INTERACTIONS OF CORTISOL,TESTOSTERONE, AND RESISTANCE TRAINING: INFLUENCE OF CIRCADIAN RHYTHMS

Diurnal variation of sports performance usually peaks in the late afternoon, coinciding with increased body temperature. This circadian pattern of performance may be explained by the effect of increased core temperature on peripheral mechanisms, as neural drive does not appear to exhibit nycthemeral variation. This typical diurnal regularity has been reported in a variety of physical activities spanning the energy systems, from Adenosine triphosphate-phosphocreatine (ATP-PC) to anaerobic and aerobic metabolism, and is evident across all muscle contractions (eccentric, isometric, concentric) in a large number of muscle groups. Increased nerve conduction velocity, joint suppleness, increased muscular blood flow, improvements of glycogenolysis and glycolysis, increased environmental temperature, and preferential meteorological conditions may all contribute to diurnal variation in physical performance. However, the diurnal variation in strength performance can be blunted by a repeated-morning resistance training protocol. Optimal adaptations to resistance training (muscle hypertrophy and strength increases) also seem to occur in the late afternoon, which is interesting, since cortisol and, particularly, testosterone (T) concentrations are higher in the morning. T has repeatedly been linked with resistance training adaptation, and higher concentrations appear preferential. This has been determined by suppression of endogenous production and exogenous supplementation. However, the cortisol (C)/T ratio may indicate the catabolic/anabolic environment of an organism due to their roles in protein degradation and protein synthesis, respectively. The morning elevated T level (seen as beneficial to achieve muscle hypertrophy) may be counteracted by the morning elevated C level and, therefore, protein degradation. Although T levels are higher in the morning, an increased resistance exercise–induced T response has been found in the late afternoon, suggesting greater responsiveness of the hypothalamo-pituitary-testicular axis then. Individual responsiveness has also been observed, with some participants experiencing greater hypertrophy and strength increases in response to strength protocols, whereas others respond preferentially to power, hypertrophy, or strength endurance protocols dependent on which protocol elicited the greatest T response. It appears that physical performance is dependent on a number of endogenous time-dependent factors, which may be masked or confounded by exogenous circadian factors. Strength performance without time-of-day–specific training seems to elicit the typical diurnal pattern, as does resistance training adaptations. The implications for this are (a) athletes are advised to coincide training times with performance times, and (b) individuals may experience greater hypertrophy and strength gains when resistance training protocols are designed dependent on individual T response. (Author correspondence: Lawrence.hayes@uws.ac.uk)     

Strength gains in obese females are unaffected by moderate dietary restriction

This study examined the effects of dietary restriction on strength gains from whole body resistance training. Comparisons were made between diet-restricted (n = 12) and non-diet-restricted (n = 10) obese women (mean +/- SD, 36.7 +/- 7.0% fat) undergoing identical 8-week resistance training regimens. Diet-restricted subjects reduced their dietary intake by 4200 kJ/day and reduced body mass by 3.9 kg over 8 weeks. Ten-repetition maximum masses were compared between the groups on biweekly intervals. Results indicated no differences between the groups with respect to the rate or magnitude of strength gains for any of the eight exercises. Significant pre- to post-test increases in strength (p less than 0.05) were found for all eight exercises. The rate or magnitude of strength gains induced by resistance training does not appear to be affected by moderate dietary restrictions in obese females.     

Human power output during repeated sprint cycle exercise: the influence of thermal stress

Thermal stress is known to impair endurance capacity during moderate prolonged exercise. However, there is relatively little available information concerning the effects of thermal stress on the performance of high-intensity short-duration exercise. The present experiment examined human power output during repeated bouts of short-term maximal exercise. On two separate occasions, seven healthy males performed two 30-s bouts of sprint exercise (sprints I and II), with 4 min of passive recovery in between, on a cycle ergometer. The sprints were performed in both a normal environment [18.7 (1.5) degrees C, 40 (7)% relative humidity (RH; mean SD)] and a hot environment [30.1 (0.5) degrees C, 55 (9)% RH]. The order of exercise trials was randomised and separated by a minimum of 4 days. Mean power, peak power and decline in power output were calculated from the flywheel velocity after correction for flywheel acceleration. Peak power output was higher when exercise was performed in the heat compared to the normal environment in both sprint I [910 (172) W vs 656 (58) W; P < 0.01] and sprint II [907 (150) vs 646 (37) W; P < 0.05]. Mean power output was higher in the heat compared to the normal environment in both sprint I [634 (91) W vs 510 (59) W; P < 0.05] and sprint II [589 (70) W vs 482 (47) W; P < 0.05]. There was a faster rate of fatigue (P < 0.05) when exercise was performed in the heat compared to the normal environment. Arterialised-venous blood samples were taken for the determination of acid-base status and blood lactate and blood glucose before exercise, 2 min after sprint I, and at several time points after sprint II. Before exercise there was no difference in resting acid-base status or blood metabolites between environmental conditions. There was a decrease in blood pH, plasma bicarbonate and base excess after sprint I and after sprint II. The degree of post-exercise acidosis was similar when exercise was performed in either of the environmental conditions. The metabolic response to exercise was similar between environmental conditions; the concentration of blood lactate increased (P < 0.01) after sprint I and sprint II but there were no differences in lactate concentration when comparing the exercise bouts performed in a normal and a hot environment. These data demonstrate that when brief intense exercise is performed in the heat, peak power output increases by about 25% and mean power output increases by 15%; this was due to achieving a higher pedal cadence in the heat.     

Generality versus specificity: a comparison of dynamic and isometric measures of strength and speed-strength

Considerable debate exists as to whether the qualities of muscle function exist as general or specific physiological capacities. If there is a generality of muscle function then strong relationships would exist between various measures of function for the same muscle(s), independent of the test contraction, mode or velocity. The purpose of this study was to examine the relationship between isometric and dynamic measures of muscle function to determine the existence of generality or specificity. A group of 22 men, experienced in weight training, were tested for lower and upper body dynamic and isometric measures of strength and speed-strength. The changes in these measures consequent to a resistance training programme were also investigated. The results of this study indicated that whilst isometric and dynamic measures of strength did significantly correlate (r=0.57-0.61), the relationship was below that required to denote statistical generality. More important, the changes in isometric and dynamic strength consequent to a dynamic heavy resistance training programme were unrelated (r=0.12-0.15). Thus the mechanisms that contribute to enhanced dynamic strength appearred unrelated to the mechanisms that contribute to enhanced isometric strength. Measures of dynamic and isometric speed-strength were unrelated, as were the changes in these measures resulting from training. The results of this study demonstrated that a generality of muscle function did not exist and that modality specific results were observed. Consequently this study calls into question the validity of isometric tests to monitor dynamically induced training adaptations.     

Effects of isokinetic training of the knee extensors on isometric strength and peak power output during cycling

Isokinetic training of right and left quadriceps femoris was undertaken three times per week for 16 weeks. One group of subjects (n = 13) trained at an angular velocity of 4.19 rad.s-1 and a second group (n = 10) at 1.05 rad.s-1. A control group (n = 10) performed no training. Maximal voluntary contraction (MVC) of the quadriceps, and peak pedal velocity nu p,peak) and peak power output (Wpeak) during all-out cycling (against loads equivalent to 9, 10, 11, 12, 13 and 14% MVC) were assessed before and after training. The two training groups did not differ significantly from each other in their training response to any of the performance variables (P > 0.05). No significant difference in MVC was observed for any group after the 16-week period (P = 0.167). The post-training increases in average Wpeak (7%) and nu p,peak (6%) during the cycle tests were each significantly different from the control group response (P = 0.018 and P = 0.008, respectively). It is concluded that 16 weeks of isokinetic strength training of the knee extensors is able to significantly improve nu p, peak and Wpeak during spring cycling, an activity which demands considerable involvement of the trained muscle group but with its own distinct pattern of coordination.     

个体化精准运动为核心的整体康复方案对冠心病介入治疗术后患者整体功能再提高的临床研究*

目的: 探讨个体化精准运动为核心的整体康复方案对冠心病介入治疗术后患者整体功能再提高的作用。方法: 选择2016 年6 月至2019 年12 月间在北京康复医院临床诊断为冠心病稳定性心绞痛患者20 例,随机分为对照组（n=10）和运动组（n=10）。全部患者择期行冠状动脉介入治疗,术后对照组患者仅进行除运动康复之外的常规治疗指导;运动组患者进行12周个体化运动为核心的心脏康复,介入前、介入后2周、康复后12周分别评估患者标准化症状限制性极限运动的心肺运动试验（CPET）指标、心脏超声、6 min步行距离（6MWD）等。结果: 所有患者均安全无并发症完成症状限制性CPET,运动组患者完成12周全程运动康复治疗。组间比较显示,介入前和介入后2周,对照组和运动组患者CPET指标以及左心室射血分数、6MWD等均无明显差异（P>0.05）。康复12周后,运动组患者无氧阈（ml/min、ml/（min·kg））、峰值摄氧量（ml/（min·kg））、氧脉搏（ml/beat）和6MWD较对照组明显升高,差异有统计学意义（P<0.05）。组内比较显示,康复治疗12周后,运动组患者无氧阈（ml/min、ml/（min·kg）、%pred）、峰值摄氧量（ml/min、ml/（min·kg）、%pred）、峰值氧脉搏（ml/beat）和6MWD均较介入前明显改善,差异有统计学意义（P<0.05）;而且与介入后2周比较,无氧阈（ml/（min·kg））和峰值摄氧量（ml/（min·kg））均明显升高,差异有统计学意义（P<0.05）。对照组患者在康复12周后无氧阈（ml/min）和峰值氧脉搏（ml/beat）较介入前改善,差异有统计学意义（P<0.05）,但CPET指标与介入后2周比较无明显差异。结论: 冠状动脉介入术后进行个体化运动康复为核心的整体管理可进一步提高冠心病稳定性心绞痛患者运动心肺功能和运动耐力。运动康复是介入术后患者二级预防的重要内容,需要大量推广。     

Serum hormone concentrations during prolonged training in elite endurance-trained and strength-trained athletes

A study of 1 year was performed on nine elite endurance-trained athletes (swimmers) and on eight elite strength-trained athletes (weightlifters) in order to examine the effects of training on the endocrine responses and on physical performance capacity. The measurements for the determination of serum hormone concentrations were performed at about 4-month intervals during the course of the year. The primary findings demonstrated that during the first and most intensive training period of the year in preparing for the primary competitions similar but statistically insignificant changes were observed in the concentrations of serum testosterone, free testosterone and cortisol in both the endurance-trained and strength-trained groups. After that period the changes in hormonal response over the year were infrequent and minor. A significant (p less than 0.01) decrease occurred in the strength-trained group in serum-free testosterone during the second period, which was characterized by the highest overall amount of training. Over the entire year the concentrations of serum hormones remained statistically unaltered in both groups. Slight but statistically insignificant increases of 1.2% +/- 0.8% and 2.1% +/- 5.1% were observed in the competitive performances over the year in the endurance-trained and strength-trained groups, respectively. The present findings in the two groups of elite athletes, who differed greatly with regard to the type of physiological loading, demonstrated that the overall hormonal responses both during the most intensive and during prolonged training periods were rather similar and the infrequent small changes remained well within the normal physiological range.(ABSTRACT TRUNCATED AT 250 WORDS)     

近红外光谱技术在运动脑功能研究中的应用

近红外光谱是一种评估生物组织氧合水平的无创性光学技术,这一技术以血液动力学原理为基础,能实时监测局部脑区的动态变化。近红外光谱作为一种客观的测量工具,在人体运动科学领域广泛运用。近红外光谱技术可用于区别体能水平、监控耐力训练和抗阻训练过程特征以及考察运动中的认知活动变化。本文综述了近红外光谱技术原理及其在抗阻运动、运动中枢疲劳和运动认知领域的运用,并对近红外光谱在运动科学领域的未来研究趋向作了分析。     

Effects of unilateral isometric strength training on joint angle specificity and cross-training

The purpose of this study was to examine the effects of unilateral isometric leg extension strength training on the strength and integrated electromyogram (IEMG) of both the trained and untrained limbs at multiple joint angles. A training (TRN) group [nine women; mean (SD) age, 20(1) years] exercised for 6 weeks with isometric leg extensions at 80% of maximal isometric torque. A control (CTL) group [eight women; 21(1) years] did not exercise. The training was performed three times per week on a Cybex II isokinetic dynamometer at a joint angle where the lever arm was 0.79 rad below the horizontal plane. The subjects were tested pre- and posttraining for maximal unilateral isometric torque in both limbs at joint angles of zero, 0.26, 0.79,1.31, and 1.57 rad below the horizontal plane. Bipolar surface electrodes were used to record the IEMG of the vastus lateralis (VL) and vastus medialis (VM) during the isometric tests. Three univariate (torque, IEMG-VL, and IEMG-VM) four-way (group x time x limb x angle) mixed factorial ANOVAs were used to analyze the data. The results indicated joint angle specificity for isometric torque in the TRN group only, with significant increases in torque at 0.79 (P = 0.0004) and 1.31 (P = 0.0039) rad. No significant increases in torque were found in the untrained limb of the TRN group or in either limb of the CTL group. Similarly, there were no significant changes in IEMG as a result of the training for the VL or VM. The joint-angle-specific strength increases without concomitant increases in IEMG were hypothesized to result from joint-angle-specific decreases in antagonistic co-contraction and/or preferential hypertropy of the quadriceps femoris at specific levels of the muscle group.     

抗阻运动对高脂饮食诱导的肥胖大鼠脂肪组织自噬和炎症因子的影响

为探讨运动对肥胖患者自噬活性和内脏脂肪组织炎症反应的影响,本研究将60只肥胖小鼠随机分为高脂饮食组(B)、正常饮食组(C)、正常饮食加耐力运动干预组(D)、正常饮食加耐力运动干预组(E).D组和E组分别进行10周的耐力和抗阻运动,然后用RT-PCR检测自噬、炎症的基因和蛋白表达.结果 显示,三个干预组的Lee指数和BF...