Prediction criteria of promising F-3 populations in durum wheat: A comparative study

Effective selection of parental material and promising segregating populations is an essential requirement for breeding success. There are many contradictive reports about the best parent selection criterion for the development of promising crosses. For the clarification of this problem field experiments were conducted for four consecutive years to compare the effectiveness of six criteria for the prediction of the most promising F-3 populations in durum wheat (Triticum durum L.): the mid-parent value, the F-1, the F-2, the (F-1 + F-2)/2, and the genetic distance among the parents as it is calculated using the SSR and RAPD molecular markers. During the first growing season (2003-2004) nine commercial cultivars of durum wheat and four landraces were crossed. The following growing season (2004-2005), 17 crosses (F-1 generation) were evaluated under low plant density (1.15 plants m(-2)) in a replicated (R-21) honeycomb design. During the third growing season (2005-2006), the four highest yielding crosses, one cross with an intermediate yield, and the three crosses with the lowest yield (172 generation) were evaluated under low plant density in a R-9 honeycomb design. Finally, in the fourth growing season (2006-2007) progeny of the aforementioned eight crosses (173 generation) and the ten parents were evaluated in a randomized complete block design in two locations. Furthermore, the genetic distance among the parents was determined using the SSR and RAPD molecular markers. It was observed that the three F-3 populations with the lowest yielding ability were the ones with the lowest mid-parental value. In addition, one of the two top F-3 populations was second in the rank according to the mid-parental value. Furthermore, the two top F-3 populations were also the highest yielding in the F-1 and F-2 generations. On the contrary, none of these crosses were predicted by the genetic distance as it was calculated using the SSR and RAPID molecular markers. It was concluded that parental pairs with high mid-parental value and high combined yield (F-1 + F-2)/2 obtained after evaluation of their F-1 and F-2 at low plant density was the most effective way to predict promising F3 populations. (C) 2008 Elsevier B.V. All rights reserved

The acute effects of an intense stretch-shortening cycle fatigue protocol on the neuromechanical parameters of lower limbs in men and prepubescent boys

The study examined the differences between boys and adults after an intense stretch-shortening cycle fatigue protocol on neuromechanical parameters of the lower limb. Thirteen boys (9–11 years old) and 13 adult men (22–28 years old) were tested for maximal isometric voluntary knee extension torque and drop jump (DJ) performance from 30 cm before and immediately after a fatigue protocol, consisted of 10 × 10 maximum effort vertical jumps. Three-dimensional kinematics, kinetics and electromyographic (EMG) parameters of the lower extremities muscles were recorded during DJs before and after the fatigue test. The results indicated that reduction in maximal isometric torque and jumping performance was significantly higher in adults compared to boys. Vertical ground reaction forces, contact time and maximum knee flexion increased in a greater extend in adults than in boys. In addition, preactivation, EMG agonist activity, knee joint stiffness and stretch reflex decreased more in adults than in boys at all the examined phases of jumping tasks. It is concluded that employed fatigue protocol induced acute reduction in performance and altered motor control during jumping in both age groups. However, the differences in the level of fatigue between the 2 groups could be attributed to neuromuscular, mechanical and kinematic parameters observed between groups. © 2017 Informa UK Limited, trading as Taylor & Francis Group

The effects of eccentric exercise-induced muscle damage on running kinematics at different speeds

This study investigated the effects of knee localised muscle damage on running kinematics at varying speeds. Nineteen young women (23.2 +/- 2.8 years; 164 +/- 8cm; 53.6 +/- 5.4kg), performed a maximal eccentric muscle damage protocol (5x15) of the knee extensors and flexors of both legs at 60rad center dot s-1. Lower body kinematics was assessed during level running on a treadmill at three speeds pre- and 48h after. Evaluated muscle damage indices included isometric torque, muscle soreness and serum creatine kinase activity. The results revealed that all indices changed significantly after exercise, indicating muscle injury. Step length decreased and stride frequency significantly increased 48 h post-exercise only at the fastest running speed (3m center dot s-1). Support time and knee flexion at toe-off increased only at the preferred transition speed and 2.5m center dot s-1. Knee flexion at foot contact, pelvic tilt and obliquity significantly increased, whereas hip extension during stance-phase, knee flexion during swing-phase, as well as knee and ankle joints range of motion significantly decreased 48h post-exercise at all speeds. In conclusion, the effects of eccentric exercise of both knee extensors and flexors on particular tempo-spatial parameters and knee kinematics of running are speed-dependent. However, several pelvic and lower joint kinematics present similar behaviour at the three running speeds examined. These findings provide new insights into how running kinematics at different speeds are adapted to compensate for the impaired function of the knee musculature following muscle damage

Neuromuscular differences between prepubescents boys and adult men during drop jump

The purpose of the present study was to determine the lower extremities biomechanical differences between prepubescent and adult males during drop jumps (DJs). Twenty-four untrained males (12 prepubescents, 12 adults) performed DJs from 20 cm height. Kinematics of the lower extremities were captured, in addition with vertical ground reaction forces (vGRFs) and EMG activity of the gastrocnemius medialis (GM), soleus (SOL) and tibialis anterior (TA) muscles. The results showed that men jumped higher, as expected, but their knees were more flexed prior to landing, and their preactivation level was higher and longer in duration compared to prepubescent boys. During landing, men had shorter contact times, lower vGRF normalized to body mass, and less maximal knee joint flexion. Regarding EMG activity men presented higher stretch reflex and higher EMG activity during the braking phase but the level of coactivation (TA to GM + SOL ratio) was lower. It is seems that pre-landing and landing patterns during a complex task such as DJ are affected by physical development. There are indications that men had higher performance in a DJ than prepubescent boys because they activated more effectively their muscles during the preactivation and braking phase. The above-mentioned data support the hypothesis that prepubescent boys might be inferior in optimal regulation of their muscle-tendon unit stiffness