Fatigue of the plantar intrinsic foot muscles increases navicular drop

Our purpose was to assess the effect of foot intrinsic muscle fatigue on pronation, as assessed with navicular drop, during static stance. Twenty-one healthy young adults participated. Navicular drop was measured before and after fatiguing exercise of the plantar foot intrinsic muscles. Surface electromyography of the abductor hallucis muscle was recorded during maximum voluntary isometric contractions (MVIC) in order to find the baseline median frequency (MedF). Subjects then performed sets of 75 repetitions of isotonic flexion contractions of the intrinsic foot muscles against a 4.55 kg weight on a custom pulley system. After each set an MVIC was performed to track shifts in MedF. After a MedF shift of at least 10%, navicular drop measurements were repeated. Subjects exhibited 10.0 ± 3.8 mm of navicular drop at baseline and 11.8 ± 3.8 mm after fatigue (p < 0.0005). The change in navicular drop was significantly correlated with change in MedF (r = .47, p = .03). The intrinsic foot muscles play a role in support of the medial longitudinal arch in static stance. Disrupting the function of these muscles through fatigue resulted in an increase in pronation as assessed by navicular drop.     

Functional electrical stimulation using microstimulators to correct foot drop: a case study

This paper presents a case study that tested the feasibility and efficacy of using injectable microstimulators (BIONs) in a functional electrical stimulation (FES) device to correct foot drop. Compared with surface stimulation of the common peroneal nerve, stimulation with BIONs provides more selective activation of specific muscles. For example, stimulation of the tibialis anterior (TA) and extensor digitorum longus (EDL) muscles with BIONs produces ankle flexion without excessive inversion or eversion of the foot (i.e., balanced flexion). Efficacy was assessed using a 3-dimensional motion analysis of the ankle and foot trajectories during walking with and without stimulation. Without stimulation, the toe on the affected leg drags across the ground. BION stimulation of the TA muscle and deep peroneal nerve (which innervates TA and EDL) elevates the foot such that the toe clears the ground by 3 cm, which is equivalent to the toe clearance in the less affected leg. The physiological cost index (PCI) measured effort during walking. The PCI equals the change in heart rate (from rest to activity) divided by the walking speed; units are beats per metre. The PCI is high without stimulation (2.29 +/- 0.37, mean +/- SD) and greatly reduced with surface (1.29 +/- 0.10) and BIONic stimulation (1.46 +/- 0.24). Also, walking speed increased from 9.4 +/- 0.4 m/min without stimulation to 19.6 +/- 2.0 m/min with surface and 17.8 +/- 0.7 m/min with BIONic stimulation. These results suggest that FES delivered by a BION is an alternative to surface stimulation and provides selective control of muscle activation.     

Effect of walking speed changes on tibialis anterior EMG during healthy gait for FES envelope design in drop foot correction.

Functional electrical stimulation may be used to correct hemiplegic drop foot. An optimised stimulation envelope to reproduce the EMG pattern observed in the tibialis anterior (TA) during healthy gait has been proposed by O'Keeffe et al. [O'Keeffe, D.T., Donnelly, A.E., Lyons, G.M., 2003. The development of a potential optimised stimulation intensity envelope for drop foot applications. IEEE Transactions on Neural Systems and Rehabilitation Engineering]. However this envelope did not attempt to account for changes in TA activity with walking speed. The objective of this paper was to provide data to enable the specification of an algorithm to control the adaptation of an envelope with walking speed. Ten young healthy subjects walked on a treadmill at 11 different walking speeds while TA EMG was recorded. The results showed that TA EMG recorded around initial contact and at toe off changed with walking speed. At the slowest velocities, equivalent to hemiplegic walking, the toe-off burst (TOB) of EMG activity had larger peak amplitude than that of the heel-strike burst (HSB). The peak amplitude ratio of TOB:HSB was 1:0.69 at the slowest speed compared to, 1:1.18 and 1:1.5 for the self-selected and fastest speed, respectively. These results suggest that an FES envelope, which produces larger EMG amplitude for the TOB than the HSB, would be more appropriate at walking speeds typical of hemiplegic patients.     

法兰地草莓的芳香类和黄酮类成分

为了解草莓(Fragaria×ananassa Duch.)法兰地品种的化学成分,采用色谱分离方法,从新鲜果实的乙醇提取物中获得19个化合物。通过波谱数据分析鉴定了它们的结构,分别为对羟基苯甲酸(1)、没食子酸乙酯(2)、鞣花酸3-O-α-L-鼠李糖苷(3)、苄基β-D-葡萄糖苷(4)、淫羊藿次苷F2(5)、苄基6-O-α-L-呋喃阿拉伯糖基-β-D-葡萄糖苷(6)、苯乙基6-O-α-L-呋喃阿拉伯糖基-β-D-葡萄糖苷(7)、反式肉桂酰基β-D-葡萄糖苷(8)、顺式肉桂酰基β-D-葡萄糖苷(9)、反式对香豆酰基β-D-葡萄糖苷(10)、顺式对香豆酰基β-D-葡萄糖苷(11)、反式阿魏酰基β-D-葡萄糖苷(12)、山柰酚(13)、反式椴树苷(14)、山柰酚3-O-β-D-葡萄糖醛酸苷(15)、槲皮素(16)、槲皮素3-O-β-D-葡萄糖苷(17)、槲皮素3-O-β-D-葡萄糖醛酸苷(18)和根皮苷(19),化合物1~12为芳香类,其余为黄酮类。所有化合物均为首次从法兰地品种中报道,化合物4~9为首次从草莓中获得。     

Age-related neuromuscular function during drop jumps.

Muscle- and movement-specific fascicle-tendon interaction affects the performance of the neuromuscular system. This interaction is unknown among elderly and consequently contributes to the lack of understanding the age-related problems on neuromuscular control. The present experiment studied the age specificity of fascicle-tendon interaction of the gastrocnemius medialis (GM) muscle in drop jump (DJ) exercises. Twelve young and thirteen elderly subjects performed maximal squat jumps and DJs with maximal rebound effort on a sledge apparatus. Ankle and knee joint angles, reaction force, and electromyography (EMG) from the soleus (Sol), GM, and tibialis anterior (TA) muscles were measured together with the GM fascicle length by ultrasonography. The results showed that the measured ankle joint stiffness (AJS) during the braking phase correlated positively with the rebound speed in both age groups and that both parameters were significantly lower in the elderly than in young subjects. In both groups, the AJS correlated positively with averaged EMG (aEMG) in Sol during the braking phase and was further associated with GM activation (r = 0.55, P < 0.01) and TA coactivation (TA/GM r = -0.4 P < 0.05) in the elderly subjects. In addition, compared with the young subjects, the elderly subjects showed significantly lower GM aEMG in the braking phase and higher aEMG in the push-off phase, indicating less utilization of tendinous tissue (TT) elasticity. These different activation patterns are in line with the mechanical behavior of GM showing significantly less fascicle shortening and relative TT stretching in the braking phase in the elderly than in the young subjects. These results suggest that age-specific muscle activation patterns as well as mechanical behaviors exist during DJs.     

A subsequent movement alters lower extremity muscle activity and kinetics in drop jumps vs. drop landings

Drop landings and drop jumps are common training exercises and injury research model tasks. Drop landings have a single landing, whereas drop jumps include a subsequent jump after initial landing. With the expected ground impact, instant and landing surface suggested to modulate landing neuromechanics, muscle activity, and kinetics should be the same in both tasks when landing from the same height onto the same surface. Although previous researchers have noted some differences between these tasks across separate studies, little research has compared these tasks in the same study. Thus, we examined whether a subsequent movement after initial landing alters muscle activity and kinetics between drop landings and jumps. Fifteen women performed 10 drop landings and drop jumps each from 45 cm. Muscle onsets and integrated muscle activation amplitudes 150 milliseconds before (preactivity) and after landing (postactivity) in the medial and lateral quadriceps, hamstrings, and lateral gastrocnemius and peak and time-to-peak vertical ground reaction forces were examined across tasks (p ≤ 0.05). When performing drop jumps, subjects demonstrated later (p = 0.02) gastrocnemius and lesser lateral gastrocnemius (p = 0.002) and medial quadriceps (p = 0.02) preactivity followed by increased postactivity in all muscles (p = 0.006), with higher peak vertical ground reaction forces (p = 0.04) but no differences in times to these peaks (p = 0.60) than drop landings. The later gastrocnemius activation, higher gastrocnemius and quadriceps postlanding amplitudes, and higher ground reaction forces in drop jumps may allow subjects to propel the body vertically after the initial landing vs. simply absorbing impact in drop landings. Our results indicate that in addition to landing surface and height, anticipation of a subsequent task changes landing neuromechanics. Generalizations of results from landing-only studies should not be made with landing followed-by-subsequent-activity studies. Landing exercises should be incorporated based on sport-specific demands.     

Strawberry Genes and Genomics

Despite its value as a crop and potential utility as an experimental system, relatively little is known about the molecular-genetic aspects of inheritance or physiology in the cultivated strawberry (Fragaria xananassa). This lack of information exists at a time when biotechnology may offer important remedies to address traditional and contemporary challenges that growers face. An improved understanding of genome structure will hasten the development of molecular markers and unveil clues to the composition of this unique, octoploid genome. Definition of gene function will guide the generation of transgenic resources for research use and possibly toward cultivar development. This review seeks to compile and present the current knowledge state of the molecular-genetic basis of cultivated strawberry genomic form and function. Ongoing studies promise to expand the use of genomic tools and appropriate model systems to rapidly discern the structural and functional basis for traits of interest to agriculture, such as those associated with disease, ripening, and volatile production. Together these studies bring new molecular tools to dissect complex traits, implement marker-assisted selection and address important physiological questions in the cultivated strawberry, the Fragaria genus, and the Rosaceae family.