INTRODUCTION:Developing a greater understanding of how the body reacts following cold water immersion (CWI) and its impact on human performance is required for the development of future monitoring technologies and countermeasures to reduce cold-induced impairments. Currently, there are no field-deployable technologies for real-time monitoring of cold-induced neurochemical and metabolic changes, limiting physiological assessment tools for monitoring the impact of cold immersion on cognitive and physical performance. Functional near-infrared spectroscopy (fNIRS) may be an effective technique for monitoring the impact of cold exposures on neurophysiological functions; however, a deeper examination of the fNIRS patterns of responses is needed to progress the interpretability of this technique in austere environments. Therefore, the purpose of this study was to examine the cerebral hemodynamic responses over the prefrontal cortex (PFC) as well as respiratory and common carotid artery (CCA) responses during a 10-minute CWI. MATERIALS AND METHODS:Twenty-six participants (age = 23.6 ± 4.3 years) completed 2 testing visits, which consisted of a 10-minute thermoneutral water immersion (TWI; 35 °C) or CWI (15 °C). Functional near-infrared spectroscopy-derived oxygenated hemoglobin (O2Hb) was measured over the PFC, as well as respiratory rate, tidal volume, and CCA diameter, were measured at the beginning and end of the immersion period. In addition, skin temperature (Tsk) and thermal perception were measured during each condition. Repeated measures ANOVA's were used to examine the condition and time course of response changes for Tsk, respiratory rate, tidal volume, thermal perception, and CCA diameter. A general linear model analysis was used to examine differences in beta values of the O2Hb between the TWI and CWI conditions. This study was approved by the university's institutional review board (IRB: 2115890). RESULTS:There was no significant change in O2Hb during the TWI condition (P = .15), however, O2Hb significantly increased during the CWI (P < .01). The CCA diameter did not change during the TWI (P = .84) but increased during the CWI (P < .01). There was a significant decrease in Tsk (P < .01) during CWI and greater thermal perception compared to TWI (P < .01), which showed no significant changes (P = .06-.82). Respiratory rate remained unchanged (P = .59). Tidal volume was significantly greater during the CWI compared to TWI (P < .01). CONCLUSIONS:Initial exposure to CWI induced a cold shock response with a 43% increase in tidal volume, without a corresponding increase in respiratory rate. This suggested a potential, intuitive, cold-mitigation strategy in cold naïve participants. In addition, the O2Hb responses indicated a short-lived, cold-induced mismatch between cerebral oxygen demand and supply. The increase in cerebral oxygenation reflects a cold-induced increase in cerebral blood flow to prevent localized temperature drops, along with elevated counter-current vascularization and metabolic heat generation.

BACKGROUND:Night vision goggles (NVG) grant warfighters a tactical advantage in low-light environments. However, NVG use can negatively affect visual acuity, depth perception, and color discrimination, which impacts warfighter safety and operational performance. Therefore, the purpose of this study was to examine the biomechanical effects in the walking phase of an obstacle clearance course and prefrontal cortex (PFC) regional oxygen saturation (rScO2) during embedded marksmanship and cognitive tasks performed with and without NVGs. METHODS:Twelve participants (21 [SD 1] years) completed an obstacle avoidance course with and without NVGs, which included pistol marksmanship assessments, cognitive assessments, and ground obstacles. Gait pattern, performance tasks, and PFC activity were recorded. RESULTS:Marksmanship performance decreased by 58.2% (P<.01), but cognitive performance was not impacted with NVG use (P=.676). Toe clearance increased by 32.2% (P<.01), toe velocity decreased by 20.5% (P<.01), and ankle dorsiflexion increased by 24.0% (P=.02) with NVG. Significant reductions in rScO2 during Marksmanship 2 (P<.01) and Cognitive Assessment Task 1 (P=.01) and 2 (P=.01) were observed. CONCLUSION:Performance decrements with NVG use are hypothesized to be primarily due to altered vision perception and increased metabolic demand affecting marksmanship performance and gait patterns. NVG training may minimize the risk of musculoskeletal injuries and improve operational performance.

PURPOSE:The purpose of this case series was to explore the feasibility and impact of a 3-week activities-based locomotor training (AB-LT) program on functional activities and neurophysiological adaptations in 5 children with cerebral palsy (CP). METHODS:Children, aged 2-6 years who were classified as Gross Motor Function Classification Scale levels III or IV, participated in the intervention 5 days per week for 3 hours per day. The Gross Motor Function Measure-66 (GMFM-66) and functional near-infrared spectroscopy neuroimaging were performed pre- and post-intervention. RESULTS:After AB-LT, increases in GMFM-66 scores were observed for Children 1 (Δ3.3), 2 (Δ5.6), 4 (Δ1.8), and 5 (Δ1.3), beyond expected natural progression. A reduction in total hemoglobin activation and increased neural demand was observed. Child 3 had minimal functional changes with no observed neurophysiological adaptations. CONCLUSIONS:The 3-week AB-LT regimen is a short duration, high-intensity program with the potential to benefit children with CP.

INTRODUCTION:Traumatic brain injury (TBI) is a significant health concern, particularly in military and sports settings. This study investigated the use of functional near-infrared spectroscopy (fNIRS) to identify TBI in Role of Care (ROC) 1 and 2 environments. This initial study aimed to begin the development of a rapid, noninvasive neuroimaging technique for assessing brain injuries in field settings. MATERIAL AND METHODS:Twelve participants, who were all Division 1 athletes, volunteered for this study (age: 21.1 ± 2.7 years). A 4 × 1 optode to receiver fNIRS grid was placed over the injured and un-injured region of the brain (control) while performing a 60-second simple reaction time test. These assessments were collected within the first 24  hours of injury, when the team's physician cleared the participant for return to activity (RTA) and return to play (RTP). All testing were performed in ROC 1 or 2 environments. A Morlet wavelet fNIRS analysis approach was then used to rapidly interpret data in field-based environments. RESULTS:The Morlet wavelet fNIRS analysis identified the injured brain region. The injured region exhibited 72% greater tHb (P = .013), 2.6-fold increase in O2Hb (P = .018), and 1.3-fold increase in hHb compared to the control region (P = .006). The average time from the initial point of injury to being cleared for RTP was 4.3 ± 2.7 weeks. The average of the simple reaction time test exhibited a decrease in reaction time from initial and RTA at the RTP timepoint (P = .016). CONCLUSION:The Morlet wavelet fNIRS analysis identified the injured region of the brain at initial, RTA, and RTP timepoints in ROC 1 and 2 environments. It did not detect differences in recovery, but there was an improvement in simple reaction time. Thus, the fNIRS analysis detected TBI's in ROC 1 and 2, but further development is needed to increase its sensitivity to tracking TBI's over time.

INTRODUCTION:Marksmanship is a fundamental skill for all servicemembers. However, the underlying neurophysiological differences in performance among marksmen remain unclear. Incorporating neurophysiological tracking such as functional near-infrared spectroscopy (fNIRS) may identify performance-based differences in prefrontal cortex (PFC) activation during dynamic marksmanship scenarios. This study examined cognitive load within the PFC during a simulated dynamic marksmanship scenario in non-proficient and proficient marksmen. METHODS:Twenty-four participants (12 men, 12 women) wore an fNIRS device over their forehead during a simulated stationary pistol marksmanship task (to determine proficiency status) and a dynamic shoot/no-shoot course of fire (COF) (to assess cognitive load). Relative concentrations of oxyhemoglobin (HbO2 ), deoxygenated hemoglobin (deoxygenated Hb), and total hemoglobin (total Hb) were tracked to quantify PFC activation differences in twelve proficient (=80% hit percentage) and twelve non-proficient (<80% hit percentage) marksmen. RESULTS:No difference in completion time was observed between groups during the dynamic COF (p=.34). However, non-proficient marksmen showed 26.3% higher HbO2 (p=.02) and 42.1% higher total Hb (p<.01) in the PFC compared to proficient marksmen. CONCLUSION:Tracking PFC hemodynamic activity identified proficiency-based differences in cognitive load during a dynamic COF. Applying fNIRS during marksmanship-related tasks may be useful in developing stress resilience and mission readiness for servicemembers.

PURPOSE:Examine the cardiovascular, muscular function, cognitive, and neural plastic responses to determine the safety and effectiveness of acute Intermittent hypoxia (AIH) at a low, high, and control fractional inspired oxygen (FiO2) dosage METHODS: Thirteen human participants performed 30-min of AIH in 60-s intervals at FiO2's of 0.21 (AIH21), 0.15 (AIH15), and 0.09 (AIH9). Heart rate variability (root mean squared of successive differences; RMSSD), heart rate, oxygen saturation (SpO2), blood pressure, muscular strength, neuromuscular activation, cerebral hemodynamic responses, cognition, symptomology, and brain-derived neurotrophic factor (BDNF) responses were measured before (Pre-AIH), after (post-AIH), and at 20-min of recovery (Recovery-AIH) RESULTS: There were no differences between AIH protocols for heart rate, RMSSD, blood pressure, or SpO2. Muscular strength improved Post-AIH for AIH15 (10 %) and AIH9 (14 %) and remained elevated (6 %) at Recovery-AIH. Neuromuscular activation increased Pre-AIH to Post-AIH for AIH15 (10 %) and AIH9 (11 %). Cerebral hemodynamic responses were not impacted between conditions. Both AIH15 and AIH9 increased BDNF Post-AIH (62 %) and Recovery-AIH (63 %) CONCLUSION: Acute intermittent hypoxia is generally safe and effective at producing neural plastic responses, but further examination of co-occurring cardiovascular diseases is needed. This study provides safety focused findings which will widen the adoption and refinement of AIH protocols.

Objectives This study examined the effects of acute normoxic and hypoxic exposure on neuromuscular and hemodynamic physiological responses performed during dynamic step muscle actions. Methods Thirteen recreationally active men (mean +/- SD age: 21.2 +/- 2.9 yrs) performed dynamic leg extensions unilaterally under Normoxic (FiO(2) = 21 %) and Hypoxic (FiO(2) = 13 %) conditions in a randomized order at 20 %, 40 %, 60 %, 80 %, and 100 % of their maximal strength. Electromyographic (EMG) amplitude, EMG frequency, (Oxygenated and Deoxygenated hemoglobin; Oxy(Hb), Deoxy(Hb)), Total hemoglobin (Total(Hb)), and skeletal muscle tissue oxygenation status (StO(2)) were measured from the vastus lateralis during all contractions. Results There were no detectable differences in the neuromuscular responses between normoxia and hypoxia for EMG amplitude (p = 0.37-0.74) and frequency (p = 0.17-0.83). For EMG amplitude there were general increases with intensity (p < 0.01-0.03). EMG frequency remained similar from 20% to 80% and then increased at 100 % effort (p = 0.02). There was no significant difference in patterns of responses for Oxy(Hb) (p = 0.870) and Total(Hb) (p = 0.200) between normoxia and hypoxia. StO(2) (p = 0.028) decreased and Deoxy(Hb) (p = 0.006) increased under hypoxia compared to normoxia during dynamic step muscle actions performed in a randomized order. Conclusion Unlike fatigue, acute hypoxemia in an unfatigued state does not impact the localized neuromuscular responses, but minimally impacts the hemodynamic responses.

ABSTRACT:Segovia, M, Salmon, OF, Ugale, C, and Smith, CM. The effects of cold exposure, hypoxia, and fatigue on pistol marksmanship and target engagement decision making in trained marksmen. J Strength Cond Res 38(11): e686-e694, 2024-This study aimed to examine the effects of cold exposure, hypoxia, and fatigue on pistol marksmanship and target engagement in trained marksmen. Twelve healthy subjects (mean ± SD age: 28.8 ± 4.0 years) performed 3 testing visits under normal/normoxic [Norm 21 ] (24° C; 21% FiO 2 ), cold/normoxic [Cold 21 ] (10° C; 21% FiO 2 ), and cold/hypoxic [Cold 14 ] (10° C; FiO 2 : 14.3) conditions. Pistol marksmanship and target engagement were assessed through draw time (DT) and shoot-no-shoot (SNS) courses of fire. The 2 protocols were performed before (T preF ) and immediately after (T postF ) a sandbag deadlift fatiguing protocol. Significance was set at p < 0.05. Significant condition × time interactions ( p = 0.01-0.03) were found for accuracy SNS (SNS acc ), misses SNS (SNS miss ), and total shots SNS (SNS tot ). Follow-up analyses indicated that SNS acc increased by 14.3% ( p = 0.03), SNS miss decreased by 34.7% ( p = 0.02), and SNS tot decreased by 10.6% ( p = 0.04) from T preF to T postF during the Cold 21 condition alone. No significance was found for these in the Norm 21 ( p = 0.08-0.22) or Cold 14 ( p = 0.18-0.47) conditions. Total time (SNS T ) to completion of the SNS ( p = 0.09) and DT ( p = 0.14) showed no significance across time or condition. Significant difference across time for Cold 14 ( p = 0.03-0.02) for reaction time was found. Exercise likely resulted in increased thermogenesis that improved tactically relevant motor skills including SNS acc , decreased SNS miss , and SNS tot in Cold 21 , but not Cold 14 . The additive effect of hypoxia coupled with exercise in the Cold 14 condition did not improve tactical performance, suggesting multi-stressor environments result in competing physiological responses. Tactical strength and conditioning specialists as well as operators should aim to improve thermoregulation during Cold 21 conditions, with exercise as a possible intervention.

Shoemaker, ME, Smith, CM, Gillen, ZM, and Cramer, JT. Sex differences in test-retest reliability of near-infrared spectroscopy during postocclusive reactive hyperemia of the vastus lateralis. J Strength Cond Res 38(2): e40-e48, 2024-The purpose of this study was to determine test-retest reliability for vascular reactivity measures and ranges for normalization of near-infrared spectroscopy (NIRS) variables from the vastus lateralis using postocclusive reactive hyperemia (PORH) procedure in male subjects, female subjects, and combined. Concentrations of oxygenated hemoglobin (Hb) + myoglobin (Mb) (O(2)Hb) and deoxygenated Hb + Mb (HHb) to derive total Hb + Mb (THb), difference in Hb + Mb signal (Hbdiff), and muscle tissue oxygen saturation (StO(2)) from the vastus lateralis were measured during the PORH in 12 male subjects (age: 23.17 +/- 1.77 years; stature: 180.88 +/- 4.59 cm; and mass: 81.47 +/- 9.68 kg) and 10 female subjects (age: 23.80 +/- 2.07 years; stature: 165.95 +/- 4.92 cm; and mass: 70.93 +/- 10.55 kg) on 2 separate days. Adipose tissue thickness at the NIRS site was measured with ultrasonography. There were no significant differences between the mean values from visit 1 to visit 2 (p > 0.076-0.985). In the composite sample, intraclass correlation coefficient (ICC) and coefficient of variation (CV) ranged from 0.35 to 0.91 and 4.74 to 39.18%, respectively. In male subjects, ICC and CV values ranged from 0.57 to 0.89 and 2.44 to 28.55%, respectively. In female subjects, ICC and CV values ranged from -0.05 to 0.75 and 7.83 to 61.19%, respectively. Although NIRS variables were overall reliable during PORH, when separated by sex, reliability in male subjects generally increased, whereas female subjects were not reliable, suggesting adipose tissue thickness may be a contributing factor. Understanding sex differences in reliability is important when using this technique for normalization or examining vascular reactivity during athletic performance. With greater utilization of NIRS monitoring in athletes to examine training adaptations, it is important for practitioners to understand the capabilities and potential limitations of the tool.

Abstract Salmon, OF, Housh, TJ, Hill, EC, Keller, JL, Anders, JPV, Johnson, GO, Schmidt, RJ, and Smith, CM. Changes in neuromuscular response patterns after 4 weeks of leg press training during isokinetic leg extensions. J Strength Cond Res 37(7): e405–e412, 2023—The purpose of this study was to identify velocity-specific changes in electromyographic root mean square (EMG RMS), EMG frequency (EMG MPF), mechanomyographic RMS (MMG RMS), and MMG MPF during maximal unilateral isokinetic muscle actions performed at 60° and 240°·s−1 velocities within the right and left vastus lateralis (VL) after 4 weeks of dynamic constant external resistance (DCER) bilateral leg press training. Twelve resistance-trained men (age: mean ± SD = 21.4 ± 3.6 years) visited the laboratory 3d·wk−1 to perform resistance training consisting of 3 sets of 10 DCER leg presses. Four, three-way analysis of variance were performed to evaluate changes in neuromuscular responses (EMG RMS, EMG MPF, MMG RMS, and MMG MPF) from the right and left VL during 1 single-leg maximal isokinetic leg extension performed at 60° and 240°·s−1 before and after 4 weeks of DCER leg press training (p < 0.05). The results indicated a 36% increase in EMG RMS for the right leg, as well as a 23% increase in MMG RMS and 10% decrease in MMG MPF after training, collapsed across velocity and leg. In addition, EMG RMS was 65% greater in the right leg than the left leg following training, whereas EMG MPF was 11% greater for the left leg than the right leg throughout training. Thus, 4 weeks of DCER leg press training provides sufficient stimuli to alter the neuromuscular activation process of the VL but not velocity-specific neuromuscular adaptations in trained males.

OBJECTIVES:This study examined effects of acute hypoxia on the neuromuscular responses (electromyographic (EMG) amplitude and EMG frequency) and localized muscle tissue oxygenated hemoglobin (oxygenated hemoglobin (OxyHb), deoxygenated hemoglobin (DeoxyHb), total hemoglobin (TotalHb), and muscle tissue oxygenation saturation (StO2) during the process of fatigue.METHODS:Fifteen male participants (21.4±2.8yr) performed leg extension repetitions to failure at 70% 1-repetition maximum until volitional exhaustion under Normoxic (FiO2:21%) and Hypoxic (FiO2:12.9%) conditions. Electromyographic amplitude, EMG frequency, OxyHb, DeoxyHb, TotalHb, and StO2 were measured from the vastus lateralis at Initial, 20, 40, 60, 80, and 100% of the repetitions to failure.RESULTS:There was no significant difference in the patterns of responses for EMG amplitude, OxyHb, or DeoxyHb between Normoxia and Hypoxia. For EMG frequency, Hypoxia was greater than Normoxia and decreased with fatigue. TotalHb and StO2 were greater under Normoxia compared to Hypoxia. The patterns of responses for EMG amplitude, DeoxyHb, and TotalHb increased throughout the repetitions to failure. OxyHb and StO2 exhibited decreases throughout the repetitions to failure for Normoxic and Hypoxic conditions.CONCLUSION:The EMG and oxygenation measurements non-invasively suggest a sympathoexcitatory response (indicated by EMG frequency) and provided complimentary information regarding the process of fatigue in normoxic and hypoxic states.

The purpose of this study was to investigate changes in gait patterns, motor dexterity, cognition, neuromuscular performance, neural activation of the prefrontal cortex, and perception of effort and exertion during a 60-min walking trial at a reduced body weight using a positive pressure treadmill (PPT). Eleven screened astronaut analog participants performed 60-min PPT sessions at either 100% (PPT100) or 20% body weight (PPT20) which were separated into six 10-min segments. During each segment, a 1-min gait analysis, Pegboard Task, Assembly Task, and Memory Recall Task were performed. Step frequency, rating of perceived physical and cognitive exertion, electromyographic amplitude and frequency from the vastus lateralis, metabolic markers, and functional near-infrared spectroscopy (fNIRS) of the prefrontal cortex were obtained for all segments during each condition. The primary findings of the study indicated that PPT20 was able to induce differences in step frequency relative to PPT100 and that PPT100 resulted in greater metabolic expenditures and electromyographic amplitude compared to PPT20. The PPT20, however, exhibited increased fNIRS prefrontal cortex activity during the Assembly Task and Memory Recall compared to the PPT100. In addition, the PPT20 resulted in an increase in Memory Recall errors compared to PPT100. In conclusion, the findings of the present study indicated that altered gait patterns associated with reduced weight does not impact basic motor dexterity tasks, such as gait and Pegboard Tasks, but does increase the difficulty of Assembly Tasks and Memory Recall in astronaut analogs. Thus, novel gait patterns can impact the cognitive loads that astronaut analogs can perform. Special considerations should be given to the impact that gravity-induced changes in gait patterns have on motor and cognitive tasks in future planetary exploration missions.

INTRODUCTION The newly implemented Army Combat Fitness Test (ACFT) of the U.S. Army seeks to revolutionize the Army's fitness culture and reduce the rate of preventable injuries among soldiers. The initial rollout of the ACFT has been met with several challenges, including a gender-neutral scoring system. The ACFT has undergone several revisions to adapt to the present state of U.S. Army physical fitness; however, the test faces several more obstacles as more data become available. The ACFT was designed to measure combat readiness, a useful tool for units facing deployment or a change in duty station to a high-altitude environment. Reduced oxygen availability (hypoxia) at high altitude influences many physiological functions associated with physical fitness, such that there is an increased demand for oxygen in exercising muscle. Therefore, the purpose was to investigate the effects of normoxic and two levels of hypoxia exposure (moderate and severe; fraction of inspired oxygen [FiO2]: 16.0% and 14.3%) during the 3-repetition deadlift (MDL), hand-release push-up (HRP), and leg tuck (LTK) events of the ACFT. MATERIALS AND METHODS Fourteen recreationally active men (n = 10) and women (n = 4) soldier analogs (27.36 ± 1.12 years, height 1.71 ± 2.79 m, weight 80.60 ± 4.24 kg) completed the MDL, HRP, and LTK at normoxia and acute normobaric moderate (MH; FiO2 16%) and severe (SH; FiO2 14.3%) hypoxic exposure. Scores and performance were recorded for each event, and heart rate (HR) and total body oxygen saturation (SpO2) were monitored throughout. Repeated-measures analysis of variance (ANOVA) was used to assess differences in modified ACFT scores, performance, HR, and SpO2 among hypoxic conditions, with follow-up one-way ANOVA and paired t-test when appropriate. RESULTS Total body oxygen saturation was decreased at MH and SH conditions compared to normoxia but did not vary between ACFT events. Heart rate was not influenced by altitude but did increase in response to exercise. Scores of the modified total and individual ACFT events were not different between normoxia, MH, and SH. There was also no difference in performance based on the amount of weight lifted during the MDL and number of repetitions of the HRP and LTK events in response to hypoxic exposure. CONCLUSIONS Performance and scores of the modified ACFT were not influenced by acute normobaric MH and SH exposure compared to normoxia. Further investigations should examine the full testing battery of the ACFT to provide a comprehensive analysis and potential evidence for such differences.

The purpose of this study was to examine the impact of independent cold and combined cold and hypoxic exposures on operational-specific task performance including pistol marksmanship, pistol magazine reload ability, and subjective and objective thermal indices before and after a whole-body physical exertional task. Twelve participants were exposed to Thermoneutral Normoxic (24 °C; FiO2 21%), Cold Normoxic (10 °C; FiO2 21%), and Cold Hypoxic (10 °C; FiO2 14%) conditions for 30min before performing pistol marksmanship at distances of 6.40 and 13.72m and a pistol magazine reload task before and after 3 sets of sandbag deadlifts at 50% body mass. Thermal perception and hand temperatures were collected before and after the physical exertion task. There were no significant differences in Pistol Accuracy performance at distances of 6.40 and 13.72m due to physical exertion, cold, or hypoxia. Following physical exertion, Pistol Accuracy was similar between Thermoneutral and Cold Normoxic conditions but lead to 17% and a 10% reduction in performance during the Cold Hypoxic condition, compared to Thermoneutral and Cold Normoxic conditions. There was no change in Pistol Accuracy for the Thermoneutral Normoxic condition. The pistol magazine reload task was not impacted by physical exertion, but there was a reduction in performance in Cold Normoxic 21% (4.04s) and Cold Hypoxic 16% (3.08s) conditions. Physical exertion did not impact hand temperature but did increase thermal perception scores for all conditions. These findings indicate that cold exposure reduced both tactical dexterity and pistol marksmanship, however, physical exertion may offset these deficits via an increase in thermal perception. Additionally, hypoxemia was the primary mediator of marksmanship performance in cold hypoxic environments following an acute bout of physical exertion. Thus, in cold mountainous environments, marksmen should be aware of their elevation and utilize brief episodes of physical activity to enhance their thermal state when marksmanship is a priority for operational success.

Objective: Near-Infrared Spectroscopy (NIRS) analysis techniques can often be complex to perform and interpret resulting in a barrier for wide-spread clinical use. The traditional Point-by-Point analysis methodology and our Post-Exertion Rate of Reperfusion method were examined during the recovery phases following repeated bouts of physical exertion to determine the physiological processes and information captured by each methodology under normal exertion conditions (FiO2: 0.210) and when in hypoxic conditions (FiO2: 0.129).Methods: To achieve this, a total of n = 15 participants performed 3 sets of leg extensions to failure at 70 % their maximal effort. A 1-min rest was performed following each set where the Point-by-Point analysis means were calculated at every 6-s time to recovery for a total of 10 mean values. The Post-Exertion Rate of Reperfusion examined the linear slopes for the entire 60-s. The near-infrared spectroscopy device was placed over the vastus lateralis and measure for muscle tissue oxygen saturation, oxygenated hemoglobin, deoxygenated hemoglobin, and total hemoglobin were obtained for both the Point-by-Point and Post-Exertion Rate of Reperfusion analysis. Results: Post-Exertion Rate of Reperfusion slopes were significantly different between normoxia and hypoxia for muscle tissue oxygen saturation (Normoxia: 0.151-0.171; Hypoxia: 0.068-0.116), oxygenated hemoglobin (Normoxia: 0.127 - 0.134; Hypoxia: 0.045 - 0.076), deoxygenated hemoglobin (Normoxia:-0.142 to-0.152; Hypoxia:-0.054 to-0.100), and total hemoglobin (Normoxia:-0.011 to 0.0250; Hypoxia:-0.009 to 0.024). Point-by-Point analysis identified significant differences between muscle tissue oxygen saturation and oxygen-ated hemoglobin, but not deoxygenated hemoglobin and total hemoglobin.Conclusion: Point-by-Point analysis and Post-Exertion Rate of Reperfusion can each provide distinctly unique information during exertional recovery. Point-by-Point analysis was ideal for detecting the onset of change in muscle oxygen status. Post-Exertion Rate of Reperfusion identified overall rates of change and was shown to be more sensitive at identifying changes in overall recovery of skeletal tissue reperfusion rates. Point-by-Point analysis and Post-Exertion Rate of Reperfusions may be utilized individually or separately to improve the interpretability of skeletal NIRS metrics within research or clinical settings.

To investigate the effects of two levels of acute hypoxic exposure and exercise compared to normoxia on the Stroop color word test. A total of 14 (4 females and 10 males) active participants with a self-reported (mean±SEM) 8.54±1.44 h/week of physical activity, performed a 3-repetition maximum hex/trap bar deadlift, Hand-Release Push-Up, and Leg Tuck events from the Army Combat Fitness Test at normoxia and normobaric hypoxia of fraction of inspired oxygen (FiO2) of 16% and 14.3%. The Stroop color-word test was administered on a touch screen device before and after the exercise battery, where participants were given congruent (word and ink color matching) and incongruent (non-matching) prompts. Peripheral oxygen saturation (SpO2) and heart rate were recorded at pre- and post-exercise. Variables obtained from the Stroop color word test were not influenced as a result of acute hypoxic exposure but did improve after an exercise battery. Peripheral oxygen saturation was greater during normoxia compared to acute hypoxic exposure which indicated a systemic change in oxygenation. The results of the present study indicated that the Stroop color-word test is not influenced by an FiO2 16% or 14.3%, however, exercise did improve Stroop score and response time.

Keller, JL, Housh, TJ, Hill, EC, Smith, CM, Schmidt, RJ, and Johnson, GO. Are there sex-specific neuromuscular or force responses to fatiguing isometric muscle actions anchored to a high perceptual intensity? J Strength Cond Res 36(1): 156-161, 2022-The purpose of this study was to use the ratings of perceived exertion (RPE) clamp model to examine sex-specific changes in neuromuscular responses and force after a sustained isometric leg extension muscle action anchored to RPE = 8. Twenty adults (10 men and 10 women) performed sustained, isometric leg extension muscle actions at RPE = 8. Electromyographic (EMG) and mechanomyographic signals were recorded from the dominant leg. Neuromuscular and force values resulting from the sustained muscle action were normalized to pretest maximal voluntary isometric contractions (MVICs). The level of significance set for the study was p <= 0.05. The pretest MVIC was significantly (p < 0.001) greater (averaged across sex) than posttest MVIC force (55.5 +/- 10.0 vs. 47.6 +/- 11.1 kg). There was a significant (p < 0.01) decrease from pretest (95.4 +/- 7.7 Hz) to posttest (76.2 +/- 5.9 Hz) in EMG mean power frequency (MPF) for the men. The normalized force (averaged across sex) decreased significantly (p < 0.001) from the initial timepoint (57.1 +/- 16.4%) to the final timepoint (44.3 +/- 15.7%) of the sustained muscle action. Normalized EMG MPF (averaged across sex) decreased significantly (p = 0.001) from the initial timepoint (96.4 +/- 17.5%) to final timepoint (87.8 +/- 18.1%). The men and women exhibited similar fatigue-induced changes in force and neuromuscular parameters; therefore, these findings did not indicate different sex-specific responses after the fatiguing task anchored to a high perception of exertion. The force corresponding to RPE = 8 did not match the anticipated value; so, RPE and percentages of MVIC cannot be used interchangeably, and sustained isometric muscle actions anchored to RPE may elicit unique neuromuscular adaptations.

Little is known about potential protective factors for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), referred to as COVID-19. Suboptimal vitamin D status is a risk factor for immune dysfunction, respiratory tract infections (RTIs), and viral infections. Supplementation of vitamin D (2000-4000 IU) has decreased incidence and complications from RTIs, respiratory distress syndrome, and pneumonia and may be beneficial in high-risk populations. Given the possible link between low vitamin D status and RTIs, such as COVID-19, this review examined whether vitamin D supplementation can be supported as a nutritional strategy for reducing risk of infection, complications, and mortality from COVID-19 and found that the relationship between vitamin D and RTIs warrants further exploration.

There is conflicting evidence of the roles vitamin D and iron have in isolation and combined in relation to muscle health. The purpose of this narrative review was to examine the current literature on the roles that vitamin D and iron have on skeletal muscle mass, strength, and function and how these nutrients are associated with skeletal muscle health in specific populations. Secondary purposes include exploring if low vitamin D and iron status are interrelated with skeletal muscle health and chronic inflammation and reviewing the influence of animal-source foods rich in these nutrients on health and performance. PubMed, Scopus, SPORT Discus, EMBAE, MEDLINE, and Google Scholar databases were searched to determine eligible studies. There was a positive effect of vitamin D on muscle mass, particularly in older adults. There was a positive effect of iron on aerobic and anaerobic performance. Studies reported mixed results for both vitamin D and iron on muscle strength and function. While vitamin D and iron deficiency commonly occur in combination, few studies examined effects on skeletal muscle health and inflammation. Isolated nutrients such as iron and vitamin D may have positive outcomes; however, nutrients within food sources may be most effective in improving skeletal muscle health.