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PubMed1993

The effect of isokinetic exercise on the relationship between blood lactate and muscle fatigue.

Exercise velocity may be an important variable in determining the amount of blood lactate accumulation during isokinetic exercise. The purpose of this study was to measure the effects of velocity-specific isokinetic exercise on blood lactate, muscle fatigue index, and rating of perceived exertion and to examine the relationship between blood lactate and muscle fatigue index. Ten experienced recreational weight trainers, aged 20-40 years, took part in a repeated measures design consisting of three separate treatments (constant angular velocity at 30, 120, and 300 degrees/sec performed at maximal effort for 1 minute by the right knee flexors and extensors). Rating of perceived exertion, blood lactate, and muscle fatigue index were measured in response to each treatment. Rating of perceived exertion was equal across all three speeds. Muscle fatigue and blood lactate increased significantly as the velocity of exercise increased. There was also a positive correlation coefficient (r = .82, < or = 0.01) between muscle fatigue index and blood lactate. The data suggested that the magnitude of muscle fatigue index and blood lactate responses are strongly dependent on the velocity of movement utilized during maximal isokinetic exercise, and there is a relationship between muscle fatigue index and blood lactate.

Adult↗
PubMed2005

Effects of distal and proximal arm muscles fatigue on multi-joint movement organization.

To investigate the strategies developed by the central nervous system to compensate for fatigue in muscles, we studied the changes in the relative mechanical contribution of the joint torques in a multi-joint movement following an isometric exhaustion test. Eighteen male subjects performed throws, moving the arm in the horizontal plane, before and after two fatigue protocols. Muscular fatigue was induced either in the distal (extensor digitorum communis) or in the proximal (triceps brachii) agonist muscle of the arm. The kinematic, kinetic and electromyographic parameters of the movement were analysed. The subjects produced two different coordinations following the fatigue protocols. In the distal fatigue condition, the wrist angular velocity was maintained by decreasing elbow active torque. In the proximal fatigue condition, the compensatory strategy involved increasing the contribution of the wrist. In fact, the control of elbow and wrist was modified in order to compensate for the different mechanical effects.

Adult↗
PubMed1988

The effects of muscle fatigue on the silent period of the masticatory muscles.

Thirteen healthy adults performed sustained clenching at 50% maximum clenching level judged electromyographically. Electromyograms were recorded from both anterior temporal and masseter muscles during clenching and the silent period latency and duration were measured. As the result of muscle fatigue, the silent period latency significantly decreased, whilst the duration significantly increased up to 3 min from the beginning of clenching.

Adult↗
PubMed2004

Neck flexor muscle fatigue is side specific in patients with unilateral neck pain.

Despite the evidence of greater fatigability of the cervical flexor muscles in neck pain patients, the effect of unilaterality of neck pain on muscle fatigue has not been investigated. This study compared myoelectric manifestations of sternocleidomastoid (SCM) and anterior scalene (AS) muscle fatigue between the painful and non-painful sides in patients with chronic unilateral neck pain. Myoelectric signals were recorded from the sternal head of SCM and the AS muscles bilaterally during sub-maximal isometric cervical flexion contractions at 25% and 50% of the maximum voluntary contraction (MVC). The time course of the mean power frequency, average rectified value and conduction velocity of the electromyographic signals were calculated to quantify myoelectric manifestations of muscle fatigue. Results revealed greater estimates of the initial value and slope of the mean frequency for both the SCM and AS muscles on the side of the patient's neck pain at 25% and 50% of MVC. These results indicate greater myoelectric manifestations of muscle fatigue of the superficial cervical flexor muscles ipsilateral to the side of pain. This suggests a specificity of the effect of pain on muscle function and hence the need for specificity of therapeutic exercise in the management of neck pain patients.

Adult↗
PubMed1996

[Peripheral muscle fatigue and ventilatory response to effort in chronic airflow limitation].

We aimed to analyze peripheral muscle fatigue and ventilatory pattern in a group of 28 individuals (12 health and 16 with chronic air flow limitation) performing incremental exercise. The level of exercise reached was significantly less for patients than for healthy subjects (107 +/- 30 W vs. 234 +/- 44 W). Minute ventilation (VE) was 54 +/- 15 l/min evolving linearly with no breaking pint, and the respiration pattern was tachypneic with high frequency (f) and low circulating volumen (VT) in patients. The ration Ti/Ttot did not change during exercise in either of the groups. Occlusion pressure (P0.1) was always higher in the patient group (p < 0.001) while mean inspiratory flow was higher at rest and at moderate levels of exercise (P < 0.05) but significantly lower at high levels (1.95 +/- 0.6 vs. 3.98 +/- 1 l.s-1). Muscle fatigue, defined as the fall in the H/L index in the electromyogram, appeared in 11/12 healthy subjects (H/L: 71 +/- 11%) and in 9/16 patients (H/L: 67 +/- 17%). There were no physical differences between the 2 groups of patients (those with and without fatigue). Patients with fatigue showed a more moderate degree of obstruction (FEV1 68 +/- 12% vs. 42 +/- 13% v. ref) with less airways impedance (p < 0.001) and hypoxia (SaO2 91.3% vs. 87%), and a better ventilatory response to exercise (VE 61 +/- 14 vs. 45 +/- 10 l/min) with a higher mean inspiratory flow (2.25 +/- 0.54 vs. 1.57 +/- 0.54 l.s-1) in spite of there being no differences in P0.1. The restricting factor was ventilatory limitation, although muscle fatigue appeared in 53% of the patients. Patients who experienced muscle fatigue had less obstruction and better ventilatory response to exercise.

Adult↗
PubMed1999

Changes in movement final position associated with agonist and antagonist muscle fatigue.

We have tested the hypothesis that agonist and antagonist muscle fatigue could affect the final position of rapid, discrete movements. Six subjects performed consecutive elbow flexion and extension movements between two targets, with their eyes closed prior to, and after fatiguing the elbow extensor muscles. The results demonstrate that elbow extension movements performed in the post-test period systematically undershot the final position as compared to pre-test movements. However, attainment of the aimed final position in elbow flexion movements was unaffected by fatiguing of the extensor muscles. Undershoot of the final position obtained in extension movements was associated with agonist muscle fatigue, a result that was expected from the point of view of current motor control theories, and that could be explained by a reduced ability of the shortening muscle to exert force. On the other hand, the absence of the expected overshoot of the final position when the antagonist is fatigued, indicates the involvement of various reflex and/or central mechanisms operating around the stretched muscle that could contribute to returning the limb to the standard final position after a brief prominent overshoot.

Adult↗
PubMed1997

Inspiratory muscle fatigue following running to volitional fatigue: the influence of baseline strength.

Respiratory muscle fatigue has been demonstrated following short-term exercise to volitional fatigue, as well as following prolonged submaximal exercise. There is some suggestion that the respiratory muscles of 'athletic' individuals have superior strength and greater fatigue resistance but it is not known whether inspiratory muscle strength influences fatigueability of the inspiratory muscles. The present study examined this question in 24 moderately trained young men. Inspiratory muscle strength was measured at residual volume using a hand held Mouth Pressure Meter before and after an incremental, multistage shuttle run to volitional fatigue. Following the run, there was a significant fall in inspiratory mouth pressures (-10.5 +/- SD 8.2%; p < 0.001 Pre- vs Post Pipeak). The subjects with the weakest inspiratory muscles exhibited significantly greater fatigue than those with the strongest (-17.0 +/- SD 7.8% c.f. 6.8 +/- SD 4.4% for the 25th and 75th percentiles respectively p < 0.01). These data support existing evidence that the respiratory muscles fatigue following high intensity exercise. In addition, they provide new evidence that this phenomenon occurs in moderately trained young men and that the severity of the fatigue is related to the baseline strength of the inspiratory muscles.

Adult↗
PubMed1986

Muscle membrane excitation and impulse propagation velocity are reduced during muscle fatigue.

In order to determine whether or not impulse propagation was impaired during muscle fatigue, evoked muscle compound potentials (MCP) and twitches were recorded, both before and after fatigue, from the first dorsal interosseus (FDI), adductor pollicis (AP), and anterior tibialis (AT) muscles following supramaximal ulnar and peroneal nerve stimulation, respectively. The muscles were fatigued by maintaining maximum voluntary isometric, index finger abduction, thumb adduction, or ankle dorsiflexion for 1-5 minutes. FDI was most markedly altered, with reduced MCP amplitude (mean 32%) and increased MCP duration (mean 47%) after only 1 minute. After fatigue of longer duration (3-5 minutes), there were corresponding reductions in both the MCP amplitudes and the twitch tensions recorded from both the FDI and ankle dorsiflexors. We conclude that (1) a reduction in both the level of excitation and impulse propagation velocity of muscle membranes occurs during muscle fatigue, and (2) the magnitude of this reduced membrane function and its contribution to the mechanisms underlying fatigue depend both on the duration and degree of fatigue, as well as on the intrinsic properties of the particular muscle.

Cell Membrane Permeability↗
PubMed2002

The effect of massage on localized lumbar muscle fatigue.

BACKGROUND: There is not enough evidence to support the efficacy of massage for muscle fatigue despite wide utilization of the modality in various clinical settings. This study investigated the influence of massage application on localized back muscle fatigue. METHODS: Twenty-nine healthy subjects participated in two experimental sessions (massage and rest conditions). On each test day, subjects were asked to lie in the prone position on a treatment table and perform sustained back extension for 90 seconds. Subjects then either received massage on the lumbar region or rested for a 5 minute duration, then repeated the back extension movement. The median frequency (MDF), mean power frequency (MNF), and root mean square (RMS) amplitude of electromyographic signals during the 90 second sustained lumbar muscle contraction were analyzed. The subjective feeling of fatigue was then evaluated using the Visual Analogue Scale (VAS). RESULTS: MDF and MNF significantly declined with time under all conditions. There was no significant difference in MDF, MNF or RMS value change between before and after massage, or between rest and massage conditions. There was a significant increase in fatigue VAS at the end of the 2nd back extension with rest condition. There was a significant difference in fatigue VAS change between massage and rest condition. CONCLUSIONS: A significant difference was observed between massage and rest condition on VAS for muscle fatigue. On EMG analysis, there were no significant differences to conclude that massage stimulation influenced the myoelectrical muscle fatigue, which is associated with metabolic and electrical changes.

Adult↗
PubMed2006

Predictive model of muscle fatigue after spinal cord injury in humans.

The fatigability of paralyzed muscle limits its ability to deliver physiological loads to paralyzed extremities during repetitive electrical stimulation. The purposes of this study were to determine the reliability of measuring paralyzed muscle fatigue and to develop a model to predict the temporal changes in muscle fatigue that occur after spinal cord injury (SCI). Thirty-four subjects underwent soleus fatigue testing with a modified Burke electrical stimulation fatigue protocol. The between-day reliability of this protocol was high (intraclass correlation, 0.96). We fit the fatigue index (FI) data to a quadratic-linear segmental polynomial model. FI declined rapidly (0.3854 per year) for the first 1.7 years, and more slowly (0.01 per year) thereafter. The rapid decline of FI immediately after SCI implies that a "window of opportunity" exists for the clinician if the goal is to prevent these changes. Understanding the timing of change in muscle endurance properties (and, therefore, load-generating capacity) after SCI may assist clinicians when developing therapeutic interventions to maintain musculoskeletal integrity.

Adolescent↗
PubMed2002

Blood flow and muscle fatigue in SCI individuals during electrical stimulation.

Our purpose was to measure blood flow and muscle fatigue in chronic, complete, spinal cord-injured (SCI) and able-bodied (AB) individuals during electrical stimulation. Electrical stimulation of the quadriceps muscles was used to elicit similar activated muscle mass. Blood flow was measured in the femoral artery by Doppler ultrasound. Muscle fatigue was significantly greater (three- to eightfold, P < or = 0.001) in the SCI vs. the AB individuals. The magnitude of blood flow was not significantly different between groups. A prolonged half-time to peak blood flow at the beginning of exercise (fivefold, P = 0.001) and recovery of blood flow at the end of exercise (threefold, P = 0.009) was found in the SCI vs. the AB group. In conclusion, the magnitude of the muscle blood flow to electrical stimulation was not associated with increased muscle fatigue in SCI individuals. However, the prolonged time to peak blood flow may be an explanation for increased fatigue in SCI individuals.

Adult↗
PubMed1990

Muscle fatigue in McArdle's disease. Muscle fibre conduction velocity and surface EMG frequency spectrum during ischaemic exercise.

The origin of fatigue in McArdle's disease is still a matter of debate. Both a reduction of muscle membrane excitability and failure of excitation-contraction (E-C) coupling have been suggested as causes. We performed intermittent isometric biceps brachii contractions (80% maximal voluntary contraction, rate 30/min) under local ischaemia in 5 McArdle's disease patients and 26 healthy controls. Our results show that in McArdle's disease the exerted force is less, the surface EMG (SEMG) amplitude steadily increases, and that the power density spectrum (PDS) shifts to lower frequencies, the latter without significant differences when compared with normals. The most important finding is that muscle membrane excitability remains unimpaired during ischaemic exercise, establishing a dominant role for intramuscular lactic acid formation in the reduction of muscle fibre conduction velocity seen in normal subjects. As is indicated by the shift of the PDS towards lower frequencies, as well as by the increase in SEMG amplitude, it can be concluded that during ischaemic exercise in patients with myophosphorylase deficiency, fatigue occurs without alterations in muscle membrane excitability and is due to a failure of E-C coupling.

Adolescent↗
PubMed1997

Respiratory muscle fatigue during simulated air combat maneuvering (SACM).

HYPOTHESIS: This study tested the hypothesis that respiratory muscle fatigue occurs during a simulated air combat maneuver (SACM) centrifuge profile. METHODS: Six subjects (four males, two females) were exposed to a SACM consisting of alternating +4 Gz to +7 Gz plateaus until volitional fatigue. Electrical activities of the diaphragm, scalene, intercostal and external oblique muscles were monitored along with esophageal pressure and ventilation. RESULTS: SACM times averaged 358 +/- 115 s. The mean frequency of the electromyographic signal of the diaphragm and scalenes during inspiration, and the intercostals during the static expiratory portion of the anti-G straining maneuver (AGSM), decreased significantly (p < 0.05) over the course of the SACM by about 9%, 10% and 4%, respectively, indicating muscle fatigue. Esophageal pressure (PES) during the straining portion of the AGSM decreased significantly from 72 +/- 20 to 66 +/- 21 mmHg (mean +/- SD). Ventilation increased significantly both at +4 Gz and +7 Gz (32 +/- 16 L.min-1 to 56 +/- 19 L.min-1 at +4 Gz and 27 +/- 5 to 35 +/- 9 L.min-1 at +7 Gz) over time. PES during a maximal AGSM at +1.4 Gz (baseline) was decreased post- vs. pre-SACM (p = 0.0575). PES exerted during a maximal static inspiratory maneuver at residual lung volume was not changed after the SACM. Inspiratory work increased significantly during the SACM. The elastance of the respiratory system did not change during the SACM, but it was significantly increased when tested after the SACM. CONCLUSION: Increased inspiratory work, decreased pressure generation during a maximal AGSM and EMG frequency shifts suggest respiratory muscle fatigue coincides with the termination of SACM.

Acceleration↗
PubMed1996

Does calf-muscle fatigue affect standing balance?

The purpose of this study was to find out whether fatiguing calf-muscle exercise affects postural sway during standing. Thirteen healthy subjects with a mean age of 25 years participated. Body sway in one leg stance was measured on a force plate before and after fatiguing exercises of the calf muscles of the subject's right leg. Repeated measurements for up to 10 min after exercises showed no increase of body sway. The results indicate that postural control in quiet standing can be maintained by compensatory mechanisms activated during muscle fatigue. A significant decrease of body sway over time on the non-fatigued leg, indicated a learning effect. A similar decrease was not observed on the fatigued leg, indicating interference of compensatory mechanisms on learning.

Adolescent↗
PubMed1995

Changes in reciprocal and transjoint inhibition induced by muscle fatigue in man.

The effects of localised muscle fatigue on group I reflex pathways were studied in the human upper limb. Activation of group I afferents originating from biceps and extensor carpi radialis (ECR) resulted in an inhibition of flexor carpi radialis (FCR) motoneurones, probably through a disynaptic pathway. Reciprocal inhibition (from ECR to FCR) and transjoint inhibition (from biceps to FCR) were compared before and during localised fatigue induced in the muscle from which group I afferents originated. Fatigue of wrist extensors did not modify the reciprocal inhibition, while during fatigue of elbow flexors the transjoint inhibition was less pronounced. This striking difference between reciprocal and transjoint inhibition is discussed in relation to the pattern of diffusion of voluntary contractions during fatigue in the human upper limb.

Adult↗
PubMed2004

Effects of modulators of sarcoplasmic Ca2+ release on the development of skeletal muscle fatigue.

The reduced release of Ca2+ from sarcoplasmic reticulum (SR) is considered a major determinant of muscle fatigue. In the present study, we investigated whether the presence of dantrolene, an established inhibitor of SR Ca2+ release, or caffeine, a drug facilitating SR Ca2+ release, modifies muscle fatigue development. Accordingly, the effects of Ca2+ release modulators were analyzed in vitro in mouse fast-twitch [extensor digitorum longus (EDL)] and slow-twitch (soleus) muscles, fatigued by repeated short tetani (40 Hz for 300 ms, 0.5 s(-1) in soleus and 60 Hz for 300 ms, 0.3 s(-1) in EDL, for 6 min). Caffeine produced a substantial increase of tetanic tension of both EDL and soleus muscles, whereas dantrolene decreased tetanic tension only in EDL muscle. In both EDL and soleus muscles, 5 microM dantrolene did not affect fatigue development, whereas 20 microM dantrolene produced a positive staircase during the first 3 min of stimulation in EDL muscle and a slowing of fatigue development in soleus muscle. The development of the positive staircase was abolished by the addition of 15 microM ML-7, a selective inhibitor of myosin light chain kinase. On the other hand, caffeine caused a larger and faster loss of tension in both EDL and soleus muscles. The results seem to indicate that the changes in fatigue profile induced by caffeine or dantrolene are mainly due to the changes in the initial tetanic tension caused by the drugs, with the resulting changes in the level of contraction-dependent factors of fatigue, rather than to changes in the SR Ca2+ release during fatigue development.

Animals↗