropometric and physical performance profiles of young elite male soccer players: A longitudinal study. J Strength Cond Res 24(10): 2677-2682, 2010-The purpose of the present longitudinal study was to explore distinctive anthropometric and physical performance characteristics of young soccer players between the age of 11 and 14 and to reveal the performance at the age of 11, which contributes to the later success. Male players of the best national male squads of the ‘cadet league’ (14 years of age; n = 26) were annually tested starting from the age of 11 for body size and composition, flexibility, power, coordination, and agility. Randomly selected untrained but physically active age-matched boys (n = 63) were also tested over 4 consecutive years. The results revealed no difference between 2 groups regarding the body size and composition (p > 0.05). The differences in flexibility emerged only at the later age, whereas the differences regarding the explosive power (as assessed by various jumps) were moderate and partly inconsistent. The most prominent advantage of the soccer players over the control subjects during the entire tested age period appeared to be movement agility and coordination (p < 0.01). Therefore, the explosive muscle power and, in particular, the agility and coordination characterize elite soccer players of 11-14 years of age but not the body size and body composition. In addition, the agility and coordination could be among the crucial factors of future success in 11-year-old players and, therefore, should be used for early selection.

Tests of Muscle Power Output: The Role of Body Size

The effect of body size on the output of the tests of directly assessed muscle power has been mainly ignored in the applied research. We hypothesized that the muscle power output would reveal a positive relationship with body size closely in line with the theoretical predictions, as well as that the strength of the studied relationship could justify standardized normalization procedures applied in routine testing. Male physical education students (n = 111) were evaluated in 10 standard tests of direct assessment of muscle power output. A standard allometric relationship P = A SB was applied to assess the relationship between the tested power output P and selected indices of body size S ( B = allometric exponent; A = parameter). The correlation coefficients obtained between the tested power output and body size ranged within 0.21 - 0.56 for body mass and 0.10 - 0.49 for body height. The mean (SD) values of the allometric exponents B obtained with respect to body mass and body height were 0.55 (0.15) and 1.15 (0.62), respectively. This relationship proved to be strong enough to merit applying a standard normalization. The normalization method should be based on body mass as a preferred index of body size, while the allometric exponent could correspond to the theoretically predicted one (i.e., B = 0.67).

Body size and countermovement depth confound relationship between muscle power output and jumping performance.

A number of studies based on maximum vertical jumps have presumed that the maximum jump height reveals the maximum power of lower limb muscles, as well as the tested muscle power output predicts the jumping performance. The objective of the study was to test the hypothesis that both the body size and countermovement depth confound the relationship between the muscle power output and performance of maximum vertical jumps. Sixty young and physically active males were tested on the maximum countermovement (CMJ) and squat jumps (SJ). The jumping performance (Hmax), peak (Ppeak) and the average power output (Pavg) during the concentric phase, countermovement depth (only in CMJ) and body mass as an index of body size were assessed. To assess the power-performance relationship, the correlations between Hmax with both Ppeak and Pavg were calculated without and with controlling for the effects of body mass, as well as for the countermovement depth. The results revealed moderate power-performance relationships (range .55<r<.64) that were comparable for CMJ and SJ jumps. When controlled for body mass, the same values were markedly higher (.61<r<.82; p<.05 for Ppeak of both jumps). When controlled for both the body mass and countermovement depth, CMJ revealed r=.88 and r=.77 for Ppeak and Pavg, respectively. Both jumps revealed stronger relationships with Ppeak than with Pavg (p<.05) when controlled for either body mass or both body mass and countermovement depth. We conclude that both body size (in CMJ and SJ) and countermovement depth (in CMJ) confound the relationship between the muscle power output with the performance of maximum vertical jumps. Regarding routine assessments of muscle power from jumping performance and vice versa, the use of CMJ is recommended, while Ppeak, rather than Pavg, should be the variable of choice.

Tests of muscle power output assess rapid movement performance when normalized for body size.

Nedeljkovic, A, Mirkov, DM, Markovic, S, and Jaric, S. Tests of muscle power output assess rapid movement performance when normalized for body size. J Strength Cond Res 23(5): 1593-1605, 2009-Among other routinely tested physical abilities, the tests of rapid movement performance and the tests of direct assessment of muscle power have been independently evaluated in complex batteries of physical fitness tests. Based on the scaling effects, we hypothesized that the tests of rapid movement performance assess the same physical ability as the tests of direct assessment of muscle power properly normalized for the effect of body size. Young physically active men (n = 111) were evaluated on 23 physical ability tests based on the assessment of muscle strength, muscle power, and rapid movement performance. When non-normalized data were used, a principle component analysis revealed a structure with overlapping tests from the above-mentioned groups including the indices of body size. However, when the indices of muscle strength and directly assessed muscle power were properly normalized for the effect of body size, the obtained structure was in line with the hypothesis. Most of the tests of both the direct assessment of muscle power and rapid movement performance proved to belong to the same factor, whereas the muscle strength tests and body size measures, respectively, loaded the remaining 2 factors. This result suggests that the rapid movement performance could be employed to assess muscle power and, possibly, the neuromuscular efficiency in general, which could be important for understanding some basic aspects of the design and function of the human locomotor system. An important practical implication of our findings could be that the direct assessment of muscle power (that usually requires expensive equipment and complex data processing procedures) could be skipped from the complex batteries of physical fitness tests and replaced by generally simpler tests of rapid movement performance.

Evaluation of a Composite Test of Kicking Performance

Abstract Berjan Bacvarevic, B, Pazin, N, Bozic, PR, Mirkov, D, Kukolj, M, and Jaric, S. Evaluation of a composite test of kicking performance. J Strength Cond Res 26(7): 1945–1952, 2012—The aim of this study was to evaluate the reliability and sensitivity of variables for the direct assessment of kicking performance in young soccer players. One hundred and six elite young soccer players were divided into 4 age groups (12–15 years). Absolute error (AE), variable error (VE), and constant error (CE) were evaluated as the variables of kicking accuracy, whereas the kicking velocity variables involved the maximum ball velocity (BVmax) and the ball velocity during accurate kicks (BVacc). Results suggested low-to-moderate reliability of the kicking accuracy (intraclass correlation coefficient [ICC] = 0.00–0.67) and high reliability of the kicking velocity variables (ICC = 0.87–0.94). Regarding the sensitivity, most of the variables detected the differences both between the dominant and nondominant legs and among the age groups. Because the evaluated variables should have a property of face validity, the findings obtained generally suggest that AE (and perhaps VE, as the measures of kicking accuracy) and both BVmax and BVacc (as the measures of kicking velocity) could be used within a routine composite test of kicking performance in young elite soccer players. Further development of the evaluated composite test of kicking performance could be based on the involvement of other kicking techniques and on testing the athletes of different ages, levels of skill, or sport specialization.

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

Abstract Knezevic, OM, Mirkov, DM, Kadija, M, Milovanovic, D, and Jaric, S. Evaluation of isokinetic and isometric strength measures for monitoring muscle function recovery after anterior cruciate ligament reconstruction. J Strength Cond Res 28(6): 1722–1731, 2014—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°·s−1. Significant between-session differences in muscle strength variables were found in the involved quadriceps (F > 6.5; p ⩽ 0.05), but not in the uninvolved leg (F < 2.5; p > 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 ⩽ 0.05) was comparable with the validity of IMT (r = 0.52–0.87; p ⩽ 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

ABSTRACT 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 4 months 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 (140–250 ms) for both knee extensors and flexors (P < 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 (0–180 ms; P < 0.01) and flexors (0–150 ms; P < 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 (<100 ms).

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 º/s and 180 º/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.