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.

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.

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.

Non-traditional HIIT-style ROTC training elicits positive bone quality and performance adaptations

Military personnel experience elevated bone injury incidence, partly due to arduous and repetitive training. Non-traditional High-Intensity Interval Training-style (HIIT) may benefit pre-enlisted Reserve Officer Training Corps (ROTC) cadet's musculoskeletal health and performance prior to military service. This study investigated 16 ROTC (n = 12 males; n = 4 females) and 15 physically active sex-, age-, and body mass-matched Controls' musculoskeletal health and performance from November to April. Total body, lumbar spine, and dual- hip dual-energy X-ray absorptiometry scans and 4%, 38%, 66% tibial peripheral quantitative computed tomography scans, blood draws (serum sclerostin and parathyroid hormone), and maximal muscle strength and aerobic capacity testing were completed. From November to April, ROTC improved bone density (DXA) of the dominant total hip and greater trochanter and non-dominant greater trochanter and 38% and 66% tibial total volumetric and cortical bone density (pQCT) similarly or more than Controls (all p ≤ 0.049). From November to April, ROTC also improved bench and leg press, and peak aerobic capacity (all p ≤ 0.013). From November to January, serum sclerostin increased (p ≤ 0.007) and remained elevated through April, while parathyroid hormone was unchanged. HIIT-style training induced positive musculoskeletal adaptations, suggesting it may be an excellent pre-service training modality for this injury prone group.

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.

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 (47M; 49F) were assessed in both arms and legs before and after a double footed ice bath (2°C) for 1min and an isometric knee extension, time to failure task. The difference between post and pre measures was defined 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 DXA scan.

RESULTS

Sex differences were found in whole body lean mass (61.5±6.7kg vs 41.2±5.4kg; P<0.001) but not fat mass amount (17.2±10.5kg vs 21.0±9.7kg; 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.

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.

Circulating microRNA responses to acute whole-body vibration and resistance exercise in postmenopausal women

Evaluating alterations in circulating microRNA (c-miRNA) expression may provide deeper insight into the role of exercise in the attenuation of the negative effects of aging on musculoskeletal health. Currently, there are sparse data on c-miRNA responses to acute exercise in postmenopausal women. The purpose of this study was to characterize the effects of acute bouts of resistance exercise and whole-body vibration on expression of selected c-miRNAs in postmenopausal women aged 65-76 years (n=10). We also examined relationships between c-miRNAs and muscle strength and bone characteristics. This randomized crossover design study compared c-miRNA responses to a bout of resistance exercise (RE) (3 sets 10 reps 70% 1 repetition maximum (1RM), 5 exercises) and a bout of whole-body vibration (WBV) (5 sets 1 min bouts 20Hz 3.38mm peak to peak displacement, Vibraflex vibration platform). DXA was used to measure body composition and areal bone mineral density (aBMD) of the total body, AP lumbar spine, and dual proximal femur. pQCT was used to measure tibia bone characteristics (4%, 38%, 66% sites). Blood samples were collected before exercise (Pre), immediately-post (IP), 60 minutes post (60P), 24 hours (24H), and 48 hours (48H) after exercise to measure serum miR-21-5p, -23a-3p, -133a-3p, -148a-3p (qPCR) and TRAP5b (ELISA). There was a significant modality × time interaction for c-miR-21-5p expression (p=0.019), which decreased from 60P to 24H after WBV only. TRAP5b serum concentrations significantly increased IP then decreased below Pre at 24H for both WBV and RE (p<0.01). Absolute changes in TRAP5b were negatively correlated with c-miR-21-5p fold changes (r= -0.642 to -0.724, p<0.05) for both exercise modalities. There were significant negative correlations between baseline c-miRNAs and bone status variables (r= -0.639 to -0.877, p<0.05). Our findings suggest that whole-body vibration is a sufficient mechanical stimulus for altering c-miR-21-5p expression, whereas a high intensity resistance exercise protocol did not elicit any c-miRNA responses in postmenopausal women. Increases in the bone resorption marker, TRAP5b, were associated with greater downregulation of c-miR-21-5p expression.

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.

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.

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.

Development of a Fitness Test Battery for Special Weapons and Tactics (SWAT) Operators-A Pilot Study

This investigation examined relationships between a Special Weapons and Tactics-specific fitness test (SORT) and an obstacle course (OC) used for qualification in fourteen male SWAT members from three local, regional police departments. The SORT included: squat, pushup, and lunge in 60 s; pullup hold; sled drag; and Yo-Yo Intermittent Recovery Test L1. The obstacle course included: 25 m sprint (repeated); window ascent; scale under a wall; 25 m serpentine run (repeated), body drag (20 m, repeated). Pearson coefficients examined SORT and OC relationships (p ≤ 0.05); intraclass correlation coefficients (ICC_2,1) assessed agreement of SORT trials. Repeated measures ANOVA evaluated differences in SORT metrics across time. Coefficients of variation (COV) examined SORT scoring consistency. The YoYo test was related to all SORT assessments (r = −0.803–0.894), except sled drag. The remaining SORT metrics were related to ≥two tests. SORT COVs ranged from 0.77–13.26% for trials 1–2 but decreased between trials 2–3 (0.95–8.97%). The OC was associated with YoYo, lunges, squats and sled drag (r = −0.790, −0.730, −0.766, and 0.802, respectively). No differences (p > 0.05) existed across SORT trials for event scores. The SORT battery appears to be a valid and reliable testing measure to assess SWAT occupational specific fitness.

Bone, Biomarker, Body Composition, and Performance Responses to 8 Weeks of ROTC Training

CONTEXT

Military personnel engage in vigorous exercise, often resulting in higher bone mineral density; however, lower leg bone injuries are common in this population. Predictors of change in tibial bone quality and strength need to be characterized in this high-risk population.

OBJECTIVE

This study aimed to examine the effects of an eight-week military training intervention on total body and site-specific bone density and tibial bone quality, serum biomarkers (parathyroid hormone and sclerostin), body composition, and physical performance. Additionally, we sought to investigate what outcome variables (biomarkers, body composition, physical performance) would be predictive of estimated tibial bone strength in college-aged Reserve Officers' Training Corps (ROTC) members.

DESIGN

Prospective Cohort Study.

SETTING

XXX University. Patients of Other Participants: ROTC (n=14 male; n=4 female) were matched for sex, age, and body mass to physically active Controls (n=14 male; n=4 female). ROTC engaged in an eight-week training intervention, while physically active Controls made no changes to their exercise routines.

MAIN OUTCOME MEASURES

Pre general health questionnaires and pre, mid, and post intervention bone scans (DXA, pQCT), serum blood draws (parathyroid hormone and sclerostin), and physical performance measures (muscle strength and aerobic capacity) were tested.

RESULTS

ROTC participants exhibited significantly increased hip bone density and content (all p≤0.03) after the eight-week intervention. Sclerostin, not PTH, was a significant positive correlate and predictor in all ROTC models for estimated bone strength at the fracture prone 38% tibial site. Both groups decreased total body and regional fat mass and ROTC increased aerobic capacity (all p≤0.05).

CONCLUSIONS

All bone, body composition, and performance measures either improved or were maintained in response to ROTC training and sclerostin should be further investigated as a potential early indicator of changes in estimated tibial bone strength in military cohorts.

Short-Term Analysis (8 Weeks) of Social Distancing and Isolation on Mental Health and Physical Activity Behavior During COVID-19

Due to the COVID-19 pandemic, cities and states adopted social distancing, social isolation, or quarantine measurements to slow the transmission of the disease. Negative mental health outcomes including depression and anxiety have been associated with social distancing or social isolation. The purpose of the present study was to examine changes in psychological health and physical activity over an 8 week period under social distancing policies during the COVID-19 pandemic. Methods: Ninety (73.3% female; age 32.04 ± 11.33) individuals participated in this study. Qualifying participants answered questions using an online survey regarding their loneliness, depressive symptoms, anxiety symptoms, mood state, and physical activity over four time points each lasting two weeks. Results: Symptoms of depression and state anxiety were increased in the population when compared to nationwide statistics from before the COVID-19 pandemic. Time point 2, ~1 month into social isolation, showed the most significant effects on mental health. During this time point, 100% of the participants showed symptoms of depression. There were no significant changes in physical activity over the 8 weeks. Loneliness, depressive symptoms, fatigue, and mood state were negatively associated with participation in physical activity. Vigor and state anxiety were associated with participation in physical activity. Conclusion: Social isolation and social distancing practices have had a negative effect on depression, anxiety, and mood over time. It appeared that depressive symptoms and total mood disturbance was elevated during time point two. Depressive symptoms were much higher than average compared to previous epidemiological data. Physical activity amount did not change over time but was associated with poor mental health.

The Acute Physiological Responses to Traditional vs. Practical Blood Flow Restriction Resistance Exercise in Untrained Men and Women

This study compared the acute physiological responses of traditional and practical blood flow restriction resistance exercise (tBFR and pBFR, respectively) and high- and low-load resistance exercise without BFR (HL and LL, respectively), as well as the potential sex differences within the aforementioned exercise methods. Fourteen men and fifteen women randomly completed the following experimental conditions: (1) tBFR, consisting of four sets of 30-15-15-15 repetitions of the bilateral horizontal leg press and knee extension exercises, at 30% of one-repetition maximum (1-RM), with a 13.5 cm wide pneumatic cuff placed at the most proximal portion of each thigh and inflated to a pressure equivalent to 50% of the participant’s total occlusion pressure; (2) pBFR, which was the same as the tBFR condition, except that an elastic band wrapped around the proximal portion of each thigh at a tightness of 7 on a 0 to 10 perceived pressure scale was used to reduce blood flow; (3) LL, same as the tBFR and pBFR protocols, except that no BFR was applied; and (4) HL, consisting of 3 sets of 10 repetitions at 80% of 1-RM, with the same 1-min rest interval between sets and a 3-min rest period between exercises. At baseline, immediately post-, 5 min post-, and 15 min post-exercise, whole-blood lactate (WBL), indices of muscle swelling (muscle thickness and thigh circumference), hematocrit and plasma volume changes, were measured as well as superficial electromyography (sEMG) amplitude during exercise. There were no significant (p > 0.05) differences between the tBFR and pBFR exercise protocols for any of the physiological parameters assessed. However, significantly greater (p < 0.05) WBL and sEMG values were observed for HL compared to the remaining exercise conditions. Finally, males displayed greater WBL levels than females at 15 min post-exercise. Interestingly, males also displayed significantly (p < 0.05) greater sEMG amplitude than females within the low-load trials during leg press, but no significant (p < 0.05) sex differences were observed during knee extension. In conclusion, tBFR and pBFR seemed to be capable of inducing the same acute physiological responses. Furthermore, males displayed greater responses than females for some of the physiological parameters measured.

Bilateral deficit in strength but not rapid force during maximal handgrip contractions

The purpose of this experiment was to evaluate the bilateral index in force and electromyographic (EMG) responses for the dominant and non-dominant hands during maximal handgrip contractions in males and females. Thirty-two right-handed participants (16 females) performed maximal unilateral and bilateral handgrip contractions on two separate visits. Bilateral indices were computed for maximal force, rate of force development (RFD₁₀₀), EMG amplitude, and the rate of EMG rise (RER). There was a bilateral deficit for maximal force in the dominant (-4.98 ± 7.39%, p < 0.001; d = 0.674) but not the non-dominant hand (-1.57 ± 9.10%, p = 0.334; d = 0.173). No deficits were observed for rapid force. The non-dominant flexor carpi radialis showed a bilateral facilitation in EMG amplitude (+12.32 ± 19.29%, p < 0.001; d = 0.638), yet a bilateral deficit for RER (-22.10 ± 27.80%, p < 0.001; d = 0.795). No sex differences were observed for any of the bilateral indices. These data suggest that maximal but not rapid force is susceptible to a bilateral deficit during contractions of the hands. The EMG responses did not parallel the force data. We show sex does not influence the magnitude or direction of the bilateral index in this muscle group.

Perceptual responses: Clinical versus practical blood flow restriction resistance exercise

The purpose of the current investigation was to compare the acute perceptual responses during low-load resistance exercise (RE) with clinical blood flow restriction (cBFR-RE) and practical blood flow restriction (pBFR-RE), and during conventional low- (LL-RE) and high-load resistance exercise (HL-RE), to determine if these responses differed between young males and females. Twenty-nine participants (14 males: 23.6±2.7years, 25.3±3.1kg/m² and 15 females: 20.3±1.6years, 23.4±1.9kg/m²) completed the following exercise conditions in a randomized design: 1) cBFR-RE, 2) pBFR-RE, 3) HL-RE, and 4) LL-RE. Low-load conditions consisted of 30-15-15-15 repetitions of two-leg press (LP) and knee extension (KE) exercises with 30% one-repetition maximum (1-RM), and HL-RE consisted of 3 sets of 10 repetitions at 80% 1-RM, all with 60s rest intervals. Ratings of perceived exertion (RPE) and discomfort were assessed before exercise and immediately following each set. RPE was significantly higher in HL-RE compared to all low-load conditions for both exercises after each set (all p<0.05). cBFR-RE resulted in significantly greater RPE than pBFR-RE and LL-RE for both exercises for sets 1-4 for LP and sets 2-3 for KE (all p<0.05). Levels of discomfort were similar between cBFR-RE and HL-RE, which tended to be significantly higher than pBFR-RE and LL-RE (p<0.05). Men reported significantly greater RPE than women following sets 2-4 during KE with cBFR-RE and sets 2 and 3 during KE for HL-RE (all p<0.05). Males also reported significantly greater discomfort than women following sets 2-4 for KE LL-RE (p<0.05). Altogether, these data suggest that pBFR-RE may provide a more favorable BFR condition based on perceptual responses and that perceptual responses may differ between sexes across varying resistance exercise conditions.

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.

Endogenous Pain Inhibitory Function: Endurance-Trained Athletes vs Active Controls

Objective

Athletes are at risk for developing chronic pain conditions, but the role of exercise in the modulation of pain in athletes has not been well established. The aim of this study was to investigate conditioned pain modulation (CPM) and exercise-induced hypoalgesia (EIH) responses between 13 endurance-trained athletes and 13 normally active controls.

Methods

In a cross-sectional, nonrandomized study with two independent groups of college-aged males and females, pressure pain thresholds (PPTs) were assessed in the vastus lateralis (VL) and brachioradialis (BR) using a pressure algometer before and after a conditioning stimulus, an isometric hand grip exercise to failure, and a 30-minute run.

Results

PPTs increased following the conditioning stimulus, indicating a CPM response, to a similar degree in the BR (19.3% ± 26.5% vs 18.6% ± 16.2%, P = 0.93) and VL (18.9% ± 25.9% vs 28.7% ± 27.4%, P = 0.73) in the athletes and controls. PPTs increased following isometric exercise to a similar extent in athletes and controls in the BR (23.9% ± 22.8% vs 28.2% ± 24.0%, P = 0.75) and VL (15.8% ± 14.8% vs 15.5% ± 11.6%, P = 0.94). Following 30 minutes of running, EIH was similar between athletes and controls in the VL (21.2% ± 17.2% vs 13.8% ± 13.3%, P = 0.23) but was attenuated in the BR of the athletes (6.1% ± 16.9% vs 20.9% ± 20%, P = 0.047).

Conclusions

Athletes and controls exhibited similar endogenous pain inhibitory function both locally and systemically following CPM and isometric, upper body exercise. After the 30-minute run, BR EIH was reduced in the athletes compared with controls, suggesting a reduced systemic response following familiar exercise—perhaps due to the exercise being perceived as less painful and/or effortful.

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.

Voluntary muscle activation and evoked volitional-wave responses as a function of torque

INTRODUCTION

This study employed a unique stimulation paradigm which allowed for the simultaneous assessment of voluntary activation levels (VA) via twitch-interpolation, and the evoked V-wave responses of the plantar flexors during submaximal and maximal contractions. Test-retest reliability was also examined.

METHODS

Fourteen participants repeated a stimulation protocol over four visits to assess VA and evoked V-wave amplitude across torque levels ranging from 20% to 100% MVC. MVC torque and EMG amplitude were also measured.

RESULTS

VA increased nonlinearly with torque production and plateaued by 80% MVC. V-wave amplitude increased linearly from 20% to 100% MVC. There were no differences in any dependent variable across visits (p > 0.05). VA demonstrated moderate to substantial reliability across all torque levels (ICC = 0.76-0.91) while V-wave amplitude exhibited fair to moderate reliability from 40% to 100% (ICC = 0.48-0.74).

DISCUSSION

We were able to reliably collect VA and the V-wave simultaneously in the plantar flexors. Collection of VA and V-wave during the same contraction provides distinct information regarding the contribution of motor-unit recruitment and descending cortico-spinal drive/excitability to force production.

Carbohydrate Mouth Rinsing Does Not Prevent the Decline in Maximal Strength After Fatiguing Exercise

Black, CD, Schubert, DJ, Szczyglowski, MK, and Wren, JD. Carbohydrate mouth rinsing does not prevent the decline in maximal strength after fatiguing exercise. J Strength Cond Res 32(9): 2466-2473, 2018-Carbohydrate (CHO) rinsing has been shown to attenuate the decline of maximal voluntary contractions (MVCs) after fatiguing exercise-perhaps through a central mechanism. This study sought to determine the effect of a CHO rinse on MVC, voluntary activation, and contractile properties after fatiguing exercise. Thirteen adults participated in a double-blind, cross-over study. Maximal voluntary contraction of the dominant knee extensors was assessed, and voluntary activation (%VA) was determined using twitch interpolation. Participants then held 50% of MVC until volitional fatigue followed by a 20-second rinse with a solution of 8% maltodextrin (CHO) or placebo (PLA). Maximal voluntary contraction and %VA were reassessed immediately and 5 minutes after exercise. Maximal voluntary contraction did not differ between the CHO and PLA conditions initially (230 ± 90 vs. 232 ± 90 N·m; p = 0.69). Maximal voluntary contraction declined after exercise (p ≤ 0.01), but no differences were found between the CHO and PLA conditions (p ≥ 0.59). %VA did not differ between conditions (91.9 ± 2.9% vs. 91.5 ± 3.8%; p ≥ 0.11) nor did it change after exercise (p = 0.57). Twitch torque, rate of torque development, and rate of torque relaxation were reduced after exercise (p ≤ 0.05) but were unaffected by CHO rinsing (p > 0.05). Unlike a previous study, a CHO rinse did not preserve MVC after fatiguing exercise. This was likely due to a lack of central fatigue induced by the exercise protocol (as %VA was unaffected) as the CHO rinse is thought to work through a central mechanism.

Adaptations in antagonist co-activation: Role in the repeated-bout effect

Eccentric exercise results in an adaptation which attenuates muscle damage from subsequent exercise—termed the “repeated-bout effect (RBE).” Purpose: Study examined antagonist co-activation and motor-unit recruitment strategy, assessed via dEMG, concomitant to the RBE. Methods: Nine participants performed 5 sub-maximal isometric trapezoid (ramp-up, hold, ramp-down) contractions at force levels corresponding to 50% and 80% of maximal isometric strength (MVC). Surface EMG signals of the biceps brachii were decomposed into individual motor-unit action potential trains. The relationship between mean firing rate (MFR) of each motor-unit and its recruitment threshold (RT) was examined using linear regression. Eccentric exercise was then performed until biceps brachii MVC had decreased by ~40%. Surface EMG of the biceps and triceps were collected during eccentric exercise. MVC, range-of-motion (ROM), and delayed onset muscle soreness (DOMS) were measured 24-hours, 72-hours, and 1-week following eccentric exercise. Three weeks later all procedures were repeated. Results: Changes in MVC (-32±14% vs -25±10%; p = 0.034), ROM (-11% vs 6%; p = 0.01), and DOMS (31.0±19mm vs 19±12mm; p = 0.015) were attenuated following the second bout of exercise. Triceps EMG was reduced (16.8±9.5% vs. 12.6±7.2%; p = 0.03) during the second bout of eccentric exercise. The slope (-0.60±0.13 vs -0.70±0.18; p = 0.029) and y-intercept (46.5±8.3 vs 53.3±8.8; p = 0.020) of the MFR vs. RT relationship was altered during contractions at 80% of MVC prior to the second bout of eccentric exercise. No changes were observed at 50% of MVC. Conclusion: A reduction in antagonist co-activation during the second bout of eccentric exercise suggests less total force was required to move an identical external load. This finding is supported by the increased negative slope coefficient and an increased y-intercept of the linear relationship between RT and MFR.

Impact of shear rate pattern on post-occlusive near-infrared spectroscopy microvascular reactivity

The primary aim of the present study was to determine the impact of acute changes in shear rate patterns, in particular retrograde shear rate, on microvascular function in 15 healthy, young men and women as determined via the post-occlusive near-infrared spectroscopy (NIRS) microvascular reactivity response. Microvascular reactivity, via NIRS-derived measurements of post-occlusion tissue saturation index (TSI%) and total microvascular hemoglobin+myoglobin concentration ([Hb]_total), were assessed in each participant before and immediately after exposure to a 30min retrograde shear treatment. Retrograde shear was achieved via a blood pressure cuff placed below the knee inflated to 75mmHg. One leg was exposed to the retrograde shear (Treatment leg) and the contralateral leg served as a non-treatment control. In the Treatment leg, significant increases in retrograde shear rate occurred during the retrograde intervention. Following the intervention, the area under the TSI% post-occlusion response curve, which represents the total microvascular reactivity response, and the absolute peak TSI% response were significantly increased compared to pre-intervention in the Treatment leg, but not the Control leg. The absolute peak [Hb]_total response was significantly increased post-intervention in both legs. These results are in contrast to our hypothesis that 75mmHg cuff inflation, designed to increase retrograde shear rate in the femoral artery would negatively affect post-occlusive microvascular reactivity. These data suggest that the current method of increasing retrograde shear rate in the intact human does not adversely impact NIRS derived measurements of microvascular reactivity.