The purpose of the study was to describe age-related changes in knee strength and thigh muscle volume on elite soccer players from late adolescence to adulthood. Totally 191 soccer player ...participated in the study and were divided into 5 age groups, i.e. under 16 (U15), 17 (U16), 19 (U18), and 22 (U21) yrs and over 22 (O22) yrs. All of U21 and O22 subjects were professional soccer players. Maximal knee extension (KE) and flexion (KF) concentric torque were measured using isokinetic dynamometer at velocities of 1.05, 3.14, and 7.85 rad/s in both of the dominant and non-dominant legs. Femur length and cross-sectional areas of the quadriceps femoris and hamstrings at the upper, middle, and lower range of the thigh were determined by magnetic resonance imaging, from which the volume of quadriceps femoris (esQF) and hamstrings (esHAM) were estimated. From U15 to U18 neither KE nor KF at 1.05 rad/s increased significantly, although those at the other faster velocities increased significantly regardless of whether the data were expressed as absolute or adjusted value to body weight. In addition, esQF and esHAM also did not increase significantly from U15 to U18. However, the largest increases were observed between U18 and U21 in KE and KF at all the velocities as well as esQF and esHAM. Furthermore, when KE and KF were divided to esQF and esHAM respectively, the values also increased significantly from U15 to U21, suggesting higher knee strength in the professional soccer players were attributed to the concomitant development of thigh muscle volume with the increased neural activation. The ratio of KF to KE and the ratio of esHam to esQF increased slightly from U15 to O22, indicating the predominant development of knee flexor muscles on soccer players after late adolescence. The data presented in this study implied that increasing knee strength with emphasis on both thigh muscle hypertrophy and adaptation of neuromuscular function was essential for younger players to achieve higher soccer playing standards.
The association between closed-chain knee extensor strength and perceived physical function following primary knee replacement has not received much attention.The purpose of this investigation was to ...determine the relationship of closed and open chain measures of strength with self-reported measures of physical function and mobility following unilateral knee replacement.
Subjects were 9 individuals (68. 7 +/- 2.3 years) approximately 16 months postsurgery. The independent variables were closed-chain (elastic) and open-chain (isometric) measures of strength, while the dependent measures were perceived physical function (WOMAC) and mobility (Timed Up and Go, TUG). The relationship between independent and dependent variables was described using Spearman Rho correlation coefficients.
Force produced during the closed-chain assessment was strongly associated to the WOMAC physical function dimension (-.96) and total WOMAC score (-.87). A poor to low relationship existed between the open-chain measure of strength and the physical function dimension (-.34) and the total WOMAC score (-.17). Force production of the entire lower limb, measured in the closed-chain was moderately related (-.62) with the TUG. The association between knee extensor isometric torque and the TUG (-.25) was low.
Closed-chain assessment of entire lower limb strength, rather than open-chain measures of knee extensor strength, may provide greater insight to functional limitations.
To assess the relationship between concentric isokinetic quadriceps and hamstring strength values with the single leg hop for distance test, a closed kinematic chain activity.
Correlational study.
...Neuromuscular Research Laboratory, University of Pittsburgh.
Subjects for this study consisted of 37 college-aged volunteers (21 men, 16 women: mean age = 22.76 +/- 3.52 years, height = 169.90 +/- 10.60 cm, weight = 69.31 +/- 14.60 kg) with no previous history of injury to the lower extremity.
Each subject performed three trials of a single leg hop for distance test for the dominant and nondominant limbs followed by isokinetic evaluation. Isokinetic strength was assessed with the Biodex System II Isokinetic Dynamometer (Biodex Medical Inc., Shirley, NY, U.S.A.) for the quadriceps and hamstrings at preset angular velocities of 60 degrees/s (5 repetitions) and 180 degrees/s (30 repetitions). Before testing, each subject completed a dynamic warm-up period that consisted of submaximal cycling at a fixed cadence of 60 revolutions/min followed subsequently by quadriceps and hamstring muscle stretching.
The distance hopped in centimeters was converted to a ratio of the distance hopped to the individual leg length measured from the anterior superior iliac spine to the medial malleolus. Isokinetic values were obtained for peak torque (Nm), peak torque/body weight (%), total work (Nm), and average power (W).
Low to moderate significant relationships were found to exist between the single leg hop for distance test and the isokinetic variables for the quadriceps and hamstrings of both limbs at each test velocity. Significant correlation coefficients ranged from r = 0.33 to r = 0.69 at 60 degrees/s and r = 0.33 and r = 0.67 at 180 degrees/s. Correlation coefficients were found to be statistically greater for the hamstrings than the quadriceps for total work and average power at 60 degrees/s and for peak torque/body weight, total work, and average power at 180 degrees/s (p < 0.05).
Concentric quadriceps and hamstring strength seem to demonstrate a significant contribution to the single leg nop for distance test; however, the hamstring muscles may play a more important role during the propulsive phase, thereby enabling subjects to jump further.
This study has been conducted to determine whether mean values of peak oxygen consumption (VO(2peak)), anaerobic test parameters and knee isokinetic test measurements are different among guanine ...nucleotide-binding protein, beta-3 (GNB3) genotype groups in a group of basketball players.
Seventy-two healthy male (mean age, 22.9 ± 5.3 years) basketball players from the first division of national league participated. We studied GNB3 gene c.825C>T (rs5443) polymorphism, then divided the subjects into three groups as CC (n = 21), CT (n = 35), and TT (n =1 6). Mean VO(2peak), Wingate anaerobic test results, and isokinetic knee muscle strength measurements were compared among the genotype groups.
Mean VO(2peak) (60.1 ± 3.9; 56.7 ± 3.6; and 57.8 ± 3.3, respectively, p < 0.01), mean anaerobic minimum power (5.1 ± 0.4; 5.3 ± 0.5; and 4.4 v 0.5 W/kg, respectively, p < 0.001), mean anaerobic power drop (57.0 ± 6.2; 54.2 ± 6.9; and 62.9 ± 5.3%, respectively, p < 0.001) were significantly different among the study groups, CC, CT, and TT. Individuals with TT genotype exerted lower performance in terms of isokinetic knee muscle strength.
The presence of 825T-allele may impair athletic performance and may serve as a genetic marker of low capacity for athletic performance in male basketball players.
PDF
