Perceived Muscle Fatigue Research Articles

Muscle endurance, neuromuscular fatigability, and cognitive control during prolonged dual-task in people with chronic obstructive pulmonary disease: a case–control study

Abstract Purpose Recent studies suggest that, compared to healthy individuals, people with chronic obstructive pulmonary disease (pwCOPD) present a reduced capacity to perform cognitive-motor dual-task (CMDT). However, these studies were focused on short-duration CMDT offering limited insight to prolonged CMDT inducing fatigue, which can be encountered in daily life. The present study aimed to explore the effect of adding a cognitive task during repeated muscle contractions on muscle endurance, neuromuscular fatigability, and cognitive control in pwCOPD compared to healthy participants. Methods Thirteen pwCOPD and thirteen age- and sex-matched healthy participants performed submaximal isometric contractions of the knee extensors until exhaustion in two experimental sessions: (1) without cognitive task and (2) with a concurrent working memory task (i.e., 1-back task). Neuromuscular fatigability (as well as central and peripheral components measured by peripheral magnetic stimulation), cognitive performance, and perceived muscle fatigue were assessed throughout the fatiguing tasks. Results Independently to the experimental condition, pwCOPD exhibited lower muscle endurance compared to healthy participants (p = 0.039), mainly explained by earlier peripheral fatigue and faster attainment of higher perceived muscle fatigue (p < 0.05). However, neither effect of cognitive task (p = 0.223) nor interaction effect (group × condition; p = 0.136) was revealed for muscle endurance. Interestingly, cognitive control was significantly reduced only in pwCOPD at the end of CMDT (p < 0.015), suggesting greater difficulty for patients with dual tasking under fatigue. Conclusion These findings provide novel insights into how and why fatigue develops in COPD in dual-task context, offering a rationale for including such tasks in rehabilitation programs.

Effect of physical activity education on shoulder girdle pain and muscle strength in participants with fibromyalgia: a pilot experimental study.

In patients with fibromyalgia, exercise and education are recommended to decrease pain level and improve pain management. The latest scientific evidence recommends to focus interventions on the upper limb. The aim of this pilot study was to compare the immediate effect of physical activity education vs. a control group on pain and muscle capacity in fibromyalgia patients. Fifty-six participants with fibromyalgia were randomized into an experimental group and a control group. The intervention consisted in watching a five-minute video that provided information about fibromyalgia, pain, kinesiophobia and physical activity. The control group watched a neutral five-minute video about beavers in Quebec. Following the video, participants performed a muscular fatigue task consisting of a repeated unilateral shoulder abduction task. At baseline and following the muscular fatigue task, maximal voluntary contraction (MVC) in shoulder abduction was assessed as well as pain level and pressure pain threshold (PPT) in the upper limb. Electromyographic activity was also assessed for upper trapezius and middle deltoid muscles. Two-way repeated measures analysis of variance was used to compare the MVC, PPT, and pain level before and after the muscular fatigue task between groups. The experimental group showed a significantly lower increase in pain than the control group in the middle deltoid muscle (p = 0.002) when assessed by verbal pain rating scale. No significant interaction or main effect of Group and Time were observed for the pain level at the upper trapezius and elbow extensor muscles nor for any of the PPT measures. According to electromyographic data, the median frequency values indicate that neither group experienced muscle fatigue during the repeated contraction task. The preliminary results suggest that a short physical activity education video positively influenced middle deltoid pain following repeated abduction in participants with fibromyalgia. Electromyographic analysis showed no evidence of objective muscle fatigue, suggesting that there might be a partial disconnection between the perception of muscle fatigue and the physiological biomarkers associated with muscle fatigue.

Assessment of Self-report, Palpation, and Surface Electromyography Dataset During Isometric Muscle Contraction

Measuring muscle fatigue involves assessing various components within the motor system. While subjective and sensor-based measures have been proposed, a comprehensive comparison of these assessment measures is currently lacking. This study aims to bridge this gap by utilizing three commonly used measures: participant self-reported perceived muscle fatigue scores, a sports physiotherapist’s manual palpation-based muscle tightness scores, and surface electromyography sensors. Compensatory muscle fatigue occurs when one muscle group becomes fatigued, leading to the involvement and subsequent fatigue of other muscles as they compensate for the workload. The evaluation of compensatory muscle fatigue focuses on nine different upper body muscles selected by the sports physiotherapist. With a cohort of 30 male subjects, this study provides a valuable dataset for researchers and healthcare practitioners in sports science, rehabilitation, and human performance. It enables the exploration and comparison of diverse methods for evaluating different muscles in isometric contraction.

Targeted Electrical Stimulation of the Superior Laryngeal Nerve – A Potential Treatment for Dysphagia in ALS

Electrical stimulation (ES) is a treatment for swallowing impairment (dysphagia) that uses surface electrodes on the anterior neck to repeatedly contract and strengthen swallowing musculature without evoking swallows. This treatment approach is generally avoided in ALS patients due to concerns over rapid muscle fatigue that may further compromise swallowing, breathing, and airway protection. However, swallowing is a sensorimotor reflex that relies on several “upstream” sensory, motor, and interneuron components that are also affected by ALS. We hypothesize that ES can be optimized for ALS by selectively stimulating the superior laryngeal nerve (SLN) to activate and treat the entire swallow reflex circuitry, rather than only the swallowing muscles. Our rationale is based on general knowledge that SLN stimulation reliably evokes swallowing in experimental studies. Here, our translational work establishes a safe and reliable ES‐SLN protocol in a mouse model of ALS with dysphagia, and then adapts the protocol for use in humans. For protocol development, ALS mice (transgenic SOD1‐G93A) underwent an invasive survival surgery at 6 months of age (clinical disease onset) for 30 minutes of direct ES‐SLN based on our prior work: 40 Hz; anodal, charge balanced rectangular pulses (400 µs pulse width, 400 µs interphase delay); up to 800 uA intensity and continuous trains of 20‐seconds ON, 10‐seconds OFF. Respiratory rate was monitored via an abdominal pneumatic sensor. Swallowing function was assessed via monthly videofluoroscopy. For translation to humans we used a noninvasive transcutaneous ES (tES) approach in five healthy adults (18‐30 years; 3 F, 2 M) using identical stimulus parameters as mice, except with a shorter pulse duration (100 µs pulse width, 25 μs interphase delay) to eliminate perceived muscle fatigue and higher stimulus intensity (up to 10 mA). Physiological monitoring (pulse oximetry, respiratory and heart rate) occurred throughout the 30‐minute session. Results showed that direct ES‐SLN in mice consistently evoked 2‐4 swallows per 20 second stimulus train without decay or adverse effects on respiratory rate (p>0.05). Moreover, this single treatment session nearly preserved lick and swallow rates at disease end stage. In humans, tES‐SLN reliably evoked 3‐6 saliva swallows per 20 second stimulus train without decay or adverse effects on physiological measures (p>0.05). However, trials were successful only in females likely due to differences in male anatomy and electrical impedance that we are troubleshooting. This preliminary work demonstrates ES can be adapted for targeted, noninvasive SLN stimulation to evoke swallowing in humans. Moreover, our preliminary work with ALS mice suggests an untapped therapeutic benefit of ES‐SLN, which provides rationale for proceeding with clinical trials for ALS patients as well as other neurological diseases. Continued investigations in mice will be essential to understand the treatment mechanisms of SLN stimulation for further optimization.

Severe acute hypoxia impairs recovery of voluntary muscle activation after sustained submaximal elbow flexion.

The purpose of this study was to determine how severe acute hypoxia alters neural mechanisms during, and following, a sustained fatiguing contraction. Fifteen participants (25±3.2years, six female) were exposed to a sham condition and a hypoxia condition where they performed a 10min elbow flexor contraction at 20% of maximal torque. For hypoxia, peripheral blood oxygen saturation ( ) was titrated to 80% over a 15min period and maintained for 2h. Maximal voluntary contraction torque, EMG root mean square, voluntary activation, rating of perceived muscle fatigue, and corticospinal excitability (motor-evoked potential) and inhibition (silent period duration) were then assessed before, during and for 6min after the fatiguing contraction. No hypoxia-related effects were identified for neuromuscular variables during the fatigue task. However, for recovery, voluntary activation assessed by motor point stimulation of biceps brachii was lower for hypoxia than sham at 4min (sham: 89%±7%; hypoxia: 80%±12%; P=0.023) and 6min (sham: 90%±7%; hypoxia: 78%±11%; P=0.040). Similarly, voluntary activation (P=0.01) and motor-evoked potential area (P=0.002) in response to transcranial magnetic stimulation of the motor cortex were 10% and 11% lower during recovery for hypoxia compared to sham, respectively. Although an of 80% did not affect neural activity during the fatiguing task, motor cortical output and corticospinal excitability were reduced during recovery in the hypoxic environment. This was probably due to hypoxia-related mechanisms involving supraspinal motor circuits. KEY POINTS: Acute hypoxia has been shown to impair voluntary activation of muscle and alter the excitability of the corticospinal motor pathway during exercise. However, little is known about how hypoxia alters the recovery of the motor system after performing fatiguing exercise. Here we assessed hypoxia-related responses of motor pathways both during active contractions and during recovery from active contractions, with transcranial magnetic stimulation and motor point stimulation of the biceps brachii. Fatiguing exercise caused reductions in voluntary activation, which was exacerbated during recovery from a 10min sustained elbow flexion in a hypoxic environment. These results suggest that reductions in blood oxygen concentration impair the ability of motor pathways in the CNS to recover from fatiguing exercise, which is probably due to hypoxia-induced mechanisms that reduce output from the motor cortex.

Enhancing Virtual Rehabilitation in Upper Limbs With Biocybernetic Adaptation: The Effects of Virtual Reality on Perceived Muscle Fatigue, Game Performance and User Experience

Virtual rehabilitation has been used during decades to provide a more personalized, controlled, and enjoyable experience on upper-limb motor rehabilitation. Since novel virtual reality (VR) technologies are now accessible and highly immersive, the challenge for a wide dissemination of virtual rehabilitation in clinical scenarios has shifted from the hardware robustness to the software intelligence. A sophisticated technique that provides physiological intelligence to novel human-computer interaction (HCI) applications is biocybernetic adaptation. The concept emerges from the electrophysiological computing field, and it proposes using body signals to detect human states (e.g. workload or fatigue) and modulate the virtual activity accordingly. This paper evaluates the effects of using biocybernetic adaptation in a virtual rehabilitation game that aims to encourage users to exert at a desirable intensity level while interacting with the virtual environment. The system relies on surface-electromyography (sEMG) signals to detect fatigue levels in real-time and adapt the game challenge dynamically. Perceived fatigue levels, game user experience, and game performance parameters are assessed after playing the game, considering two different visualization modalities: non-immersive (conventional flat screen) and immersive (VR headset). Results revealed how the biocybernetic system in the immersive condition not only produced lower levels of perceived fatigue compared with the non-immersive, but also, created a more enjoyable and positive experience in a controlled experiment with 24 healthy subjects. Moreover, participants in the immersive condition showed a better performance in the virtual game and higher usability levels scored by users compared with the non-immersive condition. To conclude, we highlight the importance of combining novel immersive approaches with physiologically aware systems to enhance the benefits of virtual rehabilitation therapies.

Functional Electrical Stimulation—A New Therapeutic Approach to Enhance Exercise Intensity in Chronic Obstructive Pulmonary Disease Patients: A Randomized, Controlled Crossover Trial

ObjectiveTo evaluate the effect of quadriceps functional electrical stimulation (FES)-cycling on exertional oxygen uptake (V˙o2) compared with placebo FES-cycling in patients with chronic obstructive pulmonary disease (COPD). DesignA randomized, single-blind, placebo-controlled crossover trial. SettingPulmonary rehabilitation department. ParticipantsConsecutive patients (N=23) with COPD Global Initiative for Chronic Obstructive Lung Disease stage 2, 3, or 4 (mean forced expiratory volume during the first second, 1.4±0.4L [50.3% predicted]) who had recently begun a respiratory rehabilitation program. InterventionTwo consecutive 30-minute sessions were carried out at a constant load with active and placebo FES-cycling. Main Outcome MeasuresThe primary outcome was mean V˙o2 during the 30-minute exercise session. The secondary outcomes were respiratory gas exchange and hemodynamic parameters averaged over the 30-minute endurance session. Lactate values, dyspnea, and perceived muscle fatigue were evaluated at the end of the sessions. ResultsFES-cycling increased the physiological response more than the placebo, with a greater V˙o2 achieved of 36.6mL/min (95% confidence interval [CI], 8.9–64.3mL/min) (P=.01). There was also a greater increase in lactate after FES-cycling (+1.5mmol/L [95% CI, .05–2.9mmol/L]; P=.01). FES-cycling did not change dyspnea or muscle fatigue compared with the placebo condition. ConclusionsFES-cycling effectively increased exercise intensity in patients with COPD. Further studies should evaluate longer-term FES-cycling rehabilitation programs.

Cardiorespiratory Response to Different Exercise Tests in Interstitial Lung Disease.

The 6-min stepper test (6MST) has been used as an alternative to the 6-min walk test (6MWT) to assess exercise tolerance in patients with interstitial lung disease (ILD). Recent data suggest that the tests may involve different energy pathways and cardiorespiratory responses. We thus aimed to compare the cardiorespiratory responses of ILD patients during the 6MWT and the 6MST. Thirty-one patients with ILD were randomized to perform both tests in the order 6MST → 6MWT (n = 16) or 6MWT → 6MST (n = 15). Gas exchange, HR, and pulse O2 saturation (SpO2) were measured continuously, and dyspnoea, leg discomfort, and blood lactate concentration were assessed before and immediately after each test. Oxygen uptake (V˙O2) was lower (P = 0.002) and respiratory equivalent ratio for O2 (V˙E/V˙O2) and RER were higher (both P < 0.001) during the 6MST compared with the 6MWT. The 6MST was also associated with higher blood lactate concentrations (6MST, 4.16 ± 1.95 mmol·L; 6MWT, 2.84 ± 1.17 mmol·L; P = 0.01), higher leg discomfort scores (6MST 5 ± 3 points, 6MWT 3 ± 2 points; P < 0.001), and smaller decreases in SpO2 (6MST -5% ± 5%, 6MWT -9% ± 6%; P < 0.001). ILD patients exhibited greater ventilatory responses and lower arterial O2 desaturation during the 6MST compared with the 6MWT. The higher lactate concentrations and perceived muscle fatigue observed during the 6MST may indicate the presence of intertest differences in active muscle metabolism that could contribute to the distinct cardiorespiratory responses.

The relationship between work productivity and acute responses at different levels of production standard times

Work productivity is typically associated with production standard times. Harder production standards generally result in higher work productivity. However, the tasks become more repetitive in harder production standard time and workers may be exposed to higher rates of acute responses which will lead to higher risks of contracting work-related musculoskeletal disorders (WMSDs). Hence, this paper seeks to investigate the relationship between work productivity and acute responses at different levels of production standard times. Twenty industrial workers performed repetitive tasks at three different levels of production standard time (PS), corresponding to “normal (PSN)”, “hard (PSH)” and “very hard (PSVH)”. The work productivity and muscle activity were recorded along these experimental tasks. The work productivity target was not attainable for hard and very hard production standard times. This can be attributed to the manifestations of acute responses (muscle activity, muscle fatigue, and perceived muscle fatigue), which increases as the production standard time becomes harder. There is a strong correlation between muscle activity, perceived muscle fatigue and work productivity at different levels of production standard time. The relationship among these variables is found to be significantly linear (R = 0.784, p < 0.01). The findings of this study are indeed beneficial to assess the existing work productivity of workers and serves as a reference for future work productivity planning in order to minimize the risk of contracting WMSDs.

Acute effects of low-level laser therapy irradiation on blood lactate and muscle fatigue perception in hospitalized patients with heart failure-a pilot study.

The objective of the present study is to evaluate the acute effects of low-level laser therapy (LLLT) on functional capacity, perceived exertion, and blood lactate in hospitalized patients with heart failure (HF). Patients diagnosed with systolic HF (left ventricular ejection fraction <45%) were randomized and allocated prospectively into two groups: placebo LLLT group (n = 10)-subjects who were submitted to placebo laser and active LLLT group (n = 10)-subjects who were submitted to active laser. The 6-min walk test (6MWT) was performed, and blood lactate was determined at rest (before LLLT application and 6MWT), immediately after the exercise test (time 0) and recovery (3, 6, and 30min). A multi-diode LLLT cluster probe (DMC, São Carlos, Brazil) was used. Both groups increased 6MWT distance after active or placebo LLLT application compared to baseline values (p = 0.03 and p = 0.01, respectively); however, no difference was observed during intergroup comparison. The active LLLT group showed a significant reduction in the perceived exertion Borg (PEB) scale compared to the placebo LLLT group (p = 0.006). In addition, the group that received active LLLT showed no statistically significant difference for the blood lactate level through the times analyzed. The placebo LLLT group demonstrated a significant increase in blood lactate between the rest and recovery phase (p < 0.05). Acute effects of LLLT irradiation on skeletal musculature were not able to improve the functional capacity of hospitalized patients with HF, although it may favorably modulate blood lactate metabolism and reduce perceived muscle fatigue.

The Effects of Cold Water Immersion on Postexercise Muscle Soreness and Fatigue

Clinical Question:Is there evidence to suggest continuous cold water immersion (CWI) as a postexercise recovery intervention is more effective at reducing perceived muscle fatigue or soreness as measured using a Visual Analog Scale (VAS) when compared with passive rest in physically active adults?Summary of Key Findings:A systematic search of the literature produced 124 studies, with two randomized controlled trials and two cross-over studies meeting the inclusion criteria.Clinical Bottom Line:There is inconsistent, limited-quality evidence to support that the use of CWI postexercise is more effective at reducing perceived muscle fatigue or soreness in physically active adults when compared with passive rest. The results of the included studies were inconsistent regarding the application of continuous CWI for 10–14 min to reduce perceived muscle fatigue and soreness when compared with passive rest. The good-quality evidence found no difference between conditions and the three limited-quality studies identified differences between the conditions.

EFFECTS OF TRADITIONAL THAI MASSAGE ON FREE THROW ACCURACY IN BASKETBALL ATHLETES

The free throw is the single most important shot in the game of basketball. The factors influencing the ability of the basketball free throw accuracy consisted of skill, standing balance, muscle fatigue, and concentration. Massage has been used for reducing muscle fatigue in sports which may affect standing balance, concentration, and free throw accuracy. However, there were no research studies available on these regards. The aim of this study was to determine the effects of traditional Thai massage (TTM) on standing balance, muscle fatigue, concentration, and basketball free throw accuracy. Thirty male basketball athletes were randomly allocated into either traditional Thai massage (TTM) group or Control (C) group after which they were swabbed to receive the other one with a 2-week washed out period. Standing balance, perceived muscle fatigue, concentration, and basketball free throw accuracy were measured before and the next day after receiving either 1-hour session of TTM or rest. The study found that balance and concentration were significantly increased (p<0.05) only in the TTM group. Fatigue was significantly decreased (p<0.05) in TTM group while it was significantly increased (p<0.05) in C group. Between-group comparison revealed that standing balance and fatigue were significantly different (p<0.05). However, free throw accuracy was not changed in both within- and between- groups comparison. We conclude that a 1-hour session TTM could increase standing balance, decrease muscle fatigue, and increase concentration but could not affect free throw accuracy in basketball athletes.

Formulation of perceived muscle fatigue based on elbow flexion task

Formulation of perceived muscle fatigue based on elbow flexion task

Older adults present better back endurance than young adults during a dynamic trunk extension exercise

Poor back endurance is a predictor of low back pain. Few studies have investigated back muscle fatigue in older people. The purpose of this study was to compare the back muscle fatigue by endurance time and perceived effort between young and older adults during dynamic exercise. Sixteen older and 16 young adults, all healthy, participated in this study. The subjects performed a fatiguing trunk extension-flexion exercise on a Roman chair until exhaustion. Endurance time and perceived muscle fatigue (Borg CR-10 scale) were used as fatigue criteria. The older adults were significantly (T<formula>_{(30)}</formula> = -2,073; p = 0.039) more resistant to back muscle fatigue (time in mean 133 ± 52 s) than the young adults (mean 97 ± 27 s). In general, both groups had the same perception of high-level fatigue during the exercise bout (T<formula>_{(29)}</formula> = 1.73; p=0.092). The older adults presented better back endurance than young adults during a dynamic trunk extension exercise. These results have implications for back endurance in the primary prevention of low back pain in both young and older adults.

Muscle fatigue in fibromyalgia is in the brain, not in the muscles: a case–control study of perceived versus objective muscle fatigue

ObjectiveTo investigate relationships between perceived and objectively measured muscle fatigue during exhausting muscle contractions in women with fibromyalgia (FM) compared with healthy controls (HC).MethodsWomen with FM and HC completed an...

Specificity of a Back Muscle Exercise Machine in Healthy and Low Back Pain Subjects

To determine whether dynamic back muscle endurance exercises in a semisitting position induce more fatigue in back muscles than that in hip extensors in healthy controls as well as in patients with nonspecific chronic low back pain. Sixteen healthy volunteers and 18 volunteers with nonspecific chronic low back pain performed trunk flexion-extension cycles until exhaustion at 60% of their strength in a machine designed for back exercise in a semisitting position with knees' angle at 135 degrees . The number of cycles and perceived muscle fatigue (Borg CR-10 scale) at five areas (upper and lower back, gluteus, hamstrings, and quadriceps) were used as fatigue criteria. EMG signals were recorded bilaterally on four back muscles, two hip extensors (gluteus maximus and biceps femoris), and the vastus medialis. The slope values of the instantaneous median frequency values computed over time were retained as EMG indices of fatigue. The number of cycles was equivalent in healthy controls (n = 23 +/- 13) and patients with back pain (n = 27 +/- 16). EMG indices of fatigue disclosed evidence of muscle fatigue in all the back muscles and the vastus medialis, contrary to hip extensors. EMG revealed significantly more muscle fatigue of lower back muscles, which was further corroborated by the Borg scale assessment. No between-group difference was obtained in any EMG comparison. These results showed that this type of exercise machine can specifically train the back muscles, and this as much in subjects with nonspecific chronic low back pain as in healthy controls. This has implications for the training of back muscle endurance, especially in patients with back pain for whom poor back muscle endurance is sometimes of concern.

The top‐down influence of ergogenic placebos on muscle work and fatigue

Placebos have been shown to induce powerful effects in a variety of medical conditions, such as pain and movement disorders, as well as to increase physical performance and endurance in healthy subjects. Here we investigated the effects of an ergogenic placebo on the performance of the quadriceps muscle, which is responsible for the extension of the leg relative to the thigh. In a first experiment, a placebo was administered along with the suggestion that it was caffeine at high dose. This resulted in a significant increase in mean muscle work across subjects, which, however, was not accompanied by a decrease of perceived muscle fatigue. In a second experiment, the placebo caffeine was administered twice in two different sessions. Each time, the weight to be lifted with the quadriceps was reduced surreptitiously so as to make the subjects believe that the 'ergogenic agent' was effective. After this conditioning procedure, the load was restored to the original weight, and both muscle work and perceived fatigue assessed after placebo administration. Compared with the first experiment, the placebo effect was larger, with a significant increase in muscle work and decrease in perceived muscle fatigue. Within the context of the role of peripheral and/or central mechanisms in muscle performance, the present findings suggest a central mechanism of top-down modulation of muscle fatigue. In addition, the difference between the first and second experiment underscores the role of learning in increasing muscle performance with placebos.

Vibration-induced muscle fatigue, a possible contribution to musculoskeletal injury.

Localized muscle fatigue resulting from 30-min sustained and intermittent grip exertions of 5% maximal voluntary contraction (MVC) with and without hand-vibration exposure (10 Hz, 7 mm displacement amplitude) was investigated. Muscle fatigue was quantified by the magnitude of the twitch force elicited in the right flexor digitorum superficialis muscle of the long finger using the low-frequency fatigue (LFF) method. The influence of vibration in the sustained grip exertion condition exacerbates fatigue as seen with the reduction in twitch force 30-60 min post-work task. Intermittent low grip force exertion conditions with and without vibration exposure show negligible fatigue, suggesting the benefit of rest in the work cycle. Perception of muscle fatigue was dissociated from the objective measure of twitch force, suggesting that LFF was not perceived. The presence of LFF and the lack of perception of LFF may increase the risk for the development of musculoskeletal disorders. The findings of this study may apply to the design of the work cycles and tasks that require the use of vibratory tools.

Subjective and objective evaluation of shoulder muscle fatigue.

In order to relate EMG signs of localized muscle fatigue to subjectively perceived muscle fatigue, a study was undertaken on 20 healthy volunteers exposing their right trapezius muscle by raising the arm to 90 degrees of abduction. Every person performed two contractions: 0 kg hand load during 5 min and 2 kg hand load during 2.5 min. Surface EMG was recorded and analysed with respect to RMS amplitude and mean power frequency (MPF). Subjective muscle fatigue was estimated with a psychophysical rating scale (Borg's CR-10 Scale). At high load level we found a significant correlation between MPF and the CR-scores (r = -0.46), but at low load level there was no correlation. At high load level there was a linear decrease of MPF with increasing load dose, but at low load level the MPF did not change, despite significant subjective fatigue. There was a linear rise of the CR-score with increasing load dose, more pronounced at high load level. It was concluded, that at low load levels common in working life, MPF and subjective scores seem to provide different fatigue information. Moreover, the MPF did not seem to work as a valid estimator of muscle fatigue at this low load level. Caution is recommended if it is to be used in static low-load situations.