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PubMed2001

[Study of blood pressure, hemodynamic, ventilatory and metabolic responses to isometric exercise performed during dynamic exercise in health subjects].

The object of this study was to study the blood pressure, haemodynamic, ventilatory and metabolic changes on isometric exercise during a dynamic effort in healthy subjects. Twelve healthy subjects underwent isometric exercise by manual prehension at 40% maximal capacity under these conditions: isolated (A), five minutes after the onset of rectangular dynamic exercise on a cycle at 60% of ventilatory threshold (B) and at the fourth minute of the recovery phase of dynamic exercise (C). The blood pressure, heart rate, stroke volume and cardiac index measured by Doppler echocardiography, systemic arterial resistances, respiratory flow and respiratory rate, were measured before and after each isometric exercise. The results showed blood pressure and heart rate to increase in a similar manner during isometric exercise under all conditions. The cardiac index increased by 29.5% +/- 8.3% (p < 0.01) under condition A and by 38.1% +/- 10% (p < 0.01) under conditions C but did not change significantly under conditions B. On the other hand, the systemic arterial resistances increased by 15.5% +/- 6.5% (p < 0.05) under conditions B, decreased by 8.8% +/- 3.9% (p < 0.05) under conditions C but did not change significantly under conditions A. The respiratory flow increased under all three conditions although the respiratory rate was only increased under conditions B. The authors conclude that, in healthy subjects, the increase in blood pressure during isometric and dynamic exercise is the result of an increase in systemic resistances whereas, during isometric exercise, it is flow-dependant.

Adult↗

PubMed2000

[Relationship between isometric exercise and myocardial ischemia in patients with coronary artery disease: an Echo-Doppler study].

OBJECTIVE: To study the relationship between isometric exercise and myocardial ischemia in patients with coronary artery disease (CAD). METHODS: Twenty CAD patients and 10 normal subjects were included in our study. All subjects performed maximal brief isometric exercise (BIE), maximal sustained isometric exercise (SIE) and dynamic exercise (DE). Hemodynamic parameters and cardiac function were measured by Echo-Doppler technique. To avoid influence of different baseline values, increment (delta%) of exercise response was used as parameter for significant analysis: delta% = (exercise values - baseline values)/baseline values x 100%. RESULTS: Positive exercise testing (PET) showed no evidence of myocardial ischemia during BIE and SIE even though their rates of perceived exertion (RPE) were similar to DE. delta% heart rate (HR) and delta% rate pressure product (RPP) were higher during DE than during SIE and BIE in negative exercise testing (NET) and normal controls (NOR) (P < 0.01), except PET during DE and SIE; delta% systolic blood pressure (SBP) was higher during DE than during BIE in NOR (P < 0.01). delta% SBP in NOR and NET during SIE was higher than during BIE (P < 0.05). delta% diastolic blood pressure (DBP) was the highest during SIE among exercises in all gropus (P < 0.05). There were no significant inter-group differences of delta% HR, delta% SBP, delta% DBP and delta% RPP during SIE, BIE and DE, except that delta% SBP during SIE was higher in NET than in NOR and PET (P < 0.05). In NOR, delta% ejection fraction (EF), delta% fractional shortening of the minor-semi axis (SF), delta% cardiac output (CO), delta% E/A was higher during DE than during SIE and BIE (P < 0.01). delta% stroke volume (SV) was similar during DE, SIE and BIE. There were no significant differences in delta% EF, delta% SF, delta% CO, delta% SV and delta% E/A during DE, SIE and BIE in both NET and PET, except lower delta% CO in NET during SIE and BIE than DE (P < 0.01). There were no inter-group differences in delta% EF, delta% SF, delta% CO and delta% E/A, except that delta% E/A was higher during SIE in NET than PET (P < 0.01). During DE, NOR and NET had higher delta% SV, delta% SF, delta% CO and delta% E/A than PET (P < 0.05). CONCLUSIONS: The incidence of myocardial ischemia in CAD patients was lower during isometric exercise than dynamic exercise at similar perceived exertion levels. Isometric exercise might protect the myocardium from ischemia through high coronary artery perfusion pressure and long perfusion duration. We suggest that application of isometric exercise in a cardiac rehabilitation program may have reasonable physiological background.

Aged↗

PubMed1992

Anterior cruciate ligament reconstruction stability with continuous passive motion. The role of isometric graft placement.

A comparison was made of the stability of isometric versus nonisometric anterior cruciate ligament (ACL) reconstructions when subjected to immediate postoperative continuous passive motion (CPM). Anterior cruciate ligament reconstructions were performed on 13 anatomic specimen knees using bone/patellar tendon/bone grafts. Nine ACL substitutions were considered isometric with maximum graft length changes of less than 1 mm. Four ACL substitutions were nonisometric with graft length changes of 3 mm or greater resulting from tightening in flexion. The specimens were subjected to CPM through 0 degrees-95 degrees knee flexion. Knee stability was remeasured with a knee arthrometer at three and 14 days after beginning CPM. All four nonisometric specimens had failed within three days, with increased anterior laxity of 2-9 mm in both the Lachman (20 degrees) and anterior drawer (90 degrees) positions. All nine isometric reconstructions successfully retained pre-CPM anterior stability within 1 mm after 14 days of CPM. This investigation illustrates the importance of isometric graft placement for ACL reconstruction success. Continuous passive motion does not appear to adversely affect immediate ACL-substitute integrity or fixation if graft placement is isometric (less than 1 mm of graft excursion through 0 degrees-110 degrees of knee motion). Continuous passive motion may cause graft deformation, fixation failure, or both, with resultant loss of knee stability if the graft is not isometrically positioned (greater than 3 mm of graft excursion resulting from tightening in flexion).

Anterior Cruciate Ligament↗

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↗

PubMed1993

Motor unit number estimation, isometric strength, and electromyographic measures in amyotrophic lateral sclerosis.

Pathologic progression in amyotrophic lateral sclerosis (ALS) results from motor neuron death, while the clinical expression also reflects the compensatory effects of collateral reinnervation consequent to lower motor neuron loss. In a cross-sectional study of ALS subjects, we made comparisons between motor unit number estimation (MUNE) values and several measures reflecting collateral reinnervation, including isometric strength, compound muscle action potential (CMAP) amplitude, surface motor unit action potential (S-MUAP) amplitude, fiber density (FD), macro-EMG potential amplitude, turns-to-amplitude (T/A) ratio, and amplitude and recruitment pattern of low threshold voluntary motor units in elbow flexor muscles. Before comparisons were made, test-retest reproducibility of these measures was assessed in ALS subjects, and is highest for isometric strength, and lower but similar for EMG measures. When the effects of multiple comparisons are considered, borderline significant correlations are found between MUNE values and isometric strength. Neither MUNE values nor isometric strength are significantly correlated with macro-EMG amplitude, FD, T/A ratio, or amplitude and recruitment rate of low threshold voluntary motor units. There are significant correlations of CMAP and S-MUAP with MUNE values, but these are statistical artifacts with no independent interpretation. We conclude that collateral reinnervation prevents isometric strength and EMG measures from accurately reflecting lower motor neuron death in ALS. MUNE measurements are better suited to provide insight into the true natural history of the disease process and may be clinically useful to follow progression and response in drug trials.

Action Potentials↗

PubMed1984

Force-velocity relation and stiffness in frog single muscle fibres during the rise of tension in an isometric tetanus.

The force-velocity (T-V) relation and the force-extension (T1) relation are determined at present times and at increasing isometric tensions during a tetanic contraction in frog single muscle fibres in which the passive compliance in series with the sarcomeres was made very small. The slope of the instantaneous T1 relation, the fibre stiffness, increases roughly in proportion to the level of the rising isometric tension at which the measurements were made. The value of V0 (the velocity of shortening under zero load) is time-independent, whereas the force T exerted during shortening at any velocity V lower than V0 increases gradually with time after the beginning of the tetanus volley and attains its steady state level before the isometric tension has attained the tetanus plateau and the fibre stiffness its final value. It is concluded that the delay of the development of the isometric tension and of the fibre stiffness with respect to the development of the T-V relation is determined by a specific factor of the contractile process. It is interesting to note that in a cross-bridge model of contraction, in which the value of the rate constant for cross-bridge formation is moderate, the recruitment of actin sites which is measured by the characteristics of the instantaneous T-V relation, is expected to lead significantly the actual cross-bridge formation, which is measured both by the instantaneous isometric tension and by the instantaneous stiffness.

Animals↗

PubMed1994

Changes of the force-velocity relation, isometric tension and relaxation rate during fatigue in intact, single fibres of Xenopus skeletal muscle.

We have studied the force-velocity relation and the relaxation speed in intact, single fibres from Xenopus during fatigue produced by repeated tetani. Slack tests were used to obtain the shortening velocity at zero load (V0) and ramp shortenings to get the force at intermediate velocities. The relaxation speed was measured as the slope during the initial linear phase of relaxation. During fatiguing stimulation isometric tension declined following a typical pattern with three phases. During the initial 10-15 tetani (phase 1) isometric tension fell to about 80% of the pre-fatigue tension (P0), while V0 showed no significant change. Thereafter V0 fell almost linearly with time, whereas isometric tension first fell very slowly (phase 2) and then rapidly (phase 3). In fatigue V0 was reduced to 46% of the control and isometric tension to 0.34 P0. The force velocity relation seemed less curved during fatigue. The relaxation speed was almost halved during phase 1 and thereafter fell more slowly to less than 10% of the control in fatigue. We suggest changes of isometric tension and shortening velocity during phase 1 and 2 to reflect altered crossbridge function due to changes of intracellular pH, inorganic phosphate and ADP concentration; the additional tension decline during phase 3 would reflect impaired Ca2+ activation of the crossbridges. The rapid slowing of relaxation during phase 1 probably involves Ca2+ saturation of parvalbumin, whereas the additional decline during phase 2 and 3 would reflect the above metabolic changes, acting either on crossbridges or active Ca2+ reuptake into the sarcoplasmic reticulum.

Adenosine Diphosphate↗

PubMed1994

The relative activation of muscles during isometric contractions and low-velocity movements against a load.

Surface electromyographic (EMG) and motor unit activity were measured in human arm muscles during isometric contractions and during movements against an elastic load. The direction of force applied proximal to the wrist and movement direction of the wrist were varied in a horizontal plane. During isometric contractions the direction in which the largest EMG activity was measured corresponded to the direction in which motor units had the smallest recruitment threshold, for each muscle. The same was found for movements against an elastic load. However, this direction was different for isometric contractions and for movements. Because the magnitude and sign of these changes varied for different muscles, this resulted in a different relative activation of muscles for the two conditions. The amplitude of the surface EMG during contractions against an elastic load was generally significantly larger than that for isometric contractions against the same load. For m. brachioradialis isometric conditions yielded occasionally increased EMG activity. The change in EMG activity could be attributed completely to changes in motor unit recruitment thresholds leading to proportionate changes in the number of recruited motor units. However, the initial firing rate of motor units at recruitment was the same under both conditions and, therefore, did not contribute to changes in amplitude of surface EMG activity.

Arm↗

PubMed1995

The role of metabolites in strength training. II. Short versus long isometric contractions.

The role of intramuscular metabolite changes in the adaptations following isometric strength training was examined by comparing the effect of short, intermittent contractions (IC) and longer, continuous (CC) contractions. In a parallel study, the changes in phosphate metabolites and pH were examined during the two protocols using whole-body nuclear magnetic resonance spectroscopy (NMRS). Seven subjects trained three time per week for 14 weeks. The right leg was trained using four sets of ten contractions, each lasting 3 s with a 2-s rest period between each contraction and 2 min between each set. The left leg was trained using four 30-s contractions with a 1-min rest period between each. Both protocols involved isometric contractions at 70% of a maximum voluntary isometric contraction (MVC). The MVC, length:tension and force:velocity relationships and cross-sectional area (CSA) of each leg were measured before and after training. The increase in isometric strength was significantly greater (P = 0.041) for the CC leg (median 54.7%; P = 0.022) than for IC (31.5%; P = 0.022). There were no significant differences between the two protocols for changes in the length:tension or force:velocity relationships. There were significant increases in muscle CSA for the CC leg only. NMRS demonstrated that the changes in phosphate metabolites and pH were greater for the CC protocol. These findings suggest that factors related to the greater metabolite changes during CC training results in greater increases in isometric strength and muscle CSA.

Adult↗

PubMed1989

Differences in the activation of m. biceps brachii in the control of slow isotonic movements and isometric contractions.

We have compared muscle activation in the control of slow isotonic movements and isometric contractions. Specific attention has been given to the contribution of the two force-grading mechanisms, the recruitment of motor units and the modulation of firing frequency in motor units that have already been recruited. The recruitment order of the m. biceps motor units under study was the same during isometric contractions and slow isotonic movements. However, the recruitment thresholds of the m. biceps units were considerably lower for both isotonic flexion and extension movements, even at velocities as low as 2 deg/s, than for isometric contractions. Furthermore, firing frequency at recruitment was found to depend on the motor task: at recruitment the motoneurone starts firing with a higher firing frequency during isotonic flexion movements and a lower firing frequency during isotonic extension movements than during isometric contractions. Two main conclusions can be drawn from these results. First of all, the concept of one single activation parameter (total synaptic drive?) cannot account for the motor-unit behaviour observed during our experiments: the relative contribution of the two force-grading mechanisms is different for different tasks. Secondly, the distribution of activity among flexor motoneurone pools is different for isometric contractions and isotonic movements.

Humans↗

PubMed1992

Determinants of isometric muscle strength in men of different ages.

Values of maximal isometric strength of five muscle groups and associated factors including occupational status, life style and health were studied in three groups of men aged from 31 to 35, 51 to 55, and 71 to 75 years. The results indicated significant differences between the age groups in isometric handgrip, elbow flexion, knee extension, trunk extension and trunk flexion strength. In the youngest group, the manual workers tended to have higher strength values in all muscle groups than the lower and higher status white collar workers, whereas among the middle-aged and oldest men the manual workers tended to have the poorest performance. Good self-rated health and the intensity of physical exercise during leisure were positively associated with muscle strength in the youngest and middle-aged groups whereas in the oldest group the most important variable was home gymnastics. The multivariate structural equation models of isometric strength differed somewhat among the age groups and in these models the above-mentioned variables accounted for from 33% to 43% of the variance in isometric strength within the age groups. The results illustrated the most important factors associated with isometric strength in samples of men of different ages and also provided suggestions as to how these determinants might influence comparisons between different age groups in respect of muscle strength.

Adult↗

PubMed1986

Effects of fatigue and recovery on electromyographic and isometric force- and relaxation-time characteristics of human skeletal muscle.

Effects of fatigue produced by a maintained 60% isometric loading on electromyographic and isometric force-time and relaxation-time characteristics of human skeletal muscle were studied in 21 males accustomed to strength training. Fatigue loading resulted in a slight but not significant change in the maximal integrated EMG of a maximal isometric contraction, and a large decrease (20.4 +/- 6.3%, p less than 0.001) in maximal force. Fatigue loading increased (p less than 0.05-0.01) neural activation of the muscles during rapidly produced submaximal isometric forces, but had a considerable adverse effect (p less than 0.001) on the corresponding force-time characteristics. Correlations between the relative changes after fatigue in the IEMG/force ratio at the maximal force level, and in the IEMG/force ratios of the early phases of the force-time curve were not significant, but gradually became significant (p less than 0.01) at higher force levels. The average IEMG of the muscles in the relaxation phase of contraction remained unaltered by fatigue, while a marked deleterious change in the relaxation-time variables (p less than 0.001) occurred concomitantly. During the subsequent 3 min rest period considerable (12.1 +/- 7.0%, p less than 0.001) recovery was noted in the maximal force, with smaller (insignificant or p less than 0.05-0.01) changes in the force-time and relaxation-time variables, while the average IEMG of force production decreased (p less than 0.01-0.001). The present findings suggest that fatigue leading to a worsening in force-time, in maximal force and in the relaxation-time parts of a maximal isometric contraction might take place primarily in the contractile processes.

Adult↗

PubMed1983

Effect of isometric and isokinetic muscle training on static strength and dynamic power.

This study investigated whether isokinetic strength training might induce changes in static and dynamic power already achieved as a result of isometric strength training. The subjects were twelve males. The isometric strength and dynamic power of elbow flexors were tested by means of an electric dynamometer and fly-wheel every two weeks. During the first 8 weeks all subjects trained the elbow flexors isometrically at four different positions of elbow joints. This training produced 27-36% gains in isometric strength and 34-46% in power. Thereafter the subjects were divided into two groups: the FG group who trained isokinetically at a fast velocity of 157 degrees . s-1, and the SG group at slow velocity of 73 degrees . s-1. After 6 weeks of training, the FG group produced a significant gain in power with light equivalent masses and the SG group did so with heavy equivalent masses. Neither group showed change in isometric strength.

Adult↗

PubMed1991

The combined effect of the cold pressor test and isometric exercise on heart rate and blood pressure.

The purpose of this study was to determine if the cold pressor test during isometric knee extension [15% of maximal voluntary contraction (MVC)] could have an additive effect on cardiovascular responses. Systolic and diastolic blood pressures, heart rate and pressure rate product were measured in eight healthy male subjects. The subjects performed the cold pressor tests and isometric leg extensions singly and in combination. The increases of systolic and diastolic blood pressure during isometric exercise were of almost the same magnitude as those during the cold pressor test. The responses of arterial blood pressure, and heart rate to a combination of the cold pressor test and isometric knee extension were greater than for each test separately. It is suggested that this additional effect of cold immersion of one hand during isometric exercise may have been due to vasoconstriction effects in the contralateral unstressed limb. In summary, the circulatory effects of the local application of cold during static exercise at 15% MVC were additive.

Adult↗

PubMed1991

Recovery of the human biceps electromyogram after heavy eccentric, concentric or isometric exercise.

Five men performed submaximal isometric, concentric or eccentric contractions until exhaustion with the left arm elbow flexors at respectively 50%, 40% and 40% of the prefatigued maximal voluntary contraction force (MVC). Subsequently, and at regular intervals, the surface electromyogram (EMG) during 30-s isometric test contractions at 40% of the prefatigued MVC and the muscle performance parameters (MVC and the endurance time of an isometric endurance test at 40% prefatigued MVC) were recorded. Large differences in the surface EMG response were found after isometric or concentric exercise on the one hand and eccentric exercise on the other. Eccentric exercise evoked in two of the three EMG parameters [the EMG amplitude (root mean square) and the rate of shift of the EMG mean power frequency (MPF)] the greatest (P less than 0.001) and longest lasting (up to 7 days) response. The EMG response after isometric or concentric exercise was smaller and of shorter duration (1-2 days). The third EMG parameter, the initial MPF, had already returned to its prefatigued value at the time of the first measurement, 0.75 h after exercise. The responses of EMG amplitude and of rate of MPF shift were similar to the responses observed in the muscle performance parameters (MVC and the endurance time). Complaints of muscle soreness were most frequent and severe after the eccentric contractions. Thus, eccentric exercise evoked the greatest and longest lasting response both in the surface EMG signal and in the muscle performance parameters.

Adult↗

PubMed1995

Isometric and isokinetic quadriceps strength in gonarthrosis; inter-relations between quadriceps strength, walking ability, radiology, subchondral bone density and pain.

Patients with osteoarthrosis suffer from disability and pain. We measured isokinetic and isometric peak torque in 20 women with gonarthrosis (GA) and in 26 healthy controls. Relationships between muscle strength, walking and stair climbing time, pain level and pain disability scores as assessed by the patients using an extensive questionnaire, radiological changes and subchondral sclerosis expressed as bone mineral density (BMD, g/cm2) of the proximal tibia were studied. Precision errors of the torque measurements in both GA patients and controls were approximately 6%. In the GA patients, isokinetic and isometric quadriceps strength was reduced by 40 and 15% (p < 0.01) respectively, and walking and stair climbing time was increased by 30% (p < 0.005). Isokinetic strength was a better predictor of pain level and pain disability scores than isometric strength and radiological stage. Walking time and stair climbing time were not associated with quadriceps strength, pain level, pain disability scores or radiological changes. Subchondral BMD was not predictive of pain. The study suggests that quadriceps strength assessed by isokinetic dynamometry in GA is a reliable measurement. Isokinetic strength was pronouncedly reduced compared to isometric strength and was a more important predictor of pain and pain disability than isometric strength. These findings should be taken into consideration when planning exercise studies and programmes in GA.

Aged↗

PubMed2003

Regulation of arterial blood pressure in humans during isometric muscle contraction and lower body negative pressure.

Previous studies have shown that the blood pressure response to isometric handgrip remains unchanged during reductions in preload induced by lower body negative pressure (LBNP). The purpose of the present study was to assess the beat-by-beat haemodynamic mechanisms allowing for precise control of mean arterial pressure (MAP). We have followed the cardiovascular variables involved in the regulation of MAP during isometric handgrip with and without additional application of LBNP during defined periods of the ongoing contraction. Sixteen subjects participated. Mean arterial blood pressure (MAP), heart rate (HR), stroke volume (SV), cardiac output (CO), blood flow velocity in the brachial artery, acral skin blood flow, as well as total (TPR) and local (LPR) peripheral resistance were continuously recorded/calculated before, during and after 2 min of handgrip both with and without concomitant LBNP. The main finding was that MAP increased at the same rate and to the same absolute level whether or not LBNP was applied. A uniform increase in MAP was observed even though the cardiovascular variables evolved differently in the periods with and without LBNP. At the onset of LBNP at -20 mmHg, there was a transient drop in MAP and a transient increase in HR, but within seconds, MAP was regulated back to the slope caused by the isometric handgrip proper. CO and SV, which were declining gradually, showed an additional marked but gradual reduction upon LBNP application. At the same time, both LPR and TPR increased markedly and continuously. In summary, the increase in MAP during isometric handgrip remained essentially unchanged by LBNP-induced alterations in preload. The increase in MAP was caused by a marked increase in peripheral resistance. This supports the concept of a central set point, continuously regulated upwards as long as the isometric handgrip persists. Furthermore, it reveals a considerable flexibility in the cardiovascular control mechanisms used to achieve the desired arterial pressure.

Adaptation, Physiological↗

PubMed2006

Maximal force during eccentric and isometric actions at different elbow angles.

The purpose of this study was to examine a course of force potentiation and/or inhibition during maximal voluntary eccentric action. Maximal voluntary force (MVC) of elbow flexion of ten healthy male volunteers was measured during isometric and isokinetic eccentric action starting from 80 degrees or 110 degrees and ending at 140 degrees elbow angle. Surface EMG was recorded from biceps brachii (BB) and brachioradialis (BR) muscles. Maximal voluntary eccentric force during the first 10 degrees of the movement was higher (P<0.001) than the maximal voluntary isometric preactivation force both in 80 degrees and in 110 degrees starting position at all three velocities (1, 2, and 4 rad s(-1)). The relative force potentiation was velocity dependent being smallest at the lowest stretching speed (P<0.01). Average EMG (aEMG) of BB and BR decreased as the joint angle increased both in eccentric and in isometric actions but the decrease in aEMG towards extension was somewhat higher in eccentric actions as compared to isometric. It was concluded that the force measured during the first 10 degrees of eccentric contraction always exceeded the maximal voluntary isometric preactivation force regardless of the joint angle or of the movement velocity. When maximal voluntary preactivation preceded the stretch, the relative force potentiation seemed to be greater at higher stretching velocities (velocity dependent) while at lower preactivation levels, the velocity dependence was not observed. Decreased muscle activation and lower maximal voluntary force towards the end of the movement suggested inhibition during maximal voluntary eccentric actions.

Adult↗