不同强度训练对大鼠骨骼肌p53和细胞色素氧化酶I亚基基因和蛋白表达的影响

目的:探讨不同强度训练对大鼠骨骼肌p53和细胞色素氧化酶(COX)I亚基基因和蛋白表达的影响。方法:18只大鼠随机分为3组:安静组(C)、中等强度训练组(MT)和大强度训练组(ST),每组6只,训练8周;采用Bedford训练方案,中等强度相当于65%VO2max,大强度相当于85%VO2max;末次训练后24h,各组大鼠安静状态下处死,取比目鱼肌和腓肠肌。采用Real-time PCR和Western Blot法分别测定比目鱼肌和腓肠肌中p53和COXI的mRNA和蛋白表达水平。结果:(1)MT组腓肠肌p53 mRNA表达显著低于C组(P<0.05)。MT组(P<0.05)和ST组(P<0.01)比目鱼肌p53蛋白表达显著高于C组;MT组腓肠肌p53蛋白表达显著低于C组(P<0.05)。(2)ST组腓肠肌COXI mRNA表达显著高于C组(P<0.05)。MT组和ST组比目鱼肌COXI蛋白表达极显著高于C组(P<0.01);MT组腓肠肌COXI蛋白表达显著低于C组(P<0.05)。结论:运动诱导的p53及COXI的基因表达存在肌纤维类型的特异性以及运动强度的敏感性,运动对p53及COXI基因表达的调控可发生在转录和转录后水平,这与肌纤维类型有关。     

不同强度训练对大鼠骨骼肌p53和细胞色素氧化酶Ⅰ亚基基因和蛋白表达的影响

目的:探讨不同强度训练对大鼠骨骼肌p53和细胞色素氧化酶(COX)I亚基基因和蛋白表达的影响.方法:18只大鼠随机分为3组:安静组(C)、中等强度训练组(MT)和大强度训练组(ST),每组6只,训练8周;采用Bedford训练方案,中等强度相当于65%VO2max,大强度相当于85%VO2max;末次训练后24h,各组大鼠安静状态下处死,取比目鱼肌和腓肠肌.采用Real-time PCR和Western Blot法分别测定比目鱼肌和腓肠肌中p53和COX Ⅰ的mRNA和蛋白表达水平.结果:(1)MT组腓肠肌p53mRNA表达显著低于C组(P<0.05).MT组(P<0.05)和ST组(P<0.01)比目鱼肌p53蛋白表达显著高于C组;MT组腓肠肌p53蛋白表达显著低于C组(P<0.05).(2)ST组腓肠肌COX Ⅰ mRNA表达显著高于C组(P<0.05).MT组和ST组比目鱼肌COX Ⅰ蛋白表达极显著高于C组(P<0.01);MT组腓肠肌COX Ⅰ蛋白表达显著低于C组(P<0.05).结论:运动诱导的p53及COX Ⅰ的基因表达存在肌纤维类型的特异性以及运动强度的敏感性,运动对p53及COX Ⅰ基因表达的调控可发生在转录和转录后水平,这与肌纤维类型有关.     

不同恢复方式对去负荷大鼠腓肠肌纤维类型组成的影响

目的:探讨自然恢复和离心运动恢复等再负荷方式对废用性骨骼肌纤维横截面积及类型的影响。方法:采用尾部悬吊模型。24只成年雌性SD大鼠按体重随机分为对照组(CON)、尾部悬吊组(TS),悬吊14天后解悬吊自然恢复组(NR)和悬吊14天后离心运动恢复组(ER),每组6只。离心运动为每天下坡跑1h,坡度-5%,跑速16 m/min,共2周。取大鼠腓肠肌进行异染性染料ATPase染色,计算腓肠肌纤维组成百分比和肌纤维横截面积(CSA)。结果:(1)TS组大鼠腓肠肌I型%和IIa%显著低于CON组(P<0.01),IIb%显著高于CON组(P<0.01);TS组Ⅰ型肌纤维CSA较CON组减少42.2%(P<0.01),Ⅱa型肌纤维CSA减少30.0%,Ⅱb型肌纤维CSA减少了17.9%(P<0.01)。(2)NR组I%与CON组无显著差异,IIa型和IIb型肌纤维CSA与CON组无显著差异。(3)ER组I%、IIa%和IIb%和横截面积均与CON组无显著性差异。(4)ER组与NR组相比,I%无显著性差异,IIa%高12.54%(P<0.01),IIb%低14.63%(P<0.01);ER组Ⅰ型肌纤维CSA为NR组的1.18倍(P<0.01),两组Ⅱa和Ⅱb型肌纤维CSA则没有显著性差异。结论:尾部悬吊造成骨骼肌废用性肌萎缩,与自然恢复相比,离心运动能较好地使废用性萎缩骨骼肌的面积和肌纤维组成百分比得到恢复。     

振动训练对大鼠骨骼肌质量和肌细胞机械生长因子mRNA表达的影响

目的:探讨不同振动训练模式对大鼠骨骼肌细胞机械生长因子(MGF)mRNA表达和肌肉质量的影响。方法:42只雄性SD大鼠,根据对其施加的不同振动频率(35Hz、25Hz和15Hz)和持续时间(15min和5min),分为7组:安静对照组、低频率短时间振动组、低频率长时间振动组、中频率短时间振动组、中频率长时间振动组、高频率短时间振动组和高频率长时间振动组。各组进行相应振频和时间的振动训练,实验持续8周。实验结束后取材,检测腓肠肌质量相关指标、CK活性和肌细胞MGF mRNA表达水平。结果:各组大鼠腓肠肌质量无显著性差异,中频长时间组和高频短时间组腓肠肌指数(肌肉/体重比值)均显著高于安静对照组(P<0.05)。中频长时间组肌纤维横截面积(CSA)和CK水平均显著高于安静对照组(P<0.05)。各训练组大鼠骨骼肌MGF mRNA表达均显著高于安静对照组,中频长时间组显著高于除高频短时间组之外的其它训练组(P<0.05)。结果提示,适宜的振动(中频率长时间)训练有助于增加腓肠肌相对质量、肌纤维横截面积和肌细胞内CK活性,增强肌细胞MGFmRNA表达。     

肝细胞生长因子对后肢固定大鼠腓肠肌细胞凋亡的影响

目的：观察肝细胞生长因子对后肢固定大鼠腓肠肌细胞凋亡的影响。方法：按照Jozsa的方法制作模型，实验组将肝细胞生长因子注射人大鼠腓肠肌；模型组注射等量生理盐水。观察骨骼肌组织的病理改变及骨骼肌细胞凋亡的改变。结果：实验组肌纤维塑形良好，线粒体形态较正常，见新生肌纤维；Bcl-2呈强阳性表达且TUNEL显示为低表达，均较模型组明显改变（P〈0.01）。结论：肝细胞生长因子能够显著降低骨骼肌细胞凋亡，有效抑制骨骼肌废用性萎缩的发生     

振动训练对大鼠骨骼肌最大力量和肌纤维形态结构的影响

目的:探讨不同频率振动训练对大鼠肌纤维形态结构的影响。方法:24只SD雄性大鼠随机分成安静对照组(C)、低频率振动训练组(L)、中频率振动训练组(M)和高频率振动训练组(H),每组6只。训练组大鼠每天接受一次振动训练,训练时间为30min(15min×2,间歇5min),振动频率分别为15 Hz、25 Hz和35 Hz,振幅为1.5mm,每周训练6次,共8周。8周后,测试大鼠后肢最大力量;取其腓肠肌制作冰冻切片,采用单克隆抗体BA-D5(lgG,anti-MHCI)、SC-71(lgG,anti-MHCIIa)和BF-F3(lgM,anti-MHCIIb)进行免疫组化染色,观察不同类型肌纤维百分比,计算不同类型肌纤维横截面积。结果:(1)与C组相比,L组和M组大鼠后肢肌肉最大力量显著增加(P<0.05)。(2)与C组相比,L组和M组大鼠腓肠肌中Ⅱx型肌纤维明显减少(P<0.05),Ⅱa型肌纤维显著增加(P<0.05)。(3)与C组相比,M组大鼠腓肠肌Ⅰ型、Ⅱa型和Ⅱb型肌纤维横截面积显著增加(P<0.05),H组Ⅰ型、Ⅱa型和Ⅱb型肌纤维横截面积显著减小(P<0.05)。结论:振动训练引起的肌肉力量增加可能与肌纤维的横截面积增加和Ⅱa肌纤维百分比增加存在一定的联系。     

高强度间歇训练对老龄大鼠骨骼肌减少症及某些氧化应激、脂肪细胞因子和炎症因子的影响

目的:探讨高强度间歇训练(HIIT)和持续性运动(MICT)对老龄大鼠运动表现、骨骼肌氧化应激、血浆超敏C-反应蛋白(hs-CRP)、白介素-6/10、脂联素和瘦素分泌的影响。方法:48只8月龄SD大鼠适应性喂养2周后进行体成分、耐力和抓力测试,随机选取12只大鼠作为成年对照组,禁食12 h后宰杀;剩下36只大鼠常规饲养10个月,18月龄时进行适应性跑台1周后随机分为三组:老龄安静组、老龄MICT组和老龄HIIT组,每组12只。之后进行8个月跑台训练,老龄MICT组以速度17 m/min进行跑台训练;老龄HIIT组以起始速度15 m/min,时间为4 min,之后跑台速度增至25 m/min,运动1 min,依次交替进行9个循环;两种运动的总时间均为45 min,1次/天,5天/周。末次训练48 h后检测体成分,并进行耐力和抓力测试;耐力测试后48 h禁食12 h宰杀,腹主动脉离心抽取血浆,连同成年对照组,采用酶联免疫吸附试验(ELISA)检测血浆和骨骼肌炎症因子(IL-6、IL-10和hs-CRP)、氧化应激(SOD、MDA、8-OHdG和4-HNE)和脂肪细胞因子(瘦素和脂联素)含量。结果:(1)与成年对照组相比,老龄安静组大鼠的体重、体脂/瘦体重比值和体脂百分比显著增加(P<0.01),瘦体重%、骨骼肌指数、抓力和耐力显著降低(P<0.01),血浆氧化应激、hs-CRP和脂联素均显著增加(P<0.05)。(2)与老龄安静组相比,老龄HIIT组大鼠体脂重量显著减少(P<0.05),瘦体重百分比、耐力、抓力和骨骼肌指数显著增加(P<0.05或P<0.01);老龄MICT组大鼠耐力显著增加(P<0.05)。(3)与老龄安静组相比,老龄HIIT组血浆氧化应激水平(MDA:P<0.05,8-OHdG:P<0.01,4-HNE:P<0.05)、慢性炎症状态(hs-CRP,IL-6/IL-10比值,IL-10)和脂联素水平显著降低(P<0.05),但血浆瘦素显著升高(P<0.05),而老龄MICT组脂联素显著降低(P<0.01);与老龄安静组相比,老龄HIIT组和老龄MICT组骨骼肌SOD2显著升高(P<0.01),8-OHdG(P<0.01)和4-HNE(P<0.05)显著降低;与MICT组相比,HIIT组大鼠骨骼肌8-OHdG (P<0.05)和MDA(P<0.01)显著降低。Pearson相关分析显示,耐力与血浆8-OHdG呈负相关(r=-0.72),血浆hs-CRP与体脂百分比(r=0.55)、MDA(r=0.58)和4-HNE(r=0.66)呈正相关,血浆瘦素与体脂%(r=-0.58)呈负相关。结论:高强度间歇训练可通过调控血浆瘦素水平,改善老龄大鼠体成分,增加骨骼肌指数,提高老龄大鼠运动表现;高强度间歇训练可降低老龄大鼠炎症与氧化应激水平。     

运动介导HSP70延缓增龄性骨骼肌萎缩的机理研究

目的:通过对自然衰老C57BL/6小鼠进行长期有氧运动干预,探讨增龄性骨骼肌萎缩发生发展过程中细胞凋亡相关蛋白的变化及运动诱导HSP70对其影响,揭示运动预防增龄性骨骼肌萎缩的作用机理。方法:27周龄雄性C57BL/6小鼠50只,经1周适应性喂养后,随机分为年轻对照组(YS组)、老年对照组(OS组)和老年运动组(OE组)。YS组(28周)小鼠经抓力测试后立即处死取材。OE组小鼠采用30周、每周3~4次、每次50分钟、75%VO2max有氧跑台运动训练(速度12米/分钟,坡度0°)。OS组与OE组小鼠喂养至60周龄后,检测抓力等指标后处死。随即分离各组小鼠腓肠肌,称重后检测小鼠骨骼肌萎缩指数(Sarcopenia index,SI),随后提取腓肠肌总蛋白。采用Western Blot检测小鼠腓肠肌组织HSP70,Cleaved Caspase-9蛋白表达水平;采用Co-IP法检测小鼠腓肠肌HSP70与Apaf-1蛋白结合量;采用TUNEL法检测小鼠腓肠肌细胞凋亡指数。结果:(1)SI变化:OS组小鼠腓肠肌SI较YS组显著减少23.09%,而OE组SI与OS组相比显著增加30.48%;(2)小鼠抓力:OS组小鼠抓力/体重比值比YS组显著减少42.74%,OE组比OS组显著增加21.51%;(3)凋亡指数检测:伴随年龄增加,OS组较YS组显著增加475.28%,而有氧运动之后,OE组小鼠凋亡指数较OS组显著减少46.41%;(4)Western Blot结果:OS组Cleaved Caspase-9表达水平较YS组显著增加45.40%,OE组较OS组显著减少33.40%;(5)腓肠肌HSP70与Apaf-1蛋白的结合量:OS组较YS组HSP70与Apaf-1结合量显著下降67.11%,运动后OE组较OS组显著增加306.31%。结论:(1)60周龄小鼠腓肠肌发生增龄性骨骼肌萎缩,30周有氧运动可显著延缓增龄性骨骼肌萎缩;(2)增龄性骨骼肌萎缩可能与骨骼肌凋亡细胞增多有关,30周有氧运动可显著抑制骨骼肌细胞凋亡;(3)30周有氧运动可增强HSP70与Apaf-1结合量,这可能是运动抑制骨骼肌细胞凋亡,延缓增龄性骨骼肌萎缩的机制之一。     

有氧运动对12月龄大鼠腓肠肌PGC-1α/Sirt3的影响

目的:探讨运动预防增龄性骨骼肌衰减中去乙酰化酶3(Sirtuin3,Sirt3)的调控机制,为运动预防肌肉衰减提供理论依据。方法:20只12月龄雄性SD大鼠随机分为对照组(CG)和运动组(EG,15 m/min,第1周30 min/d,每周递增5min,跑台坡度为5%,6 d/w,4 w),每组10只。腓肠肌切片HE染色计算横截面积百分比;测定大鼠腓肠肌Mn-SOD、MDA含量;ELISA法测定8-羟基脱氧鸟苷(8-hydroxy-2deoy-guanosine,8-OHd G)含量;Western Blot法检测大鼠腓肠肌细胞内Sirt3和PGC-1α蛋白含量变化。结果:(1)HE染色的组织切片中运动组大鼠腓肠肌所占面积百分比显著高于对照组(P<0.05)。(2)运动组大鼠腓肠肌Mn-SOD活性高于对照组(P<0.01);MDA、8-OHd G含量低于对照组(P<0.05,P<0.01);(3)运动组大鼠腓肠肌PGC1-α和Sirt3蛋白表达量高于对照组(P<0.01)。结论:适度有氧运动通过促进12月龄大鼠腓肠肌PGC1-α和Sirt3蛋白表达,提高抗氧化酶活性,减轻骨骼肌过氧化损伤,预防增龄性骨骼肌衰减。     

运动性蛋白尿与肾脏细胞凋亡及氧自由基代谢关系的研究

目的 :观察大鼠不同强度运动后肾脏细胞凋亡及氧自由基变化与运动性蛋白尿之间的关系 ,以期进一步阐明运动性蛋白尿的发生机制。方法 :36只雄性SD大鼠随机分为安静对照组、中等强度运动组和大强度运动组。运动后 2小时取材 ,采用原位缺口末端标记 (TUNEL)和流式细胞术分别检测大鼠肾脏凋亡细胞及Bax、Bcl- 2基因的表达 ;同时检测大鼠肾脏组织超氧化物歧化酶 (SOD)、谷胱甘肽过氧化物酶 (GSH -Px)、丙二醛 (MDA)含量及运动后各实验组大鼠尿蛋白含量。结果 :运动后大强度组肾脏凋亡细胞显著增加 ,凋亡调控基因Bax/Bcl - 2比值上升 (P <0 0 1) ,尿蛋白含量显著升高 ,反映肾脏组织细胞抗氧化能力的SOD及GSH -Px活性显著下降 ,而MDA含量显著升高。结论 :大强度运动造成肾脏细胞凋亡及氧自由基增加可能参与了运动性蛋白尿的发生过程。     

Strenuous resistance exercise effects on magnetic resonance diffusion parameters and muscle–tendon function in human skeletal muscle

Purpose:

To assess the effects of strenuous exercise on magnetic resonance diffusion parameters and muscle–tendon complex function in skeletal muscle.

Materials and Methods:

Six men performed ankle plantar flexion exercises with eccentric contraction. The fractional anisotropy (FA), λ₁, λ₂, λ₃, mean diffusivity (MD), and T₂ values in the triceps surae muscles were measured by magnetic resonance diffusion tensor and spin‐echo imaging. Passive torque of plantar flexors, maximal voluntary isometric plantar flexion torques (MVIP), and Achilles tendon stiffness during MVIP were measured by combined ultrasonography and dynamometry. Plasma creatine kinase and muscle soreness were also assessed. These parameters were measured before and 1–8 days postexercise.

Results:

The medial gastrocnemius exhibited significantly decreased FA 2–5 days after, increased λ₂ 3 days after, and increased λ₃ 2 and 3 days after exercise. This muscle also showed significantly increased MD and T₂ values 3 days postexercise. MVIP significantly decreased 2 and 3 days postexercise, while passive torque significantly increased 2 days postexercise. Creatine kinase and muscle soreness increased 3–5 days and 1–5 days postexercise, respectively.

Conclusion:

Exercise‐induced muscle damage manifested as significant changes in muscle diffusion parameters with muscle–tendon complex dysfunction and delayed‐onset muscle soreness. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

To stretch or not to stretch: the role of stretching in injury prevention and performance

Stretching is commonly practiced before sports participation; however, effects on subsequent performance and injury prevention are not well understood. There is an abundance of literature demonstrating that a single bout of stretching acutely impairs muscle strength, with a lesser effect on power. The extent to which these effects are apparent when stretching is combined with other aspects of a pre‐participation warm‐up, such as practice drills and low intensity dynamic exercises, is not known. With respect to the effect of pre‐participation stretching on injury prevention a limited number of studies of varying quality have shown mixed results. A general consensus is that stretching in addition to warm‐up does not affect the incidence of overuse injuries. There is evidence that pre‐participation stretching reduces the incidence of muscle strains but there is clearly a need for further work. Future prospective randomized studies should use stretching interventions that are effective at decreasing passive resistance to stretch and assess effects on subsequent injury incidence in sports with a high prevalence of muscle strains.     

Differential muscle hypertrophy and edema responses between high‐load and low‐load exercise with blood flow restriction

We sought to determine whether early increases in cross‐sectional area (CSA) of different muscles composing the quadriceps with low‐load resistance training with blood flow restriction (LL‐BFR) were mainly driven by muscle hypertrophy or by edema‐induced swelling. We also compared these changes to those promoted by high‐load resistance training (HL‐RT). In a randomized within‐subject design, fifteen healthy, untrained men were submitted to magnetic resonance imaging (MRI) for CSA and edema‐induced muscle swelling assessment (fast spin echo inversion recovery, FSE‐STIR). MRI was performed in LL‐BFR and HL‐RT at baseline (W0) and after 3 weeks (W3), with a further measure after 6 weeks (W6) for HL‐RT. Participants were also assessed at these time points for indirect muscle damage markers (range of motion, ROM; muscle soreness, SOR). CSA significantly increased for all the quadriceps muscles, for both LL‐BFR and HL‐RT at W3 (all P < .05) compared to W0. However, FSE‐STIR was elevated at W3 for all the quadriceps muscles only for HL‐RT (all P < .0001), not LL‐BFR (all P > .05). Significant increases and decreases were shown in SOR and ROM, respectively, for HL‐RT in W3 compared to W0 (both P < .05), while these changes were mitigated at W6 compared to W0 (both P > .05). No significant changes in SOR or ROM were demonstrated for LL‐BFR across the study. Early increases in CSA with LL‐BFR seem to occur without the presence of muscle edema, whereas initial gains obtained by HL‐RT were influenced by muscle edema, in addition to muscle hypertrophy.     

The association between muscular power from childhood to adulthood and adult measures of glucose homeostasis

This study aimed to assess whether the longitudinal association between childhood muscular fitness and adult measures of glucose homeostasis persist despite changes in muscular fitness across the life course. This prospective longitudinal study included 586 participants who had their muscular power (standing long jump distance), cardiorespiratory fitness (CRF), and waist circumference measured as children (aged 9, 12, 15 years) and again 20 years later as adults. In adulthood, these participants also provided a fasting blood sample which was tested for glucose and insulin. Glucose homeostasis measures including insulin resistance (HOMA2‐IR) and beta cell function (HOMA2‐β) were estimated. Child and adult muscular power levels were separated into thirds, and tracking groups (persistently low, decreasing, persistently moderate, increasing, and persistently high) were created. Sex‐stratified multivariable linear regression models were used to examine the association between muscular power tracking groups and adult measures of glucose homeostasis. Compared with males with persistently high muscular power, males with increasing and persistently low muscular power had higher fasting insulin (increasing: β = 1.12 mU/L, P = .04; persistently low: β = 2.12 mU/L, P = .001) and HOMA2‐β (increasing: β = 8.50%, P = .03; persistently low: β = 11.27%, P = .01) independent of CRF and males with persistently low muscular power had greater fasting insulin (β = 1.22 mU/L, P = .02) and HOMA2‐IR (β = 0.14, P = .02) independent of waist circumference. Non‐significant associations were present for females. For males, maintaining persistently high muscular power between childhood and adulthood could lead to a healthier adult glucose homeostasis profile.     

The magnitude of intramuscular deoxygenation during exercise is an unreliable measure to diagnose the cause of leg pain

We measured intramuscular oxygenation in the anterior tibial muscle of 176 patients with exercise‐induced leg pain by noninvasive near‐infrared spectroscopy before, during, and after an exercise test that elicited the symptoms. Clinical investigation was performed after each test. Intramuscular pressure was measured in patients with nonconclusive findings. Chronic anterior compartment syndrome (CACS) was diagnosed in 47 patients, and other causes for the leg pain were diagnosed in 129 patients by clinical means. The mean level of oxygenation decreased to 33 ± 19% in patients with CACS and to 34 ± 19% in patients without CACS compared with baseline level (100%) at rest before exercise. The level of oxygenation was below 20% during the exercise test in 12 of 47 (26%) patients with CACS and in 30 of 129 (23%) patients without CACS. The time required for reoxygenation after the cessation of exercise was 61 ± 34 s in patients with CACS and 46 ± 20 s in patients without CACS (P < 0.05). We conclude that the magnitude of intramuscular deoxygenation during exercise is an unreliable measure to diagnose CACS. However, the time for reoxygenation returning to baseline level following an exercise test is a valuable adjunct in diagnosing CACS.     

长期模拟失重大鼠心肌收缩性能的改变

应用在体及离体实验对一批悬吊90d大鼠的心肌收缩性能进行了观察。在体实验结果表明：悬吊组大鼠左室舒张本压及主动脉血压与对照组无显著性差别（P＞0．05）；但悬吊组大鼠左心室内压峰值较对照组降低16％（P＜0．01），左心室内压最大上升速率与最大下降速率也分别较对照组减慢28％（P＜0．05）与21％（P＜0．05）。对同一批大鼠的离体乳头肌，又用等长收缩灌流技术观察了力学特性变化。结果是：反映心肌收缩强度的指标，如最大发展张力（DT），在两组间无显著差别；反映心肌收缩速度的指标，如最大张力发展速率对DT的校正值，悬吊组较对照组降低了17．2％（P＜0．05）；反映收缩时程的指标，如悬吊组的至峰张力收缩时间与至峰张力发展速率收缩时间分别较对照组延长了12．7％（P＜0．01）和22．2％（P＜0．05）；反映心肌舒张的时程指标，如张力下降一半时间与至峰张力下降速率舒张时间分别较对照组延长183％（P＜0．01）与20．3％（P＜0．01）。以上结果表明，长期模拟失重大鼠心肌收缩性能明显降低，并主要表现为心肌收缩速率减慢和收缩与舒张时程延长。     

Low-intensity training dissociates metabolic from aerobic fitness

This study investigated the effect of prolonged whole-body low-intensity exercise on blood lipids, skeletal muscle adaptations and aerobic fitness. Seven male subjects completed a 32-day crossing of the Greenland icecap on cross-country skies and before and after this arm or leg cranking was performed on two separate days and biopsies were obtained from arm and leg muscle, and venous blood was sampled. During the crossing, subjects skied for 342+/-42 min/day and body mass was decreased by 7.1+/-0.7 kg. Peak leg oxygen uptake (4.6+/-0.2 L/min) was decreased (P<0.05) by 7% whereas peak arm oxygen uptake (3.0+/-0.2 L/min) remained unchanged. Total and low-density lipoprotein cholesterol (5.0+/-0.2 and 3.20.2 mmol/L) were decreased by 8% and 20%, respectively. Muscle beta-hydroxy-acyl-CoA dehydrogenase activity was increased with 22% in arm (P=0.08) and remained unchanged in leg muscle. Hormone sensitive lipase activity was similar in arm and leg muscle prior to the expedition and was not significantly affected by the crossing. In conclusion, an improved blood lipid profile and thus metabolic fitness was present after prolonged low-intensity training and this occurred in spite of a decreased aerobic fitness and an unchanged arm and leg muscle hormone-sensitive lipase activity.     

Changes in motor unit characteristics after eccentric elbow flexor exercise

Morphological evidence suggests that fast-twitch fibers are prone to disruption of their membrane structures by eccentric exercise. However, it is unclear how this is reflected in the discharge rate and action potential propagation of individual motor units, especially at high contraction levels. High-density surface electromyograms were recorded from biceps brachii muscle and decomposed to individual motor unit action potentials at isometric contraction levels between 10% and 75% of maximal voluntary contraction (MVC) before intermittent maximal elbow flexor eccentric exercise, and two hours (2H), two days (2D) and four days (4D) post-exercise. Maximal voluntary force decreased by 21.3±5.6% 2H and by 12.6±11.1% 2D post-exercise. Motor unit discharge rate increased and mean muscle fiber conduction velocity decreased, at the highest isometric contraction levels only (50% and 75% of MVC) at 2H post-exercise. These results indicate that eccentric exercise can disturb the function of motor units active at high contraction levels in the early stages after exercise, which seems to be compensated by the central nervous system with an increase in neural drive during submaximal isometric contractions.