Late onset polio sequelae: disabilities and handicaps in a population-based cohort of the 1956 poliomyelitis outbreak in The Netherlands.

OBJECTIVE: To investigate the prevalence of new neuromuscular symptoms, disabilities, and handicaps in a group of polio survivors. DESIGN: A self-constructed health questionnaire about neuromuscular complaints and disability and handicap levels during the stable period after recovery from polio and at present. SUBJECTS: Three hundred fifty subjects, derived from the 1,784 polio cases registered during the 1956 polio outbreak in The Netherlands. RESULTS: Respondents totaled 260 (74%), 27 of whom denied or did not recall having had paralytic poliomyelitis. The remaining 233 subjects comprised the study group (mean age, 44yrs; range, 39 to 77; SD = 6.3). Frequency of all neuromuscular complaints at present time was significantly higher than that during the stable period after polio (range in p of .001 to .004). Fifty-eight percent of cases reported an increase in muscle weakness in comparison with muscle condition during the stable period. Fifty-six percent reported an increase in disabilities, mainly a restriction in gait functions. Fifty-three percent reported increased handicaps with regard to occupation and social integration, and there was an increased need for adaptive measures and devices. CONCLUSION: Nearly 60% of a sample of Dutch survivors of the 1956 polio outbreak experience late onset polio sequelae, resulting in increased severity of disabilities and handicaps.     

Lumbar muscle fatigue and recovery in patients with long-term low-back trouble--electromyography and health-related factors

OBJECTIVE: The aim was to explore the validity and reliability of EMG for assessing lumbar muscle fatigue. DESIGN: Patients with long-term low-back trouble (n=57) were compared to a healthy reference group (n=55). Back muscle fatigue and recovery were studied in relation to health-related factors. BACKGROUND: EMG spectral variables are important tools in the assessment of patients with low-back trouble. The influence of disability on these variables needs further investigation. METHODS: EMG from the lower back muscles was recorded during a 45 s trunk extension at 80% of maximal voluntary contraction torque and during recovery. Disability was studied using questionnaires. RESULTS: The reliability was high for maximal voluntary contraction torque and EMG initial median frequency, lower for the median frequency slope, and insufficient for median frequency recovery half-time. The patients had lower maximal voluntary contraction torque, higher initial median frequency at L5 level, flatter slope, and longer recovery half-time than the healthy subjects did. However, for subjects with significantly negative slope, indicating fatigue, there was no significant difference in slope between patients and healthy subjects, while, for subjects without such fatigue, patients showed significantly flatter slopes at L5. The sensitivity/specificity of the test was 86%/78%. The most significant variables selected with logistic regression were maximal voluntary contraction torque and initial median frequency at L5. Patients without significantly negative slopes during contraction and/or not exponential-like EMG recovery scored worse on several items concerning disability and self-efficacy. CONCLUSIONS: EMG spectral variables in combination with torque might be used for classification. For patients with long-term low-back trouble, the ability to fatigue the lumbar muscles sufficiently to obtain a significantly negative slope during an 80% maximal voluntary contraction may be a sign of better functioning. RELEVANCE: The ability to fatigue the back muscles during a test requiring a high force output might be achieved with back muscle training focused on increasing strength and self-efficacy.     

Poliomyelitis: extinct by year 2000--but not over.

This is a comparative analysis of findings from a sample of individuals who had poliomyelitis with findings from seminal works on post polio syndrome. The sample included 148 individuals who developed poliomyelitis earlier in life. The findings are compared with the seminal studies of Halstead (1985a, 1985b). Seventy-two percent of the sample were experiencing post polio syndrome, defined as having progressive fatigue and one other symptom of sequelae to a moderate or severe degree. The mean age of the sample was 54. The majority of subjects had some college education, were married, belonged to support groups, and were employed. The mean age for contracting polio was 10.5, with a mean of 3.8 years to maximum recovery. At onset of the initial illness, 121 subjects were hospitalized. The period of stability from the point of maximum recovery to onset of sequelae had a mean of 29.8 years. Fatigue and muscle weakness at onset were predictive for developing sequelae. Subjects' lifestyle changes are reported. Implications focus on workplace issues. This study supports and extends the findings of the seminal works.     

Gender influence on fatigability of back muscles during intermittent isometric contractions: a study of neuromuscular activation patterns

BACKGROUND: Gender difference in the fatigability of muscles can be attributed to muscle mass (or strength) and associated level of vascular occlusion, substrate utilization, muscle composition, and neuromuscular activation patterns. The purpose of this study was to assess the role of neuromuscular activation patterns to explain gender differences in back muscle fatigability during intermittent isometric tasks. METHODS: Sixteen males and 15 females performed maximal voluntary contractions (Strength) and a fatigue test to exhaustion (fatigue criterion=time to exhaustion), while standing in a static dynamometer measuring L5/S1 extension moment. The fatigue test consisted of repetitions of an 8-s cycle (1.5 s ramp to reach 40% of maximal voluntary contraction +5s plateau at 40% of maximal voluntary contraction +1.5s rest). Surface electromyography signals were collected bilaterally from 4 back muscles (multifidus at the L5 level, iliocostalis lumborum at L3, and longissimus at L1 and T10). FINDINGS: Males were stronger (P<0.05) than females (316, SD 82>196, SD 25 Nm) but showed significantly shorter time-to-exhaustion values (7.1, SD 5.2<13.0, SD 6.1 min.), the latter result being corroborated by electromyographic indices of fatigue. However, the gender effect on time to exhaustion disappeared when accounting for Strength, thus supporting the muscle mass hypothesis. Among the various electromyographic indices computed to assess neuromuscular activation patterns, the amount of alternating activity between homolateral and between contralateral muscles showed a gender effect (females>males). INTERPRETATION: These results support the muscle mass hypothesis as well as the neuromuscular activation hypothesis to explain gender differences in back muscle fatigability.     

Comparison of recovery strategies on muscle performance after fatiguing exercise

OBJECTIVE: The objective of this study was to assess the influence of different relaxation modes: stretching (ST), active recovery (AR), and passive recovery (PR) on muscle relaxation after dynamic exercise of the quadriceps femoris. DESIGN: Ten healthy male volunteers between 24 and 38 yrs of age participated in this study. After the warm-up, subjects performed three sets of dynamic leg extension and flexion (at an angle of 20-110 degrees) at 50% of previously determined maximal voluntary contraction (MVC), with 30 secs. of rest between sets. Immediately after completing the leg exercise, one of the relaxation methods was applied, in a randomized order (AR, PR, ST). Then, subjects performed isometric knee extension at 50% of MVC to the point of fatigue, and surface electromyogram (EMG) of the vastus lateralis muscle was measured. RESULTS: After AR, the mean MVC was significantly (P < 0.05) higher than after PR and ST. Moreover, there was no difference in MVC between AR and baseline (P > 0.05). Total time of the effort during EMG measurement was significantly lower for all three recovery modes than at baseline. During the effort after both PR and ST, there was no significant increase in motor unit activation, but a significant increase was noted after AR (P < 0.05). There was no difference in frequency between any of the recovery modes and baseline (P > 0.05). CONCLUSION: The results of this study suggest that the most appropriate and effective recovery mode after dynamic muscle fatigue involves light, active exercises, such as cycling with minimal resistance.     

Disability and functional assessment in former polio patients with and without postpolio syndrome

OBJECTIVES: To compare perceived health problems and disability in former polio subjects with postpolio syndrome (PPS) and those without postpolio syndrome (non-PPS), and to evaluate perceived health problems, disability, physical performance, and muscle strength. DESIGN: Cross-sectional survey; partially blinded data collection. SUBJECTS: One hundred three former polio subjects, aged 32 to 60yrs. This volunteer sample came from referrals and patient contacts. Criterion for PPS: new muscle weakness among symptoms. MAIN OUTCOME MEASURES: Nottingham Health Profile (NHP), adapted D-code of the International Classification of Impairments, Disabilities and Handicaps, performance test, and muscle strength assessment. RESULTS: PPS subjects (n = 76) showed higher scores (p < .001) than non-PPS subjects (n = 27) within the NHP categories of physical mobility, energy, and pain. On a 16-item Polio Problems List, 78% of PPS subjects selected fatigue as their major problem, followed by walking outdoors (46%) and climbing stairs (41%). The disabilities of PPS subjects were mainly seen in physical and social functioning. No differences in manually tested strength were found between patient groups. PPS subjects needed significantly more time for the performance test than non-PPS subjects and their perceived exertion was higher. Perceived health problems (NHP-PhysMobility) correlated significantly with physical disability (r = .66), performance-time (r = .54), and muscle strength (r = .38). With linear regression analysis, 54% of the NHP-PhysMobility score could be explained by the performance test (time and exertion), presence of PPS, and muscle strength, whereas strength itself explained only 14% of the NHP-PhysMobility score. CONCLUSIONS: PPS subjects are more prone to fatigue and have more physical mobility problems than non-PPS subjects. In former polio patients, measurements of perceived health problems and performance tests are the most appropriate instruments for functional evaluation.     

Quantifying human muscle strength, endurance and fatigue

Physiologic methods have been developed to objectively quantify muscle strength, endurance, and fatigability. Isometric force and rectified/integrated electromyogram were simultaneously recorded during the three phases of a recording session: pre-fatigue, fatigue (1 min duration) and post-fatigue recovery (up to 10 min). Five parameters of muscle performance were computed: Maximum force (MF) exerted during isometric voluntary contraction (muscle strength); Force-time integral--area under force-time plot (endurance); Fatigue index (FI) (% reduction in MF); Neuromuscular efficiency (force/mV of EMG recruited), and Recovery time (RT). Normal values based on data from 20 normal subjects were determined for four muscles: index finger abductor, elbow flexors, knee extensors, and ankle dorsiflexors. Neuromuscular efficiency (NME) decreased significantly (20 to 70%) at the end of the fatigue phase; it generally increased to the pre-fatigue level in 2 to 10 min, during the recovery phase. The period needed to reach pre-fatigue level was referred to as RT. The elbow flexors had the highest mean FI (48%) and the longest RT (greater than 6 min); the ankle dorsiflexors had the lowest mean FI (34%) and the shortest RT (1.5 min). These methods have been used also to evaluate the effects of weight training in two patients with neuromuscular disorders.     

Knee muscle isometric strength,voluntary activation and antagonist co-contraction in the first six months after stroke

Purpose: Muscle weakness may contribute to functional problems after stroke, but is rarely addressed during rehabilitation. Functional problems are commonly thought to be caused by abnormal movement patterns or possibly disuse atrophy. We investigated voluntary isometric strength, activation and the extent of co-contraction in the knee muscles during the first six months during stroke. Methods: Twelve stroke patients (58 3 years, mean SEM, 7 female) were studied bilaterally on admission for rehabilitation (21 1 days after stroke) and then at 1, 2, 3, and 6 months. Twenty healthy controls (61 5 years, 17 female) were tested once on their preferred leg. Subjects performed maximal voluntary contractions of the quadriceps and hamstring muscles. Simultaneous measurements were made of agonist force and surface EMG from agonist and antagonist muscles. Voluntary activation was estimated using the twitch superimposition technique. Results: Both paretic muscles showed lower (p 0.01-0.0005) voluntary strength than both non-paretic and control muscles until three months after stroke. Co-contraction of antagonists was similar in all groups and greater during knee extension than flexion. Stroke patients showed considerable bilateral voluntary activation failure (25-40%, p 0.01-0.001) throughout the study while most control subjects did not (group mean 7%). Conclusions: The muscle weakness and bilateral activation failure in the stroke patients was not explained by either excessive antagonist activity or disuse atrophy. They had potential for increased voluntary strength and if this were addressed during rehabilitation, then the rate and extent of functional recovery might be enhanced.     

Knee muscle isometric strength, voluntary activation and antagonist co-contraction in the first six months after stroke

Purpose: Muscle weakness may contribute to functional problems after stroke, but is rarely addressed during rehabilitation. Functional problems are commonly thought to be caused by abnormal movement patterns or possibly disuse atrophy. We investigated voluntary isometric strength, activation and the extent of co-contraction in the knee muscles during the first six months during stroke. Methods: Twelve stroke patients (58 3 years, mean SEM, 7 female) were studied bilaterally on admission for rehabilitation (21 1 days after stroke) and then at 1, 2, 3, and 6 months. Twenty healthy controls (61 5 years, 17 female) were tested once on their preferred leg. Subjects performed maximal voluntary contractions of the quadriceps and hamstring muscles. Simultaneous measurements were made of agonist force and surface EMG from agonist and antagonist muscles. Voluntary activation was estimated using the twitch superimposition technique. Results: Both paretic muscles showed lower (p 0.01-0.0005) voluntary strength than both non-paretic and control muscles until three months after stroke. Co-contraction of antagonists was similar in all groups and greater during knee extension than flexion. Stroke patients showed considerable bilateral voluntary activation failure (25-40%, p 0.01-0.001) throughout the study while most control subjects did not (group mean 7%). Conclusions: The muscle weakness and bilateral activation failure in the stroke patients was not explained by either excessive antagonist activity or disuse atrophy. They had potential for increased voluntary strength and if this were addressed during rehabilitation, then the rate and extent of functional recovery might be enhanced.     

Postural steadiness during quiet stance does not associate with ability to recover balance in older women

BACKGROUND: Fall risk depends on ability to maintain balance during daily activities, and on ability to recover balance following a perturbation such as a slip or trip. We examined whether similar neuromuscular variables govern these two domains of postural stability. METHODS: We conducted experiments with 25 older women (mean age=78 yrs, SD=7 yrs). We acquired measures of postural steadiness during quiet stance (mean amplitude, velocity, and frequency of centre-of-pressure movement when standing with eyes open or closed, on a rigid or compliant surface). We also measured ability to recover balance using the ankle strategy after release from a forward leaning position (based on the maximum release angle where recovery was possible, and corresponding values of reaction time, rate of ankle torque generation, and peak ankle torque). FINDINGS: We found that balance recovery variables were not strongly or consistently correlated with postural steadiness variables. The maximum release angle associated with only three of the sixteen postural steadiness variables (mean frequency in rigid, eyes open condition (r=0.36, P=.041), and mean amplitude (r=0.41, P=.038) and velocity (r=0.49, P=.015) in compliant, eyes closed condition). Reaction time and peak torque did not correlate with any steadiness variables, and rate of torque generation correlated moderately with the mean amplitude and velocity of the centre-of-pressure in the compliant, eyes closed condition (r=0.48-0.60). INTERPRETATION: Our results indicate that postural steadiness during quiet stance is not predictive of ability to recover balance with the ankle strategy. Accordingly, balance assessment and fall prevention programs should individually target these two components of postural stability.     

Electromyography-controlled exoskeletal upper-limb-powered orthosis for exercise training after stroke

OBJECTIVE: Robot-assisted exercise shows promise as a means of providing exercise therapy for weakness that results from stroke or other neurological conditions. Exoskeletal or "wearable" robots can, in principle, provide therapeutic exercise and/or function as powered orthoses to help compensate for chronic weakness. We describe a novel electromyography (EMG)-controlled exoskeletal robotic brace for the elbow (the active joint brace) and the results of a pilot study conducted using this brace for exercise training in individuals with chronic hemiparesis after stroke. DESIGN: Eight stroke survivors with severe chronic hemiparesis were enrolled in this pilot study. One subject withdrew from the study because of scheduling conflicts. A second subject was unable to participate in the training protocol because of insufficient surface EMG activity to control the active joint brace. The six remaining subjects each underwent 18 hrs of exercise training using the device for a period of 6 wks. Outcome measures included the upper-extremity component of the Fugl-Meyer scale and the modified Ashworth scale of muscle hypertonicity. RESULTS: Analysis revealed that the mean upper-extremity component of the Fugl-Meyer scale increased from 15.5 (SD 3.88) to 19 (SD 3.95) (P = 0.04) at the conclusion of training for the six subjects who completed training. Combined (summated) modified Ashworth scale for the elbow flexors and extensors improved from 4.67 (+/-1.2 SD) to 2.33 (+/-0.653 SD) (P = 0.009) and improved for the entire upper limb as well. All subjects tolerated the device, and no complications occurred. CONCLUSION: EMG-controlled powered elbow orthoses can be successfully controlled by severely impaired hemiparetic stroke survivors. This technique shows promise as a new modality for assisted exercise training after stroke.     

Electrophysiologic study of the quadriceps muscles during fatiguing exercise and recovery: a comparison of symptomatic and asymptomatic postpolio patients and controls

This study was performed to determine whether deficits in muscle strength, work capacity, and ability to recover strength after exhaustion in symptomatic postpolio subjects were due to central inhibition (lassitude) or other physiologic differences. We studied 34 symptomatic polio subjects, 16 asymptomatic polio subjects, and 41 control subjects. Root mean squared electromyography (RMS-EMG) and the median frequency (Fm) of the power spectrum of the quadriceps muscle was determined with surface electrodes during maximal volitional contraction (MVC) of isometric knee extension, an endurance test to exhaustion at 40% of maximal torque, and strength recovery testing that was performed at regular intervals for 10 minutes postexhaustion. Initial Fm during MVC and during the 40% MVC endurance test were similar in all three groups. The Fm decreased during the endurance test and increased during recovery similarly in all three groups. The RMS-EMG also changed in parallel fashion in all three groups during the same procedures. During recovery, a similar degree of RMS-EMG facilitation was seen in all three groups. Thus, reduction in strength, work capacity, and ability to recover from fatiguing exercise do not appear to be related to central factors (lassitude); they are probably related to other factors, such as local muscle fatigue. Each group appears to fatigue and recover in a similar manner electrophysiologically, although symptomatic polio subjects have a deficit in strength recovery, apparently due to local muscular fatigue.     

Contributors to fatigue resistance of the hamstrings and quadriceps in cerebral palsy

Background

The purpose of this study was to elucidate relationships between quadriceps and hamstrings voluntary muscle fatigue and upper motor lesion impairments in cerebral palsy in order to gain a better understanding of their contribution to the observed fatigue resistance.

Methods

Seventeen ambulatory subjects with cerebral palsy (mean age: 17.0, SD = 4.8 years) were recruited. Quantitative measures of strength, spasticity, cocontraction, and stiffness for both muscle groups were collected on an isokinetic dynamometer and entered in a factor analysis. The resulting factors were used as independent variables in a multiple regression analysis with quadriceps and hamstrings fatigue as dependent variables.

Findings

Five independent factors explained 90% of the variance. In order of loadings, higher hamstring cocontraction and spasticity and lower hamstring strength were associated with lower levels of hamstring fatigue. Higher quadriceps cocontraction and lower quadriceps strength were the most predictive of lower levels of quadriceps fatigue.

Interpretation

Greater motor impairments of the agonist muscle, particularly cocontraction, spasticity, and weakness, were associated with lower rates of muscle fatigue of the same muscle during performance of a voluntary fatigue protocol for the hamstrings and quadriceps. Muscles are highly adaptable; therefore, the results of this study suggest that the observed fatigue resistance may be due to the effect of the primary neural insult on motor unit recruitment and rate modulation or the result of secondary adaptations to spasticity, weakness, or excessive cocontraction.     

Spectral analysis of surface electromyography (EMG) of upper esophageal sphincter-opening muscles during head lift exercise

Although recent studies have shown enhancement of deglutitive upper esophageal sphincter opening in healthy elderly patients performing an isometric/isotonic head lift exercise (HLE), the muscle groups affected by this process are not known. A shift in the spectral analysis of surface EMG activity seen with muscle fatigue can be used to identify muscles affected by an exercise. The objective of this study was to use spectral analysis to evaluate surface EMG activities in the suprahyoid (SHM), infrahyoid (IHM), and sternocleidomastoid (SCM) muscle groups during the HLE. Surface EMG signals were recorded continuously on a TECA Premiere II during two phases of the HLE protocol in eleven control subjects. In the first phase of the protocol, surface EMG signals were recorded simultaneously from the three muscle groups for a period of 20 s. In the second phase, a 60 s recording was obtained for each of three successive trials with individual muscle groups. The mean frequency (MNF), median frequency (MDF), root mean square (RMS), and average rectified value (ARV) were used as spectral variables to assess the fatigue of the three muscle groups during the exercise. Least squares regression lines were fitted to each variable data set. Our findings suggest that during the HLE the SHM, IHM, and SCM muscle groups all show signs of fatigue; however, the SCM muscle group fatigued faster than the SHM and IHM muscle groups. Because of its higher fatigue rate, the SCM muscle group may play a limiting role in the HLE.     

Mechanisms underlying muscle fatigue differ between multiple sclerosis patients and controls: a combined electrophysiological and neuroimaging study

Increased sense of fatigue is an important and conspicuous symptom in multiple sclerosis (MS). Muscle fatigue is associated with increased sense of fatigue in MS (Steens et al., 2011). The aim of this study was to investigate mechanisms that can explain muscle fatigue in MS patients and controls. We assessed changes in cortical activation (BOLD), voluntary activation (twitch interpolation) and muscle force during a sustained maximal voluntary contraction (MVC) in twenty MS patients and twenty healthy controls.In control participants, individual differences in force decline (mean 65% MVC, 8 SD) during the sustained maximal contraction could be accounted for by differences in maximal voluntary force (R²: 0.49, p = 0.001); stronger participants presented a larger force decline. The small decline in voluntary activation (mean 7.8%, 11.8 SD) did not contribute significantly to the force decline. During the sustained contraction, the force decline was accompanied by an increase in cortical activation in the main motor areas.In MS patients, the differences in the decline in force (mean 67% MVC, 9 SD) were significantly associated (R²: 0.51, p = 0.001) with a decline in voluntary activation (mean 20.1%, 20.6 SD) and not with maximal force or decline in rest twitch. The corresponding cortical activation in motor areas showed an increase in the first two intervals of the sustained contraction but declined during the last interval.Our data indicate that muscle fatigue during a sustained contraction in MS patients is associated with changes in the voluntary activation that are not sufficiently compensated by increased cortical activation. Control participants, however, show increased cortical activation to compensate for these fatigue-related changes in voluntary activation and the major cause of force decline is therefore to be found in the periphery (muscles).     

Intrinsic muscle strength and voluntary activation of both lower limbs and functional performance after stroke

The objective of this study was to assess the nature of muscle weakness in both legs after stroke compared with able-bodied control individuals and to examine whether there is a relationship between the degree of muscle weakness and coactivation of knee extensors and flexors as well as voluntary activation capacity of knee extensors of both paretic and non-paretic legs and indices of functional performance. Maximal voluntary isometric torques of knee extensors (MVCe) and flexors (MVCf) were determined in 14 patients (bilaterally) and 12 able-bodied controls. Simultaneous measurements were made of torque and surface EMG from agonist and antagonist muscles. Coactivation was calculated. Supramaximal triplets were evoked with electrical stimulation to estimate maximal torque capacity and degree of voluntary activation of knee extensors. MVCs, activation and coactivation parameters were correlated to scores of seven functional performance tests. MVCe, MVCf and voluntary activation were lower in paretic lower limb (PL) compared with both non-paretic lower limb (NL) and control. Besides, all these parameters of NL were also lower than control. Electrically evoked torque capacity of knee extensors of PL was about 60% of both NL and control, which were not significantly different from each other. Strong significant correlations between strength, as well as voluntary activation, and functional performance were found. Coactivation did not correlate well with functional performance. Thus, whereas for NL activation failure can explain weakness, for PL both activation failure and reduced intrinsic torque capacity are responsible for the severe weakness. Activation capacity and muscle strength correlated strongly to functional performance, while coactivation did not.     

Cardiorespiratory and neuromuscular deconditioning in fatigued and non-fatigued breast cancer survivors

Purpose

Fatigue is one of the most commonly reported side effects during treatment for breast cancer and can persist following treatment completion. Cancer-related fatigue after treatment is multifactorial in nature, and one hypothesized mechanism is cardiorespiratory and neuromuscular deconditioning. The purpose of this study was to compare cardiorespiratory and neuromuscular function in breast cancer survivors who had completed treatment and met the specified criteria for cancer-related fatigue and a control group of breast cancer survivors without fatigue.

Methods

Participants in the fatigue (n?=?16) and control group (n?=?11) performed a maximal exercise test on a cycle ergometer for determination of peak power, power at lactate threshold, and VO₂ peak. Neuromuscular fatigue was induced with a sustained submaximal contraction of the right quadriceps. Central fatigue (failure of voluntary activation) was evaluated using twitch interpolation, and peripheral fatigue was measured with an electrically evoked twitch.

Results

Power at lactate threshold was lower in the fatigue group (p?=?0.05). There were no differences between groups for power at lactate threshold as percentage of peak power (p?=?0.10) or absolute or relative VO₂ peak (p?=?0.08 and 0.33, respectively). When adjusted for age, the fatigue group had a lower power at lactate threshold (p?=?0.02) and absolute VO₂ peak (p?=?0.03). There were no differences between groups in change in any neuromuscular parameters after the muscle-fatiguing protocol.

Conclusions

Findings support the hypothesis that cardiorespiratory deconditioning may play a role in the development and persistence of cancer-related fatigue following treatment. Future research into the use of exercise training to reduce cardiorespiratory deconditioning as a treatment for cancer-related fatigue is warranted to confirm these preliminary findings.     

EMG signs of neuromuscular fatigue related to the ventilatory threshold during cycling exercise

We questioned whether electromyographic (EMG) signs of neuromuscular fatigue accompany the changes in respiratory variables measured at the ventilatory threshold (VTh) during exercise on a cycloergometer. This was based on the assumption that the activation of muscle afferents sensitive to accumulation of lactate and potassium is suspected to elicit both the EMG signs of fatigue and hyperventilation. In 39 subjects performing an incremental cycling, the EMG estimates of neuromuscular fatigue in vastus lateralis were a non-linear increase in root mean square (RMS), a decrease in median frequency (MF), a non-linear increase in low-frequency EMG energies (EL), and/or a decrease in high-frequency energies (EH). VTh was determined from a non-linear increase in VCO2 [VTh(VCO2 slope)] and an increased value of the respiratory equivalent for oxygen [VTh(VE/VO2)]. We measured a significant increase in venous blood concentration of lactate and potassium, and a significant pHv fall at VTh. One EMG estimate of fatigue was detected in 33/39 individuals and two EMG estimates in 17 subjects. Highly significant positive correlations were found between the oxygen uptakes corresponding to each EMG estimate and to each detection criterion of VTh. These observations suggest that the activation of muscle sensory pathways contribute to the mechanism of VTh.     

Polio and postpolio sequelae: the lived experience

Many polio survivors who have been asymptomatic for a number of years are now experiencing problems with fatigue, weakness, pain, and cold intolerance. Treatment is possible, and support groups are available to deal with postpolio sequelae.