Changes in Brain Activity Immediately Post-Exercise Indicate a Role for Central Fatigue in the Volitional Termination of Exercise.

Electroencephalography (EEG) allows for the evaluation of real time changes in brain (electrocortical) activity during exercise. A few studies have examined changes in electrocortical activity using stationary cycling, but the findings have been mixed. Some of these studies have found increases in brain activity following exercise, while others have found decreases in brain activity following exercise. Hence, it is of importance to identify post-exercise changes in brain activity. Sixteen healthy, untrained subjects (8 males; 8 females) participated in the study. All 16 participants performed a graded exercise test (GXT) to volitional exhaustion on an upright cycle ergometer. Continuous EEG recordings were sampled before (PRE) and immediately following (IP) the GXT. Regions of interest were primarily the dorsolateral prefrontal cortex (DLPFC), ventrolateral prefrontal cortex (VLPFC), and left and right motor cortex (MC). In the DLPFC, a frontal asymmetry index was also identified. There was a statistically significant increase in theta power in the DLPFC, VLPFC, and left and right MC from PRE to IP (all p < 0.05). There was also a shift towards right hemisphere asymmetry at the IP time point in the DLPFC (p < 0.05). Finally, there was an increase in alpha power from PRE to IP in the right MC (p < 0.05). EEG could prove to be an important way to measure the effects of central fatigue on brain activity before and immediately following exercise.

Delayed-Onset Muscle Soreness Alters Mechanical Sensitivity, but Not Thermal Sensitivity or Pain Modulatory Function.

Introduction: Many clinical musculoskeletal pain conditions are characterized by chronic inflammation that sensitizes nociceptors. An unresolved issue is whether inflammation affects all nociceptors in a similar manner. Exercise-induced muscle damage (EIMD) has been proposed as a model for simulating clinical inflammatory pain in healthy samples. We sought to test the effect of EIMD on various painful stimuli (pressure and thermal), central pain processing (via the nociceptive flexion reflex) and endogenous pain modulation via conditioned pain modulation and exercise-induced hypoalgesia. Methods: Eighteen participants (9F, age: 24.6 ± 3.3) were recruited for repeated measures testing and each completed pain sensitivity testing prior to and 48 hours after an eccentric exercise protocol. The participants performed a minimum of 6 rounds of 10 eccentric knee extension exercises to induce muscle damage and localized inflammation in the right quadriceps. Force decrements, knee range-of-motion, and delayed onset muscle soreness (DOMS) were used to quantify EIMD. Results: There was a significant main effect of time for pressure pain (%diff; -58.9 ± 23.1; p = 0.02, ηp2 = 0.28) but no significant main effect was observed for limb (%diff; -15.5 ± 23.9; p = 0.53, ηp2 = 0.02). In contrast, there was a significant interaction between time and limb (p < 0.001, ηp2 = 0.47) whereby participants had lower pressure pain sensitivity in the right leg only after the damage protocol (%diff; -105.9 ± 29.2; p = 0.002). Discussion: Individuals with chronic inflammatory pain usually have an increased sensitivity to pressure, thermal, and electrical stimuli, however, our sample, following muscle damage to induce acute inflammation only had sensitivity to mechanical pain. Exercise induced inflammation may reflect a peripheral sensitivity localized to the damaged muscle rather than a global sensitivity like those with chronic pain display.

Ankle dorsiflexion asymmetry and the relationship with walking performance in people with multiple sclerosis.

BACKGROUND: Multiple sclerosis (MS) is a neurological disease characterized by demyelination disrupting the central nervous system. Persons with MS may exhibit symptomatic strength asymmetry (SA) that impacts motor gait and ankle mobility. The purpose of the present study was to investigate ankle dorsiflexion SA in people with MS and its relationship to functional performance. RESEARCH QUESTION: Is their a difference in dorsiflexion SA in MS participants compared to healthy individuals and does it impact functional performance? METHODS: 13 MS participants (EDSS 3.5 + 1.8) and 13 age matched NON-MS participants underwent maximal isometric (MVC) dynamometry testing for ankle dorsiflexion in both limbs to determine SA. Participants performed three functional tasks of walking performance. RESULTS: There was a significant intra-limb MVC difference in the MS group, and significantly greater isometric SA (p < 0.007) and isokinetic SA (p < 0.04) in the MS group compared to healthy individuals. The MS group exhibited significant correlations between outcomes of functional walking performance with isokinetic but not isometric SA. There was no significant correlation between disability status and functional task performance. SIGNIFICANCE: Ankle dorsiflexion SA is negatively correlated with functional performance in MS participants. MS disability status was not a predictor of functional task performance, and symptom testing may be appropriate to assess walking ability in persons with MS.

Cerebral blood flow dynamics: Is there more to the story at exercise onset?

A monoexponential model characterizing cerebral blood velocity dynamics at the onset of exercise may mask dynamic responses by the cerebrovasculature countering large fluctuations of middle cerebral artery blood velocity (MCAv) and cerebral perfusion pressure (CPP) oscillations. Therefore, the purpose of this study was to determine whether the use of a monoexponential model attributes initial fluctuations of MCAv at the start of exercise as a time delay (TD). Twenty-three adults (10 women, 23.9 ± 3.3 yrs; 23.7 ± 2.4 kg/m2 ) completed 2 min of rest followed by 3 mins of recumbent cycling at 50 W. MCAv, CPP, and Cerebrovascular Conductance index (CVCi), calculated as CVCi = MCAv/MAP × 100 mmHg, were collected, a lowpass filter (0.2 Hz) was applied, and averaged into 3-second bins. MCAv data were then fit to a monoexponential model [ΔMCAv(t) = Amp(1 - e-(t-TD)/τ )]. TD, tau (τ), and mean response time (MRT = TD + τ) were obtained from the model. Subjects exhibited a TD of 20.2 ± 18.1 s. TD was directly correlated with MCAv nadir (MCAvN ), r = -0.560, p = 0.007, which occurred at similar times (16.5 ± 15.3 vs. 20.2 ± 18.1 s, p = 0.967). Regressions indicated CPP as the strongest predictor of MCAvN ( R a 2 $$ {R}_a^2 $$ = 0.36). Fluctuations in MCAv were masked using a monoexponential model. To adequately understand cerebrovascular mechanisms during the transition from rest to exercise, CPP and CVCi must also be analyzed. A concurrent drop in cerebral perfusion pressure and middle cerebral artery blood velocity at the start of exercise forces the cerebrovasculature to respond to maintain cerebral blood flow. The use of a monoexponential model characterizes this initial phase as a time delay and masks this large important response.

Higher rating of perceived exertion and lower perceived recovery following a graded exercise test during menses compared to non-bleeding days in untrained females.

The underrepresentation of the female population in exercise sciences could be attributed, at least in part, to difficulty in appropriately accounting for the effects of the menstrual cycle (MC). Previous studies examining the effects of the MC on aerobic performance and subjective measures of aerobic performance show conflicting results. Purpose: The study examined how the MC affects the objective and subjective measures of aerobic performance within untrained female participants and in comparison with untrained male participants assessed at similar time intervals. Methods: Twenty-one participants (12 females and 9 males) completed a graded exercise test (GXT) on a cycle ergometer. The female participants were tested during their early follicular (EF; menses), ovulatory (O), and mid-luteal (ML) phases of the MC. The male participants were included as the control group and were randomly assigned to a menstrual cycle phase for each visit. During GXT, maximal oxygen consumption (VO2max), respiratory exchange ratio (RER), maximal heart rate (HRmax), peak blood lactate, and rating of perceived exertion (RPE) were determined. Twenty-four hours post-exercise, the perceived recovery status (PRS) was assessed. The MC phase was estimated using basal body temperature (BBT) in the female participants. Results: The male participants obtained a higher peak power and VO2max compared to the female participants (p < 0.05). All objective measures of aerobic performance did not significantly differ across the MC phases or time points that were tested. In the untrained female participants, an effect of the MC phase on RPE was found, with RPE being higher at EF (8.92 ± 0.79) compared to O (7.67 ± 1.23; p < 0.05) and ML (7.75 ± 1.06; p < 0.05). In addition, an effect of the MC phase on PRS was found, with perceived recovery being lower at EF (6.83 ± 0.94) compared to O (8.83 ± 1.12) and ML (8.67 ± 0.65; all p < 0.005) for the untrained female participants. No significant differences in RPE and PRS were found between tests in the untrained male participants. The female participants had lower perceived recovery following EF (6.83 ± 0.94) compared with the male participants (9.00 ± 1.00; p < 0.001). Conclusion: The untrained female participants perceived greater exertion during GXT and impaired recovery following GXT in EF compared to O and ML. These results may be attributed to either a drop in female sex hormone concentrations or discomfort associated with menses. The male participants did not exhibit any changes over time. Future studies using subjective parameters such as perceived exertion to track the internal load of training in the naturally menstruating female population should consider menses.

Lean Mass is Associated with, but Does Not Mediate Sex Differences in Pressure Pain Sensitivity in Healthy Adults.

Background: Sex differences exist in pain sensitivity, however, the underlying mechanism(s) that explain these differences are not fully understood. Pain sensitivity has been shown to be influenced by body mass index, but limited data exist on the role of body composition on pain sensitivity. The purpose was to examine the influence of body composition on pain sensitivity in males and females. Methods: This cross-sectional study design used pressure pain thresholds (PPT) of 87 participants (45 female) who were assessed in the vastus lateralis (leg PPT) and brachioradialis (arm PPT) using a pressure algometer. Fat and lean tissue were assessed via dual-energy X-ray absorptiometry (DXA). A two group by two limb, repeated measured ANOVA was used to assess differences between limbs and sex. Spearman correlations and hierarchical regression analyses were employed to determine the association between body composition and PPT. Results: Males had higher PPTs then females (P<0.05) and had higher DXA assessed lean and lower levels fat mass (P<0.05). Total body and limb specific lean mass was associated with PPTs (r≥0.34; P<0.05). Hierarchical regression analysis revealed lean mass was a significant predictor of 8% of the variance in arm PPT (P<0.006) and 18% of the variance in leg PPT (P<0.001). However, lean mass was not found to statistically mediate the observed sex differences in PPT. Conclusion: This finding suggests lean mass may play a previously unknown role in sex differences in pressure pain sensitivity. Future studies are needed to confirm this finding and a larger sample size is likely required to have sufficient power to perform the mediation analysis.

Symptomatic but not Asymptomatic COVID-19 Impairs Conditioned Pain Modulation in Young Adults.

Pain is a common symptom reported in COVID-19 patients. Impaired endogenous pain-modulatory mechanisms such as conditioned pain modulation (CPM), and exercise-induced hypoalgesia (EIH) have been found in chronic pain conditions but is often overlooked in acute conditions that evoke painful symptoms, such as COVID-19. The purpose was to compare pressure-pain sensitivity, CPM, and EIH function among individuals who previously had COVID-19, both symptomatically and asymptomatically, and a healthy control group. Pressure pain thresholds of 59 participants were assessed in the forearm and leg using a pressure algometer before and after 1) submersion of their dominant foot in cold water (2°C) for 1min; and 2) isometric knee extension performed to task-failure at 25% of their maximal contraction. The CPM response was attenuated in individuals who were infected with symptomatic COVID-19 (N = 26) compared to asymptomatic COVID-19 (N = 13) in arm (-1.0% ± 20.3 vs 33.3% ± 26.2; P < .001) and leg (12.8% ± 22.0 vs 33.8% ± 28.2; P = .014) and compared to controls (N = 20) in arm only (-1.0% ± 26.2 vs 23.4% ± 28.2; P = .004). The EIH response was not different between groups. CPM was impaired in individuals who had symptomatic COVID-19, which may have long-term implications on pain modulation. PERSPECTIVE: This study reveals that CPM was impaired in individuals who had symptomatic COVID-19 during the first wave of COVID-19, pre vaccine. These findings present a preliminary motive to study the long-term implications of COVID-19 and its effects on pain modulation.

Body composition does not influence conditioned pain modulation and exercise-induced hyperalgesia in healthy males and females.

BACKGROUND: Obese individuals report a higher susceptibility to chronic pain. Females are more likely to have chronic pain and excess adipose tissue. Chronic pain is associated with dysfunctional pain-modulatory mechanisms. Body composition differences may be associated with pain modulation differences in males and females. The purpose of this study was to investigate body composition (lean vs fat mass) differences and pain-modulatory functioning in healthy males and females. METHODS: Pressure pain thresholds (PPT) of 96 participants (47 M; 49F) were assessed in both arms and legs before and after a double-footed ice bath (2°C) for 1 min and an isometric knee extension, time to failure task. The difference between post- and pre-measures was defined as conditioned pain-modulatory (CPM) response (ice bath) and exercise-induced hypoalgesia (EIH) response. Whole-body and site-specific fat and lean tissue were assessed via the DXA scan. RESULTS: Sex differences were found in whole-body lean mass (61.5 ± 6.7 kg vs 41.2 ± 5.4 kg; p < 0.001) but not fat mass amount (17.2 ± 10.5 kg vs 21.0 ± 9.7 kg; p = 0.068). No effect of sex was found between limb CPM (p = 0.237) and limb EIH (p = 0.512). When controlling for lean mass, there was no significant effect of sex on CPM (p = 0.732) or EIH (p = 0.474) response. Similar findings were found for fat mass. CONCLUSION: The lack of difference suggests that males and females have similar modulatory functioning. It appears that in healthy adults free from chronic pain, neither fat mass nor lean mass has an influence on endogenous pain-modulatory function. SIGNIFICANCE: Men and women exhibited similar CPM and EIH despite marked differences in body composition. Our findings suggest whole-body and limb-specific lean tissue mass and fat mass do not influence CPM and EIH in adults without chronic pain.

Functional intermuscular reduction in spasticity for people with multiple sclerosis.

BACKGROUND: Eighty-five percent of people with multiple sclerosis (MS) incur gait impairments debilitating enough to significantly impact their function. OBJECTIVES: The aim of this study was to determine if a novel combination of intermuscular electrical stimulation, followed by functional electrical stimulation combined with supported bodyweight treadmill training, would improve gait, decrease spasticity and fatigue, and improve muscle strength. METHODS: Using a pre-post experimental design, we implemented this combination six-week protocol in 16 individuals with MS. We completed summary statistics and longitudinal pre-post results using Wilcoxon sign rank tests with Bonferroni adjustment. RESULTS: Participants responded with median increases of 29.4 feet (p < 0.0001) during the Six Minute Walk Test, median decreases of 0.7 s (p = 0.0011) in the 25-Foot Walk Test, median increases of 3.8 toe taps to fatigue (p = 0.0306) and median increases of 5.0 heel raises (p = 0.0093). Significant changes were noted in the Modified Ashworth Scale, both after intermuscular electrical stimulation (median change = -0.5 p = 0.0039) and after treadmill walking (median change = -0.5, p < 0.0005). CONCLUSIONS: Results of this novel protocol suggest this intervention combination has the potential to decrease spasticity, and improve gait speed and endurance in individuals with MS. Observed changes in mobility occurred without accompanying increases in fatigue.

Relationship between soleus H-reflex asymmetry and postural control in multiple sclerosis.

BACKGROUND: Impaired postural control is a common symptom in people with multiple sclerosis. Multiple sclerosis frequently presents with asymmetric motor involvement. One measurement yet to be evaluated for asymmetry in people with multiple sclerosis is the soleus Hoffmann reflex. PURPOSE: To measure the soleus Hoffmann reflex between limbs and correlate reflex asymmetry with postural control. MATERIAL AND METHODS: 16 participants completed four sessions of Hoffmann reflex testing and one session of balance testing. RESULTS: Multiple sclerosis participants had significantly greater reflex asymmetry (p = 0.01). The multiple sclerosis group had a significantly lower overall sensory organization testing composite score (p < 0.05), indicating sensory interpretation conflict that resulted in greater postural instability. Multiple sclerosis participants produced a significantly shorter endpoint and maximum excursion (p < 0.01) during limits of stability testing. Hoffmann reflex asymmetry was negatively related to forward endpoint excursion (p < 0.05), maximum excursion (p ≤ 0.01). CONCLUSIONS: Multiple sclerosis participants had greater soleus Hoffmann reflex asymmetry, which appears to significantly influence forward postural control.Implications for rehabilitationSoleus Hoffmann reflex asymmetry appears to influence postural stability.The soleus Hoffmann reflex is capable of adapting to different modes of exercise; therefore, to reduce H-reflex asymmetry it is recommended to individualize physical rehabilitative programming.Assessing the soleus Hoffmann reflex in people with multiple sclerosis during health screenings could be of use to clinical and rehabilitative practitioners.

Carbohydrate Mouth Rinsing Does Not Alter Central or Peripheral Fatigue After High-Intensity and Low-Intensity Exercise in Men.

ABSTRACT: Black, CD, Haskins, KR, Bemben, MG, and Larson, RD. Carbohydrate mouth rinsing does not alter central or peripheral fatigue after high-intensity and low-intensity exercise in men. J Strength Cond Res 36(1): 142-148, 2022-Carbohydrate (CHO) mouth rinsing improves performance during endurance exercise. However, its ability to attenuate fatigue during strength-based exercise is less certain. This study sought to determine the effects of a CHO mouth rinse on torque production and voluntary activation (VA%) after high-intensity and low-intensity isometric exercise. Twelve male subjects (22.5 ± 2.3 years; 183.5 ± 6.5 cm; 82.2 ± 13.9 kg) completed 4 testing sessions in a double-blind crossover fashion. Knee extension maximal voluntary isometric strength (MVC) was assessed before(Pre), immediately (iPost-Ex), and 5 minutes (5-min Post Ex) after isometric exercise performed at 80% or 20% of MVC. An 8% CHO solution or placebo (PLA) was rinsed for 20 seconds after exercise. VA% was determined by twitch interpolation. A 2 condition (CHO vs. PLA) × 2 contraction intensity (20 vs. 80%) × 3 time (Pre, iPost Ex, and 5-min Post Ex) completely within subject-repeated measured analysis of variance was performed; statistical significance was set at p ≤ 0.05. Greater reductions in MVC were found at iPost-Ex after exercise at 20% compared with 80% of MVC (-25 ± 14% vs. -11 ± 8%; p < 0.001) as well as for VA% (-17 ± 14% vs. -8 ± 14%; p < 0.004). No differences were observed in the CHO vs. PLA condition (p ≥ 0.34). We were successful in eliciting differing levels of central and peripheral fatigue by exercising at a low and high intensity. Despite significantly larger declines in VA% after exercise at 20% of MVC, CHO mouth rinsing had no effects compared with placebo on any measured variable.

Social Distancing, Psychological Mood and Physical Activity Behavior During COVID-19 in the United States.

Social distancing, during previous epidemics, has been shown to lead to poor mental health outcomes and reduced physical activity. The purpose of the present study was to examine the relationships between self-reported psychological state and physical activity behaviors of individuals under social distancing policies during the COVID-19 pandemic. 199 individuals (29.85 ± 10.22 yrs) in the United States who had been in social distancing for 2-4 weeks participated in this study. Participants answered a questionnaire regarding feelings of loneliness, depression, anxiety, mood state, and physical activity. 66.8% of participants had depressive symptoms and 72.8% had symptoms of anxiety. Loneliness was correlated with depression (r = 0.66), trait anxiety (r = 0.36), fatigue (r = 0.38), confusion (r = 0.39), and total mood disturbance (TMD; r = 0.62). Participation in total physical activity was negatively associated with depressive symptoms (r = -0.16) and TMD (r = -0.16). State anxiety was positively associated with participation in total physical activity (r = 0.22). In addition, a binomial logistic regression was performed to predict participation in sufficient physical activity. The model explained 45% of the variance in physical activity participation and correctly categorized 77% of cases. Individuals with higher vigor scores had an increased likelihood of participating in sufficient physical activity. Loneliness was associated with negative psychological mood state. Individuals with higher feelings of loneliness, depressive symptoms, trait anxiety, and negative mood state were observed to spend less time engaged in physical activity. Higher state anxiety was positively associated with engagement in physical activity.

An evaluation of the reliability of the foot-tapping test in a healthy sample.

The foot-tapping test (FTT) can be used to assess upper motor neuron dysfunction in clinical populations. However, relatively little is known regarding the reliability or normative values of the FTT in either healthy or clinical populations. Although several different FTT methods have been used, no study to date has demonstrated the reliability or validity of FTT by comparing it across several different counting methods in healthy persons. This unfortunately limits its usefulness in medicine and research. OBJECTIVE: This study sought to examine the reliability and validity of the FTT in healthy individuals to determine its usefulness and to make recommendations for its implementation in clinical populations. Furthermore, the concurrent validity and reliability of using a force plate as an objective measure of foot-taps was considered. DESIGN: Thirty-eight healthy individuals had their foot-tapping assessed using Live, Force Plate, and Video Counting methods over four separate visits. METHODS: Participants were seated as per previous FTT recommendations and asked to tap their foot in 10-second intervals while the number of taps was counted via Live, Video, and Force Plate counters. This was done with both legs, with shoes ON and OFF, and repeated over four separate visits. RESULTS: Despite significant differences between repeat trials for Force Plate and Video Counts (∼2 foot-taps, p < 0.01), test-retest reliability was high for all three methods (Pearson's R > 0.90). Dominant foot trials were higher (∼2 foot-taps, p < 0.05) than Non-dominant for all three counts. When performed with shoes ON, counts were higher (∼2 foot-taps, p < 0.05) than OFF for the Live and Force Plate counts. Reliability between visits was high (ICC > 0.80) and only the Video count was significantly lower for Visit 1 (p < 0.01). CONCLUSIONS: Given findings, the authors suggest using a Force Plate counting method and have compiled a list of suggestions for future implementation of the FTT.

Effects of Group Running on the Training Intensity Distribution of Collegiate Cross-Country Runners.

ABSTRACT: Farrell III, JW, Dunn, A, Cantrell, GS, Lantis, DJ, Larson, DJ, and Larson, RD. Effects of group running on the training intensity distribution of collegiate cross-country runners. J Strength Cond Res 35(10): 2862-2869, 2021-Collegiate cross-country training is often conducted and prescribed in a group setting. This may result in the application of an inappropriate training stimulus to athletes due to potentially different physiological responses to the same training prescription. The aim of this investigation was to quantify the training intensity distribution (TID) of a collegiate cross-country team and the associated physiological adaptions. Sixteen subjects, 8 male subjects and 8 female subjects, performed a graded exercise test before and after observational period to determine peak oxygen consumption (V̇o2peak), the speed (S@), heart rate (HR@), and oxygen consumption (V̇o2@) associated with 2 and 4 mmol·L-1 of blood lactate. Training intensity distribution was quantified by assessing time spent in 3 intensity zones calculated as zone 1 (low intensity, HR values HR@2 and HR@4). No statistical differences were observed between male subjects and female subjects for percent of training time spent in zones 1, 2, and 3. No significant interactions were observed between sex and time for performance variables. Male subjects and female subjects improved V̇o2peak, S@4, and V̇o2@4 with male subjects also increasing V̇o2@2. No significant differences were observed between male subjects and female subjects when comparing percent changes for variables. Examining individual data showed that 2 female subjects experienced performance decrements and trained proportionally more in zones 2 and 3 compared with the overall group. The TID and performance decrements of the 2 highlighted subjects suggest that conducting training in a group setting may potentially be detrimental for some collegiate runners.

Cerebrovascular responses to graded exercise in young healthy males and females.

Although systemic sex-specific differences in cardiovascular responses to exercise are well established, the comparison of sex-specific cerebrovascular responses to exercise has gone under-investigated especially, during high intensity exercise. Therefore, our purpose was to compare cerebrovascular responses in males and females throughout a graded exercise test (GXT). Twenty-six participants (13 Females and 13 Males, 24 ± 4 yrs.) completed a GXT on a recumbent cycle ergometer consisting of 3-min stages. Each sex completed 50W, 75W, 100W stages. Thereafter, power output increased 30W/stage for females and 40W/stage for males until participants were unable to maintain 60-80 RPM. The final stage completed by the participant was considered maximum workload(Wmax ). Respiratory gases (End-tidal CO2 , EtCO2 ), middle cerebral artery blood velocity (MCAv), heart rate (HR), non-invasive mean arterial pressure (MAP), cardiac output (CO), and stroke volume (SV) were continuously recorded on a breath-by-breath or beat-by-beat basis. Cerebral perfusion pressure, CPP = MAP (0. 7,355 distance from heart-level to doppler probe) and cerebral vascular conductance index, CVCi = MCAv/CPP 100mmHg were calculated. The change from baseline (Δ) in MCAv was similar between the sexes during the GXT (p = .091, ωp2  = 0.05). However, ΔCPP (p < .001, ωp2  = 0.25) was greater in males at intensities ≥ 80% Wmax and ΔCVCi (p = .005, ωp2  = 0.15) was greater in females at 100% Wmax . Δ End-tidal CO2 (ΔEtCO2 ) was not different between the sexes during exercise (p = .606, ωp2  = -0.03). These data suggest there are sex-specific differences in cerebrovascular control, and these differences may only be identifiable at high and severe intensity exercise.

Menstrual Cycle Effects on Exercise-Induced Fatigability.

Estrogen and progesterone have distinct concentrations across the menstrual cycle, each one promoting several physiological alterations other than preparing the uterus for pregnancy. Whether these physiological alterations can influence motor output during a fatiguing contraction is the goal of this review, with an emphasis on the obtained effect sizes. Studies on this topic frequently attempt to report if there is a statistically significant difference in fatigability between the follicular and luteal phases of the menstrual cycle. Although the significant difference (the P-value) can inform the probability of the event, it does not indicate the magnitude of it. We also investigated whether the type of task performed (e.g., isometric vs. dynamic) can further influence the magnitude by which exercise-induced fatigue changes with fluctuations in the concentration of ovarian hormones. We retrieved experimental studies in eumenorrheic women published between 1975 and 2019. The initial search yielded 921 studies, and after manual refinement, 46 experimental studies that reported metrics of motor output in both the follicular and luteal phases of the menstrual cycle were included. From these retrieved studies, 15 showed a statistical difference between the luteal and follicular phases (seven showing less fatigability during the luteal phase and eight during the follicular phase). The effect size was not consistent across studies and with a large range (-6.77; 1.61, favoring the luteal and follicular phase, respectively). The inconsistencies across studies may be a consequence of the differences in the limb used during the fatiguing contraction (upper vs. lower extremity), the type of contraction (isometric vs. dynamic), the muscle mass engaged (single limb vs. full body), and the techniques used to define the menstrual cycle phase (e.g., serum concentration vs. reported day of menses). Further studies are required to determine the effects of a regular menstrual cycle phase on the exercise-induced fatigability.

Sex differences in bone density, geometry, and bone strength of competitive soccer players.

OBJECTIVES: To examine sex differences in bone characteristics in competitive soccer players. METHODS: 43 soccer players (male, n=23; female, n=20), and 43 matched controls (males, n=23; females, n=20), completed the study. Areal BMD (aBMD) of the total body, lumbar spine, and dual femur and tibiae volumetric BMD (vBMD), bone geometry, and bone strength variables (pQCT) were measured. Bone-specific physical activity and training history were assessed. RESULTS: Male soccer players had significantly greater (p≤0.05) total body and hip aBMD, hip strength indices and 4% and 38% tibia variables than females. Regression analyses determined that BFLBM, not sex, was the strongest predictor of bone variables. Female soccer players exhibited significantly greater percent differences from controls for tibiae variables than males (p≤0.05). Soccer players had greater aBMD and hip strength indices than controls (p≤0.040). Soccer-specific asymmetries were found for 38% total area (2.1%) and pSSI (3.8%), favoring the non-dominant leg (both p≤0.017). CONCLUSION: Bone characteristics adjusted for body size were greater in male versus female soccer players. However, body composition variables were more important predictors of bone characteristics than sex. There were no sex differences in the magnitude of limb asymmetries, suggesting skeletal responsiveness to mechanical loading was similar in males and females.

Can Blood Flow Restricted Exercise Improve Ham:Quad Ratios Better Than Traditional Training?

Muscular deficiencies between the quadriceps and hamstrings are prevalent among women and often lead to knee injury and ACL tears. The purpose of this study was to examine whether short term resistance training with or without blood flow restriction (BFR) could improve hamstring:quadricep ratios (H:Q) and reduce the chance for injury. Women (n = 14; 18-25 yrs) were randomly assigned to either a traditional resistance training (RT: n = 8) or BFR resistance training in combination with traditional RT (RT+BFR: n = 6) group. Subjects trained 3 days/week for 6 weeks. The RT group completed 3 sets of 10 reps at 70% of their one-repetition maximum (1RM) with 1-minute rest between sets. The RT+BFR group completed the first 5 exercises similar to the RT group but performed the two-leg hamstring curl under blood flow restriction at 50% of occlusive pressure and 30% 1RM, completing 4 sets (30, 15, 15, 15) with 30 seconds rest between sets. Training effects were assessed using a two-way repeated measures ANOVA. Statistical significance was set at p≤0.05. There were significant (p < 0.05) main effects for time, with all muscle groups increasing strength but no significant main effects or interaction for the H:Q ratios at four testing speeds (60°/s, 180°/s, 240°/s, and 300°/s). This study found that hamstring strength with low load (30% 1RM) BFR training was improved to a similar extent as the hamstrings trained with the traditional high load (75% 1RM) program even though less external weight was used during training. H:Q ratios showed small non-significant increases post-training for both groups.

Evaluation of Power Production Asymmetry during Cycling in Persons with Multiple Sclerosis.

Lower limb asymmetries have been observed in persons with multiple sclerosis (PwMS), and have been associated with mobility impairment. An incremental cycling test was performed on a cycle ergometer to determine peak power output (PPO) and peak oxygen consumption (VO2peak). Then, participants cycled at 50%, 60%, and 70% of their PPO to assess the contribution of each lower limb to power production. Two-way repeated measures ANOVA was used to detect group × intensity differences in power production asymmetry. Eight PwMS and six healthy individuals (Non-MS) completed the study. No statistically significant (p > 0.05) group × intensity interactions or main effects were present when examining between-limb differences in power production. The current data do not indicate a statistically significant difference in power production asymmetry between groups and exercise intensities. Previous research has established a 10% difference between contralateral limbs as a threshold for asymmetry. The average asymmetry in power production in PwMS exceeded the 10% threshold at all measured outputs, suggesting the presence of asymmetry in power production.

Estimation of critical end-test torque using neuromuscular electrical stimulation of the quadriceps in humans.

Characterization of critical power/torque (CP/CT) during voluntary exercise requires maximal effort, making difficult for those with neuromuscular impairments. To address this issue we sought to determine if electrically stimulated intermittent isometric exercise resulted in a critical end-test torque (ETT) that behaved similar to voluntary CT. In the first experiment participants (n = 9) completed four bouts of stimulated exercise at a 3:2 duty cycle, at frequencies of 100, 50, 25 Hz, and a low frequency below ETT (Sub-ETT; ≤ 15 Hz). The second experiment (n = 20) consisted of four bouts at a 2:2 duty cycle-two bouts at 100 Hz, one at an intermediate frequency (15-30 Hz), and one at Sub-ETT. The third experiment (n = 12) consisted of two bouts at 50 Hz at a 3:2 duty* cycle with proximal blood flow occlusion during one of the bouts. ETT torque was similar (p ≥ 0.43) within and among stimulation frequencies in experiment 1. No fatigue was observed during the Sub-ETT bouts (p > 0.05). For experiment 2, ETT was similar at 100 Hz and at the intermediate frequency (p ≥ 0.29). Again, Sub-ETT stimulation did not result in fatigue (p > 0.05). Altering oxygen delivery by altering the duty cycle (3:2 vs. 2:2; p = 0.02) and by occlusion (p < 0.001) resulted in lower ETT values. Stimulated exercise resulted in an ETT that was consistent from day-to-day and similar regardless of initial torque, as long as that torque exceeded ETT, and was sensitive to oxygen delivery. As such we propose it represents a parameter similar to voluntary CT.