Blood flow restriction attenuates surface mechanomyography lateral and longitudinal, but not transverse oscillations during fatiguing exercise

Objective. Surface mechanomyography (sMMG) can measure oscillations of the activated muscle fibers in three axes (i.e.X,Y, andZ-axes) and has been used to describe motor unit activation patterns (X-axis). The application of blood flow restriction (BFR) is common in exercise studies, but the cuff may restrict muscle fiber oscillations. Therefore, the purpose of this investigation was to examine the acute effects of submaximal, fatiguing exercise with and without BFR on sMMG amplitude in theX,Y, andZ-axes among female participants.Approach. Sixteen females (21 ± 1 years) performed two separate exercise bouts to volitional exhaustion that consisted of unilateral, submaximal (50% maximal voluntary isometric contraction [MVIC]) intermittent, isometric, leg extensions with and without BFR. sMMG was recorded and examined across percent time to exhaustion (%TTE) in 20% increments. Separate 2-way repeated measures ANOVA models were constructed: (condition [BFR, non-BFR]) × (time [20, 40, 60, 80, and 100% TTE]) to examine absolute (m·s-2) and normalized (% of pretest MVIC) sMMG amplitude in theX-(sMMG-X),Y-(sMMG-Y), andZ-(sMMG-Z) axes.Main results. The absolute sMMG-X amplitude responses were attenuated with the application of BFR (mean ± SD = 0.236 ± 0.138 m·s-2) relative to non-BFR (0.366 ± 0.199 m·s-2, collapsed across time) and for sMMG-Y amplitude at 60%-100% of TTE (BFR range = 0.213-0.232 m·s-2versus non-BFR = 0.313-0.445 m·s-2). Normalizing sMMG to pretest MVIC removed most, but not all the attenuation which was still evident for sMMG-Y amplitude at 100% of TTE between BFR (72.9 ± 47.2%) and non-BFR (98.9 ± 53.1%). Interestingly, sMMG-Z amplitude was not affected by the application of BFR and progressively decreased across %TTE (0.332 ± 0.167 m·s-2to 0.219 ± 0.104 m·s-2, collapsed across condition.)Significance. The application of BFR attenuated sMMG-X and sMMG-Y amplitude, although normalizing sMMG removed most of this attenuation. Unlike theXandY-axes, sMMG-Z amplitude was not affected by BFR and progressively decreased across each exercise bout potentially tracking the development of muscle fatigue.

Arterial stiffness mediates the association between age and processing speed at low levels of microvascular function in humans across the adult lifespan

The function of micro- and macrovessels within the peripheral vasculature has been identified as a target for the investigation of potential cardiovascular-based promoters of cognitive decline. However, little remains known regarding the interaction of the micro- and macrovasculature as it relates to cognitive function, especially in cognitively healthy individuals. Therefore, our purpose was to unravel peripheral factors that contribute to the association between age and processing speed. Ninety-nine individuals (51 men, 48 women) across the adult life span (19-81 yr) were used for analysis. Arterial stiffness was quantified as carotid-femoral pulse-wave velocity (cfPWV) and near-infrared spectroscopy assessed maximal tissue oxygenation (Sto2max) following a period of ischemia. Processing speed was evaluated with Trail Making Test (TMT) Parts A and B. Measures of central (cPP) and peripheral pulse pressure (pPP) were also collected. Moderated mediation analyses were conducted to determine contributions to the age and processing speed relation, and first-order partial correlations were used to assess associations while controlling for the linear effects of age. A P ≤ 0.05 was considered statistically significant. At low levels of Sto2max, there was a significant positive (b = 1.92; P = 0.005) effect of cfPWV on time to completion on TMT part A. In addition, cPP (P = 0.028) and pPP (P = 0.027) remained significantly related to part A when controlling for age. These results suggested that the peripheral microvasculature may be a valuable target for delaying cognitive decline, especially in currently cognitively healthy individuals. Furthermore, we reinforced current evidence that pulse pressure is a key endpoint for trials aimed at preventing or delaying the onset of cognitive decline.NEW & NOTEWORTHY Arterial stiffness partially mediates the association between age and processing speed in the presence of low microvascular function, as demarcated by maximum tissue oxygenation following ischemia. Central and peripheral pulse pressure remained associated with processing speed even after controlling for age. Our findings were derived from a sample that was determined to be cognitively healthy, which highlights the potential for these outcomes to be considered during trials aimed at the prevention of cognitive decline.

Sex-specific microvascular and hemodynamic responses to passive limb heating in young adults

OBJECTIVE

We examined sex-specific microvascular reactivity and hemodynamic responses under conditions of augmented resting blood flow induced by passive heating compared to normal blood flow.

METHODS

Thirty-eight adults (19 females) completed a vascular occlusion test (VOT) on two occasions preceded by rest with or without passive heating in a randomized, counterbalanced order. Skeletal muscle tissue oxygenation (StO2 , %) was assessed with near-infrared spectroscopy (NIRS), and the rate of desaturation and resaturation as well as maximal StO2 (StO2max ) and prolonged hypersaturation (area under the curve, StO2AUC ) were quantified. Before the VOT, brachial artery blood flow (BABF), vascular conductance, and relative BABF (BABF normalized to forearm lean mass) were determined. Sex × condition ANOVAs were used. A p-value ≤.05 was considered statistically significant.

RESULTS

Twenty minutes of heating increased BABF compared to the control (102.9 ± 28.3 vs. 36.0 ± 20.9 mL min-1 ; p < .01). Males demonstrated greater BABF than females (91.9 ± 34.0 vs. 47.0 ± 19.1 mL min-1 ; p < .01). There was no sex difference in normalized BABF. There were no significant interactions for NIRS-VOT outcomes, but heat did increase the rate of desaturation (-0.140 ± 0.02 vs. -0.119 ± 0.03% s-1 ; p < .01), whereas regardless of condition, males exhibited greater rates of resaturation and StO2max than females.

CONCLUSIONS

These results suggest that blood flow is not the primary factor causing sex differences in NIRS-VOT outcomes.

Examining Relationships between Cognitive Flexibility, Exercise Perceptions, and Cardiovascular Disease Risk Factors

Adults do not engage in enough physical activity. Investigating cognitive and physiological factors related to improving this behavior-and reducing health risks-remains a public health priority. Our objective was to assess whether cognitive flexibility influenced perceptions and choice of exercise programs and whether flexibility was associated with cardiovascular disease (CVD) risk factors. Independent sample groups of college-aged adults (18-24 yrs) participated in two studies. Data were collected on individuals' degree of cognitive flexibility (both self-reported and objectively measured), perceptions and choice of exercise programs, and health status markers known to be associated with CVD (vascular function, muscular strength, and body composition). Vascular function was assessed with a near-infrared spectroscopy device, strength was defined as handgrip, and body composition was estimated via digital circumferences. Self-reported flexibility reliably predicted individuals' choice of exercise program and perceptions of effort required for success on an exercise program. The relationships among CVD risk factors and objectively measured cognitive flexibility were not significant, demonstrating that identifying a healthy individual's degree of performance-based cognitive flexibility does not predict health status. Furthermore, although greater self-reported trait flexibility (rigidity) is known to predict higher (lower) likelihood of physical activity, this finding should not be extrapolated to also assume that flexibility (rigidity), as measured by objective cognitive tests, is associated with reduced CVD risk in healthy adults. We posit a rationale for how understanding cognitive flexibility and rigidity can play an impactful role in improving adherence to exercise prescriptions targeted to reducing risks.

Acute Effects of Continuous and Intermittent Blood Flow Restriction on Sprint Interval Performance and Muscle Oxygen Responses

ABSTRACT

Wizenberg, AM, Gonzalez-Rojas, D, Rivera, PM, Proppe, CE, Laurel, KP, Stout, JR, Fukuda, DH, Billaut, F, Keller, JL, and Hill, EC. Acute effects of continuous and intermittent blood flow restriction on sprint interval performance and muscle oxygen responses. J Strength Cond Res 37(10): e546-e554, 2023-This investigation aimed to examine the acute effects of continuous and intermittent blood flow restriction (CBFR and IBFR, respectively) during sprint interval training (SIT) on muscle oxygenation, sprint performance, and ratings of perceived exertion (RPE). Fifteen men (22.6 ± 2.4 years; 176 ± 6.3 cm; 80.0 ± 12.6 kg) completed in random order a SIT session with CBFR, IBFR (applied during rest), and no blood flow restriction (NoBFR). Each SIT session consisted of two 30-second all-out sprint tests separated by 2 minutes. Peak power (PP), total work (TW), sprint decrement score (S dec ), RPE, and muscle oxygenation were measured during each sprint. A p value ≤0.05 was considered statistically significant. PP decreased to a greater extent from sprint 1 to sprint 2 during CBFR (25.5 ± 11.9%) and IBFR (23.4 ± 9.3%) compared with NoBFR (13.4 ± 8.6%). TW was reduced similarly (17,835.6 ± 966.2 to 12,687.2 ± 675.2 J) from sprint 1 to sprint 2 for all 3 conditions, but TW was lower (collapsed across time) for CBFR (14,320.7 ± 769.1 J) than IBFR (15,548.0 ± 840.5 J) and NoBFR (15,915.4 ± 771.5 J). There were no differences in S dec (84.3 ± 1.7%, 86.1 ± 1.5%, and 87.2 ± 1.1% for CBFR, IBFR, and NoBFR, respectively) or RPE, which increased from sprint 1 (8.5 ± 0.3) to sprint 2 (9.7 ± 0.1). Collective muscle oxygenation responses increased across time and were similar among conditions, whereas increases in deoxy[heme] and total[heme] were greatest for CBFR. Applying BFR during SIT induced greater decrements in PP, and CBFR resulted in greater decrements in work across repeated sprints. The larger increases in deoxy[heme] and total[heme] for CBFR suggested it may induce greater metabolite accumulation than IBFR and NoBFR when combined with SIT.

Changes in Neuromuscular Response Patterns After 4 Weeks of Leg Press Training During Isokinetic Leg Extensions

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.

Sex differences in NIRS derived values of reactive hyperemia persist after experimentally controlling for the ischemic vasodilatory stimulus

Men and women exhibit different near-infrared spectroscopy (NIRS) outcomes in response to vascular occlusion tests (VOT), which may be due to phenotypic characteristics or different degrees of desaturation during ischemia. The minimum skeletal muscle tissue oxygenation (StO_2min) observed during a VOT may be the primary determinant of reactive hyperemic (RH) responses. Our purpose was to determine the contribution StO_2min and participant characteristics including adipose tissue thickness (ATT), lean body mass (LBM), muscular strength, and limb circumference to NIRS-derived indices of RH. Also, we aimed to determine if matching StO_2min would eliminate NIRS-VOT sex differences. Thirty-one young adults completed one or two VOTs during which the vastus lateralis was continuously assessed for StO₂. The men and women each completed a standard VOT with a 5-min ischemic phase. The men completed a second VOT with a shortened ischemic phase to produce a matching StO_2min to the minimum of the women observed during the standard VOT. Mean sex differences were determined with t-tests and relative contributions were assessed with multiple regression and model comparison approaches. During the 5-min ischemic phase, the men exhibited greater upslopes (1.97±0.66 vs. 1.23±0.59%∙s^-1) and greater StO_2max than the women (80.3±4.17 vs. 76.2±2.86%). Analysis revealed StO_2min was a greater contributor to upslope than sex and/or ATT. For StO_2max, sex was the only significant predictor (r²=0.26, men ~ 4.09% > women). Experimentally matching StO_2min did not eliminate the sex differences in upslope or StO_2max, suggesting that characteristics other than the degree of desaturation primarily provoke sex differences in RH.

Effects of Sex and Cuff Pressure on Physiological Responses during Blood Flow Restriction Resistance Exercise in Young Adults

PURPOSE

The purpose of this study was to examine the physiological responses resulting from an acute blood flow restriction resistance exercise bout with two different cuff pressures in young, healthy men and women.

METHODS

Thirty adults (18-30 yr) completed a bilateral leg extension blood flow restriction bout consisting of four sets (30-15-15-15 repetitions), with cuffs applied at pressures corresponding to 40% and 60% of the minimum arterial occlusion pressure (AOP) needed to completely collapse the femoral arteries. During each of these conditions (40% and 60% AOP), physiological measures of near-infrared spectroscopy (NIRS) and EMG amplitude (EMG AMP) were collected from the dominant or nondominant vastus lateralis. After each set, ratings of perceived exertion (RPE) were collected, whereas only at baseline and at the end of the bout, mean arterial pressure (MAP) was assessed. Separate mixed-factorial ANOVA models were used to examine mean differences in the change in EMG AMP and NIRS parameters during each set. The absolute RPE and MAP values were also examined with separate ANOVAs. A P value ≤0.05 was considered statistically significant.

RESULTS

Regardless of sex or cuff pressure, the change in EMG AMP was lower in set 1 (14.8%) compared with the remaining sets (22.6%-27.0%). The 40% AOP condition elicited the greatest changes in oxy[heme] and deoxy[heme], while also providing lower RPEs. For MAP, there was an effect for time such that MAP increased from preexercise (87.5 ± 4.3 mm Hg) to postexercise (104.5 ± 4.1 mm Hg).

CONCLUSIONS

The major findings suggested that the 40% AOP condition permitted the greatest amount of recovery during the interset rest. In addition, there did not seem to be any meaningful sex-related difference in this sample of young healthy adults.

No effect of coactivation on fatigue-induced decreases in isokinetic and isometric torque in healthy young male adults

BACKGROUND

Antagonist activation may contribute to fatigue-induced decreases in torque while assisting in the maintenance of joint stability. This study utilized a reciprocal, slow velocity (60°·s^-1) forearm flexion and extension fatiguing task to examine the contributions of coactivation to torque production at slow and moderate (180°·s^-1) velocities, as well as during a maximal voluntary isometric contraction (MVIC).

METHODS

Twelve recreationally active men (mean ± SD: age = 21.7 ± 1.6 years; body mass = 83.5 ± 8.8 kg; height = 179.4 ± 5.2 cm) completed isokinetic (60 and 180°·s^-1) and isometric pre-testing of forearm flexion and extension, followed by 50 maximal, reciprocal, isokinetic muscle actions at 60°·s^-1, followed by post-testing. The amplitude (AMP) of the electromyographic (EMG) signals from the biceps and triceps brachii were simultaneously recorded. Torque and EMG AMP were normalized to the corresponding values from the pre-testing peak torque movements. Repeated measures ANOVAs and pairwise comparisons were used to identify mean changes in torque, EMG AMP, and coactivation ratios.

RESULTS

The torque analyses indicated greater (p < 0.03) decreases for 180°·s^-1 (24%) and MVIC (23%) than 60°·s^-1 (14%) for forearm flexion. For forearm extension, there were no differences (p > 0.05) in fatigability between velocities. For EMG AMP there were no changes (p > 0.05) from pre- to post-testing for any velocity or movement. There were no changes (p > 0.05) in the coactivation ratio for forearm flexion, but significant increases (13.6 ± 6.6 to 16.9 ± 6.0; p = 0.003) for forearm extension, collapsed across Velocity.

CONCLUSIONS

There was velocity- and movement-specific fatigability for forearm flexion and extension. The parallel, fatigue-induced EMG AMP responses indicated that coactivation did not contribute to the decreases in torque and would not affect elbow joint stability.

An examination of the relationship among plasma brain derived neurotropic factor, peripheral vascular function, and body composition with cognition in midlife African Americans/Black individuals

African American/Black individuals have been excluded from several lines of prominent neuroscience research, despite exhibiting disproportionately higher risk factors associated with the onset and magnitude of neurodegeneration. Therefore, the objective of the current investigation was to examine potential relationships among brain derived neurotropic factor (BDNF), peripheral vascular function, and body composition with cognition in a sample of midlife, African American/Black individuals. Midlife adults (men: n = 3, 60 ± 4 years; women: n = 9, 58 ± 5 years) were invited to complete two baseline visits separated by 4 weeks. Peripheral vascular function was determined by venous occlusion plethysmography, a dual-energy X-ray absorptiometry was used to determine body composition, and plasma was collected to quantify BDNF levels. The CNS Vital Signs computer-based test was used to provide scores on numerous cognitive domains. The principal results included that complex attention (r = 0.629) and processing speed (r = 0.734) were significantly (p < 0.05) related to the plasma BDNF values. However, there was no significant (p > 0.05) relationship between any vascular measure and any cognitive domain or BDNF value. Secondary findings included the relationship between lean mass and peak hyperemia (r = 0.758) as well as total hyperemia (r = 0.855). The major conclusion derived from these results was that there is rationale for future clinical trials to use interventions targeting increasing BDNF to potentially improve cognition. Additionally, these results strongly suggest that clinicians aiming to improve cognitive health via improvements in the known risk factor of vascular function should consider interventions capable of promoting the size and function of skeletal muscle, especially in the African American/Black population.

Neurovascular Dysfunction in Diverse Communities With Health Disparities-Contributions to Dementia and Alzheimer's Disease

Alzheimer's disease and related dementias (ADRD) are an expanding worldwide crisis. In the absence of scientific breakthroughs, the global prevalence of ADRD will continue to increase as more people are living longer. Racial or ethnic minority groups have an increased risk and incidence of ADRD and have often been neglected by the scientific research community. There is mounting evidence that vascular insults in the brain can initiate a series of biological events leading to neurodegeneration, cognitive impairment, and ADRD. We are a group of researchers interested in developing and expanding ADRD research, with an emphasis on vascular contributions to dementia, to serve our local diverse community. Toward this goal, the primary objective of this review was to investigate and better understand health disparities in Alabama and the contributions of the social determinants of health to those disparities, particularly in the context of vascular dysfunction in ADRD. Here, we explain the neurovascular dysfunction associated with Alzheimer's disease (AD) as well as the intrinsic and extrinsic risk factors contributing to dysfunction of the neurovascular unit (NVU). Next, we ascertain ethnoregional health disparities of individuals living in Alabama, as well as relevant vascular risk factors linked to AD. We also discuss current pharmaceutical and non-pharmaceutical treatment options for neurovascular dysfunction, mild cognitive impairment (MCI) and AD, including relevant studies and ongoing clinical trials. Overall, individuals in Alabama are adversely affected by social and structural determinants of health leading to health disparities, driven by rurality, ethnic minority status, and lower socioeconomic status (SES). In general, these communities have limited access to healthcare and healthy food and other amenities resulting in decreased opportunities for early diagnosis of and pharmaceutical treatments for ADRD. Although this review is focused on the current state of health disparities of ADRD patients in Alabama, future studies must include diversity of race, ethnicity, and region to best be able to treat all individuals affected by ADRD.

Greater Neuromuscular Fatigue Following Low Load Blood Flow Restriction than Non Blood Flow Restriction Resistance Exercise Among Recreationally Active Men

PURPOSE

The purpose of this study was to examine the acute effects of low-load blood flow restriction (LLBFR) and low-load non-BFR (LL) on neuromuscular function following a bout of standardized, fatiguing leg extension muscle actions.

METHODS

Fourteen men (mean age ± SD = 23±4 yrs) volunteered to participate in this investigation and randomly performed LLBFR and LL on separate days. Resistance exercise consisted of 75 isotonic, unilateral leg extension muscle actions performed at 30% of one-repetition maximum. Prior to (pretest) and after (posttest) performing each bout of exercise, strength and neural assessments were determined.

RESULTS

There was no pretest to posttest differences between LLBFR and LL for maximal voluntary isometric contraction (MVIC) torque or V-wave/M-wave responses (muscle compound action potentials assessed during a superimposed MVIC muscle action) which exhibited decreases (collapsed across condition) of 41.2% and 26.2%, respectively. There were pretest to posttest decreases in peak twitch torque (36.0%) and sEMG (29.5%) for LLBFR but not LL, and larger decreases in voluntary activation for LLBFR (11.3%) than LL (4.5%).

CONCLUSIONS

These findings suggested that LLBFR elicited greater fatigue-induced decreases in several indices of neuromuscular function relative to LL. Despite this, both LLBFR and LL resulted in similar decrements in performance as assessed by maximal strength.

Coactivation does not contribute to fatigue-induced decreases in torque during reciprocal, isokinetic muscle actions

BACKGROUND: Studies of coactivation have typically utilized single movement isometric or isokinetic fatiguing muscle actions. OBJECTIVE: The purpose of the current study was to examine coactivation of the biceps brachii (BB) and triceps brachii (TB) in response to a maximal, reciprocal, isokinetic fatiguing task of the forearm flexors and extensors at slow (60∘/s) and moderate (180∘/s) isokinetic velocities in men. METHODS: Ten men (mean ± SD: age = 21.6 ± 1.3 years) completed 50 consecutive, maximal, reciprocal, isokinetic muscle actions of the right forearm flexors and extensors at 60 and 180∘/s. The amplitude (AMP) and mean power frequency (MPF) contents of the electromyographic (EMG) and mechanomyographic (MMG) signals from the BB and TB were recorded simultaneously throughout the fatiguing task. Repeated measures ANOVAs with Tukey post hocs were used to determine mean differences for the torque and neuromuscular parameters across repetitions. RESULTS: The torque analyses indicated greater fatigability at 180∘/s, compared to 60∘/s (p= 0.02). There were no significant changes in EMG AMP for either muscle during flexion or extension at 60∘/s (p> 0.05). At 180∘/s, there were significant increases in agonist EMG AMP (p= 0.01 to 0.004), however, no changes in antagonist EMG AMP (p> 0.05). For EMG MPF, there were significant decreases during flexion and extension (p< 0.001 to p= 0.02) at both velocities, collapsed across Muscle. There were no significant (p> 0.05) changes across repetition for MMG AMP or MPF. CONCLUSIONS: This study indicated velocity-specific responses to fatigue, with a greater magnitude of fatigability at 180∘/s. Furthermore, despite increases in EMG AMP of the agonist muscles at 180∘/s only, it was not sufficient to alter the ratio of coactivation, likely due to common neural drive between muscles. Thus, the decreases in torque in the present study were not attributable to increases in coactivation.

Handgrip exercise induces sex-specific mean arterial pressure and oxygenation responses but similar performance fatigability

Women exhibit an attenuated exercise pressor reflex (EPR) when compared to men. The influence of sex-specific mechanisms related to the EPR and performance fatigability remain to be fully elucidated. The purpose was to determine the impact of oxygenation and metabolic efficiency on sex-specific performance fatigability and increases in mean arterial pressure (MAP) resulting from a fatiguing isometric handgrip (IHG). Twenty-four adults volunteered to perform an IHG at 25% at maximal voluntary isometric contractions (MVICs). Pre- and posttest MVICs were conducted to quantify performance fatigability. MAP was collected at 3 timepoints. A near-infrared spectroscopy device was attached to the forearm to derive the following signals: oxy[haem], deoxy[haem], total[haem], and diff[haem]. These values were normalized and examined across time in 5% segments of time-to-task-failure. Metabolic efficiency was defined as the ratio force:deoxy[haem]. During the IHG, there was a decline in oxy[haem] for the men (b = -0.075), whereas the women demonstrated an increase (b = 0.117). For the men, the diff[haem] tracked the mean oxy[haem] response, but there was no change for the women. The men exhibited greater declines in metabolic efficiency, yet there were no sex differences in PF (46.6 ± 9.7% vs. 45.5 ± 14.2%). For relative MAP, the men (24.5 ± 15.1%) exhibited a greater (p = .03) increase than the women (11.0 ± 17.6%). These results indicated the EPR was more prominent for the men, perhaps due to differences in mechanical stimuli and a lack of ability to maintain metabolic efficiency. However, these physiological differences did not induce a sex difference in performance fatigability.

Sex differences in muscle excitation and oxygenation, but not in force fluctuations or active hyperemia resulting from a fatiguing, bilateral isometric task

It remains to be fully elucidated if there are sex-specific physiological adjustments within the human neuromuscular and vascular systems that contribute to symptoms of fatigue during a sustained bilateral task. This, in part, is likely due to various limitations in experimental design such as an inability to independently record force fluctuations from each limb.Objective. Therefore, the purpose of the current study was to examine the fatigue-induced changes in muscle excitation, force fluctuations, skeletal muscle tissue saturation (StO₂), and muscle blood flow resulting from a sustained, bilateral task.Approach. Thirty healthy, college-aged adults (15 males, 15 females) performed a bilateral leg task at 25% of maximum voluntary isometric (MVIC). Before and after the task, MVICs were completed. Resting and post-task femoral artery blood flow (FABF) were determined. Muscle excitation was quantified as electromyographic amplitude (EMG AMP) from the right and left vastus lateralis. During the task, force fluctuations were determined independently from each leg. The StO₂signal was collected with a near-infrared spectroscopy device attached to the right vastus lateralis. The rate of change in these variables was calculated via simple linear regression. The exercise-induced magnitude of change in MVIC (i.e. performance fatigability) and FABF (i.e. active hyperemia) was determined.Main Results. There was no sex difference in the percent decline in MVIC (20.5 ± 20.1% versus 16.4 ± 3.5%;p> 0.05). There were no inter-leg differences in EMG AMP or force fluctuations. The males exhibited a faster rate of increase in EMG AMP (b= 0.13 versusb= 0.08;p< 0.001), whereas the females exhibited a slower rate of decline in StO₂(b= -0.049 versusb= -0.080). There was no sex difference in force fluctuations or change in FABF.Significance. Males and females likely have different neuromuscular strategies and muscle characteristics, but these did not elicit a sex difference in performance fatigability.

The effects of blood flow restriction resistance training on indices of delayed onset muscle soreness and peak power

BACKGROUND: Low-load resistance training with blood flow restriction (LL + BFR) attenuated delayed onset muscle soreness (DOMS) under some conditions. OBJECTIVE: The purpose of this study examined the effects of reciprocal concentric-only elbow flexion-extension muscle actions at 30% of peak torque on indices of DOMS. METHODS: Thirty untrained women (mean ± SD; 22 ± 2.4 years) were randomly assigned to 6 training days of LL + BFR (n= 10), low-load non-BFR (LL) (n= 10), or control (n= 10). Participants completed 4 sets (1 × 30, 3 × 15) of submaximal (30% of peak torque), unilateral, isokinetic (120∘s-1) muscle actions. Indices of DOMS including peak power, resting elbow joint angle (ROM), perceived muscle soreness (VAS), and pain pressure threshold (PPT) were assessed. RESULTS: There were no changes in peak power, ROM, or VAS. There was a significant interaction for PPT. Follow-up analyses indicated PPT increased for the LL + BFR condition (Day 5 > Day 2), but did not decrease below baseline. The results of the present study indicated LL + BFR and LL did not induce DOMS for the elbow extensors in previously untrained women. CONCLUSION: These findings suggested LL + BFR and LL concentric-only resistance training could be an effective training modality to elicit muscular adaptation without inducing DOMS.

The effects of phosphocreatine disodium salts plus blueberry extract supplementation on muscular strength, power, and endurance

BACKGROUND

Numerous studies have demonstrated the efficacy of creatine supplementation for improvements in exercise performance. Few studies, however, have examined the effects of phosphocreatine supplementation on exercise performance. Furthermore, while polyphenols have antioxidant and anti-inflammatory properties, little is known regarding the influence of polyphenol supplementation on muscular strength, power, and endurance. Thus, the purpose of the present study was to compare the effects of 28 days of supplementation with phosphocreatine disodium salts plus blueberry extract (PCDSB), creatine monohydrate (CM), and placebo on measures of muscular strength, power, and endurance.

METHODS

Thirty-three men were randomly assigned to consume either PCDSB, CM, or placebo for 28 days. Peak torque (PT), average power (AP), and percent decline for peak torque (PT%) and average power (AP%) were assessed from a fatigue test consisting of 50 maximal, unilateral, isokinetic leg extensions at 180°·s^- 1 before and after the 28 days of supplementation. Individual responses were assessed to examine the proportion of subjects that exceeded a minimal important difference (MID).

RESULTS

The results demonstrated significant (p < 0.05) improvements in PT for the PCDSB and CM groups from pre- (99.90 ± 22.47 N·m and 99.95 ± 22.50 N·m, respectively) to post-supplementation (119.22 ± 29.87 N·m and 111.97 ± 24.50 N·m, respectively), but no significant (p = 0.112) change for the placebo group. The PCDSB and CM groups also exhibited significant improvements in AP from pre- (140.18 ± 32.08 W and 143.42 ± 33.84 W, respectively) to post-supplementation (170.12 ± 42.68 W and 159.78 ± 31.20 W, respectively), but no significant (p = 0.279) change for the placebo group. A significantly (p < 0.05) greater proportion of subjects in the PCDSB group exceeded the MID for PT compared to the placebo group, but there were no significant (p > 0.05) differences in the proportion of subjects exceeding the MID between the CM and placebo groups or between the CM and PCDSB groups.

CONCLUSIONS

These findings indicated that for the group mean responses, 28 days of supplementation with both PCDSB and CM resulted in increases in PT and AP. The PCDSB, however, may have an advantage over CM when compared to the placebo group for the proportion of individuals that respond favorably to supplementation with meaningful increases in muscular strength.

Acute changes in muscle thickness, edema, and blood flow are not different between low-load blood flow restriction and non-blood flow restriction

The purpose of the present study was to examine the acute changes in muscle swelling (as assessed by muscle thickness and echo intensity) and muscle blood flow associated with an acute bout of low-load blood flow restriction (LLBFR) and low-load non-blood flow restriction (LL) exercise. Twenty women (mean ± SD; 22 ± 2years) volunteered to perform an acute exercise bout that consisted of 75 (1 × 30, 3 × 15) isokinetic, reciprocal, concentric-only, submaximal (30% of peak torque), forearm flexion and extension muscle actions. Pretest, immediately after (posttest), and 5-min after (recovery) completing the 75 repetitions, muscle thickness and echo intensity were assessed from the biceps brachii and triceps brachii muscles and muscle blood flow was assessed from the brachial artery. There were no between group differences for any of the dependent variables, but there were significant simple and main effects for muscle and time. Biceps and triceps brachii muscle thickness increased from pretest (2.13 ± 0.39 cm and 1.88 ± 0.40 cm, respectively) to posttest (2.58 ± 0.49 cm and 2.17 ± 0.43 cm, respectively) for both muscles and remained elevated for the biceps brachii (2.53 ± 0.43 cm), but partially returned to pretest levels for the triceps brachii (2.06 ± 0.41 cm). Echo intensity and muscle blood flow increased from pretest (98.0 ± 13.6 Au and 94.5 ± 31.6 ml min^-1 , respectively) to posttest (109.2 ± 16.9 Au and 312.2 ± 106.5 ml min^-1 , respectively) and pretest to recovery (110.1 ± 18.3 Au and 206.7 ± 92.9 ml min^-1 , respectively) and remained elevated for echo intensity, but partially returned to pretest levels for muscle blood flow. The findings of the present study indicated that LLBFR and LL elicited comparable acute responses as a result of reciprocal, concentric-only, forearm flexion and extension muscle actions.

Performance fatigability and the bilateral deficit during maximal, isokinetic leg extensions in men and women

BACKGROUND: Few studies have examined sex differences in performance fatigability and the bilateral deficit in a dynamic modality. OBJECTIVES: The purpose of this study was to examine: 1) Leg-, mode-, and sex-specific differences in performance fatigability during maximal, dynamic leg extension muscle actions and; 2) the time course of fatigue-induced changes in the bilateral deficit for both men and women. METHODS: Eleven men and 11 women participated in 3 test visits consisting of 50 maximal, concentric, isokinetic leg extensions at 60∘/s. Each visit was randomized to perform either unilateral right leg only (RL), unilateral left leg only (LL), or bilateral (BL) leg extensions. RESULTS: The BL performance fatigability was significantly (p< 0.001) less than RL and LL. Both men and women demonstrated significant (p< 0.001) declines in moment and an attenuation of the bilateral deficit throughout the fatiguing task. There were no differences between sex for performance fatigability (p= 0.128) or the bilateral deficit (p= 0.102). CONCLUSIONS: Unilateral muscle actions were more susceptible to fatigue than BL muscle actions. Men exhibited an earlier decline in moment than women, however, men and women exhibited similar magnitudes and patterns of decline in the bilateral deficit.

The acute and early phase effects of blood flow restriction training on ratings of perceived exertion, performance fatigability, and muscular strength in women

BACKGROUND: Blood flow restriction (BFR) resistance training (RT) has garnered recent interest, but female-specific data remains scarce. OBJECTIVE: The purpose was to examine the effects of 2-wks of low-load concentric, isokinetic, reciprocal forearm flexion and extension training, with and without BFR on perceptual responses, performance fatigability, and muscular strength. METHODS: Twenty women were assigned to a BFRT or a non-BFRT group. Each group trained at 30% of concentric peak moment. Each session consisted of 75 concentric, isokinetic, reciprocal forearm flexion extension muscle actions. RPEs were recorded following each set. Pretest and posttest maximal voluntary isometric contraction (MVIC) force was measured, and percent decline was defined as performance fatigability. RESULTS: The RPE values (p< 0.05) increased across sets. Strength (collapsed across muscle action) increased (p< 0.05) from 0-wk (23.7 ± 3.2 Nm) to 2-wk (26.8 ± 2.7 Nm). Independent of group and muscle action, performance fatigability (p< 0.05) increased from 0-wk (10.9 ± 5.0%) to 2-wk (14.1 ± 4.4%). CONCLUSIONS: 2-wks of low-load concentric, reciprocal forearm flexion and extension training resulted in similar training-induced changes in perceptual responses, performance fatigability, and muscular strength between BFRT and non-BFRT. These findings may reduce concerns of increased perceptual responses following BFRRT compared to non-BFRRT.

Task-specific performance fatigability and the bilateral deficit during isokinetic leg extensions

OBJECTIVES

The purpose of the present study was to compare the fatigue-induced changes in performance fatigability, bilateral deficit, and patterns of responses for the electromyographic (EMG) and mechanomyographic (MMG) amplitude (AMP) and mean power frequency (MPF), during unilateral and bilateral maximal, fatiguing leg extensions.

METHODS

Nine men (Mean±SD; age =21.9±2.4 yrs; height =181.8±11.9 cm; body mass =85.8±6.2 kg) volunteered to perform 50 consecutive maximal, bilateral (BL), unilateral dominant (DL), and unilateral non-dominant (NL) isokinetic leg extensions at 180°·s^-1, on 3 separate days. Electromyographic and MMG signals from both vastus lateralis (VL) muscles were recorded. Repeated measures ANOVAs were utilized to examine mean differences in normalized force, EMG AMP, EMG MPF, MMG AMP, MMG MPF and the bilateral deficit.

RESULTS

The results demonstrated a Condition × Repetition interaction for normalized force (p=0.004, η²_p=0.222) and EMG MPF (p=0.034, η²_p=0.214) and main effects for Repetition for EMG AMP (p=0.019, η²_p=0.231), MMG AMP (p<0.001, η²_p=0.8550), MMG MPF (p=0.009, η²_p=0.252), and the bilateral deficit (p<0.001, η²_p=0.366).

CONCLUSIONS

The findings demonstrated less performance fatigability during the BL than the unilateral tasks, likely due to a reduced relative intensity via interhemispheric inhibition that attenuated the development of excitation-contraction coupling failure during the BL task.

Performance fatigability and neuromuscular responses for bilateral and unilateral leg extensions in men

OBJECTIVES

This study examined performance fatigability and the patterns of neuromuscular responses for electromyographic (EMG) and mechanomyographic (MMG) amplitude (AMP) and mean power frequency (MPF) during bilateral (BL) and unilateral (UL) maximal, isokinetic leg extensions.

METHODS

Peak torque for each repetition and EMG and MMG signals from the non-dominant vastus lateralis were recorded in 11 men during 50 BL and UL maximal, concentric, isokinetic leg extensions at 60^o·s^-1 that were performed on separate days. Separate repeated measures ANOVAs were performed to examine the normalized isokinetic torque and neuromuscular parameters.

RESULTS

Normalized isokinetic peak torque demonstrated a significant Conditions by Repetition interaction (p<0.001, η²_p= 0.594). There were no interactions, but significant main effects for Repetition with increases in EMG AMP (p<0.001; η²_p=0.255) and decreases in EMG MPF (p<0.001; η²_p=0.650), MMG AMP (p<0.001; η²_p=0.402), and MMG MPF (p<0.001; η²_p=0.796). In addition, EMG MPF and MMG AMP demonstrated main effects for Condition (p=0.031; η²_p=0.387 and p=0.002; η²_p=0.64, respectively) with the BL exhibiting greater values than UL leg extensions for both parameters.

CONCLUSIONS

The current findings indicated greater performance fatigability during UL versus BL leg extensions, but similar patterns of neuromuscular responses consistent with the Muscle Wisdom Hypothesis.

Are There Sex-Specific Neuromuscular or Force Responses to Fatiguing Isometric Muscle Actions Anchored to a High Perceptual Intensity?

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 XX(X): 000-000, 2019-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.

Performance fatigability and neuromuscular responses for bilateral versus unilateral leg extensions in women

The purpose of this study was to compare isokinetic peak torque and the patterns of responses for electromyographic (EMG) and mechanomyographic (MMG), amplitude (AMP) and mean power frequency (MPF) for bilateral (BL) versus unilateral (UL), maximal, isokinetic leg extensions. Eleven recreationally trained women (Mean ± SD: age 22.9 ± 0.9 yrs; body mass 60.5 ± 10.1 kg; height 167.2 ± 6.4 cm) performed 50 maximal, BL and UL isokinetic leg extensions at 60° s^-1 on separate days. Electromyographic and MMG signals from the vastus lateralis of the nondominant leg were recorded. Five separate 2 (Condition [BL and UL]) × 10 (Repetitions [5-50]) repeated measures ANOVAs were performed to examine normalized EMG AMP, EMG MPF, MMG AMP, MMG MPF, and isokinetic torque. The results indicated no significant interactions or main effects for EMG AMP and MMG AMP. There were significant interactions for normalized isokinetic peak torque (p < 0.001, η²_p = 0.493) and MMG MPF (p = 0.003, η²_p = 0.234). For EMG MPF, there was no significant interaction, but significant main effects for Condition (p = 0.003, η²_p = 0.607) and Repetitions (p < 0.001, η²_p = 0.805). The current findings demonstrated greater performance fatigability for UL than BL leg extensions. Both modalities exhibited similar patterns of neuromuscular responses that were consistent with the Muscular Wisdom hypothesis.

Variable resistance training versus traditional weight training on the reflex pathway following four weeks of leg press training

Purpose: The purpose of this study was to examine the changes in reflex-electromechanical delay (EMD) as a result of 2- and 4-wks of variable resistance training (VRT) or dynamic constant external resistance (DCER) leg press training. Material and Methods: Thirty-six men were randomised into either the Control, DCER, or VRT groups. The DCER and VRT groups performed 3 sets of 10 leg press repetitions 3-d·wk^-1 for 4-wks. Reflex-EMD was measured at Baseline, Week-2, and Week-4. Results: The reflex-EMD durations decreased from Baseline at Week-2 and Week-4 for the VRT group, but not the DCER or Control groups. The reflex response < electrochemical process < mechanical process < total reflex-EMD for all groups. Conclusions: VRT elicited greater reflex adaptations compared to DCER training which indicated that VRT may be beneficial to incorporate into training or physical therapy programmes for pilots, soldiers, elderly, athletes, or professions that require quick reflexes and response times.

Inter- and Intra-Individual Differences in EMG and MMG during Maximal, Bilateral, Dynamic Leg Extensions

The purpose of this study was to compare the composite, inter-individual, and intra-individual differences in the patterns of responses for electromyographic (EMG) and mechanomyographic (MMG) amplitude (AMP) and mean power frequency (MPF) during fatiguing, maximal, bilateral, and isokinetic leg extension muscle actions. Thirteen recreationally active men (age = 21.7 ± 2.6 years; body mass = 79.8 ± 11.5 kg; height = 174.2 ± 12.7 cm) performed maximal, bilateral leg extensions at 180°·s⁻¹ until the torque values dropped to 50% of peak torque for two consecutive repetitions. The EMG and MMG signals from the vastus lateralis (VL) muscles of both limbs were recorded. Four 2(Leg) × 19(time) repeated measures ANOVAs were conducted to examine mean differences for EMG AMP, EMG MPF, MMG AMP, and MMG MPF between limbs, and polynomial regression analyses were performed to identify the patterns of neuromuscular responses. The results indicated no significant differences between limbs for EMG AMP (p = 0.44), EMG MPF (p = 0.33), MMG AMP (p = 0.89), or MMG MPF (p = 0.52). Polynomial regression analyses demonstrated substantial inter-individual variability. Inferences made regarding the patterns of neuromuscular responses to fatiguing and bilateral muscle actions should be considered on a subject-by-subject basis.

A biosignal analysis for reducing prosthetic control durations: a proposed method using electromyographic and mechanomyographic control theory

OBJECTIVES

This project proposes a unique methodology utilizing electromyography and mechanomyography to determine the intensity of a desired movement which may be useful in further developing decomposition algorithms for prosthetic controls.

METHODS

Ten males performed isometric leg extension muscle actions corresponding to 20, 40, 60, 80, and 100% of their maximal voluntary isometric contraction force. The duration and amplitude of the gross lateral movement of the mechanomyographic signal as well as electromechanical delay were measured during each contraction.

RESULTS

The results indicated that the duration of the gross lateral movement decreased with increases in intensity (20<40=60<80<100% maximal voluntary isometric contraction) and that the amplitude of the gross lateral movement increased with increases in intensity (20<40=60<80<100% maximal voluntary isometric contraction). In addition, electromechanical delay decreased with each increase in intensity. These measurements occurred within 40 ms from the onset of the electromyographic signal.

CONCLUSIONS

Thus, these measurements may be incorporated into existing prosthetic control algorithms to reduce grasp times and identify the intensity of a movement earlier. In addition, the gross lateral movement and electromechanical delay measurements may provide more intuitive controls for prosthetic users.

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   <  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 effects of Shilajit supplementation on fatigue-induced decreases in muscular strength and serum hydroxyproline levels

Background

Shilajit is a safe, fluvic mineral complex exudate that is common to Ayurvedic medicine and is composed of fulvic acids, dibenzo-α-pyrones, proteins, and minerals. The purpose of this study was to examine the effects of 8 weeks of Shilajit supplementation at 250 mg·d^− 1 (low dose) and 500 mg·d^− 1 (high dose) versus placebo on maximal voluntary isometric contraction (MVIC) strength, concentric peak torque, fatigue-induced percent decline in strength, and serum hydroxyproline (HYP).

Methods

Sixty-three recreationally-active men (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \overline{X} $$\end{document}X¯ ± SD: 21.2 ± 2.4 yr.; 179.8 ± 6.3 cm; 83.1 ± 12.7 kg) volunteered to participate in this study. The subjects were randomly assigned to the high dose, low dose, or placebo group (each group: n = 21). During pre-supplementation testing, the subjects performed 2 pretest MVICs, 2 sets of 50 maximal, bilateral, concentric isokinetic leg extensions at 180°·s^− 1 separated by 2-min of rest, and 2 posttest MVICs. Following 8 weeks of supplementation, the subjects repeated the pre-supplementation testing procedures. In addition, the groups were dichotomized at the 50th percentile based on pre-supplementation MVIC and baseline HYP. Mixed model ANOVAs and ANCOVAs were used to statistically analyze the dependent variables for the total groups (n = 21 per group) as well as dichotomized groups.

Results

For the upper 50th percentile group, the post-supplementation adjusted mean percent decline in MVIC was significantly less for the high dose group (8.9 ± 2.3%) than the low dose (17.0 ± 2.4%; p = 0.022) and placebo (16.0 ± 2.4%; p = 0.044) groups. There was no significant (p = 0.774) difference, however, between the low dose and placebo groups. In addition, for the upper 50th percentile group, the adjusted mean post-supplementation baseline HYP for the high dose group (1.5 ± 0.3 μg·mL^− 1) was significantly less than both the low dose (2.4 ± 0.3 μg·mL^− 1; p = 0.034) and placebo (2.4 ± 0.3 μg·mL^− 1, p = 0.024) groups.

Conclusions

The results of the present study demonstrated that 8 weeks of PrimaVie® Shilajit supplementation at 500 mg·d^− 1 promoted the retention of maximal muscular strength following the fatiguing protocol and decreased baseline HYP. Thus, PrimaVie® Shilajit supplementation at 500 mg·d^− 1 elicited favorable muscle and connective tissue adaptations.

Sex-Related Differences in the Accuracy of Estimating Target Force Using Percentages of Maximal Voluntary Isometric Contractions vs. Ratings of Perceived Exertion During Isometric Muscle Actions

Keller, JL, Housh, TJ, Smith, CM, Hill, EC, Schmidt, RJ, and Johnson, GO. Sex-related differences in the accuracy of estimating target force using percentages of maximal voluntary isometric contractions vs. ratings of perceived exertion during isometric muscle actions. J Strength Cond Res 32(11): 3294-3300, 2018-The purpose of this study was to examine sex-related differences in the accuracy of estimating actual target force and to compare the accuracy of estimating actual target force using percentages of maximal voluntary isometric contraction (MVIC) or ratings of perceived exertion (RPE) values during isometric leg flexion and leg extension muscle actions. Twenty adults, 10 women and 10 men, (mean ± SD age: 22.9 ± 2.9 years) completed pretest MVICs to calculate actual target force values at 10, 30, 50, 70, and 90% of MVIC. Additional trials were then randomized for estimating actual target force using percentages of MVIC or RPE values during isometric leg flexion or leg extension. For isometric leg flexion, the women and men overestimated (p ≤ 0.05) the actual target force at 10% for the percentage of MVIC and RPE trials and underestimated the actual target force at 90% for the RPE trial. For isometric leg extension, the women overestimated the actual target force at 10% for the percentage of MVIC trial and RPE trial. The men overestimated actual target force at 10 and 30% for the percentage of MVIC trial and overestimated actual target force at 10% during the RPE trial for isometric leg extension. Also, the men underestimated actual target force at 90% for both the percentage of MVIC trial and RPE trial. Men require more familiarization than women to accurately estimate isometric leg extension force values. Caution should be used when estimating force production as a percentage of MVIC or RPE value for training prescriptions.

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 > 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.