Cognitive Function is Unaffected during Acute Hypoxic Exposure but was Improved Following Exercise

International Journal of Exercise Science 15(5): 1481-1491, 2022. 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

Simulated Altitude via Re-Breathing Creates Arterial Hypoxemia but Fails to Improve Elements of Running Performance

International Journal of Exercise Science 11(6): 187-197, 2018. Acclimatization to altitude has been shown to improve elements of performance. Use of simulated altitude is popular among athletes across the sports spectrum. This work was on a handheld, re-breathing device touted to enhance performance. Seven recreationally-trained athletes used the device for 18 hours over the course of the 37-day intervention trial. The elevations simulated were progressively increased from 1,524m to 6,096m. To ascertain potential efficacy, four performance trials were included (familiarization, baseline, and 2 follow-ups). Hematological (hematocrit, hemoglobin, and lactate), physiological (respiratory exchange ratio, heart rate, and oxygen consumption), and perceptual (Borg’s RPE) variables were monitored at rest, during two steady state running economy stages, and at maximal effort during each visit. The device is clearly capable of creating arterial hypoxemic conditions equating to high altitude. This fact is exemplified by average pulse oximetry values of approximately 78.5% in the final 6-day block of simulation. At the same time, there were no changes observed in any hematological (p\u3e0.05), physiological (p\u3e0.05), or perceptual (p\u3e0.05) variable at either follow-up performance trial. Relative VO2 data was analyzed with a 15-breath moving average sampling frequency in accordance with our recent findings (Scheadler et al.) reported in Medicine and Science in Sports and Exercise. Effect sizes are reported within, but most were trivial (d=0.0-0.19). Overall, findings align with speculation that a more robust altitude stimulus than can be offered by short-term arterial hypoxemia is required for changes to be evidenced. The device has shown some promise in other work, but our data is not supportive

Muscle- and Mode-Specific Responses of the Forearm Flexors to Fatiguing, Concentric Muscle Actions

Background: Electromyographic (EMG) and mechanomyographic (MMG) studies of fatigue have generally utilized maximal isometric or dynamic muscle actions, but sport- and work-related activities involve predominately submaximal movements. Therefore, the purpose of the present investigation was to examine the torque, EMG, and MMG responses as a result of submaximal, concentric, isokinetic, forearm flexion muscle actions. Methods: Twelve men performed concentric peak torque (PT) and isometric PT trials before (pretest) and after (posttest) performing 50 submaximal (65% of concentric PT), concentric, isokinetic (60°·s-1), forearm flexion muscle actions. Surface EMG and MMG signals were simultaneously recorded from the biceps brachii and brachioradialis muscles. Results: The results of the present study indicated similar decreases during both the concentric PT and isometric PT measurements for torque, EMG mean power frequency (MPF), and MMG MPF following the fatiguing workbout, but no changes in EMG amplitude (AMP) or MMG AMP. Conclusions: These findings suggest that decreases in torque as a result of fatiguing, dynamic muscle actions may have been due to the effects of metabolic byproducts on excitation–contraction coupling as indicated by the decreases in EMG MPF and MMG MPF, but lack of changes in EMG AMP and MMG AMP from both the biceps brachii and brachioradialis muscles

Time Course of Changes in Neuromuscular Responses at 30% versus 70% 1 Repetition Maximum during Dynamic Constant External Resistance Leg Extensions to Failure

International Journal of Exercise Science 10(3): 365-378, 2017. The purpose of the current study was to examine the time course of changes in neuromuscular responses from the vastus medialis (VM) during low versus high intensity dynamic constant external resistance (DCER) leg extension muscle actions to failure. Thirteen men performed DCER leg extensions to failure at 30% and 70% 1-repetition maximum (1-RM) as well as 1-RM measurements pretest and posttest. Electromyogaphy and mechanomyographic signals were measured from the VM. There were no differences in neuromuscular responses pretest versus posttest 1-RM. There were time-dependent differences between the 30% and 70% 1-RM protocols. The initial phase of the 30% 1-RM protocol exhibited increases in electromyographic-amplitude and mechanomyographic amplitude, but no changes at 70% 1-RM. The middle phases indicated decreases in mechanomyographic amplitude at 30% 1-RM, but increases in mechanomyographic amplitude at 70% 1-RM. The 70% 1-RM protocol had earlier decrease in mechanomyographic frequency than 30% 1-RM. Both protocols in the final phases exhibited increases in electromyographic amplitude and mechanomyogrpahic-amplitude, but decreases in electromyographic frequency and mechanomyographic frequency. Low and high intensity DCER leg extensions to failure have time-dependent differences in neuromuscular responses during the process of fatigue which suggested that motor unit activation strategies may by influenced by the intensity of a fatiguing workbout. Thus, examining the time course of changes in neuromuscular responses during a fatiguing workbout allowed for the identification of the time-points associated with the onset of fatigue

The Impact of Simulated Altitude on Selected Elements of Running Performance

Background: Simulating altitude at sea level is increasingly more popular among recreationally-trained athletes across the sports spectrum. The AltO2Lab is a commercially-available, handheld, rebreathing apparatus purported to simulate altitude. Currently, there is an overall dearth of evidence regarding the efficacy of the device. Purpose: The goal of this study was to add evidence supporting or challenging the effectiveness of the device to improve selected running performance-related variables and to investigate the time-course of changes should benefits be evidenced. Methods: The 37-day protocol included familiarization, baseline, and 2 follow-up visits during which time hematological (hematocrit and lactate), physiological (running economy, maximal VO2, and heart rate), and psychological (Borg RPE) variables were monitored at rest, during relative submaximal, and/or maximal treadmill exercise. Altitude training days (18 days; one hour each day) were fitted within the 37-day time-line to occur after the baseline visit but before the respective follow-up visits. Specifically, the altitude training took place in 3, 6-day blocks of device usage with exposure, monitored by oximetry, intensifying across the days and blocks. Twelve days of altitude training were completed before the first follow-up visit while the final 6 days of altitude training were completed between the first and second follow-up visit. In this manner, the follow-ups could serve to evaluate the potential effectiveness of the device and narrow the time course of changes to a specific usage duration. Results: Six, recreationally-trained athletes (Females = 4; Males = 2; Age = 22.0 ± 2.9 yrs.; Baseline VO2max 52.7 ± 6.7) enrolled in the study. One subject was removed due to noncompliance. Overall, simulated altitude at the prescribed, intensifying dosage, failed to change both hematocrit (p = 0.469) and VO2max (p = 0.184) when analyzed by repeated measures analysis of variance. Additionally, no differences were found for secondary variables including: running economy, heart rate, lactate or RPE (all p \u3e 0.05). Conclusion: Presently, the AltO2Lab failed to improve selected variables related to running performance. This finding is in contrast to previous investigations with the device but it does align with the knowledge that a stronger stimulus might be necessary to induce HIF-mediated erythropoiesis to the extent that the cascade could alter hematological and subsequently performance ability through enhanced oxygen-carrying capacity. These results are preliminary and a final cohort will complete testing before concluding results will be disseminated

The validity of the EMG and MMG techniques to examine muscle hypertrophy

Objective: The purpose of this investigation was to examine the ability of the electromyographic (EMG) and mechanomyographic (MMG) amplitude versus torque relationships to track group and individual changes in muscle hypertrophy as a result of resistance training. Approach: Twelve women performed four weeks of forearm flexion blood flow restriction (BFR) resistance training at a frequency of three times per week. The training was performed at an isokinetic velocity of 120°∙s−1 with a training load that corresponded to 30% of concentric peak torque. Muscle hypertrophy was determined using ultrasound-based assessments of muscle cross-sectional area from the biceps brachii. Training-induced changes in the slope coefficients of the EMG amplitude and MMG amplitude versus torque relationships were determined from the biceps brachii during incremental (10%–100% of maximum) isometric muscle actions. Main results: There was a significant (p \u3c 0.001; d = 2.15) mean training-induced increase in muscle cross-sectional area from 0 week (mean ± SD = 5.86 ± 0.65 cm2) to 4 weeks (7.42 ± 0.80 cm2), a significant (p = 0.023; d = 0.36) decrease in the EMG amplitude versus torque relationship (50.70 ± 20.41 to 43.82 ± 17.76 μV∙Nm−1), but no significant (p = 0.192; d = 0.17) change in the MMG amplitude versus torque relationship (0.018 ± 0.009 to 0.020 ± 0.009 m∙s−2∙Nm−1). There was, however, great variability for the individual responses for the EMG and MMG amplitude versus torque relationships. Significance: The results of the present study indicated that the EMG amplitude, but not the MMG amplitude versus torque relationship was sensitive to mean changes in muscle cross-sectional area during the early-phase of resistance training. There was, however, great variability for the individual EMG amplitude versus torque relationships that limits its application for identifying individual changes in muscle hypertrophy as a result of BFR

The Need for Reporting Metabolic Sampling Interval in Publication: An Example Using Maximal VO2 Values and Running Economy

Background: Knowledge of metabolic outcomes, such as maximal oxygen consumption (VO2) or running economy, has wide-ranging application. Metabolic outcomes are widely reported in literature yet the metabolic sampling interval (example: breath-by-breath, 30-sec average) utilized for collection is rarely ever stated. Purpose: The purposes of the present investigation were to probe the potential discrepancies created when analyzing running economy and VO2max raw metabolic data with four different metabolic sampling intervals. Methods: Five recreationally-active and endurance-trained subjects were included in the present analysis and four metabolic sampling intervals were analyzed: 30-sec average, 20-sec average, 8-breath, and 4-breath. Subjects engaged in 4-min running economy phases at 55 and 65% of their VO2max before entering into a maximal protocol purposed to elicit VO2max in 8-12 minutes. Utilizing the steady state and maximal VO2 data, metabolic sampling intervals were analyzed for their effect on reported VO2 values. Results: For running economy at 55%, there was no differences found (f = 0.207; df = 1.862; p = 0.799) between sampling frequencies when analyzed by repeated measures analysis of variance and corrected with Greenhouse-Geisser for a violation of sphericity. For running economy at 65%, there were also no differences ­found (f = 1.456; df = 3; p = 0.799) between sampling frequencies. For inspection, the relative VO2 values were: 27.2 (±3.1), 27.9 (±4.1), 28.4 (±3.6), and 28.8 (±5.1) for the 30-sec, 20-sec, 8-breath, and 4-breath average, respectively. Maximal VO2 values of 53.0 (±6.6), 55.1 (±7.2), 55.1 (±7.2), and 59.6 (±9.4) for the 30-sec, 20-sec, 8-breath, and 4-breath average, respectively, were found to be significantly different (f = 21.062; df = 1.278; p \u3c 0.001) after adjusting for a violation of sphericity (p \u3c 0.001). Bonferroni analysis indicated differences between the 30-sec average and all other averages and also the 20-sec and 8-breath averages when compared against the 4-breath average. The 4-breath average yielded the highest VO2max value. Coincidentally, the 20-sec and 8-breath averages were identical. Conclusion: In the present investigation of raw metabolic data, sampling interval was found to impact the maximal oxygen consumption (VO2max) values but not running economy values when investigating a small sample of data with four select sampling intervals. The report of maximal VO2 is rather common in the literature and knowing sample interval is vital for between-study comparison, determination of regression-related activities, or for pre-post comparison of data from the same or different labs

The Contributions of Arterial Cross‑Sectional Area and Time‑Averaged Flow Velocity to Arterial Blood Flow

Background: Ultrasound has been used for noninvasive assessments of endothelial function in both clinical and athletic settings and to identify changes in muscle blood flow in response to exercise, nutritional supplementation, and occlusion. The purposes of the present study were to examine the reliability and relative contributions of arterial cross‑sectional area and time‑averaged flow velocity to predict muscle blood flow as a result of fatiguing exercise in men and women. Methods: Eighteen healthy men and 18 healthy women performed 50 consecutive eccentric repetitions of the elbow flexors at 60% of their pretest eccentric peak torque at a velocity of 180° s−1. Test‑retest reliability and stepwise linear regression analyses were performed to determine the ability of arterial cross‑sectional area and time‑averaged flow velocity to predict brachial artery muscle blood flow for the men, women, and combined sample. Results: There was no systematic test versus retest mean differences (P \u3e 0.05) for any of the ultrasound determined variables. The two‑variable regression models significantly improved the ability to predict muscle blood flow and were associated with smaller standard error of the estimates (3.7%–10.1% vs. 16.8%–37.0% of the mean baseline muscle blood flow values) compared to the one‑variable models. Conclusions: The findings of the present study supported the use of ultrasound for reliable assessments of arterial diameter, arterial cross‑sectional area, time‑averaged flow velocity, and muscle blood flow from the brachial artery in men and women. Furthermore, time‑averaged flow velocity was a more powerful predictor of muscle blood flow than arterial cross‑sectional area

Effects of intensity on muscle-specific voluntary electromechanical delay and relaxation electromechanical delay

The purposes of this study were to examine: 1) the potential muscle-specific differences in voluntary electromechanical delay (EMD) and relaxation electromechanical delay (R-EMD), and 2) the effects of intensity on EMD and R-EMD during step incremental isometric muscle actions from 10 to 100% maximal voluntary isometric contraction (MVIC). EMD and R-EMD measures were calculated from the simultaneous assessments of electromyography, mechanomyography, and force production from the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) during step isometric muscle actions. There were no differences between the VL, VM, and RF for the voluntary EMDE-M (onsets of the electromyographic to mechanomyographic signals), EMDM-F (onsets the mechanomyographic to force production), or EMDE-F (onsets of the electromyographic signal to force production) as well as R-EMDE-M (cessation of electromyographic to mechanomyographic signal), R-EMDM-F (cessation of mechanomyographic signal to force cessation), or R-EMDE-F (cessation of electromyorgraphic signal to force cessation) at any intensity. There were decreases in all EMD and R-EMD measures with increases in intensity. The relative contributions from EMDE-M and EMDM-F to EMDE-F as well as R-EMDE-M and R-EMDM-F to R-EMDE-F remained similar across all intensities. The superficial muscles of the quadriceps femoris shared similar EMD and R-EMD measurements

Co-Activation, Estimated Anterior and Posterior Cruciate Ligament Forces, and Motor Unit Activation Strategies during the Time Course of Fatigue

This study aimed to combine co-activation as well as anterior and posterior cruciate ligament force estimations with the motor unit activation strategies employed by the primary muscles that are involved in the movement at the knee joint. Fourteen male subject performed 25 maximal concentric isokinetic leg extension muscle actions at 120 s-1. Electromyographic and mechanomyographic signals from the vastus lateralis and bicep femoris, as well as force, were used to measure co-activation, and estimated anterior and posterior ligament forces during the time course of fatigue. There were decreases in quadriceps force and increases in hamstring force during the 25 leg extensions. The posterior cruciate ligament force was greater than the anterior cruciate ligament force during each leg extension. Both the posterior and anterior cruciate ligament forces decreased during the 25 leg extensions. Each muscle indicated unique neuromuscular responses, which may explain the decreases in quadriceps force and increases in the hamstring force. The combination of anterior and posterior cruciate ligament force estimation and motor unit activation strategies helped to provide a better understanding of the fatigue-related mechanism that was utilized to avoid injury and increase or maintain joint stability during the time course of fatigue