有氧运动对自发性高血压大鼠肾脏纤维化的影响

 目的 探讨有氧运动对自发性高血压大鼠(SHR)肾脏纤维化的影响并探讨肾小管上皮－间质转化(EMT)在其间的作用机制。方法 将10只Wistar-Kyoto大鼠作为正常血压对照组(WKY),30只雄性SHR按照随机数字表法分为高血压安静组(SHR-S)和高血压运动组(SHR-E),每组15只。WKY和SHR-S组在鼠笼内安静饲养,SHR-E组进行8周跑台运动。实验后,利用无创血压仪检测尾动脉血压;测定24 h尿蛋白(UP)、血尿素氮(BUN)和血清肌酐(SCr)含量评价肾功能;Masson染色进行肾脏病理组织学观察并获取纤维化指数(FI);免疫印迹测定转化生长因子β₁(TGF-β₁)、磷酸化Smad2/3(p-Smad2/3)、α-平滑肌肌动蛋白(α-SMA)和E-钙黏蛋白(E-CA)表达量。结果 与WKY组比较,SHR-S组血压[SBP:(177.3±17.2) mmHg vs. (110.6±13.3)mmHg,P<0.05;DBP:(108.1±6.3) mmHg vs. (75.6±4.9) mmHg,P<0.05;MAP:(131.1±7.4) mmHg vs. (87.3±4.7) mmHg,P<0.05]、肾脏FI[(7.87±1.89)% vs. (0.43±0.05)%,P<0.05]、UP[(197.3±41.6) mg/24 h vs. (89.2±9.5) mg/24 h,P<0.05]、BUN[(14.3±2.9) mmol/L vs. (4.9±1.0) mmol/L,P<0.05]和SCr[(98.6±10.1) μmol/L vs. (35.8±4.3) μmol/L,P<0.05]升高,TGF-β₁、p-Smad2、p-Smad3和α-SMA蛋白表达上调(P<0.05),E-CA蛋白表达下调(P<0.05);与SHR-S组比较,SHR-E组血压[SBP:(152.3±14.2) mmHg vs. (177.3±17.2) mmHg,P<0.05;DBP:(93.1±9.7) mmHg vs. (108.1±6.3) mmHg,P<0.05;MAP:(112.8±7.9) mmHg vs. (131.1±7.4) mmHg,P<0.05]、肾脏FI[(3.02±0.91)% vs. (7.87±1.89)%,P<0.05]、UP[(127.9±25.7)mg/24 h vs. (197.3±41.6) mg/24 h,P<0.05]、BUN[(6.8±1.7) mmol/L vs. (14.3±2.9) mmol/L,P<0.05]和SCr[(50.3±6.0) μmol/L vs. (98.6±10.1) μmol/L,P<0.05]下降,TGF-β₁、p-Smad2、p-Smad3和α-SMA蛋白表达下调(P<0.05),E-CA蛋白表达上调(P<0.05)。结论 有氧运动可能通过调控TGF-β₁/Smad信号途径抑制高血压肾病大鼠肾小管EMT,进而改善肾脏纤维化并提高肾功能。     

血氨在士兵体能训练监控中的应用

 目的探讨血氨(bloodammonia,BA)作为部队军事体能训练监控指标的可行性。方法90名武警某部战士随机分为3组,分别进行100m跑、400m障碍和蛙跳训练。测定各组训练前后BA、血乳酸(bloodlacticacid,Bla)、肌酸激酶(creatinekinase,CK)和血浆游离DNA(cell-freeplasmaDNA,cf-DNA)的变化,分析BA与其他各指标的相关关系并计算Pearson相关系数。结果三组各指标基础值(训练前水平)均无统计学差异(P>0.05)。与训练前比较,100m组BA、CK和cf-DNA均显著升高(均为P<0.01),而Bla无统计学变化(P>0.05);400m障碍组和蛙跳组所有指标均显著升高(均为P<0.01)。相关分析显示,100m组BA与CK、cf-DNA均呈显著正相关(分别为P<0.05和P<0.01),而与Bla无显著相关性(P>0.05);400m障碍组和蛙跳组BA与Bla、CK、cf-DNA均呈显著正相关(均为P<0.01)。结论BA可作为士兵无氧训练科目简便易行的监控指标。     

武警士兵无氧运动能力与5 km跑成绩的相关性研究

 目的 探讨武警士兵无氧运动能力与5 km跑成绩的相关性,为科学训练提供理论依据。方法 52名武警士兵在标准400 m跑道进行50、400 m和5 km跑测试,记录运动成绩并换算为速度(分别记作ν_{50 m}、ν_{400 m}和ν_{5 km}),利用气体分析仪进行最大摄氧量(VO_2max)和通气阈(VT)测试。以ν_{50 m}、ν_{400 m}作为无氧运动能力的指标,以VO_2max和VT作为有氧运动能力的指标。ν_{5 km}与各变量之间的关系使用简单相关分析并计算Pearson相关系数(r);利用偏相关分析(校正其他相关变量)探讨ν_{5 km}与有氧、无氧运动能力的关系并计算偏相关系数(R)及决定系数(R²)。结果 简单相关分析显示,BMI(r＝-0.428,P<0.01)与ν_{5 km}显著负相关,训练年限(r＝0.375,P<0.05)、VO_2max(r＝0.848,P<0.01)、VT(r＝0.316,P<0.01)、ν_{400 m}(r＝0.652,P<0.01)均与ν_{5 km}显著正相关。偏相关分析显示,VO_2max、ν_{400 m}和VT解释了ν_{5 km}总变异(R²)的82.4%,各R²分别为51.1%、24.1%和7.2%。结论 有氧运动能力是5 km跑成绩的决定因素,但无氧运动能力同样不可忽视。在制定5 km训练计划时,应适当增加无氧训练的比例。     

某部士兵高温高强度军事训练对血清生化指标的影响及其意义

 目的 分析某部士兵高温高强度军事训练对血清生化指标的影响及其意义。方法 随机选取某部参加10 km长跑训练士兵52例,于训练前后进行生化指标检测,比较训练前后生化指标的变化。结果 (1)训练后电解质Ca⁺、Na⁺较训练前升高[(2.6±0.07)mmol/L vs. (2.5±0.06)mmol/L,(145.2±1.6)mmol/L vs. (141.9±5.5)mmol/L,P<0.01],Mg⁺、K⁺较训练前降低[(0.9±0.06)mmol/L vs. (1.0±0.07)mmol/L,(4.4±0.4)mmol/L vs. (5.0±0.4)mmol/L,P<0.01];(2)训练后AST较训练前升高[(20.7±6.6)μmol/L vs. (18.7±4.2)μmol/L,P<0.01],ALT、GGT、ALP、TBIL、DBIL训练前后差异无统计学意义;(3)训练后Cr、UA、LAC较训练前升高[(74.1±11.2)μmol/L vs. (67.4±14.6)μmol/L,(426.4±77.3)μmol/L vs. (411.2±78.3)μmol/L,(7.4±0.6)μmol/L vs. (4.4±0.7)μmol/L,P<0.01],Urea、β₂-MG训练前后差异无统计学意义;(4)训练后LDH、CK较训练前升高[(229.9±24.1)U/L vs. (188.3±31.2)U/L,(188.3±57.2)U/L vs. (149.6±58.8)U/L,P<0.01],CHE、CK-MB训练前后的改变差异无统计学意义。结论 高温高强度训练可对机体造成影响,但未发生器官损伤,在训练后及时补充电解质,是尽快恢复体力的有效措施。     

高原低氧环境下军事训练对武警新兵微循环功能的影响

 目的 观察高原低氧环境下军事训练对武警新兵微循环功能的影响,为指导高原地区军事、体能训练提供科学依据。方法 试验在青海( 海拔约3000 m,大气压力60.49 kPa ) 和天津( 海拔约4 m,大气压力101.08 kPa ) 完成。受试者为武警某部新兵连战士,将受试者分为3组,分别为平原籍平原训练组(对照组,60人)、平原籍高原训练组(A组,62人)和高原籍高原训练组(B组,38人)。所有受试者进行12周训练,训练强度相同。训练前和训练后第4、8、12周用XXG-E3 型自动心血管功能诊断仪记录微循环功能指标,并对受试者甲襞微循环进行检测。结果 在高原低氧环境下军事训练新兵血容量明显减少,以A组减少最为显著(P<0.05);B组半更新率低于其他两组(P<0.05),平均滞留时间和半更新时间高于其他两组(P< 0.05);B组形态积分和流态积分高于对照组(P<0.05);A组襻周积分[(2.78±0.85)vs(0.93±0.34)]和流态积分[(1.33±0.34)vs(0.59±0.31)]显著高于对照组(P<0.05)。结论 高原籍战士的微循环功能对高原训练适应性较强,平原籍战士高原低氧军事训练应当逐步增加训练量,以减少高原反应和微循环障功能碍的发生。     

不同训练方式对武警战士血浆肌酸激酶和血浆游离DNA的影响

 目的 观察不同训练方式对武警战士血浆肌酸激酶(CK)和血浆游离DNA(cf-DNA)的影响,探寻军事训练过程中早期诊断运动性疲劳和运动性肌肉损伤的敏感标志物。方法 45名某部队武警战士随机分为3组,分别为有氧训练组(5 km跑)、向心力量训练组(俯卧撑和仰卧起坐)和离心力量训练组(原地蹲跳和蛙跳),每组各15人。于训练前、训练后即刻、训练后30 min、1 h、12 h和24 h测定血浆CK和cf-DNA。结果 有氧训练组各时间点血浆CK和cf-DNA均无显著性变化(P>0.05)。向心力量训练组血浆CK在训练后12 h显著升高[(315±95) vs (134±45) U/L,P<0.01],24 h即恢复至安静水平[(151±71) vs (134±45) U/L,P>0.05];cf-DNA在训练后即刻显著升高[(59.1±12.7) vs (43.4±8.0) pg/μl,P<0.05],30 min达峰值[(95.3±13.6) vs (43.4±8.0) pg/μl,P<0.01],12 h即恢复至安静水平[(47.7±10.9) vs (43.4±8.0) pg/μl,P>0.05]。离心力量训练组血浆CK与cf-DNA的变化与向心力量组基本一致,但各时间点升高幅度均高于向心力量组(P<0.01)。结论 cf-DNA对运动的反应具有训练方式依赖性,中等强度有氧训练对cf-DNA的影响不大,力量训练特别是离心力量训练对cf-DNA的影响最大;cf-DNA可能是军事训练中早期诊断运动性疲劳和运动性肌肉损伤的敏感标志物。
     

瑞芬太尼静脉分娩镇痛在妊娠期高血压疾病中的应用

 目的 探讨瑞芬太尼静脉分娩镇痛对妊娠期高血压(妊高症)的应用效果及安全性。方法 选择符合顺产条件的妊高症产妇80例,随机分为观察组(静脉瑞芬太尼组)和对照组(硬膜外组),记录产妇不同时间点的平均动脉压(MAP)、心率(HR)、呼吸频率(RR)和脉搏氧饱和度(SpO₂);测定各个时点产妇的VAS评分,分析产妇的满意度评分;记录各个产程时间及母婴不良反应;测定新生儿Apgar评分及脐血血气。结果 两组在T₀(处理前10 min)时MAP、HR、RR差异无统计学意义;而在处理后10 min(T₁)、处理后60 min(T₂)、分娩后10 min(T₃)、分娩后2 h(T₄)这四个时间点的比较中,观察组的MAP均高于对照组,差异具有统计学意义(P<0.05);两组在T₀(处理前10 min)时的VAS评分差异无统计学意义,观察组在镇痛后各个时点(T₁-T₂)的VAS评分均高于对照组(P<0.05),但两组的患者满意度评分比较,差异无统计学意义(P>0.05);观察组的产程时间短于对照组(P<0.05);观察组产妇的低血压和下肢麻木发生率低于对照组(P<0.05),头晕发生率高于对照组(P<0.05);两组新生儿血气分析结果和窒息发生率比较,差异无统计学意义。结论 瑞芬太尼静脉分娩镇痛应用于妊高症产妇时循环稳定,依从性较好。     

武警官兵腹股沟疝修补术不同术式应用的回顾性研究

 目的 比较经腹腔腹膜前腹股沟疝修补术(transabdominal preperitoneal,TAPP)、完全腹膜外腹股沟疝修补术(totally extraperitoneal,TEP)和常规腹股沟疝修补术的优缺点,探讨应用于武警官兵的术式选择。方法 回顾性分析2012-01至2018-01医院治疗武警官兵腹股沟疝的临床资料,总结手术疗效、并发症及术后恢复效果。结果 128例均成功完成手术。TAPP组手术时间明显长于常规手术组及TEP组(P<0.05)。常规手术组术后住院时间明显长于TAPP组及TEP组(P<0.05)。常规手术组第2天VAS评分明显高于TAPP、TEP组(P<0.05)。术后1个月,常规手术组在IPQ评分0分、参加日常训练及固定执勤任务、参加3 km越野跑的比例明显低于TAPP、TEP组(P<0.05)。术后3个月,常规手术组参加3 km越野跑的比例仍明显低于TAPP组、TEP组(P<0.05)。结论 腹腔镜下腹股沟疝修补手术具有微创、疼痛轻、恢复快、并发症少等优点,武警官兵能较早恢复日常训练及执勤任务,特别是TEP术式更值得部队医院推广。     

小剂量依托咪酯联合丙泊酚对全麻诱导效果的影响

 目的 探讨小剂量依托咪酯联合丙泊酚用于全麻诱导对血流动力学、麻醉深度的影响并观察其不良反应。方法 选择2018-10至2020-12解放军总医院第一医学中心择期行全麻手术患者90例,随机分为丙泊酚(A组)、依托咪酯(B组)、依托咪酯联合丙泊酚组(C组),每组30例。A组静脉注射丙泊酚2.0 mg/kg,B组静脉注射依托咪酯0.3 mg/kg,C组静脉注射依托咪酯0.075 mg/kg、丙泊酚1.0 mg/kg。诱导完成后行气管插管,观察记录诱导前(T₀)、插管前(T₁)、插管后1、3、5 min(T₂-T₄)3组患者平均动脉压(mean arterial pressure, MAP)、心率(heart rate,HR)及脑电双频指数(bispectral index, BIS)的变化,记录3组患者注射痛、肌阵挛、高血压、低血压、BIS<30等不良反应发生率。结果 C组诱导后的MAP高于A组(P<0.05),C组在T_1-4时刻MAP高于A组,T₂时刻MAP低于B组(P<0.05),且诱导后HR低于B组,T₂时刻HR低于B组(P<0.05),BIS低于A组,T₁时刻BIS高于B组,T_2-3时刻低于A组,T₄时刻低于A组,高于B组(P<0.05),注射痛和低血压发生率低于A组(0.0% vs. 36.7%,3.3% vs. 33.3%),肌阵挛发生率低于B组(3.3% vs. 66.7%),高血压、BIS<30发生率低于A、B组(3.3% vs. 40.0%、70.0%,0.0% vs. 30.0%、60.0%),差异均有统计学意义(P<0.05)。结论 预注射依托咪酯进行麻醉诱导,于插管前注射丙泊酚对全麻的血流动力学和麻醉深度影响小,不良反应发生率低。     

显微镜下精索静脉结扎术对青年原发性精索静脉曲张患者的安全性评价

 目的 探讨显微镜下精索静脉结扎术对青年原发性精索静脉曲张患者的安全性。方法 80例在我院确诊为原发性精索静脉曲张患者,随机分为观察组和对照组各40例,观察组接受显微镜下精索静脉结扎术,对照组接受经后腹膜精索静脉结扎术,比较两组的手术情况、精子质量、并发症情况及复发情况。结果 观察组和对照组相比,术后卧床时间[(1.05±0.45)d vs (5.36±0.72)d],差异有统计学意义(P<0.05)、住院总时间[(6.12±0.44)d vs (7.92±0.56)d]明显缩短,差异有统计学意义(P<0.05),NRS疼痛评分[(1.03±0.35) vs (2.75±0.48)]明显下降(P<0.05);术后3个月,观察组与对照组相比,精子密度[(68.25±7.72)×10⁶/ml vs (54.36±5.45)×10⁶/ml,P<0.05]、精子活动力a级[(25.36±3.12)％ vs (20.12±2.25)％],均明显升高(P<0.05);观察组术后静脉曲张复发率明显低于对照组(P<0.05)。结论 显微镜下精索静脉结扎术有助于减小手术创伤,促进术后恢复,提高精子质量,预防远期复发。     

Muscle metabolism during sprint exercise in man: influence of sprint training.

In order to examine the influence of sprint training on metabolism and exercise performance during sprint exercise, 16 recreationally-active, untrained, men (VO2peak= 3.8+/-0.1 l.min(-1)) were randomly assigned to either a training (n= 8) or control group (n= 8). Each subject performed a 30-sec cycle sprint and a test to measure VO2peak before and after eight weeks of sprint training. The training group completed a series of sprints three times per week which progressed from three 30-sec cycle sprints in weeks 1 and 2, to six 30-sec sprints in weeks 7 and 8. Three mins of passive recovery separated each sprint throughout the training period. Muscle samples were obtained at rest and immediately following the pre- and post-training sprints and analysed for high energy phosphagens, glycogen and lactate; the activities of both phosphofructokinase (PFK) and citrate synthase (CS) were also measured and muscle fibre types were quantified. Training resulted in a 7.1% increase in mean power output (p<0.05), an 8% increase in VO2peak (p< 0.001), a 42% increase (p< 0.01) in CS activity and a 17% increase (p< 0.05) in resting intramuscular glycogen content. In contrast, neither PFK activity nor fibre type distribution changed with training. An increase (p< 0.05) in mean power output and attenuated (p< 0.01) ATP degradation were observed during sprint exercise following training. Glycogen degradation during sprint exercise was unaffected by sprint training. These data demonstrate that sprint training may have enhanced muscle oxidative but not glycolytic capacity.     

The effect of time-of-day and Ramadan fasting on anaerobic performances

This study was designed to assess the effects of Ramadan-intermittent-fasting (RIF) and time-of-day on muscle power and fatigue during the Wingate test. In a randomized design, 10 football players completed a Wingate test at 07:00 and 17:00?h on 3 different occasions: one week before Ramadan (BR), the second week of Ramadan (SWR) and the fourth week of Ramadan (ER). There was an interval of 36-h between any 2 successive tests. During the Wingate test, peak power (PP), mean power (MP) and the fatigue index (FI) were recorded. While PP, MP and FI were greater in the evening than in the morning during BR (p<0.001), these diurnal variations in muscle power disappeared during the month of Ramadan (i.?e., SWR and ER) due to a significant decrease in PP and MP in the evening (p<0.001). However, the diurnal variation in FI when measured at 17:00?h increased during this month (p<0.001). In addition, ratings of perceived exertion and fatigue were higher in the evening during Ramadan in comparison with BR. These results suggest that Ramadan might modify the circadian rhythm of muscle power and fatigue during the Wingate test by decreasing power output and increasing muscle fatigue at the time of the acrophase.     

Relationship between upper body anaerobic power and freestyle swimming performance

The purpose of this study was to examine the role of upper body anaerobic power, as measured by the Wingate Anaerobic Arm Test (WAAT), in 50-m sprint swim performance. Thirty competitive age-group swimmers (14 males and 16 females) participated in this investigation. Subjects had been training daily for 5 months prior to the study, swimming an average of 6,000 m.d-1, 6 d.wk-1. Swimmers performed a WAAT and a 50-m time-trial. Peak power (PP), mean power (MP) and fatigue index (FI) were determined for the WAAT. Subjects also reported their current competition performances for all distances up to 400 m. Significant relationships were obtained between swim speed over 50 m (S50) and PP (r = 0.82, p less than 0.001), S50 and MP (r = 0.83, p less than 0.001), and S50 and FI (r = 0.41, p less than 0.05). PP and MP showed significant but generally decreasing correlations with swim speed as distance increased. Substantial relationships (r = 0.74-0.96, p less than 0.001) were found between S50 and swim speeds over distances up to and including 400 m. This study shows a strong relationship exists between upper body anaerobic power, as measured by the WAAT, and performance in both sprint and longer distance (400 m) swim events. The WAAT may serve as a useful tool for coaches to objectively evaluate and monitor the upper body anaerobic power of competitive swimmers.     

Effect of short recovery intensities on the performance during two Wingate tests

PURPOSE: To assess the effects of the intensity of short recoveries on performance by a Wingate test and on the deoxyhemoglobin variations. METHODS: Twelve male subjects performed a graded test and three sessions of repeated all-out tests with different recovery natures. The repeated all-out tests included two sprints: a 15-s Wingate test followed by a 30-s Wingate test. The recovery between the two was 15 s in duration and was either passive, active at 20% of maximal aerobic power, or active at 40% of maximal aerobic power. Changes in deoxyhemoglobin were measured using by the near-infrared spectroscopy technique. RESULTS: Mean power (517 +/- 26 W) and peak power (1085 +/- 153 W) of the 30-s Wingate test performed after passive recovery were significantly higher (P < 0.05) than mean power and peak power performed after active recovery at 20% (484 +/- 30 and 973 +/- 112 W, respectively) and 40% of maximal aerobic power (492 +/- 35 and 928 +/- 116 W, respectively). Deoxyhemoglobin variations were significantly higher (P < 0.05) during the passive recovery (12.8 +/- 5.3 microM) than during the active recovery conditions at 20% (4.3 +/- 2.6 microM) and 40% of maximal aerobic power (3.9 +/- 2.6 microM). CONCLUSION: These results demonstrate that when two Wingate tests are performed almost successively but with a short recovery between the two, passive recovery is more appropriate than active recovery to restore the performance level.     

Physical fitness and performance. Fatigue responses during repeated sprints matched for initial mechanical output

PURPOSE: To compare muscle fatigability during two sets of repeated cycling sprints matched for initial mechanical output in a nonfatigued and fatigued state. METHODS: Eight young men performed 10, 6-s all-out sprints on a cycle ergometer interspersed with 30 s of recovery, followed, after 6 min of passive recovery, by five 6-s sprints, again interspersed by 30 s of recovery. RESULTS: On the basis of total work (TW), performance in sprint 11 (79.8 +/- 4.8 J.kg) was not significantly different to performance in sprint 4 (80.3 +/- 5.3 J.kg; P = 0.81). The decrease in TW for the five sprints after sprint 4 (i.e., sprints 4 to 8) averaged 14.5% (P < 0.001), which was significantly less than the decrement in TW from sprints 11 to 15 (20.3%; P < 0.05). Despite no significant differences in TW values achieved in sprints 4 and 11, the amplitude of the electromyogram (EMG) signal (i.e., root mean square (RMS)) recorded during sprint 11 (0.398 +/- 0.03 V) was 12.0% lower (P < 0.05) than in sprint 4 (0.452 +/- 0.02 V). In contrast, values of EMG median frequency (MF) recorded during sprint 4 (85.5 +/- 5.5 Hz) and 11 (89.3 +/- 7.2 Hz) were not significantly different (P = 0.33). However, the rate of decrease in EMG activity (i.e., RMS and MF) was similar for the two set of sprints. CONCLUSIONS: These findings suggest that previous fatiguing repeated-sprint exercise, followed by a rest period, induces greater fatigability during subsequent repeated-sprint exercise, regardless of the initial mechanical output, and that these changes are associated with acute neuromuscular adjustments.     

A 2.5 min cold water immersion improves prolonged intermittent sprint performance

ObjectivesWe investigated if cold water immersion (CWI) affects exercise performance during a prolonged intermittent sprint test (IST), designed to mimic activity patterns of team-sports.DesignRandomized-crossover design.MethodsTen male team-sport players completed 3 IST protocols (two 40-min “halves” of repeated 2-min blocks consisting of a 8-s “all-out” sprint, 100-s active recovery and 12-s rest) on a cycle ergometer at normothermic conditions. Each “half” was separated by a 15 min recovery period of either: (i) passive rest, (ii) 5-min CWI at 8 °C (CWI-5) or (iii) 2.5-min CWI at 8 °C (CWI-2.5), in a random counterbalanced order.ResultsPhysical performance, core temperature (T_core) and heart rate were not different among conditions in the first half. In the passive rest trial, total work (TW) and peak power (PP) were lower during the second half (TW: 5.04 ± 1.11 kJ; PP: 929 ± 286 W) than the first half (TW: 5.66 ± 1.02 kJ; PP: 1009 ± 266 W); while TW and PP were not different between halves following CWI-5 (first half, TW: 5.34 ± 1.02 kJ, PP: 1016 ± 283 W; second half, TW: 5.19 ± 1.38 kJ; PP: 996 ± 318 W) and CWI-2.5 (first half, TW: 5.47 ± 1.19 kJ, PP: 966 ± 261 W; second half, TW: 5.25 ± 1.17 kJ; PP: 952 ± 231 W). T_core was lower until the 20^th minute of the second half after CWI-5 and CWI-2.5 compared with passive rest.ConclusionsA post-exercise 2.5–5-min CWI attenuates the reductions in prolonged sprint performance that occur in the second half of team sports, due, at least partly, to reductions in core temperature and associated increase in heat storage.     

Gender differences in anaerobic power of the arms and legs--a scaling issue

PURPOSE: Physiological variables must be scaled for body size differences to permit meaningful comparisons between groups. Using allometric scaling, this study compared the anaerobic performance, using both arms and legs, of men and women. Ten active male and 10 active female subjects performed the leg cycling and arm cranking in a 30-s all-out Wingate test (WAnT). Regional measurements of the legs, gluteal area, arms, and torso taken using dual-energy x-ray absorptiometry (DXA) served as indicators of lower body active musculature (LBAMM) and upper body (UBAMM) active musculature. RESULTS: Body mass (BM) was the best predictor (i.e., r = 0.93-0.96) for peak power (PP) and mean power (MP) generated from sprint cycling and arm cranking. Sex differences for leg and arm power (i.e., PP and MP) were identified in absolute terms and then expressed in ratio to BM(1.0). When the same data were allometrically scaled to BM and expressed as power function ratios (Power;BM(b)), the sex differences in PP and MP for sprint cycling were nullified (female:male ratio x 100: 100-103%), but remained for arm cranking (female:male power ratio x 100: 69-84%). CONCLUSIONS: These results confirmed that anaerobic power of the upper body and lower body were best normalized to BM and, when statistically appropriate methods were used to take into account differences in BM, PP, and MP generated from sprint cycling were similar for both men and women. In contrast, after allometric scaling for BM, men remained more powerful than women for the supramaximal arm cranking task. Qualitative differences in the upper body musculature between men and women are speculated to account for the more powerful performance of men, but confirmatory evidence using noninvasive techniques is warranted.     

Effects of age and recovery duration on peak power output during repeated cycling sprints

The aim of the present study was to investigate the effects of age and recovery duration on the time course of cycling peak power and blood lactate concentration ([La]) during repeated bouts of short-term high-intensity exercise. Eleven prepubescent boys (9.6 +/- 0.7 yr), nine pubescent boys (15.0 +/- 0.7 yr) and ten men (20.4 +/- 0.8 yr) performed ten consecutive 10 s cycling sprints separated by either 30 s (R30), 1 min (R1), or 5 min (R5) passive recovery intervals against a friction load corresponding to 50 % of their optimal force (50 % Ffopt). Peak power produced at 50 % Ffopt (PP50) was calculated at each sprint including the flywheel inertia of the bicycle. Arterialized capillary blood samples were collected at rest and during the sprint exercises to measure the time course of [La]. In the prepubescent boys, whatever recovery intervals, PP50 remained unchanged during the ten 10 s sprint exercises. In the pubescent boys, PP50 decreased significantly by 18.5 % (p < 0.001) with R30 and by 15.3 % (p < 0.01) with R1 from the first to the tenth sprint but remained unchanged with R5. In the men, PP50 decreased respectively by 28.5 % (p < 0.001) and 11.3 % (p < 0.01) with R30 and R1 and slightly diminished with R5. For each recovery interval, the increase in blood [La] over the ten sprints was significantly lower in the prepubescent boys compared with the pubescent boys and the men. To conclude, the prepubescent boys sustained their PP50 during the ten 10 s sprint exercises with only 30 s recovery intervals. In contrast, the pubescent boys and the men needed 5 min recovery intervals. It was suggested that the faster recovery of PP50 in the prepubescent boys was due to their lower muscle glycolytic activity and their higher muscle oxidative capacity allowing a faster resynthesis in phosphocreatine.     

Single-fiber MHC polymorphic expression is unaffected by sprint cycle training

PURPOSE: The present investigation examined single-fiber MHC alterations in response to high-intensity, short-duration, sprint cycle training. METHODS: Ten untrained college-age male subjects participated in 8 wk of a progressive sprint cycle training program. Training involved 15-s maximal sprints separated by 5 min of rest beginning with four sprints x 2 d in week 1 and increasing to six sprints x 3 d at week 8. Muscle samples from the vastus lateralis were obtained before and after training. A 30-s sprint cycle test was used to evaluate performance before and after training. RESULTS: For the 30-s sprint, mean power and total work increased from pre to post. Single-fiber analyses revealed a reduction in the MHC IIx isoform (2.0 +/- 1.0 to 0.2 +/- 0.1%, pre to post, P < 0.05) and an increase in MHC IIa (P = 0.08), whereas there was no change in hybrid fiber composition (total hybrids = 24%). Generally, MHC IIa content increased and MHC IIx decreased (P < 0.05) as demonstrated by homogenate analyses of tissue samples. CONCLUSIONS: We report that as little as 32 min of high-intensity sprint cycle training over 8 wk is sufficient to improve sprinting performance. This training response is accompanied by an increase in MHC IIa and reduction in MHC IIx content of the vastus lateralis. However, short-duration, high-intensity, sprint cycle training does not cause a reduction in hybrid muscle fiber content.