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The purpose of the study was to assess the influence of short, intermediate, and long muscle lengths on dorsiflexor force steadiness and the discharge characteristics of motor units in tibialis anterior during submaximal isometric contractions. Steady contractions were performed at 5 target forces (5, 10, 20, 40, and 60% maximal voluntary contraction, MVC) for 3 ankle angles (75°, 90°, and 105°). MVC force was less (p = 0.043) at the smallest joint angle compared with the other two angles. The absolute (standard deviation) and normalised amplitudes (coefficient of variation) of the force fluctuations were similar for all 3 ankle angles at each target force. The coefficient of variation for force decreased progressively from 5% to 20% MVC force and then it plateaued at 40% and 60% MVC force. At all target forces, the mean discharge rate (MDR) of the motor units at 75° was greater than at 90° (p = 0.006) and 105° (p = 0.034). Moreover, the MDR was similar for 5% and 10% MVC forces and then increased gradually until 60% MVC force (p < 0.005). The variability in discharge times (coefficient of variation for interspike interval) and variability in neural drive (coefficient of variation of filtered cumulative spike train) were similar at all ankle angles. Variability in neural drive had a greater influence on force steadiness than did the variability in discharge times. Changes in ankle-joint angle did not influence either the normalised amplitude force fluctuations during steady submaximal contractions or the underlying modulation of the discharge characteristics of motor units in tibialis anterior. [ABSTRACT FROM AUTHOR]

The purpose of the study was to evaluate the influence of changes in ankle- and knee-joint angles on force steadiness and the discharge characteristics of motor units (MU) in soleus when the plantar flexors performed steady isometric contractions. Submaximal contractions (5, 10, 20, and 40% of maximum) were performed at two ankle angles (75° and 105°) and two knee angles (120° and 180°) by 14 young adults. The coefficient of variation of force decreased as the target force increased from 5 to 20% of maximal force, then remained unaltered at 40%. Independently of knee angle, the coefficient of variation for force at the ankle angle of 75° (long length) was always less (p<0.05) than that at 105° (shorter length). Mean discharge rate, discharge variability, and variability in neural activation of soleus motor units were less (p<0.05) at the 75° angle than at 105°. It was not possible to record MUs from medial gastrocnemius at the knee angle of 120° due to its minimal activation. The changes in knee-joint angle did not influence any of the outcome measures. The findings underscore the dominant role of the soleus muscle in the control of submaximal forces produced by the plantar flexor muscles. [ABSTRACT FROM AUTHOR]

Exercises for lumbar multifidus (LM) muscle are important for injury and low back pain prevention and treatment. This study examined the differences in LM contraction thickness between variations of the superman and bird dog exercises. Twenty-one recreational athletes performed the superman exercise from the prone position with the following grading: rest, right upper extremity lift (RU), right lower extremity (RL) and upper and lower extremities lift (UL). They also performed the following bird dog variations from the quadruped position: rest, RU, RL and left upper - right lower extremity lift (LURL). LM muscle thickness of both sides was recorded using two ultrasonography (US) devices. LM thickness during superman-UL, was significantly greater compared with the other exercises and significantly lower during upper extremity exercises compared with lower extremity exercises (p < 0.05). No significant differences in LM thickness between sides was found (p > 0.05). The US measurements of LM thickness displayed good to excellent intrarrater reliability for both muscle sides. It appears that superman-UL is the most effective exercise for a greater contraction thickness of LM. Further, in order to progressively increase LM muscle thickness, upper extremity tasks should be performed prior to lower extremity tasks and combined upper and lower lifting tasks. [ABSTRACT FROM AUTHOR]

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Aim: The main purpose of the study was to investigate kicking kinematics and performance in young-trained soccer players according to age, playing status, and biological maturity.Methods: Youth male soccer players (N = 105) from five age groups (under-11, under-13, under-15, under-17, and under-20) were evaluated. Four digital video cameras (300 Hz) captured the participants' lower extremity and ball kinematics during penalty kick trials using dominant limb.Results: It was possible to identify non-linear differences in angular joint kinematics (displacement and velocity) of hip, knee and ankle across age-groups. Kicked ball speed and lower extremity mechanical factors discriminated among under-15 players with distinct status (e.g., ball speed and foot-to-ball speed ratio: starters > non-starters and non-participating substitutes; effect size = 1.05 to 1.49 [large]). Estimated maturity offset was not correlated with performance outputs in any age-group (r = −0.28 to 0.39; P > 0.05).Conclusion: We conclude that from ages ~10 to 19 years, differences in kicking kinematics and performance vary across time in youth players. Transition phase between under-13 to under-15 appears the most sensible period for powerful instep kick performance development. Kicking speed in youth soccer is discriminated according to player status, but not estimated biological maturity. [ABSTRACT FROM AUTHOR]

Background: The study examined the effects of a 4-week intensive isometric and isotonic stabilization exercise program on dimensions of health-related quality of life (HRQL) in women with chronic low back pain (CLBP). Methods: A total of 39 women (27-72 years old) provided data in an experimental study with a 9-month follow-up. Random allocation was undertaken for the two treatment groups out of the 3 groups: isometric stabilization (n = 13), isotonic stabilization (n = 13), and a control group (n = 13) that did not participate in any form of exercise. Health-related quality of life measures using the Short-Form 36 Health Survey were assessed before program initiation, immediately after program termination, and 4 times postintervention for a period of 9 months. Results: The isometric stabilization group displayed large improvements in bodily pain and vitality for women with CLBP attending a 4-week intensive isometric stabilization exercise program. The effects were retained for a period of 9 months after program termination. Conclusions: Isometric stabilization exercises reduce pain and enhance vitality as dimensions of HRQL among women with chronic low back pain with such effects lasting for at least 9 months. [ABSTRACT FROM AUTHOR]

This study examined whether the association between hamstring (H) and quadriceps (Q) strength with size depends on the region and the muscle used to examined cross-sectional area (CSA). Maximum isometric contraction knee extension and flexion torque was obtained from 20 young participants while Q and H CSA was recorded using extended field of view ultrasonography at four sections along the thigh. Stepwise linear regression models using the maximum CSA of individual muscles showed a significant association of quadriceps (R2 = 0.793) and hamstring (R2 = 0.275) CSA with MVC torque (p < 0.05). The association was lower when maximum or section-specific muscle group CSAs were used as indices of size. The H:Q CSA ratio showed a significant association (R2 = 0.275, p < 0.05) and a moderate correlation (r = 0.48) with H:Q torque ratio. These results indicated that the association between muscle CSA and strength differs between the knee extensors and flexors. Amongst the various indices of muscle size, the combination of maximum CSA values of each muscle displayed the greatest relationship between strength and CSA. The H:Q CSA ratio can explain a significant but small part of the H:Q isometric strength ratio. [ABSTRACT FROM AUTHOR]

Bridging exercises with abdominal hollowing are often used as a regimen for improving spinal stability. Lately, this type of training has become very popular among elite athletes, creating a need for more demanding exercises. The purpose of this study was to investigate whether the use of additional external resistance is beneficial for abdominal muscle recruitment during bridge exercise. Tissue movement of the transversus abdominis (TrA) and the rectus abdominis (RA) was recorded with the use of two synchronized ultrasonic devices, in 20 healthy college students. From the hook-lying position participants were examined in eight different exercise conditions: a) rest, b) abdominal drawing-in maneuver (ADIM), c) bridge, d) bridge- ADIM, e) bridge with 10KG, f) bridge- ADIM with 10KG, g) bridge with 20KG and h) bridge-ADIM with 20KG. Analysis of variance (ANOVA) showed a statistically significant increase in TrA thickness when performing the bridge exercise combined with ADIM compared to rest mode (p < .05). RA thickness decreased when the ADIM was performed, compared to rest (p < 0.05). No significant difference in TrA and RA thickness when exercising with and without external resistance was observed (p > 0.05). The main outcome of this study was that external loading provided some extra level of difficulty, yet it was not beneficial for abdominal muscle recruitment, when performing a supine bridge exercise. [ABSTRACT FROM AUTHOR]

The aim of this study was to examine the differences in muscle architecture during isometric tests between children and adults. Eight boys (age= 11.2 ± 0.26 years) and eight men (age= 22.3 ± 2.01 years) performed plantar flexion isometric efforts at angles of -15°, 0°, 15° at 0%, 40%, 60%, 80% of MVC. Analysis of variance tests indicated that adults showed greater fascicle length from rest to 80% of MVC (p < .05), greater pennation angle at 80% and 100% of MVC (p < .05) and greater aponeuroses displacement at levels of effort greater than 60% of MVC (p < .05). These differences observed in MG would appear to favor better utilization of the force-length and the force-velocity relationships, of the muscle in adults compared with children. [ABSTRACT FROM AUTHOR]

Examines the reliability of maximum isometric force-time parameters during a leg press test in pubertal basketball players. Development of muscular strength and power of lower limbs; Use of multijoint tests; Stabilization of dynamometer.

Examines the reliability of isokinetic concentric and eccentric strength in circumpubertal soccer players. Importance of isokinetic parameters in the establishment of strength testing parameters; Importance of bilateral difference in isokinetic movement as a predictor of injury; Uses of the examination of isokinetic strength profiles.

Analysis of plantar pressure during sport movement performance can provide significant information to athletes and coaches regarding sport performance and plantar loads. In tennis, the serve is one of the most difficult and most important strokes. The purpose of this study was to examine the plantar pressure differences between the flat, slice and topspin serves with the "foot back" serving technique on GreenSet tennis surfaces (tennis surfaces provided for professional and high-level play) of junior athletes aged 10 to 16. The results showed that the loads were higher on the rear (right) back foot of all the three serves. The Fmax was higher in foot toes for all types of serve and the peak pressure was higher in slice serve in the metatarsal forefoot region of the back right foot. The results showed that the technique applied, mainly to the footwork, varies between types of serves. Therefore, each type of the three serves has a different profile for plantar pressures and loads. [ABSTRACT FROM AUTHOR]