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At least 19 recordsLinked to original sources

PubMed1977

Lactate in fast and slow twitch skeletal muscle fibres of man during isometric contraction.

Concentration of lactate in fast and slow twitch fibres, respectively, were determined in m. quadriceps femoris after sustained contractions at 25%, 50%, and 75% of maximal voluntary isometric contraction (MVC) until exhaustion as well as after interrupted exercises at 25% and 50% MVC. Maximal lactate concentrations were only found at 50% of MVC performed to exhaustion. Lactate concentration was higher in slow twitch (ST) fibres at 50% MVC compared to in ST fibres at 25% MVC, and higher in fast twitch (FT) fibres at 50% MVC compared to in FT fibres at 75% MVC. After short time isometric exercise (i.e. 75% to exhaustion and 50% and 25% performed for the same period of time as 75% MVC) lactate concentration, expressed as lactate ratio (lactate concentration in FT fibres/lactate concentration in ST fibres) was found to be positively correlated to percent FT fibres (r=0.89). Lactate ratio ranged 0.5-2.0, i.e. at onset of isometric exercise, lactate concentration increase was faster in ST fibres in the muscle rich in ST fibres and faster in FT fibres when the muscle wasrich in FT fibres.

Age Factors↗

PubMed2026

Acute pre-exercise oral intake of cacao polyphenols attenuates central fatigue development during sustained low-intensity ankle dorsiflexion exercise in healthy young male adults.

This double-blind, randomized, crossover study investigated whether acute cacao polyphenol (CP) ingestion attenuates neuromuscular fatigue in 19 healthy young male adults. After consuming CP or placebo, participants performed sustained isometric ankle dorsiflexion at 25% of maximal voluntary isometric contraction (MVIC) torque until task failure. Neuromuscular function (MVIC torque, voluntary activation [VA%], doublet torque) and electromyographic activity were assessed before, immediately after, and during recovery (1 and 5 min). Salivary chromogranin A and α-amylase were measured at baseline and 1 min post-task. Only VA% and chromogranin A showed significant condition × time interactions (p = 0.027-0.039). VA% significantly decreased from before to immediately after the task and 1 min post-task in both conditions (p ≤ 0.002), with significantly higher values in the CP condition than in placebo immediately after and 1 min post-task (p ≤ 0.037). Chromogranin A significantly increased from baseline to 1 min post-task in the placebo condition (p < 0.001) but not in the CP condition (p = 0.083). These findings suggest that acute CP ingestion attenuates the decline in central motor drive and autonomic stress responses following strenuous exercise, without altering performance or peripheral recovery, supporting its potential as a nutritional strategy for modulating central fatigue.

Humans↗

PubMed2026

Muscle mechanical and architectural adaptations in response to different endurance training modalities in older adults.

INTRODUCTION: This study examined the effects of various cycling endurance training modalities, matched for total workload, on muscle mechanical and architectural characteristics in older adults. METHODS: Fifty healthy participants (25 females, 59-79 yrs) were randomly assigned to five age and sex matched groups: one control and four workload-matched training groups (moderate-intensity continuous, heavy-intensity continuous, high-intensity interval, and heavy-intensity continuous in eccentric cycling). Training consisted of three weekly sessions over 8 weeks, with evaluations conducted at the beginning and end of the intervention with maximal voluntary isometric contractions at five different knee angles (90, 75, 60, 45, 30°) and maximal concentric and eccentric isokinetic contractions at five different knee angular velocities (45, 90, 150, 210, 250°/s). Maximum voluntary isometric torque (Tmax) and optimal knee angle (KAopt) were obtained from the isometric contractions; eccentric torque (Tecc) and maximum concentric knee angular velocity (Vmax) were obtained from the isokinetic contractions. The muscle architecture of vastus lateralis (VL) at rest (muscle thickness, pennation angle, and fascicle length) was investigated as well. RESULTS: No statistical differences were detected between groups or time points in VL architecture, in KAopt and in Vmax. A main effect of time was observed for Tmax (p < 0.001, η2p = 0.458) and Tecc (p = 0.002, η2p = 0.191) in all the investigated training groups. The within-group comparisons indicate significant increases in Tmax in the training groups, but not in the control group. CONCLUSIONS: Commonly applied endurance exercises improve muscle mechanical capacity (Tmax and Tecc) in older adults, with no structural (architectural) muscle remodelling, when matched for workload.

Humans↗

PubMed2026

Effects of passive blood flow restriction on muscle function following exercise-induced muscle damage in recreationally active males.

This investigation examined the effects of passive blood flow restriction (pBFR) on indices of exercise-induced muscle damage (EIMD) in recreationally active males. Fifteen males completed six consecutive visits (±2 hours). Participants completed 3 × 25 maximal, unilateral, isokinetic (60°·s-1), concentric-eccentric leg extensions on both legs. Each leg was randomly assigned to receive pBFR (80% arterial occlusion pressure) or sham (20 mmHg) at 0, 24, 48, 72, and 96 hours post-EIMD. Perceived muscle soreness, range of motion (ROM), pain pressure threshold (PPT), concentric peak torque (CPT), and maximal voluntary isometric contraction (MVIC) torque were assessed and analyzed using separate linear mixed-effects models. Perceived muscle soreness increased at 24 hours (mean difference [meandiff] = 4.9 au; p < 0.001) and recovered by 96 hours (p = 0.482), with no differences between conditions (p = 0.450). ROM (meandiff = -3.1°; p = 0.040), PPT (meandiff = -1.63 kgf; p < 0.001), CPT (meandiff = -27.7 Nm; p < 0.001), and MVIC torque (meandiff = -30.8 Nm; p < 0.001) decreased at 24 hours, with recovery occurring between 48-96 hours. Condition-specific differences were observed for ROM (meandiff = 2.5°; p < 0.001), PPT (meandiff = 0.49 kgf; p = 0.005), CPT (meandiff = 6.2 Nm; p = 0.020), and MVIC torque (meandiff = 7.1 Nm; p = 0.044), which were greater in pBFR than sham. These findings suggested that pBFR may reduce impairments in ROM, PPT, CPT, and MVIC torque following EIMD, despite a similar recovery trajectory between conditions.

Humans↗

PubMed1976

Effect of strength training on enzyme activities and fibre characteristics in human skeletal muscle.

Progressive strength training was performed 3 times a week for 8 weeks by 14 male students (19-31 yrs.). The training program consisted mainly of dynamic exercises for the leg extensors with maximal or close to maximal loads. The training caused significant improvements in dynamic and isometric strength. One repetition maximum in squats increased with 67%, Sargent jump with 22%, and maximal voluntary isometric contraction (MVC) with 13%, respectively. Body weight and leg muscle circumferences remained unchanged after training, whereas total body potassium, lean body mass and calculated total muscle mass increased, suggesting a change in body composition with training. Muscle biopsies were obtained from vastus lateralis for fibre analyses and determination of enzyme activities. There were no changes in muscle fibre composition or fibre area with training. The activities of Mg2+ stimulated ATPase, creatine phosphokinase and phosphofructokinase remained unchanged, whereas myokinase activity was increased after training from (1.41 to 1.52 moles x 10(-4) x g-1 x min-1, p less than 0.05). After training significant correlations (p less than 0.01) were demonstrated between Mg2+ stimulated ATPase activity and % fast twitch fibres (% FT) (r = 0.67), as well as between myokinase activity and % FT (r = 0.86).

Adenosine Triphosphatases↗

PubMed1976

Effect of beta-adrenoreceptor blockers on heart rate and blood pressure in dynamic and isometric exercise.

Previous studies on the effects on heart rate and blood pressure in normals and hypertensive patients during dynamic exercise (ergometer bicycling or treadmill walking) and isometric exercise (sustained handgrip) are reviewed. In one study utilising sub-maximal bicycle exercise in hypertensives, there was a 43% increase in heart rate for a 33% increase in systolic pressure and 5% fall in diastolic pressure. Beta-adrenoreceptor blockade decreased the heart rate level by 18 to 19% for a decrease of systolic blood pressure level by 4 to 11%, whereas the diastolic pressure level was unaffected. A protocol is described utilising a blind indirect blood pressure recording machine ("Auto-Manometer") with which cuff inflation and deflation are automatic and constant, and blood pressure values stored at suitable Korotkov sound phases. The machine also records heart rate. By this method, isometric exercise at 50% of maximal voluntary contraction (sustained handgrip) has been studied in normals and hypertensives off and on different treatments. Both in normals and established hypertensives, there was about a 25% increase in systolic blood pressure during isometric exercise for about a 22% increase in diastolic blood pressure, and 26% increase in heart rate. Normotensive women had the lowest rise in blood pressure and the highest rise in heart rate. Beta-Adrenoreceptor blocking agents lowered heart rate during isometric exercise by 15 to 20% but did not affect the blood pressure level. Since resting blood pressure levels were decreased, the percentage rise in pressure was enhanced following beta-blockers. A combination of a beta-blocker, clonidine and/or a vasodilator produced a reduction in both systolic (24%) and diastolic (12%) pressure, as well as in heart rate (18%), during isometric exercise.

Adrenergic beta-Antagonists↗

PubMed1978

Energy metabolism in different human skeletal muscles during voluntary isometric contractions.

The energy turnover in contracting skeletal muscle was studied by measuring the rate of temperature rise during voluntary, isometric contractions and circulatory arrest in M. soleus, M. sacrospinalis and M. biceps brachii in 14 males, by thermoelements inserted in the muscles. A linear relationship between rate of temperature rise and force intensity given as per cent of maximal voluntary contraction (MVC) was demonstrated in biceps (r = 0.95), but not so clearly confirmed in soleus (r = 0.73). Muscle biopsies were taken from the same muscles and fibre type distribution was determined histochemically by staining for ATPase. The rate of heat production at MVC showed positive correlation to the percentage of fast twitch (FT) fibres in the muscles (r = 0.90). Linear extrapolation indicates that the maximal energy turnover in human FT fibres is approximately six times that of slow twitch (ST) fibres during voluntary isometric contractions.

Adult↗

PubMed1978

Force-time characteristics and fiber composition in human leg extensor muscles.

Recording of the force-time (f-t) characteristics of muscular contraction expresses the rate at which tension is developed. To further understand the problems involved in force production during voluntary contraction, the f-t curve was registered during maximal voluntary isometric extension of both legs performed in the sitting position with the knee angle at 107 degrees. 38 athletes representing various sport events, five pairs of monozygous, and ten pairs of dizygous twins were used as subjects. The reference group consisted of eight normal men. The data disclosed that the time to produce certain force levels showed good trial-to-trial and satisfactory day-to-day reproducibility below tension levels of 0.9 x PO. At these force levels the time of tension development was positively (p less than 0.05) related to the per cent distribution of slow twitch fibers in the vastus lateralis muscle. This result is consistent with animal experiments concerning the mechanical characteristics of slow and fast muscles. In addition, it was observed that the athletic groups had f-t curves different from the other subjects. Genetic factors had only slight influence on the f-t measurement.

Biomechanical Phenomena↗

PubMed1977

Human skeletal muscle function: description of tests and normal values.

1. The force produced by isometric contractions of the quadriceps muscle have been studied during maximal voluntary contractions and when a substantial part of the muscle was electrically stimulated via surface electrodes. 2. In normal children and adults, the force of a maximal voluntary contraction of the quadriceps was proportional to body weight. 3. The function of the quadriceps has been described in terms of the force/frequency curve, speed of relaxation and the rate of loss of force during 18 s stimulation at 30 Hz and 100 Hz. 4. The functional characteristics of adductor pollicis when stimulated via the ulnar nerve were essentially similar to those of the quadriceps. 5. Studies of the function of these two muscles are complementary since quadriceps femoris is amenable to needle biopsy investigations of its structure and chemistry whereas adductor pollicis is more suitable for electrophysiological studies.

Adolescent↗

PubMed1978

Effect of isometric hand-grip exercise on the carotid sinus baroreceptor reflex in man.

1. The changes in R--R heart interval that result from step-increase and step-decrease in carotid sinus transmural pressure induced by a variable pressure neck chamber were measured in seven normal men. Observations were made at rest, and during isometric hand-grip exercise at 24%, 44% and 64% of maximal voluntary contraction. 2. The response of heart interval to increase in carotid sinus transmural pressure was progressively and markedly diminished according to the strength of hand-grip. This effect was fully developed from the moment of onset of the exertion. 3. The response of heart interval to decrease in carotid sinus transmural pressure was much less consistently affected by hand-grip exercise.

Adult↗

PubMed2026

Comparing the Effects of Push and Hold Isometric Training on Strength and Musculotendinous Adaptations: A Within-Subject Randomized Controlled Trial.

Lum, D, Oranchuk, DJ, Chen, SE, and Kong, PW. Comparing the effects of push and hold isometric training on strength and musculotendinous adaptations: A within-subject randomized controlled trial. J Strength Cond Res 40(9): 1050-1058, 2026-Despite recent interest in delineating pushing (PIMA) and holding (HIMA) isometric muscle actions, training-induced adaptations have not been examined. As such, we compared the strength and morphological adaptations between PIMA and HIMA training. Twenty limbs across 10 adults (5 men, 5 women, age: 31.4 ± 6.5 years) were randomly assigned to PIMA or HIMA conditions and underwent 12 training sessions over 6 weeks. PIMA required subjects to exert force against a fixed lever while the HIMA limb maintained a set joint angle while resisting an isotonic lever. During each contraction, subjects had to exert force at 70% of maximal voluntary contraction for 20 seconds at an 80° knee angle, for 4-6 repetitions. Subjects completed isometric, concentric, and eccentric knee extension assessments for both limbs before and after the intervention. Pre- and postintervention ultrasound scans were performed to determine quadriceps muscle architecture and patellar tendon thickness. Increased isometric torque was found following both conditions (p < 0.05, g = 0.30-0.36), while concentric (p < 0.05, g = 0.31) and eccentric (p < 0.01, g = 0.50) torque only increased following PIMA. Both conditions increased muscle thickness (p < 0.05, g = 0.27-0.88) and vastus lateralis fascicle length (p < 0.05, g = 0.20-0.31). Only HIMA increased patellar tendon thickness (p < 0.05, g = 0.12). The increase in total quadriceps (p < 0.05, g = 0.46) and especially rectus femoris (p < 0.05, g = 1.44) thickness was greater in HIMA. The results suggest that PIMA may be more effective at improving strength, while HIMA may be superior for inducing morphological adaptations. Larger sample sizes and more ecologically valid training programs are warranted to further elucidate potential differences between different isometric types.

Humans↗

PubMed1979

The control of blood flow through human forearm muscles following brief isometric contractions.

1. The blood flow through the forearm was measured 2 sec after single, brief isometric hand-grip contractions. The tension and duration of those contractions varied from 10 to 100% of the maximal voluntary contraction (m.v.c.) and from 2 to 12 sec, respectively. 2. The blood flow increased linearly with tension up to about 60% m.v.c. but further increases in tension, up to 100% m.v.c., did not elicit higher blood flows than were found at 60% m.v.c. The same relationship between tension and the resultant blood flow held for all durations of contractions, from 2 to 12 sec. The blood flow immediately after (2 sec) contractions at a given tension increased linearly with the duration of the contraction, from 2 to 12 sec. Maximal exercise blood flow was approached only in response to the longest contractions (12 sec) at tensions of 60% m.v.c. or higher. 3. Brief alterations (2--5 sec) of transmural pressure across blood vessels did not result in a significant change of blood flow, either in the resting forearm or when the vessels were dilated by brief, isometric contractions. When the tension was applied or released either rapidly or gradually ('ramp' contractions) there was no correlation between the rate of change of stretch on arterial vessels and the resultant blood flow. However, there was a direct relationship between a force--time integral (duration of contraction x peak tension) and blood flow. All these results make it clear that changes in blood flow in the forearm elicited by brief isometric contractions are not the result of a myogenic reflex but are metabolically induced. 4. Successive contractions exerted at 60% m.v.c. for 4 sec induced a blood flow of 21.2 +/- 1.6 ml.min-1.100 ml.-1 when a rest interval of 8 sec was allowed between the contractions. Blood flows remained constant at this submaximal level, even when muscular fatigue was induced, and when there was an accompanying large increase in blood pressure. 5. Isometric muscular activity by the contralateral arm which resulted in fatigue, associated with a large increase in mean blood pressure, did not alter the level of vasodilation that was induced by brief, isometric contractions in the 'test' arm. 6. It is suggested that the vasodilatation in response to intermittent isometric contractions is the result of metabolic vasodilatation of distal segments and continued sympathetic vasoconstriction of the proximal segments of the forearm vascular bed.

Blood Pressure↗

PubMed1975

Constituents of human muscle in isometric fatigue.

Three subjects performed five successive isometric contractions to fatigue; the tension in any one experiment was constant at tensions varying from 20 to 80% of the maximal voluntary contraction (MVC). The interval between contractions was held constant at 11 min. Muscle biopsy specimens were obtained at the start of the experiment, after the first, fourth, and fifth, and before the second and fifth of the successive contractions. The concentrations of ATP, CP, glycogen, and lactate were measured in each sample of muscle. Changes in ATP and glycogen were insufficient to be held accountable for the development of isometric fatigue. Changes in CP and lactate were large after fatigue at intermediate tensions, but those of CP were considered unlikely to be responsible for the fatigue. At tensions of 30-50% MVC the increase in lactate could be responsible for fatigue either directly or by indirect changes in pH; at higher and lower tensions the possibility that lactate is directly implicated in the development of fatigue seems remote.

Adenosine Triphosphate↗

PubMed1978

Blood flow in the resting forearm during prolonged contralateral isometric handgrip at maximal effort.

1. In earlier studies we have shown that muscle contraction performed as handgrip at constant force, one third of maximal voluntary contraction (MVC), induces a rapid vasodilation in the resting contralateral forearm which in all probability is neurogenically mediated, followed by a relative increase in resistance.2. The maintenance of contraction at one third MVC for 2 min requires continuously increasing effort because of fatigue, as also evidence by the e.m.g. The biphasic response of the vascular bed may then be related to the increasing intensity of somatomotor activation which is needed to maintain contraction force, or, alternatively, to differences in vasomotor activity on initiation of and continued muscle activity.3. To elucidate these two possibilities blood flow in the resting forearm was measured during contralateral handgrips at constant maximal effort for 6 min (in which case force will drop) and compared to handgrip at constant force, one third MVC, for 2 min.4. The flow reaction during prolonged contraction at maximal effort was similar to that induced by contraction at constant force with a marked transient lowering of vascular resistance, although maximal vasodilation tended to be more pronounced and occur earlier.5. The results indicate that the rapid decrease in vascular resistance is related primarily to the initiation of somatomotor activity, whereas continued muscle contraction produces a relative increase in vasoconstrictor activity irrespective of changes in contraction effort.

Adult↗

PubMed1978

[Plasma renin activity response to isometric handgrip exercise in normotensive and hypertensive patients (author's transl)].

1) Plasma renin activity (PRA) response to isometric exercise was studied before and after the intravenous administration of 0.2 mg/kg of propranolol in 8 normotensive and 10 normal renin hypertensive patients. 2) Handgrip exercise at the 30% level of maximal voluntary contraction (MVC) for four minutes induced a significant increase in PRA in either normotensive or normal renin hypertensive patients, while the increase in PRA in normal renin hypertensive patients was significantly higher than that in normotensive patients. 3) Pretreatment with the administration of propranolol inhibited an increase in PRA after handgrip exercise in either normotensive or normal renin hypertensive patients. 4) The results suggest that isometric handgrip exercise can induce an augmentation in renin release mainly by stimulation of the sympathetic nervous system in either normotensive or normal renin hypertensive patients. The possible mechanism of the exaggerated response in PRA to handgrip exercise in normal renin hypertensive patients has been discussed.

Adolescent↗

PubMed1979

Muscular fatigue and rate of tension development.

The effects of long-term fatigue upon maximal force and peak rate of tension development (PRTD) (dF/dt max) are studied in man (elbow flexors), in the rat (pseudo-isolated gastrocnemius muscle) and in the frog (isolated sartorius muscle). The muscles are fatigued by voluntary anisometric anisotonic contractions against an elastic resistance in man, and by maximal tetanic contractions in the frog and the rat. In man, the excitation level of the muscle is controlled by the integrated surface EMG of the biceps brachii. In the animals, the muscles are stimulated by a neurostimulator. The PRTD and the maximal isometric force are measured during fatigue tests. In man, frog and rat, the maximal voluntary isometric torque or the maximal force and the PRTD decrease initially more or less rapidly according to the power developed during the fatigue process, and then less rapidly. The relationship between PRTD and maximal force is linear in the animals and curvilinear in man. The variations of maximal force and PRTD are discussed in relation to the level of excitation of the muscles and of the composition in different motor units types and their spatio-temporal recruitment. From a biomechanical point of view, it seems necessary to study the behavior of the series elastic component during the evolution of long term fatigue.

Animals↗

PubMed1979

Effect of beta-adrenergic blockade on haemodynamic responses to dynamic and isometric exercise in angina pectoris.

The effect of treatment for 1--4 weeks with metoprolol, a beta 1-selective blocking agent, or alprenolol, on the heart rate and blood pressure response to isometric exercise was studied in two groups of 12 patients with angina. Measurements were made during the peak effect of metoprolol 10, 40 or 50 mg, and alprenolol 200 mg as Aptin Durules. After 1 min of sustained handgrip at 50% of maximal voluntary contraction, systolic (6--15%) and diastolic (8--12%) blood pressure after both drugs was significantly lower than without any beta-blockade; Heart rate was decreased by 19--22% by metroprolol but not by alprenolol. The blood pressure rise during handgrip was not attenuated by either drug. The rise in heart rate was significantly reduced (by 36--50%) by metoprolol 40 and 50 mg and alprenolol 200 mg. No patient experienced angina during handgrip. In contrast, all but one were restricted by angina during bycycle exercise without treatment, at a level that produced the same increase in heart rate as the handgrip test, vis. 3 min at a load of 33 W). The cardiovascular response to sustained handgrip is too small to provide a useful challenge for determinatin of the anti-anginal efficacy of drugs. However, slight ECG changes of ischaemia did occur during handgrip, which were reversed by beta-blockade.

Adrenergic beta-Antagonists↗

PubMedDate not supplied

Amplitude of the surface electromyogram during fatiguing isometric contractions.

Five voluntee subjects held isometric handgrip contractions at specific submaximal tensions until the required tension could no longer be maintained. At the start of those contractions, the amplitude of the surface electromyogram (EMG) was linearly related to the tension exerted; the amplitude of the EMG increased linearly throughout these substained contractions by a constant amount--about 30% of the maximum. During sustained contractions, brief, intermittent maximal efforts showed that strength declined linearly at all tensions. At 25% maximal voluntary contraction (MVC), there was a linear fall in the EMG amplitude associated with the brief maximal efforts, but the fall in strength was more rapid than the fall in EMG amplitude. At 70% MVC, there was no fall in the EMG amplitude in response to the brief maximal efforts, while the muscle strength fell linearly.

Adult↗