Guilherme H. Elcadi

Oxygenation and hemodynamics do not underlie early muscle fatigue for patients with work-related muscle pain

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 (StO2%) 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 StO2% 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.

NEAR INFRARED SPECTROSCOPY AS A USEFUL RESEARCH TOOL TO MEASURE PREFRONTAL CORTEX ACTIVITY DURING VISUALLY DEMANDING NEAR WORK

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 (HbO2) 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 (ΔHbO2) 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 ΔHbO2 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.

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

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 (dlPFC) 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 dlPFC 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 (ΔHbO2), deoxygenated hemoglobin (ΔHHb) and total hemoglobin (ΔtHb). 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 ΔHbO2 and ΔtHb 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 HbO2, HHb, and tHb, recorded over the dlPFC with fNIRS, can be used to assay the degree to which supervisory oculomotor control processes are activated during visually deficient near work.

A Comparison of Mental and Visual Load Resulting from Semi-automated and Conventional Forest Forwarding: An Experimental Machine Simulation Study

The purpose of the present study was to extend the knowledge of functional linkages between visual and mental load, performance, and prefrontal cortex (PFC) activity, during forestry forwarding work. Eleven healthy participants, range 21–51 years old, with a minimum of 1-year work experience, carried out the task of loading logs along a standardized path in a machine simulator during two counterbalanced test conditions: (i) conventional crane control, and; (ii) semi-automated crane control. Mental load was assessed by quantification of oxygenated hemoglobin (HbO2) concentration changes over the right dorsolateral prefrontal cortex (dlPFC) via non-invasive functional near infrared spectrometry (fNIRS). Visual, autonomic, and motoric control variables were measured and analyzed in parallel along with the individual level of performance. Linear Mixed Models (LMM) analysis indicated more mental load during conventional crane work. Collectively, our data suggest that fNIRS is a viable tool which can be used in neuroergonomic research to evaluate physiological activity levels in PFC.

A Strong Correlation Between Dorsolateral Prefrontal Cortex And Vastus Lateralis Activity During Running To Fatigue

Fatigue is a phenomenon of pronounced importance in sports. Recently, there is strong evidence of interplay between the prefrontal cortex and motor output during fatiguing contractions. The dorsola ...

Reproducibility And Gender Comparisons Of Oxygenation, Blood Flow And Oxygen Consumption For The Forearm: 1746

Reproducibility and gender comparisons of oxygenation, blood flow and oxygen consumption for the forearm

Oxygenation and myoelectric activity in the forearm and shoulder muscles of males and females

Oxygenation and myoelectric activity in the forearm and shoulder muscles of males and females