Recent advances in the understanding of the repeated bout effect: the protective effect against muscle damage from a single bout of eccentric exercise

The repeated bout effect refers to the adaptation whereby a single bout of eccentric exercise protects against muscle damage from subsequent eccentric bouts. While the mechanism for this adaptation is poorly understood there have been significant recent advances in the understanding of this phenomenon. The purpose of this review is to provide an update on previously proposed theories and address new theories that have been advanced. The potential adaptations have been categorized as neural, mechanical and cellular. There is some evidence to suggest that the repeated bout effect is associated with a shift toward greater recruitment of slow twitch motor units. However, the repeated bout effect has been demonstrated with electrically stimulated contractions, indicating that a peripheral, non-neural adaptation predominates. With respect to mechanical adaptations there is evidence that both dynamic and passive muscle stiffness increase with eccentric training but there are no studies on passive or dynamic stiffness adaptations to a single eccentric bout. The role of the cytoskeleton in regulating dynamic stiffness is a possible area for future research. With respect to cellular adaptations there is evidence of longitudinal addition of sarcomeres and adaptations in the inflammatory response following an initial bout of eccentric exercise. Addition of sarcomeres is thought to reduce sarcomere strain during eccentric contractions thereby avoiding sarcomere disruption. Inflammatory adaptations are thought to limit the proliferation of damage that typically occurs in the days following eccentric exercise. In conclusion, there have been significant advances in the understanding of the repeated bout effect, however, a unified theory explaining the mechanism or mechanisms for this protective adaptation remains elusive.     

Effects of vaginal progesterone administration on uterine contractility at the time of embryo transfer

Objective: To investigate whether uterine contractility at the time of embryo transer (ET) can be reduced by early onset of luteal support with progesterone administered vaginally.

Design: Prospective analysis.

Setting: Assisted reproduction unit.

Patient(s): Eighty-four women undergoing 84 GnRH-a and FSH/hCG cycles for IVF-ET were studied.

Intervention(s): Vaginal progesterone was randomly started on the day of oocyte retrieval (group A, n = 43) or on the evening of ET (group B, n = 41). On the day of hCG administration and just before ET, 2-minute sagittal uterine scans were obtained by ultrasound and digitized with an image analysis system for assessing uterine contraction frequency.

Main Outcome Measure(s): Uterine contraction frequency.

Result(s): Whereas uterine contraction frequency was similar in both groups on the day of hCG (4.6 ± 0.3 and 4.5 ± 0.3 contractions per minute, respectively), only women in group A showed decreased uterine contraction frequency on the day of ET (2.8 ± 0.2 vs. 4.2 ± 0.3 contractions per minute).

Conclusion(s): Vaginal progesterone administration starting on the day of oocyte retrieval induced a decrease in uterine contraction frequency on the day of ET as compared with preovulatory values. Uterine relaxation before ET is likely to improve IVF-ET outcome by avoiding the displacement of embryos from the uterine cavity.     

Response to high-intensity eccentric muscle contractions in persons with myopathic disease

Although the response to intense eccentric muscle contractions is well described in normal subjects, concern exists about possible untoward effects in persons with myopathic diseases. We investigated 14 subjects with slowly progressive muscular dystrophies including myotonic muscular dystrophy (n = 9), facioscapulohumeral dystrophy (n = 2), limb-girdle syndrome (n = 2), and Becker muscular dystrophy (n = 1). Control subjects consisted of 18 able-bodied persons. Subjects performed two sets of eight maximal-effort eccentric repetitions of the elbow flexors, with measurement of maximal concentric strength, serum creatine kinase, resting and flexed arm angle, arm circumference, and soreness at days 0, 3, and 7. Although the myopathic group had less initial strength, both groups demonstrated a similar response to the protocol over 7 days. Both groups had a significant rise in serum creatine kinase, which was still elevated at 7 days (P < 0.05). The control group demonstrated a slightly greater injury response in terms of soreness, resting and flexed arm angles, and arm swelling. Both groups of subjects appeared to respond similarly to an acute bout of eccentric contractions. However, the potential long-term effects of this type of exercise in persons with myopathic diseases remains unknown.     

The effect of electrical stimulation on leg muscle pump activity in spinal cord-injured and able-bodied individuals

The purpose of this study was to examine the difference in: (1) effective muscle pump activity (MPA) between voluntary and electrically (ES) induced contractions in able-bodied subjects (ABS); and (2) ES-induced MPA between spinal cord-injured (SCI) individuals and ABS. MPA was measured as relative volume changes in the calf using strain-gauge plethysmography during repeated muscle contractions in the supine position while venous outflow was impeded by a thigh cuff inflated to a range of pressures. Ten SCI individuals and ten ABS participated in this study. ABS showed no significant difference between voluntary and electrically induced MPA [58.1 (18.4)% versus 67.7 (8.7)%, respectively]. SCI individuals showed a significantly lower ES-induced MPA than ABS [21.5 (15.9)% versus 67.7 (8.7)%, respectively]. The low MPA in SCI individuals may be explained by: (1) extensive leg muscle atrophy and/or (2) an “atrophic” vascular system in the legs. The electrical current level seemed to influence MPA (43 mA, 21.5% versus 60 mA, 30.8%) for SCI individuals, whereas no influence of muscle contraction rate on MPA was observed in ABS. The results of this study demonstrate that although ES-induced leg muscle contractions result in adequate MPA in ABS, it leads to significantly less effective MPA in SCI individuals. Accepted: 21 March 2000     

ECG abnormalities and stroke incidence

In this review, the authors discuss the role of ECG in prediction of stroke. ECG plays an important role in detection of several stroke risk factors/predictors including atrial fibrillation and left ventricular hypertrophy; both are components of the Framingham Stroke Risk Score. Multiple other ECG traits have also emerged as potential predictors of stroke, namely cardiac electrical/structural remodeling – Q wave, QRS/QT duration, bundle blocks, P wave duration/amplitude/dispersion, other waveform angles and slopes; higher automaticity – ectopic beats; and re-entry – atrial tachyarrhythmia; and higher vulnerability to arrhythmia – heart rate and its variability. Most of these predictors are not ready for prime time yet; however, further research focusing on their role in risk stratification and prevention of stroke may be useful. In this article, the authors discuss the prevalence, mechanisms and clinical applications of traditional and novel ECG markers in the prevention and treatment of stroke.     

针刺激发感传对颈动脉和椎动脉血流量作用的观察

本文介绍引用美国 Sramek 介绍的头部总血流量的测定方法,以针刺激发感传方法对主要以椎动脉供血不足的椎动脉型颈椎病55例,和颈动脉供血不足的缺血性脑血管疾病66例进行了临床疗效和实验观察,结果提示,气至病所组疗效最明显,有感传组次之,局感组相对最差。实验结果提示针刺激发感传后使血管痉挛得以缓解,降低了血管紧张度和阻塞程度,使颈动脉、椎动脉血流量明显增加,起到了通经脉、调气血、活血化瘀及改善脑循环的作用。     

Electrocardiographic Characteristics of Ventricular Arrhythmias Arising from the Aortic Sinuses of Valsalva: A Case Report and Review of the Literature

We describe a patient with frequent, symptomatic, and drug-refractory premature ventricular contractions (PVCs) with a right bundle branch block, inferior axis morphology suggestive of a left ventricular outflow tract (LVOT) origin. Successful ablation of the PVCs was performed from the left coronary cusp of the aortic valve. We discuss our patient and review the literature regarding patients with ventricular arrhythmias arising from the coronary cusps, with special emphasis on the use of the electrocardiogram to aid localization of the focus.     

Central fatigue of the first dorsal interosseous muscle during low-force and high-force sustained submaximal contractions

The aim of this study was to compare the extent of central fatigue in the first dorsal interosseous (FDI) muscle of healthy adults in low, moderate and high-force submaximal contractions. Nine healthy adults completed four experimental sessions where index finger abduction force was recorded during voluntary contractions and in response to brief trains (five pulses at 100 Hz) of electrical stimulation. The ability to maximally activate FDI under volition, or voluntary activation, and its change with sustained activity (central fatigue) was assessed using the twitch interpolation technique. The fatigue tasks consisted of continuous isometric index finger abduction contractions held until exhaustion at four target force levels: 30%, 45%, 60% and 75% of the maximal voluntary contraction. The main finding was the presence of central fatigue for the 30% task, but not for the three other fatigue tasks. The extent of central fatigue was also associated with changes in a measure reflecting the status of peripheral structures/mechanisms. It appears that central fatigue contributed to task failure for the lowest force fatigue task (30%), but not for the other (higher) contraction intensities.     

Unusual association of a unique CAG interruption in 5′ of DM1 CTG repeats with intergenerational contractions and low somatic mosaicism

Myotonic dystrophy type 1 (DM1) is a dominant multisystemic disorder associated with high variability of symptoms and anticipation. DM1 is caused by an unstable CTG repeat expansion that usually increases in successive generations and tissues. DM1 family pedigrees have shown that ～90% and 10% of transmissions result in expansions and contractions of the CTG repeat, respectively. To date, the mechanisms of CTG repeat contraction remain poorly documented in DM1. In this report, we identified two new DM1 families with apparent contractions and no worsening of DM1 symptoms in two and three successive maternal transmissions. A new and unique CAG interruption was found in 5′ of the CTG expansion in one family, whereas multiple 5′ CCG interruptions were detected in the second family. We showed that these interruptions are associated with maternal intergenerational contractions and low somatic mosaicism in blood. By specific triplet‐prime PCR, we observed that CTG repeat changes (contractions/expansions) occur preferentially in 3′ of the interruptions for both families.