Mutation-specific CAR T cells as precision therapy for IGLV3-21R110 expressing high-risk chronic lymphocytic leukemia

The concept of precision cell therapy targeting tumor-specific mutations is appealing but requires surface-exposed neoepitopes, which is a rarity in cancer. B cell receptors (BCR) of mature lymphoid malignancies are exceptional in that they harbor tumor-specific-stereotyped sequences in the form of point mutations that drive self-engagement of the BCR and autologous signaling. Here, we use a BCR light chain neoepitope defined by a characteristic point mutation (IGLV3-21R110) for selective targeting of a poor-risk subset of chronic lymphocytic leukemia (CLL) with chimeric antigen receptor (CAR) T cells. We develop murine and humanized CAR constructs expressed in T cells from healthy donors and CLL patients that eradicate IGLV3-21R110 expressing cell lines and primary CLL cells, but neither cells expressing the non-pathogenic IGLV3-21G110 light chain nor polyclonal healthy B cells. In vivo experiments confirm epitope-selective cytolysis in xenograft models in female mice using engrafted IGLV3-21R110 expressing cell lines or primary CLL cells. We further demonstrate in two humanized mouse models lack of cytotoxicity towards human B cells. These data provide the basis for advanced approaches of resistance-preventive and biomarker-guided cellular targeting of functionally relevant lymphoma driver mutations sparing normal B cells.

Barriers and enablers of vigorous intermittent lifestyle physical activity (VILPA) in physically inactive adults: a focus group study

BACKGROUND

Vigorous Intermittent Lifestyle Physical Activity (VILPA) refers to brief bouts of vigorous intensity physical activity performed as part of daily living. VILPA has been proposed as a novel concept to expand physical activity options among the least active. As a nascent area of research, factors which impede or encourage VILPA in physically inactive adults are yet to be explored. Such information is pertinent in the design of future interventions. We examined the barriers and enablers of VILPA among physically inactive adults using the Capability, Opportunity, Motivation, Behavior (COM-B) model as a conceptual framework.

METHODS

We recruited a sample of self-identified physically inactive middle-aged and older adults (N = 78) based in Australia to take part in 19 online focus groups across three age groups: young-middle (age 35-44), middle (age 45-59) and old (age 60-76). We analyzed interviews using a critical realist approach to thematic analysis. Identified barriers and enablers were subsequently mapped onto the COM-B model components.

RESULTS

The data generated 6 barriers and 10 enablers of VILPA that corresponded to COM-B concepts. Barriers included physical limitations (physical capability), perceptions of aging, need for knowledge (psychological capability), environmental constraints (physical opportunity), perceptions of effort and energy, and fear (automatic motivation). Enablers included convenience, reframing physical activity as purposeful movement, use of prompts and reminders (physical opportunity), normalization of taking the active option, gamification (social opportunity), sense of achievement, health improvements, personally salient rewards (reflective motivation), identity fit, and changing from effortful deliberation to habitual action (automatic motivation).

CONCLUSION

The barriers and enablers of VILPA span capability, opportunity, and motivation beliefs. Promoting the time-efficient nature and simplicity of VILPA requiring no equipment or special gym sessions, the use of prompts and reminders at opportune times, and habit formation strategies could capitalize on the enablers. Addressing the suitability of the small bouts, the development of specific guidelines, addressing safety concerns, and explicating the potential benefits of, and opportunities to do, VILPA could ameliorate some of the barriers identified. Future VILPA interventions may require limited age customization, speaking to the potential for such interventions to be delivered at scale.

First experience with 224Radium-labeled microparticles (Radspherin®) after CRS-HIPEC for peritoneal metastasis in colorectal cancer (a phase 1 study)

Background

Peritoneal metastasis (PM) from colorectal cancer carries a dismal prognosis despite extensive cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (CRS-HIPEC). With a median time to recurrence of 11-12 months, there is a need for novel therapies. Radspherin® consists of the α-emitting radionuclide radium-224 (²²⁴Ra), which has a half-life of 3.6 days and is adsorbed to a suspension of biodegradable calcium carbonate microparticles that are designed to give short-range radiation to the serosal peritoneal surface linings, killing free-floating and/or tumor cell clusters that remain after CRS-HIPEC.

Methods

A first-in-human phase 1 study (EudraCT 2018-002803-33) was conducted at two specialized CRS-HIPEC centers. Radspherin® was administered intraperitoneally 2 days after CRS-HIPEC. Dose escalation at increasing activity dose levels of 1-2-4-7-MBq, a split-dose repeated injection, and expansion cohorts were used to evaluate the safety and tolerability of Radspherin®. The aim was to explore the recommended dose and biodistribution using gamma-camera imaging. The results from the planned safety interim analysis after the completion of the dose-limiting toxicity (DLT) period of 30 days are presented.

Results

Twenty-three patients were enrolled: 14 in the dose escalation cohort, three in the repeated cohort, and six in the expansion cohort. Of the 23 enrolled patients, seven were men and 16 were women with a median age of 64 years (28-78). Twelve patients had synchronous PM stage IV and 11 patients had metachronous PM [primary stage II; (6) and stage III; (5)], with a disease-free interval of 15 months (3-30). The peritoneal cancer index was median 7 (3-19), operation time was 395 min (194-515), and hospital stay was 12 days (7-37). A total of 68 grade 2 adverse events were reported for 17 patients during the first 30 days; most were considered related to CRS and/or HIPEC. Only six of the TEAEs were evaluated as related to Radspherin®. One TEAE, anastomotic leakage, was reported as grade 3. Accordion ≥3 grade events occurred in a total of four of the 23 patients: reoperation due to anastomotic leaks (two) and drained abscesses (two). No DLT was documented at the 7 MBq dose level that was then defined as the recommended dose. The biodistribution of Radspherin® showed a relatively even peritoneal distribution.

Conclusion

All dose levels of Radspherin® were well tolerated, and DLT was not reached. No deaths occurred, and no serious adverse events were considered related to Radspherin®.Clinical Trial Registration: Clinicaltrials.gov, NCT03732781.

First experience with 224Radium-labelled microparticles (radspherin) after CRS-HIPEC for peritoneal metastasis in colorectal cancer (a phase 1 study)

3599

Background: Peritoneal metastasis (PM) from colorectal cancer carries a dismal prognosis. Improved survival can be achieved by combining extensive cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (CRS-HIPEC). However, median time to recurrence is short (11-12 months) and there is a need for novel therapies to prevent subsequent PM. Radspherin consists of the α-emitting radionuclide radium-224 (224Ra), half-life 3.6 days, adsorbed to a suspension of biodegradable calcium carbonate microparticles, designed to give short-range radiation to the serosal peritoneal surface, aiming to kill remaining free cancer cells and small tumor cell clusters. Methods: A first-in-man phase 1 study (EudraCT 2018-002803-33) was conducted at two specialized CRS-HIPEC centers. Radspherin was injected in the abdominal cavity through a catheter 2 days after CRS-HIPEC. Dose escalation at increasing dose levels of 1-2-4-7-MBq, repeated injection and expansion cohorts evaluated the safety and tolerability of Radspherin, explored maximal tolerated dose and biodistribution by using single photon-emission computed tomography/computed tomography (SPECT/CT) imaging. Results from the planned safety interim analysis after completion of the dose-limiting toxicity (DLT) period are presented. Results: Twenty-three patients were enrolled, dose escalation cohort (14), repeated cohort (3) and expansion cohort (6). Nineteen patients were treated in Oslo/ 4 in Uppsala. Twelve patients had synchronous PM Stage IV and 11 metachronous PM (Stage II (6), Stage III (5). Disease-free interval 15 months (3-39); males (7), females (16); median age 64 years (28-78). Peritoneal cancer index was median 7 (3-19), operation time 395 minutes (194-515) and hospital stay 12 days (7-37). Accordion ≥3 grade events (6); including anastomotic leaks (2); abscess (1); drains (2) and missed lesion (1), all reported as serious adverse events (SAEs). The 7MBq dose was selected as recommended dose as no DLT was observed. A total of 185 treatment emergent adverse effects (TEAE) were recorded, most were of low grade and considered related to CRS and/or HIPEC. Few patients (7) had TEAEs considered related to a combined impact of Radspherin and CRS-HIPEC. The biodistribution of Radspherin showed a relatively even peritoneal distribution, and no patients had compartments of the abdominal cavity without radioactivity (cold spots), and low number had hot spots. Long-term safety, dosimetry and first efficacy results of Radspherin will be reported after 12 months follow up period. Conclusions: All dose levels of Radspherin were well tolerated with DLT not reached. No deaths occurred and no SAEs were considered related to Radspherin. The biodistribution of Radspherin showed good peritoneal distribution of the radiolabeled microparticles. Clinical trial information: 2018-002803-33.

Take a Stand!-a multi-component intervention aimed at reducing sitting time among office workers-a cluster randomized trial

Background

Prolonged sitting time has been associated with adverse health outcomes. Interventions at work may contribute to reduced sitting. The objective was to test if a multicomponent work-based intervention can reduce sitting time and the number of prolonged sitting periods (> 30 min), increase the number of sit-to-stand transitions and decrease waist circumference and body fat percentage among office workers. Primary outcomes were: change in sitting time, prolonged sitting periods and sit-to-stand transitions at follow-up 1 month later.

Methods

At four workplaces, 19 offices (317 workers in total) were cluster randomized for intervention or control. The intervention included the appointment of local ambassadors, management support, environmental changes, a lecture and a workshop. Sitting time was measured using an ActiGraph GT3X+ fixed on the thigh. Data were processed using Acti4 software providing data on time spent sitting, standing and doing other activities. Control participants were instructed to behave as usual. Follow-up measurements were obtained after 1 and 3 months.

Results

At 1 and 3 months, total sitting time was 71 ( P < 0.001) and 48 min ( P < 0.001) lower per 8-h workday in the intervention group compared with the control group. At 1 month, the number of prolonged sitting periods was lower (-0.79/8-h workday, P < 0.001) and sit-to-stand transitions were higher (+14%/sitting hour, P = 0.001) in the intervention compared with the control group. After 3 months, trends persisted. The body fat percentage was lower by 0.61 percentage points ( P = 0.011) in the intervention group compared with the control group after 3 months.

Conclusions

The multicomponent workplace-based intervention was effective in reducing sitting time, prolonged sitting periods and body fat percentage, and in increasing the number of sit-to-stand transitions.

Occupational and leisure-time physical activity and workload among construction workers - a randomized control study

BACKGROUND

There is a lack of quantification of occupational physical activity (OPA) and leisure time physical activity (LTPA) among construction workers.

OBJECTIVES

To describe physical activity energy expenditure (PAEE), physical workload, and the effect of a PA-intervention among construction workers.

METHODS

Sixty-seven Construction workers self-reported their physical activity (PA), had PA assessed directly (PAEE), and observed OPA using the tool "Posture, Activity, Tools and Handling." The PA-intervention (Intervention; n = 29, Controls; n = 24) included 3x20-min training/week for 12 weeks.

RESULTS

Baseline median OPA was 5036 MET-min/week and LTPA 2842 MET-min/week, p < 0.01. OPA directly recorded was (mean ± SE): 56.6 ± 3.2 J/kg/min and LTPA was: 35.7 ± 2.2 J/kg/min (p < 0.001). Manual material handling was performed for ≥ 25% of working time by more than 50% of the participants. Post-intervention, the training group reduced overall PAEE compared to the control group but not specifically during work.

CONCLUSIONS

OPA was within the maximum recommended level of 1/3 proposed in consensus guidelines but did not decrease with PA-intervention.

Properties of the Tampa Scale for Kinesiophobia across Workers with Different Pain Experiences and Cultural Backgrounds: A Rasch Analysis

The main aim of this study was to evaluate whether the construct validity of the Tampa Scale for Kinesiophobia (TSK) is consistent with respect to its scaling properties, unidimensionality and targeting among workers with different levels of pain. The 311 participating Danish workers reported kinesiophobia by TSK (13 statement version) and number of days with pain during the past year (less than 8 days, less than 90 days and greater than 90 days). A Rasch analysis was used to evaluate the measurement properties of the TSK in the workers across pain levels, ages, genders and ethnicities. The TSK did not fit the Rasch model, but removing one item solved the poorness of fit. Invariance was found across the pain levels, ages and genders. Thus, with a few modifications, the TSK was shown to capture a unidimensional construct of fear of movement in workers with different pain levels, ages, and genders.

Comparison of objectively measured and self-reported time spent sitting

Until recently, methods for objective quantification of sitting time have been lacking. The aim of this study was to validate self-reported measures against objectively measured total sitting time and longest continuous time with uninterrupted sitting during working hours, leisure time on workdays and leisuredays. Objective diurnal measurement of sitting time was obtained among 26 office workers with 2 accelerometers (ActiGraph GT3X+) for a 7-day period. Customized software (Acti4) was used to identify sitting time separated from other sedentary behaviours. Self-reported sitting time was obtained from a retrospective 7-day questionnaire. A generalized linear model showed the difference between the methods. No significant correlations were found between objective and self-reported sitting time (r<0.315). Total sitting time was significantly underestimated (2.4 h) on a leisureday (p<0.001) and uninterrupted sitting time was in all 3 time settings significantly overestimated (0.4-0.5 h) (p<0.045). Poor agreement (mean difference between 0.5 to -2.4 h) between objectively measured and self-reported sitting time was shown in Bland-Altman plots with wide (3.3-10.8 h) limits of agreement. This study showed a great individual variation and a general lack of agreement between self-reported vs. objectively measured total and uninterrupted sitting time. Objective measures are recommended for determining sitting time.

Selective activation of intra-muscular compartments within the trapezius muscle in subjects with Subacromial Impingement Syndrome. A case-control study

Neuromuscular control of the scapular muscles is important in the etiology of shoulder pain. Electromyographical (EMG) biofeedback in healthy people has been shown to support a selective activation of the lower compartment of the trapezius muscle, specifically. The aim of the present paper was to investigate whether patients with Subacromial Impingement Syndrome (SIS) were able to selectively activate the individual compartments within the trapezius muscle, with and without EMG biofeedback to the same extent as healthy controls (No-SIS). Fifteen SIS and 15 No-SIS participated in the study. Sessions with and without visual biofeedback were conducted. Surface EMG was recorded from four compartments of the trapezius muscle. Selective activation was defined as activation above 12% with other muscle parts below 1.5% or activation ratio at or above 95% of the total activation. Without biofeedback significantly fewer SIS subjects than No-SIS achieved selective activation (p=0.02-0.03). The findings of the study show that without biofeedback No-SIS had a superior scapular muscle control. However, when provided with visual EMG feedback the SIS group performed equally well as the No-SIS group. This indicated that individuals with SIS may benefit from biofeedback training to gain control of the neuromuscular function of the scapular muscle.

Should physical activity recommendation depend on state of low back pain?

BACKGROUND

Leisure time physical activity is recommended for preventing long-term sickness absence (LTSA). Although low back pain (LBP) is a risk factor for sickness absence and physical activity is recommended for people with LBP, it is unknown if leisure time physical activity prevents LTSA among persons with different levels of LBP.

METHODS

Prospective cohort study among 8655 Danish female healthcare workers responding to a questionnaire in 2004-2005 on leisure time physical activity and LBP, and subsequently followed for 1 year on periods with LTSA ∼2 consecutive weeks or more of sickness absence in a national register of social transfer payments (DREAM). Multi-adjusted Cox regression analysis was used to model risk estimates for LTSA associated with low, moderate, high and very high leisure time physical activity at baseline among healthcare workers with no LBP (0 days past 12 months, n = 2761), non-chronic LBP (1-30 days the past 12 months, n = 3942) and persistent LBP (>30 days the past 12 months, n = 1952).

RESULTS

A strongly reduced risk for LTSA from high leisure time physical activity was found among healthcare workers with no LBP [hazard ratio (HR): 95% confidence interval (CI) 0.47:0.23-0.97 for low vs. very high activity] and non-chronic LBP (HR: 95%CI 0.43:0.23-0.84 of low vs. very high activity), but not among healthcare workers with persistent LBP (HR: 95%CI 1.15:0.55-2.44 of low vs. very high activity).

CONCLUSIONS

Leisure time physical activity is a strong predictive factor on LTSA among female healthcare workers with no and non-chronic LBP, but not among those with more persistent LBP.

Physical exercise, body mass index and risk of chronic arm pain: longitudinal data on an adult population in Norway

AIM

The aim of this study was to prospectively investigate the association between leisure time physical exercise, body mass index (BMI) and risk of chronic arm pain.

METHODS

The study population comprises 14,041 women and 13,674 men in the Norwegian HUNT Study without musculoskeletal pain or physical impairment at baseline in 1984-86. Chronic arm pain was assessed at follow-up in 1995-97. A generalized linear model was used to calculate adjusted relative risks (RRs).

RESULTS

At follow-up, 2205 women and 1458 men reported chronic arm pain. Level of physical exercise was inversely associated with risk of chronic arm pain (P-trend, ≤0.03 for both sexes). Compared with inactive persons, women and men who exercised ≥ 2 h/week had adjusted RRs of 0.84 [95% confidence interval (CI), 0.73-0.96] and 0.74 (95% CI, 0.63-0.87), respectively. BMI was positively associated with risk of chronic arm pain (P-trend, ≤0.002 for both sexes). Compared with normal-weight persons, women and men classified as obese (BMI ≥ 30 kg/m2) had adjusted RRs of 1.26 (95% CI, 1.11-1.44) and 1.29 (95% CI, 1.07-1.57), respectively. Combined analysis showed that obese women and men who exercised  ≥ 1 h/week had a RR of 1.20 (95% CI 0.97-1.48) compared with normal-weight women and men with a similar activity level, whereas the RR was 1.41 (95% CI 1.21-1.65) for obese women and men who were physically inactive.

CONCLUSION

Regular physical exercise reduces risk of chronic arm pain while high BMI increases the risk. Exercise can to some extent compensate for the adverse effect of obesity on risk of chronic arm pain.

Does occupational lifting and carrying among female health care workers contribute to an escalation of pain-day frequency?

BACKGROUND

The aim of the study was to investigate if different frequencies, loads and trunk postures of occupational lifting and carrying increases the risk of sub-chronic (1-30 days last 12 months) low back pain (LBP) to become persistent (>30 days last 12 months) among female health care workers.

METHODS

Female health care workers answered a questionnaire about occupational lifting or carrying frequency (rarely, occasionally and frequently), load (low: 1-7 kg, moderate: 8-30 kg and heavy: >30 kg) and trunk posture (upright or forward bent back), and days with LBP in 2005 and 2006.

RESULTS

The odds ratio (OR) for developing persistent LBP in 2006 from these characteristics of occupational lifting and carrying was investigated with multi-adjusted logistic regressions among female health care workers with sub-chronic LBP (n = 2381) in 2005. Among health care workers with sub-chronic LBP, increased risk of persistent LBP was found from frequently lifting or carrying with forward bent back of moderate loads (OR: 1.63; 95% CI: 1.15-2.33) and heavy loads (OR: 1.56; 95% CI: 1.04-2.34). No increased risk for LBP to develop into a persistent condition was found for frequent lifting with upright back, frequent lifting or carrying of light loads, or occasionally lifting or carrying of any loads.

CONCLUSIONS

Preventive initiatives for sub-chronic LBP to develop into a persistent condition ought to focus on reducing frequent lifting and carrying of moderate and heavy loads with forward bent back.

Spreading of chronic pain between body regions: prospective cohort study among health care workers

OBJECTIVE

To estimate the prognostic value of pain in one body region on the risk for developing chronic pain in other body regions.

METHODS

Prospective cohort study among 5052 Danish female health care workers responding to a baseline and follow-up questionnaire in 2005 and 2006, respectively. Using adjusted logistic regression analysis, the risk for developing chronic pain (>30 days last year) at follow-up in the low back (among those without low back pain during the last year at baseline) when experiencing sub-chronic (1-30 days last year) or chronic pain in other body regions (i.e., the neck/shoulders and/or the knees at baseline) was modelled. Similar risks were modelled for developing chronic pain in the neck/shoulders and knees.

RESULTS

Chronic pain in the neck/shoulders (OR 3.14; 95% CI 1.74-5.70) or knees (OR 2.57; 95% CI 1.28-5.16) at baseline increased the risk for developing chronic pain in the low back at follow-up. Likewise, chronic pain in the neck/shoulders (OR 2.39; 95% CI 1.36-4.17) or low back (OR 1.82 95%; CI 1.07-3.09) at baseline increased the risk for developing chronic pain in the knees at follow-up. The risk for developing chronic neck/shoulder pain was not significantly increased when having pain in the low back or knees at baseline.

CONCLUSION

Among health care workers, chronic musculoskeletal pain in one body region increases the risk for developing chronic pain in other pain-free body regions. Prevention of musculoskeletal disorders among health care workers should focus holistically on the musculoskeletal system.

The health paradox of occupational and leisure-time physical activity

BACKGROUND

Occupational and leisure-time physical activity are considered to provide similar health benefits. The authors tested this hypothesis.

METHODS

A representative sample of Danish employees (n=7144, 52% females) reported levels of occupational and leisure-time physical activity in 2005. Long-term sickness absence (LTSA) spells of ≥3 consecutive weeks were retrieved from a social-transfer payment register from 2005 to 2007.

RESULTS

341 men and 620 females experienced a spell of LTSA during the period. Cox analyses adjusted for age, gender, smoking, alcohol, body mass index, chronic disease, social support from immediate superior, emotional demands, social class and occupational or leisure-time physical activity showed a decreased risk for LTSA among workers with moderate (HR 0.85, CI 0.72 to 1.01) and high (HR 0.77, CI 0.62 to 0.95) leisure-time physical activity in reference to those with low leisure-time physical activity. In contrast, an increased risk for LTSA was shown among workers with moderate (HR 1.59, CI 1.35 to 1.88) and high (HR 1.84, CI 1.55 to 2.18) occupational physical activity referencing those with low occupational physical activity.

CONCLUSION

The hypothesis was rejected. In a dose-response manner, occupational physical activity increased the risk for LTSA, while leisure-time physical activity decreased the risk for LTSA. The findings indicate opposing effects of occupational and leisure-time physical activity on global health.

Duration of differential activations is functionally related to fatigue prevention during low-level contractions

The aim of this study was to investigate the importance of duration of differential activations between the heads of the biceps brachii on local fatigue during prolonged low-level contractions. Fifteen subjects carried out isometric elbow flexion at 5% of maximal voluntary contraction (MVC) for 30 min. MVCs were performed before and at the end of the prolonged contraction. Surface electromyographic (EMG) signals were recorded from both heads of the biceps brachii. Differential activation was analysed based on the difference in EMG amplitude (activation) between electrodes situated at the two heads. Differential activations were quantified by the power spectral median frequency of the difference in activation between the heads throughout the contraction. The inverse of the median frequency was used to describe the average duration of the differential activations. The relation between average duration of the differential activations and the fatigue-induced reduction in maximal force was explored by linear regression analysis. The main finding was that the average duration of differential activation was positively associated to relative maximal force at the end of the 30 min contraction (R(2)=0.5, P<0.01). The findings of this study highlight the importance of duration of differential activations for local fatigue, and support the hypothesis that long term differential activations prevent fatigue during prolonged low-level contractions.

Selective activation of neuromuscular compartments within the human trapezius muscle

Task-dependent differences in relative activity between "functional" subdivisions within human muscles are well documented. Contrary, independent voluntary control of anatomical subdivisions, termed neuromuscular compartments is not observed in human muscles. Therefore, the main aim of this study was to investigate whether subdivisions within the human trapezius can be independently activated by voluntary command using biofeedback guidance. Bipolar electromyographical electrodes were situated on four subdivisions of the trapezius muscle. The threshold for "active" and "rest" for each subdivision was set to >12% and <1.5% of the maximal electromyographical amplitude recorded during a maximal voluntary contraction. After 1h with biofeedback from each of the four trapezius subdivisions, 11 of 15 subjects learned selective activation of at least one of the four anatomical subdivisions of the trapezius muscle. All subjects managed to voluntarily activate the lower subdivisions independently from the upper subdivisions. Half of the subjects succeeded to voluntarily activate both upper subdivisions independently from the two lower subdivisions. These findings show that anatomical subdivisions of the human trapezius muscle can be independently activated by voluntary command, indicating neuromuscular compartmentalization of the trapezius muscle. The independent activation of the upper and lower subdivisions of the trapezius is in accordance with the selective innervation by the fine cranial and main branch of the accessory nerve to the upper and lower subdivisions. These findings provide new insight into motor control characteristics, learning possibilities, and function of the clinically relevant human trapezius muscle.

Differential activation of regions within the biceps brachii muscle during fatigue

AIM

To examine the occurrence of repeated differential activation between the heads of the biceps brachii muscle and its relation to fatigue prevention during a submaximal contraction.

METHODS

Thirty-nine subjects carried out an isometric contraction of elbow flexion at 25% of maximal voluntary contraction (MVC) until exhaustion. A grid of 13 by 10 electrodes was used to record surface electromyographic signals from both heads of the biceps brachii. The root-mean-square of signals recorded from electrodes located medially and laterally was used to analyse activation differences. Differential activation was defined as periods of 33% different activation level between the two heads of the biceps brachii muscle.

RESULTS

Differential muscle activation was demonstrated in 30 of 33 subjects with appropriate data quality. The frequency of differential activation increased from 4.9 to 6.6 min(-1) at the end of the contractions with no change in duration of the differential activations (about 1.4 s). Moreover, the frequency of differential activation was, in general, negatively correlated with time to exhaustion.

CONCLUSION

The observed differential activation between the heads of the biceps brachii can be explained by an uneven distribution of synaptic input to the motor neurone pool. The findings of this study indicate that differential activation of regions within a muscle does not prevent fatigue at a contraction level of 25% of MVC.

EMG amplitude distribution changes over the upper trapezius muscle are similar in sustained and ramp contractions

AIM

To investigate whether global motor unit recruitment to compensate for muscle fatigue during sustained contraction and to regulate force increase during ramp contraction are controlled in similar manners in the upper trapezius muscle.

METHODS

Fourteen subjects performed a 10-s ramp contraction from 0% to 90% of maximal voluntary contraction (MVC) and a 3-min sustained contraction at 25% MVC. Both contractions involved isometric shoulder elevation with a multi-channel surface electromyographical grid placed on the skin above the muscle. To evaluate the global muscle activation pattern, the changes in spatial amplitude distribution of the sustained and the ramp contraction were examined and compared.

RESULTS

In both contraction types, the upper part of the trapezius muscle was spatially non-uniform (inhomogeneous) activated. Throughout the sustained contraction, the amplitude distribution of the upper trapezius muscle became more similar to the amplitude distribution at higher force levels.

CONCLUSION

These findings support the hypothesis that global motor unit recruitment to compensate for muscle fatigue during a sustained contraction, and to regulate force increase during a ramp contraction is controlled in a similar manner. Consequently, they confirm fundamental principles of motor unit activation based on recordings of limited motor unit samples.

On-line signal quality estimation of multichannel surface electromyograms

When multichannel surface-electromyography (MCSEMG) systems are used, there is a risk of recording low-quality signals. Such signals can be confusing for analysis and interpretation and can be caused by power-line interference, motion artifacts or poor electrode-skin contact. Usually, the electrode-skin impedance is measured to estimate the quality of the contact between the electrodes and the skin. However, this is not always practical, and the contact can change over short time-scales. A fast method is described to estimate the quality of individual signals of monopolar MCSEMG recordings based on volume conduction of myo-electric signals. The characteristics of the signals were described using two descriptor variables. Outliers (extreme data points) were detected in the two-dimensional distributions of the descriptor variables using a non-parametric technique, and the quality of the signals was estimated by their outlier probabilities. The method's performance was evaluated using 1 s long signals visually classified as very poor (G 1), poor (G2) or good quality (G3). Recordings from different subjects, contraction levels and muscles were used. An optimum threshold at 0.05 outlier probability was proposed and resulted in classification accuracies of 100% and > 70% for G I and G2 signals, respectively, whereas <5% of the G3 signals were classified as poor. In conclusion, the proposed method estimated MCSEMG signal quality with high accuracy, compared with visual assessment, and is suitable for on-line implementation. The method could be applied to other multichannel sensor systems, with an arbitrary number of descriptor variables, when their distributions can be assumed to lie within a certain range.