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PubMed2003

Gender-specific knee extensor torque, flexor torque, and muscle fatigue responses during maximal effort contractions.

The purpose of this study was to examine gender differences in knee extensor and flexor peak torque, work, power, and muscle fatigue during maximal effort isokinetic contractions. Subjects included 19 healthy male and 20 healthy female volunteers. Following a dynamic warm-up period, subjects performed 30 reciprocal, concentric maximal knee extension and flexion contractions at a pre-set angular velocity of 3.14 rad x s(-1) on the Biodex Isokinetic Dynamometer. Values for knee extensor peak torque, work, and power were calculated for each repetition over an angular displacement of 1.05 rad for each repetition. The single highest repetition value for knee extensor and flexor peak torque, work, and power was then calculated relative to body mass (N x m x kg(-1), J x kg(-1), W x kg(-1)) and allometric-scaled (N x m x kg(-) (n), J x kg(-) (n), W x kg(-) (n)) units. The allometric-scaled units were derived from a log-log transformation and linear regression analysis to calculate the exponent to which body mass is raised. The rate of quadriceps femoris muscle fatigue was calculated as the decline in each isokinetic variable by the linear slope from the single highest repetition value through the 30th repetition, and by two different fatigue indexes. The results demonstrate higher knee extension and flexion peak torque, work, and power in absolute, relative, and allometric-scaled units for males compared to females. Males exhibited higher fatigue rates for both muscle groups of each isokinetic variable than females, as described by the slope and the fatigue index, except when adjusted for peak values via analysis of covariance. The findings suggest that during maximal-effort muscle contractions, males exhibit a higher susceptibility to muscle fatigue than females, a phenomenon that may be related to an inherent ability to generate higher knee extensor and flexor torque.

Adult↗

PubMed1995

Effects of local muscle fatigue on three-dimensional scapulohumeral rhythm.

The relationship of scapulothoracic motion to glenohumeral motion, commonly referred to as the scapulohumeral rhythm, has been the subject of numerous investigations. The purpose of this study was to assess the effects of localized muscular fatigue on three-dimensional scapulothoracic motion and the resulting scapulohumeral rhythm during elevation of the humerus in the plane of the scapula. A six-degree-of-freedom digitizing system (Metrecom(TM)) was used to define scapular and trunk reference frames, and three-dimensional Eulerian angles were determined for scapular motion for 0-135 degrees of humeral elevation before and after fatigue of the upper and lower trapezius muscles. Local muscle fatigue was determined using spectral analysis of electromyographic signals for the upper and lower trapezius muscles. The results demonstrated an average of 22% decrease in the median frequencies of the muscles sampled following resistive exercise, suggesting a state of local muscle fatigue. Concomitant with the fatigue was a selective decrease in scapulothoracic motion about two of the three scapular axes. RELEVANCE: Occupational and recreational conditions often require repetitive overhead elevations of the arms, resulting in muscular fatigue and various pathologies. During repetitive arm elevations the scapulohumeral rhythm or synchronization between the humerus and the scapula is balanced to allow the most efficient elevation of the arm. A better understanding of this much-discussed scapulohumeral rhythm and the changes induced by muscular fatigue may provide insight into the pathomechanics associated with shoulder dysfunction.

Journal Article↗

PubMed1986

A delivery-independent blood flow effect on skeletal muscle fatigue.

The hypothesis that hyperperfusion decreases muscle fatigue by increasing O2 and substrate delivery to the muscle was tested. Canine gastrocnemius-plantaris in situ preparations were stimulated at 5 Hz for 4 min during a free-flow control period and for 20 min during a pump-perfused experimental period. O2 delivery during these two periods was matched either by decreasing blood flow in animals breathing 100% O2 (high O2/low flow) [experimental-to-control ratio (E/C) = 0.97 + 0.02] or by increasing the blood flow in animals breathing 14% O2 (low O2/high flow) (E/C = 1.01 + 0.01). Plasma flow estimated from hematocrit to approximate substrate delivery was matched in the two contraction periods either by maintaining blood flow at the steady-state level (constant flow) (E/C = 0.98 + 0.10) or by increasing flow in animals with a dextran for 6% of blood volume exchange (dilute/high flow) (E/C = 1.02 + 0.02). E/C for initial developed tension was 1.00 + 0.02. Over 20 min, developed tension decreased 15.0 + 1.1% with low O2/high flow and 16.0 + 1.8% with dilute/high flow. Tension decreased by 28.0 + 3.0 and 27.8 + 1.5% with high O2/low flow and constant flow, respectively. Thus hyperperfusion decreased fatigue by a mechanism independent of increased O2 and substrate delivery.

Animals↗

PubMed2006

Influence of diaphragm and rib cage muscle fatigue on breathing during endurance exercise.

Inspiratory muscle fatigue (IMF) can develop during exhaustive exercise and cause tachypnea or rapid shallow breathing. We assessed the effects of rib cage muscle (RCM-F) and diaphragm fatigue (DIA-F) on breathing pattern and respiratory mechanics during high-intensity endurance exercise. Twelve healthy subjects performed a constant-load (85% maximal power) cycling test to exhaustion with prior IMF and a cycling test of similar intensity and duration without prior IMF (control). IMF was induced by resistive breathing and assessed by oesophageal and gastric twitch pressure measurements during cervical magnetic stimulation. Both RCM-F and DIA-F increased RCM and abdominal muscle force production during exercise compared to control. With RCM-F, tidal volume decreased while it increased with DIA-F. RCM-F was associated with a smaller increase in end-expiratory oesophageal pressure (i.e. decrease in lung volume) than DIA-F. These results suggest that RCM-F and not DIA-F is associated with rapid shallow breathing and that lowering the operating lung volume with DIA-F may help to preserve diaphragmatic function.

Adult↗

PubMed2003

Influence of environmental temperature on exercise-induced inspiratory muscle fatigue.

Exercise in the heat has detrimental effects on circulation that might negatively influence endurance performance. If blood is diverted away from the inspiratory muscles to the skin during exercise in the heat, exercise-induced inspiratory muscle fatigue might be exacerbated. Thus, we hypothesised that prolonged heavy endurance exercise in the heat would impair exercise performance and exacerbate inspiratory muscle fatigue compared to exercise in a thermo-neutral environment. Using a crossover design, seven male endurance trained subjects [mean (SEM) maximum oxygen uptake = 62.2 (1.5) ml x kg(-1) x min(-1)] were assigned at random to either a group that exercised in the heat at an ambient temperature of 35 degrees C (H) or a group that exercised in the cool at 15 degrees C (C). Maximum inspiratory mouth pressure at zero flow (P(0)), pressure normalised maximum relaxation rate (MRR/ P(0)), time constant for the pressure decay (tau), and maximum inspiratory flow at 30% P(0) (V(30)) were assessed immediately before and reassessed within 2, 30, and 60 min of completing a pre-loaded time trial [40 min at 65% peak power, plus approximately 30 min time trial] on a cycle ergometer. Group H completed the time trial 432 (135) s slower than group C [2285 (180) vs 1852 (122) s, respectively; Delta=24 (8)%, P=0.0094]. Repeat measurements within 2 min post-exercise revealed significant declines in P(0), MRR/ P(0), tau, and V(30) from baseline values, but no between-group differences were observed. In conclusion, heavy sustained exercise in the heat impaired subsequent time-trial performance but did not exacerbate inspiratory muscle fatigue in endurance-trained subjects.

Adult↗

PubMed1982

[An optimized filter band analyzer for quantification of localized muscle fatigue].

A filter bank analyzer is described which determines the central frequency of the electromyographic signal as a characteristic value and exhibits it continuously. In contrast with previous methods, this analyzer needs only a narrow frequency band and few filters to obtain exact quantitative results. The filter bank parameters are determined by adapting them to the amplitude spectra of electromyograms during fatiguing dynamic muscle work. Six parallel band-pass filters transmit the expected average spectral function, with minimized differences in the frequency range from 18 Hz to 140 Hz. The systematic error of the center frequency amounts to less than 0.5%, when using precision filters with high roll-off. An example compares the shift of center frequency method with the fatigue index of myoelectrical activity.

Electromyography↗

PubMed1996

The effects of muscle fatigue on and the relationship of arm dominance to shoulder proprioception.

It is hypothesized that proprioceptive information plays an important role in joint stabilization and that muscle fatigue may alter proprioceptive ability. The purpose of this study was to determine what effect shoulder muscle fatigue has on glenohumeral proprioception and to examine the relationship between arm dominance and shoulder proprioception. Eighty subjects without a history of glenohumeral pathology participated. Each was seated on an isokinetic dynamometer with a randomly selected shoulder positioned in 90 degrees of abduction and elbow flexion. With vision blinded, the arm was passively positioned in 75 degrees of external rotation for 10 seconds, then passively returned to the neutral starting position. Three trials each of active and passive repositioning (2 degrees/sec) were recorded. Following a fatigue protocol, both active and passive repositioning were reassessed. Testing order was randomized. A significant difference was detected between pre- and post-fatigue scores. No significant difference was detected between dominant and nondominant extremities. No relationship between arm dominance and shoulder proprioception was established. It is concluded that shoulder proprioception is diminished in the presence of shoulder muscle fatigue, suggesting clinical rehabilitation protocols must emphasize increasing muscular endurance.

Adult↗

PubMed1993

Cromakalim does not protect against skeletal muscle fatigue in an anaesthetized rat model of acute hindlimb ischaemia.

The effects of the potassium (K+) channel opener, cromakalim, on skeletal muscle performance were studied in a model of acute hindlimb ischaemia in the anaesthetized rat. Twitch contractions to direct electrical stimulation of the extensor digitorum and tibialis anterior skeletal muscles were recorded following administration of cromakalim (10-100 micrograms kg-1 i.v.) under normal and reduced whole limb blood flow. With normal blood flow, twitch responses (0.5 and 1 Hz) of the hindlimb skeletal muscles were sustained for > 30 min. Controlled adjustment of the perfusion pressure in the contralateral hindlimb to 45, 30 or 0 mm Hg by partial or total occlusion of the abdominal aorta produced a pressure-related fall in flow to the working hindlimb, and a corresponding increase in the rate of muscle fatigue. Cromakalim (10-100 micrograms kg-1 i.v.) produced a dose-dependent reduction in mean carotid arterial blood pressure, femoral arterial pressure and hindlimb vascular resistance together with an increase in iliac artery blood flow and heart rate, but did not attenuate skeletal muscle fatigue under the different conditions of muscle work and ischaemia employed. A similar profile was observed with levcromakalim (15 micrograms kg-1 i.v.), the active enantiomer of cromakalim. These results demonstrate that in the direct muscle-stimulated hindlimb of the anaesthetized rat, the K+ channel opener cromakalim does not prevent acute ischaemia-induced skeletal muscle fatigue. The previous observation that K+ channel openers improve nutritive blood flow in a chronic model of rat hindlimb ischaemia is not reflected by an improvement in muscle function in the present study.

Animals↗

PubMed2006

Investigations of back muscle fatigue by simultaneous 31P MRS and surface EMG measurements.

Investigations of back muscle fatigue are important for understanding the role of muscle strain in the development of low back pain. The aim of this contribution is to review the two main techniques used for in vivo investigations of metabolic and electrophysiological changes, namely magnetic resonance phosphorous spectroscopy ((31)P MRS) and surface electromyography (SEMG), and to report some of our recent results on simultaneous measurements using these techniques during isometric back-muscle contraction in volunteers. Since it appears that electrophysiological and metabolic factors are simultaneously involved in the processes of fatigue and muscle recovery during load application, simultaneous acquisition of complete information is quite promising for obtaining new insights into the metabolic origin of electrophysiological changes or vice versa. Performing these measurements simultaneously, however, is more intricate owing to the occurrence of signal artifacts caused by mutual signal interferences of both techniques. Besides these mutual disturbances, further experimental difficulties are related to spatial limitations within the bore of clinical whole-body high-field magnetic resonance (MR) systems (1.5 T) and the sensitivity of MR measurements to motion-induced artifacts. Our own experimental results are presented, and problems that occur using both techniques simultaneously, as well as possibilities to resolve them, are discussed. The results shed light on the interrelation of electrophysiological and metabolic changes during fatigue of the back muscle while performing an exercise.

Adenosine Triphosphate↗

PubMed1999

Wavelet analysis of electromyography for back muscle fatigue detection during isokinetic constant-torque exertions.

STUDY DESIGN: An investigation of the effects of human trunk extensor muscle fatigue on the temporal change in frequency content of the electromyogram as quantified using the Fourier and wavelet transforms during the performance of repetitive dynamic trunk extension. OBJECTIVE: To evaluate whether alterations in the Fourier and wavelet transform measures were consistent with a shift of the signal power to lower frequencies, and to determine which measures were more highly correlated with the decline in maximal trunk extension torque. SUMMARY OF BACKGROUND DATA: Objective assessment of trunk muscle fatigue is likely to play a more important role in the rehabilitation and prevention of low back injuries, given the association between lack of trunk muscle endurance and acquisition of low back pain. Validation of new methods designed to quantify the level of fatigue using the surface electromyogram is necessary before these techniques can be used in industrial rehabilitation settings. The wavelet transform is a recent development in the signal processing of electromyograms that shows promise as a method for assessment of fatigue. METHODS: Trunk muscle electromyograms obtained from study participants performing repetitive isokinetic trunk extension endurance tests were analyzed using the wavelet and the traditional Fourier methods. Trunk extension torque was controlled at 35% and 70% of the participants' maximal voluntary contraction while they exerted at 5 and 10 repetitions per minute. The decline in maximal trunk extension torque was measured once per minute. Linear regression quantified the rate of change in Fourier and wavelet measures caused by fatigue, whereas Pearson's correlation coefficient determined their association with the decline in maximum torque. RESULTS: Changes in the characteristics of the electromyogram were consistent with a shift to lower frequencies: The signal power at higher frequencies was reduced, whereas the power at lower frequencies was elevated. The amount of change was dependent on the task conditions (exertion level and repetition rate). The wavelet-based measures demonstrated as strong an association with the decline in maximal torque output as the Fourier-based measures. CONCLUSIONS: This study demonstrates that assessment of trunk muscle fatigue during isokinetic movementis possible using both Fourier and wavelet measurements. However, the methods were not as likely to change significantly during lower rates of exertion. These methods, when implemented in a controlled setting, may be used to document the rehabilitation process and guide preventive exercise training.

Adult↗

PubMed1985

Effect of inspiratory muscle fatigue on breathing pattern.

Our aim was to determine whether inspiratory muscle fatigue changes breathing pattern and whether any changes seen occur before mechanical fatigue develops. Nine normal subjects breathed through a variable inspiratory resistance with a predetermined mouth pressure (Pm) during inspiration and a fixed ratio of inspiratory time to total breath duration. Breathing pattern after resistive breathing (recovery breathing pattern) was compared with breathing pattern at rest and during CO2 rebreathing (control breathing pattern) for each subject. Relative rapid shallow breathing was seen after mechanical fatigue and also in experiments with electromyogram evidence of diaphragmatic fatigue where Pm was maintained at the predetermined level during the period of resistive breathing. In contrast there was no significant difference between recovery and control breathing patterns when neither mechanical nor electromyogram fatigue was seen. It is suggested that breathing pattern after inspiratory muscle fatigue changes in order to minimize respiratory sensation.

Adult↗

PubMed1994

Physical training of children with juvenile chronic arthritis. Effects on force, endurance and EMG response to localized muscle fatigue.

We examined force, endurance and the electromyographic response to muscle fatigue in ten children with juvenile chronic arthritis (JCA) and ten age-matched healthy controls before and after physical training. Our main finding was a reduced electromyographic response to localized muscle fatigue in the patient group. After training there was a tendency towards a normalized response pattern. A possible explanation may be selective type-II muscle fiber atrophy, and recovery of these fibers after training.

Adolescent↗

PubMed1988

Tracheal occlusion pressure: a simple index to monitor respiratory muscle fatigue during acute respiratory failure in patients with chronic obstructive pulmonary disease.

STUDY OBJECTIVE: To assess respiratory muscle fatigue in acute respiratory failure in patients with chronic obstructive pulmonary disease and evaluate its influence on weaning patients from mechanical ventilation. DESIGN AND PATIENTS: We studied the time course of tracheal occlusion pressure (P0.1) and high-to-low ratio of the diaphragmatic electromyogram in 16 patients in acute respiratory failure with chronic obstructive pulmonary disease. METHODS: All patients were intubated and studied during a 15-minute weaning period from ventilation. Minute ventilation (VE), arterial blood gases, P0.1 and high-to-low ratio of the diaphragm were measured every day from the onset to the end of acute failure (before extubation) at 5 and 15 minutes into the weaning period. The diaphragmatic electromyogram was recorded with an esophageal electrode and the high-to-low ratio of the electrical signal analyzed to assess diaphragmatic fatigue. MEASUREMENTS AND MAIN RESULTS: In all patients P0.1 was markedly increased (7.1 +/- 2.4 cm H2O, mean +/- SE) on the first day of acute failure and did not change during weaning. In 11 patients, P0.1 had decreased to 4.7 +/- 1.8 cm H2O (P less than or equal to 0.002) before extubation (which was done after 5 to 9 days). In these patients, the high-to-low ratio of the diaphragm decreased rapidly-during the first minutes of weaning on the first day of acute failure and remained low throughout weaning, whereas before extubation no decrease in high-to-low ratio was seen during weaning. In 5 patients, P0.1 did not change significantly from the onset of acute failure and the high-to-low ratio remained low before extubation. These 5 patients had to be reintubated within 2 to 6 days. In both groups of patients, VE did not change significantly from the first to last day of acute failure (10.3 +/- 3 compared with 10.7 +/- 2.1 min-1), whereas blood gases during room air breathing improved significantly from the first to last day of acute failure, respectively, in each group (arterial oxygen pressure [PaO2], 33.5 +/- 1.5 compared with 44 +/- 9 mm Hg (P less than or equal to 0.05) and PaO2 56 +/- 2.3 compared with 49 +/- 2 mm Hg (P less than 0.005). CONCLUSIONS: Extubation should not be done in patients with respiratory muscle fatigue despite improvement in arterial blood gases and clinical status; and P0.1 provides a valid and simple index to assess the likelihood of respiratory muscle fatigue.

Acute Disease↗

PubMed1995

Overview: potential role of segmental motor circuitry in muscle fatigue.

This chapter reviews several mechanisms that the CNS may use to mitigate muscle fatigue, including intrinsic motoneuron properties and feedback systems. The emphasis is on the effects of sensory inputs on spinal cord interneurons including: Renshaw cells; Ib inhibitory interneurons; interneurons mediating presynaptic inhibition; Ia inhibitory interneurons; and interneuronal networks constituting central pattern generators for locomotion. This exercise brings out how little is known about the operation of these circuits in dealing with muscle fatigue.

Animals↗

PubMed2001

Hypoxia/fatigue-induced degradation of troponin I and troponin C: new insights into physiologic muscle fatigue.

Conditions such as respiratory failure and cardiopulmonary arrest can expose the diaphragm to hypoxemia. In skeletal muscles, fatiguing stimulation renders muscles hypoxic, which has long been known to dramatically reduce muscle function. We have previously demonstrated that fatiguing stimulation under hypoxic conditions disrupts both the excitation-contraction coupling (ECC) process and the isometric contractile properties (ICP) in intact diaphragm muscle strips and the contractile properties of skinned fibers isolated from these muscles. Here we have analyzed the effects of intermittent fatiguing stimulation on specific muscle proteins in muscle strips from mouse diaphragms that have been exposed to hypoxia. We report for the first time that the effects of hypoxia-fatigue, namely to decrease maximal tetanic force, maximal calcium-activated force and calcium sensitivity of the mouse diaphragm muscle, are associated with the degradation of troponins TnI and TnC (Western blot analysis). The concentrations of TnT and actin did not change under these same conditions. Because troponins are integrally involved in regulating the interaction between actin and myosin during the cross-bridge cycle, the degradation of TnI and TnC may explain the effects of hypoxia-fatigue on the ICP. This interpretation is supported by the observations that extraction of troponins from control skinned fibers mimics the effects of hypoxia-fatigue on contractile function and that incorporation of native troponins into fibers isolated from hypoxic-fatigued muscles partially restores function.

Animals↗

PubMed2003

[Spectral analysis of electromyography of low back muscle fatigue induced by simulated driving].

OBJECTIVE: To evaluate the effects of different vibration frequency on the back muscle fatigue during simulated driving. METHODS: Thirty-six subjects performed three simulated driving experiments under three vertical vibration frequencies which were 1.8, 4.0, 6.0 Hz respectively and the driving time was 90 minutes. At the same time the electromyography of low back was recorded. RESULTS: The median frequencies calculated from the power spectrum were decreased exponentially under three vertical vibration frequencies, especially under 4.0 Hz vibration frequency. CONCLUSION: The 4.0 Hz vibration frequency has the most important effect on the back muscle fatigue under simulated driving condition.

Adult↗

PubMed1995

Muscle fatigue in early fibromyalgia.

OBJECTIVE: To compare the processes connected with muscle fatigue during prolonged exercise in patients with fibromyalgia (FM) with studies of healthy individuals. METHODS: Nine female patients with FM, all employed in full or part time, performed repetitive isometric contractions of the quadriceps muscles at 30% of maximal voluntary contraction (MVC) force in 6 s with 4 s rest between until exhaustion. RESULTS: The MVC and electrically stimulated tetanic forces fell continually and almost in parallel, indicating no central fatigue. The relaxation rate of the muscle became gradually faster as previously seen in healthy subjects. Plasma catecholamine concentrations remained unchanged during the exercise period, whereas a modest rise in blood lactate and plasma K+ was seen. The electromyographic (EMG) amplitude recorded during contractions increased gradually, while no changes were seen in EMG recorded in resting periods between contractions. Heart rate and VO2 rose gradually and a small exercise induced pain was recorded. CONCLUSION: Our study showed normal physiological muscle fatigue responses, except for the lack of increase in plasma catecholamine concentrations during exercise.

Adult↗

PubMed1989

Muscle fatigue, effects of training and disuse.

The study of muscle fatigue started about a century ago, when it was proposed that the observed decrease in force during prolonged voluntary contractions resulted from changes in central processes which reduced the motor drive. In the middle of this century it was noticed that this loss of force could not be restored by maximal electrical stimulation of the motor nerve, and thus the importance of peripheral mechanisms, located beyond the motoneuron, was emphasized. However, it was not clear which peripheral site was most important in decreasing the muscle mechanical capacity during fatigue. More recently, the comparison between peripheral failures during sustained and intermittent contractions indicated that recorded mechanical changes underwent deterioration which was not closely related to the recorded electrical changes. It was thus proposed that muscle intracellular processes dominate the force decrease during muscle fatigue. This concept has been substantiated by the study of standard fatigue tests performed in control, trained, and disused human muscles, as reviewed in this paper.

Action Potentials↗