Gentle exercise with a previously inactive muscle group hastens the decline of blood lactate concentration after strenuous exercise

Summary The aim of this study was to elucidate the mechanism by which the disappearance of blood lactate following severe exercise is enhanced during active recovery in comparison with recovery at rest. Rates of decline of arterialised venous blood lactate concentrations in man after maximal one-leg exercise were compared during four different modes of recovery: passive (PR), exercise of the muscles involved in the initial exercise (SL), exercise of the corresponding muscles in the hitherto-inactive leg (OL), or exercise of one arm (RA). Recovery exercise workloads were each 40% of the onset of blood lactate accumulation (OBLA) for the limb used. In comparison with PR, SL and OL accelerated the fall in blood lactate to similar extents whereas RA was without effect. The first-order rate constant (min^–1) for decline of arterialised venous blood lactate concentration after the intense exercise was 0.027 (0.003) in PR, 0.058 (0.025) in SL, 0.034 (0.002) in OL, and in RA was 0.028 (0.002) [mean (SEM),n = 6 subjects]. Preliminary studies had shown that RA in isolation elevated blood lactate whereas SL and OL did not. Thus, with appropriate workloads, exercise of either hitherto active or passive muscles enhanced blood lactate decline during recovery from intense exercise. This suggests that the effect resulted principally from the uptake and utilisation of lactate in the circulation by those exercising muscles rather than from increased transport of lactate to other sites of clearance by sustained high blood flow through the previously active muscles.     

Cross-validation of the 20- versus 30-s Wingate anaerobic test

The 30-s Wingate anaerobic test (30-WAT) is the most widely accepted protocol for measuring anaerobic response, despite documented physical side effects. Abbreviation of the 30-WAT without loss of data could enhance subject compliance while maintaining test applicability. The intent of this study was to quantify the validity of the 20-s Wingate anaerobic test (20-WAT) versus the traditional 30-WAT. Fifty males (mean ± SEM; age = 20.5 ± 0.3 years; Ht = 1.6 ± 0.01 m; Wt = 75.5 ± 2.6 kg) were randomly selected to either a validation (N = 35) or cross-validation group (N = 15) and completed a 20-WAT and 30-WAT in double blind, random order on separate days to determine peak power (PP; W kg⁻¹), mean power (MP; W kg⁻¹), and fatigue index (FI; %). Utilizing power outputs (relative to body mass) recorded during each second of both protocols, a non-linear regression equation (Y _20WAT+10 = 31.4697 e^−0.5[ln(X _second/1174.3961)/2.6369²]; r ² = 0.97; SEE = 0.56 W kg⁻¹) successfully predicted (error ∼10%) the final 10 s of power outputs in the cross-validation population. There were no significant differences between MP and FI between the 20-WAT that included the predicted 10 s of power outputs (20-WAT+10) and the 30-WAT. When derived data were subjected to Bland–Altman analyses, the majority of plots (93%) fell within the limits of agreement (±2SD). Therefore, when compared to the 30-WAT, the 20-WAT may be considered a valid alternative when used with the predictive non-linear regression equation to derive the final power output values.     

Effects of a 200 W–15 min cycling exercise on postural control during quiet standing in healthy young adults

The purpose of the present experiment was to investigate the immediate effects of a cycling exercise on postural control during quiet standing in healthy young adults. To this aim, 12 university students were asked to stand upright as immobile as possible, with their eyes closed, prior to and following a 15 min cycling exercise performed at a power output of 200 W. Centre of foot pressure (CP) displacements, recorded using a force platform along both the medio-lateral (ML) or antero-posterior (AP) axes, were used to compute the motions of the vertical projection of the centre of gravity (CG _v ) and those of the difference between the CP and the CG _v (CP − CG _v ). Metabolic (heart rate, respiratory exchange ratio and blood lactate concentration) and psychological (rate of perceived exertion) measurements ensured that subjects were fatigued at the end of the cycling exercise. The cycling exercise induced a decreased of both CG _v and CP − CG _v motions along the AP-axis, whereas no significant changes were observed along the ML-axis. These discrepancies of the postural effects according to the direction of balance are likely to stem from the directionally sensitive activity of postural muscles, when considering (1) what the cycling exercise involved in terms of joints and tendons receptors stimulation and lower limb muscles recruitment (i.e. sagittal plane movers of the lower extremities) and (2) the skeletal muscles involved in postural control during quiet standing (i.e. sagittal and frontal plane movers of the lower extremities for the AP and ML balance, respectively).     

Aerobic–anaerobic transition intensity measured via EMG signals in athletes with different physical activity patterns

The purpose of the present study was to investigate the use of electromyographic signals (EMG), to determine the EMG threshold (EMGT) in four lower extremity muscles and to compare these thresholds with the second ventilatory threshold (VT2) in subjects participating in different sports and at different performance levels. Forty-nine subjects (23.8 ± 5.7 years, 182.7 ± 5.3 cm, 79.1 ± 8.6 kg) including eleven cyclists, ten team-handball players, nine kayakers, eight power lifters and eleven controls were investigated utilizing a cycle ergometer. Respiratory gas exchange measures were collected and EMG activity was continuously recorded from four muscles (vastus lateralis, vastus medialis, biceps femoris and gastrocnemius lateralis). The VO₂max averaged 56.1 ± 11.1 ml kg⁻¹ min⁻¹, the average aerobic power was 348.5 ± 61.0 W and the corresponding VT2 occurred at 271.4 ± 64.0 W. The EMGT ranged from 80 to 98% of power output for the different muscles. The VT2 and EMG thresholds from four different muscles were not different. When thresholds were analyzed among different groups of subjects, no significant difference was observed between VT2 and EMGT despite threshold differences between the groups. All four EMGT were significantly related to maximal aerobic power (r = 0.73–0.83) and were highly correlated to each other (r = 0.57–0.88). In conclusion, EMGT can be used to determine the VT2 for individuals independent of sport specificity or performance level.     

<Emphasis Type="Italic">V</Emphasis>O<Subscript>2</Subscript>max during successive maximal efforts

The concept of VO₂max has been a defining paradigm in exercise physiology for >75 years. Within the last decade, this concept has been both challenged and defended. The purpose of this study was to test the concept of VO₂max by comparing VO₂ during a second exercise bout following a preliminary maximal effort exercise bout. The study had two parts. In Study #1, physically active non-athletes performed incremental cycle exercise. After 1-min recovery, a second bout was performed at a higher power output. In Study #2, competitive runners performed incremental treadmill exercise and, after 3-min recovery, a second bout at a higher speed. In Study #1 the highest VO₂ (bout 1 vs. bout 2) was not significantly different (3.95 ± 0.75 vs. 4.06 ± 0.75 l min⁻¹). Maximal heart rate was not different (179 ± 14 vs. 180 ± 13 bpm) although maximal V _E was higher in the second bout (141 ± 36 vs. 151 ± 34 l min⁻¹). In Study #2 the highest VO₂ (bout 1 vs. bout 2) was not significantly different (4.09 ± 0.97 vs. 4.03 ± 1.16 l min⁻¹), nor was maximal heart rate (184 + 6 vs. 181 ± 10 bpm) or maximal V _E (126 ± 29 vs. 126 ± 34 l min⁻¹). The results support the concept that the highest VO₂ during a maximal incremental exercise bout is unlikely to change during a subsequent exercise bout, despite higher muscular power output. As such, the results support the “classical” view of VO₂max.     

siRNA沉默VDAC1对MCF-7细胞增殖、周期的影响及其作用机制

[目的]观察siRNA沉默VDAC1基因对乳腺癌MCF-7细胞增殖及细胞周期的影响.[方法]针对人VDAC1基因设计并合成siRNA,并将VDAC1-siRNA转染MCF-7细胞后,应用实时荧光定量PCR和Western印迹法检测MCF-7细胞中VDAC1的表达水平,MTT法检测MCF-7细胞的增殖情况,流式细胞术检测MCF-7细胞的周期分布,同时Western印迹法检测周期蛋白D1的表达.[结果]MCF-7细胞转染VDAC1-siRNA后能够有效抑制VDAC1的表达,显著抑制其增殖水平,促使MCF-7细胞发生G1期阻滞,同时下调Cyclin D1蛋白表达.[结论]VDAC1沉默能够有效抑制人乳腺癌MCF-7细胞增殖,促使细胞发生G1期阻滞.VDAC1可作为乳腺癌治疗的新靶点.     

Menstrual Cycle and its Disorders in Women with Congenital Heart Disease

Objectives. To investigate the age at menarche, the prevalence of menstrual cycle (interval) disorders, and determinants in women with congenital heart disease (CHD). Design. Using two CHD registries, 1802 (82%) of the 2196 women with CHD contacted (aged 18–58 years) provided written informed consent. After exclusion of patients with genetic disorders known to be associated with menstrual cycle disorders, 1593 eligible patients remained. Interviews by telephone and reviews of medical records were conducted. Results. Overall, the age at menarche was slightly increased in women with CHD (13.3 vs. 13.1 years in the general population), mainly attributable to an increased prevalence of primary amenorrhea (n = 147; 9.2%). Other menstrual cycle disorders were documented: secondary amenorrhea (n = 181, 11.4%), polymenorrhea (n = 103, 6.5%), oligomenorrhea (n = 90, 5.6%), and menorrhagia (n = 117, 6.5%). The occurrence of these disorders also depended on the presence of cyanotic heart disease, surgical status, the number of surgical interventions, and the severity of CHD. Discussion. Menstrual cycle disturbances, in particular primary amenorrhea, were frequently observed in this population. Patients with complex (cyanotic) heart disease needing repeated surgical interventions prior to menarche are especially at risk.     

Atrioventricular nodal re-entrant tachycardia with QRS voltage and cycle length alternation and aberrant conduction due to two distinct antegrade slow pathways.

QRS voltage and cycle length alternation can be seen during supraventricular re-entrant tachycardias, especially in atrioventricular (AV) re-entrant tachycardia. We present a case of a 20-year-old man, in which AV nodal re-entrant tachycardia (AVNRT) shows alternation of QRS voltage and cycle length, as well as right bundle branch block aberration due to a re-entrant circuit using two distinct, beat-to-beat alternating slow AV nodal pathways antegradely and a single fast pathway retrogradely. Although more than one antegrade slow pathway exists, creation of a single lesion at the right posterior atrial septum using the conventional right-sided approach successfully eliminated AVNRT.     

纳米金对SPC-A1肺癌细胞体外放射增敏作用的研究

目的 研究纳米金联合兆伏级射线对肺腺癌SPC-A1细胞的体外放射增敏作用,并从细胞周期、细胞凋亡角度探讨纳米金的放射增敏机制。方法 选用肺腺癌SPC-A1细胞进行体外培养,采用CCK-8法检测不同浓度纳米金（0、1、0.5、0.25、0.125、0.0625 mmol／L）处理SPC-A1细胞24、48、72 h后的细胞毒性,确定纳米金溶液的实验浓度;经纳米金溶液培养的SPC-A1细胞株分别给予6 MV X线和4 MeV电子线照射0、1、2、4、6、8 Gy后,体外细胞培养克隆法研究纳米金的放射增敏作用,计算存活分数。使用单击多靶模型公式拟合,计算出Dq、D0等放射生物学参数和放射增敏比（SER）;流式细胞仪检测纳米金处理SPC-A1细胞24 h后各组的细胞凋亡和细胞周期的变化。结果 不同浓度纳米金处理不同时间后,对SPC-A1细胞的增殖无明显抑制,确定以纳米金溶液初始浓度（0.25 mmol／L）作为实验浓度。直径25 nm、0.25 mmol／L的纳米金粒子联合6 MV X线和4 MeV 电子线照射SPC-A1细胞的SER分别是1.111和1.214。流式细胞仪检测显示,纳米金不增加细胞的凋亡,但能明显增加射线对细胞的凋亡作用。细胞周期显示纳米金能加速细胞的G0／G1期,使细胞周期阻滞在G2／M期。结论 纳米金联合6 MV X线或4 MeV 电子线对SPC-A1细胞有放射增敏作用,其机制可能与增加射线对细胞的凋亡和细胞周期同步化有关。     

肿瘤放射敏感性的研究进展

恶性肿瘤是一种多发病,常见病,严重威胁着人类的生命健康。在手术、放疗、化疗这三种主要治疗手段中,放疗因其适应证宽、疗效较好而有着不可置疑的重要地位。然而在治疗过程中,依然存在着辐射抵抗和辐射耐受现象,大大降低了放射治疗的疗效。因此提高肿瘤的放疗敏感性已成为目前研究的重点和热点。本文就近年国内外学者对提高肿瘤放疗敏感性问题的研究进展做一述评。