Fatigue Patterns Research Articles

Effect of different recovery patterns on repeated-sprint ability and neuromuscular responses

We examined the effect of recovery pattern on mechanical and neuromuscular responses in active men during three repeated-sprint ability tests consisting of ten 6-s cycling sprints. Within each test, the recovery duration was manipulated: constant, increasing, and decreasing recovery pattern. Maximal voluntary contractions of the knee extensors were performed before and after the repeated-sprint ability tests to assess strength and electromyographic activity [root mean square (RMS)] of the quadriceps muscle. We observed different fatigue patterns for peak and mean power output between recovery patterns, with earlier decrements recorded during the increasing recovery pattern. Total work performed over the ten sprints was also lower in the increasing recovery pattern (43.8 ± 5.4 kJ; P < 0.05). However, the decreasing recovery pattern induced a greater overall power output decrement across the sprints (−15.8%; P < 0.05), compared with the increasing recovery pattern (−5.1%) but not the constant recovery pattern (−10.1%). The decreasing recovery pattern was also associated with higher post-sprint RMS values (+16.2%; P < 0.05). Therefore, the recovery pattern within successive short sprints may influence repeated-sprint ability, and may lead to greater post-sprint neuromuscular adjustments when recovery intervals decrease between sprints. We conclude that peripheral impairments caused the major differences in repeated-sprint ability between recovery patterns.

Symptom burden in patients undergoing autologous stem-cell transplantation

Patients who undergo autologous peripheral blood stem cell (PBSC) transplantation experience multiple symptoms that adversely affect quality of life. We assessed symptoms during the acute phase of autologous PBSC transplantation to determine the severity of individual symptoms and to determine overall symptom profiles in 100 patients with multiple myeloma or non-Hodgkin's lymphoma. Study subjects completed the blood and marrow transplantation module of the M. D. Anderson Symptom Inventory before hospitalization, during conditioning, on day of transplantation, at nadir (the time of lowest white blood cell count) and on day 30 post-transplantation. Additional symptom, quality-of-life and medical status measures were collected. Symptom means were mild at baseline, intensified during conditioning, peaked at nadir and decreased by day 30. At nadir, the most severe symptoms for the entire patient sample were lack of appetite, fatigue, weakness, feeling sick, disturbed sleep, nausea and diarrhea. Cancer diagnosis was a significant predictor of changes in symptoms over time. The patterns of fatigue, pain, sleep disturbance and lack of appetite were significantly different for patients with multiple myeloma as compared with patients with non-Hodgkin's lymphoma.

(712): Predictors of patterns of pain, fatigue and insomnia in the elderly during the first year following a cancer diagnosis

Pain, fatigue and insomnia (PFI) are among the most prevalent, distressing, and under managed symptoms experienced by cancer patients. Research has demonstrated that PFI co-occur; what remains unclear are the patterning and stability of PFI patterns, and the patient, disease and treatment characteristics that predict PFI patterns over time. Specifically, do patient age, sex, comorbidity, cancer site or stage, or treatment regimen predict patterns of PFI and their changes over time? This study was a secondary analysis of a dataset comprised of 867 elders (46% female) who were newly diagnosed with breast (27%), colorectal (18%), lung (26%) or prostate (29%) cancer and followed at 6-8, 12-16, 24 and 52 weeks following diagnosis.

Application of Surface Electromyography in Assessing Muscle Recruitment Patterns in a Six-Minute Continuous Rowing Effort

Specific sequences of muscle coordination exist in movements of every sport. In particular, sports involving repetitive movement patterns such as rowing may rely more heavily on coordinated muscle contraction sequencing in order to produce optimal performance. The aim of this study was to monitor the fatigue patterns of the major muscles engaged during the rowing stroke in rowers of varying abilities during a 6-minute continuous maximal rowing effort on a Concept II rowing ergometer. Sixteen male rowers were categorized into 5 groups based on years of training and their average pace of the 6-minute continuous maximal rowing effort. Continuous surface electromyography signals, recorded from brachioradialis, biceps brachii, middeltoid, rectus abdominis, erector spinae, rectus femoris, biceps femoris, and medial gastrocnemius, were used to investigate the influence of local muscle fatigue on optimal muscle coordination sequences during the rowing exercise. Rowers who performed better on the ergometer test and had more rowing experience tended to portray muscle recruitment patterning, which alternately emphasized different major muscle groups in a form of sharing of workload. This sharing allowed mean peak frequency restitution to take place in some muscles, while others took on more of the workload. The muscles of rowers with less experience and lower levels of performance did not appear to exhibit this same phenomenon known as biodynamic compensation. If coaches have a clearer picture of the fatigue patterns and recruitment strategies occurring in their athletes during a maximal effort row, strength training program adaptations could be made to compensate for weaker areas, which may assist rowers in attaining and sustaining more optimal patterns and strategies throughout the exercise effort.

Impact of Hypobaric Hypoxia in Pressurized Cabins of Simulated Long‐Distance Flights on the 24 h Patterns of Biological Variables, Fatigue, and Clinical Status

Long‐distance flights can cause a number of clinical problems in both passengers and crewmembers. Jet lag as well as mild hypoxia resulting from incomplete cabin pressurization could contribute to these problems. The objective of this study was to assess, using a chronobiological approach, the clinical impact of diurnal hypobaric, hypoxic exposure on fatigue and other common symptoms encountered during high‐altitude exposure and to measure changes in blood chemistry (i.e., plasma creatinine, urea, uric acid, sodium, calcium, phosphorus, glycemia, and lipids). Fourteen healthy, diurnally active (from 07:00 to 23:00 h) male volunteers, aged 23 to 39 yrs, spent 8.5 h in a hypobaric chamber (08:00 to 16:30 h), at a simulated altitude of 8,000 ft (2,438 m). This was followed by an additional 8.5 h of study four weeks later at a simulated altitude of 12,000 ft (3,658 m). Clinical data were collected every 2 h between 08:00 and 18:00 h, and biological variables were assayed every 2 h over two (control and hypoxic‐exposure) 24 h cycles. Clinical symptoms were more frequent with the 12,000 ft exposure. Wide interindividual variability was observed in the clinical tolerance to prolonged hypobaric hypoxia. The 24 h profiles of most biochemical variables were significantly altered at each altitude, with changes in mean plasma levels and a tendency toward phase delay, except for uric acid, which showed a phase advance. Changes in appetite mainly occurred with the simulated 12,000 ft exposure and may have been associated with changes in the postprandial glycemia profile. Finally, though the observed biochemical changes were significant, their clinical relevance must be clarified in studies involving actual long‐distance flights.

Electronic diary evidence on energy erosion in clinical burnout.

Burnout is generally defined as a state of severe exhaustion. So far, research has predominantly focused on relatively mild burnout in employees able to work despite their complaints. This study examines energy depletion in clinical burnout (e.g., the severest cases on extended sick leave) by comparing the diurnal patterns of fatigue and exhaustion with those of healthy individuals. Sixty clinically burned-out and 40 healthy participants kept an electronic diary for 14 days, 7 times a day, yielding a total of 8,116 diary entries. This study shows that burned-out individuals typically suffer continuously from a severe fatigue throughout the day. The resulting flattened diurnal cycles mark a stable exhaustion that is uncommon in healthy persons. The current results provide novel support for the existence of severe energy erosion in clinical burnout.

Course of Fatigue Between Two Cycles of Adjuvant Chemotherapy in Breast Cancer Patients

The purpose of this study was to determine the course of fatigue in patients with breast cancer between 2 cycles of adjuvant chemotherapy, from the day of administration until the day of the next infusion. In a prospective cohort study, a sample of 151 patients with breast cancer receiving adjuvant chemotherapy was recruited from 6 hospitals in mainly the south of the Netherlands. Patients reported their experience of fatigue in a diary, the Shortened Fatigue Questionnaire, on a daily basis between the third and fourth treatment with adjuvant chemotherapy. Patients were treated with either a doxorubicin containing schedule or with cyclophosphamide, methotrexate, and 5-fluorouracil (CMF, 28 days). In the 28-day regimens, infusions were given on day 1 and day 8. The days after completion of the third and the start of the fourth treatment with chemotherapy were statistically analyzed. We tested the hypothesis that the maximum fatigue score occurs in the first 4 days after treatment. The mean age of the sample was 47.2 years (SD = 8.8). Most women (84%) were married or lived together with a partner. The majority (80%) of all patients had been diagnosed with stage II breast cancer. The division between mastectomies (47%) and lumpectomies (52%) was approximately equal. Sixty percent of the patients received radiotherapy before the third treatment with chemotherapy and/or in the period they kept the diary. A chaotic pattern of fatigue between the 2 cycles of chemotherapy emerged. Smooth (splines) curves showed an average highest level of fatigue on day 3 from the start. For the 28-day regimens, another distinct peak was seen around day 11. A relatively larger number of patients experienced peak fatigue levels before day 5. The course of fatigue in the CMF group was significantly different compared with the doxorubicin regimens. The fatigue peak in the CMF group was lower. Women taking cyclophosphamide orally experienced the peak level of fatigue significantly later. Influences of other variables were not observed in any chemotherapy group. Cancer-related fatigue has a chaotic nature. The first days after treatment with chemotherapy are the worst. The type of chemotherapy has a significant impact on the course of fatigue. Improved understanding of the nature and course of fatigue could equip healthcare providers better for informing patients about what they may expect. Future research should include interventions aimed at reducing or coping with fatigue.

Patterns of fatigue among seafarers during a tour of duty

Work-related fatigue is associated with sickness absence and mental and physical health problems, and may increase the risk of accidents and injuries at work. Relatively little is known about fatigue among seafarers, particularly during a tour of duty. The aim of this study was to describe the pattern of day to day fatigue among seafarers during a tour at sea. Participants from the offshore support, short sea and coastal, and deep sea sectors of the UK shipping industry completed daily diaries. Information about sleep and fatigue was collected each day on waking and retiring. Fatigue on waking was a more sensitive measure of cumulative occupational fatigue than fatigue on retiring. Fatigue on waking increased between the start and end of tour. This increase took place in particular during the first week at sea, and was most apparent among those on shorter tours of duty. Day to day changes in fatigue are measurable, and may vary among particular sub-groups of seafarers. Used among larger groups, such a diary method could help identify times and activities associated with the greatest risk.

Understanding global transition assessments

Several methods currently used for determining meaningful or important change in health-related quality of life (HRQoL) measures are anchored by global transition items. It can be empirically demonstrated that patients' responses to these gold standards for change do not adequately incorporate the prior condition, yet these transition items play an influential role in patient-clinician communications and cannot be disregarded. This follow-up study queried patients to better understand how they ascertained their transition assessments. Prior to their qualitative interviews, the 41 participants in this study had completed 1 year of enrollment in a clinical study with bi-monthly HRQoL telephone interviews that included the SF-36 and a disease-specific HRQoL instrument (asthma, COPD, or heart disease), as well as global transition assessments for each instruments domains. We used face-to-face cognitive interview and the think aloud approaches to obtain qualitative clues for understanding patient reports of HRQoL changes over time. Interview transcripts were coded using the four components of the Rapkin-Schwarz Appraisal Model: frame of reference; sampling strategy; standards of comparison; and combinatory algorithm. Patients' explanations for determining global transition item responses often focused on current mobility and fatigue patterns, physicians' statements about their conditions, comparisons of their current states with the prior health conditions, and strong personal convictions that reflected a resistance to voicing any emotional changes. Patients also expressed primary health concerns, like back pain, that were not related to the chronic conditions (asthma, COPD or heart disease) under investigation. HRQoL studies and patient-clinician communications that incorporate global transition assessments to anchor the interpretations of HRQoL changes should also consider additional relevant questions to understand the process patients uses to appraise and report changes in HRQoL.

Electrical Manifestations of Muscle Fatigue During Concentric and Eccentric Isokinetic Knee Flexion-Extension Movements

The quantification of the progression of muscle fatigue during a sustained contraction is a valuable tool in several clinical applications, ranging from the evaluation of functional impairment to the development of specific rehabilitative and training protocols. In these fields, great importance is given to isokinetic contractions. The aim of this paper was twofold: first, to propose signal processing methods for assessing the spectral changes of the surface myoelectric signal due to fatigue during isokinetic concentric and eccentric knee flexion-extension movements at a given angular velocity (60 degrees/s); second, to analyze the electrical manifestations of muscle fatigue of four thigh muscles (vastus lateralis, vastus medialis, rectus femoris, and biceps femoris) in the two contraction modalities (i.e. concentric versus eccentric). We demonstrated that, when considering concentric contractions, localized muscle fatigue can be assessed by computing the mean frequency of the frequency marginal of the time-frequency distribution derived from the surface myoelectric signal collected during each contraction cycle. Stronger nonstationarities were observed in the surface myoelectric data recorded within each cyclical movement of the studied eccentric exercise. Thus we propose the computation of the instantaneous mean frequency of the signal based on an original cross-time-frequency algorithm, which proved more sensitive than the frequency marginal in tracking the spectral changes associated with localized muscle fatigue. We derived the average fatigue pattern of the investigated muscles from experimental data recorded from a sample population consisting of twenty healthy subjects and we statistically compared the two contraction modalities. Our results showed that the electrical manifestations of muscle fatigue during concentric contractions were higher than those found during eccentric contractions, although in the latter modality the torque exerted and the mechanical work produced by the subjects were larger than those recorded during the concentric exercise. The results presented in this paper have potential clinical application and they could play an important future role in investigations of muscle behavior during dynamic, highly fatiguing contractions.

Patterns of fatigue during a course of chemotherapy: Results from a multi-centre study

Fatigue is a highly prevalent condition among patients with cancer affecting between 70% and 100% and patients describe their fatigue experiences as the most distressing of symptoms. However, the management of fatigue is complicated by our current lack of understanding of its pathophysiology. This study aimed to gain an insight into the longitudinal fatigue experiences of patients receiving chemotherapy. A convenience sample of patients receiving chemotherapy (n=249) were recruited and recorded their fatigue experiences using a paper questionnaire for 14 consecutive days following each cycle of chemotherapy. Fatigue was reported in 57% of all completed questionnaires. Patients report fatigue as a relatively constant presence following chemotherapy. Moreover, fatigue experiences increase over consecutive cycles of chemotherapy. This study supports the existing evidence illustrating fatigue as a significant problem for patients with cancer and provides new data demonstrating patterns of fatigue over the duration of a course of chemotherapy. Understanding this experience of fatigue should prompt health professionals providing care for this patient population to seek and test a range of management strategies to help patients maintain their quality of life during cancer treatment.

Disturbed sleep and fatigue in occupational burnout

The purpose of this study was to investigate sleep with polysomnography and self-ratings and the diurnal pattern of sleepiness and fatigue in a group suffering from severe occupational burnout. Twelve white-collar workers on long-term sick leave (>3 months) and 12 healthy controls with high and low scores on the Shirom Melamed Burnout Questionnaire (SMBQ) were included. A 1-night polysomnographic recording (after habituation) was carried out at home, and sleepiness and mental fatigue were rated at different times of the day for weekdays and the weekend. Precipitating factors at the time of the illness at work and real life were considered, and different dimensions of occupational fatigue were described. A repeated-measures analysis of variance using two or three within group factors was used to analyze the data. The main polysomnographic findings were more arousals and sleep fragmentation, more wake time and stage-1 sleep, lower sleep efficiency, less slow wave sleep and rapid eye movement sleep, and a lower delta power density in non-rapid eye movement sleep in the burnout group. The burnout patients showed pronounced sleepiness and mental fatigue at most times of the day for weekdays without reduction during weekends. The precipitating factor was occupational stress (psychiatric interview), and work stress indicators were increased. Occupational burnout is characterized by impaired sleep. It is suggested that impaired sleep may play a role in the development of fatigue or exhaustion in burnout.

Cancer-related fatigue: A critical appraisal

This aim of this systematic review was to determine the prevalence and pattern of cancer-related fatigue (CRF), and identify factors associated with its development. Relevant literature was identified through an electronic database search using specified keywords. Included studies investigated CRF in adult cancer patients using a multidimensional fatigue measure. The methodological quality was assessed using six published standards. CRF is apparent both during and after anti-cancer therapy, however, the prevalence of CRF varied between studies. The variables associated with the development and persistence of CRF remain to be identified. Inconsistencies were evident in the pattern of CRF and its associated factors. This is likely to have arisen from the inherent difficulties in the measurement of a subjective sensation, further complicated by the myriad of outcome measures used. More methodologically sound research; assessing CRF from the commencement of therapy, considering all pertinent variables is needed.

Fatigue and Physical Activity in Patients Undergoing Hematopoietic Stem Cell Transplant

To examine the patterns of fatigue, physical activity, health status, and quality of life before and after high-dose chemotherapy and hematopoietic stem cell transplantation (HSCT) and to examine the feasibility of obtaining real-time fatigue and physical activity data. Prospective, repeated measures. Two midwestern academic medical centers. Convenience sample of autologous or allogeneic patients undergoing HSCT (N = 20 baseline, N = 17 post-transplant). Subjects were assessed over a five-day period before and after HSCT for a total of 10 days. Subjects rated fatigue intensity three times daily and wore a wrist actigraph to measure physical activity. At the end of both five-day periods, subjects completed measures of perceived health status (European Organization for Research and Treatment of Cancer Quality of Life Questionnaire-Core 30) and life satisfaction Quality of Life Index). Fatigue, physical activity, perceived health status, and quality of life. Study results indicate that fatigue significantly increased and physical activity decreased following high-dose chemotherapy and HSCT. The decline coincided with diminished physical, emotional, role, and cognitive functioning. The symptoms that patients experienced (i.e., fatigue, pain, nausea and vomiting, sleep disturbances, appetite loss, and diarrhea) increased during the acute post-transplant period. No significant changes in life satisfaction were found. The study findings suggest that patients receiving high-dose chemotherapy followed by HSCT experience increased fatigue, reduced physical activity, diminished functioning, and poorer quality of life immediately after transplant. Findings demonstrate that real-time fatigue and physical activity data can feasibly be collected in acutely ill patients. Patients undergoing HSCT require considerable supportive nursing care immediately following transplant. Clinicians and researchers need to strive for effective symptom management to improve the likelihood of successful outcomes.

Neuromuscular fatigue development during maximal concentric and isometric knee extensions

This study aimed to investigate mechanisms of neuromuscular fatigue during maximal concentric and isometric leg extensions inducing similar torque decrements. Nine physically active men performed two separate fatiguing sessions maintained until similar torque decreases were obtained. The first session, only conducted under isokinetic concentric conditions (CON), consisted of three series of 30 maximal voluntary concentric knee extensions (60 degrees/s). The second session, exclusively isometric (ISO), mimicked the torque decreases registered during the CON session while performing three long-lasting ISO contractions. Maximal voluntary torque, activation level (twitch interpolation technique), electromyographic activity (root mean square and median frequency) of the vastus lateralis muscle, and electrically evoked doublet-twitch mechanical properties were measured before and at the end of each of the three series. After the three series, similar torque decrements were obtained for both fatiguing procedures. The total fatiguing contraction durations were not different among procedures. With equivalent voluntary torque decrements, the doublet-twitch amplitude reduction was significantly greater (P<0.01) during the two first series of the CON procedure compared with ISO. No difference was observed for the third series. Although no difference was recorded with fatigue for median frequency changes between CON and ISO, activation levels and root mean square values demonstrated greater reductions (P<0.05) for all three series during the ISO procedure compared with CON. Performing CON or ISO fatiguing exercises demonstrated different fatigue origins. With CON exercises, peripheral fatigue developed first, followed by central fatigue, whereas with ISO exercises the fatigue pattern was inverted.

Simultaneous Media Experience and Synesthesia

A study of muscles of the dystrophic mouse has failed to substantiate earlier claims that these muscles were especially resistant to fatigue <i>in vitro</i> or that fast muscles are preferentially damaged. It has been found that the fast muscle selected for previous studies is very often unable to withstand isolation in an organ bath if it is working, and both the difficulty in removing the normal gastrocnemius muscle intact and the need to trim it surgically contribute independently toward its deterioration <i>in vitro</i>. The smaller dystrophic gastrocnemius muscle is less liable to excision damage, is able to satisfy its resting metabolic needs in nutrient solution, and requires no damaging dissection, but is nevertheless unable to recover normally from fatigue. Using EDL and soleus muscles which are small enough to withstand isolation <i>in vitro</i>, no differences are found between fatigue patterns of normal and dystrophic specimens. Responses to rest, KCl, and 2 mM caffeine are also quite similar, and the only distinguishing biomechanical characteristic we have found in dystrophic mouse muscle is a weaker contraction and a longer total twitch time.

70 μM caffeine treatment enhances in vitro force and power output during cyclic activities in mouse extensor digitorum longus muscle

Caffeine ingestion by human athletes has been found to improve endurance performance primarily acting via the central nervous system as an adenosine receptor antagonist. However, a few studies have implied that the resultant micromolar levels of caffeine in blood plasma (70 microM maximum for humans) may directly affect skeletal muscle causing enhanced force production. In the present study, the effects of 70 microM caffeine on force and power output in isolated mouse extensor digitorum longus muscle were investigated in vitro at 35 degrees C. Muscle preparations were subjected to cyclical sinusoidal length changes with electrical stimulation conditions optimised to produce maximal work. 70 microM caffeine caused a small but significant increase (2-3%) in peak force and net work produced during work loops (where net work represents the work input required to lengthen the muscle subtracted from the work produced during shortening). However, these micromolar caffeine levels did not affect the overall pattern of fatigue or the pattern of recovery from fatigue. Our results suggest that the plasma concentrations found when caffeine is used to enhance athletic performance in human athletes might directly enhance force and power during brief but not prolonged activities. These findings potentially confirm previous in vivo studies, using humans, which implied caffeine ingestion may cause acute improvements in muscle force and power output but would not enhance endurance.

Effect Of Stretch-shortening Cycle Exercises On The Mechanical And Neuromuscular Properties

PURPOSE To compare the effects of Stretch-Shortening Cycle (SSC) exercises on the mechanical and neuromuscular properties during the vertical jump for non-experienced jumpers and experienced jumpers. METHODS Sixteen subjects were recruited for the experiments. The First group (EJ), had at least 10 years of experience in jump training and therefore constituted experienced jumpers. The second group (NEJ) had at least five years of experience in the college sports but no prior experience in jump training. For the fatigue exercise, subjects were instructed to perform a long lasting SSC exercises inducing 50% of decraese in Maximal Isometric Force (MVC). For the testing protocols a leg press was used to measure isometric force and dynamic concentric movements at 40%, 50% and 60% of each subject's 1RM. A force plate was used to measure force, power, and height during the squat jump (SJ) and the countermovement jump (CMJ) on both feet. A 3-D system was used to analyze kinematic data for the most prominent protuberance of the hip greater trochanter, lateral femoral epicondyle of the knee, and the ankle lateral maleolus during each jumping exercises. Joint moment and stiffness of the knee was calculated using an inverse dynamics approach given segmental displacements, velocities, and accelerations obtained from the kinematic record and the force plate data. Myoelectric signals were recorded for the following muscles: vastus medialis, vastus lateralis, and biceps femoris for the jumping and leg press exercises. RESULTS For both groups, the SSC exercise suppressed voluntary isometric force and maximal concentric power (p<0.0006) and SJ performance (p<0.008) while only the experienced jumpers maintained their performance during the CMJ after fatigue exercise. EMG analysis (as interpreted through the root mean square and mean power frequency values) showed that the maximal concentric power, SJ and CMJ were performed similarly before and after the fatigue exercise for both the EJ and NEJ groups. CONCLUSIONS The major finding in our study was that non-experienced and experienced jumpers differ in their patterns of fatigue (as interpreted through the jump performance findings and the kinematic data). It appears that for the experienced jumpers, fatiguing the knee extensor did not affect the CMJ height. The experienced jumpers re-optimize knee extensor muscle recruitment by altering their jump strategy during the CMJ (as interprted through the increase in the eccentric and transition phases). Exhausting SSC exercise induced local muscle impairment and a decrease in muscle performance, which is not simply a direct effect of central command fatigue.

Course of mental fatigue and motivation in breast cancer patients receiving adjuvant chemotherapy

The purpose of this study is to determine the course of fatigue referring to cognitive symptoms (scale 'mental fatigue') as well as the motivation to start any activity (scale 'reduced motivation'), as a function of chemotherapy, in breast cancer patients undergoing adjuvant chemotherapy. In a prospective cohort study a sample of 157 patients with breast cancer was interviewed at the first, third and fifth cycle of adjuvant chemotherapy as well as 4 and 12 weeks after completion of adjuvant chemotherapy. Patients were treated with standard adjuvant chemotherapy, either a doxorubicin containing schedule or CMF (cyclophosphamide, methotrexate and fluorouracil). The psychological dimensions of fatigue were measured by the Multidimensional Fatigue Inventory. A linear multilevel model was used for analysing the courses. The course of mental fatigue and motivation were not affected by the type of chemotherapy. The course of mental fatigue and motivation varied, but seemed to be stable during the treatment of chemotherapy. After the completion of chemotherapy, a weak improvement was seen. Relatively many patients experienced depressive symptoms during the study. These symptoms were correlated with both dimensions of fatigue. At all measurements mental fatigue was influenced by type of operation where women with a mastectomy were significantly more mentally fatigued than women that had undergone a lumpectomy, but nevertheless they were significantly more motivated to start any activity. Age, marital status, number of treatments and the interval between the operation and the first treatment of chemotherapy also seemed to be important determinants. An unequivocal pattern of mental fatigue and reduced motivation during as well as after adjuvant chemotherapy was not found. Depressive symptoms were definitely related to these variables. Type of operation had a significant impact on mental fatigue and motivation to start any activity. Health care providers should be aware of the high rate of patients who experience depressive symptoms during and after the treatment of chemotherapy. Further research should include the trajectory preceding adjuvant chemotherapy and a longer study period afterwards. Moreover, the exact influence of the variables 'age', 'marital status', 'number of treatments' and 'the interval between the operation and the first treatment of chemotherapy' on fatigue is unclear and needs further study.

Skeletal muscle contractile performance and ADP accumulation in adenylate kinase-deficient mice

The production of AMP by adenylate kinase (AK) and subsequent deamination by AMP deaminase limits ADP accumulation during conditions of high-energy demand in skeletal muscle. The goal of this study was to investigate the consequences of AK deficiency (-/-) on adenine nucleotide management and whole muscle function at high-energy demands. To do this, we examined isometric tetanic contractile performance of the gastrocnemius-plantaris-soleus (GPS) muscle group in situ in AK1(-/-) mice and wild-type (WT) controls over a range of contraction frequencies (30-120 tetani/min). We found that AK1(-/-) muscle exhibited a diminished inosine 5'-monophosphate formation rate (14% of WT) and an inordinate accumulation of ADP ( approximately 1.5 mM) at the highest energy demands, compared with WT controls. AK-deficient muscle exhibited similar initial contractile performance (521 +/- 9 and 521 +/- 10 g tension in WT and AK1(-/-) muscle, respectively), followed by a significant slowing of relaxation kinetics at the highest energy demands relative to WT controls. This is consistent with a depressed capacity to sequester calcium in the presence of high ADP. However, the overall pattern of fatigue in AK1(-/-) mice was similar to WT control muscle. Our findings directly demonstrate the importance of AMP formation and subsequent deamination in limiting ADP accumulation. Whole muscle contractile performance was, however, remarkably tolerant of ADP accumulation markedly in excess of what normally occurs in skeletal muscle.