雌性宽肋盘腹蛛的种内形态变异（蜘蛛目，螲蟷蛛科）

通过研究同一种群雌性宽肋盘腹蛛Cyclocosmia latusicosta Zhu,Zhang ＆ Zhang,2006,发现该种个体间在体长、步足长度、齿堤齿的形态与数量、圆盘肋数及纳精囊长宽之比等方面变异较大;宽肋盘腹蛛与里氏盘腹蛛Cyclocosmia ricketti（Pocock,1901）的区别主要是圆盘印痕中央是否存在纽扣状突起.     

拟环纹豹蛛附肢体毛感受器的扫描电镜观察

通过对拟环纹豹蛛(Pardosa pseudoannulata)附肢体毛(触毛、听毛、味觉感觉毛)的扫描电子显微镜观察,发现拟环纹豹蛛的触毛与体表形成的角度为锐角,触毛粗大,毛干较挺立,周围有绒毛环绕,触毛主要分布在蜘蛛体触肢的跗节、胫节和步足的跗节、胫节、端部处,其中第一步足分布最多,其数量较听毛和化学感觉毛多。拟环纹豹蛛的听毛细而长,基本垂直于表皮,毛囊深窝有褶皱,听毛主要分布于触肢和第四步足的胫节上,其余腿节分布较少,不同部位的听毛在形态、长度上没有太大的差别。拟环纹豹蛛的味觉感觉毛基部四周有微微隆起的圆形毛囊,味觉感觉毛大于听毛又小于触毛,四周被绒毛环绕,主要分布于蜘蛛的第一步足和第二步足的跗节胫节处,在触肢和螯肢也有少量分布。     

不同温度条件下异色瓢虫四龄幼虫亲缘关系对自残行为的影响

在14、18、22、24℃及30℃下对异色瓢虫Harmonia axyridis(Pallas)的不同同血缘的四龄幼虫自残行为及其对生长发育的影响进行研究。结果表明,异色瓢虫四龄幼虫自残发生概率受环境温度条件影响显著。在22-24℃处理范围内同血缘个体间自残发生概率均显著小于非同血缘个体。自残滞后时间同样受环境温度条件影响显著,且在同一温度条件下同血缘个体间均显著小于非同血缘处理。个体间相互攻击率不受环境温度变化影响,而在高于22℃下受血缘关系影响显著。此外,总受攻击次数在不同温度处理间差异显著。同血缘个体间自残后死亡率随温度增加而减少,均在30%以上。而非同血缘个体间自残后死亡率不受温度变化影响,均在70%以上。自残后残存个体的化蛹率及成虫羽化率均不受环境温度变化及个体间血缘关系的影响,化蛹率除30℃处理外均在90%以上,而在各温度下两血缘处理的羽化率均大于70%。     

近亲幽灵蛛用于兼性群居生活的时间消耗

所谓近亲幽灵蛛（Pholcus affinis）的兼性群居生活,是指他们可以单独生活,也可以几个个体共栖于一张网上成为一组。本文使用焦点动物追踪法,研究不同大小的组（指组内个体数量多少）、不同年龄阶段的蜘蛛在组内生活中用于“消耗性”行为（移动、织网、弹跳、拨丝或种内相互作用）的时间耗费。主要结论包括：蜘蛛的年龄和组的大小影响组内成员的付出。在不同大小的组里,2～3龄幼蛛（S型）、亚成体或成体（L型）用在“消耗性”行为上所用的时间百分率没有显著性差异,但4～5龄幼蛛（M型）随着组内成员的增多而要花费更多的时间。当组内个体数量超过3个,L型和M型蜘蛛之间有着更多的相互作用,而S型蜘蛛不论组内个体多少,其个体之间相互作用都很少。研究结果同时显示,近亲幽灵蛛在不同发育阶段有不同的群居生活策略。     

异色瓢虫幼虫对卵的种内自残和种间捕食

自残现象的发生在异色瓢虫Harmonia axyridis中很是常见,为明确自残行为对其存活和生长发育的影响,在非选择性条件下我们对异色瓢虫幼虫对非姊妹卵的种内自残和对七星瓢虫Coccinella septempunctata卵的种间捕食进行了研究。结果表明,异色瓢虫取食同种卵和异种卵均可完成生长发育,与取食蚜虫相比：①其从卵到成虫及蛹期的发育历期明显缩短（P<0.05）,其中1龄幼虫发育历期缩短非常明显（P<0.01）;②自然条件下高死亡率的1龄幼虫的存活率明显提高（P<0.05）;③2-4龄幼虫、蛹和成虫的体重变轻（P<0.05）,且体长在4龄幼虫间也表现出显著差异（P<0.05）。这表明异色瓢虫种内自残和种间捕食对其在食物恶劣条件下延续种群至关重要,但对种群的繁衍却不是最理想的途径。     

马氏沼虾蚤状幼体发育特征及其与罗氏沼虾幼体的形态差异

马氏沼虾(Macrobrachium malcolmsonii)的幼体从孵化到变态为幼虾要经过多次蜕皮,每次蜕皮均伴随形态及附肢特征的改变。采用显微观测摄像法对马氏沼虾Z1-Z12各期幼体样本30尾进行了观察,测量结果表明Z2与Z1在复眼上存在较大差异,Z3与Z2、Z4与Z5的主要分期特征均位于尾节上,Z6的腹部出现腹足萌芽,Z7与Z8的形态差异在于第一触角内鞭和外鞭的附肢变化,判别Z9-Z12的主要分期依据为步足、腹足和额角形态。因此通过观察Z1-Z12幼体第1触角上的内鞭和外鞭,第2触角上的触角鞭和触角片,头胸甲上的额角、背刺、复眼和第1、2对步足,腹部的附肢、尾节和尾扇等形态变化,及测定各期幼体附肢的分节数和刚毛数等可量性状上的差异,可为马氏沼虾蚤状幼体分期提供生物学依据;此外还对马氏沼虾与罗氏沼虾幼体的形态差异进行了比较,通过测定幼体触角鞭的分节数量,为两种沼虾幼体之间的鉴别提供参考数据。       

黄褐新园蛛和茶色新园蛛幼蛛各龄期的比较

黄褐新园蛛(Neoscon,doenitzi)和茶色新园蛛(N.theisi)为我国农田常见害虫天敌。其幼蛛特征尚未见报道。鉴于在调查和统计种群数量时常易混淆。为此将两种蜘蛛通过室内饲养获得各龄期标本,进行描述。其各部位的量度统一以蜕皮后三天的幼蛛进行测量,比较如下:一龄幼蛛均在卵囊内。体淡黄色。附肢半透明状。头胸部的放射沟及颈沟均不显。眼列较为相似。但茶色新园蛛各眼显著大且黑于黄褐新园蛛。身体及附肢上具短毛。黄褐新园蛛腹部较茶色新园蛛圆。茶色新园蛛腹部背面隐约可见淡黄色的斑块。二龄幼蛛两种园蛛腹背均具淡黄色斑块,但黄褐新园…     

味觉毛在不同蜘蛛类群中的形态、数量和分布

化学通讯是蜘蛛最基础和最普遍的种内和种间通讯方式之一,蜘蛛体表的味觉毛能够接触性的或者近距离地感知环境中的化学物质,但味觉毛的相关研究仅在少数几种蜘蛛中有过报道。我们通过扫描电镜对分别对幽灵蛛、弱蛛、泰莱蛛、幽灵蛛、蟹蛛和球蛛共5科32种蜘蛛味觉毛的形态、数量和分布进行了观察,结果显示：蜘蛛味觉毛一般呈“S”形或弧形;毛根部与体表形成较大角度,末端开口。一般分布在步足的跗节和后跗节,一些种类在步足胫节亦有味觉毛分布。所观察的蜘蛛中绝在部分种类在触肢上未发现味觉毛,仅有两种蟹蛛 (Thomisus labefactus Lysiteles inflatus) 和一种球蛛 (Phycosoma mustelinum) 在触肢上有味觉毛。味觉毛的数量在不同蜘蛛种类中有较大差异,从十几根到上百根不等。蜘蛛味觉毛的形态、数量和分布等特征除了与遗传相关外,亦有可能与其生境和生活方式等有关。     

花尾榛鸡的非对称性比和成体存活率

1999至2002年,在法国东南部的阿尔卑斯山,通过无线电追踪方法研究了花尾榛鸡的性比问题。首先,我们通过直接观测无线电标记雄性的配对比例,在消除可能的捕捉误差后,发现繁殖种群性比为1．26（即未配对的雄性占21％）。然后,我们估计了标记个体的存活率和繁殖成功率。在假设窝扩散时幼体的性比平衡的前提下,通过两性和两个年龄组（幼体,〈10月龄的个体;成体〉10月龄的个体）的确定性统计模型,得到的理论性比为1．22（即未配对的雄性占18％）,这一结果与实际观测的性比十分接近。我们认为,雌性死亡率高导致的两性存活率差异可以解释雄性性比偏高现象。我们进而讨论了花尾榛鸡整个分布区内居间强度的非对称性比的适应意义,以及在衰退的花尾榛鸡种群中雌性数量极端不足的后果[动物学报52（4）：655—662,2006]。     

洱海周边2种寄生蜂对拟环纹豹蛛和星豹蛛卵孵化的影响

为探讨Hidryta sp．和Idris sp．对云南洱海周边拟环纹豹蛛Pardosa pseudoannulata（Boes．＆Str．）和星豹蛛Pastvigera C．L．Koch卵孵化的影响,对具卵囊的拟环纹豹蛛和星豹蛛进行为期1年的野外采集和室内卵囊孵化观察,发现Hidryta sp．寄生蜘蛛卵囊后,每个卵囊内仅羽化出1只蜂,不再有幼蛛孵化出;而被Idris sp．寄生后每个卵囊羽化出一至数十只蜂,仍有幼蛛孵化出。比较未被寄生与被寄生蜘蛛卵囊的孵化量显示,拟环纹豹蛛未被寄生与被Idrissp．寄生后的孵化量间无显著差异（P〉0．05）;星豹蛛未被寄生与被Idris sp．寄生后的孵化量问存在显著差异（P〈0．01）。比较单位个体孵化量显示,Hidrytasp．对拟环纹豹蛛卵孵化的影响程度大于Idris sp．;而Hidrytasp．对星豹蛛卵孵化的影响程度小于Idris sp．。     

Leg autotomy in a spider has minimal costs in competitive ability and development

A number of species have the ability to autotomize limbs voluntarily, but animals that have lost limbs often face substantial costs. We examined the frequency of leg loss and its effects on competitive ability and development in the spider Holocnemus pluchei (Araneae: Pholcidae), a family of spiders known for its readiness to autotomize legs. Leg loss was common in field populations, with 7.5% of all surveyed spiders missing at least one leg, most commonly one of the anterior pair. More spiders were missing multiple legs than expected by chance, suggesting that leg loss events are not independent. Large adult spiders were missing legs more frequently than were small spiders. The competitive ability of injured males was tested in three contexts. In the field, no effect of leg loss was found on the ability of spiders to remain in webs into which they were introduced. In the laboratory, no effect of leg loss was found on the ability to fight with a single opponent over a prey, except that injured spiders were more likely to lose high-intensity fights. There was no difference between intact and injured males in their ability to compete with three females for limited prey. Leg loss significantly affected development time. The moult interval during the instar in which the injury occurred increased by approximately 15%. However, the growth rate for injured spiders was slightly but not significantly faster in the instar following leg loss, and total development time of the two instars together did not differ significantly between treatments. No spider showed any signs of regeneration. We conclude that, although there were some statistically significant differences between intact and injured males, these are unlikely to have major impacts on fitness, in contrast to findings in other species. Copyright 1999 The Association for the Study of Animal Behaviour.     

Bioelectrical impedance vs. four-compartment model to assess body fat change in overweight adults

Objective: The Tanita TBF‐305 body fat analyzer is marketed for home and clinical use and is based on the principles of leg‐to‐leg bioelectrical impedance analysis (BIA). Few studies have investigated the ability of leg‐to‐leg BIA to detect change in percentage fat mass (%FM) over time. Our objective was to determine the ability of leg‐to‐leg BIA vs. the four‐compartment (4C) model to detect small changes in %FM in overweight adults. Research Methods and Procedures: Thirty‐eight overweight adults (BMI, 25.0 to 29.9 kg/m²; age, 18 to 44 years; 31 women) participated in a 6‐month, randomized, double‐blind, placebo‐controlled study of a nutritional supplement. Body composition was measured at 0 and 6 months using the Tanita TBF‐305 body fat analyzer [using equations derived by the manufacturer (%FM_T‐Man) and by Jebb et al. (%FM_T‐Jebb)] and the 4C model (%FM_4C). Results: Subjects in the experimental group lost 0.9%FM_4C (p = 0.03), a loss that did not reach significance using leg‐to‐leg BIA (0.6%FM_T‐Man, p = 0.151; 0.6%FM_T‐Jebb, p = 0.144). We observed large standard deviations (SDs) in the mean difference in %FM between the 4C model and the Tanita_Manufacturer (2.5%) and Tanita_Jebb (2.2%). Ten subjects fell outside ±1 SD of the mean differences at 0 and 6 months; those individuals were younger and shorter than those within ±1 SD. Discussion: Leg‐to‐leg BIA performed reasonably well in predicting decreases in %FM in this group of overweight adults but resulted in wide SDs vs. %FM_4C in individuals. Cross‐sectional determinations of %FM of overweight individuals using leg‐to‐leg BIA should be interpreted with caution.     

Soft tissue body composition differences in monozygotic twins discordant for spinal cord injury.

To determine the effect of paralysis on body composition, eight pairs of male monozygotic twins, one twin in each pair with paraplegia, were studied by dual-energy X-ray absorptiometry. Significant loss of total body lean tissue mass was found in the paralyzed twins compared with their able-bodied co-twins: 47.5 +/- 6. 7 vs. 60.1 +/- 7.8 (SD) kg (P < 0.005). Regionally, arm lean tissue mass was not different between the twin pairs, whereas trunk and leg lean tissue masses were significantly lower in the paralyzed twins: -3.0 +/- 3.3 kg (P < 0.05) and -10.1 +/- 4.0 kg (P < 0.0005), respectively. Bone mineral content of the total body and legs was significantly related to lean tissue mass in the able-bodied twins (R = 0.88 and 0.98, respectively) but not in the paralyzed twins. However, the intrapair difference scores for bone and lean tissue mass were significantly related (R = 0.80 and 0.81, respectively). The paralyzed twins had significantly more total body fat mass and percent fat per unit body mass index than the able-bodied twins: 4.8 kg (P < 0.05) and 7 +/- 2% (P < 0.01). In the paralyzed twins, total body lean tissue was significantly lost (mostly from the trunk and legs), independent of age, at a rate of 3.9 +/- 0.2 kg per 5-yr period of paralysis (R = 0.87, P < 0.005). Extreme disuse from paralysis appears to contribute to a parallel loss of bone with loss of lean tissue in the legs. The continuous lean tissue loss may represent a form of sarcopenia that is progressive and accelerated compared with that in ambulatory individuals.     

Comparative Density of Hair Sensilla on the Legs of Cavernicolous and Epigean Harvestmen (Arachnida: Opiliones)

To allow an animal to behave appropriately, the location of sensorial structures is expected to be related to their function. As the different leg pairs of arachnids may have different functions (probing x supporting the body), one could expect them to have a different density of sensilla. Moreover, different regions of the same leg (dorsal, lateral, and ventral) would also be expected to have different densities of sensilla, according to the use of each region (e.g., the ventral part is often in contact with the substrate while the dorsal part is not). As cavernicolous animals are expected to be more sensitive than their epigean relatives, one could also expect a different density of sensilla when comparing cavernicolous and epigean animals. Using three epigean and three cavernicolous species of harvestmen (Arachnida, Opiliones), this study aimed at describing the morphology of hair sensilla on the legs and answering three questions: (1) Are there differences in the density of hair sensilla between the dorsal, lateral and ventral regions of each leg pair of the same individual? (2) Are there differences in the density of hair sensilla between the leg pairs of the same individual? (3) Are there differences in the density of hair sensilla when comparing the leg pairs of individuals of cavernicolous and non-cavernicolous species? The tarsi and metatarsi of all right legs of the six studied species were analyzed under a scanning electron microscope. The results (P < 0.05) showed that, in general: the ventral region of the tarsus was denser in sensilla trichodea than the lateral and dorsal regions, particularly on legs I and II; the density of sensilla chaetica did not differ on legs III and IV, but was greater on the dorsal region of legs I and II; the ventral part of legs I had the higher density of sensilla trichodea of the four pairs, whereas the second pair had the lower density; Holcobunus citrinus (Eupnoi) was the species with higher density of sensilla trichodea, on all legs; the cavernicolous species had a lower density of sensilla than the epigean species. The results are tentatively related to harvestmen behavior.     

The impact of limb autotomy on mate competition in blue crabs Callinectes sapidus Rathbun

Summary This study is the first to demonstrate experimentally that autotomy (self-amputation of a body part) adversely affects competition for mates. Experiments were conducted using blue crabs Callinectes sapidus Rathbun to examine the consequences of limb loss and pairing precedence on mate acquisition by males. Two adult males of equivalent size were introduced sequentially into pools containing a sexually-receptive female and observed after 24 h and 48 h. One male in each pair was left intact, while the other experienced: (1) no autotomy, (2) autotomy of one cheliped, or (3) autotomy of both chelipeds, one walking leg, and one swimming leg. In the absence of a competitor (first 24 h), both intact and injured males established precopulatory embraces with females. Intact males were highly successful (84–95%) in defending females from intact or injured intruders in the second 24 h period. Both autotomy treatments, however, significantly reduced the ability of males to defend females from intact intruders. Females in experiments suffered greater frequency of limb loss than did males. In the field, paired blue crabs showed significantly higher incidence of limb loss than unpaired crabs. Limb loss frequency increases with body size, and field observations indicated that larger males may be more successful than smaller males in obtaining females. Both experimental manipulations and field studies provide strong evidence for mate competition in this ecologically and commercially important portunid species.     

The Effect of Limb Loss on the Courtship and Mating Behavior of the Wolf Spider Pardosa milvina (Araneae: Lycosidae)

Limb loss is common in the wolf spider Pardosa milvina, appearing in nearly one third of adult males but occurring less frequently among adult females and juveniles. Since males wave their first pair of legs during courtship displays, the reproductive consequences of limb loss may be significant. We measured the courtship and mating effects of the loss of one, two, or four legs among adult male P. milvina. Missing one or two legs did not significantly reduce a male's ability to mate, but missing four legs was detrimental to mating success, reduced both courtship intensity and copulation duration, and increased cannibalism frequency. Results suggest behavioral flexibility in compensating for limited leg loss and a defensive function of the anteriormost legs to thwart female cannibalism attempts.     

Relationship of fat mass and serum estradiol with lower extremity bone in persons with chronic spinal cord injury

In the spinal cord injury (SCI) population, a relationship between adiposity and leg bone has not been reported, nor one between serum estradiol and leg bone mass. A cross-sectional, comparative study of 10 male pairs of monozygotic twins discordant for SCI was performed. Relationships were determined among bone mineral density (BMD), bone mineral content (BMC), lean mass, fat mass, and serum sex steroids. In the twins with SCI, significant relationships were evident between leg BMD or BMC with total body percent fat (r2= 0.49, P < 0.05; r2= 0.45, P = 0.05), leg fat mass (r2 = 0.76, P < 0.0005; r2= 0.69, P = 0.005), and serum estradiol (r2= 0.40, P = 0.05; r2= 0.37, P = 0.05). By stepwise regression analysis, in the twins with SCI, leg fat mass was found to be the single most significant predictor of leg BMD or BMC (F = 12.01, r2= 0.76, P = 0.008; F = 50.87, r2= 0.86, P < 0.0001). In the able-bodied twins, leg lean mass correlated with leg BMD and BMC (r2= 0.58, P = 0.01; r2= 0.87, P = 0.0001). By use of within-pair differences, significant correlations were found for leg lean mass loss with leg BMD loss (r2= 0.56, P = 0.01) or leg BMC loss (r2= 0.64, P = 0.0005). In conclusion, in twins with SCI, significant correlations were observed between fat mass and leg BMD or BMC as well as between serum estradiol values and leg BMD. The magnitude of the leg muscle mass loss was correlated with the magnitude of bone loss.     

Interactive effects of leg autotomy and incline on locomotor performance and kinematics of the cellar spider,Pholcus manueli

Leg autotomy can be a very effective strategy for escaping a predation attempt in many animals. In spiders, autotomy can be very common (5–40% of individuals can be missing legs) and has been shown to reduce locomotor speeds, which, in turn, can reduce the ability to find food, mates, and suitable habitat. Previous work on spiders has focused mostly on the influence of limb loss on horizontal movements. However, limb loss can have differential effects on locomotion on the nonhorizontal substrates often utilized by many species of spiders. We examined the effects of leg autotomy on maximal speed and kinematics while moving on horizontal, 45° inclines, and vertical (90°) inclines in the cellar spider Pholcus manueli, a widespread species that is a denizen of both natural and anthropogenic, three‐dimensional microhabitats, which frequently exhibits autotomy in nature. Maximal speeds and kinematic variables were measured in all spiders, which were run on all three experimental inclines twice. First, all spiders were run at all inclines prior to autotomization. Second, half of the spiders had one of the front legs removed, while the other half was left intact before all individuals were run a second time on all inclines. Speeds decreased with increasing incline and following autotomy at all inclines. Autotomized spiders exhibited a larger decrease in speed when moving horizontally compared to on inclines. Stride length decreased at 90° but not after autotomy. Stride cycle time and duty factor increased after autotomy, but not when moving uphill. Results show that both incline and leg autotomy reduce speed with differential effects on kinematics with increasing incline reducing stride length, but not stride cycle time or duty factor, and vice versa for leg autotomy. The lack of a significant influence on a kinematic variable could be evidence for partial compensation to mitigate speed reduction.     

Effect of the amount of body condition loss from the dry to near calving periods on the subsequent body condition change, occurrence of postpartum diseases, metabolic parameters and reproductive performance in Holstein dairy cows

We investigated the effect of body condition loss from the dry to near calving periods on the subsequent body condition change, the occurrence of postpartum diseases, the serum metabolic parameters total cholesterol, triglyceride, glucose, and urea nitrogen and the number of days to first breeding after calving in Holstein dairy cows. Body condition scoring (using a 5-point scale with quarter-point divisions) was performed on 67 pregnant Holstein dairy cows. Cows were scored once for body condition during the dry period (prepartum day 35 +/- 16), near calving (postpartum day 5 +/- 4), and subsequently at months 1 (+/- day 4), 2 (+/- day 5), 3 (+/- day 5), and 4 (+/- day 4) of lactation. At the same time, blood samples were collected to evaluate serum total cholesterol, triglyceride, glucose and urea nitrogen concentrations. Cows were categorized based on body condition loss from the dry to near calving periods into two groups: the moderate condition loss group (0-0.75 points, n=41), or the marked condition loss group (1.0-1.5 points, n=26). Regular reproductive health examination was conducted by the same investigator once a week. The marked condition loss group lost more body condition (P<0.01) than the moderate condition loss group consistently until month 1 of lactation. The recovery of body condition in the marked condition loss group was more delayed (P<0.01) than in the moderate condition loss group from months 1 to 4 of lactation. The occurrence of metritis and metabolic diseases (including abomasal displacement, milk fever, ketosis) was greater (P<0.01) in the marked condition loss group (62 and 23%) than in the moderate condition loss group (27 and 2%), respectively. The total cholesterol concentration was lower (P<0.05) in the marked condition loss group (167 +/- 5.3 mg/dl) than in the moderate condition loss group (183 +/- 5.8 mg/dl) at month 1 of lactation, however, the cholesterol levels at the other periods were not different (P>0.05) between the two groups. The triglyceride, glucose, and urea nitrogen concentrations were not different (P>0.05) from the dry period to month 4 of lactation between the two groups. The number of days to first breeding after calving was longer (P<0.05) in the marked condition loss group (103 +/- 7.8 day) than in the moderate condition loss group (87 +/- 5.3 day). We conclude that marked body condition loss from the dry to near calving periods results in the increased occurrence of postpartum metabolic and reproductive diseases, decreased serum total cholesterol concentrations at month 1 of lactation and a longer interval to first breeding after calving in Holstein dairy cows, probably due to the more severe energy deficit reflected by unfavorable body condition score change during early lactation.     

Effect of isometric strength training of mechanical, electrical, and metabolic aspects of muscle function

Monozygous twin pairs (two female and four male) were used in a strength training study so that one member of each pair served as training subject (TS) and the other members as nonexercising controls (CS). TS trained four times a week for 12 weeks with maximal isometric knee extensions of the right leg. The parameters studied included muscle strength, endurance time, electromyographic activity, and activities of several key enzymes in nonoxidative an oxidative muscle metabolism. The results disclosed that in addition to a 20% increase in isometric knee extension strength in the trained leg of TS, an average increase of 11% was observed in strength of TS untrained leg. CS did not demonstrate any change in muscle strength. Training also included an improvement in the maintenance of a static load of 60% of the pretraining maximum. Increase in the maximum integrated electromyographic activity (IEMG) of the rectus femoris muscle occurred concomitantly with the knee extension strength. Traning also caused reduction in the IEMG/tension ratio at submaximal loads indicating a more econimical usage of the rectus femoris muscles. Muscle biopsies taken from the vastus lateralis muscle showed that the enzyme activities of MDH, SDH, and HK were higher, and LDH and CPK lower in the trained leg as compared to the nontrained control leg of TS or to the values of the untrained member of the twin pair. It is concluded that isometric strength training as used in the present study can cause increased recruitment of the availabel motor unit pool, improved efficiency at submaximal loads, and surprisingly also enchancement of the oxidative metabolism in the muscle.