Influence of falling height on the excitability of the soleus H-reflex during drop-jumps

Aim: The stretch‐shortening cycle (SSC) is characterized by stretching of the target muscle (eccentric phase) prior to a subsequent shortening in the concentric phase. Stretch reflexes in the eccentric phase were argued to influence the performance of short lasting SSCs. In drop‐jumps, the short latency component of the stretch reflex (SLR) was shown to increase with falling height. However, in jumps from excessive heights, the SLR was diminished. So far, it is unclear whether the modulation of the SLR relies on spinal mechanisms or on an altered fusimotor drive. The present study aimed to assess the spinal excitability of the soleus Ia afferent pathway at SLR during jumps from low height (LH – 31 cm) and excessive height (EH – 76 cm). Methods: In 20 healthy subjects (age 25 ± 3 years), H‐reflexes were timed to occur at the peak of the SLR during drop‐jumps from LH and EH. Results: H‐reflexes were significantly smaller at EH than at LH (P < 0.05). Neither soleus and tibialis anterior background EMG nor the size of the maximum M‐wave changed with falling height. Conclusion: Differences in the H‐reflex between EH and LH indicate that spinal mechanisms are involved in the modulation of the SLR. A decreased excitability of the H‐reflex pathway at EH compared with LH is argued to serve as a ‘prevention strategy’ to protect the tendomuscular system from potential injuries caused by the high load. It is argued that pre‐synaptic inhibition of Ia afferents is most likely responsible for the change in H‐reflex excitability between the two jump conditions.     

Abnormal corticospinal tract modulation of the soleus H reflex in patients with pure spastic paraparesis

Central motor conduction time (CMCT) is usually abnormally prolonged in leg muscles of patients with pure hereditary spastic paraparesis (PHSP). One consequence of such abnormality should be an abnormal timing in the modulation of segmental reflexes, which might be more relevant for the pathophysiology of spasticity-related gait disturbances than just the CMCT delay. We examined the effects of transcranial magnetic stimulation (TMS) on the soleus H reflex in 13 control subjects and 11 PHSP patients using a conditioning (TMS) and test (H reflex) paradigm. Interstimulus interval (ISI) was 0-100ms in steps of 10ms. The amplitude of the H reflex at each interval was expressed as percentage of the control H reflex and the conditioned curves were compared between control subjects and patients. In control subjects, TMS-induced facilitation of the H reflex with two well-defined phases: early (ISIs 10 and 20ms) and late (ISIs 70-90ms). In patients, the early phase of facilitation was significantly reduced, while there was facilitation at 40ms that was not present in control subjects. However, neither the characteristics of the MEP nor the differential modulation of the H reflex correlated significantly with clinical measures of motor dysfunction. Our results indicate an abnormal effect of TMS on the H reflex in PHSP patients. This suggests that the excitability of interneurons and soleus motoneurons is not modified in tune with the arrival of descending inputs. Desynchronization of the descending volley may contribute to both the lack of early facilitation and the presence of abnormal facilitatory phases.     

Temperature dependence of soleus H-reflex and M wave in young and older women

The purpose of this study was to investigate the effect of altered local temperature on soleus H-reflex and compound muscle action potential (M wave) in young and older women. H-reflex and M wave responses were elicited in 10 young (22.3±3.3 years) and 10 older (72.5±3.2 years) women at three muscle temperatures: control (34.2±0.3°C), cold (31.3±0.5°C) and warm (37.1±0.2°C). H-reflex output, expressed as the ratio between maximal H-reflex and maximal M wave (H_max/M_max), was lower in the older, compared with the younger, group, regardless of temperature. In control temperature conditions, for example, the H_max/M_max ratio was 36.8±24% in the young and 25.4±20% in the older (P<0.05). Warming had no effect on the H-reflex output in either group, whilst cooling increased H-reflex output only in the younger group (+28%). In both groups, cooling increased (+5.3%), and warming decreased (–5.5%) the H-reflex latency. This study confirms that older individuals experience a reduced ability to modulate the reflex output in response to a perturbation. In a cold environment, for example, the lack of facilitation in the reflex output, along with a delayed reflex response could be critical to an older individual in responding to postural perturbations thus potentially compromising both static and dynamic balance.     

Neural adaptations to strength training: moving beyond transcranial magnetic stimulation and reflex studies

It has long been believed that training for increased strength not only affects muscle tissue, but also results in adaptive changes in the central nervous system. However, only in the last 10 years has the use of methods to study the neurophysiological details of putative neural adaptations to training become widespread. There are now many published reports that have used single motor unit recordings, electrical stimulation of peripheral nerves, and non-invasive stimulation of the human brain [i.e. transcranial magnetic stimulation (TMS)] to study neural responses to strength training. In this review, we aim to summarize what has been learned from single motor unit, reflex and TMS studies, and identify the most promising avenues to advance our conceptual understanding with these methods. We also consider the few strength training studies that have employed alternative neurophysiological techniques such as functional magnetic resonance imaging and electroencephalography. The nature of the information that these techniques can provide, as well as their major technical and conceptual pitfalls, are briefly described. The overall conclusion of the review is that the current evidence regarding neural adaptations to strength training is inconsistent and incomplete. In order to move forward in our understanding, it will be necessary to design studies that are based on a rigorous consideration of the limitations of the available techniques, and that are specifically targeted to address important conceptual questions.     

Effects of plyometric training on passive stiffness of gastrocnemii muscles and Achilles tendon

Plyometric training is commonly used to improve athletic performance; however, it is unclear how each component of the muscle-tendon complex (MTC) is affected by this intervention. The effects of 14?weeks of plyometric training on the passive stiffness of the gastrocnemii muscles and Achilles tendon was determined simultaneously to assess possible local adaptations of elastic properties. The passive force-length relationship of the gastrocnemii MTC and elongation of the gastrocnemii muscles were determined using ultrasonography during passive cyclic stretching in 19 subjects divided into trained (n?=?9) and control (n?=?10) groups. An upward trend in stiffness of the gastrocnemii MTC (P?=?0.09) and a significant increase in the intrinsic gastrocnemii muscle stiffness were found (P??0.05). Considering the lack of change in gastrocnemii muscle geometry, the change in the gastrocnemii muscle stiffness may be mainly due to a change in the intrinsic mechanical properties of the muscular tissues.     

Effects of acute exercise on the soleus H-reflex and self-reported anxiety after caffeine ingestion

The effects of moderate intensity cycling exercise on the soleus H-reflex and state anxiety were examined among 16 individuals whose anxiety was experimentally manipulated by consumption of a large dose of caffeine. The soleus H-reflex and state anxiety were measured before and 1 h after consuming caffeine or placebo and then again 10 min after 30 min of either cycling at an intensity of 60% VO(2peak) or quiet rest. We found that (1) caffeine consumption did not influence the amplitude of the soleus H-reflex, but it did increase state anxiety; (2) acute exercise reduced the soleus H-reflex after consumption of either caffeine or placebo, but it reduced state anxiety only after consumption of caffeine; and (3) there was no evidence of a relationship between changes in the soleus H-reflex and state anxiety. Exercise-induced anxiolysis does not appear to underlie the postexercise reduction of the soleus H-reflex.     

Effect of ischemia on contractile and histochemical properties of the rat soleus muscle

Ligature and section of the abdominal aorta results in only minor and temporary functional and metabolic changes in the slow soleus muscle of the rat. A very small decrease in maximal tetanic tension corresponds to a few scattered areas of damaged and necrotic muscle fibres, in which decreased succinic dehydrogenase and loss of phosphorylase activity was observed.A new experimental approach, i.e. ligature and section of the abdominal aorta combined with terminal devascularisation, preserving intact tendons and innervation of the muscle causes maximal muscle ischemia, followed by an almost complete loss of tetanic tension output, marked shortening of contraction time and profound morphological and histochemical changes. The decrease in succinic dehydrogenase and ATPase activities and loss of phosphorylase activity occur in the majority of degenerating muscle fibres except for a thin rim of peripheral fibres during the first 4 days. Subsequently, the contractile properties recover gradually and enzyme activities reappear in the regenerating muscle fibres simultaneously with new revascularisation. Thirty days after the operation all the parameters observed returned to control values.Deceased August 6, 1977     

Effect of acute unloaded arm versus leg cycling exercise on the soleus H-reflex in adults with multiple sclerosis

This study compared the effect of acute bouts of unloaded arm versus leg cycling exercise on spasticity of the lower legs in persons with multiple sclerosis (MS) and then examined post-activation depression (PAD) as a possible mechanism for the anti-spastic effects of acute exercise. Participants (N = 10) had relapsing-remitting MS, slight to moderate spasticity of the soleus muscle, and were independently ambulatory. Spasticity was measured in the soleus muscle using the H-reflex and modified Ashworth scale (MAS). PAD was measured in the soleus muscle based on a simple, standardized protocol for modifying the parameters for evoking the H-reflex. In three separate sessions participants undertook 20 min of either unloaded arm cycling exercise, unloaded leg cycling exercise, or control (quiet sitting) conditions in a random order, and data were collected before and after all three conditions. The H-reflex and MAS were significantly decreased after both unloaded arm and leg cycling exercise and significantly increased after quiet sitting. There was no change over time in PAD among the conditions. The reduction in the H-reflex was ∼50% larger after leg than arm cycling exercise, whereas the reduction in MAS scores was ∼20% larger after leg than arm cycling exercise. Such findings provide support for anti-spastic potential of both arm and leg cycling exercise on spasticity of the legs, but indicate that the effect is larger for the musculature that is activated during cycling and not explained by PAD.     

Effects of stretch-shortening cycle training on mechanical properties and fibre type transition in the rat soleus muscle

The effects of exercise training on mechanical properties and fibre type transitions have been investigated in rat soleus muscle. The exercise was a repetition of stretch-shortening cycles. A method of dual controlled releases was applied to obtain tension/extension curves, which characterize the elastic behaviour of the series elastic component (SEC), and the force/velocity relationship characterizing the contractile elements. Other contractile measurements included: contraction time (t _c), half-relaxation time (t _1/2) and twitch/tetanus ratio (P _t/P _o). Additionally, the muscle fibre type composition was determined by a classical histochemical method. A 12-week period of training induced a significantly higher percentage of fast-twitch fibres and a lower percentage of slow-twitch fibres (P<0.01). This fibre adaptation led to a significant (P<0.01) decrease in t _c and an increase in maximum shortening velocity (V _max). An increase in compliance of the SEC was also observed. This elastic adaptation is interpreted in terms of modification of the active components of the SEC. All the histochemical and mechanical data presented in this study show that rat soleus muscles trained by stretch-shortening cycles acquired faster characteristics. Thus the results confirm that a slow-twitch to a fast-twitch fibre transition is obtainable in mature rats.     

Influence of lower body negative pressure release on soleus H reflex,respiratory sensations and reflexes in human subjects

Using a physiological model of acutely increasing venous return into the lungs, i.e. by applying and then releasing lower body negative pressure (LBNP) to mimic the natural stimulus of juxtapulmonary capillary (J) or pulmonary C fibre receptors, produced an immediate and significant reduction in the amplitude of the Hoffman (H) reflex by 81 ± 4% (P = 0.001) in a majority of subjects 70% (n = 5). Accompanying this was a notable change in the respiratory pattern with tidal volume (V_T) increasing in all subjects from (mean) 0.462 ± .038 to 0.777 ± .061 l/min (P = 0.001) and the respiratory rate (F_R) in 40% from 14 ± 1 to 24 ± 0.8 breaths/min. A feeling of pressure in throat, upper chest was reported by all and a shortness of breath-by 70% of the subjects. These were similar in nature to the respiratory sensations felt with threshold doses of intravenous lobeline, a well-established chemical stimulant of J receptors. All effects lasted for 15–20 s and within a minute the parameters resumed their earlier control values.     

TH1型/TH2型细胞因子对滋养层及蜕膜内分泌功能的影响

目的　探讨辅助T细胞 (TH) 1型 / 2型细胞因子对人绒毛组织及蜕膜组织内分泌功能的影响。方法　应用新鲜绒毛组织和蜕膜组织建立体外分泌人绒毛膜促性腺激素 (hCG)及催乳素(PRL)的模型。hCG及PRL的分泌水平应用放免法 (RIA)进行分析测定。结果　TH1型细胞因子γ干扰素 (IFN γ)在一定的浓度范围内 (10～ 10 0 0ng/ml)对绒毛组织分泌hCG有明显的抑制作用 (P <0 .0 1) ;而TH2型细胞因子白细胞介素 4 (IL 4 ) (1～ 10ng/ml)则有明显的促进作用 (P <0 .0 1)。TH1型细胞因子IFN γ低浓度时 (1～ 10ng/ml)对蜕膜组织分泌PRL有刺激作用 (P <0 .0 5 ) ,高浓度时 (10 0～10 0 0ng/ml)则有抑制作用 (P <0 .0 1) ;TH2型细胞因子IL 4对PRL分泌的调节作用与对hCG分泌的作用相类似。结论　TH1型 /TH2型细胞因子可能通过影响滋养层及蜕膜内分泌功能而在早期妊娠中起重要的免疫调节作用。     

Effects of cycling exercise on the soleus H-reflex and state anxiety among men with low or high trait anxiety

The present study examined the effects of low- and high-intensity cycling exercise on the H-reflex and state anxiety among men having low (n=20) or high (n=20) trait anxiety. Participants completed measures of state anxiety and underwent elicitation and recording of the H-reflex in the soleus muscle before and 10 min after three 20-min conditions: (1) quiet rest, (2) cycling at 40% VO2peak, and (3) cycling at 70% VO2peak. We found that (1) exercise, but not quiet rest, resulted in a reduction of the H-reflex; the magnitude of the reduction did not differ between men having low or high trait anxiety; (2) exercise and quiet rest resulted in similar reductions of state anxiety, and the magnitude of the reductions was larger for men having high trait anxiety than low trait anxiety; and (3) reductions of the H-reflex were unrelated to reductions of self-reported state anxiety across all three conditions. Contrary to prior opinion, the postexercise reduction in the H-reflex reported by previous researchers and in the present study appears to be unrelated to self-reported anxiety after exercise.     

孕酮对人T淋巴细胞体外活化CD69表达的作用

目的：探讨孕酮（Ｐｒｏｇｅｓｔｅｒｏｎｅ,Ｐｒｏｇ）及地塞米松（Ｄｅｘａｍｅｔｈａｓｏｎｅ,Ｄｅｘ）对人外周血Ｔ淋巴细胞体外活化ＣＤ６９表达的作用。方法：以女性健康志愿者（１０名）为研究对象,以蛋白激酶Ｃ的刺激剂佛波醇酯（Ｐｈｏｒｂｏｌ ｅｓｔｅｒ,ＰＤＢ）为Ｔ淋巴细胞的活化剂,采用双荧光染色流式细胞技术。检测ＣＤ３＾＋的Ｔ淋巴细胞表达早期活化表面分子ＣＤ６９的百分率,以观察Ｐｒｏｇ、Ｄｅｘ及Ｐｒｏ０ｇ加上Ｄｅｘ对外周血Ｔ淋巴细胞体外活化的作用。结果：在体外培养条件下,无论单独使用Ｐｒｏｇ还是Ｄｅｘ均地强低剂量ＰＤＢ刺激ＣＤ６９的表达。然而,与单独使用Ｐｒｏｇ或Ｄｅｘ的作用相比。Ｐｒｏｇ加上Ｄｅｘ明显减弱低剂量ＰＤＢ的活化ＣＤ６９的表达。结论：同时使用Ｐｒｏｇ与Ｄｅｘ可明显抑制Ｔ淋巴细胞的体外活化,提示在临床上     

微囊化转mIL-12基因细胞介导荷瘤小鼠TH1/TH2的漂移

目的　观察微囊化mIL 1 2基因修饰的 (中国仓鼠卵巢 )CHO细胞皮下移植对荷瘤小鼠TH1 TH2 类细胞因子的影响 ,进一步了解外源性IL 1 2对TH1 TH2 平衡的调节作用 ,同时探讨微囊化基因工程细胞移植治疗恶性肿瘤的可行性。方法　将mIL 1 2基因转染到正常细胞CHO ,然后进行微囊化 ,移植到荷瘤小鼠的皮下。 2 0d后 ,测定小鼠血清TH1 和TH2 类细胞因子IFN γ、IL 2、IL 1 2和IL 4、IL 1 0的水平。结果　经微囊化mIL 1 2基因修饰的CHO细胞皮下移植干预治疗后 ,小鼠血清TH1 细胞因子IFN γ、IL 2、IL 1 2水平明显升高 (P <0 .0 5) ,而TH2 类细胞因子IL 4、IL 1 0则明显降低 (P <0 .0 5)。结论　外源性mIL 1 2促进荷瘤小鼠TH1 细胞的分化 ,使TH1 TH2 向着TH1 方向漂移 ;微囊化基因工程细胞的移植 ,有望替代基因工程药物 ,成为恶性肿瘤生物免疫治疗的平台     

Effect of altered thyroid state on the in situ mechanical properties of adult cat soleus

To determine the responsiveness of cat hindlimb muscles to thyroid manipulation, adult female cats were made hypothyroid (thyroidectomy plus tapazole treatment), hyperthyroid (synthroid pellets), or maintained euthyroid. After 4 months, the hypothyroid soleus had slower time-to-peak (TPT, 80%) and half-relaxation (HRT) times, whereas the hyperthyroid soleus had faster TPT (20%) and HRT than euthyroid cats. The tension at low stimulation frequencies (5-15 Hz) was higher in hypothyroid and lower in hyperthyroid cats compared to euthyroid cats. Muscle weight, maximum twitch and tetanic (Po) tensions, and maximum rates of shortening (Vmax) were similar across groups. The soleus of hypothyroid cats was more fatigable than normal. The myosin heavy chain (MHC) composition, based on gel electrophoresis, was unaffected by thyroid hormone manipulation. Based on the reaction of monoclonal antibodies for specific MHCs, some fast fibers in the hypothyroid cats coexpressed developmental MHC. These data indicate that 4 months of an altered thyroid state result in changes in the isometric twitch speed properties of the cat soleus, but not the tension-related or isotonic properties. Further, a chronic decrease in thyroid hormone had a greater impact than a chronic increase in thyroid hormone on the mechanical properties of the adult cat soleus.     

Influence of different properties of a reaction time task on the pre-movement gating of input from Ia afferents to motoneurons

Summary The monosynaptic reflex (H reflex) is facilitated before movement onset in human subjects who are performing a conditioned plantar flexion of the ankle in a reaction time task. The aim of this study was to investigate how tightly this gating of Ia spindle input is coupled with the conditioned muscle contraction. Test H reflexes were elicited at various times during the reaction time (RT) in order to test the efficacy of Ia volleys on the soleus motoneurons. Tactile, auditory and visual go stimuli were used. The RT to a tactile stimulus was about the same as the RT to an auditory stimulus although distance and therefore conduction time from the site of stimulation to the cerebral cortex was much larger for the tactile than for the auditory modality. The RT to visual stimulation was about 20 ms longer than to the other two modalities. Although central latencies depended clearly on the stimulus modality the duration of the H reflex facilitation, i.e. the interval between the onset of the facilitation and the onset of the voluntary muscle contraction, was always the same. Similarly, the reflex facilitation was insensitive to the succeeding contrast of a visual go stimulus. The subjects were also examined in visual RT tasks in which different advance information about the laterality and the execution of the contraction was given. By combination the following four RT situations were realized: (1) simple, go, (2) choice, go, (3) simple, go — no go and (4) choice, go — no go. RT was shortest in the simple go and increased by about 65 ms in the choice, go and the simple, go — no go situation. It lengthened, however, less than 130 ms in the choice, go — no go situation indicating an interaction between the factors laterality and execution of the contraction. As with various stimulus modalities and succeeding contrasts, the premovement H reflex facilitation remained constant irrespective of the complexity of the RT task. This property was however not observed if data obtained within one RT task (constant modality, simple, go) were processed. There was a highly significant positive correlation between the duration of the facilitation and RT. The duration of the EMG burst of the conditioned contraction was, however, independent of RT. These results were interpreted as indicating that RT depended on attention which affects most central components of RT and that the interval between the onset of the gating process and the onset of the contraction (duration of the H reflex facilitation) might depend on several supraspinal motor centers whereas the duration of the EMG burst might be computed locally. Several studies including the present one provide a possible explanation for the lag between the onset of the H reflex facilitation and the movement onset. The relatively slow speed at which presynaptic inhibition at Ia afferents can be removed necessitates an early onset such that a fully operative spinal reflex for assistance of muscle contractions and correction of perturbances is assured at movement onset.     

Effects of sprint and endurance training on passive stress–strain relation of fast‐ and slow‐twitch skeletal muscle in Wistar rat

We investigated the effects of endurance and sprint training on the passive mechanical properties of fast‐twitch (FT) and slow‐twitch (ST) skeletal muscles. Eight‐week‐old male Wistar rats (n=18) were divided into three groups: control (C), sprint‐trained (S) and endurance‐trained (E). The trained animals exercised for 10 weeks on a treadmill. Under anaesthesia, Plantaris and Soleus muscles were deformed cyclically in vivo at 0.33 mm s^–1 with length increments of 1 mm in successive cycles until rupture. The rupture of muscle occurs at belly. Stress–strain relation were constructed using the maximum stress and maximum strain in each cycle. The data were fitted to an S‐shaped curve. The curve‐fitting parameters for trained and untrained muscles showed significant statistical differences. Stress and strain at rupture and maximum deformation energy were statistically greater for trained ST muscles (both groups) than for the controls. The changes induced by the present training protocols were not significant in Plantaris. The above results suggest the plasticity of passive structure caused by activity‐demands.