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.

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.

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.

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.

Acute and Chronic Bone Marker and Endocrine Responses to Resistance Exercise With and Without Blood Flow Restriction in Young Men.

In this study, we compared acute and chronic bone marker and hormone responses to 6 weeks of low intensity (20% 1RM) blood flow restriction (BFR20) resistance training to high intensity (70% 1RM) traditional resistance training (TR70) and moderate intensity (45% 1RM) traditional resistance training (TR45) in young men (18-35 years). Participants were randomized to one of the training groups or to a control group (CON). The following training programs were performed 3 days per week for 6 weeks for knee extension and knee flexion exercises: BFR20, 20%1RM, 4 sets (30, 15, 15, 15 reps) wearing blood flow restriction cuffs around the proximal thighs; TR70, 70% 1RM 3 sets 10 reps; and TR45, 45% 1RM 3 sets 15 reps. Muscle strength and thigh cross-sectional area were assessed at baseline, between week 3 and 6 of training. Acute bone marker (Bone ALP, CTX-I) and hormone (testosterone, IGF-1, IGFBP-3, cortisol) responses were assessed at weeks 1 and 6, with blood collection done in the morning after an overnight fast. The main findings were that the acute bone formation marker (Bone ALP) showed significant changes for TR70 and BFR20 but there was no difference between weeks 1 and 6. TR70 had acute increases in testosterone, IGF-1, and IGFBP-3 (weeks 1 and 6). BFR20 had significant acute increases in testosterone (weeks 1 and 6) and in IGF-1 at week 6, while TR45 had significant acute increases in testosterone (week 1), IGF-1 (week 6), and IGFBP-3 (week 6). Strength and muscle size gains were similar for the training groups. In conclusion, low intensity BFR resistance training was effective for stimulating acute bone formation marker and hormone responses, although TR70 showed the more consistent hormone responses than the other training groups.

Associations of serum IL-6 with muscle, bone, and adipose tissue in women.

This cross-sectional study examined the associations between serum interleukin-6 (IL-6) and muscle, bone, and fat parameters in recreationally active women. One-hundred forty-five women (48.7 ± 17.8 years; 164.4 ± 7.1 cm; 66.8 ± 10.7 kg; and 24.7 ± 3.9 kg/m2) underwent dual energy x-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT) assessments to determine total and regional muscle, bone, and fat parameters. Muscle performance of the knee extensors was examined via isometric, isotonic, and isokinetic dynamometry assessments, and serum IL-6 was measured via enzyme linked immunosorbent assay. Serum IL-6 was inversely associated with thigh muscle cross-sectional area (mCSA, r = -0.28, p < 0.01); isometric strength (r = -0.19, p < 0.05); hip areal bone mineral density [aBMD] (r = -0.18, p < 0.05); trochanter aBMD (r = -0.23, p < 0.01); total body aBMD (r = -0.20, p < 0.05); cortical volumetric bone density at 38 and 66% tibia (r = -0.18 and r = -0.19, respectively, both p < 0.05), and 66% cortical thickness (r = -0.17, p < 0.05). These associations were present after adjusting for age, BMI, and physical activity. Thigh mCSA was significantly lower in the tertile possessing the greatest IL-6 compared to the lowest tertile (p < 0.01); after adjusting for age, body mass index, and physical activity. Collectively, these observations indicate that IL-6 is inversely associated with skeletal muscle and bone parameters independent of relevant confounders. These observations bolster the prognostic value of serum IL-6.

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.

Sex-Specific Associations Between Bone-Loading Score and Adiposity Markers in Middle-Aged and Older Adults.

The authors examined sex-specific relationships between fat mass index (FMI), android/gynoid (A/G) fat ratio, relative skeletal muscle mass index, and Bone-Specific Physical Activity Questionnaire derived bone-loading scores (BLSs) in middle-aged and older adults (men, n = 27; women, n = 33; age = 55-75 years). The FMI, A/G fat ratio, and relative skeletal muscle mass index were estimated by dual-energy X-ray absorptiometry. The Bone-Specific Physical Activity Questionnaire was used to assess: (a) BLSpast (age 1 until 12 months before the study visit), (b) BLScurrent (last 12 months), and (c) BLStotal (average of [a] and [b]) scores. Separate multiple linear regression analysis of (a) age, FMI, and relative skeletal muscle mass index and (b) age, height, and A/G fat ratio versus BLS revealed that FMI and A/G fat ratio were negatively associated with BLSpast and BLStotal (p < .05) in women only. Adiposity and, specifically, central adiposity is negatively related to bone-loading physical activity in middle-aged and older women.

Sclerostin and Dickkopf-1 Characteristics According to Age and Physical Activity Levels in Premenopausal Women.

We aimed to compare serum concentrations of sclerostin and DKK-1 in young (20-30 yrs, n = 25) and middle-aged (35-45 yrs, n = 25) premenopausal women and based on physical activity (PA) status. PA status was assessed by the International Physical Activity Questionnaire (low-moderate (≤ 2999 MET-min/week) and high (≥ 3000 MET-min/week). Serum sclerostin and DKK-1 levels were measured in fasting morning blood samples by ELISA. Areal bone mineral density (aBMD) was measured by DXA, and non-dominant tibia bone characteristics were assessed by pQCT. After adjusting for total body aBMD, middle-aged women had significantly (p < 0.001) higher (0.54 ± 0.01 ng/mL) serum sclerostin than young women (0.41 ± 0.01 ng/mL), and sclerostin was positively correlated with age (rs = 0.065, p ≤ 0.001) and total PA score (rs = 0.33, p = 0.021). Young women had higher left trochanter aBMD (p = 0.036) than middle-aged women and aBMD variables were higher (all p ≤ 0.043) in the high active group. Middle-aged women had higher 38% cortical vBMD than young women (p = 0.021), otherwise young women had higher values for pQCT variables (all p ≤ 0.036). Sclerostin showed significant correlations (r = 0.32 to 0.58, all p ≤ 0.026) with spine aBMD for the entire cohort and for each age group. Middle-aged women had significant correlations between sclerostin and hip aBMD sites (r = 0.043 to 0.56, all p ≤ 0.031). Sclerostin and cortical vBMD were positively correlated in the entire cohort (r = 0.35 to 0.50; both p < 0.013); split by age group, middle-aged women had positive correlations (r = 0.45 to 0.61 age and, all p ≤ 0.021) between sclerostin and pQCT variables. No significant differences for physical activity were observed for serum DKK-1 concentrations. Serum sclerostin concentrations were positively associated with age and bone characteristics in premenopausal women; however, these findings were not evident for circulating DKK-1. Further research is needed to elucidate the mechanisms for the discordant results in these Wnt inhibitors.

Bone, Biomarker, Body Composition, and Performance Responses to 8 Weeks of Reserve Officers' Training Corps Training.

CONTEXT: Military personnel engage in vigorous exercise, often resulting in higher bone mineral density; however, leg bone injuries occur frequently in this population. Predictors of change in tibial bone quality and strength need to be characterized in this high-risk population. OBJECTIVES: To examine the effects of an 8-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 and to investigate which outcome variables (biomarkers, body composition, and physical performance) predict estimated tibial bone strength in college-aged Reserve Officers' Training Corps (ROTC) participants. DESIGN: Prospective cohort study. SETTING: University of Oklahoma. PATIENTS OR OTHER PARTICIPANTS: The ROTC participants (14 males, 4 females) were matched for sex, age, and mass to physically active control participants (14 males, 4 females). The ROTC participants engaged in an 8-week training intervention, while the physically active control group made no changes to their exercise routines. MAIN OUTCOME MEASURE(S): Preintervention general health questionnaires were completed. Pre-, mid-, and postintervention bone scans (dual-energy x-ray absorptiometry and peripheral quantitative computed tomography); serum blood draws (parathyroid hormone and sclerostin); and physical performance measures (muscle strength and aerobic capacity) were obtained. RESULTS: The ROTC participants exhibited increased hip bone density mineral and content (both P values ≤ .02) after the 8-week intervention. Sclerostin, but not parathyroid hormone, was a positive correlate and predictor in all ROTC models for estimated bone strength at the fracture-prone 38% tibial site (ie, 38% of the tibial length proximal to the distal end of the tibia). Both groups displayed decreased total body and regional fat mass, and ROTC participants' aerobic capacity increased (all P values ≤ .05). CONCLUSIONS: All bone, body composition, and performance measures either improved or were maintained in response to ROTC training. Sclerostin should be further investigated as a potential early indicator of changes in estimated tibial bone strength in military cohorts.

Skeletal Muscle Adaptations Following 80 Weeks of Resistance Exercise in Older Adults.

BACKGROUND AND PURPOSE: We followed and documented skeletal muscle adaptations from 4 resistance exercise (RE) prescriptions in older adults over the course of a 2-year, 80-week training study. METHODS: Forty-three older men and women-65.2 (3.5) years, 167.2 (7.5) cm, and 72.5 (14.7) kg-completed one of the following RE prescriptions: high-load 2 days per week (HL2D; n = 12), low-load 2 days per week (LL2D; n = 9), high-load 3 days per week (HL3D, n = 12), or low-load 3 days per week (LL3D, n = 10). High-load prescriptions consisted of 3 sets of 8 repetitions with 80% 1-repetition maximum (1-RM) and low-load prescriptions completed 3 sets of 16 repetitions with 40% 1-RM. Each session consisted of 12 exercises targeting major muscle groups and training loads were adjusted every fifth week to maintain progressive overload. Participants completed 40 weeks of supervised training, had a 2-month break, and then resumed another 40 weeks of supervised training. Bone-free lean body mass (BFLBM) and appendicular lean mass (ALM) were assessed via dual-energy x-ray absorptiometry and muscle cross-sectional area (mCSA) of the rectus femoris with diagnostic ultrasound across the intervention. RESULTS AND DISCUSSION: Groups responded similarly with significant increases in total strength (54.9%), upper body strength (42.7%), lower body strength (61.5%), and specific strength (50.3%, strength/BFLBM) over 80 weeks (all P < .001). Significant increases for BFLBM (3.0%), ALM (3.5%), and mCSA (48.7%) were also observed (all P ≤ .019). The only difference among groups indicated HL3D displaying significantly greater percent increase than LL2D for ALM (P = .043). CONCLUSIONS: Resistance exercise performed 2 or 3 days per week with moderate to heavy loads can improve muscle strength and induce small but perhaps clinically significant increases in BFLBM and mCSA in older adults over a 2-year period of supervised training.

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.

Site-Specific Bone Differences and Energy Status in Male Competitive Runners and Road Cyclists.

The interaction between mechanical loading and energy availability on bone health in male endurance athletes merits further investigation. The purpose of this study was to compare bone status in male competitive runners and road cyclists and to investigate the influence of energy availability (EA) on bone mineral density (BMD). 18 competitive runners and 19 road cyclists (20-50 years) participated in this study. Areal BMD and body composition were assessed by dual energy x-ray absorptiometry. Volumetric bone variables at the 4% and 66% tibia sites were assessed by peripheral quantitative computed tomography. Energy availability (EA, 7-day dietary and exercise logs) and resting metabolic rate (RMR, open circuit spirometry) were measured as indicators of energy status. Bone loading history, calcium intake, and training history were assessed by questionnaires. After adjusting for age, runners had significantly greater (p < 0.05) areal BMD (femoral neck, left total hip), Z-scores (total body, hips sites), total bone mineral content and trabecular variables (bone mineral content, volumetric BMD, bone strength index) at tibia 4% site, and total volumetric BMD at tibia 66% site than the cyclists (p ≤ 0.05). At the tibia 66% site, cyclists had significantly greater (p < 0.05) total area, periosteal circumference, endosteal circumference, and strength-strain index than runners. Energy variables were similar for runners and cyclists; however, RMR and RMR ratio (measured RMR/predicted RMR) were significantly lower in cyclists (p < 0.001). In conclusion, there were site-specific differences in hip and tibia bone characteristics between runners and cyclists. RMR was associated with several bone outcomes; however, EA was not related to bone health in runners or to dual energy x-ray absorptiometry bone variables in cyclists.

Equalization of Training Protocols by Time Under Tension Determines the Magnitude of Changes in Strength and Muscular Hypertrophy.

ABSTRACT: Martins-Costa, HC, Lacerda, LT, Diniz, RCR, Lima, FV, Andrade, AGP, Peixoto, GH, Gomes, MC, Lanza, MB, Bemben, MG, and Chagas, MH. Equalization of training protocols by time under tension determines the magnitude of changes in strength and muscular hypertrophy. J Strength Cond Res 36(7): 1770-1780, 2022-The aim of this study was to investigate the effects of 2 training protocols equalized by tension (TUT) on maximal strength (1 repetition maximum [RM]), regional cross-sectional areas (proximal, middle, and distal), and total cross-sectional areas (sum of the regional cross-sectional areas) of the pectoralis major and triceps brachii muscles. Thirty-eight men untrained in resistance training participated in the study and were allocated under 3 conditions: Protocol 3s (n = 11; 12 repetitions; 3s repetition duration), Protocol 6s (n = 11; 6 repetitions; 6s repetition duration), and Control (n = 11; no training). Training protocols (10 weeks; bench press exercise) were equated for TUT (36 seconds per set), number of sets (3-4), intensity (50-55% of 1RM), and rest between sets (3 minutes). Analysis of variance was used to examine a percentage change in variables of interest across the 3 groups with an alpha level of 0.05 used to establish statistical significance. Protocols 3s and 6s showed no differences in the increase of total and regional muscle cross-sectional areas. There were no differences in regional hypertrophy of the pectoralis major muscle. In the triceps brachii muscle, the increase in distal cross-sectional area was greater when compared with the middle and proximal regions. Both experimental groups had similar increases in the 1RM test. In conclusion, training protocols with the same TUT promote similar strength gains and muscle hypertrophy. Moreover, considering that the protocols used different numbers of repetitions, the results indicate that training volumes cannot be considered separately from TUT when evaluating neuromuscular adaptations.

The Evolution of Blood Flow Restricted Exercise.

The use of blood flow restricted (BFR) exercise has become an accepted alternative approach to improve skeletal muscle mass and function and improve cardiovascular function in individuals that are not able to or do not wish to use traditional exercise protocols that rely on heavy loads and high training volumes. BFR exercise involves the reduction of blood flow to working skeletal muscle by applying a flexible cuff to the most proximal portions of a person's arms or legs that results in decreased arterial flow to the exercising muscle and occluded venous return back to the central circulation. Safety concerns, especially related to the cardiovascular system, have not been consistently reported with a few exceptions; however, most researchers agree that BFR exercise can be a relatively safe technique for most people that are free from serious cardiovascular disease, as well as those with coronary artery disease, and also for people suffering from chronic conditions, such as multiple sclerosis, Parkinson's, and osteoarthritis. Potential mechanisms to explain the benefits of BFR exercise are still mostly speculative and may require more invasive studies or the use of animal models to fully explore mechanisms of adaptation. The setting of absolute resistive pressures has evolved, from being based on an individual's systolic blood pressure to a relative measure that is based on various percentages of the pressures needed to totally occlude blood flow in the exercising limb. However, since several other issues remain unresolved, such as the actual external loads used in combination with BFR, the type of cuff used to induce the blood flow restriction, and whether the restriction is continuous or intermittent, this paper will attempt to address these additional concerns.

Muscle Performance Changes with Age in Active Women.

The purpose of this study was to examine age-related differences in muscle performance in women divided into young (YW, 20-39 years, n = 29) middle-aged (MAW, 40-59 years, n = 33), and older (OW, ≥60 years, n = 40) age groups. METHODS: Hand grip strength, vertical jump performance, and knee extensor (KE) strength (0 deg/s, 60 deg/s, and 240 deg/s), speed of movement (SoM; at 1 Nm, 20%, 40%, and 60% isometric strength), and endurance (30-repetition test at 60 degs/s and 240 deg/s) were assessed. Computed tomography-acquired muscle cross-sectional area (mCSA) was measured and included to determine specific strength (KE strength/mCSA). RESULTS: Hand grip strength was similar across groups, while jump performance declined with age (YW and MAW > OW, p < 0.001). KE strength declined significantly with age (all conditions p < 0.01), while specific strength was similar across groups. SoM was significantly higher for YW and MAW compared to OW (both p < 0.01). An age × velocity interaction revealed YW KE endurance was similar between conditions, whereas MAW and OW displayed significantly better endurance during the 60 deg/s condition. OW displayed impaired KE endurance at 240 deg/s (vs. YW and MAW, p < 0.01) but improved at 60 deg/s (vs. YW, p < 0.01). Dynamic torque decline increased with age (YW < OW, p = 0.03) and was associated with intramuscular adipose tissue (r = 0.21, p = 0.04). CONCLUSIONS: Performance declines were most evident among OW, but few performance deficits had emerged in MAW. Interestingly, strength declines disappeared after normalizing to mCSA and endurance appears to be velocity-dependent.

Ipsilateral and contralateral responses following unimanual fatigue with and without illusionary mirror visual feedback.

Illusionary mirror visual feedback alters interhemispheric communication and influences cross-limb interactions. Combining forceful unimanual contractions with the mirror illusion is a convenient way to provoke robust alterations within ipsilateral motor networks. It is unknown, however, if the mirror illusion affects cross-limb fatigability. We examine this concept by comparing the ipsilateral and contralateral handgrip force and electromyographic (EMG) responses following unimanual fatigue with and without illusionary mirror visual feedback. Participants underwent three experimental sessions (mirror, no-mirror, and control), performing a unimanual fatigue protocol with and without illusionary mirror visual feedback. Maximal handgrip force and EMG activity were measured before and after each session for both hands during maximal unimanual and bimanual contractions. The associated EMG activity from the inactive forearm during unimanual contraction was also examined. The novel findings demonstrate greater relative fatigability during bimanual versus unimanual contraction following unimanual fatigue (-31.8% vs. -23.4%, P < 0.01) and the mirror illusion attenuates this difference (-30.3% vs. -26.3%, P = 0.169). The results show no evidence for a cross-over effect of fatigue with (+0.62%, -2.72%) or without (+0.26%, -2.49%) the mirror illusion during unimanual or bimanual contraction. The mirror illusion resulted in significantly lower levels of associated EMG activity in the contralateral forearm. There were no sex differences for any of the measures of fatigability. These results demonstrate that the mirror illusion influences contraction-dependent fatigue during maximal handgrip contractions. Alterations in facilitatory and inhibitory transcallosal drive likely explain these findings.NEW & NOTEWORTHY Illusionary mirror visual feedback is a promising clinical tool for motor rehabilitation, yet many features of its influence on motor output are unknown. We show that maximal bimanual force output is compromised to a greater extent than unimanual force output following unimanual fatigue, yet illusionary mirror visual feedback attenuates this difference. The mirror illusion also reduces the unintended EMG activity of the inactive, contralateral forearm during unimanual contraction.

Physiological and Perceptual Responses to Aerobic Exercise With and Without Blood Flow Restriction.

ABSTRACT: Silva, JCG, Domingos-Gomes, JR, Freitas, EDS, Neto, GR, Aniceto, RR, Bemben, MG, Lima-dos-Santos, A, and Cirilo-Sousa, MS. Physiological and perceptual responses to aerobic exercise with and without blood flow restriction. J Strength Cond Res 35(9): 2479-2485, 2021-Although previous studies have demonstrated the potential benefits of aerobic exercise (AE) with blood flow restriction (BFR), these findings have been limited by the approaches used to determine the occlusive pressure. In addition, the physiological and perceptual responses of AE with BFR compared to high-intensity interval exercise (HIIE) remain unclear. Thus, we investigated the physiological and perceptual responses to AE with and without BFR, and HIIE. Twenty-two men were randomly assigned to 4 experimental conditions: AE (40% of maximal oxygen consumption [V˙o2peak]), AE with 50% of BFR (AE-BFR: 40% VV˙o2peak), HIIE (80% V˙o2peak), and a no exercise control condition (CON: 50% of BFR). Each exercise bout lasted 18 minutes, during which oxygen consumption (V˙o2), heart rate (HR), and ratings of perceived exertion (RPE) were measured at rest and at every 3 minutes during exercise. Ratings of discomfort before and after each trial. The HIIE condition induced the greatest increases in V˙o2 and HR (p < 0.05), whereas AE-BFR was significantly (p < 0.05) greater than AE and CON. HIIE and AE-BFR also elicited the greatest (p < 0.05), but similar (p > 0.05), increases in RPE during exercise, although AE-BFR was significantly greater than HIIE immediately after exercise (p < 0.05). AE-BFR and HIIE also induced similar levels of discomfort after exercise (p > 0.05). In conclusion, HIIE induced the greatest increases in V˙o2 and HR, although the perceptual responses were essentially the same compared with AE-BFR. However, albeit inferior to HIIE, V˙o2 was greater during AE-BFR compared with AE, indicating that this training method may be used to replace HIIE and still significantly elevate V˙o2.