To Örebro University

To improve current understandings of physical workload (WL) in elite bandy, 10 bandy players were monitored for heart rate (HR) during 13 matches over 1 championship season. Participants were divided into 5 subgroups according to playing position-libero, defender, halves, midfielder, and forward. Heart rate measurements were analyzed with 2 different methods to compute physical WL-(a) percentage of total time spent in different HR zones (HRres) and (b) WL based on the Edwards method. Also determined was the time spent at HR levels above the lactate threshold (LT). A one-way analysis of variance was used for analysis. For WL, according to the Edwards method, significant differences (p = 0.05) were shown between the groups with defenders presenting the highest scores, and forwards and liberos the lowest. A significant difference (p = 0.05) was found between liberos and halves and the other positions as to how much time they spent in zone 70-80% of HRres. In 91-100% of HRres, there was a distinct difference between defenders and the other positions and also forwards differed significantly from liberos, defenders, and halves (p = 0.05). The libero spent only 1% of the time over the LT, whereas the midfielder spent approximately 27% of the time over the LT. Overall, defenders showed the greatest WL during a match and liberos the lowest. The practical implications of these findings can help coaches and trainers design training methods specific to each position and individualized training sessions for each player in elite bandy.

This study determined the day-to-day reliability of NIRS-derived oxygenation responses (a dagger StO(2)%) for isometric contractions and for cuff occlusion. Twenty-four subjects (12 males and 12 females) were tested for 2 days (4-6 days interval). Variables generated were: (1) a dagger StO(2)% for isometric contractions (10, 30, 50 and 70% MVC) for descending trapezius (TD) and extensor carpi radialis (ECR) muscles; (2) slope changes in total haemoglobin (HbTslope) and deoxyhaemoglobin (HHbslope) for the ECR using upper arm venous (VO, 50 mmHg) and arterial occlusion (AO, 250 mmHg); (3) recovery slopes (Rslope) for oxygen saturation (StO(2)) following isometric contractions and AO. For each variable, an intraclass correlation (ICC) was calculated to assess the ability to differentiate between subjects, and limits of agreement (LOA) were computed to assess day-to-day consistency of the measurement. ICCs for Delta StO(2)% were lowest at 10% MVC for both ECR (0.58) and TD (0.55), and highest at 30% MVC for ECR (0.95) and at 70% MVC for TD (0.79). For both muscles, LOA for Delta StO(2)% was lowest at 10% and highest at 50 and 70% MVC. ICC for HbTslope was 0.17. For HHbslope ICC was higher for AO (0.83) than for VO (0.73), and LOA was lower for AO. For the ECR Rslope ICCs ranged from 0.88 to 0.90 for contraction, but was lower for AO (0.33); LOA was lowest at 70% MVC. For trapezius Rslope ICCs ranged from 0.63 to 0.73 and LOA was lowest at 30% MVC. For this study, establishing reliability data for the ECR and TD and including variables commonly reported are expected to have meaning for future NIRS studies of work-related upper-extremity pain as well as for other NIRS research and clinical applications.

We tested hypotheses of (a) reduced oxygen usage, oxygen recovery, blood flow and oxygen consumption; and (b) increased muscle activity for patients diagnosed with work-related muscle pain (WRMP) in comparison to healthy controls. Oxygenation was measured with near infrared spectroscopy (NIRS), and muscle activity with EMG for the extensor carpi radialis (ECR) and trapezius descendens (TD) muscles. Eighteen patients with diffuse neck-shoulder-arm pain and 17 controls (matched in age and sex) were equipped with NIRS and EMG probes. After determining an individual's maximum voluntary contraction (MVC) force, short-term (20 s) isometric contractions for the ECR and TD of 10, 30, 50 and 70 % MVC generated a dagger StO(2) and StO(2)% recovery (Rslope) from NIRS, and RMS%(max) from EMG signals. In addition, upper arm venous (VO) and arterial (AO) occlusions generated slopes of total hemoglobin (HbTslope) and deoxyhemoglobin (HHbslope) for the resting ECR as surrogates of blood flow and oxygen consumption, respectively. Mixed model analyses, t tests, and Mann-Whitney test were used to assess differences between groups. There was no significant difference in MVC between groups for either muscle. Also, a dagger StO(2)%, Rslope for either muscle, and ECR-HbTslope were not different between groups, thus our hypotheses of reduced oxygen use, recovery, and blood flow for patients were not confirmed. However, patients had a significantly lower ECR-HHbslope confirming our hypothesis of reduced consumption. Further, there was no difference in RMS%(max) during contractions meaning that the hypothesis of increased activity for patients was not confirmed. When taking into account the number of NIRS variables studied, differences we found between our patient group and healthy controls (i.e., in forearm oxygen consumption and shoulder oxygen saturation level) may be considered modest. Overall our findings may have been impacted by the fact that our patients and controls were similar in muscle strength, which is in contrast to previous studies.

The aim was to investigate the relationship between oxygen saturation (StO(2)%) measured with near-infrared spectroscopy (NIRS) and myoelectric activity (root mean square, RMS) for the extensor carpi radialis (ECR) and trapezius muscles. In addition, gender differences were examined for submaximal (10-70% MVC) and sustained (10% MVC for 5 min) isometric contractions. Thirteen males and 15 females participated. Changes in StO(2)% (a dagger StO(2)%) and RMS, expressed as percentages of maximum, were calculated for each submaximal contraction. A good correlation between a dagger StO(2)% and RMS was seen for the ECR (r = -0.53) and a moderate correlation seen for the trapezius muscle (r = -0.44). The ANOVA showed a significant decrease in ECR-a dagger StO(2)% over force with females demonstrating a tendency for larger changes than males. ECR-RMS increased over force with no impact of gender. For the trapezius, a dagger StO(2)% decreased over force but was not gender dependent. Trapezius-RMS increased over force with females demonstrating a tendency for greater change than males. For the sustained contraction, ECR-StO(2)% changed over time but was not gender dependent. ECR-RMS increased over time with females showing a greater response than males. Trapezius-StO(2)% changed over time and differed between genders, i.e., males increased while females decreased. RMS increased over time similarly for both genders. In conclusion, our data show that the ECR and trapezius aerobic demands during isometric contractions are negatively correlated to electromyography (EMG) RMS. The present study also suggests some gender specificity for forearm and shoulder myoelectric activity and oxygenation for submaximal and sustained contractions.

Patients suffering from work-related muscle pain (WRMP) fatigue earlier during exercise than healthy controls. Inadequate oxygen consumption and/ or inadequate blood supply can influence the ability of the muscles to withstand fatigue. However, it remains unknown if oxygenation and hemodynamics are associated with early fatigue in muscles of WRMP patients. In the present study we applied near-infrared spectroscopy (NIRS) on the extensor carpi radialis (ECR) and trapezius (TD) muscles of patients with WRMP (n = 18) and healthy controls (n = 17). Our objective was to determine if there were group differences in endurance times for a low-level contraction of 15% maximal voluntary contraction (MVC) -sustained for 12-13 min, and to see if these differences were associated with differences in muscle oxygenation and hemodynamics. At baseline, oxygen saturation (StO(2)%) was similar between groups for the ECR, but StO2% was significantly lower for TD for the WRMP patients (76%) compared to controls (85%) (P < 0.01). Also, baseline ECR blood flow was similar in the two groups. For both muscles there were a larger number of patients, compared to controls, that did not maintain the 15% MVC for the allotted time. Consequently, the endurance times were significantly shorter for the WRMP patients than controls (medians, ECR: 347 s vs. 582 s; TD: 430 s vs. 723 s respectively). Responses in StO(2)% during the contractions were not significantly different between groups for either muscle, i.e. no apparent difference in oxygen consumption. Overall, we interpret our findings to indicate that the early fatigue for our WRMP patients was not associated with muscle oxygenation and hemodynamics.

Aims: Our purpose was to determine whether Transcranial Direct Current Stimulation (tDCS) improves performance in untrained individuals for supramaximal intermittent exercise.

Methods: In a cross-over design, 11 healthy male subjects (26.8 ± 4.6 years) performed four Wingate trials after 20 minutes of anodal or sham tDCS over the left Insular Cortex (IC). For performance indexes, Relative Peak Power (RPP), Relative Average Power (RAP) and Fatigue Index (FI) were computed. Also, a Rating of Perceived Exertion (RPE) and Electromyography (EMG) signal were used to assess central and muscle fatigue development.

Results: There was a significant difference over trials on all performance indexes, but there were no significant condition x trial interactions for any of the indexes. RPE increased significantly over trials, but there was no condition x trial interaction. There was no significant difference over trials on EMG for the rectus femoris and vastus medialis muscles; however, EMG decreased over trials for the vastus lateralis muscle. Furthermore, there was no condition x trial interaction on the EMG signal for any of the muscles.

Conclusion: Our findings suggest that the anodal tDCS technique has no impact on physical performance, perceived exertion nor muscle fatigue development for supramaximal intermittent exercise. 

OCCUPATIONAL APPLICATIONS Effort, which overrides the need for rest and recuperation to avoid deterioration in visual performance, is commonplace in many contemporary workplaces. The prefrontal cortex is capable of allocating more mental/physical resources to carry out a given work task in the presence of fatigue. However, adverse musculoskeletal and mental health consequences are an anticipated outcome of this since fatigue is a physiological sign of the need for recuperative rest. This article outlines the current evidence suggesting that probing into prefrontal brain activity with near-infrared spectroscopy could advance progress in visual ergonomic research, and pilot data are provided that exemplify the proposed approach. Improved understanding of the age-related health consequences of straining the brain and/or the eyes "to see well" will likely help ergonomic stakeholders find better methods to meet the needs of safer and more productive work environments.

TECHNICAL ABSTRACT Background: Unlike the usual skeletal muscles, ciliary muscles responsible for focusing the crystalline eye lens and extraocular muscles responsible for convergence eye movements appear resistant to fatigue. Purpose: The dual goals of this article are to briefly outline the current evidence that suggests that probing into blood flow and hemodynamic prefrontal brain activity with near-infrared spectroscopy could advance progress in visual ergonomic research and to provide pilot data exemplifying the proposed approach. Methods: The vision task consisted of sustained focusing on a contrast-varying black-and-white Gabor grating. Four participants with a median age of 46 (interquartile range 44-50) fixated the grating from a distance of 65 cm. Three counterbalanced 10-minute tasks required central fixation and accommodation/convergence on the grating target through (i) 0.0 diopter lenses, (ii) -1.5 diopter lenses, and (iii) -3.5 diopter lenses while maintaining maximal focus. Non-invasive measurements of local oxyhemoglobin (HbO(2)) were quantified with a one-channel near-infrared spectrometer. The near-infrared spectroscopy probe was placed on the prefrontal cortex in the vicinity of the right dorsolateral prefrontal cortex or Brodmann area 46. Accommodation response and contrast threshold were measured in parallel. Results: General estimating equation analyses showed that baseline-subtracted dorsolateral prefrontal cortex blood flow (Delta HbO(2)) increased significantly over time in all three lens conditions. The effect of time may be caused by a continuous increase in mental effort to compensate for progressively more mental fatigue induced by increased visual attention. The increase of dorsolateral prefrontal cortex Delta HbO(2) was also larger in magnitude in participants with larger amplitudes accommodation response (i.e., in participants who minimized deterioration in visual performance). Conclusion: The results from this study indicate that oxyhemoglobin changes recorded over the dorsolateral prefrontal cortex with near-infrared spectroscopy can be used to assay the degree to which the visual system is strained during demanding near work.

A Corrigendum on

Prefrontal Cortex Oxygenation Evoked by Convergence Load Under Conflicting Stimulus-to-Accommodation and Stimulus-to-Vergence Eye-Movements Measured by NIRS

by Richter, H. O., Forsman, M., Elcadi, G. H., Brautaset, R., Marsh, J. E., and Zetterberg, C. (2018). Front. Hum. Neurosci. 12:298. doi: 10.3389/fnhum.2018.00298

In the original article, there was a mistake in Figure 5A (left panel) as published.

Figure 5A (left panel) should show Ctrl Low convergence group, not Conv Low convergence group. The corrected Figure 5A (left panel) appears below. The authors apologize for this error and state that this does not change the scientific conclusions of the article in any way.

The original article has been updated.

Purpose: To extend our knowledge of the functional linkages between visual fatigue and regional cerebral prefrontal cortex (PFC) oxygenation, we measured time related hemodynamic changes over the right dorsolateral prefrontal cortex (dIPFC) during convergence load under conflicting stimulus-to-accommodation and stimulus-to-vergence eye movements with and without concurrent mental load.

Methods: Twenty healthy participants with a median age of 28 years (range: 18-44 years) fixated upon a vertical bar presented separately to the left and right eyes, using polarized filters, during four counterbalanced 10-min periods: (i) no accommodation/vergence conflict (Control, Ctrl): (ii) added convergence load and accommodation/vergence conflict (Conv); (iii) added cognitive load only (Cog) and; (iv) a combination of added cognitive and convergence load and accommodation/vergence conflict (Cc). Viewing distance was 65 cm. Non-invasive measurements of hemodynamic activity over the dIPFC were quantified by functional near-infrared spectroscopy (fNIRS). During the two-convergence load conditions, the horizontal disparity of the two bars varied dynamically from no disparity to a disparity set 20% below the individual threshold for diplopia. Cognitive load was induced by the n-back-2 test which required the subject to memorize and recall the changing colors of the horizontal bars and decide when a given color was the same as that occurring two colors previously. fNIRS data were averaged over 10-s windows centered at 0, 2, 4, 6, 8, and 10 min of each task, subtracted from a 20-s baseline window immediately preceding the visual task, and then represented as changes in oxygenated hemoglobin (Delta HbO(2)), deoxygenated hemoglobin (Delta HHb) and total hemoglobin (Delta tHb).

Results: Linear mixed model analyses showed that hemodynamic activity was systematically influenced by time (p < 0.001). The group-averaged time-related level of change across the viewing conditions did not differ when compared with one another (p > 0.05). Larger convergence eye-movement responses under conflicting stimulus-to-accommodation, and stimulus-to-vergence over time, increased Delta HbCO(2) and Delta tHb only in condition Cc and after 8 min of task time (p < 0.10 for min(-6) and min(-8): p < 0.05 for min(-10)).

Discussion: Collectively, our data suggest that HbCO(2), HHb, and tHb, recorded over the dIPFC with fNIRS, can be used to assay the degree to which supervisory oculomotor control processes are activated during visually deficient near work.

Background

Peripheral muscle factors are presumed to be important contributors to the reduced exercise capacity in congenital heart disease (CHD), but the mechanisms are poorly understood.

Purpose

To investigate if muscle oxygenation in the calf muscle is impaired in adults with complex CHD in comparison to controls.

Method

Seventy-four adults with complex CHD (35.6±14.3 years, females n=22) were recruited from centers specialized in adult CHD. Seventy-four age and gender matched subjects were recruited as controls. Muscle oxygenation was successfully determined using near-infrared spectroscopy on the medial portion of m. gastrocnemiusin 63 patients and 67 controls. Measurements were made at rest, during venous occlusion to estimate blood flow (BF – indicated by the slope increase of total haemoglobin, HbT), at the start of isotonic unilateral heel-lifts to exhaustion, and immediately after exercise.

Results

In comparison to controls, patients had a lower muscle saturation (StO2) at rest, albeit not statistically significant, (66±17% vs. 60±19%, p=0.07), and a lower BF (0.38±0.21 vs. 0.31±0.21 HbTx3.5sec^–1, p=0.07). For exercise, compared to the controls, patients had a slower desaturation rate at exercise onset (−11.7±5.8% vs. −7.7±4.3%. StO2x3.5sec^–1, p<0.001), and both a slower resaturation rate (6.1±3.8% vs. 3.9±3.7% StO2x3.5sec^–1, p=0.002) and a slower half recovery time (16.8±11.1 vs. 28.6±21.2 sec, p<0.001) post exercise.

Conclusion

The lower muscle oxygenation and blood flow at rest, and the slower oxygenation kinetics during exercise may give insight to the mechanism for the reduced exercise capacity commonly found in adults with complex CHD. This finding may also provide implications for design of rehabilitation programs for these patients.

BACKGROUND: Adults with complex congenital heart disease (CHD) show reduced aerobic exercise capacity and impaired skeletal muscle function compared with healthy peers. Peripheral muscle factors are presumed to be important contributors to the aerobic capacity, but the mechanisms are poorly understood. The aim of the present study was to investigate differences between adults with CHD and controls in muscle oxygenation kinetics at rest, and during and after exercise.

METHODS: Seventy-four patients with complex CHD (mean age 35.6 ± 14.3 years, female n = 22) were recruited. Seventy-four age- and sex-matched subjects were recruited as controls. Muscle oxygenation was successfully determined on the anterior portion of the deltoid muscle using near-infrared spectroscopy in 65 patients and 71 controls. Measurements were made at rest, during isotonic shoulder flexions (0-90°) to exhaustion, and during recovery.

RESULTS: The patients with CHD performed fewer shoulderflexions (40 ± 17 vs 69 ± 40; P<0.001), had lower muscle oxygen saturation (StO2) at rest (58 ± 18% vs 69 ± 18%; P<0.001), slower desaturation rate at exercise onset (-9.7 ± 5.9 vs -15.1 ± 6.5% StO2 x 3.5 s1, P<0.001), and slower resaturation rate post exercise (4.0 ± 2.7 vs 5.4 ± 3.6% StO2 x 3.5 s1; P = 0.009) compared with the controls.

CONCLUSIONS: In comparison with age- and sex-matched controls, adults with complex CHD had slower oxygenation kinetics. This altered skeletal muscle metabolism might contribute to the impaired skeletal muscle endurance capacity shown and thereby also to the reduced aerobic capacity in this population.