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Abstract: Lillquist, T, Mahoney, SJ, Kotarsky, C, McGrath, R, Jarajapu, Y, Scholten, SD, and Hackney, KJ. The effect of direct and remote postexercise ischemic conditioning on muscle soreness and strength 24 hours after eccentric drop jumps. J Strength Cond Res 37(9): 1870-1876, 2023-Strategic limb occlusion applied after exercise may facilitate recovery, not only in directly targeted tissue but also in remote areas of the body. The purpose of this study was to determine if postexercise ischemic conditioning (PEIC) applied directly to one leg facilitated recovery in the targeted leg and the contralateral leg that did not receive direct PEIC. Twenty active men participated in a single-blind, randomized, crossover design. Subjects completed 2 paired testing sessions (PEIC and control-SHAM) that included pre-assessments and 24-hour postassessments. Each paired testing session included an eccentric drop jump task, which has been shown to increase lower-body muscle soreness and decrease strength. After each drop jump task, occlusion cuffs were immediately applied. In the PEIC session, ∼198 mm Hg was applied directly to one leg (PEIC-Direct), whereas the contralateral leg received a nonphysiological stimuli of 20 mm Hg (PEIC-Remote). In the control-SHAM session, both legs directly and remotely received the 20 mm Hg pressure. Unilateral pre-assessments and 24-hour postassessments included muscle soreness using a visual analog scale and strength via peak torque assessment across the force-velocity spectrum (flexion/extension 60/60, 120/120, 180/180, 240/240, 300/300 °·s -1 ), and a maximal eccentric extension (30/30 °·s -1 ). Muscle soreness was significantly increased ( p < 0.05) at 24 hours compared with pretreatment except for PEIC-Direct (1.19 ± 0.78 vs. 2.32 ± 1.48, p = 0.096). Across the force-velocity spectrum, there were no significant differences observed between any associated pretest and posttest ( p > 0.05). PEIC applied directly to target leg after eccentric drop jumps attenuated perceived quadriceps muscle soreness 24 hours post; however, there was no effect on muscle strength., (Copyright © 2023 National Strength and Conditioning Association.)

Background: Measures of handgrip strength have not only emerged as a clinically viable screening tool for determining risk for morbidity, functional disability, and early mortality, but also for helping to identify cognitive deficits. However, the phenomena that links low handgrip strength with cognitive decline remains unclear. The role of the muscular and neural systems, and their adaptations to muscle strengthening activities over the life course, may provide important information for how age-related changes to muscle mass, strength, and neural capacity influence cognition. Moreover, disentangling how handgrip strength and cognitive function are associated may help to inform healthcare providers working with aging adults and guide targeted interventions aiming to preserve muscle and cognitive functioning., Objective: To 1) highlight and summarize evidence examining the associations of handgrip strength and cognitive functioning, and 2) provide directions for future research in this area., Methods: Articles from the PubMed database were searched from November 2018-May 2019. The search term algorithm, inclusion and exclusion criteria were pre-specified by investigators., Results: Several cross-sectional and longitudinal studies have revealed that measures of handgrip strength were associated with cognitive declines regardless of age demographics and the presence of comorbidities., Conclusion: Handgrip strength can be used in clinical and epidemiological settings for helping to determine the onset and progression of cognitive impairment. Future research should continue to examine how handgrip strength and cognitive function are linked.

Background: The use of magnetic resonance imaging (MRI) derived functional cross-sectional area (FCSA) and intramuscular adipose tissue (IMAT) to define skeletal muscle quality is of fundamental importance in order to understand aging and inactivity-related loss of muscle mass., Objectives: This study examined factors associated with lower-extremity skeletal muscle quality in healthy, younger, and middle-aged adults., Design: Cross-sectional study., Setting and Participants: Ninety-eight participants (53% female) were classified as younger (20-35 years, n=50) or middle-aged (50-65 years, n=48) as well as sedentary (≤1 day per week) or active (≥3 days per week) on self-reported concurrent exercise (aerobic and resistance)., Measurements: All participants wore an accelerometer for seven days, recorded a three-day food diary, and participated in magnetic resonance imaging (MRI) of the lower limbs. Muscle cross-sectional area (CSA) was determined by tracing the knee extensors (KE) and plantar flexors, while muscle quality was established through the determination of FCSA and IMAT via color thresholding., Results: One-way analysis of variance and stepwise regression models were performed to predict FCSA and IMAT. KE-IMAT (cm2) was significantly higher among sedentary (3.74 ± 1.93) vs. active (1.85 ± 0.56) and middle-aged (3.14 ± 2.05) vs. younger (2.74 ± 1.25) (p < 0.05). Protein intake (g•kg•day-1) was significantly higher in active (1.63 ± 0.55) vs. sedentary (1.19 ± 0.40) (p < 0.05). Sex, age, concurrent exercise training status, and protein intake were significant predictors of KE FCSA (R2 = 0.71, p < 0.01), while concurrent exercise training status and light physical activity predicted 33% of the variance in KE IMAT (p < 0.01)., Conclusion: Concurrent exercise training, dietary protein intake, and light physical activity are significant determinants of skeletal muscle health and require further investigation to mitigate aging and inactivity-related loss of muscle quality., Competing Interests: There are no conflicts of interest.

INTRODUCTION: Microgravity leads to a progressive loss in muscular strength, endurance, and aerobic capacity (Vo 2peak ). Blood flow restricted (BFR) exercise has been shown to elicit rapid gains in muscular strength and Vo 2peak . Rowing exercise combined with BFR could be a supplemental countermeasure to maintain preflight muscle function and Vo 2peak , especially within future space vehicles with restricted physical volume. METHODS: There were 20 men who completed 19 min of rowing exercise during CON or BFR in a randomized order. Exercise intensity for all sets was 30% of peak work load achieved during a separate incremental maximal exercise test. Kaatsu training cuffs were inflated around each leg during BFR. Muscle oxygen saturation (Smo₂) and heart rate (HR) were measured throughout exercise and rest. Rate of perceived exertion (RPE) and muscle activation, using surface electromyography (sEMG), were measured during the last 30 s of each exercise set. Blood pressure (BP) and whole blood lactate ([La - ] b ) were measured at rest and postexercise. RESULTS: Smo₂ declined significantly in BFR during exercise and rest by 13% and 14%, respectively. HR and RPE showed significant increases during BFR (120.5 ± 5.53 vs. 128.9 ± 9.86 bts · min -1 ) (9.8 ± 1.85 vs. 11.8 ± 1.88 arbitrary units). No differences were observed for BP, [La - ] b , and sEMG. DISCUSSION: Findings indicate exercise intensity and cuff pressure elicited acute muscular, cardiovascular, and perceptual responses. BFR rowing exercise could be advantageous as an adjunct for future exercise countermeasures where aerobic and anaerobic exercise may be performed on one device or in limited physical space. Mahoney SJ, Dicks ND, Lyman KJ, Christensen BK, Hackney KJ. Acute cardiovascular, metabolic, and muscular responses to blood flow restricted rowing exercise . Aerosp Med Hum Perform. 2019; 90(5):440-446.

Synopsis Restoration of skeletal muscle mass and strength is critical to successful outcomes following orthopaedic surgery. Blood flow restriction (BFR) resistance exercise has emerged as a promising means of augmenting traditional low-intensity physical rehabilitation exercise and has yielded successful outcomes in a wide range of applications. Though BFR is well tolerated and safe for most individuals, patients who have undergone orthopaedic surgery may be an exception, due to their heightened risk for venous thromboembolism (VTE). While the pathogenesis of VTE is multifactorial and specific to the individual, it is commonly described as a combination of blood stasis, endothelial injury, and alterations in the constituents of the blood leading to hypercoagulability. The collective literature suggests that, given the pathogenic mechanisms of VTE, limited use of a wide, partially occluding cuff during resistance exercise should be low risk, and the likelihood that BFR would directly cause a VTE event is remote. Alternatively, it is plausible that BFR may enhance blood flow and promote fibrinolysis. Of greater concern is the individual with pre-existing asymptomatic VTE, which could be dislodged during BFR. However, it is unknown whether the direct risk associated with BFR is greater than the risk accompanying traditional exercise alone. Presently, there are no universally agreed-upon standards indicating which postsurgical orthopaedic patients may perform BFR safely. While excluding all these patients from BFR may be overly cautious, clinicians need to thoroughly screen for VTE signs and symptoms, be cognizant of each patient's risk factors, and use proper equipment and prescription methods prior to initiating BFR. J Orthop Sports Phys Ther 2019;49(1):17-27. Epub 12 Sep 2018. doi:10.2519/jospt.2019.8375.

Background: Bed rest studies have shown that high load (HL) resistance training can mitigate the loss of muscle size and strength during musculoskeletal unloading; however, not all individuals are able to perform HL resistance exercise. Blood flow restricted (BFR) resistance exercise may be a novel way to prevent maladaptation to unloading without requiring HL exercise equipment. This study evaluated the muscular training adaptations to HL and BFR resistance training during unilateral lower limb suspension (ULLS), a human limb unloading model. ULLS allows for evaluation of exercise training in both weight-bearing and nonweight-bearing legs within the same individual., Methods: There were 13 participants who completed 25 d of ULLS and were counterbalanced to: 1) HL, N = 6; or 2) BFR, N = 7, training groups. During ULLS, HL and BFR performed unilateral leg press and heel raise exercise (3 d/wk)., Results: In weight-bearing legs, both HL and BFR increased knee extensor muscle cross-sectional area (CSA) and strength. In nonweight-bearing legs, knee extensor CSA and strength increased only in HL and decreased with BFR., Conclusion: HL and BFR resistance exercise were both effective exercise programs for the weight-bearing leg. However, BFR exercise was not as effective as HL resistance exercise in the nonweight-bearing leg. These data show that exercise that improved muscle CSA and strength in ambulatory weight-bearing conditions was not sufficient to maintain muscle function during unloading. For the preservation of muscle CSA and strength, BFR exercise should be considered an adjunct but not a primary exercise countermeasure for future space missions. Hackney KJ, Downs ME, Ploutz-Snyder L. Blood flow restricted exercise compared to high load resistance exercise during unloading. Aerosp Med Hum Perform. 2016; 87(8):688-696.

Existing models of muscle deconditioning such as bed rest are expensive and time-consuming. We propose a new model utilizing a weighted suit to manipulate muscle strength, power, or endurance relative to body weight. The aims of the study were to determine as to which muscle measures best predict functional task performance and to determine muscle performance thresholds below which task performance is impaired. Twenty subjects performed seven occupational astronaut tasks (supine and upright seat egress and walk, rise from fall, hatch opening, ladder climb, object carry, and construction board activity), while wearing a suit weighted with 0-120 % of body weight. Models of the relationship between muscle function/body weight and task completion time were developed using fractional polynomial regression and verified with pre- and post-flight astronaut performance data. Spline regression was used to identify muscle function thresholds for each task. Upright seat egress and walk was the most difficult task according to the spline regression analysis thresholds. Thresholds normalized to body weight were 17.8 N/kg for leg press isometric force, 17.6 W/kg for leg press power, 78.8 J/kg for leg press work, 5.9 N/kg isometric knee extension and 1.9 Nm/kg isokinetic knee extension torque. Leg press maximal isometric force/body weight was the most reliable measure for modeling performance of ambulatory tasks. Laboratory-based manipulation of relative strength has promise as an analog for spaceflight-induced loss of muscle function. Muscle performance values normalized to body weight can be used to predict occupational task performance and to establish relevant strength thresholds.

In 1991, Hans Berg and colleagues published the first research investigation using unilateral lower limb suspension (ULLS) as a human model to study the influence of unloading on skeletal muscle. ULLS requires a participant to perform all activities with axillary crutches while wearing one thick-soled shoe. The elevated shoe eliminates ground contact with the adjacent foot, thereby unloading the lower limb. Today, ULLS is a well-known ground-based analog for microgravity. The present review will synthesize the physiological findings from investigations using ULLS to study the deleterious effects of unloading. Compromised human performance and the neuromuscular, musculoskeletal and circulatory mechanisms leading to altered function will be a major emphasis of the work. Results from prolonged bed rest will also be included in order for general comparisons to be made between analogs. Finally, the efficacy of exercise to mitigate the negative consequences of unloading is presented.

Introduction: The recovery of muscle size and function following musculoskeletal unloading has received little attention in the scientific literature. Nutritional factors such as total energy, protein intake, and the pre- and/or post-exercise consumption of amino acid-carbohydrate (AACHO) have been shown to be important for enhancing training adaptations in recreational exercisers., Purpose: A preliminary study was conducted to explore the interaction between nutrition and resistance exercise during reconditioning from unloading., Methods: Muscle CSA, strength, and endurance were measured during a control period following 30 d of unilateral lower limb suspension (Post-ULLS) and after 18 d of reconditioning (ReCon). Six participants consumed either AACHO (979 kJ, 36 g carbohydrate, 22.5 g protein) or placebo (PLAC) prior to resistance exercise (3 d x wk(-1)) during reconditioning. Total daily energy and macronutrient intake were evaluated from dietary journals., Results: From Post-ULLS to ReCon, muscle endurance increased 1.1 +/- 0.6 min in AACHO and decreased 1.3 +/- 0.7 min in PLAC. Muscle CSA (6 +/- 2 vs. 5 +/- 3 cm2) and strength (105 +/- 53 vs. 81 +/- 37 N) increased similarly in AACHO and PLAC, respectively. When groups were pooled there was a significant correlation between daily protein intake and the recovery of muscle CSA (r = 0.81)., Discussion: Although our findings are preliminary, timing AACHO intake during reconditioning was beneficial for muscular endurance, while overall protein intake was associated with increased muscle size. A systematic evaluation into the synergistic relationship between nutrition and exercise during muscular recovery from prolonged unloading is warranted.

The purpose of this investigation was to determine the effect of an acute bout of high-volume, full-body resistance training with an eccentric concentration on resting energy expenditure (REE) and indicators of delayed-onset muscle soreness (DOMS). Eight resistance trained (RT) and eight untrained (UT) participants (mean: age = 23.5 years; height = 180.76 cm; weight = 87.58 kg; body fat = 19.34%; lean mass = 68.71 kg) were measured on four consecutive mornings for REE and indicators of DOMS: creatine kinase (CK) and rating of perceived muscle soreness (RPMS). Delayed-onset muscle soreness was induced by performing eight exercises, eight sets, and six repetitions using a 1-second concentric and 3-second eccentric muscle action duration. A two-factor repeated-measures analysis of variance revealed that REE was significantly (p < 0.05) elevated at 24, 48, and 72 hours post compared with baseline measures for both UT and RT groups. Ratings of perceived muscle soreness were significantly elevated within groups for UT and RT at 24 and 48 hours post and for UT only at 72 hours post compared with baseline (p < 0.05). Nonparametric analyses revealed that CK was significantly increased at 24 hours post for both UT and RT and at 48 and 72 hours post for UT only compared with baseline (p < 0.05). Resting energy expenditure and indicators of DOMS were higher in UT compared with RT on all measures, but no significant differences were determined. The main finding of this investigation is that full-body resistance training with an eccentric concentration significantly increased REE up to 72 hours postexercise in UT and RT participants.