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Biomedical subjects

A J Sargeant

Publications and source records attributed to A J Sargeant.

At least 19 recordsLinked to original sources
PubMed1992

Growth-related change in specific force but not in specific power of rat fast skeletal muscle.

The effect of growth on the dynamic performance of rat medial gastrocnemius muscle was studied. From approximately 1.5 to 5 months of age specific force increased by 18%. Reductions were found in both optimal stimulation frequency (from 120 to 100 Hz) and optimal shortening velocity (by 16%) indicating that the fibres became slower. Specific power did not change during growth but was obtained at a lower shortening velocity. Possible mechanisms for the observed changes are discussed.

Aging↗
PubMed1991

Effect of lowered muscle temperature on the physiological response to exercise in men.

The effect of low muscle temperature on the response to dynamic exercise was studied in six healthy men who performed 42 min of exercise on a cycle ergometer at an intensity of 70% of their maximal O2 uptake. Experiments were performed under control conditions, i.e. from rest at room temperature, and following 45 min standing with legs immersed in a water bath at 12 degrees C. The water bath reduced quadriceps muscle temperature (at 3 cm depth) from 36.4 (SD 0.5) degrees C to 30.5 (SD 1.7) degrees C. Following cooling, exercise heart rate was initially lower, the mean difference ranged from 13 (SD 4) beats.min-1 after 6 min of exercise, to 4 (SD 2) beats.min-1 after 24 min of exercise. Steady-state oxygen uptake was consistently higher (0.2 l.min-1). However, no difference could be discerned in the kinetics of oxygen uptake at the onset of exercise. During exercise after cooling a significantly higher peak value was found for the blood lactate concentration compared to that under control conditions. The peak values were both reached after approximately 9 min of exercise. After 42 min of exercise the blood lactate concentrations did not differ significantly, indicating a faster rate of removal during exercise after cooling. We interpreted these observations as reflecting a relatively higher level of muscle hypoxia at the onset of exercise as a consequence of a cold-induced vasoconstriction. The elevated steady-state oxygen uptake may in part have been accounted for by the energetic costs of removal of the extra lactate released into the blood consequent upon initial tissue hypoxia.

Adult↗
PubMed1991

Influence of an active pre-stretch on fatigue of skeletal muscle.

In activities such as running, many muscles of the lower extremities appear to be actively stretched before they are allowed to shorten. In this study we investigated the effect of an active pre-stretch on the fatigability of muscles. Thus muscle contractions were compared in which shortening was preceded by an active isometric phase or by an active stretch. Rat medial gastrocnemius muscle-tendon complexes (with arrested blood flow) performed a series of ten repeated contractions (1.s-1) with either an active stretch or an isometric phase preceding the shortening. Contraction duration (0.45 s), and shortening duration (0.3 s), distance (6 mm) and velocity (20 mm.s-1) were the same in both types of contraction. Work output during the ten shortening phases was approximately 40% higher in the contractions with an active pre-stretch; in contrast, high-energy phosphate utilization was similar. Over the ten repeated contractions reduction of work output during the shortening phases of both types of contraction was similar in absolute terms (approx. 9.5 mJ). It is suggested that all the extra work performed during the shortening phases after a pre-stretch originated from sources other than cross-bridge cycling, which are hardly affected by fatigue. However, reduction of work output in relative terms, which is how the reduction is often expressed in voluntary exercise, was less after a pre-stretch (26% vs 32%), giving the impression of protection against fatigue by an active pre-stretch.

Animals↗
PubMed1991

Effect of shortening velocity on work output and energy cost during repeated contractions of the rat EDL muscle.

The effect of shortening velocity on the reduction in work output, energy consumption and efficiency during repetitive contractions has been determined in rat extensor digitorum longus muscle. Muscles in situ (with occluded blood flow, 37 degrees C) were stimulated to perform 40 successive contractions (at 4 Hz) with a total duration of the exercise period of 10 s and shortening velocities of either 25, 50 or 75 mm.s-1 (whole muscle-tendon complex). Care was taken that work output during the shortening phase of the first contraction was the same for the different velocities used. Total work output of the 40 contractions was not significantly different between the three groups with different shortening velocities; nor was there a significant difference in the high-energy phosphate consumption over this 10-s exercise period. However, when the ratio of total work output and total energy consumption was calculated a significantly higher efficiency (25-30% in comparison with the efficiency of the other two velocities) was found with the shortening velocity of 50 mm.s-1. There was no significant difference in efficiency between shortening velocities of 25 and 75 mm.s-1. This suggests that with this protocol efficiency showed a velocity-dependent pattern that may have the same shape as the power/velocity curve. Whereas total work output during the 10-s exercise period was not significantly different between the velocities studied, the time course of the changes in work output was quite different. With shortening velocities of 50 and 75 mm.s-1 work output initially increased by maximally 6% and 12% respectively in contrast to a steady level in the contractions with a velocity of 25 mm.s-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Effect of fatigue on maximal power output at different contraction velocities in humans.

The effect of fatigue as a result of a standard submaximal dynamic exercise on maximal short-term power output generated at different contraction velocities was studied in humans. Six subjects performed 25-s maximal efforts on an isokinetic cycle ergometer at five different pedaling rates (60, 75, 90, 105, and 120 rpm). Measurements of maximal power output were made under control conditions [after 6 min of cycling at 30% maximal O2 uptake (VO2max)] and after fatiguing exercise that consisted of 6 min of cycling at 90% VO2max with a pedaling rate of 90 rpm. Compared with control values, maximal peak power measured after fatiguing exercise was significantly reduced by 23 +/- 19, 28 +/- 11, and 25 +/- 11% at pedaling rates of 90, 105, and 120 rpm, respectively. Reductions in maximum peak power of 11 +/- 8 and 14 +/- 8% at 60 and 75 rpm, respectively, were not significant. The rate of decline in peak power during the 25-s control measurement was least at 60 rpm (5.1 +/- 2.3 W/s) and greatest at 120 rpm (26.3 +/- 13.9 W/s). After fatiguing exercise, the rate of decline in peak power at pedaling rates of 105 and 120 rpm decreased significantly from 21.5 +/- 9.0 and 26.3 +/- 13.9 W/s to 10.0 +/- 7.3 and 13.3 +/- 6.9 W/s, respectively. These experiments indicate that fatigue induced by submaximal dynamic exercise results in a velocity-dependent effect on muscle power. It is suggested that the reduced maximal power at the higher velocities was due to a selective effect of fatigue on the faster fatigue-sensitive fibers of the active muscle mass.

Adult↗
PubMed1989

Optimum cycle frequencies in hand-rim wheelchair propulsion. Wheelchair propulsion technique.

To study the effect of different cycle frequencies on cardio-respiratory responses and propulsion technique in hand-rim wheelchair propulsion, experienced wheelchair sportsmen (WS group; n = 6) and non-wheelchair users (NW group; n = 6) performed wheelchair exercise tests on a motor-driven treadmill. The WS group wheeled at velocities of 0.55, 0.83, 1.11 and 1.39 m.s-1 and a slope of 2 degrees. The NW group wheeled at 0.83, 1.11 and 1.39 m.s-1 and a 1 degree slope. In each test, a 3-min period at a freely chosen cycle frequency (FCF: 100%) was followed by four 3-min blocks of paced cycle frequencies at 60%, 80%, 120% and 140% FCF. Effects of both cycle frequency and velocity on physiological and propulsion technique parameters were studied. Analysis of variance showed a significant effect (p less than 0.05) of cycle frequency on oxygen cost and gross mechanical efficiency in both the WS and NW group. This indicated the existence of an optimum cycle frequency which is close to the FCF at any given velocity. The optimum cycle frequency increased with velocity from 0.67 to 1.03 cps over the range studied (p less than 0.05). Oxygen cost was approximately 10% less at 100% FCF than at 60% or 140% FCF. Gross mechanical efficiency for the WS group at 100% FCF was 8.5%, 9.7%, 10.4% and 10.1%, respectively, at the four velocities.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Changes in velocity of shortening, power output and relaxation rate during fatigue of rat medial gastrocnemius muscle.

The force-velocity characteristics of rat medial gastrocnemius muscle have been determined by measuring the force sustained during constant velocity releases of the muscle stimulated in situ at an ambient temperature of 26 degrees C. The velocity of unloaded shortening was determined using the "slack" test and rate of relaxation from the half time of force loss at the end of stimulation. Measurements were first made on fresh muscles using short contractions and then during a series which consisted of a 15 s contraction (fatigued muscle), followed by 15 min recovery and a 1 s contraction (recovered muscle). After a 5 min recovery period the sequence was repeated. Comparison was made between the fatigued and recovered state in each preparation in order to allow for any change in the preparation during the course of the experiment. After 15 s contraction the fatigued muscles showed a marked reduction in all parameters measured. In fatigued muscles the isometric force fell to 48 +/- 15% (mean +/- SD) and there was a decrease in maximum velocity of shortening to 66%. These changes in the force-velocity relationship were accompanied by slowing of relaxation so that the half time of relaxation nearly doubled. The consequence of these changes was that the maximum power output was reduced by a much greater extent than was the isometric force (75% vs. 52%). It is suggested that the changes in force-velocity characteristics reflect a reduction in cross-bridge cycling in fatigued muscle.

Animals↗
PubMed1989

Age-related effects of fatigue and recovery from fatigue in rat medial gastrocnemius muscle.

Force-velocity, power-velocity and unloaded shortening data were obtained from in situ medial gastrocnemius muscle-tendon complexes (stimulated at 60 Hz) with intact circulation of mature male rats (approximately 125 days old). Measurements were carried out at the end of a long (15 s) contraction (fatigued muscles) or with a short (1 s) contraction either in the fresh state (fresh muscles) or in muscles which had recovered for 15 min after a long contraction. Compared to the fresh state fatigue reduced isometric force by 57%, maximal shortening velocity by approximately 40% and maximal power output by 81%. These reductions were similar to data previously obtained with younger rats (40 days old). However, the velocity data of the muscles which had recovered for 15 min after a long contraction showed a greater reduction in the mature rats. This difference between the two age groups together with a difference in the changes in the initial parts of the isometric force time curves suggest an age-dependent response of the fast-fatigable fibre population of these mixed muscles. In a separate series of experiments the underlying mechanism of the recovery from fatigue was studied in a group of young rats. Fatigue was induced with five long (15 s) contractions (each at 5 min intervals). The recovery of isometric force and power output was monitored with short contractions which indicated a plateau of recovery but the absolute values were still reduced after 60 min (85 and 71% of prefatigue values, respectively). Phosphocreatine concentration recovered rapidly, whereas the ATP concentration was still markedly reduced after 1 h of recovery. The time courses of recovery of inosine-5'-monophosphate (IMP) and lactate concentrations resembled those of force and power output. Thus it is possible that age-dependent differences in IMP and/or lactate production may play a role in fatigue and recovery from fatigue.

Adenosine Monophosphate↗
PubMed1988

Age-related changes in power output during repetitive contractions of rat medial gastrocnemius muscle.

Changes in isometric force, power output and relaxation rate have been measured during repetitive tetanic contractions in 2 groups of rats of different ages. During the first 5 contractions there were no differences between a young and mature group. In contrast to isometric force production, which decreased about 3% per contraction, power output initially increased to 108% of the power output in the first contraction. A greater reduction in power output and relaxation rate after the 5th contraction indicated a greater reduction of the cross-bridge cycling rate in the younger rats. ATP, phosphocreatine and lactate concentrations after the last contraction were not different between the age-groups. In contrast IMP production, which has been suggested may play a regulatory role during fatigue was twice as high in the young rats. Judged by isometric force production there is no age-related difference in fatiguability. However, profound differences were observed in power output, which indicates that quantification of fatigue as a loss of isometric force may be seriously misleading when considering the functional status of the muscle for normal dynamic contractions.

Actins↗
PubMed1988

Influence of muscle dimensions on economy of isometric exercise in rat medial gastrocnemius muscles in situ.

The effect of muscle dimensions on economy (force-time integral divided by the amount of energy utilized) was investigated in male rats (body mass range 95-490 g), anaesthetized with pentobarbital. The medial gastrocnemius muscle in situ performed 6 maximal isometric contractions of 350 ms duration (1.s-1) at twitch optimum length at 35 degrees C. The areas under the 6 time-force curves were added to obtain force-time integral of the experiment. Differences of concentrations of ATP, phosphocreatine and lactate between experimental and contralateral (resting) muscles were used to calculate high-energy phosphate consumption due to stimulation. Muscle mass and cross-sectional area increased (approximately +400% and +300%, respectively) over the rat body mass range studied. Muscle length and length of the most distal fibre bundle increased by approximately 17 mm and 4 mm, respectively. Force-time integral (N.s) increased proportional to cross-sectional area whereas high-energy phosphate consumption (mumoles) increased proportional to muscle mass. The relative fraction of the total energy consumption utilized for force-independent processes was independent of rat body mass. The economy of the actomyosin system was unaffected during growth, whereas economy of the whole muscle decreased during growth by approximately 30% (p less than 0.001). The effect of muscle dimensions on economy is discussed with respect to human endurance capacity measured by voluntary isometric contractions.

Animals↗
PubMed1988

Propelling efficiency of front-crawl swimming.

In this study the propelling efficiency (ep) of front-crawl swimming, by use of the arms only, was calculated in four subjects. This is the ratio of the power used to overcome drag (Pd) to the total mechanical power (Po) produced including power wasted in changing the kinetic energy of masses of water (Pk). By the use of an extended version of the system to measure active drag (MAD system), Pd was measured directly. Simultaneous measurement of O2 uptake (VO2) enabled the establishment of the relationship between the rate of the energy expenditure (PVO2) and Po (since when swimming on the MAD system Po = Pd). These individual relationships describing the mechanical efficiency (8-12%) were then used to estimate Po in free swimming from measurements of VO2. Because Pd was directly measured at each velocity studied by use of the MAD system, ep could be calculated according to the equation ep = Pd/(Pd + Pk) = Pd/Po. For the four top class swimmers studied, ep was found to range from 46 to 77%. Total efficiency, defined as the product of mechanical and propelling efficiency, ranged from 5 to 8%.

Adult↗
PubMed1987

The effect of oral supplementation with L-carnitine on maximum and submaximum exercise capacity.

Two trials were conducted to investigate the effects of L-carnitine supplementation upon maximum and submaximum exercise capacity. Two groups of healthy, untrained subjects were studied in double-blind cross-over trails. Oral supplementation of 2 g per day L-carnitine was used for 2 weeks in the first trial and the same dose but for 4 weeks in the second trial. Maximum and submaximum exercise capacity were assessed during a continuous progressive cycle ergometer exercise test performed at 70 rpm. In trial 1, plasma concentrations of lactate and beta-hydroxybutyrate were measured pre- and post-exercise. In trial 2, pre- and post-exercise plasma lactate were measured. The results of treatment with L-carnitine demonstrated no significant changes in maximum oxygen uptake (VO2max) or in maximum heart rate. In trial 1, there was a small improvement in submaximal performance as evidenced by a decrease in the heart-rate response to a work-load requiring 50% of VO2max. The more extensive trial 2 did not reproduce the significant result obtained in trial 1, that is, there was no significant decrease in heart rate at any given submaximal exercise intensity, under carnitine-supplemented conditions. Plasma metabolic concentrations were unchanged following L-carnitine, in both trials. It is concluded, that in contrast to other reports, carnitine supplementation may be of little benefit to exercise performance since the observed effects were small and inconsistent.

3-Hydroxybutyric Acid↗
PubMed1987

Effect of muscle temperature on leg extension force and short-term power output in humans.

The effect of changing muscle temperature on performance of short term dynamic exercise in man was studied. Four subjects performed 20 s maximal sprint efforts at a constant pedalling rate of 95 crank rev.min-1 on an isokinetic cycle ergometer under four temperature conditions: from rest at room temperature; and following 45 min of leg immersion in water baths at 44; 18; and 12 degrees C. Muscle temperature (Tm) at 3 cm depth was respectively 36.6, 39.3, 31.9 and 29.0 degrees C. After warming the legs in a 44 degrees C water bath there was an increase of approximately 11% in maximal peak force and power (PPmax) compared with normal rest while cooling the legs in 18 and 12 degrees C water baths resulted in reductions of approximately 12% and 21% respectively. Associated with an increased maximal peak power at higher Tm was an increased rate of fatigue. Two subjects performed isokinetic cycling at three different pedalling rates (54, 95 and 140 rev.min-1) demonstrating that the magnitude of the temperature effect was velocity dependent: At the slowest pedalling rate the effect of warming the muscle was to increase PPmax by approximately 2% per degree C but at the highest speed this increased to approximately 10% per degree C.

Adult↗
PubMed1987

Human muscle function following prolonged eccentric exercise.

4 subjects performed repeated eccentric contractions with leg extensors during prolonged downhill walking (-25% gradient) at 6.44 km.h-1 until collapse due to muscle weakness (range of exercise duration 29 to 40 min). During the exercise oxygen uptake rose progressively from approximately 45% of the previously determined VO2max at 10 min to approximately 65% at the end of the exercise. Following the exercise there was an immediate, significant, and sustained reduction in maximal voluntary isometric contraction, and short term (anaerobic) power output measured concentrically on an isokinetic ergometer. These reductions in muscle function persisted for 96 hours post exercise, and were reflected by significant reductions in the tension generated at low frequency (20 Hz) relative to higher frequency (50 Hz) percutaneous stimulation of the quadriceps. All four subjects showed an increase in plasma levels of creatine kinase post eccentric exercise. Performing concentric contractions by walking uphill for one hour at a significantly greater metabolic cost failed to induce comparable reductions in muscle function. These results provide evidence for the consequences of prolonged eccentric work upon dynamic function which complements earlier reports of structural, enzymatic, and static function changes.

Adult↗
PubMed1987

Applied physiology of speed skating.

Speed skating exercise can be better understood by taking account of physiological and biomechanical considerations. Comparison with other sports shows the unique and peculiar way of skating propulsion. The relatively long lasting isometric muscle contractions during the gliding phase, alternated with high power output push-offs, place unusual demands on the (local) energy delivering systems. The short and explosive push-off needs a specific pattern of motor unit recruitment. Some mixture of slow twitch (to sustain skating posture) and fast twitch fibres (to effect push off) in the hip and knee extensors seems necessary for optimal skating performance.

Biomechanical Phenomena↗
PubMed1987

Effect of prior exercise on maximal short-term power output in humans.

The effect of prior exercise (PE) on subsequent maximal short-term power output (STPO) was examined during cycling exercise on an isokinetic ergometer. In the first series of experiments the duration of PE at a power output equivalent to 98% maximum O2 uptake (VO2max) was varied between 0.5 and 6 min before measurement of maximal STPO. As PE duration increased subsequent STPO fell to approximately 70% of control values after 3-6 min. In series ii the effect of varying the intensity of PE of fixed 6-min duration was studied in five subjects. After PE less than 60% VO2max there was an increase of 12% in STPO, but after greater than 60% VO2max there was a progressive fall in STPO as PE intensity increased, indicating a reduction of approximately 35% at 100% VO2max compared with control values. In series iii we examined the effect on STPO of allowing a recovery period after a fixed intensity (mean = 87% VO2max) of 6 min PE before measurement of STPO. This indicated a rapid recovery of dynamic function with a half time of approximately 32 s, which is similar to the kinetics of PC resynthesis and taken with the other findings suggests the dominant role that PC exerts on the STPO under these conditions.

Adult↗
PubMed1986

Strength training and power output: transference effects in the human quadriceps muscle.

The effects of strength training of the quadriceps on peak power output during isokinetic cycling has been investigated in group of 17 young healthy volunteers. Subjects trained by lifting near-maximal loads on a leg extension machine for 12 weeks. Measurements of maximal voluntary isometric force were made at 2-3 week intervals and a continual record was kept of the weights lifted in training. Peak power output was measured at 110 rev min-1 and at either 70 or 80 rev min-1 before and after the 12 week training period. Measurements of maximum oxygen uptake (VO2max) were made on 12 subjects before and after training. The greatest change was in the weights lifted in training which increased by 160-200%. This was accompanied by a much smaller increase in maximum isometric force (3-20%). There was no significant change in peak power output at either speed. The VO2max remained unchanged with training. The role of task specificity in training is discussed in relation to training regimes for power athletes and for rehabilitation of patients with muscle weakness.

Adolescent↗