Estimation of active force-length characteristics of human vastus lateralis muscle

The length and angles of fascicles were determined for the vastus lateralis muscle (VL) using ultrasonography in 6 subjects performing ramp isometric knee extension. The subject increased torque from zero (relax) to maximum (MVC) with the knee positioned every 15 degrees, from 10 degrees to 100 degrees flexion (0 degrees = full extension). As the knee was positioned closer to extension, fascicle length was shorter [116 +/- 4.7 (mean +/- SEM) mm at 100 degrees vs. 88 +/- 4.1 mm at 10 degrees (relax)]. The fascicle length of the VL decreased with increasing torque at each knee position [116 +/- 4.7 (relax) to 92 +/- 4.3 mm (MVC) at 100 degrees]. On the other hand, fascicle angles increased with an increase in torque. These changes reflected the compliance of the muscle-tendon complex which increased as the knee reached a straight position. The estimated muscle force of the VL was maximal (2,052 +/- 125 N) for a fascicle length of 78 +/- 2.7 mm (i.e. optimum length) with the knee positioned at 70 degrees of flexion. The relationship between muscle force and fascicle length indicated that the VL uses the ascending (knee < 70 degrees), plateau (70 degrees), and descending regions (> 70 degrees) of the force-length curve.     

Changes in torque and electromyographic activity of the quadriceps femoris muscles following isometric training

BACKGROUND AND PURPOSE: The purpose of this study was to examine the effect of isometric training of the quadriceps femoris muscles, at different joint angles, on torque production and electromyographic (EMG) activity. SUBJECTS: One hundred seven women were randomly assigned to one of four groups. Three groups trained with isometric contractions three times per week at a knee flexion angle of 30, 60, or 90 degrees. The fourth group, which served as a control, did not exercise. METHODS: Isometric torque was measured using a dynamometer, and EMG activity was measured using a multichannel EMG system. Measurements were obtained during maximal isometric contraction of the quadriceps femoris muscles at 15-degree increments from 15 to 105 degrees of knee flexion. Measurements were taken before and after 8 weeks of training. RESULTS: Following isometric exercise, increased torque and EMG activity occurred not only at the angle at which subjects exercised, but also at angles in the range of motion at which exercise did occur. Further analyses indicated that exercising in the lengthened position for the quadriceps femoris muscles (90 degrees of knee flexion) produced increased torque across all angles measured and appeared to be the more effective position for transferring strength and EMG activity to adjacent angles following isometric training as compared with the shorter positions of the muscle (30 degrees and 60 degrees of knee flexion). CONCLUSION AND DISCUSSION: These findings suggest that an efficient method for increasing isometric knee extension torque and EMG activity throughout the entire range of motion is to exercise with the quadriceps femoris muscles in the lengthened position.     

The effect of temperature on potassium chloride contracture in cat myocardium

1. Contracture was induced in cat myocardium by exposure to 140 mM-KC1 In isotonic Tyrode solution. Force of contracture expressed as mg/mm2 (muscle cross-sectional area) falls with increasing cross-sectional area. 2. The effect of temperature on isometric force developed during contracture was evaluated both in normal (untreated) atrial and ventricular muscle and following treatment with sympatholytic drugs. 3. The force of contracture was not significantly affected by sympatholytic drugs at 36 degrees C. 4. In normal atrial and ventricular muscle, force of contracture decreased when the muscle was cooled from 36 to either 29 or 20 degrees C. 5. In atrial muscle, the effect of temperature was not changed by sympatholytic drugs. In contrast, exposure to sympatholytic drugs increased contracture force developed by ventricular muscle at 20 degrees C. Also, contracture force was significantly greater at 20 than at 36 degrees C in ventricular muscle from reserpine-pretreated cats. 6. It is suggested that ventricular muscle becomes more sensitive to the relaxing effects of endogenous catecholamines at temperature is lowered. 7. The differences shown between atrial and ventricular muscle with respect to the effect of temperature and sympatholytic drugs on contracture force may result from the differing amounts of sarcoplasmic reticulum found in these types of cardiac muscle and also from different mechanisms of "excitation-contracture" coupling in atrial and ventricular muscle.     

Caffeine counteracts the ergogenic action of muscle creatine loading

This study aimed to compare the effects of oral creatine (Cr) supplementation with creatine supplementation in combination with caffeine (Cr+C) on muscle phosphocreatine (PCr) level and performance in healthy male volunteers (n = 9). Before and after 6 days of placebo, Cr (0.5 g x kg-1 x day-1), or Cr (0.5 g x kg-1 x day-1) + C (5 mg x kg-1 x day-1) supplementation, 31P-nuclear magnetic resonance spectroscopy of the gastrocnemius muscle and a maximal intermittent exercise fatigue test of the knee extensors on an isokinetic dynamometer were performed. The exercise consisted of three consecutive maximal isometric contractions and three interval series of 90, 80, and 50 maximal voluntary contractions performed with a rest interval of 2 min between the series. Muscle ATP concentration remained constant over the three experimental conditions. Cr and Cr+C increased (P < 0.05) muscle PCr concentration by 4-6%. Dynamic torque production, however, was increased by 10-23% (P < 0.05) by Cr but was not changed by Cr+C. Torque improvement during Cr was most prominent immediately after the 2-min rest between the exercise bouts. The data show that Cr supplementation elevates muscle PCr concentration and markedly improves performance during intense intermittent exercise. This ergogenic effect, however, is completely eliminated by caffeine intake.     

Influence of central command and ergoreceptors on the splanchnic circulation during isometric exercise

The splanchnic circulation can make a major contribution to blood flow changes. However, the role of the splanchnic circulation in the reflex adjustments to the blood pressure increased during isometric exercise is not well documented. The central command and the muscle chemoreflex are the two major mechanisms involved in the blood pressure response to isometric exercise. This study aimed to examine the behaviour of the superior mesenteric artery during isometric handgrip (IHG) at 30% maximal voluntary contraction (MVC). The pulsatility index (PI) of the blood velocity waveform of the superior mesenteric artery was taken as the study parameter. A total of ten healthy subjects [mean age, 21.1 (SEM 0.3) years] performed an IHG at 30% MVC for 90 s. At 5 s prior to the end of the exercise, muscle circulation was arrested for 90 s to study the effect of the muscle chemoreflex (post exercise arterial occlusion, PEAO). The IHG at 30% MVC caused a decrease in superior mesenteric artery PI, from 4.84 (SEM 1.57) at control level to 3.90 (SEM 1.07) (P = 0.015). The PI further decreased to 3.17 (SEM 0.70) (P = 0.01) during PEAO. Our results indicated that ergoreceptors may be involved in the superior mesenteric artery vasodilatation during isometric exercise.     

Acetazolamide reduces peripheral afferent transmission in humans

Carbonic anhydrase has been localized in skeletal muscle and nerve, thus, inhibition with acetazolamide (ACZ) may alter nerve and/or muscle function in healthy humans. ACZ (3 oral doses 14, 8, and 2 h prior to testing) reduced isometric force (37%) and peak to peak electromyographic (EMG) amplitude (1.38 mV to 0.83 mV), while increasing EMG latency associated with a unilateral Achilles tendon-tap. Reflex recovery profiles, following a contralateral conditioning tap, were similar in both placebo and ACZ experiments. ACZ led to significant changes in Hmax/Mmax ratio (52.19/14.42 to 45.73/15.65) and H-reflex latency (34.18 +/- 2.54 ms to 35.24 +/- 2.74 ms). Motor nerve conduction velocity and maximal voluntary isometric torque (knee extensors) were unaltered by ACZ. These data suggest that inhibition of the tendon-tap reflex and associated isometric force, following ACZ, is related to impairment of synaptic integrity between la fibers of the muscle spindle and the alpha motor neuron and not impairment of the muscle spindle or force-generating capacity.     

Genetic association of apolipoprotein E with age-related macular degeneration

Several investigators have studied the deficit in maximal voluntary force that is said to occur when bilateral muscle groups contract simultaneously. A true bilateral deficit (BLD) would suggest a significant limitation of neuromuscular control; however, some of the data from studies in the literature are equivocal. Our purpose was to determine whether there is a BLD in the knee extensors of untrained young male subjects during isometric contractions and whether this deficit is associated with a decreased activation of the quadriceps, increased activation of the antagonist muscle, or an alteration in motor unit firing rates. Twenty subjects performed unilateral (UL) and bilateral (BL) isometric knee extensions at 25, 50, 75, and 100% maximal voluntary contraction. Total UL and BL force (delta 3%) and maximal rate of force generation (delta 2.5%) were not significantly different. Total UL and BL maximal vastus lateralis electromyographic activity (EMG; 2.7 +/- 0.28 vs. 2.6 +/- 0.24 mV) and coactivation (0.17 +/- 0.02 vs. 0.20 +/- 0.02 mV) were also not different. Similarly, the ratio of force to EMG during submaximal UL and BL contractions was not different. Analysis of force production by each leg in UL and BL conditions showed no differences in force, rate of force generation, EMG, motor unit firing rates, and coactivation. Finally, assessment of quadriceps activity with the twitch interpolation technique indicated no differences in the degree of voluntary muscle activation (UL: 93.6 +/- 2.51 Hz, BL: 90.1 +/- 2.43 Hz). These results provide no evidence of a significant limitation in neuromuscular control between BL and UL isometric contractions of the knee extensor muscles in young male subjects.     

The effect of femoral tunnel position and graft tensioning technique on posterior laxity of the posterior cruciate ligament-reconstructed knee

We report the effects of femoral tunnel position and graft tensioning technique on posterior laxity of the posterior cruciate ligament-reconstructed knee. An isometric femoral tunnel site was located using a specially designed alignment jig. Additional femoral tunnel positions were located 5 mm proximal and distal to the isometric femoral tunnel. With the graft in the proximal femoral tunnel, graft tension decreased as the knee flexed; with the graft in the distal femoral tunnel, graft tension increased as the knee flexed. When the graft was placed in the isometric femoral tunnel, a nearly isometric graft tension was maintained between 0 degrees and 90 degrees of knee flexion. One technique tested was tensioning the graft at 90 degrees of knee flexion while applying an anterior drawer force of 156 N to the tibia. This technique restored statistically normal posterior stability to the posterior cruciate ligament-deficient knee between 0 degrees and 90 degrees for the distal femoral tunnel position, between 0 degrees and 75 degrees for the isometric tunnel position, and between 0 degrees and 45 degrees for the proximal tunnel position. When the graft was tensioned with the knee in full extension and without the application of an anterior drawer force, posterior translation of the reconstructed knee was significantly different from that of the intact knee between 15 degrees and 90 degrees for all femoral tunnel positions.     

Effects of a muscle exercise program on exercise capacity in subjects with osteoarthritis

Maximal aerobic power and muscle function have been shown to decrease with age and to be even lower in patients with osteoarthritis (OA). This study was designed to determine if subjects with OA who underwent only a muscle exercise program had improved exercise capacity and cardiovascular fitness. A maximal graded exercise test was given before and after 3 months of exercise (isometric, isotonic, and isometric force generated as a function of time contractions, three times a week). Maximal strength and the tension-time index improved significantly. Peak aerobic power increased from 15.99 +/- 3.96 mL.kg-1.min-1 to 20.34 +/- 3.29 mL.kg-1.min-1. On average, maximal walking speed increased from 2.0 +/- 0.6 mph to 2.4 +/- 0.7mph. Exercise time increased 22%, from 9.2 +/- 2.3 minutes to 11.2 +/- 2.7 minutes. There were significant reductions in submaximal heart rate (15b.min-1) and systolic blood pressure (15mmHg) after training. It would appear that the reduction in aerobic fitness of subjects with OA is secondary to their reduced muscle function. By improving muscle function, increases in exercise capacity and aerobic fitness occurred.     

Brief periods of occlusion and reperfusion increase skeletal muscle force output in humans

Prolonged periods of ischemia/reperfusion are known to deleteriously affect skeletal muscle performance. However, in animal models, brief bouts of both skeletal and cardiac muscle ischemia/reperfusion have been shown to decrease skeletal muscle injury and increase skeletal muscle force output, a phenomenon termed "preconditioning". Because there are transient periods of ischemia/reperfusion during isometric and concentric muscle contractions, the purpose of this study was to examine how short duration forearm occlusion/reperfusion prior to exercise, influenced isometric skeletal muscle force output in humans. Eleven subjects (6 men and 5 women, mean age 25 +/- 1 years) participated in this study. Using a Biodex multijoint ergometer, a protocol of isolated, isometric forearm wrist flexions was utilized to measure muscle force output in two separate trials. In the first trial, 15 isometric maximal voluntary contractions (MVCs) of the wrist flexors were performed in 20 intervals interspersed with 10 s of rest. In the second trial, forearm occlusion was induced (2 min at 200 mmHg by blood pressure cuff occlusion, with 10 s of hyperemia) prior to exercise. Following cuff occlusion, an identical exercise protocol was followed, i.e. 15 isometric wrist flexor MVCs performed in 20 intervals interspersed with 10 s of rest. The total force output over 15 MVCs was greater following intermittent cuff occlusion (no occlusion 2619 +/- 320 ft.lbs vs cuff occlusion 2986 +/- 195 ft.lbs; p < 0.05). The mean force output per MVC also increased during exercise following intermittent cuff occlusion (no occlusion 174 +/- 21 ft.lbs vs cuff occlusion 199 +/- 13 ft.lbs; p < 0.05). In a second set of experiments, we found a 3 to 4 fold hyperemic blood flow following cuff occlusion. These data suggest that brief periods of cuff occlusion/reperfusion may increase repetitive MVC force output by skeletal muscle. Although further study is needed to fully understand the effects of occlusion/reperfusion on skeletal muscle force output, we hypothesize that, in part, this putative effects is secondary to the hyperemic blood flow which follows cuff occlusion.     

Racial differences in muscle strength in disabled older women

This study examines racial differences in muscle strength, and associations of muscle strength to level of physical activity and severity of disability, among a community sample of 254 black and 665 white, moderately to severely disabled women aged 65 and older. Potential confounders that were adjusted for in the models included age, body weight and height, joint pain, number of chronic conditions, and socioeconomic status. Hand grip, hip flexion, and knee extension forces were measured using portable hand-held dynamometers in the participants' homes. Hand grip strength was measured as the maximal isometric force. Hip flexion and knee extension forces were measured as the greatest force the tester had to apply to break the isometric contraction. A declining strength gradient was observed with increasing severity of disability and for decreasing level of physical activity in both races. At equal levels of disability or physical activity, blacks had better hand grip and hip flexion strength, but knee extension strength did not differ by race. The greater hand grip and hip flexion strength found in black women may be related to their greater muscle mass and known racial differences in body dimensions. No consistent racial differences were observed in the relationship between physical activity and muscle strength, or muscle strength and disability, suggesting that the role of muscle strength in the disablement process does not differ between races. Physical activity and exercise programs may be feasible ways to prevent worsening of disability in blacks and whites.     

CT angiography of the abdominal arteries

The aims of this study were to investigate if low-frequency fatigue (LFF) dependent on the duration of repeated muscle contractions and to compare LFF in voluntary and electrically induced exercise. Male subjects performed three 9-min periods of repeated isometric knee extensions at 40% maximal voluntary contraction with contraction plus relaxation periods of 30 plus 60 s, 15 plus 30 s and 5 plus 10 s in protocols 1, 2 and 3, respectively. The same exercise protocols were repeated using feedback-controlled electrical stimulation at 40% maximal tetanic torque. Before and 15 min after each exercise period, knee extension torque at 1, 7, 10, 15, 20, 50 and 100 Hz was assessed. During voluntary exercise, electromyogram root mean square (EMGrms) of the vastus lateralis muscle was evaluated. The 20-Hz torque:100-Hz torque (20:100 Hz torque) ratio was reduced more after electrically induced than after voluntary exercise (P < 0.05). During electrically induced exercise, the decrease in 20:100 Hz torque ratio was gradually (P < 0.05) reduced as the individual contractions shortened. During voluntary exercise, the decrease in 20:100 Hz torque ratio and the increase in EMGrms were greater in protocol 1 (P < 0.01) than in protocols 2 and 3, which did not differ from each other. In conclusion, our results showed that LFF is dependent on the duration of individual muscle contractions during repetitive isometric exercise and that the electrically induced exercise produced a more pronounced LFF compared to voluntary exercise of submaximal intensity. It is suggested that compensatory recruitment of faster-contracting motor units is an additional factor affecting the severity of LFF during voluntary exercise.     

Changes in muscle morphology, electromyographic activity, and force production characteristics during progressive strength training in young and older men

Effects of a 10-week progressive strength training program composed of a mixture of exercises for increasing muscle mass, maximal peak force, and explosive strength (rapid force production) were examined in 8 young (YM) (29+/-5 yrs) and 10 old (OM) (61+/-4 yrs) men. Electromyographic activity, maximal bilateral isometric peak force, and maximal rate of force development (RFD) of the knee extensors, muscle cross-sectional area (CSA) of the quadriceps femoris (QF), muscle fiber proportion, and fiber areas of types I, IIa, IIb, and IIab of the vastus lateralis were evaluated. Maximal and explosive strength values remained unaltered in both groups during a 3-week control period with no training preceding the strength training. After the 10-week training period, maximal isometric peak force increased from 1311+/-123 N by 15.6% (p <.05) in YM and from 976+/-168 N by 16.5% (p <.01) in OM. The pretraining RFD values of 4049+/-791 N*s(-1) in YM and 2526+/-1197 N*s(-1) in OM remained unaltered. Both groups showed significant increases (p < .05) in the averaged maximum IEMGs of the vastus muscles. The CSA of the QF increased from 90.3+/-7.9 cm2 in YM by 12.2% (p <.05) and from 74.7+/-7.8 cm2 in OM by 8.5% (p <.001). No changes occurred in the muscle fiber distribution of type I during the training, whereas the proportion of subtype IIab increased from 2% to 6% (p < .05) in YM and that of type IIb decreased in both YM from 25% to 16% (p < .01) and in OM from 15% to 6% (p < .05). The mean fiber area of type I increased after the 10-week training in YM (p < .001) and OM (p < .05) as well as that of type IIa in both YM (p < .01) and OM (p < .01). The individual percentage values for type I fibers were inversely correlated with the individual changes recorded during the training in the muscle CSA of the QF (r=-.56, p < .05). The present results suggest that both neural adaptations and the capacity of the skeletal muscle to undergo training-induced hypertrophy even in older people explain the gains observed in maximal force in older men, while rapid force production capacity recorded during the isometric knee extension action remained unaltered during the present mixed strength training program.     

Morphological and physical characterization of the capsular layer of Vibrio cholerae O139

Low-speed isokinetic exercise has been recommended to exert a maximal contraction and produce greater muscle torque than high-speed exercise in young adults. The purpose of this study was to compare the effectiveness of low- and high-speed isokinetic exercise programs for increasing muscle torque in young and elderly people. Twenty healthy elderly and 20 young subjects participated. The elderly subjects were divided into two groups. One group performed high-speed (300 degrees/s) isokinetic exercise training three times a week for the dominant-side knee extensor and low-speed (60 degrees/s) exercise for the non-dominant side for 6 weeks. The other group was trained using the reverse exercise regime. The training program for the young subjects was the same as that for the elderly groups. All subjects had their knee extensor torque evaluated with an isokinetic test before and at 2-week intervals during the training program. For young and elderly groups, both high- and low-speed isokinetic exercise training increased extensor torque in low- and high-speed tests. For the young group, low-speed exercise effectively improved muscle torque at low and high speeds. The improvement in slow muscle torque was significantly greater than that in fast muscle torque. For the elderly subjects, high-speed isokinetic exercise produced the greatest muscle torque at high speed in the first 2 weeks of training, and demonstrated a sharp increase in muscle torque in the final 2 weeks. Low-speed exercise frequently caused knee stress and the inability of some elder subjects to continue the exercises with maximal effort. Our findings indicate that high-speed exercise may be more appropriate for the elderly, and low-speed exercise may be more appropriate for younger people.     

Relationship between sarcomere length and active force in rabbit papillary muscle

Isometric peak twitch force (stimulation frequency 0.5/s; 29.5-30.5 degrees C) was correlated with sarcomere length in isolated papillary muscles of the rabbit. Sarcomere length was measured from photographic recordings (1.5 ms exposure time) performed at rest between contractions and at the time of isometric peak twitch force. The sarcomere length at rest was found to be relatively uniform throughout the preparation and to be linearly related to the overall muscle length within the range Lmax-0.85Lmax. The distribution of sarcomere lengths increased considerably as the muscle went from rest to activity. Studies of surface markers showed different degrees of shortening (or elongation) of individual segments along the length of the preparation. The mean resting sarcomere length at Lmax (the optimum muscle length for force production) was 2.44 +/- 0.01 micron (grand mean +/- S.E., 7 muscles). The means active sarcomere length at Lmax was 2.29 +/- 0.04 micron. Active force declined steeply as the muscle length was reduced below Lmax. At a resting sarcomere length of 2.0 micron, active force was approximately 1/3 of the maximum. The observed differences between the length-tension relat-onships in myocardium (twitch responses) and skeletal muscle (tetanic contractions) are discussed on the basis of a length dependency of the activation process in cardiac muscle.     

Mild combined immunodeficiency in identical twins

Fourteen adult cats were exercised on a motor-driven treadmill 5 days each week for 6 weeks to determine the effect of exercise conditioning on the intrinsic contractile state of the myocardium. The exercise program was sufficient to produce a cardiovascular training effect manifested by slower exercising heart rates and resting heart rates after atropine by the end of the 6th week. The mechanical function of the isolated right ventricular papillary muscle from exercised cats was compared with that of 17 sedentary adult cats. There were no significant differences between exercised and control cats in in heart weight-body weight ratios, resting and active lenght - tension relations, maximal rate of isometric force development at the peak of the length-tension curve (Lmax), time to peak force at Lmax, maximal force development with paired stimulation and norepinephrine, or force-velocity relations. These results indicate that the intrinsic state of feline myocardium is unaffected by exercise conditioning.     

Rapid-staged strategy for concomitant critical carotid and left main coronary disease with left ventricular dysfunction: IABP use

Fascicle length, pennation angle, and tendon elongation of the human tibialis anterior were measured in vivo by ultrasonography. Subjects (n = 9) were requested to develop isometric dorsiflexion torque gradually up to maximal at the ankle joint angle of 20 degrees plantarflexion from the anatomic position. Fascicle length shortened from 90 +/- 7 to 76 +/- 7 (SE) mm, pennation angle increased from 10 +/- 1 to 12 +/- 1 degrees, and tendon elongation increased up to 15 +/- 2 mm with graded force development up to maximum. The tendon stiffness increased with increasing tendon force from 10 N/mm at 0-20 N to 32 N/mm at 240-260 N. Young's modulus increased from 157 MPa at 0-20 N to 530 MPa at 240-260 N. It can be concluded that, in isometric contractions of a human muscle, mechanical work, some of which is absorbed by the tendinous tissue, is generated by the shortening of muscle fibers and that ultrasonography can be used to determine the stiffness and Young's modulus for human tendons.     

Contractile properties of aged avian muscle after stretch-overload

The effects of ageing on muscle contractile adaptations to stretch-overload was examined in the anterior latissimus dorsi (ALD) muscle of 12 old (90 weeks of age) and 12 young adult (10 weeks of age) Japanese quails. A weight corresponding to 12% of the birds' body weight was attached to one wing for 30 days, while the contralateral wing served as the intra-animal control. In vitro contractile measurements were made at 25 degrees C by indirect stimulation of the ALD by its nerve (pulse 0.2 ms). Compared with young adult twitch characteristics, aged muscles had significantly greater contraction time (149 +/- 9 ms vs. 174 +/- 16 ms). Stretch-overload increased contraction time to 162 +/- 7 ms in young muscles and 215 +/- 14 ms in old muscles. Ageing and overload resulted in a greater fusing of twitches at stimulation frequencies of 5 and 10 Hz which resulted in a leftward shift of the force-frequency curve at these frequencies, relative to young adult control muscles. Maximal shortening velocity (Vmax) decreased from 2.6 +/- 0.3 to 1.2 +/- 0.1 muscle lengths/s in young muscles after overload. Vmax in old control muscles was similar to young muscles after stretch, but stretch further decreased Vmax in old muscles to 0.8 muscle lengths/s. Maximal tetanic force and specific force were similar in young and old muscles, both before and after stretch. These data indicate that ageing induces a slowing of both twitch contractile characteristics and shortening velocity in the ALD, without affecting maximal force capabilities.     

Effects of strength and endurance training on isometric muscle strength and walking speed in elderly women

The separate effects of 18 weeks of intensive strength and endurance training on isometric knee extension (KE) and flexion (KF) strength and walking speed were studied in 76- to 78- year-old women. Maximal voluntary isometric force for both KE and KF was measured in a sitting position on a custom-made dynamometer chair at a knee angle of 60 degrees from full extension. Maximal walking speed was measured over a distance of 10 m. The endurance-trained women increased KE torque and KE torque/body mass after the first 9 weeks of training when compared with the controls. when comparing the baseline, 9 week and 18 week measurements within the groups separately, both the endurance- and strength-training groups increased KE torque, KE torque/body mass and walking speed. Individual changes in KE torque/body mass before and after 18 weeks of training averaged 19.1% in the strength group, 30.9% in the endurance group and 2.0% in the controls. This study indicates that in elderly women the effects of physical training on muscle strength and walking speed occur after endurance as well as strength training. The considerable interindividual variation in change of muscle performance is also worth noticing.     

The effect of temperature on contractile activation of intact and chemically skinned 'catch' muscle fibre bundles of Mytilus edulis

The effect of temperature (5-35 degrees C) on maximum force production was examined in intact and chemically skinned muscle fibre bundles (10-25 fibres) from the anterior byssus retractor muscle of Mytilus edulis. In intact fibre bundles, 10 microM acetylcholine induced a tonic contraction which had a magnitude of 65.4 +/- 4.0 N cm-2 (n = 30) at 23 degrees C. Activation by caffeine (20 mM) produced a force response which was 157.1 +/- 7.9% (n = 16) of the acetylcholine response at 23 degrees C and acetylcholine and caffeine together produced force which was not significantly different from the response to caffeine alone. At 5 degrees C the acetylcholine and caffeine responses were decreased by 9.6 +/- 3.4% (n = 6) and 14.6 +/- 2.8% (n = 8) compared with the respective responses at 23 degrees C. However, there was no significant reduction of the response induced by the combined action of acetylcholine and caffeine when the temperature was decreased from 23 degrees C to 5 degrees C. The 20-80% of peak force activation time increased by about one order of magnitude for all acetylcholine, caffeine and combined acetylcholine-caffeine-induced responses when the temperature was decreased from 23-5 degrees C. Repeated exposure of the intact preparation to caffeine caused a marked decrease in the caffeine-induced response (complete abolition of force after the third exposure to caffeine), but the response to caffeine could be fully restored following one acetylcholine-induced activation. The maximum Ca(2+)-activated force after skinning the preparation with saponin was not significantly different from the caffeine or combined acetylcholine-caffeine-induced responses before skinning. In the saponin skinned fibre preparation a drop in temperature from 23 degrees C to 15 degrees C or 5 degrees C decreased the maximum Ca(2+)-activated force by 13.2 +/- 1.4% (n = 8) and 41.4 +/- 3.1% (n = 5) respectively. The activation time between 20-80% of the peak Ca(2+)-activated force increased at 15 degrees C and 5 degrees C by a factor of 1.5 +/- 0.1 (n = 5) and 6.8 +/- 1.1 (n = 5) respectively when compared to corresponding values at 23 degrees C. The relaxation half-time decreased by a factor of 1.7 +/- 0.2 (n = 5) and 3.0 +/- 0.2 (n = 5) at 15 degrees C and 5 degrees C respectively compared with that at 23 degrees C.(ABSTRACT TRUNCATED AT 400 WORDS)