Bilateral isokinetic training reduces the bilateral leg strength deficit for both old and young adults

The bilateral limb deficit (BLD) describes the difference in maximal or near-maximal force generating capacity of muscles when they are contracted alone and in combination with the contralateral muscles. This study examined the effects of a 6-week (three times per week) bilateral leg strength training programme on BLD in younger and older adults. Data were collected from 33 subjects during slow (45°/s) isokinetic knee extensions and flexions before and after the training programme. After training, the BLD was reduced for extension (73.3–86.9%; P<0.001) but not for flexion (67.5–71.2%; P=0.13) regardless of age and gender. This study suggests that difficulty in recruiting all muscle units during a task involving bilateral activation can be improved by training, although such an effect appears to depend on the muscle group appreciated.     

The bilateral leg strength deficit is present in old, young and adolescent females during isokinetic knee extension and flexion

The bilateral limb deficit (BLD) describes the difference in maximal or near maximal force generating capacity of muscles when they are contracted alone or in combination with the contralateral muscles. A deficit occurs when the summed unilateral force is greater than the bilateral force. This study examined the presence of the BLD during isokinetic knee extensions and flexions in a group of adolescent females (n = 8, mean of 15 ± 1 years) and compared with previously reported data by this researcher of adult and older females. Data were collected from subjects during slow (45 deg/s) isokinetic knee extensions and flexions and it was found that a BLD exists during both extension and flexion regardless of age. Furthermore, this study is the first to examine the presence of the deficit in an adolescent population. Myoelectric signal (MES) data showed that there is no difference between bilateral and unilateral isokinetic knee extensions and flexions regardless of age group.     

Bilateral deficit expressions and myoelectric signal activity during submaximal and maximal isometric knee extensions in young,athletic males

The bilateral limb deficit (BLD) describes the difference in maximal or near maximal force generating capacity of muscles when they are contracted alone or in combination with the contralateral muscles. A deficit occurs when the summed unilateral force is greater than the bilateral force. This study examined the presence of the BLD during submaximal (25, 50, 75% of MVC) and maximal (100% MVC) isometric knee extensions in a group of young, athletic males (n = 6, mean age of 22 ± 3 years, mean height = 177.7 ± 6.4 cm, mean weight = 72.4 ± 5.2 kg). Torque and myoelectric signal (MES) data were collected from three superficial muscles of the quadriceps (vastus lateralis, vastus medialis and rectus femoris) during submaximal and maximal isometric knee extensions and it was found that a similar BLD exists using either torque or MES data. MES data showed that there were differences between bilateral and the total unilateral isometric knee extension regardless of percent contraction. This suggests that the BLD may be due to neural mechanisms and that future studies should examine the relationship between torque and the corresponding MES activity.     

Altered biomechanics in bilateral total knee replacement patients during stair negotiation

BackgroundMany total knee replacement (TKR) patients need to have a contralateral knee replacement. Biomechanical differences between first and second replaced limbs of bilateral TKR have not been examined during stair negotiation. Additionally, it is unknown whether hip and ankle biomechanics of bilateral patients are altered. We examined hip, knee, and ankle biomechanics of first and second replaced limbs bilateral patients, as well as replaced and non-replaced limbs of unilateral patients, during stair ascent and descent.MethodsEleven bilateral TKR patients (70.09 ± 5.41 years, 1.71 ± 0.08 m, 91.78 ± 13.00 kg) and 15 unilateral TKR patients (64.93 ± 5.11 years, 1.75 ± 0.09 m, 89.18 ± 17.55 kg) were recruited. Patients performed three to five trials of stair ascent and descent. The second step, during ascent, was the step of interest when analyzing each limb. A 2 × 2 (limb × group) analysis of variance was performed to determine differences between limbs and groups.ResultsDuring ascent, bilateral patients exhibited decreased peak loading-response knee extension (KEM) and push-off plantarflexion moments. Unilateral replaced limb KEM was lower than non-replaced limbs. During descent, bilateral patients descended the staircase significantly slower, had lower peak loading-response vertical ground reaction force and KEM, and push-off KEM. Bilateral patients had higher peak loading-response hip extension and push-off plantarflexion moments, and increased knee adduction ROM, compared with unilateral TKA patients.ConclusionsBilateral patients exhibited similar hip, knee, and ankle joint moments between first and second replaced limbs. Substantial differences in hip, knee, and ankle biomechanics during stair negotiation in bilateral patients compared with unilateral patients may indicate a more complex adaptation strategy present in these patients.     

Hypertrophy with unilateral resistance exercise occurs without increases in endogenous anabolic hormone concentration

We aimed to gain insight into the role that the transitory increases in anabolic hormones play in muscle hypertrophy with unilateral resistance training. Ten healthy young male subjects (21.8 ± 0.4 years, 1.78 ± 0.04 m, 75.6 ± 2.9 kg; mean ± SE) engaged in unilateral resistance training for 8 week (3 days/week). Exercises were knee extension and leg press performed at 80–90% of the subject’s single repetition maximum (1RM). Blood samples were collected in the acute period before and after the first training bout and following the last training bout and analyzed for total testosterone, free-testosterone, luteinizing hormone, sex hormone binding globulin, growth hormone, cortisol, and insulin-like growth factor-1. Thigh muscle cross sectional area (CSA) and muscle fibre CSA by biopsy (vastus lateralis) were measured pre- and post-training. Acutely, no changes in systemic hormone concentrations were observed in the 90 min period following exercise and there was no influence of training on these results. Training-induced increases were observed in type IIx and IIa muscle fibre CSA of 22 ± 3 and 13 ± 2% (both P < 0.001). No changes were observed in fibre CSA in the untrained leg (all P > 0.5). Whole muscle CSA increased by 5.4 ± 0.9% in the trained leg (P < 0.001) and remained unchanged in the untrained leg (P = 0.76). Isotonic 1RM increased in the trained leg for leg press and for knee extension (P < 0.001). No changes were seen in the untrained leg. In conclusion, unilateral training induced local muscle hypertrophy only in the exercised limb, which occurred in the absence of changes in systemic hormones that ostensibly play a role in muscle hypertrophy.     

Bilateral deficit phenomenon and the role of antagonist muscle activity during maximal isometric knee extensions in young, athletic men

The bilateral limb deficit (BLD) phenomenon is the difference in maximal or near maximal force generating capacity of muscles when they are contracted alone or in combination with the contralateral muscles. A deficit occurs when the summed unilateral force is greater than the bilateral force. The BLD has been observed by a number of researchers in both upper and lower limbs, in isometric and in dynamic contractions. The underlying cause of the deficit remains unknown. One possible explanation is that the deficit occurs due to differences in antagonist muscle coactivation between unilateral and bilateral contractions. In order to examine this potential cause, this research examined torque and electromyography (EMG) during isometric bilateral and unilateral knee extension under three different joint angles (0°, 45°, and 90°) in a group of young, athletic males (n = 10, mean age of 24.5 ± 2.7 years, height = 180 ± 4.71 cm, and weight = 82.5 ± 17.8 kg). Torque and EMG data were collected from three superficial muscles of the quadriceps (vastus lateralis, vastus medialis, and rectus femoris) as well as two muscles of the antagonist hamstrings (biceps femoris and semitendinosus) during maximal isometric knee extensions. The BLD was only observed during the 45° contractions. Further examination of the data found that the antagonist muscle activity was similar during both bilateral and unilateral contractions suggesting that the deficit is not due to alterations in antagonist muscle patterns between unilateral and bilateral contractions.     

Lateral specificity in resistance training: the effect of bilateral and unilateral training

Maximal voluntary strength of simultaneous bilateral exertion has been shown to be small compared to the sum of the unilateral exertions. Three experiments were conducted to determine the effects of bilateral and unilateral resistance training on this bilateral deficit and to compare these in hands, arms, and legs. In each experiment, the subjects were divided into three groups: unilateral training group, bilateral training group, and control group. The subjects of the training group performed maximal isometric handgrip training in experiment I, and maximal isokinetic arm and leg extension training in experiments II and III. In each experiment, the subjects of the training group continued one of these resistance training exercises three times a week, for 6 weeks. The increase in handgrip strength of the bilateral training group produced in the bilateral condition [5.1 (SEM 2.4)%, after 3 weeks, 6.4 (SEM 2.3) %, after 6 weeks] was significantly greater compared with the control group [?1.1 (SEM 1.0) %, after 3 weeks, ?1.5 (SEM 1.1) %, after 6 weeks. The increase in leg extension power of the bilateral training group produced in the bilateral condition [16.1 (SEM 9.6) %, after 3 weeks, 24.1 (SEM 7.4) %, after 6 weeks] was significantly greater compared with the unilateral training group [?5.0 (SEM 3.4) %, after 3 weeks, ?3.4 (SEM 4.2) %, after 6 weeks] and the control group [?4.3 (SEM 2.5) %, after 3 weeks, 1.5 (SEM 5.5) %, after 6 weeks]. The increase in handgrip strength of the unilateral training group produced in the unilateral condition [7.3 (SEM 1.7) %, after 3 weeks] was significantly greater compared with the control group [?0.9 (SEM 1.8) %, after 3 weeks]. The increase in arm extension power of the unilateral training group produced in the unilateral condition [7.2 (SEM 1.8) %, after 6 weeks] was significantly greater compared with the bilateral training group [?3.0 (SEM 2.3) %, after 6 weeks] and the control group [?2.1 (SEM 2.6) %, after 6 weeks]. Bilateral indexes (BI) were shifted in a positive direction by bilateral training and tended to shift in a negative direction by unilateral training. With regard to the magnitude of change in BI, there were no significant differences among handgrip, arm extension, and leg extension training. It is suggested that there is lateral specificity in resistance training and that there is no difference among body parts in the modification of bilateral deficit by lateral training.     

Neuromuscular performance in voluntary bilateral and unilateral contraction and during electrical stimulation in men at different ages

A group of 33 men divided into three different age groups, M30 years (n = 11), M50 years (n = 12) and M70 years (n = 10) volunteered as subjects for examination of their maximal voluntary isometric bilateral and unilateral forces and force-time curves of the knee extensor muscle group as well as electromyogram activity of the vastus lateralis, vastus medialis and rectus femoris muscles of the right and/or left leg contractions. Electrical stimulation (ES) of 50 Hz was also given by two surface tin electrodes for each subject and each leg separately with the maximal tolerable intensity for recording the isometric force evoked. The maximal force produced by the voluntary isometric unilateral knee extension combined with ES was also measured. Maximal voluntary bilateral force of 1142 (SD 82) N in M30 was greater (P < 0.001) and the force of 1094 (SD 228) N in M50 was also greater (P < 0.05) than that of 962 (SD 70) N recorded for M70. The shapes of the isometric force-time curves, especially in absolute values, differed also among the groups so that the force produced during the early positions of the curve were in M30 greater (P < 0.05-0.001) than the force produced M50 and in M70. Neither the maximal voluntary bilateral force per the summed unilateral force nor the average integrated EMG between the bilateral and unilateral conditions differed significantly from each other either in M30, M50 or in M70. The force produced by pure ES was significantly greater in M30 (P < 0.05) than in M50 and M70, but the latter two groups were not significantly different. When ES was combined with the voluntary contractions, the absolute force values declined (P < 0.05-0.001) with increasing age similarly to those forces produced by the voluntary contractions alone. The present results suggest that increasing age results in great decreases both in the maximal voluntary strength and explosive force characteristics of the neuromuscular system but no bilateral deficit may necessarily be observed either in neural activation or in force production in a simple single joint isometric force production task of the knee extensors. The finding that no difference was observed between M50 and M70 in the force caused by ES alone despite the difference in maximal voluntary force indicated that in addition to the well-known age-related peripheral decrease in muscle mass, maximal voluntary neural activation of these muscles may also decrease to some extent contributing in part to the decrease in strength, especially at older ages.     

Maximal voluntary force of bilateral and unilateral leg extension

The aims were: (1) to investigate whether the 10-20% lower force during bilateral (BL) as compared to unilateral (UL) leg extension could be due to a general inability to activate fully a large number of muscles simultaneously, (2) to analyse the EMG signal of the quadriceps femoris during leg extensions, (3) to study the BL/UL force ratio in extension of the knee, and (4) to study the BL/UL leg extension force ratio in untrained and trained subjects. A 10% lower maximal voluntary isometric force was demonstrated during BL as compared to UL leg extension. This force discrepancy did not change when a total arm load of 250 N was applied simultaneously. Nor did the absolute force levels change, which indicates that the lower BL leg extension force is not due to a general mechanism of reduced activation with an increased number of muscles recruited in maximal voluntary contractions. Integrated EMG activity, mean power frequency and root mean square value of the EMG amplitude did not differ between UL and BL leg extensions. The knee extension force was slightly greater (4%) during BL than UL contractions. These findings are arguments against a reduced activation of the knee extensor muscles being the cause of the lower bilateral leg extension force. No differences in BL/UL force ratio were noted between groups of untrained and trained subjects despite the fact that several of the trained groups do different forms of BL leg extensions regularly. Thus, it does not appear that training readily affects the BL/UL leg extension force ratio.     

Neuromuscular adaptations during bilateral versus unilateral strength training in middle-aged and elderly men and women

Twelve middle-aged men and 12 middle-aged women in the 50-year-old age group (M50; range 44–57 years; W50; 43–57), and 12 elderly men and 12 elderly women in the 70-year-old age group (M70; 59–75; W70; 62–75) volunteered as subjects in order to examine effects of 12-week progressive heavy resistance strength training on electromyographic activity (EMG), muscle cross-sectional area (CSA) of the quadriceps femoris and maximal concentric force in a one repetition maximum (1 RM) test of the knee extensor muscles. One half of the subjects in each group performed the knee extension (and flexion) exercises only bilaterally (BIL), while another half performed the exercises only unilaterally (UNIL). None of the subject groups demonstrated statistically significant changes in any of the 1 RM values during the 2 week control period with no training (between week -2 and 0) preceding the actual experimental training. However, the 12-week training resulted in increases (P<0.05–0.001) in 1 RM values in each group so that the average relative increase of 19±12% (P<0.001) in bilateral 1 RM in all BIL trained subjects was greater (P<0.05) than that of 13±8% (P<0.001) recorded for all UNIL trained subjects. The average relative increases of 17±11% (P<0.001) and 14±14% (P<0.001) in unilateral 1 RM values of the right and left leg in all UNIL trained subjects were greater (P<0.05) than those of 10±18% (P<0.001) and 11±11% (P<0.001) recorded for all BIL trained subjects, respectively. The relative average increase of 19±19% (P<0.001) observed in the maximum averaged IEMG of both legs during the bilateral actions in all BIL trained subjects was greater (P<0.05) than that of 10±17% (P<0.05) recorded for all UNIL trained subjects. The relative increases of 14±12% (P<0.001) and 11±6% (P<0.001) recorded for the CSA in all BIL and UNIL trained subjects did not differ significantly from each others. The present findings suggest that progressive heavy resistance strength training leads to great increases in maximal dynamic strength of the trained subjects accompanied by both considerable neural adaptations and muscular hypertrophy not only in middle-aged but also in elderly men and women. Both bilateral and unilateral exercises are effective to produce functional and structural adaptations in the neuromuscular system, although the magnitude of functional strength increase seems to be specific to the type of exercise used, further supporting the principle of specificity in the design of strength programmes.     

Changes in fitness and shipboard task performance following circuit weight training programs featuring continuous or interval running

Summary Pre- and post-physiological data were collected on 57 Navy men (¯x age=19.5 years) who participated in either circuit weight training/ continuous run (CWT/CR) (N=31) or circuit weight training/interval run (CWT/IR) (N=26) programs. Measured variables included 4 measures of upper torso dynamic strength (one repetition maximum [1RM] for arm curl, bench press, shoulder press, and lat pull-down); two measures of lower torso dynamic strength (1RM) for knee extension and leg press); one measure of power (number of revolutions completed on an arm ergometer (Monark^®) at maximum drag); three measures of muscular endurance (number of repetitions at 60% 1RM for bench press and leg press and maximal number of bent-knee sit-ups in 120 s); one stamina measure (time to exhaustion on a cycle ergometer (Monark^®) maximal work capacity [MWC] test; and three simulated shipboard tasks: manikin shoulder drag, open/secure a water tight door and paint bucket carry. Composite shipboard performance derived from the summed time (s) required to complete the three tasks was also calculated. Results show performance on the manikin shoulder drag and majority of evaluative fitness measures was significantly (p<0.05) enhanced following both circuit weight training/run formats. Significantly (p<0.05) higher values for shoulder press (F=7.2), arm ergometer (F=5.3), and sit-ups (F=6.8) and lower values for leg press muscular endurance (F=5.1) were observed in CWT/IR when compared to CWT/CR. Regression analysis yielded the following prediction equation: Composite shipboard performance (s)=194.15097-1.59492 (arm curl) -0.18369 (leg press)r=0.74.It can be concluded that exercise participation was associated with differential changes in fitness but not job performance. Furthermore, the association between fitness gains and job criteria performance appeared to be specific to the task modelled. Important predictors of criterion task performance included parameters of upper torso and lower torso muscular strength.Report No. 85-33 was supported by the Naval Medical Research and Development Command, Department of the Navy, under research Work Unit M0096-PN.001-1050. The views presented in this paper are those of the authors. No endorsement by the Department of the Navy has been given or should be inferred     

Similar hormonal responses to concentric and eccentric muscle actions using relative loading

Conventional resistance exercise is performed using sequential concentric (CON) and eccentric (ECC) contractions, utilizing the same muscle load. Thus, relative to maximal CON and ECC resistance, the ECC contraction is loaded to a lesser degree. We have recently shown that at the same absolute load, CON contractions are associated with greater growth hormone (GH) but similar total testosterone (TT) and free testosterone (FT) responses compared with ECC contractions and attributed the larger GH response to greater relative CON loading. In the present study, we have examined the same endocrine parameters to six different upper and lower body exercises using relative loading rather than absolute loading, hypothesizing that GH responses would be similar for CON and ECC actions, but TT and FT responses would be greater after ECC contractions. Seven young men with recreational weight training experience completed an ECC and CON muscle contraction trial on two different occasions in a counterbalanced fashion. The exercises consisted of four sets of 10 repetitions of lat pull-down, leg press, bench press, leg extension, military press, and leg curl exercises at 65% of an ECC or CON 1–RM with 90 s between sets and exercises. CON and ECC actions were performed at the same speed. ECC 1-RMs were considered to be 120% of the CON 1-RM for the same exercise. Blood samples were collected before, immediately after, and 15 min after the exercise. GH significantly increased across both trials but was not different between the two trials. Total testosterone was not significantly altered in response to either trial; however, free testosterone concentrations increased in response to both ECC and CON trials. Data suggest that CON and ECC muscle contractions produce similar GH, T, and free testosterone responses with the same relative loading.     

Relationship between the modifications of bilateral deficit in upper and lower limbs by resistance training in humans

Maximal voluntary strength of simultaneous bilateral exertion is known to be small compared to the sum of the unilateral exertions. This phenomenon is called bilateral deficit and the purpose of this study was to investigate whether it operates in both upper and lower limbs. A group of 7 female and 32 male students were divided into 4 training groups and a control group. The unilateral arm or leg training group performed maximal isokinetic arm or leg extensions using each arm or leg unilaterally. The bilateral arm or leg training group trained using bilateral extensions of both arms or legs. The groups in training continued these two types of resistance exercise 3 days a week, for 6 weeks. The control subjects did not train. The improvement in power brought about by training was compared from the viewpoint of whether the limbs (arms or legs) were trained or not and whether the mode of test power exertion (bilateral or unilateral) was the same as performed during training or not. The power in the trained limbs using the same regime as that during training (3.0% after 3 weeks, 7.7% after 6 weeks) showed the largest improvement ratio. This agrees with the specificity theory in resistance training. The increase in power in untrained limbs using the same regime as during training (2.1% after 3 weeks, 3.5% after 6 weeks; P?P?相似文献   

Muscle activity of the core during bilateral,unilateral, seated and standing resistance exercise

Little is known about the effect of performing common resistance exercises standing compared to seated and unilaterally compared to bilaterally on muscle activation of the core. Thus, the purpose of this study was to compare the electromyographic activity (EMG) of the superficial core muscles (i.e. rectus abdominis, external oblique and erector spinae) between seated, standing, bilateral and unilateral dumbbell shoulder presses. 15 healthy males performed five repetitions at 80% of one-repetition maximum of the exercises in randomized order. Results were analyzed with a two-way analysis of variance and a Bonferroni post hoc test. The position × exercise interaction was significantly different for rectus abdominis (P = 0.016), but not for external oblique (P = 0.100) and erector spinae (P = 0.151). The following EMG results were observed: For rectus abdominis: ~49% lower in seated bilateral versus unilateral (P < 0.001), similar in standing bilateral versus unilateral (P = 0.408), ~81% lower in bilateral seated versus standing (P < 0.001), ~59% lower in unilateral seated versus standing (P < 0.001); For external oblique: ~81% lower in seated bilateral versus unilateral (P < 0.001), ~68% lower in standing bilateral than unilateral (P < 0.001), ~58% lower in bilateral seated versus standing (P < 0.001), ~28% lower in unilateral seated versus standing (P = 0.002); For erector spinae: similar in seated bilateral versus unilateral (P = 0.737), ~18% lower in standing bilateral versus unilateral (P = 0.001), similar in seated versus standing bilateral (P = 0.480) and unilateral (P = 0.690). In conclusion, to enhance neuromuscular activation of the superficial core muscles, standing exercises should be used instead of seated exercises, and unilateral exercises should be used instead of bilateral exercises.     

Effects of creatine monohydrate ingestion in sedentary and weight-trained older adults

To investigate the effects of an oral creatine supplementation in older adults, 32 elderly subjects (67–80 years; 16 females, 16 males) were randomly assigned to four equivalent subgroups (control-creatine; control-placebo; trained-creatine; trained-placebo) based on whether or not they took part in an 8-week strength training programme and an 8-week oral creatine monohydrate creatine supplementation programme. The strength training programme consisted of three sets of eight repetitions at 80% of one-repetition maximum, for leg press, leg extension and chest press, 3 days a week. The 52-day supplementation programme consisted of 20 g of creatine monohydrate (or glucose) and 8 g of glucose per day for the initial 5 days followed by 3 g of creatine monohydrate (or glucose), and 2 g of glucose per day. Prior to and after the training and supplementation periods, body mass, body fat, lower limb muscular volume, 1-, 12-repetitions maxima and isometric intermittent endurance tests for leg press, leg extension and chest press were determined. In all groups, no significant changes in anthropometric parameters were observed. For all movements, the increases in 1- and 12-repetitions maxima were greater (P < 0.02) in trained than control subjects. No significant interactions (supplementation/training/time) were observed for the 1-, 12-repetitions maxima, and the isometric intermittent endurance, whatever the movement considered. We conclude that oral creatine supplementation does not provide additional benefits for body composition, maximal dynamical strength, and dynamical and isometric endurances of healthy elderly subjects, whether or not it is associated with an effective strength training.     

Protein supplementation before and after resistance training in older men

We determined the effects of protein supplementation immediately before (PRO-B) and after (PRO-A) resistance training (RT; 12 weeks) in older men (59–76 years), and whether this reduces deficits in muscle mass and strength compared to younger men (18–40 years). Older men were randomized to PRO-B (0.3 g/kg protein before RT + placebo after RT, n=9), PRO-A (placebo before + protein after RT, n=10), or PLA (placebo before and after RT, n=10). Lean tissue mass, muscle thickness of the elbow, knee, and ankle flexors and extensors, and leg and bench press strength were measured before and after RT and compared to databases of younger subjects (n=22–60). Myofibrillar protein degradation (3-methylhistidine) and bone resorption (cross-linked N-telopeptides) were also measured before and after RT. Lean tissue mass, muscle thickness (except ankle dorsi flexors), and strength increased with training (P<0.05), with little difference between groups. There were no changes in 3-methylhistidine or cross-linked N-telopeptides. Before RT, all measures were lower in the older compared to younger groups (P<0.05), except for elbow extensor muscle thickness. Following training, muscle thickness of the elbow flexors and ankle dorsi flexors and leg press strength were no longer different than the young, and elbow extensor muscle thickness was greater in the old men (P<0.05). Supplementation with protein before or after training has no effect on muscle mass and strength in older men. RT was sufficient to overcome deficits in muscle size of the elbow flexors and ankle dorsi flexors and leg press strength in older compared to younger men.     

The effect of varying the time of concentric and eccentric muscle actions during resistance training on skeletal muscle adaptations in women

This study investigated the effect of manipulating the time to complete both the concentric (CON) and eccentric (ECC) muscle actions during resistance training on strength, skeletal muscle properties and cortisol in women. Twenty-eight women (mean ± SE age = 24.3 ± 1.1 year) with strength training experience completed three training sessions per week for 9 weeks. Two sets of four lower body exercises (leg press, parallel squat, knee extension and knee flexion) were completed using 6–8 RM intensity. The long CON (LC) group performed the CON action for 6 s and the ECC action for 2 s, while the long ECC (LE) group completed the CON and ECC phases for 2 and 6 s, respectively. Both groups experienced significant increases in leg press CON only, ECC only and combined ECC and CON maximal strength (1 RM). Immunohistochemical analyses demonstrated that both types I and IIA vastus lateralis fibre areas significantly increased following LC training while only type I fibre area increased following LE training. There was a decrease in MHCIId(x) with a concomitant increase in MHCIIa (P < 0.05) in both groups. Twenty-four hour urinary cortisol significantly increased after LC training only. It was concluded that LC resistance training was more effective than LE for increasing both types I and IIA fibre area and cortisol when time under tension and intensity of muscle actions were matched between the two modes of resistance training in young healthy women.     

Hypertrophy without increased isometric strength after weight training

Summary Eight men (20–23 years) weight trained 3 days week^–1 for 19 weeks. Training sessions consisted of six sets of a leg press exercise (simultaneous hip and knee extension and ankle plantar flexion) on a weight machine, the last three sets with the heaviest weight that could be used for 7–20 repetitions. In comparison to a control group (n = 6) only the trained group increased (P<0.01) weight lifting performance (heaviest weight lifted for one repetition, 29%), and left and right knee extensor cross-sectional area (CAT scanning and computerized planimetry, 11%, P<0.05). In contrast, training caused no increase in maximal voluntary isometric knee extension strength, electrically evoked knee extensor peak twitch torque, and knee extensor motor unit activation (interpolated twitch method). These data indicate that a moderate but significant amount of hypertrophy induced by weight training does not necessarily increase performance in an isometric strength task different from the training task but involving the same muscle group. The failure of evoked twitch torque to increase despite hypertrophy may further indicate that moderate hypertrophy in the early stage of strength training may not necessarily cause an increase in intrinsic muscle force generating capacity.     

开链和闭链训练治疗膝关节半月板损伤

背景:开链训练和闭链训练均可应用于膝关节半月板损伤,然而两种方法的机制不一样,临床未见两种训练方法改善膝关节半月板损伤的报道。目的:观察开链训练和闭链训练对青年人膝关节半月板损伤疗效的影响。方法:49例青年人膝关节半月板损伤采用康复保守治疗的患者,随机数字表法将入选患者分为2组,生物反馈开链组(n=25)采用基础治疗联合终末伸膝生物反馈训练,蹬踏闭链组(n=24)采用基础治疗联合单侧下肢蹬踏训练。其中基础治疗包括电针、手法治疗、徒手运动疗法;生物反馈开链训练采用加拿大Thought公司生产的Myotrac infiniti生物反馈仪进行刺激训练;蹬踏闭链训练采用德国GYM80智能力量训练系统蹬踏配件进行训练。1次/d,连续3周。使用膝关节屈、伸、全关节活动度,目测类比评定级法评分、改良Lysholm膝关节评分、日常生活活动能力评分进行疗效评价。研究方案的实施符合四川省骨科医院的相关伦理要求,患者对试验过程完全知情同意。结果与结论:①在关节活动度方面:生物反馈开链组屈、伸、全关节活动度优于治疗前(P<0.05);蹬踏闭链组伸、全关节活动度优于治疗前(P<0.05);生物反馈开链组较蹬踏闭链组改善关节活动度较好,但组间差异无显著性意义(P>0.05);②在疼痛和功能方面:2组治疗后目测类比评定级法评分、改良Lysholm膝关节评分、日常生活活动能力评分优于治疗前(P<0.05);蹬踏闭链组治疗后日常生活活动能力评分好于生物反馈开链组(P<0.05);2组在改善膝关节活动度、疼痛和功能方面均有效果;③结果说明,生物反馈开链组在改善关节活动度方面疗效较好;在控制疼痛的基础上,蹬踏闭链组在改善膝关节功能和日常生活活动能力方面疗效较好。     

Strength-velocity relationship and fatiguability of unilateral versus bilateral arm extension

Summary Strength-velocity relations and fatigue resistance in an arm bench press manoeuvre were compared between conditions of bilateral (BL, both arms acting together) and unilateral muscle contraction in 9 young men. BL and UL (sum of the 2 arms acting singly) strength was similar for isometric and slow isokinetic maximal voluntary contractions (MVC); at high velocities BL MVC declined more than UL. In both types of contractions a curvilinear relation was observed between strength and velocity, with significantly higher peak torques (PT) being produced under isometric conditions than for slow velocity efforts (p<0.01). Mean declines in PT during 100 repetitive MVCs of approximately 70s were to 25% of initial values for the BL fatigue test and to 37% for UL (p<0.01). In contrast to results of a similar investigation of leg extension in the same subjects, the arms showed (1) no BL deficit of strength in the initial part of the strength-velocity curve and (2) approximately twice as much fatigue in repetitive contractions. These physiological differences may stem from the varying habitual activity patterns of the arms and legs.