A new sledge jump system that allows almost natural reactive jumps

AimSledge jump systems (SJS) are often employed to examine the underlying mechanical and neuromuscular mechanisms of the stretch-shortening cycle (SSC) as they allow the systematic variation of impact velocity and energy. However, in existing SJS the jumps are not very comparable to natural jumps because of the long contact times (～200%), which prevent the storage of kinetic energy. The aim of the present study was to evaluate if an ultra-light sledge, built in a way that joint movement is barely restricted, allows jumps that are comparable to natural jumps.MethodsGround reaction forces, kinematic and electromyographic (EMG) data of 21 healthy subjects were compared between normal hoppings (NH) on the ground and hoppings in a custom-built SJS (sledge hoppings, SH).ResultsNormalized to NH, the ground contact times for the SH were prolonged (+22%), while the peak forces (?21%) and the preactivity of the soleus and gastrocnemius medialis muscles were reduced (?20% and ?22%, respectively). No significant changes were observed for the iEMG of the short latency response of those muscles (+1% and +8%) and the ranges of motion in the ankle, knee and hip joint (differences of 1, 1 and 2 degrees). The reduced peak forces were associated with a reduced leg stiffness (?21%).ConclusionThe new system allows reactive jumps that are rather comparable to natural jumps. Therefore, the new SJS seems to be an adequate system in order to examine the SSC under controlled and almost natural conditions.     

Neuromuscular and balance responses to flywheel inertial versus weight training in older persons

AimLoss of muscle strength and balance are main characteristics of physical frailty in old age. Postural sway is associated with muscle contractile capacity and to the ability of rapidly correcting ankle joint changes. Thus, resistance training would be expected to improve not only strength but also postural balance.MethodsIn this study, age-matched older individuals (69.9±1.3 years) were randomly assigned to flywheel (n=12), or weight-lifting (n=12) groups, training the knee extensors thrice weekly for 12 weeks. The hypotheses were that owing to a larger eccentric loading of the knee extensors, flywheel training would result in (a) greater gains in quadriceps strength; (b) greater improvements in balance performance compared with weight-lifting training. Isokinetic dynamometry, B-mode ultrasonography, electromyography, percutaneous muscle stimulation and magnetic resonance imaging were employed to acquire the parameters of interest.ResultsFollowing training, knee extensors peak isokinetic power increased by 28% (P<0.01) in the flywheel group with no change in the weight-lifting group. Adaptations of the gastrocnemius muscle also occurred in both groups. The gastrocnemius characteristic with the highest response to training was tendon stiffness, with increases of 54% and 136% in the weight-lifting and flywheel groups, respectively (P<0.01). The larger increase in tendon stiffness in the flywheel group was associated with an improvement in postural balance (P<0.01).ConclusionQuadriceps flywheel loading not only produces a greater increase in power than weight training but its physiological benefits also transfer/overspill to the plantarflexor muscle–tendon unit resulting in a significantly improved balance. These findings support our initial hypotheses.     

Active leg stiffness and energy stored in the muscles during maximal counter movement jump in the aged

The purpose of this study was to examine the effects of age on active leg stiffness adjustment, electromyogram (EMG) activities and energy stored during eccentric and concentric phases in performing a maximal functional task involving stretch-shorten cycle. Ten young (24.3 ± 2 years) and 10 old (68.6 ± 5 years) healthy male subjects were filmed during maximal performance of counter movement jump (CMJ) and squat jump (SJ) on force plate. Integrated EMG (IEMG), ground reaction force (GRF), active leg stiffness, energy stored/returned and active work done by the muscles were compared between two groups on eccentric (ECC) and concentric (CON) phases of CMJ. The GRF, leg stiffness and energy stored in ECC and GRF, IEMG, energy returned and active work in CON were less in the elderly (p < 0.05). These results demonstrate that the neuromuscular function of adjusting active stiffness, storing elastic energy and optimizing the performance may decrease with age during CMJ.     

The influence of foot position on body dynamics

During locomotion, the human body exhibits inherent dynamic properties such as mass (M), stiffness (K) and damping (B). During the gait cycle, foot contact with the ground progresses from the heel to the toe. Contact forces between the foot and ground are defined as ground reaction forces (GRF). It is unclear how body dynamics are affected by foot landing position. If the shape of GRF is indicative of body dynamics, our understanding of gait patterns in normal and pathologic conditions may improve. The aims of this study were to determine:(1) whether foot landing position affects the inherent dynamics of the human body and (2) the extent to which the GRF curve reflects the response of inherent body dynamics to sudden loading.Eight non-disabled control volunteers performed a series of small jumps and landed on one leg with a fully extended knee in three foot landing positions: heel, mid-foot, and toe. They then walked at self-paced velocity over force plates. For each foot landing position, values of K, B and the dimensionless damping coefficient, ξ, were calculated from the period of vertical body oscillations, T, and compared with an ANOVA test. In addition, the time between the two peaks of the vertical GRF, T_GRF, was compared with T. We found that that K and B decreased and ξ did not change (p<0.01) between heel to toe-landing positions. T_GRF was not different than T for the toe-landing position, which suggests that the dynamic body response has major impact on the shape of GRF.     

Agonist versus antagonist muscle fatigue effects on thigh muscle activity and vertical ground reaction during drop landing

BackgroundAgonist and antagonist co-activation plays an important role for stabilizing the knee joint, especially after fatigue. However, whether selective fatigue of agonists or antagonist muscles would cause different changes in muscle activation patterns is unknown.HypothesisKnee extension fatigue would have a higher influence on landing biomechanics compared with a knee flexion protocol.Study designRepeated-measures design.MethodsTwenty healthy subjects (10 males and 10 females) performed two sets of repeated maximal isokinetic concentric efforts of the knee extensors (KE) at 120° s^?1 until they could no longer consistently produce 30% of maximum torque. On a separate day, a similar knee flexion (KF) fatigue protocol was also performed. Single leg landings from 30 cm drop height were performed before, in the middle and after the end of the fatigue test. The mean normalized electromyographic (EMG) signal of the vastus medialis (VM), vastus lateralis (VL), biceps femoris (BF) and gastrocnemius (GAS) at selected landing phases were determined before, during and after fatigue. Quadriceps:hamstrings (Q:H) EMG ratio as well as sagittal hip and knee angles and vertical ground reaction force (GRF) were also recorded.ResultsTwo-way analysis of variance designs showed that KE fatigue resulted in significantly lower GRF and higher knee flexion angles at initial contact while maximum hip and knee flexion also increased (p < 0.05). This was accompanied by a significant decline of BF EMG, unaltered EMG of vastii and GAS muscles and increased Q:H ratio. In contrast, KF fatigue had no effects on vGRFs but it was accompanied by increased activation of VM, BF and GAS while the Q:H increased during before landing and decreased after impact.ConclusionFatigue responses during landing are highly dependent on the muscle which is fatigued.     

Compliant bipedal model with the center of pressure excursion associated with oscillatory behavior of the center of mass reproduces the human gait dynamics

Although the compliant bipedal model could reproduce qualitative ground reaction force (GRF) of human walking, the model with a fixed pivot showed overestimations in stance leg rotation and the ratio of horizontal to vertical GRF. The human walking data showed a continuous forward progression of the center of pressure (CoP) during the stance phase and the suspension of the CoP near the forefoot before the onset of step transition. To better describe human gait dynamics with a minimal expense of model complexity, we proposed a compliant bipedal model with the accelerated pivot which associated the CoP excursion with the oscillatory behavior of the center of mass (CoM) with the existing simulation parameter and leg stiffness. Owing to the pivot acceleration defined to emulate human CoP profile, the arrival of the CoP at the limit of the stance foot over the single stance duration initiated the step-to-step transition. The proposed model showed an improved match of walking data. As the forward motion of CoM during single stance was partly accounted by forward pivot translation, the previously overestimated rotation of the stance leg was reduced and the corresponding horizontal GRF became closer to human data. The walking solutions of the model ranged over higher speed ranges (~1.7 m/s) than those of the fixed pivoted compliant bipedal model (~1.5 m/s) and exhibited other gait parameters, such as touchdown angle, step length and step frequency, comparable to the experimental observations. The good matches between the model and experimental GRF data imply that the continuous pivot acceleration associated with CoM oscillatory behavior could serve as a useful framework of bipedal model.     

Effects of various midsole densities of basketball shoes on impact attenuation during landing activities

The purpose of this study was to examine effects of shoe midsole densities and mechanical demands (landing heights) on impact shock attenuation and lower extremity biomechanics during a landing activity. Nine healthy male college athletes performed 5 trials of step-off landing in each of 9 test conditions, i.e., a combination of landings in shoes of 3 midsole densities (soft, normal, hard) from each of 3 landing potential energy (PE) levels (low, median, high). Ground reaction forces (GRF), accelerations (ACC) of the tibia and forehead, and sagittal kinematic data were sampled simultaneously. A 3 x 3 two-way (surface x height) repeated-measures analysis of variance (ANOVA) was performed on selected kinematic, ACC, and GRF variables; a 3 x 3 x 3 three-way (surface x height x joint) ANOVA was performed on variables related to eccentric muscular work. The GRF results showed that the forefoot peak GRF in the normal and hard midsoles was significantly greater than the soft midsole at the low and median PEs. Rearfoot peak GRF was significantly greater for the hard midsole than for the soft and normal midsoles at the median and high PEs, respectively. The peak head and tibia peak ACC were also attenuated in similar fashion. Kinematic variables did not vary significantly across different midsoles, nor did energy absorbed through lower extremity extensors in response to the increased shoe stiffness. Knee joint extensors were shown to be dominant in attenuating the forefoot impact force across the landing heights. The results showed limited evidence of impact-attenuating benefits of the soft midsole in the basketball shoes.     

Effects of whole-body vibration on bone properties in aged rats

Objective:This study aimed to explore optimal conditions of whole-body vibration (WBV) for improving bone properties in aged rats.Methods:Eighty-week-old rats were divided into baseline control (BC), age-matched control (CON) and experimental groups, which underwent WBV (0.5 g) at various frequencies (15, 30, 45, 60 or 90 Hz) or WBV (45 Hz) with various magnitudes (0.3, 0.5, 0.7 or 1.0 g) for 7 weeks. After interventions, femur bone size, bone mechanical strength and circulating bone formation/resorption markers were measured, and trabecular bone microstructure (TBMS) and cortical bone geometry (CBG) of femurs were analyzed by micro-CT.Results:Several TBMS parameters and trabecular bone mineral content were significantly lower in the 15 Hz WBV (0.5 g) group than in the CON group, suggesting damage to trabecular bone. On the other hand, although frequency/magnitude of WBV did not influence any CBG parameters, the 0.7 g and 1.0 g WBV (45 Hz) group showed an increase in tissue mineral density of cortical bone compared with the BC and CON groups, suggesting the possibility of improving cortical bone properties.Conclusion:Based on these findings, it should be noted that WBV conditions are carefully considered when applied to elderly people.     

Age- and gender-related development of stretch shortening cycle during a sub-maximal hopping task

The aim of this study was to analyse the effects of age and gender (and their interaction) on a stretch shortening cycle solicited during a hopping task. For this aim, 147 girls and 148 boys aged 11 to 20 years, who were enrolled in middle school or secondary school with no experience in sport activity, or training less than three times per week, performed 3×5 hops in place. Leg-stiffness, jump-height and reactive-strength indices were assessed using an accelerometer (Myotest). The participants were selected in order to form five age groups: 11 12, 13-14, 15-16, 17-18 and 19-20 years. Regression analysis between force and centre of mass displacement revealed spring-mass behaviour for all groups (r²=.73-.89), meaning that beginning at the age of 11 years, children are able to perform complex inter-muscular coordination of the lower limbs, revealing efficient neural control early in childhood. Leg stiffness increased from 24.7 ± 10.6 kN · m⁻¹ at 11-12 years to 44.1 ± 14 kN · m⁻¹ in boys, with a small increase until 16 years (+17%) and a large increase between 17 and 20 years (+32.7%). In girls, leg stiffness increased from 26.6 ± 9 kN · m⁻¹ at 11-12 years to 39.4 ± 10.9 kN · m⁻¹ at 19-20 years, with a curious decrease in leg stiffness at 17-18 years, probably due to an increase in the percentage of fat at this age (25%). While no gender effect was found, the reactive-strength index revealed that, from 15-16 years onward, boys were better able to produce high levels of force in a shorter time than girls. The age of 15-16 years is a threshold of maturity and gender differentiation, where the boys investigated are more efficient in the stretch shortening cycle.     

Effects of Heavy Strength Training on Running Performance and Determinants of Running Performance in Female Endurance Athletes

Purpose

The purpose of the current study was to investigate the effects of adding strength training to normal endurance training on running performance and running economy in well-trained female athletes. We hypothesized that the added strength training would improve performance and running economy through altered stiffness of the muscle-tendon complex of leg extensors.

Methods

Nineteen female endurance athletes [maximal oxygen consumption (VO_2max): 53±3 ml∙kg^-1∙min^-1, 5.8 h weekly endurance training] were randomly assigned to either normal endurance training (E, n = 8) or normal endurance training combined with strength training (E+S, n = 11). The strength training consisted of four leg exercises [3 x 4–10 repetition maximum (RM)], twice a week for 11 weeks. Muscle strength, 40 min all-out running distance, running performance determinants and patellar tendon stiffness were measured before and after the intervention.

Results

E+S increased 1RM in leg exercises (40 ± 15%) and maximal jumping height in counter movement jump (6 ± 6%) and squat jump (9 ± 7%, p < 0.05). This was accompanied by increased muscle fiber cross sectional area of both fiber type I (13 ± 7%) and fiber type II (31 ± 20%) in m. vastus lateralis (p < 0.05), with no change in capillary density in m. vastus lateralis or the stiffness of the patellar tendon. Neither E+S nor E changed running economy, fractional utilization of VO_2max or VO_2max. There were also no change in running distance during a 40 min all-out running test in neither of the groups.

Conclusion

Adding heavy strength training to endurance training did not affect 40 min all-out running performance or running economy compared to endurance training only.     

Synthesis of 3-aroyl-4-aryl-1-isopropylamino-4-piperidinols and evaluation of the cytotoxicities of the compounds against human hepatoma and breast cancer cell lines

Abstract

Some 4-piperidinol derivatives were synthesized and their cytotoxicity was tested against human hepatoma (Huh7) and breast cancer (T47D) cells. Aryl part was changed as phenyl in 2a, 4-methylphenyl in 2b, 4-methoxyphenyl in 2c, 4-chlorophenyl in 2d, 4-fluorophenyl in 2e, 4-bromophenyl in 2f, 4-nitrophenyl in 2g and 2-thienyl in 3. Compounds were synthesized and reported for the first time by this study except 2a and 2d. Chemical structures were confirmed by ¹H NMR, ¹³C NMR, IR, MS and elemental analyses. Compounds 2a (3.1 times), 2c (3.8 times), 2f (4.6 times), 2g (1.3 times) and 3 (3.2 times) had 1.3–4.6 times higher cytotoxic potency than the reference compound 5-FU against Huh7 cell line while all the compounds synthesized had shown lower activities against T47D cell line than 5-FU. In the light of these results, compounds 2a, 2c, 2f, 2g and 3 may serve as model compounds for further studies.     

Effective leg stiffness in running

Leg stiffness is a common parameter used to characterize leg function during bouncing gaits, like running and hopping. In the literature, different methods to approximate leg stiffness based on kinetic and kinematic parameters are described. A challenging point in estimating leg stiffness is the definition of leg compression during contact. In this paper four methods (methods A–D) based on ground reaction forces (GRF) and one method (method E) relying on temporal parameters are described. Leg stiffness calculated by these five methods is compared with running patterns, predicted by the spring mass model.The best and simplest approximation of leg stiffness is method E. It requires only easily accessible parameters (contact time, flight time, resting leg length, body mass and the leg's touch down angle). Method D is of similar quality but additionally requires the time-dependent progression of the GRF. The other three methods show clear differences from the model predictions by over- or underestimating leg stiffness, especially at slow speeds.Leg stiffness is derived from a conceptual model of legged locomotion and does not exist without this model. Therefore, it is important to prove which experimental method is suited best for approximating the stiffness in a specific task. This will help to interpret the predictions of the conceptual model in comparison with experimental data.     

Efficient Homolactic Fermentation by Kluyveromyces lactis Strains Defective in Pyruvate Utilization and Transformed with the Heterologous LDH Gene

A high yield of lactic acid per gram of glucose consumed and the absence of additional metabolites in the fermentation broth are two important goals of lactic acid production by microrganisms. Both purposes have been previously approached by using a Kluyveromyces lactis yeast strain lacking the single pyruvate decarboxylase gene (KlPDC1) and transformed with the heterologous lactate dehydrogenase gene (LDH). The LDH gene was placed under the control the KlPDC1 promoter, which has allowed very high levels of lactate dehydrogenase (LDH) activity, due to the absence of autoregulation by KlPdc1p. The maximal yield obtained was 0.58 g g⁻¹, suggesting that a large fraction of the glucose consumed was not converted into pyruvate. In a different attempt to redirect pyruvate flux toward homolactic fermentation, we used K. lactis LDH transformant strains deleted of the pyruvate dehydrogenase (PDH) E1α subunit gene. A great process improvement was obtained by the use of producing strains lacking both PDH and pyruvate decarboxylase activities, which showed yield levels of as high as 0.85 g g⁻¹ (maximum theoretical yield, 1 g g⁻¹), and with high LDH activity.     

Vibration induced osteogenic commitment of mesenchymal stem cells is enhanced by cytoskeletal remodeling but not fluid shear

Consistent across studies in humans, animals and cells, the application of vibrations can be anabolic and/or anti-catabolic to bone. The physical mechanisms modulating the vibration-induced response have not been identified. Recently, we developed an in vitro model in which candidate parameters including acceleration magnitude and fluid shear can be controlled independently during vibrations. Here, we hypothesized that vibration induced fluid shear does not modulate mesenchymal stem cell (MSC) proliferation and mineralization and that cell's sensitivity to vibrations can be promoted via actin stress fiber formation. Adipose derived human MSCs were subjected to vibration frequencies and acceleration magnitudes that induced fluid shear stress ranging from 0.04 Pa to 5 Pa. Vibrations were applied at magnitudes of 0.15g, 1g, and 2g using frequencies of both 100 Hz and 30 Hz. After 14 d and under low fluid shear conditions associated with 100 Hz oscillations, mineralization was greater in all vibrated groups than in controls. Greater levels of fluid shear produced by 30 Hz vibrations enhanced mineralization only in the 2g group. Over 3 d, vibrations led to the greatest increase in total cell number with the frequency/acceleration combination that induced the smallest level of fluid shear. Acute experiments showed that actin remodeling was necessary for early mechanical up-regulation of RUNX-2 mRNA levels. During osteogenic differentiation, mechanically induced up-regulation of actin remodeling genes including Wiskott–Aldrich syndrome (WAS) protein, a critical regulator of Arp2/3 complex, was related to the magnitude of the applied acceleration but not to fluid shear. These data demonstrate that fluid shear does not regulate vibration induced proliferation and mineralization and that cytoskeletal remodeling activity may play a role in MSC mechanosensitivity.     

Cross-training effect of chronic whole-body vibration exercise: a randomized controlled study

Abstract

Purpose: To determine whether unilateral leg whole-body vibration (WBV) strength training induces strength gain in the untrained contralateral leg muscle. The secondary aim was to determine the potential role of spinal neurological mechanisms regarding the effect of WBV exercise on contralateral strength training.

Materials and Methods: Forty-two young adult healthy volunteers were randomized into two groups: WBV exercise and Sham control. An isometric semi-squat exercise during WBV was applied regularly through 20 sessions. WBV training was applied to the right leg in the WBV group and the left leg was isolated from vibration. Sham WBV was applied to the right leg of participants in the Control group. Pre- and post-training isokinetic torque and reflex latency of both quadricepses were evaluated.

Results: The increase in the strength of right (vibrated) knee extensors was 9.4?±?10.7% in the WBV group (p?=?.001) and was 1.2?±?6.6% in the Control group (p?=?.724). The left (non-vibrated) extensorsvibrated) knee extensors w4?±?8.4% in the WBV group (p?=?.038), whereas it decreased by 1.4?±?7.0% in the Control (p?=?.294). The strength gains were significant between the two groups. WBV induced the reflex response of the quadriceps muscle in the vibrated ipsilateral leg and also in the non-vibrated contralateral leg, though with a definite delay. The WBV-induced muscle reflex (WBV-IMR) latency was 22.5?±?7.7?ms for the vibrated leg and 39.3?±?14.6?ms for the non-vibrated leg.

Conclusions: Chronic WBV training has an effect of the cross-transfer of strength to contralateral homologous muscles. The WBV-induced muscular reflex may have a role in the mechanism of cross-transfer strength.