电刺激对过氧化氢诱导衰老肌管细胞能量代谢的影响

目的：运用电刺激肌管细胞收缩模拟骨骼肌收缩,并观察其对过氧化氢（H₂O₂）诱导的C₂C₁₂细胞衰老模型能量代谢相关指标表达的影响,以此研究体外肌管收缩对衰老骨骼肌细胞能量代谢影响的分子机制。方法：使用不同浓度的H₂O₂诱导肌管细胞建立衰老模型,并用β-半乳糖苷酶染色检测衰老水平;电刺激干预培育成功的衰老肌细胞,并分为对照组（C组）、H₂O₂诱导衰老组（H组）、对照+电刺激组（CE组）、H₂O₂诱导衰老+电刺激组（HE组）。各组细胞通过Western blot法对PGC-1α蛋白表达进行检测,ATP水平测试盒测量ATP水平。结果：经过浓度为100 μmol/L H₂O₂诱导肌管细胞24 h后成功构建骨骼肌细胞衰老模型。与C组比较,H组的ATP水平表达呈非常显著性的下降（P＜0.01）;CE组的ATP水平较C组呈非常显著性升高（P＜0.01）;HE组的ATP水平虽低于C组,但高于H组,且呈非常显著性差异（P＜0.01）;与C组相比,H组PGC-1α蛋白表达下降,呈非常显著性差异（P＜0.01）;HE组PGC-1α蛋白表达虽低于C组,但较H组呈非常显著性升高（P＜0.01）。结论：H₂O₂是诱导骨骼肌肌管细胞衰老的一种有效方式,衰老肌管细胞的ATP和PGC-1α蛋白表达水平显著下降,进行电刺激干预后可以有效提高衰老肌管细胞ATP水平和PGC-1α蛋白表达。     

Physiologic Effects of Distance Running Training on Teenage Females1

Abstract

The purpose of this study was to investigate selected physiological changes that occurred with distance training in teenage females. Two groups of untrained teenage females were matched on [Vdot]O₂ max, percent utilization of [Vdot]O ₂ @ 9.66 km/hr, peak heart rate, and percent body fat. One group served as control (n = 9) while the other (n =10) underwent a 20-week training program designed to gradually increase the subjects' average mileage from 0 to 32.2 km per week. At the end of the 20 weeks, a MANOVA revealed significant mean differences within the trained group and no significant mean differences within the control group. The univariate analysis revealed that significant (p <0.05) mean differences found within the training group were for [Vdot]O ₂ max (45.1 vs. 49.3 ml · kg ^–1 · min ^–1 ), percent utilization of [Vdot]O ₂ @9.66 km/hr (76.5% vs. 67.5%), and economy VO ₂ @9.66 km/hr (34.5vs.33.2 ml · kg ^–1 · min ^–1 ). Of the variables which exhibited significant training effects, percent utilization of [Vdot]O ₂ max showed the greatest relative change, a 12.2% decrease, with [Vdot]O ₂ max showing a 9.3% increase. The posttest results were similar to the research literature for training effects found for males and other age groups.     

Effect of Toe Clips during Bicycle Ergometry on [Vdot]O2 max

Abstract

Previous investigators have yielded conflicting results in testing the hypothesis that the use of toe clips during bicycle ergometry produces a higher maximal oxygen uptake ([Vdot]O ₂ max) than testing without toe clips. Eight men, four competitive cyclists and four competitive distance runners volunteered to participate in three randomized [Vdot]O ₂ max tests: 1) a treadmill running lest, 2) a bicycle ergometer test using standard toe clips, and 3) a test on the same ergometer without toe clips. The highest mean [Vdot]O ₂ max was observed in the treadmill condition as expected. However, no statistically significant difference in mean [Vdot]O ₂ max or performance time was observed between the toe-clip and no toe-clip conditions. Based on these results, the research hypothesis was rejected and no favorable physiological effect may be attributed to the use of toe clips.     

Effect of Caffeine Ingestion on Cardiorespiratory Endurance in Men and Women

Abstract

The effect of caffeine ingestion on submaximal endurance performance of 15 females and 13 males was investigated. After completing a [Vdot]O ₂ max test, each subject performed two submaximal cycling tests at approximately 75% of [Vdot]O ₂ max to exhaustion. For the caffeine (C) trials, 300 mg of caffeine was added to 250 ml of decaffeinated coffee and ingested one hour prior to the exercise. The decaffeinated (D) trial involved consuming 250 ml of decaffeinated coffee an hour prior to the test. The C and D trials were administered randomly using a standard double blind design. Physiological parameters were monitored each 9, 10, and 11 minute intervals throughout each trial and averaged. As expected the [Vdot]O ₂ (L · min ^?1 ), [Vdot]E and work outputs (kgm) were significantly (p < 0.001) higher for the males than the females. All other variables, time to exhaustion, [Vdot]O ₂ (ml · kg · min ^?1 ), R, HR, and rating of perceived exertion (RPE) were not significantly (p > 0.05) different between the sexes for either the C or D trials. Time to exhaustion was 14.4 and 3.1% longer for the C trials for the females and males, respectively, however these increases were not significant (p > 0.05). Furthermore, there were no significant differences (p > 0.05) for any of the measured variables during successive 10 minute work intervals between the C and D trials for either sex. These results do not support the general use of caffeine in moderate amounts as an ergogenic aid for either males or females, but from a practical point it appears that caffeine may have an ergogenic effect on specific individuals.     

A Reliable Method for the Measurement of Constant Load Maximal Endurance Performance on the Bicycle Ergometer

Abstract

The purpose of this study was to examine the relationships of achievement goal orientations and perceived motivational climate to perceptions of the intensity and direction of competitive state anxiety in a sample of university athletes representing various team sports. Although some studies have demonstrated that task orientation and mastery climate are associated with adaptive emotional patterns and ego orientation and performance climate are linked to less adaptive emotions, others have not verified these findings. In the present study, structural equation modeling was used to test these links. The results showed that perceptions of a performance climate were associated with ego orientation, whereas perceptions of a mastery climate were linked to task orientation. Furthermore, no significant links were found between task orientation and direction of competitive anxiety, while it was shown that the impact of ego orientation on the intensity and direction of cognitive and somatic anxiety was exerted through self-confidence. No significant direct links were found between motivational climates and competitive anxiety, thus implying that motivational climates may have an indirect impact on affective responses through the different goal orientations. The findings of the present study are discussed along with suggestions for examining situational and individual difference variables that may explain the relationships between intensity and direction of competitive anxiety and achievement goals and motivational climates.     

Validity of Palpation Recovery Pulse Rate to Estimate Exercise Heart Rate Following Four Intensities of Bench Step Exercise

Abstract

Previous investigations regarding activity during the post-knowledge of results (KR) interval have considered the performance of interference groups over KR-supplied acquisition trials as indicative of effects upon learning. The absence of transfer tests in these studies, however, preclude such an assumption. Indeed, the use of a retention test in the present investigation (no-KR trials following an interpolated phase) provided evidence suggesting that, while activity during the post-KR interval is detrimental to performance, no such assumption can be made regarding this effect upon learning. These findings are discussed relative to recent arguments that some of the commonly accepted “Laws of KR” may be contradictory when applied simultaneously to motor learning and performance.     

Training Responses of Speed Skaters during a Competitive Season

Abstract

The purpose of this study was to test the effects of a 10-month exercise program on bone mineral content (BMC) and bone mineral content/bone width (BMC/BW) of postmenopausal women. Thirty-one women (ages 57-83) completed either a general aerobics exercise program (n = 10), a general aerobics plus upper body weight training exercise program (n = 10), or served as nonexercising control subjects (n = 11). Average compliance rates for the exercise subjects ranged from 72 to 80%. All subjects were pre- and posttested for BMC and BMC/BW in the radius of the nondominant forearm. ANOVA results indicated that there were significant differences between the exercise and control subjects in the amount of change in BMC and in BMC/BW (p < .05) during the course of the study. The exercise subjects experienced mean increases of 1.38% and 1.33% in BMC and BMC/BW, respectively, whereas the control group had decreases of 2.50% and 258%. No significant differences were found for subjects in the two types of exercise programs, suggesting that the effects of exercise relative to maintenance of bone density may be general as well as localized.     

Pygmalion in the Gym: A Model for the Communication of Teacher Expectations in Physical Education

Abstract

Much research on teacher expectations has focused on ways in which teacher perceptions of student ability can ultimately affect student performance. The majority of this research has indicated that teacher expectations not only determine certain types of student performance, but also serve to sustain low and high levels of performance. Observational research has also demonstrated that differential teacher-student interactions are related to certain levels of teacher expectations. For example, it has been shown that high expectancy students receive more praise, acceptance of ideas, contact and wait time, and more response opportunities than low expectancy students. Much of this research has been generated from studies related to classroom instruction. Very little of this research, however, has been operational in the physical education setting. One reason for this is the absence of a model in physical education through which this type of research can be generated. This article presents such a model showing how expectations are formed, how they are communicated, and how they sustain low and high levels of student growth and performance. The model further illustrates the causal relationship among teacher expectations, dyadic interactions and student growth and performance. Suggestions for future research techniques to determine causal flow among variables are also presented.     

Children’s Aerobic Trainability and Related Questions

In response to Armstrong’s recent Special Topics review of “Top 10 Research Questions Related to Youth Aerobic Fitness,” this commentary revisits some of the points raised, particularly in relation to the question of whether a child?adult trainability difference does indeed exist. Discussed are the validity of much of the existing pediatric maximal oxygen consumption data upon which trainability conclusions are drawn, why differential trainability is likely a fact rather than a doubt, a reasoned novel approach to explaining the phenomenon, and how that explanation can bear upon and answer several of the other raised questions. The commentary is intended to inspire and encourage fresh thinking not only in relation to pediatric aerobic trainability, but more generally, regarding pediatric exercise physiology and performance and how they differ from those of adults.     

Individualised training at different intensities,in untrained participants,results in similar physiological and performance benefits

This study compared effects of training at moderate, high, or a combination of the two intensities (mixed) on performance and physiological adaptations, when training durations were individualised. Untrained participants (n = 34) were assigned to a moderate, high, or mixed group. Maximal oxygen uptake (V?O_2max), power output at V?O_2max (MAP), time-to-exhaustion and gross efficiency were recorded before and after four weeks of cycling training (four times per week). The moderate group cycled at 60% MAP in blocks of 5 min with 1 min recovery, and training duration was individualised to 100% of pre-training time-to-exhaustion. The high group cycled at 100% MAP for 2 min with 3 min recovery, and training duration was set as the maximum number of repetitions completed in the first training session. The mixed group completed two moderate- and two high-intensity sessions each week, on alternate days. V?O_2max, MAP, and time-to-exhaustion increased after training (P < 0.05), but were not different between groups (P > 0.05). The mixed group improved their gross efficiency at 50% MAP more than the other two groups (P = 0.044) after training. When training is individualised for untrained participants, similar improvements in performance and physiological measures are found, despite marked differences in exercise intensity and total training duration.     

Cardiorespiratory fitness in urban adolescent girls: associations with race and pubertal status

Cardiorespiratory fitness affords health benefits to youth. Among females, weight-relative fitness declines during puberty and is lower among African American (AA) than Caucasian girls. Data indicate racial differences in pubertal timing and tempo, yet the interactive influence of puberty and race on fitness, and the role of physical activity (PA) in these associations have not been examined. Thus, independent and interactive associations of race and pubertal development with fitness in adolescent girls, controlling for PA were examined. Girls in grades 5–8 (n = 1011; Caucasian = 25.2%, AA = 52.3%, Other Race group = 22.5%) completed the Pubertal Development Scale (pubertal stage assessment) and Fitnessgram® Progressive Aerobic Cardiovascular Endurance Run (PACER) test (cardiorespiratory fitness assessment). PA was assessed by accelerometry. Bivariate and multivariate analyses were used to examine associations among race, pubertal stage and fitness, controlling for vigorous PA, AA, and pubertally advanced girls demonstrated lower fitness than Caucasian and less mature counterparts. Puberty and race remained significantly associated with fitness after controlling for vigorous PA. The interaction effect of race and puberty on fitness was non-significant. The pubertal influence on fitness is observed among AA adolescents. Associations between fitness and race/puberty appear to be independent of each other and vigorous PA. Pubertally advanced AA girls represent a priority group for fitness interventions.     

Critical power derived from a 3-min all-out test predicts 16.1-km road time-trial performance

Abstract

It has been shown that the critical power (CP) in cycling estimated using a novel 3-min all-out protocol is reliable and closely matches the CP derived from conventional procedures. The purpose of this study was to assess the predictive validity of the all-out test CP estimate. We hypothesised that the all-out test CP would be significantly correlated with 16.1-km road time-trial (TT) performance and more strongly correlated with performance than the gas exchange threshold (GET), respiratory compensation point (RCP) and V?O₂ max. Ten club-level male cyclists (mean±SD: age 33.8±8.2 y, body mass 73.8±4.3 kg, V?O₂ max 60±4 ml·kg^?1·min^?1) performed a 10-mile road TT, a ramp incremental test to exhaustion, and two 3-min all-out tests, the first of which served as familiarisation. The 16.1-km TT performance (27.1±1.2 min) was significantly correlated with the CP (309±34 W; r=?0.83, P<0.01) and total work done during the all-out test (70.9±6.5 kJ; r=?0.86, P<0.01), the ramp incremental test peak power (433±30 W; r=?0.75, P<0.05) and the RCP (315±29 W; r=?0.68, P<0.05), but not with GET (151±32 W; r=?0.21) or the V?O₂ max (4.41±0.25 L·min^?1; r=?0.60). These data provide evidence for the predictive validity and practical performance relevance of the 3-min all-out test. The 3-min all-out test CP may represent a useful addition to the battery of tests employed by applied sport physiologists or coaches to track fitness and predict performance in atheletes.